U.S. patent application number 15/814346 was filed with the patent office on 2018-12-06 for optical modules having an improved optical signal to noise ratio.
The applicant listed for this patent is Infinera Corparation. Invention is credited to Timothy Butrie, Perter W. Evans, Fred A. Kish, JR., John Osenbach, Michael Reffle, Jie Tang, Jiaming Zhang.
Application Number | 20180351684 15/814346 |
Document ID | / |
Family ID | 64458394 |
Filed Date | 2018-12-06 |
United States Patent
Application |
20180351684 |
Kind Code |
A1 |
Osenbach; John ; et
al. |
December 6, 2018 |
OPTICAL MODULES HAVING AN IMPROVED OPTICAL SIGNAL TO NOISE
RATIO
Abstract
Consistent with the present disclosure, a photonic integrated
circuit (PIC) is provided that has 2 N channels (N being an
integer). The PIC is optically coupled to N optical fibers, such
that each of N polarization multiplexed optical signals are
transmitted over a respective one of the N optical fibers. In
another example, each of the N optical fibers supply a respective
one of N polarization multiplexed optical signals to the PIC for
coherent detection and processing. A multiplexer and demultiplexer
may be omitted from the PIC, such that the optical signals are not
combined on the PIC. As a result, the transmitted and received
optical signals incur less loss and amplified spontaneous emission
(ASE) noise. In addition, optical taps may be more readily employed
on the PIC to measure outputs of the lasers, such as widely tunable
lasers (WTLs), without crossing waveguides. In addition, wavelength
locker (WLL) circuitry may be provided on the PIC.
Inventors: |
Osenbach; John; (Kutztown,
PA) ; Zhang; Jiaming; (Macungie, PA) ; Tang;
Jie; (Fogelsville, PA) ; Butrie; Timothy;
(Hellertown, PA) ; Reffle; Michael; (Center
Valley, PA) ; Kish, JR.; Fred A.; (Palo Alto, CA)
; Evans; Perter W.; (Mountain House, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Infinera Corparation |
Annapolis Junction |
MD |
US |
|
|
Family ID: |
64458394 |
Appl. No.: |
15/814346 |
Filed: |
November 15, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62422031 |
Nov 15, 2016 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04B 10/07955 20130101;
H04B 10/506 20130101; H04J 14/0221 20130101; H04J 14/021 20130101;
H04B 10/614 20130101; H04J 14/06 20130101 |
International
Class: |
H04J 14/02 20060101
H04J014/02; H04B 10/079 20060101 H04B010/079; H04B 10/50 20060101
H04B010/50 |
Claims
1. An optical device, comprising: a first substrate; a plurality of
lasers provided on the first substrate; a first plurality of
modulators that respectively modulate a first optical output of
each of the plurality of lasers, the first plurality of modulators
being provided on the first substrate; a second plurality of
modulators that respectively modulate a second optical output of
each of the plurality of lasers, the second plurality of modulators
being provided on the first substrate; a first plurality of
waveguides, each of which being optically coupled to a respective
one of the first plurality of modulators, each of the first
plurality of waveguides extending to an edge of the substrate and
supplying a corresponding one of a first plurality of modulated
optical signals; a second plurality of optical waveguides, each of
which being optically coupled to a corresponding one of the second
plurality of modulators, each of the second plurality of waveguides
extending to the edge of the substrate and supplying a
corresponding one of a second plurality of modulated optical
signals; at least one rotator that rotates a polarization of the
first plurality of modulated optical signals; at least one
polarization beam combiner configured to receive the polarization
rotated first plurality of modulated optical signals and the second
plurality of modulated optical signals, said at least one
polarization beam combiner having at least one output that supplies
the polarization rotated first plurality of modulated optical
signals and the the second plurality of modulated optical signals,
said at least one output of the polarization beam combiner being
configured to be optically coupled to a plurality of optical
fibers; an integrated circuit, which provides radio frequency (RF)
drive signals to the first plurality of modulators and the second
plurality of modulators; and a second substrate, the first
substrate and the integrated circuit being provided on the second
substrate.
2. An optical device in accordance with claim 1, wherein the first
substrate and the integrated circuit are flip chip and
thermo-compression bonded to the second substrate.
3. An optical device in accordance with claim 1, further including
a heat spreader attached to the integrated circuit.
4. An optical device in accordance with claim 2, wherein the
optical device further comprises: a plurality of transmission lines
that carries the radio frequency drive signals to the first
plurality of modulators and the second plurality of modulators,
wherein each of the first plurality of modulators constitutes a
corresponding one of a first plurality of lumped elements and each
of the second plurality of modulators constitutes a corresponding
one of a second plurality of lumped elements.
5. An optical device in accordance with claim 4, wherein the RF
circuitry in the integrated circuit constitutes first circuitry,
and the integrated circuit further including second circuitry that
provides control signals to devices on the first substrate and
receives monitoring signals indicative of a performance of the
devices.
6. An optical device in accordance with claim 2, wherein the
integrated circuit includes RF circuitry, the second substrate
further comprising: a plurality of transmission lines that carries
the radio frequency drive signals from the RF circuitry to the
first plurality of modulators and the second plurality of
modulators, wherein each of the first plurality of modulators
constitutes a corresponding one of a first plurality of traveling
wave elements and each of the second plurality of modulators
constitutes a corresponding one of a second plurality of traveling
wave elements.
7. An optical device in accordance with claim 6, wherein the
circuitry constitutes first circuitry, the integrated circuit
further including second circuitry that provides control signals to
devices on the first substrate and receives monitoring signals
indicative of a performance of the devices.
8. An optical device in accordance with claim 1, further including:
a plurality of lenses, each of which optically coupling a
corresponding output of each of the plurality of polarization beam
combiners to a corresponding one of a plurality of optical
fibers.
9. An optical device in accordance with claim 1, further including:
a heat managing element that is thermally coupled to the first
substrate, the heat managing element providing mechanical support
to the first substrate, and the heat managing element transferring
heat output from the first substrate, the heat managing element
including at least one of a heat spreader, a thermal electric
cooler, a heat pipe, and a heat sink.
10. An optical device, comprising: a first substrate; a plurality
of lasers provided on the first substrate, each of the plurality of
lasers being a local oscillator laser, each of the plurality of
lasers being a local oscillator laser; a first plurality of
waveguides, each of which being provided on the first substrate and
extending to an edge of the first substrate; a second plurality of
waveguides, each of which being provided on the first substrate and
extending to the edge of the first substrate; a first plurality of
optical hybrid circuits provided on the first substrate, each of
the first plurality of optical hybrid circuits receiving a
respective one of a first plurality of optical signals from a
corresponding one of the first plurality of waveguides and a first
portion of light output from a respective one of the plurality of
lasers, each of the first plurality of optical hybrid circuits
providing a respective one of a first plurality of groups of mixing
products; and a second plurality of optical hybrid circuits
provided on the first substrate, each of the second plurality of
optical hybrid circuits receiving a respective one of a second
plurality of optical signals from a corresponding one of the second
plurality of waveguides and a second portion of the light output
from a respective one of the plurality of lasers, each of the
second plurality of optical hybrid circuits providing a respective
one of a second plurality of groups of mixing products, the first
and second pluralities of optical hybrid circuits being provided on
the substrate; first groups of photodiodes, each group of
photodiodes of the first group of photodiodes receiving at least
one output from a corresponding one of the first plurality of
optical hybrid circuits; second groups of photodiodes, each group
of photodiodes of the second groups of photodiodes receiving at
least one output from a corresponding one of the second plurality
of optical hybrid circuits; at least one polarization beam splitter
to receive at at least one input a plurality of polarization
multiplexed optical signals and supplying a first plurality of
optical signals at at least a first output and a second plurality
of optical signals at least a second output, said at least one
polarization beam splitter being provided on the second substrate;
at least one polarization rotator that rotates a polarization of
the first plurality of optical signals, such that the first
plurality of optical signals is output from said at least one
polarization rotator to a corresponding one of the plurality of
third waveguides, and each of the second plurality of optical
signals is output from said at least one polarization beam
splitters to corresponding one of the plurality of fourth
waveguides; an integrated circuit, which receives radio frequency
signals output from the first plurality of groups of photodiodes
and the second plurality of groups of photodiodes; and a second
substrate, the first substrate and the integrated circuit being
provided on the second substrate.
11. An optical device in accordance with claim 10, wherein the
first substrate and the integrated circuit are flip chip and
thermo-compression bonded to the second substrate.
12. An optical device in accordance with claim 10, further
including a heat spreader attached to the integrated circuit.
13. An optical device in accordance with claim 11, wherein the
optical device further includes: a transmission line that carries
the radio frequency signals, wherein each photodiode in each of the
first groups of photodiodes and each photodiode in each of the
second groups of photodiodes constitutes a lumped element.
14. An optical device in accordance with claim 13, wherein the
integrated circuit including first circuitry that receives the
radio frequency signals and second circuitry that provides control
signals to devices on the first substrate and receives monitoring
signals indicative of a performance of the devices.
15. An optical device in accordance with claim 11, wherein the
optical device further comprising: a transmission line that carries
the radio frequency signals, wherein each photodiode in each of the
first groups of photodiodes and each photodiode in each of the
second groups of photodiodes constitutes a traveling wave
element.
16. An optical device in accordance with claim 15, wherein the
integrated circuit further including first circuitry that receives
the radio frequency signals and second circuitry that provides
control signals to devices on the first substrate and receives
monitoring signals indicative of a performance of the devices.
17. An optical device in accordance with claim 10, further
including: a plurality of lenses, each of which optically coupling
a corresponding output of each of the plurality of polarization
beam combiners to a corresponding one of a plurality of optical
fibers.
18. An optical device in accordance with claim 1, wherein the first
substrate and the integrated circuit are flip chip bonded to the
second substrate.
19. An optical device in accordance with claim 10, wherein the
first substrate and the integrated circuit are flip chip bonded to
the second substrate.
Description
RELATED APPLICATION
[0001] This application claims priority under 35 U.S.C. .sctn. 119
to U.S. Provisional Patent Application No. 62/422,031, filed on
Nov. 15, 2016, the content of which is incorporated by reference
herein in its entirety.
BACKGROUND
[0002] Wavelength division multiplexed (WDM) optical communication
systems are known in which multiple optical signals, each having a
different wavelength and each modulated to carrying a different
data stream, are multiplexed or combined and transmitted on an
optical fiber. At a receive end of the fiber, such optical signals
are demultiplexed or separated, detected, and the data stream
carried by each optical signal is recovered.
[0003] WDM optical communication systems including photonic
integrated circuits (PICs) are also known. Such PICs, may include
various optical devices integrated on a common semiconductor
substrate. In a transmitter, such PICs may include lasers,
modulators, and optical amplifiers, and an optical combiner or
multiplexer, among other devices. At the receive end, the PICs may
include optical amplifiers, a power splitter or demultiplexer, and,
in the case of a coherent receiver, optical hybrid circuits.
[0004] Conventionally, prior to input to the multiplexer, each
optical signal may be amplified by a corresponding optical
amplifier on the PIC. Each optical amplifier, however, may output,
in addition to the optical signal, so-called amplified spontaneous
emission (ASE) light at wavelengths other than the optical signal
wavelength. Such ASE light may include wavelengths that extend into
and overlap with the optical signal wavelengths. When the WDM
signal with ASE is provided to an erbium doped fiber amplifier, the
optical signals, as well as the ASE may be amplified. Accordingly,
ASE light may be a source of noise in WDM optical communication
systems and cause errors in transmission. Such noise may contribute
to a low launch optical signal to noise ratio (LOSNR) and a low
OSNR in a received optical signal (ROSNR).
[0005] In addition, the multiplexer may introduce loss into each
optical signal when such optical signals are combined. If the
multiplexer, such as a power combiner, does not include spectral
filtering, power loss may be incurred. Such power loss is typically
a function of 1/N, where N is the number of optical signals
supplied to the multiplexer. Power loss may result in an additional
1 to 2 dB of loss. Accordingly, an optical signal supplied to such
multiplexers may incur a loss of 9-10 dB, but less or more loss may
be observed depending on the number of optical signals that are
combined by the multiplexer.
SUMMARY
[0006] Consistent with an aspect of the present disclosure, the
multiplexer and demultiplexer may be omitted, such that the optical
signals are not combined on the PIC, and each optical signal is
transmitted on a corresponding optical fiber coupled to the
PIC.
[0007] Since the optical signals are not combined, ASE noise is
significantly reduced. However, if optical multiplexing is desired,
each amplified optical signal may be supplied to a corresponding
filter that eliminates or substantially attenuates ASE light at
wavelengths other than the optical signal wavelength. As a result,
when such filtered optical signals are combined in the multiplexer,
the ASE noise is substantially reduced in the output WDM signal
compared to a WDM signal including unfiltered amplified optical
signals. Since the resulting WDM optical signal has reduced ASE
noise, simpler, less expensive erbium doped fiber amplifiers may be
provided that do not require further filtering or spectral shaping
to lower ASE. Moreover, erbium doped fiber amplifiers in the
receiver may be omitted since optical signals supplied to the
receiver have improved OSNR, and, therefore, less amplification may
be required.
[0008] Further, since optical multiplexers often have a fixed
number of inputs, by omitting such optical multiplexers, additional
optical signals may be readily added by providing an additional
fiber for each signal. Accordingly, optical communication systems
consistent with an aspect of the present disclosure may scale more
efficiently than those that include multiplexers or combiners with
a fixed number of inputs. Moreover, by removing multiplexers and
demultiplexers from the PIC, waveguides that route optical signals
on the PIC may be laid out with fewer restrictions, so that such
waveguides may have fewer bends and/or a reduced radius of
curvature. Moreover, PIC layouts may be made more compact. In
addition, optical taps may be more readily employed on the PIC to
measure outputs of the lasers, such as widely tunable lasers (WTLs)
without crossing waveguides. A novel wavelength locker (WLL) may
thus be employed, as described below.
[0009] Consistent with a further aspect of the present disclosure,
by omitting the multiplexer in the transmit side PICs and the
splitter or demultiplexer in the receive side PICs, both transmit
and receive PICs may have a simpler layout. Alternatively,
additional functionality or circuits may be integrated into the
PICs. For example, a receiver for tracking and locking wavelengths
of each optical signal may be incorporated into both the transmit
and receive PICs, as discussed in greater detail below. In
addition, a transceiver PIC may be employed including both receiver
devices (such as photodiodes and 90 degree optical hybrids) and
transmitter devices (SOAs and modulators) on a common substrate.
Such transceiver PICs may include a laser that is used both as a
local oscillator and an optical source for the modulators.
Alternatively, the transmit and receive portions of the transceiver
PIC may include separate lasers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1a shows a transceiver consistent with an aspect of the
present disclosure;
[0011] FIG. 1b shows an example of a portion of the transceiver
shown in FIG. 1a;
[0012] FIG. 1c shows an example of a modulator consistent with an
aspect of the present disclosure;
[0013] FIGS. 1dand 1e show examples of waveguide structures
consistent with an aspect of the present disclosure;
[0014] FIGS. 2a and 2b show additional examples of transceivers
consistent with the present disclosure;
[0015] FIG. 2c shows an example of a transmitter block consistent
with a further aspect of the present disclosure;
[0016] FIGS. 3, 4a, and 4b show examples of wavelength control
circuitry consistent with an additional aspect of the present
disclosure;
[0017] FIGS. 5-10, 11a, 11b, and 12-14 show examples of various
packaging configurations consistent with an aspect of the present
disclosure;
[0018] FIGS. 15-35 show various examples of free-space optics
configurations consistent with an aspect of the present
disclosure;
[0019] FIGS. 36-44 show the same configuration as that shown in
FIG. 34, but with different emission angles and far field
angles;
[0020] FIGS. 45-47 show examples of transmission modules consistent
with the present disclosure;
[0021] FIGS. 48-55 list and show various parameters associated with
lenses that may be employed in the various embodiments herein;
[0022] FIG. 56 is a plan view of a transmitter configuration
consistent with an aspect of the present disclosure;
[0023] FIG. 57 show a perspective view of the transmitter
configuration shown in FIG. 56;
[0024] FIG. 58 shows an example in which outputs are coupled to
rotators and PBCs on a PLC;
[0025] FIGS. 59 and 60 show examples of transmitter/receiver
modules consistent with further aspects of the present disclosure;
and
[0026] FIGS. 61-63 show examples in which a PIC and an ASIC may be
provided on a common interposer.
DETAILED DESCRIPTION
[0027] The following detailed description of example
implementations refers to the accompanying drawings. The same
reference numbers in different drawings may identify the same or
similar elements.
[0028] FIG. 1a shows an example of a transceiver consistent with
the present disclosure. In this example, the transceiver includes
separate Tx (transmit) and Rx (receive) PICs provided in Tx (1010)
and Rx (1013) modules. As noted above, however, the Tx and Rx PIC
devices may be provided on one PIC substrate with a laser used as
both an optical source and a local oscillator or with two separate
lasers in the Rx and Tx portions of the transceiver PIC. The
transceiver may include a plurality of transmitter channels Tx Ch1
to Tx Ch n. Tx Ch1 and Tx Ch n are shown in FIG. 1a as having the
same or similar structure and including the same or similar
devices. The modulated optical signal output from Tx Ch1, however,
may have a first wavelength and the optical signal output from Tx
Ch n may have a second wavelength different from the first
wavelength. Moreover, each of optical channels Tx Ch1 to Tx Ch n
supplies a corresponding one of a plurality of modulated optical
signals, each having a corresponding one of a plurality of
wavelengths.
[0029] A driver circuit, which may be provided in an integrated
circuit (such as one of ICs IC1 to IC8), which may include an
application specific integrated circuit (ASIC) or a digital signal
processor (DSP) may provide radio frequency (RF) drive signals
corresponding to the transmitted data to modulators provided in
channel Tx Ch 1 on the Tx PIC. The modulators may receive light
from a widely tunable laser (WTL). In addition, the modulators may
include Mach Zehnder (MZ) modulators (labeled IQ MZM in FIG. 1)
having a nested pair configuration in which a first nest pair of MZ
modulators receives light output (a first portion of light output
from laser WTL) from one side S1 or facet of the WTL and a second
pair of MZ modulators receives light output (a second portion of
light output from laser WTL) from the second side S2 or facet of
the WTL.
[0030] A first MZ modulator of the first pair may modulate part of
a first portion the received light from the first side S1 of the
WTL in accordance with selected radio frequency (RF) drive signals
to provide a first in-phase component of the modulated optical
signal and the second MZ modulator of the pair may modulate another
part of the first portion of the received light from the first side
S1 of the WTL in accordance with other RF drive signals to provide
a first quadrature component of the modulated optical signal.
Similarly, light output from the second side S2, a second portion
of the light output from the WTL, is modulated based on additional
RF drive signals supplied to a second IQ MZM to provide second
in-phase and quadrature components of another modulated optical in
accordance with additional drive signals. As further shown in FIG.
1a, light output from each of IQ MZMs in Tx Ch 1 is provided to a
corresponding optional semiconductor optical amplifier (SOA) to
amplify such light and offset optical losses incurred during
modulation and propagation along Tx Ch 1.
[0031] Light output from both sides of the WTL has a transverse
electric (TE) polarization. In order to further increase capacity
of the transmitted optical signal and to minimize interference
between the outputs of the IQ MZMs, light output from the first IQ
MZM is supplied from the Tx PIC on respective waveguides WG that
extend to an edge of substrate 1011. Such light may be directed
toward a waveguide on a planar lightwave circuit (Tx PLC) by a pair
of lenses L1 and L2 (such as silicon lenses) and an isolator
provided between the lenses. Len L1 may be a collimating lens and
lens L2 may be a focusing lens that focuses the optical signals
onto corresponding waveguides in Tx Block 1 to n of the Tx PLC
(planar light wave circuit) on substrate 1014.
[0032] Both the Tx PLC and the Tx PIC may be provided on a third
substrate or Tx interposer, which may also include a substrate made
of silicon or a dielectric, such as silicon dioxide. The PLC may
include a substrate made of silicon or a dielectric, such as
silicon dioxide, and the devices provided on the PLC may be
silicon-based. For example, as shown in FIG. 1a, a rotator may be
provided on the Tx PLC to rotate the polarization of modulated
light from the first IQ MZM from a TE polarization to a transverse
magnetic (TM) polarization that is preferably orthogonal to the TE
polarization. The TE polarization of light from the second IQ MZM,
however, is maintained, and the TM polarized light is combined with
the TE polarized light in a polarization beam combiner (PBC)
provided on the Tx PLC. The PBC, in turn, provides a polarization
multiplexed output having a first wavelength on a corresponding
waveguide WG5. The WTL, IQ MZMs, SOA, isolator, lenses, rotator,
and PBC may collectively be referred to herein as a Tx Block 1,
which, as further shown in FIG. 1a, is part of Tx Ch 1. Tx Block 2
to n may have the same or similar structure as Tx Block 1 and may
similarly provide corresponding polarization multiplexed outputs,
each of which having a respective one of a plurality wavelengths.
Thus, by polarization multiplexing the TE and TM signals, capacity
can be increased compared to transmission of signals having a
single polarization.
[0033] The rotators shown in FIG. 1a may be arranged in a first
array and the polarization beam splitters may be arranged in a
second array. In addition, the polarization beam combiners may be
arranged in an array.
[0034] The output of the Tx Block 1 may be provided to a variable
optical attenuator (VOA) to selectively attenuate the received
polarization multiplexed optical signal to have desired power
level. Optical taps provided at the input and output of the VOA may
be provided to tap off a small portion of the received light and
supply such portions to corresponding photodiodes. The photodiodes,
in turn, convert the received light portions to corresponding
electrical signals which are fed to additional circuitry that can
monitor the power, for example, of light input to and output from
the VOA.
[0035] Thus, FIG. 1a shows an optical device, such as module 1010
including substrate 1011 upon which the TX PIC may be provided.
Substrate 1011 (also referred to as a PIC substrate or TX PIC
substrate herein) may be made of a Group material and may include
indium phosphide (InP) or gallium arsenide (GaAs). Alternatively,
substrate 1011 may include silicon. 2N (N being integer) outputs
may be provided on the substrate 1011, each of which including a
respective one of 2N waveguides (WG1 and WG2), each of the 2N
waveguides (WG1 and WG2) carries a respective one of 2N optical
signals, such that the 2N waveguides may be outputs of PIC
substrate 1011. Each of the 2N optical signals including an
in-phase component and a quadrature component, and each of the 2N
waveguides extending to edge El of substrate 1011. N lasers (WTL)
are also provided on substrate 1011, and each of first N waveguides
(WG1) of the 2N waveguides being optically coupled to a respective
one of the N lasers (WTL). Each of the first N waveguides WG1
supplies a first portion of the light generated by a respective one
of the N lasers (WTL) and may be provided to a corresponding one of
N semiconductor optical amplifiers (SOAs) via a corresponding
modulator MZM IQ.
[0036] As further shown in FIG. 1a, each of second N waveguides
(WG2) is optically coupled to a respective one of the N lasers
(WTL), such that each waveguide WG2 supplies a second portion of
the light generated by a respective one of the WTL lasers to a
corresponding one of another group of N SOAs via a respective
modulator MZM IQ.
[0037] Module 1010 further includes a second substrate 1014 having
third N (N being equal to n above) waveguides WG3, each of which
being optically coupled to a corresponding one of the first N
waveguides WG1 via collimating lens L1, an isolator, and a focusing
line L2. The third N waveguides WG3 are provided on second
substrate 1020. In addition, fourth N waveguides WG4 are provided
on substrate 1014. Each of fourth waveguides WG4 is optically
coupled to a corresponding one of the second N waveguides WG2 via a
corresponding collimating lens L1, an additional isolator, and a
focusing lens L2. The fourth N waveguides WG4 are also provided on
the second substrate.
[0038] Substrate 1014 may further include a plurality (N)
polarization elements, such the rotators and associated
polarization beam combiners (PBCs) shown in FIG. 1a. Each PBC has a
first port optically coupled to a respective one of waveguides WG3,
a second port optically coupled to a respective one of waveguides
WG4, and a third port that connects to a corresponding fifth
waveguide WG5.
[0039] In the example shown in FIG. 1a, light output from sides S1
and S2 of each laser or WTL is modulated by a corresponding nested
Mach-Zehnder modulator IQ MZM. As shown in FIG. 1b and consistent
with an additional aspect of the present disclosure, however, light
may be output from one slide of the laser (WTL) may be provided to
a power splitter having first and second outputs. The first output
supplies a first portion of the light output from the laser to a
first IQ MZM and a portion of the light output from laser is
provided from a second output of the splitter.
[0040] Each laser may be tunable. In one example, each of the N
lasers is a widely tunable laser that is tunable over a 35 nm range
of wavelengths between 1460 nm and 1625 nm. In another example,
each of the N lasers is a widely tunable laser that is tunable over
a 17.5 nm range of wavelengths between 1460 nm and 1625 nm.
Alternatively, each laser may be a distributed feedback (DFB) laser
that is tunable over a 2 nm range of wavelengths between 1460 nm
and 1625 nm or a widely tunable laser having a grating.
[0041] As noted above, each of modulators MZM IQ may be a nested
Mach-Zehnder modulator. FIG. 1c illustrates an example of a nested
Mach-Zehnder modulator, which includes a pair of parallel connected
Mach-Zehnder modulators 106 and 112. The pair 106, 112 may receive
a first portion of light output from a given laser (WTL). A second
portion of light from the laser may be provided to a second nested
Mach-Zehnder modular (IQ MZM) as further shown in FIG. 1a. Pair
106,112 may supply in-phase (I) and quadrature (Q) components of
one of the first N modulated optical signals on one of waveguides
WG1, for example. The second IQ MZM may supply I and Q components
of one of the second N modulated optical signals supplied to one of
waveguides WG2.
[0042] As further shown in FIG. 1c, a portion of the light output
from one of the lasers (WTL) is provided to splitter 111 which
supplies a first part of the light portion on waveguide 111-a to
Mach-Zehnder modulator 106 and a second portion on waveguide 111-b
to Mach-Zehnder modulator 112. Mach-Zehnder modulator 106 has first
(106-a) and second (106-b) arms, and Mach-Zehnder modulator 112 has
first (112-a) and second (112-b) arms. One or more of a phase
adjuster 107-a, electrode 107-c, and amplitude adjuster 107-c may
be provided along arm 106-a. One or more of these or similar
devices may also be provided along one or more of arms 106-b,
112-a, and 112-b.
[0043] Phase adjuster 107-a may be provided to adjust a phase of
light propagating in arm 106-a, and amplitude adjuster 107-b may be
provided to adjust an amplitude or intensity of such light.
Amplitude adjuster 107-b may be a variable optical attenuator, for
example. Both phase adjuster 107-a and amplitude adjuster 107-b may
be semiconductor devices having a p-i-n structure, for example.
Electrode 107-c may be provided to apply an electric field to one
or more portions of the waveguide that constitutes arm 107-a to
thereby alter or change the refractive index of the waveguide. As a
result, when the light propagating in arm 106-a combines in
combiner 115 via with light propagating in arm 106-b, the combined
optical signal may be phase and/or amplitude modulated in
accordance with an I component of the modulated optical signal.
Similarly, Mach-Zehnder modulator 112 supplies a component, but the
output from modulator 112 is supplied to phase adjuster 109, which,
in turn, adjusts the phase of the signal output from modulator 112
by 90 degrees. Accordingly, the output of phase adjuster 109 may be
the Q component of the modulated optical. Both I and Q components
are combined by combiner 131 and output as one of the first N
modulated optical signal to one of waveguides WG1.
[0044] Returning to FIG. 1a, the outputs of each tap (located at
downstream from a given variable optical attenuator (VOA) are
provide to a combiner or multiplexer, which combines the outputs of
each of channels Tx Ch1 to Tx Chn. The multiplexer may be an
arrayed waveguide grating, for example. In the example, shown in
FIG. 1a, a plurality of multiplexers may be provided, each of which
being coupled to receive a corresponding group of channels. In
another example, a single multiplexer may combine the outputs of
each channel Tx Ch1 to Tx Chn. Each multiplexer output is coupled
to a respective fiber, and each fiber may be coupled or connected
to one or more erbium doped fiber amplifiers.
[0045] As further shown in FIG. 1a, received optical signals may be
amplified by EDFAs having 10% and 2% monitoring taps at the input
and output therefore, for example. The incoming optical fibers
carrying these optical signals may be coupled to the inputs of a
corresponding demultiplexer or power splitter. The demultiplexer
may include an arrayed waveguide grating, for example. Each
demultiplexer has a plurality of outputs, such that collectively, N
(N is equal to n in the FIG. 1a) inputs or input fibers are provide
to receiver PLC substrate 1016 in the example shown in FIG. 1a of
Rx module 1012. Each fiber may carry one or more polarization
multiplexed optical signals (e.g., N). A plurality, e.g., N
polarization elements, such as polarization beam splitter (PBS) may
be provided on substrate 1016. Each such PBS has a first output
that supplies a TE component (itself an optical signal) to
waveguide WG5 and a second output that supplies a TM component
(itself also an optical signal) of a respective one of received
polarization multiplexed optical signals (e.g., N polarization
multiplexed optical signals). The TM component is provided to a
corresponding one of a plurality (e.g., N) polarization rotators on
substrate 1016. Each rotator rotates a polarization of the received
TM component (optical signal) such that the signal output from each
rotator has a TE polarization. The rotated optical signals are
supplied to a corresponding one of waveguides WG6.
[0046] Respective waveguide WG6 supplies a corresponding one of the
rotated optical signals (N such signals) to a corresponding one of
waveguides WG7 (inputs, for example) via collimating lens L3 and
focusing lens L4. Similarly, respective waveguide WG5 supplies a
corresponding one of the TE optical signals (N such signals) to a
corresponding one of waveguides WG8 via another collimating lens L3
and another focusing lens L4.
[0047] Waveguides WG7 and WG8 (inputs of the RX PIC substrate)
supplies respective optical signals to corresponding optical hybrid
circuits, which in this example are 90 degree optical hybrid
circuits. Each optical hybrid circuit receives first and second
power split portion of light output from a side S of a local
oscillator laser (WTL). The first and second power split portions
are provided from first and second outputs, respectively, of a
coupler or splitter coupled to side S of the local oscillator laser
WTL.
[0048] The received optical signals from waveguides WG7 and WG8 are
mixed with light from local oscillator lasers (WTL) in the optical
hybrid circuits. The optical hybrids, in turn, supply groups of
mixing products to groups of photodiodes. In the example shown in
FIG. 1a, N local oscillator lasers are associated with 2N optical
hybrid circuits and 2N groups of photodiodes (PDs). The local
oscillator lasers, optical hybrids circuits, and photodiode groups
may be provided on substrate 1013 (also referred to herein as a PIC
substrate or an RX PIC substrate), which may include a Group
material, such as InP or GaAs, or silicon. Substrate 101 may also
be provided in module 1012 and both substrates 1013 and 1016 may be
provided on an Rx interposer substrate, similar to or the same as
Tx interposer substrate noted above.
[0049] The groups of photodiodes generate radio frequency (RF)
signals that are fed to corresponding ones of integrated circuits
(ICs) 1 to 8. The ICs may include known transimpedance amplifiers
(TIAs), analog to digital converters (ADCs) and carrier recover
circuitry.
[0050] In accordance with a further aspect of the present
disclosure, a plurality of spot size converters or mode adapters
may be provided as part of end portions of each of the above
described waveguides. Such spot size converters are shown in FIG.
1d as being provided at end portions of waveguides WG1 and WG2
along the facet or edge of the TX PIC substrate. Spot size
converters may similarly be provided as part of end portions of the
other waveguides described herein adjacent or abutting the edge or
facet of the PIC as well as other substrates described herein
having waveguides provided thereon. Spot size converters may be
provided to reduce the amount of diffraction of light that is
emitted form the PIC, for example. Each of N spot size converters
may be provided for each of N waveguides WG1 and each of N spot
size converters may be provided for each of N waveguides WG2, for
example.
[0051] FIG. 1e shows an example in which one of the waveguides
having a spot size converter is tilted at a non-perpendicular angle
.theta. relative to a facet of the PIC substrate to minimize back
reflections.
[0052] As further shown in FIG. 1a, each of the polarization
rotators may be arranged in a first array and each of polarization
combiners may be arranged in a second array.
[0053] As noted above, by omitting the multiplexer and
demultiplexer in modules 1010 and 1012, the advantages noted above
may be achieved.
[0054] FIGS. 2A and 2B show a system including modules 1010 and
1012. As shown in FIGS. 2a and 2b, tracking filters, photodiodes,
and VOAs are provided off the PLC substrate 1020. Consistent with
the present disclosure, however, such devices may be included or
integrated on the PLC substrate 1020, for example. That is,
tracking filters and VOAs which may be made of silicon based
materials may be well suited for integration on substrate 1020,
which may also be silicon based. Other PLC devices, such as the
rotator and PBC/PBS may also be silicon based. With respect to
photodiodes, however, hybrid packaging may be provided in order to
provide the photodiodes on the PLC substrate. Further, the PLC may
be made from silicon photonics (SiP) type materials, which include
waveguides having a core that is predominantly silicon based rather
silicon oxynitride based. In that case, substrate 1020 may be a
silicon photonics substrate having such waveguides with a silicon
based core.
[0055] In the examples shown in FIGS. 2A and 2B, the
multiplexer/combiner and demultiplexer/splitter are omitted. As
noted above, by transmitting and receiving optical signals in
separate channels, without multiplexing/demultiplexing on the PIC,
ASE noise is reduced and LOSNR associated with the transmitted
optical signal, as well as ROSNR associated with the received
signal at the receiver, are increased. In addition, as further
noted above, since the multiplexer may be omitted, as in FIG. 2a,
optical signals output from each Tx Block may have more power than
if such optical signals were multiplexed, as in FIG. 1a. Since the
optical signal have more power and can reach the receiver with
sufficient power, an EDFA that would otherwise boost optical power
at the receiver is not required.
[0056] In FIG. 2a each transmit channel Tx Ch 1 to n in FIG. 2a
includes, in addition to a corresponding Tx Block, an isolator and
an erbium doped fiber amplifier (EDFA) including an erbium doped
fiber (EDF), 980 nm pump laser that supplies pump light via a
wavelength division multiplexer (WDM) to the EDF in a
co-propagating fashion, for example. A monitoring diode and tap
(5%) may also be provided at the input to the EDFA. The output of
the EDFA may be supplied to an isolator (it is noted that in each
instance herein, isolators may be provided in order to block or
substantially reduce any back reflected light, which may interfere,
for example, with the operation of the WTL lasers).
[0057] Optical signals output from the isolator may next be input
to a tracking filter that is configured to filter light at
wavelengths other than the optical signal wavelength in order to
reduce ASE. That is the tracking filter, which may be tunable, has
a bandpass that includes the wavelengths of one or more of the
transmitted (i.e., modulated) optical signals. A VOA may then be
provided to adjust the power of light output from the filter to a
desired level and a monitoring tap (2%, for example) and photodiode
may be provided at the output of the VOA. In each of the above
examples, the attenuation of the VOAs may be adjusted based, at
least in part, on the monitored power at the output of each such
VOA.
[0058] As further shown in FIG. 2a, the EDFA amplifiers at the
input to the receiver module 1012 may be omitted, thereby reducing
costs and system complexity. However, VOAs may be provided with
associated monitoring taps at the inputs and outputs thereof to
adjust the incoming optical power to the receivers to a desired
level on each incoming fiber.
[0059] The transceiver shown in FIG. 2b is similar to that shown in
FIG. 2a, with the exception that a multiplexer is provided that
combines the optical signals supplied from each of Tx Ch 1 to Tx Ch
n. Such amplification and filtering, as noted above, prior to the
multiplexer input may further improve optical signal to noise ratio
(OSNR) performance, such that the OSNR is increased compared to
optical signals that are not subject to such filtering an
amplification.
[0060] FIG. 2c shows an alternative configuration for Tx Block 1.
It is understood that the remaining Tx Blocks 2 to n may have the
same or similar structure as the example shown in FIG. 2c. Further,
in order to simplify FIG. 2c, the lenses and isolator are not
shown. Tx Block 1 shown in FIG. 2c is similar to that shown in
FIGS. 1, 2a, and 2b, with the exception that an additional SOA is
provided at the input to both IQ MZMs. By providing two SOAs for
each polarization, i.e., each output of the IQ MZMs, the modulated
optical signals may have sufficient power so that EDFAs, such as
those shown in FIGS. 2a and 2b, may be unnecessary, provided that
back reflections at the facets of waveguides WG1 and WG2, for
example, can be sufficiently reduced.
[0061] FIG. 3 shows an example of a transmit portion of a
transceiver consistent with a further aspect of the present
disclosure. Here, Tx Blocks 1 to N are similar or the same as the
Tx Blocks discussed above in regard to FIG. 1a. However, additional
circuitry is included for wavelength locking, i.e., adjusting the
wavelength of each optical signals to a desired value. In
particular, a laser, such as a distributed feedback (DFB) laser
("Align DFB") may provide a wavelength reference to which the
wavelengths of the other optical signals may be adjusted. The Align
DFB supplies light to a VOA that adjusts the power of such light to
a desired level to permit accurate wavelength control. The light is
then split with a first portion being provided to via a waveguide
on the Tx PLC to a control circuit, such as an a thermal wavelength
locker including a beam splitter, Fabry-Perot etalon (FP) and first
and second photodiodes to sense the light at the input and output
of the etalon. Based on the outputs of the photodiodes, the
wavelength of light output from the Align DFB may be controlled to
a desired value.
[0062] A second portion of the light output from the Align DFB may
be supplied to a receiver including delay line interferometer
including a splitter, a first waveguide having an optical length
longer (i.e., a delay line) than a second waveguide, and 90 degree
optical hybrid. The wavelength of each optical signal may be locked
individually. That is, in order to lock the wavelength of light
output from WTL1, the VOAs associated with each of remaining lasers
WTL2 to WTLn are controlled to effectively block light supplied
from such remaining lasers. Accordingly, a portion of light output
from WTL1 via a tap provided between a first IQ MZM and an SOA is
supplied to a VOA (for power adjustment) and a second tap as an
input to the Delay Line Interferometer. The delay line in
conjunction with the 90 degree optical hybrid and splitter may
generate mixing products indicative of the difference in wavelength
between the Align DFB light and the light output from WTL1. Such
mixing products are sensed by photodiodes, which generate
electrical signals that are subject to further processing to
generate control signals for adjusting the wavelength of light
output from WTL1 so that the difference between that wavelength and
the wavelength of light output from the Align DFB is a desired
value. At which point, the wavelength of the WTL1 light may be
locked. In a similar fashion, VOAs shown in FIG. 3 may be
controlled to selectively block all but one of WTL1 to WTLn to
supply light to the Delay Line Interferometer for wavelength
locking. An advantage of the wavelength locker (WLL) circuitry
shown in FIG. 3 is that, by multiplexing tapped portions of light
output from each of WTL1 to WTLn fewer input/output (I/O)
connections are made to the PIC, as opposed to a conventional
approach in which a separate I/O connection may be provided for
each WTL output. Moreover, in the Tx PIC shown in FIG. 3, the WLL
is integrated such that the taps can be provided on the PIC
substrate.
[0063] The Delay Line Interferometer has a 25 GHz free spectral
range (FSR), which is indicative of the of the capture range of the
wavelength locker.
[0064] VOA monitoring optical taps and photodiodes, as shown in
FIG. 1a, may be also provided at the inputs and outputs of the VOAs
shown in FIG. 3.
[0065] Further, the polarization of the TE and TM components of
each optical signal may be monitored and adjusted or calibrated
with per polarization VOAs and SOAs.
[0066] MZ modulator control may be achieved by further modulating
optical signals output from the modulators with a low frequency
tone and detecting those tones to isolate the modulation of an
optical signal having a particular wavelength. Based on such tone
monitoring, the modulators bias point, for example, may be adjusted
or controlled. Such control may be achieved on a per wavelength or
per optical signal basis.
[0067] FIGS. 4a and 4b show block diagrams of a transmitter and
receiver, respectively, consistent with a further aspect of the
present disclosure. In particular, FIG. 4a shows optical splitters
that receive light from one side of a corresponding WTL. Each
splitter supplies a first portion of the received light to a first
nested MZ modulator pair and a second portion to a second nested MZ
modulator pair. In contrast, as noted above with respect to FIGS.
1a, 2a and 2b, light from opposite facets of each WTL is supplied
to corresponding nest MZ modulator pairs. Further, first and second
alignment lasers are provided to align the PIC with the PLC in both
the transmitter (FIG. 4a) and receiver (FIG. 4b). Further,
wavelength locking similar to that described above in connection
with FIG. 3 can be carried out to adjust the wavelength of each WTL
local oscillator laser in FIG. 4b.
[0068] In greater detail, FIG. 3 shows an optical device, such as
module 310 including a substrate (TX PIC) with a plurality of
lasers (WTL1 to WTLn) provided thereon. In addition, a first
plurality of modulators IQ MZM are provided on the substrate that
respective modulate a first output or first portion of light
supplied from a first side S1 of each WTL, and a second plurality
of modulators (IQ MZM) modulate a second output or second portion
of light supplied from side S2 of each WTL. Module 310 further
includes first waveguides WG1, each of which being optically
coupled to a respective one of the first plurality of IQ MZM
modulators, each of the plurality of first waveguides WG1 extending
to edge E1 of the TX PIC substrate and being optically coupled to a
respective one of the first plurality of IQ MZM modulators.
[0069] Module 310 also includes a plurality of second optical
waveguides WG2, each of which being optically coupled to a
corresponding one of the second IQ MZMs and receiving a second
portion of light supplied from side S2 of each WTL. Each of
waveguides WG2 also extending to edge E1 of the TX PIC substrate
and being optically coupled to a respective one of the second IQ
MZMs.
[0070] A plurality of taps (tap 1 to tap n) are provided on the TX
PIC substrate. Each of the plurality of taps supplying a power
split portion of each of a first plurality of optical signals
supplied by a corresponding one of the IQ MZMs coupled to a side S1
of a respective WTL. A plurality of variable optical attenuators
(VOA 1 to VOA n) are also provided on the substrate, and each
receives a corresponding one of the power split portions from a
corresponding one of the taps (tap 1 to tap n). The outputs of each
VOA are fed by a combiner or tap to a third waveguide WG3, which in
turn supplies the VOA outputs to a receiver circuit.
[0071] As noted above, in operation, each VOA is controlled, such
that one VOA at any given time is controlled to pass the power
split portion of light it receives to the WG3 and on to the
receiver circuit, so that the VOAs selectively pass such light to
the receiver circuit. Based on an outputs of the receiver circuit,
a control circuit may adjust the wavelength of each WTL, for
example by adjusting the temperature of a heater adjacent each
WTL.
[0072] As further noted above, an alignment laser may be provided
that supplies light to an additional VOA that selectively supplies
light to a splitter or coupler having a first output coupled to
waveguide WG3 (and on to the receiver circuit) and a second output
coupled to an a thermal wavelength locker 312 via an optical path
that traverses the TX PLC substrate. Wavelength locker 312 may
include a beam splitter and associated first photodiode,
Fabry-Perot (FP) etalon and a second photodiode to lock alignment
DFB in a known manner. The wavelength of the alignment DFB laser
serves as a reference for the wavelengths of light output from each
of the WTLs. Although a coupler is shown for supplying power split
portion of the light output form the alignment laser to wavelength
locker 312 and the receiver circuit, it is understood that light
from opposing sides of the alignment laser may be supplied to
wavelength locker 312 and the receiver circuit, respectively.
[0073] The receiver circuit includes a delay line interferometer,
which includes a splitter having first and second output coupled to
first ends waveguides WG4 and WG5, respectively. Waveguide WG4 has
a longer length than WG5 and thus constitutes a delay line. Second
ends of waveguides WG4 and WG5 are coupled to input of a 90 degree
hybrid, for example, which may include a multimode (MMI) coupler.
The 90 degree optical hybrid has a plurality of outputs (four in
this example), each of which be coupled to a respective photodiode,
which may be provided on the Tx PIC substrate.
[0074] Variations in wavelength cause each photodiode the receive
different amounts of light. Accordingly, by detecting the
photocurrent generated by each photodiode in the control circuit,
the wavelength of each WTL laser may be monitored and adjusted, as
noted above.
[0075] FIG. 4a, showing a transmit portion 410 similar to module
1010, will next be described in greater detail. Transmit portion
410 includes lasers WTL1 to WTL N+1, for example, each of which
supplying light to a respective one of a plurality of splitters.
Each splitter has three outputs, which supplying first, second, and
third portions of the received light, respectively. the first and
second portions of the received light are supplied to first (MZM X)
and second (MZM Y) modulators, respectively, associated with a
corresponding one of each laser (WTL 1 to WTL N+1). A third portion
of the output laser light is supplied to a respective one of a
plurality of VOAs, which, in a manner similar to that discussed
above in connection with FIG. 3, selectively supply the third
portion of light from each WTL laser to an input of a multiplexer.
The multiplexer, in turn, supplies the selected third portion to a
receiver having a similar construction to that described above.
Namely, the receiver shown in FIG. 4a includes a delay
interferometer, having first (WG1) and second (W2) waveguides (WG1
being the delay line and being longer than WG2), a 2 input/4 output
MMI coupler supplying outputs a plurality (e.g., four) photodiodes.
In a manner similar to that discussed above, the photodiodes supply
electrical signals to a control circuit, which, based on such
electrical signals, controls or adjusts the wavelength of each of
lasers WTL 1 to WTL N+1.
[0076] As further shown in FIG. 4a, an alignment laser (ALN laser
2) also supplies light via a VOA to an additional input of the
multiplexer. ALN laser 2 may serve as a wavelength references, for
controlling the wavelength of light output from the other lasers.
An additional laser (ALN Laser 1) may also be provided, via a
waveguide (WG) that passes across the TX PLC substrate to insure
proper spatial alignment with fiber of a fiber array coupled to
transmit portion 410. Light output from a second side of ALN Laser
2 may also be provided to a pass though waveguide WG to another
fiber of the fiber array for similar spatial alignment or fiber
coupling purposes. Both ALN laser 1 and ALN laser 2 may be a DFB
laser.
[0077] In the example shown in FIG. 4a, light from opposite sides
of ALN laser 2 is used for wavelength control and alignment
purposes, respectively. However, a coupler or splitter may be
provided that receives light from one side of ALN laser 2 to
provide a first portion of the received light for alignment
purposes and a second portion of the received light for wavelength
control purposes. Such a splitter configuration is shown in FIG.
1b.
[0078] Further, light output (a first portion) from one side of
each WTL in FIG. 4a may be provided to MZM X, for example, as shown
in FIG. 1a. Light from the second side (a part of the light output
from the WTL laser) may then be provided to a coupler or splitter,
such as that shown in FIG. 1b with a first output of the splitter
providing a second portion of the laser light to MZM Y, for
example, and a third portion of the laser light to one of the VOAs
shown in FIG. 4a.
[0079] In addition, a splitter may be provided to supply a portion
of light output from ALN laser 2 on the pass through waveguide, for
example, to a wavelength locker circuit (second control circuit) to
control the wavelength of ALN laser 2 in a manner similar to that
discussed above.
[0080] Turning to FIG. 4b, receiver module 450 will next be
described in detail. Receiver module 450 is similar in structure
and operation as receiver module 1012. For example, both receiver
modules have waveguides feeding light to corresponding optical
hybrid circuits, which also receiver light from corresponding local
oscillators, and provide mixing products to groups of photodiodes.
However, like transmitter module 410 shown in FIG. 4a, each local
oscillator lasers (WTL1 to WTL N+1) supplies light to a
corresponding one of a plurality of splitters. Each splitter, in
turn, supplies a first portion of the received light to a
corresponding one of first 90 degree optical hybrid circuits
(90.degree. Hyb X), a second portion to a corresponding one of
second 90 degree optical hybrid circuits (90.degree. Hyb Y), and a
third portion to a respective one of a plurality of VOAs. Each of
the first 90 degree optical hybrids is also coupled to a
corresponding one of a plurality of first waveguides (WG1) and each
of the second 90 degree optical hybrids is further coupled to a
corresponding one of a plurality of second waveguides (WG2). Each
first waveguide WG1 supplies a polarization rotated first optical
signal output from a corresponding polarization beam splitter
(PBS), and each second waveguide WG2 supplies a second signal from
the corresponding PBS located on the RX PLC substrate in a manner
similar to that described above.
[0081] Each VOA selectively supplies the third portion of light
from each local oscillator WTL to a corresponding input of the
multiplexer, and the multiplexer, in turn, provides the selected
third portion to a receiver including a DLI interferometer and
having structure similar to or the same as that described above for
wavelength control. In the example shown in FIG. 4b, the receiver
is located off the RX PIC substrate, but may also be provided on
the substrate as in FIG. 4a.
[0082] Moreover, in the example shown in FIG. 4a, light from one
side of ALN laser 2 is used for wavelength control and alignment
purposes. A coupler or splitter may be provided that receives such
light from one side of ALN laser 2 to provide a first portion of
the received light for alignment purposes and a second portion of
the received light for wavelength control purposes. Such a splitter
configuration is shown in FIG. 1b. It is understood, however, that
light from both sides of ALN laser 2 may be used for alignment and
wavelength control purposes, respectively, as in FIG. 4a.
[0083] Further, as in FIG. 4a, light output (a first portion) from
one side of each WTL may be provided to 90.degree. Hyb X, for
example, as shown in FIG. 1a. Light from the second side (a part of
the light output from the WTL laser) may then be provided to a
coupler or splitter, such as that shown in FIG. 1b with a first
output of the splitter providing a second portion of the laser
light to 90.degree. Hyb Y, for example, and a third portion of the
laser light to one of the VOAs shown in FIG. 4b.
[0084] In addition, a splitter may be provided to supply a portion
of light output from ALN laser 2 on the pass through waveguide, for
example, to a wavelength locker circuit (second control circuit) to
control the wavelength of ALN laser 2 in a manner similar to that
discussed above. Also, light from ALN laser 1 may be passed across
the Rx PLC in a manner similar to that discussed above in
connection with FIG. 4a for spatial alignment or to align each
fiber of the fiber array with waveguide (WG) input to each PBS.
Further, it is understood that receiver module 450 may be commonly
housed with transmit module 410 or provided on a common interposer
substrate as in FIG. 1a.
[0085] In each of the above-described embodiment, the elements that
provide the optical outputs of the TX PIC or provide optical inputs
to the RX PIC are formed on a PLC substrate. Consistent with the
present disclosure, free space optics (FSO) including lenses,
polarization rotators, PBCs, PBSs, and isolators may be provided as
bulk or individual devices which are not integrated on a substrate.
Various FSO configurations will next be described with reference to
FIGS. 5-44 to provide polarization multiplexed optical signals
to/from optical fibers, such as an array of fibers. In the
foregoing description, it is understood that the RX and/or TX PICs
described above in connection with FIGS. 1a, 1b, 1c, 2a, 2b, 2c, 3,
4a, and 4b may be employed in each of these FSO configurations.
[0086] In FIGS. 5 and 6, drive signals (Tx) and data carrying
signals (Rx) for example, are provided along a side opposite the
side that optical signals are output from the PIC ("180.degree.
handedness"). In addition, a high temperature co-fired ceramic
(HTCC) may employed as the package material and electrical
connection to the PIC may be provided on a low temperature co-fired
ceramic. As further shown in FIG. 5, each optical signal is
supplied to a corresponding optical fiber in the ribbon fiber
cable. In this example, the ribbon fiber cable may include nine
fibers.
[0087] Further, in FIG. 5, the Tx PIC may be flip-chip or flip-chip
compression bonded to the interposer. It is understood, however,
that the Rx PIC may also be bonded to the interposer, for example,
as shown in FIG. 1a. The Rx PIC may also be flip-chip or flip-chip
compression bonded to the interposer. In addition, in the example
shown in FIG. 5, only the Tx PIC is bonded to the interposer.
However, both Tx and Rx PICs may be bonded to the same interposer
or to respective interposers in a transceiver package. Further, a
transceiver PIC having both Tx and Rx circuits, such as the
transceiver PIC noted above, may be attached, by, for example, flip
chip bonding to an interposer.
[0088] FIG. 7 shows detailed plan and cross-sectional views of a
package housing a receiver. In this example, the edge of the RX PIC
that receives optical signals from the PLC is angled so as to
minimize back reflections that may interfere with operation of the
WTL local oscillators. In addition, the lens array shown in FIG. 7
may correspond to the lenses discussed above. Here, the lens array
is mounted on a carrier or substrate. The configuration shown in
FIG. 7 permits "interleaved TE and TM waveguides" in which
waveguides on the PIC and PLC are paired, and one waveguide of each
pair carries TE polarized optical signals and the other waveguide
of each pair carries TM polarized optical signals. Other features
of FIG. 7 are noted in the drawing.
[0089] FIG. 8 shows an example of a transmitter package including
an angled PIC facet for reduced back reflections, a lens array for
coupling between the PIC and PLC, and an isolator before the PLC
(with a wedge after the isolator to permit a horizontally mounted
PLC). Other features of FIG. 8 FIG. are noted in the drawing.
[0090] FIGS. 9 and 10 illustrate transmitter packaging examples in
which the lenses are omitted, and light is coupled from the PIC to
PLC by direct coupling or butt coupling. In FIG. 9, the optical
fibers carrying optical signals generated by the PIC are oriented
such that end segments of the fibers are straight or form a 180
degree angle with a direction at which optical signals are output
from the PIC. In FIG. 10, however, the optical fiber segments are
oriented at a 90 degree angle, for example, to further minimize
back reflection. Other angles, however, are contemplated
herein.
[0091] Alternative package configurations are shown in FIGS. 11a
and 11b in which optical fibers are supplied through a side of the
package (FIG. 11a) that is oriented 90 degrees relative to the
output signal direction form the PIC, as well as through a side of
the package (FIG. 11b) whereby the optical fibers extend parallel
to and form a 180-degree angle with the optical signal output
direction.
[0092] FIG. 12 shows various transmitter packaging configurations
and views in which the PIC and PLC are directly attached to one
another or butt joined.
[0093] FIG. 13 shows cross-sectional and perspective view of
packages in which lens arrays are provided adjacent the PIC and the
PLC to optically couple optical signals from the PIC to the PLC in
the transmitter.
[0094] FIG. 14 shows an alternative view of a fiber array supplying
optical signals at a 90-degree angle relative to a PIC output/input
direction. Here, the PIC and PLC may be coupled to one another with
an epoxy or the optical signals may pass through an air gap.
[0095] FIG. 15 is a plan view of transmitter or receiver that shows
details of an exemplary lens array. Here, stepped lenses may be
employed to direct light from the PIC to the PLC or from the PLC to
the PIC. In this example, the far field angle of light output from
the PIC is 23 degrees and emission angle is 23 degrees to minimize
back reflections. The pitch between adjacent waveguides is
preferably less than or equal to 1 mm and preferably less than 600
microns, and in this example, is 250 microns. FIG. 16 shows
perspective view of the transmitter or receiver shown in FIG.
15.
[0096] FIG. 17 shows an alternative configuration in which the PIC
is not oriented at an angle relative to the PLC, but the emission
angle is maintained at 23 degrees. FIG. 18 shows a perspective view
of the configuration shown in FIG. 17.
[0097] FIGS. 19 and 20 show plan and perspective view of an
alternative arrangement in which the emission angle from the PIC is
zero degrees and the far field angle is 25 degrees.
[0098] FIGS. 21 and 22 show plan and perspective view of another
exemplary arrangement in which the lens array directs light outside
the plane of the PIC (upward and out of the paper in the lower
drawing in FIG. 21).
[0099] FIG. 23 shows a further exemplary arrangement in which the
PBC and PBS are implement half wave plate or retarder. In this
example, the PLC is omitted, and the output of the rotated TM light
is output (or received in the instance of a receiver) directly to
an array of lenses and to an array of single mode fibers (SMF). In
a receiver configuration, light is input to the fiber lens array,
split by the half wave plate or retarder and TE light is supply to
both inputs of the PIC via the PIC lens array.
[0100] FIG. 24 shows a perspective view of the configuration shown
in FIG. 23.
[0101] FIGS. 25 and 26 show plan and perspective views of a
configuration in which wedge-shaped isolators are provided to
further direct light output from the transmitter PIC through the
PBC/PBS block. Thus, the PIC, isolator, and half wave plate can be
arranged linearly as opposed to the bent arrangement shown in FIGS.
23 and 24.
[0102] FIGS. 27 and 28 show plan and perspective view of a similar
configuration as that shown in FIGS. 25 and 26, but the wedges have
been omitted. Instead, lenses may be provided that collect and
direct the light through the isolator.
[0103] FIG. 27 shows a PIC substrate, which, in the case of a TX
PIC, includes lasers, modulators, and waveguides, and other
features noted in the above description of FIGS. 1a, 1b, 1c, 2a,
2b, 2c, 3, 4a, and 4b. Consistent with an aspect of the present
disclosure, at least one optical element is provided that
collimates, focuses, rotates a polarization of at least one of, or
combines modulated optical signals (e.g., TE and TE' optical signal
output from the PIC). In addition, in the example shown in FIG. 27,
an array of lenses in the Fiber Lens Array couples light to/from an
array of single mode optical fibers in the SMF Array.
[0104] In greater detail, waveguides WG1 and WG2 as shown in FIG. 1
may be tilted to form a non-perpendicular angle .theta. with facets
F1 and F2, respectively (see also FIG. 36). The tilt angle
associated with waveguides WG1 may be the same or different than
the tilt angle associated with waveguides WG2. Such tilting may
reduce back reflections which may interfere with operation of
lasers on the TX PIC, such as the WTL lasers discussed above. Each
of N waveguides WG1 supplies a respective one of N TE polarized
modulated optical signals to a corresponding one of N lenses in
Array1. Similarly, each of N waveguides WG2 supplies a respective
one of N TE polarized modulated optical signals (designated TE' in
FIG. 27) to a corresponding one of lenses in Array2. Each of the
lenses in Array1 and Array 2, which may extend parallel to PIC or
waveguide facets or edges F1 and F2 (both of which may be portions
of the same facet or edge), may be a collimating lens to collimate
the received optical signals. The collimated optical signals next
pass through an isolator, which is shown as a bulk isolator,
although a plurality of individual optical isolators may be
provided, one for each modulated optical signal, as shown in FIG.
1a, for example. The N optical signals output from Array1 are next
supplied to a beam splitter and the optical signals supplied from
Array2 are fed to a half wave plate, for example, which may rotate
the polarization of such signals from a TE polarization to a TM
polarization. The rotated signals are reflected off a reflector or
mirror to splitter/combiner, which may include a beam splitter or
reflector to reflect the rotated (TM) optical signals to the fiber
lens array and allow the non-rotated (TE) optical signals from
Array1 to pass through to the fiber lens array. Thus, Block 1, in
this example, is a polarization beam combiner, such that each of N
lenses in the fiber lens array receives a corresponding one of N
polarization multiplexed optical signals, wherein each polarization
multiplexed optical signals includes a respective one of the
unrotated TE optical signals form Array1 and a rotated (TM) from
Array2. Each N lens in the Fiber lens array may focus or couple
each of N received polarization multiplexed optical signals into a
corresponding one of N fibers in single mode fiber (SMF) array.
[0105] In a receive configuration, the optical signal flow
described above may be reversed. For example, each of N
polarization multiplexed optical signals may be input from a
corresponding optical fiber in the SMF array, and each such signal
may be supplied to a corresponding one of N lenses in the Fiber
Lens Array. Each such lens, when configured to receive optical
signals from the SMF array, collimates such optical signals and
supplies the signals to Block 1. The splitter/combiner plate or
component (e.g., a beam splitter or reflector) is configured to
reflect TM polarized light (signal) or component of each
polarization multiplexed optical signal while allowing the TE
polarized light (signal) or component to pass to Array1. The TM
signal is reflected off of the mirror in Block 1 and directed
toward the rotator of half wave plate, which rotates the
polarization of the TM signal to have a TE polarization. The
rotated optical signals are then fed to a corresponding one of N
lenses Array2, and, as noted above, the received TE signals are
supplied to a corresponding one of lenses in Array1.
[0106] Each lens in Array1 and Array2 is configured to focus, in
this example, the received optical signals onto a corresponding one
of the waveguides (WG) on the RX PIC, as described above in
connection with FIG. 1a, for example. As further described above,
the received optical signals are fed to corresponding optical
hybrids for further processing.
[0107] In the above example, each of the lenses in Array1 and
Array2 is tilted relative to facet F1, for example. However, in the
embodiment shown in FIG. 15, the PIC substrate may be tilted
relative to the propagation direction of the collimated optical
signals by an angle .theta., and waveguides WG2 in FIG. 15 may be
perpendicular to facet F or edge of the PIC.
[0108] In addition, although a block is shown having bulk
components, such as the half wave plate, isolator, and combiner
splitter that rotate and combine each of the received optical
signals, it is understood that individual polarization rotators,
combiners and splitters may be provided on a channel by channel
basis. For example, the individual polarization rotators,
combiners, and splitters shown in FIGS. 1a, 59, and 60 may be
provided as stand alone components instead of being integrated or
otherwise provided on a substrate.
[0109] In addition, waveguides WG1 and WG2 may be provided
perpendicular to the PIC facet, as shown in FIG. 29. Here, lenses
in the PIC lens array also extend parallel to facet F and each lens
in the PIC lens array (including Array1 and Array2) are not tilted
but are also oriented parallel to facet F.
[0110] FIGS. 29 and 30 show plan and perspective view of another
configuration in which the emission angle of light output from the
PIC is zero degrees. This configuration may be subject to back
reflections.
[0111] FIGS. 31 and 32 show plan and perspective views of an
arrangement in which the isolator is oriented at an angle relative
to the PIC and a wedge (made of silicon, for example) directs light
to the PBC/PBS and to the lens array and fiber array. As shown in
FIG. 31, the optical path associated with optical signals
propagating through the isolator and to the PBC/PBS block is bent,
such that the propagation direction of such optical signals is
changed
[0112] FIG. 33 shows a ray trace diagram of light output from the
PIC. Here, performance may depend on incident angles to the PBC.
Also, fiber facets are not aligned to be on the same plane, and
waveguides may cross one another in the PIC. The configuration
shown in FIG. 33 does not include a mode transformer.
[0113] FIG. 34 shows an example of a ray trace diagram in which
cylindrical lenses are used to couple light from the PIC to the
isolators, for example.
[0114] FIG. 35 shows an alternative configuration in which a
photonic wire is used to couple optical signals from the PIC to the
PLC.
[0115] FIGS. 36-44 show the same configuration as that shown in
FIG. 34, but with different emission angles and far field angles.
In FIG. 36, for example, multiple optical signals, each having a
different wavelength are fed to each lens (PIC lens) and the
polarization multiplexed output of the Block 1 (in a TX or transmit
configuration) are supplied to one lens, instead of each being
supplied to a corresponding one of a plurality of lenses, as in
FIG. 27. Here, N polarization multiplexed signals are fed to a
number of lenses in the PIC lens array that is less than N.
Further, the lenses disclosed herein may be provided as a plurality
of discrete lenses or as a single piece, as a single lens that
receives multiple optical signals, as in FIG. 36, for example, or a
plurality of lenses that are fused or bonded or formed from a
single of suitable material.
[0116] FIG. 45 shows an alternative configuration similar to that
shown in FIG. 2a but including tracking filters in a micro-optics
box. Each of the tracking filters supplies a corresponding optical
signal to a respective VOA, which adjust the power each such
optical signal prior to input to a passive multiplexer or power
combiner, for example. As further shown in FIG. 45, each VOA has
associated monitoring taps and photodiodes to adjust measure and
thus control the optical power output from each VOA. In addition, a
plurality of (or N) splitters or taps are provided that are coupled
to a corresponding waveguide WG1. Each tap has an input that
receives light from a corresponding laser via an optional
corresponding SOA, first output that provides part of such light,
and a second output that provides a portion of the light generated
by the laser, albeit modulated, on a corresponding one of
waveguides WG1. As further shown in FIG. 45, the second output of
each tap feeds connects to a corresponding one of N photodiodes.
Similarly, taps and associated photodiodes may be provided that are
coupled to each of waveguides WG2. As noted above, there may be N
(N being an integer) waveguides WG1 and N waveguides WG2 (for a
total of 2N waveguides), such that a respective one of N taps and
photodiodes are coupled to each waveguide WG1 and a respective one
of N taps and associated photodiodes are coupled to each waveguide
WG2 (a total of 2N taps and photodiodes).
[0117] FIG. 46 shows a configuration like that shown in FIG. 45,
but with the EDFAs prior to the multiplexer being omitted. Further,
in FIG. 47, both the EDFAs and the tracking filter are omitted.
[0118] FIGS. 48-55 list and show various parameters associated with
lenses that may be employed in the various examples discussed
above. As noted previously, such lenses may be made of silicon. In
particular, light is directed toward a portion of each lens in
these examples, as opposed to impinging across the entire face of
the lens.
[0119] In FIG. 56, a plan view of a transmitter configuration
including an array of such lenses is shown, and FIG. 57 show a
perspective view of the transmitter shown in FIG. 56.
[0120] FIG. 58 shows an example in which outputs are coupled to
rotators and PBCs on the PLC. In order to simplify FIG. 58, only
selected couplings are shown. A mode adapter may be provided at the
output of each PBC and relatively close to the edge of the PLC in
order to couple the modulated optical signals to the lens array
with reduced loss. The lens array, in turn, may direct the optical
signals to corresponding a corresponding isolator in an array of
isolators. Each isolator passes the received optical signal to a
corresponding optical fiber.
[0121] FIG. 59 illustrates another embodiment consistent with an
aspect of the present disclosure. FIG. 59 shows a PIC substrate,
which, in the case of a TX PIC, includes lasers, modulators, and
waveguides, and other features noted in the above description of
FIGS. 1a, 1b, 1c, 2a, 2b, 2c, 3, 4a, and 4b. Consistent with an
aspect of the present disclosure, at least one optical element is
provided that collimates, focuses, rotates a polarization of at
least one of, or combines modulated optical signals (e.g., TE and
TE' optical signal output from the PIC). In addition, in the
example shown in FIG. 59, an array of lenses in the Fiber Lens
Array couples light to/from an array of single mode optical fibers
in the SMF Array.
[0122] In greater detail, waveguides WG1 and WG2 as shown in FIG. 1
may be tilted to form a non-perpendicular angle .theta. with facet
F, as noted above with respect to FIG. 27. Each of N waveguides WG1
supplies a respective one of N TE polarized modulated optical
signals to a corresponding one of N lenses in the PIC lens.
Similarly, each of N waveguides WG2 supplies a respective one of N
TE polarized modulated optical signals (designated TE' in FIG. 59)
to a corresponding one of lenses in the PIC lens array. Each of the
lenses in the PIC lens array, which may extend parallel to PIC or
waveguide facets or edges F, may be a collimating lens to collimate
the received optical signals. Each of the TE collimated signals is
supplied to a corresponding one of a plurality of groupings or
blocks, each block including a splitter/combiner, a rotator, and a
mirror. Likewise, each TE' collimated signal is supplied to a
corresponding block. As shown in FIG. 59, the blocks or groupings
are provided in an array.
[0123] A rotator in each block, such as a half wave plate, rotates
the polarization of each TE's signal, such that each TE' signal has
a TM polarization. The rotated signal in each block is next
provided to a mirror, which reflects the rotated signal to a
combiner. The combiner in each block also receives a corresponding
one of the TE signals, such that corresponding TE signal passes
through the combiner, while the rotated TE' signal (now TM) is
reflected by the combiner, as shown in FIG. 59. As a result, a
polarization multiplexed signal is formed and output from each
block. Each polarization multiplexed signal is provided to a
corresponding lens in the Fiber Lens Array and focused on to an end
of a respective fiber. In the Examiner shown in FIG. 59, 2N (N=6)
waveguides provide optical signals to N blocks or groupings, which,
in turn provide each of N polarization multiplexed optical signals
to a corresponding one of N fibers.
[0124] An additional waveguide (WG (align)) may be provided to
supply light for alignment of the PIC, PIC lens array, blocks,
fiber lens array and fiber.
[0125] In a receive configuration, the optical signals propagate in
the reverse direction relative to that described above to an RX
PIC. Namely, each of N polarization multiplexed optical signals are
supplied by a corresponding one of N optical fibers via a
corresponding lens in the fiber lens array to a respective block.
In the receive configuration, each lens in the fiber lens array
collimates the received optical signal. The splitter in each block
or grouping passes a respective one of the received TE polarized
optical signals or components of the polarization multiplexed
signal, but reflects the corresponding TM optical signal or
component to the mirror, which directs the TM optical signal to the
rotator or half waveplate in the block. The rotator, in turn
rotates the polarization of the TM signal, such that the TM signal
has a TE polarization and the rotated signal is directed to a
corresponding one of waveguides WG2 as a TE's optical signal. The
TE optical signal is supplied from the splitter and output to a
corresponding one of waveguide TE. Both optical signals are then
subject to mixing with local oscillator late, conversion to
electrical signals and further processing, as discussed above.
[0126] FIG. 60 shows a configuration similar to that shown in FIG.
59. In FIG. 60, however, the optical fibers are provided in a fiber
array, such as in a ribbon cable. In addition, end portions of each
fiber may be mounted or attached to a support.
[0127] In the above examples, the lenses provided in the PIC lens
array and the Fiber Lens array may be attached to one another, be
mounted on a support. Alternatively, the lenses may collectively be
formed as a unitary in or integral unit, as shown in the figures
above. In addition, the lenses may be provided as part of a complex
lens.
[0128] In the above examples, N lasers are provided, and optical
signals are supplied to N optical fibers. It is understood,
however, the free space optics and PLC implementations discussed
above may couple to more than N or less than N optical fibers. For
example, additional optical fibers that do not carry optical
signals may be provided as spare fibers to carry optical signals in
the event of a fault in a working fiber or may be used in the event
additional capacity is required. Accordingly, coupling to M optical
fibers is also contemplated herein where is an integer less than N
or greater than N.
[0129] A further embodiment of the present disclosure will next be
described with reference to FIG. 61. In FIG. 61 a PIC (provided on
a first substrate), which may include any one or both of the
above-described RX PIC and TX PIC, may be provided on an
interposer, which may be a substrate (a second substrate) which may
include an insulative or semiconductor material. An integrated
circuit, such as an application specific integrated circuit (ASIC)
may further be provided on the interposer substrate. If the PIC is
a TX PIC, the ASIC may provide relatively high frequency or radio
frequency (RF) drive signals to the above-described modulators in
the TX PIC over a plurality of transmission lines formed on or in
the interposer substrate. In one example, the modulators described
above have a relatively short length that does not require
termination with a fixed impedance or resistance. Such modulators
constitute lumped elements, as shown in FIG. 61. In another
example, the modulators have a longer length and are provided with
a termination having such fixed impedance or resistance. Such
modulators constitute traveling wave elements, and the termination
for such traveling wave element may be provided off the PIC
substrate (FIG. 62) or on the PIC substrate (FIG. 63). Monitoring
signals (indicative of the performance of devices on the PIC) may
be output from the PIC to the ASIC and control signals (for
controlling or adjusting a parameter associated with a device on
the PIC, such as a wavelength of light output from a laser or the
attenuation of a VOA) output from the ASIC to the PIC are typically
at relatively low frequency, and may be referred to as DC (direct
current) signals that are generated and received by DC circuitry in
the ASIC. RF drive signals, however, may be generated by RF
circuitry in the ASIC. The DC control signals may be supplied
through "DC control" electrodes or traces on the interposer
substrate. DC controls traces may also supply such DC signal off
the interposer. Connection to the DC control traces may be made
with wire bonding to bond pads on the interposer. Connections to
the RF transmission lines, however, may be made through
thermo-compression bonding.
[0130] If the PIC is an RX PIC, the same or similar connections DC
and RF connections would be made. The transmission lines, however,
may carry RF signals from the above-described photodiodes to the
ASIC for further processing by, for example, transimpedance
amplifiers, analog-to-digital conversion, and carrier recovery. As
noted above, such photodiodes receive modulated optical signal
mixed with local oscillator light from the optical hybrid circuits.
The photodiodes may have a relative short length and may thus
constitute lumped elements. Alternatively, the photodiodes may have
a relative long length and constitute travelling wave elements, in
which case, a termination impedance or resistance may be provided
on or off the PIC, as noted above.
[0131] In one example, the PIC and the ASIC are flip chip bonded to
interposer substrate. For ease of explanation, optical outputs of
the PIC, the optical fibers, and the coupling to the optical fibers
described above are not shown in FIGS. 61-63. In addition, FIG. 6
shows a heat managing element may be provided that is thermally
coupled to the PIC and an ASIC. In FIG. 6, the heat managing
element may include a heat spreader and a thermal electric cooler.
Alternatively, either one of these elements may be employed. In
addition, the heat managing element may include a heat pip or a
heat sink.
[0132] Other embodiments will be apparent to those skilled in the
art from consideration of the specification. It is intended that
the specification and examples be considered as exemplary only.
* * * * *