U.S. patent application number 15/405209 was filed with the patent office on 2018-03-22 for thermally compensating spot-size converter for an athermal laser.
This patent application is currently assigned to Oracle International Corporation. The applicant listed for this patent is Oracle International Corporation. Invention is credited to Jock T. Bovington, Stevan S. Djordjevic, Ashok V. Krishnamoorthy, Xuezhe Zheng.
Application Number | 20180083420 15/405209 |
Document ID | / |
Family ID | 61600206 |
Filed Date | 2018-03-22 |
United States Patent
Application |
20180083420 |
Kind Code |
A1 |
Bovington; Jock T. ; et
al. |
March 22, 2018 |
THERMALLY COMPENSATING SPOT-SIZE CONVERTER FOR AN ATHERMAL
LASER
Abstract
A laser includes a reflective gain medium (RGM) comprising an
optical gain material coupled with an associated reflector. The RGM
is coupled to a spot-size converter (SSC), which optically couples
the RGM to an optical reflector through a silicon waveguide. The
SSC converts an optical mode-field size of the RGM to an optical
mode-field size of the silicon waveguide. A negative thermo-optic
coefficient (NTOC) waveguide is fabricated on top of the SSC. In
this way, an optical signal, which originates from the RGM, passes
into the SSC, is coupled into the NTOC waveguide, passes through
the NTOC waveguide, and is coupled back into the SSC before passing
into the silicon waveguide. During operation, the RGM, the
spot-size converter, the NTOC waveguide, the silicon waveguide and
the silicon mirror collectively form a lasing cavity for the
athermal laser. Finally, a laser output is optically coupled to the
lasing cavity.
Inventors: |
Bovington; Jock T.; (La
Jolla, CA) ; Djordjevic; Stevan S.; (San Diego,
CA) ; Zheng; Xuezhe; (San Diego, CA) ;
Krishnamoorthy; Ashok V.; (San Diego, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Oracle International Corporation |
Redwood Shores |
CA |
US |
|
|
Assignee: |
Oracle International
Corporation
Redwood Shores
CA
|
Family ID: |
61600206 |
Appl. No.: |
15/405209 |
Filed: |
January 12, 2017 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
62398366 |
Sep 22, 2016 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 6/122 20130101;
G02B 2006/12135 20130101; H01S 5/141 20130101; H01S 5/02469
20130101; G02B 6/1228 20130101; H01S 5/0612 20130101; G02B 6/0011
20130101 |
International
Class: |
H01S 5/068 20060101
H01S005/068; H01S 5/30 20060101 H01S005/30; H01S 5/22 20060101
H01S005/22 |
Goverment Interests
GOVERNMENT LICENSE RIGHTS
[0002] This invention was made with U.S. government support under
Agreement No. HR0011-08-9-0001 awarded by DARPA. The U.S.
government has certain rights in the invention.
Claims
1. An athermal laser, comprising: a reflective gain medium (RGM)
comprising an optical gain material coupled with an associated
reflector; a silicon waveguide; a silicon mirror, which is
optically coupled to the silicon waveguide; a spot-size converter
(SSC), which optically couples the RGM to the silicon waveguide,
wherein the SSC converts an optical mode-field size of the RGM to
an optical mode-field size of the silicon waveguide; a negative
thermo-optic coefficient (NTOC) waveguide comprised of an NTOC
material fabricated on top of the SSC, whereby an optical signal,
which originates from the RGM, passes into the SSC, is coupled into
the NTOC waveguide, passes through the NTOC waveguide, and is
coupled back into the SSC before passing into the silicon
waveguide; wherein the RGM, the spot-size converter, the NTOC
waveguide, the silicon waveguide and the silicon mirror
collectively form a lasing cavity for the athermal laser; and a
laser output, which is optically coupled out of the lasing
cavity.
2. The athermal laser of claim 1, wherein the lasing cavity
includes a length l.sub.Si through silicon, a length l.sub.NTOC
through the NTOC material, a length l.sub.OGM through the optical
gain material, and a negligible length through the SSC; wherein the
effective refractive index of silicon is n.sub.Si, the effective
refractive index of the NTOC material is n.sub.NTOC, and the
effective refractive index of the optical gain material is
n.sub.OGM; wherein the effective thermo-optic coefficient (TOC) of
silicon is dn.sub.Si/dT, the effective TOC of the NTOC material is
dn.sub.NTOC/dT, and the effective TOC of the optical gain material
is dn.sub.OGM/dT; and wherein
l.sub.NTOC.apprxeq.l.sub.OGM*(dn.sub.OGM/dT-dn.sub.Si/dT)/(dn.sub.Si/dT-d-
n.sub.NTOC/dT), whereby the effective TOC of a portion of the
lasing cavity that passes through the optical gain material and the
NTOC material is substantially the same as the TOC of silicon.
3. The athermal laser of claim 1, wherein the silicon mirror
comprises one of: a microring mirror, and a distributed Bragg
reflector (DBR).
4. The athermal mirror of claim 1, wherein the silicon mirror is a
tunable silicon mirror, which includes a thermal-tuning
mechanism.
5. The athermal laser of claim 1, wherein the silicon mirror is an
athermal silicon mirror, which includes a cladding of the NTOC
material.
6. The athermal laser of claim 1, wherein a bottom surface of the
NTOC, which is in contact with the SSC, is clad with a low-index
dielectric material; and wherein a top surface of the NTOC is
covered by one of the following: air, a low-index dielectric
material, and a polymer.
7. The athermal laser of claim 1, wherein the RGM in located on a
gain chip that is separate from a silicon photonic chip, which
includes the silicon waveguide, and the silicon mirror.
8. The athermal laser of claim 1, wherein the NTOC material
comprises titanium dioxide (TiO.sub.2).
9. The athermal laser of claim 1, wherein the spot-size converter
is comprised of one of the following: silicon oxynitride (SiON),
wherein the nitrogen-to-oxygen ratio may vary; and stoichiometric
or low-stress silicon nitride (SiNx).
10. The athermal laser of claim 1, wherein the optical gain
material is comprised of a III-V semiconductor.
11. A system, comprising: at least one processor; at least one
memory coupled to the at least one processor; and an optical
transmitter for communicating optical signals generated by the
system, wherein the optical transmitter includes an athermal laser
comprising: a reflective gain medium (RGM) comprising an optical
gain material coupled with an associated reflector; a silicon
waveguide; a silicon mirror, which is optically coupled to the
silicon waveguide; a spot-size converter (SSC), which optically
couples the RGM to the silicon waveguide, wherein the SSC converts
an optical mode-field size of the RGM to an optical mode-field size
of the silicon waveguide; a negative thermo-optic coefficient
(NTOC) waveguide comprised of an NTOC material fabricated on top of
the SSC, whereby an optical signal, which originates from the RGM,
passes into the SSC, is coupled into the NTOC waveguide, passes
through the NTOC waveguide, and is coupled back into the SSC before
passing into the silicon waveguide; wherein the RGM, the spot-size
converter, the NTOC waveguide, the silicon waveguide and the
silicon mirror collectively form a lasing cavity for the athermal
laser; and a laser output, which is optically coupled out of the
lasing cavity.
12. The system of claim 11, wherein the lasing cavity includes a
length l.sub.Si through silicon, a length l.sub.NTOC through the
NTOC material, a length l.sub.OGM through the optical gain
material, and a negligible length through the SSC; wherein the
effective refractive index of silicon is n.sub.Si, the effective
refractive index of the NTOC material is n.sub.NTOC, and the
effective refractive index of the optical gain material is
n.sub.OGM; wherein the effective thermo-optic coefficient (TOC) of
silicon is dn.sub.Si/dT, the effective TOC of the NTOC material is
dn.sub.NTOC/dT, and the effective TOC of the optical gain material
is dn.sub.OGM/dT; and wherein
l.sub.NTOC.apprxeq.l.sub.OGM*(dn.sub.OGM/dT-dn.sub.Si/dT)/(dn.sub.Si/dT-d-
n.sub.NTOC/dT), whereby the effective TOC of a portion of the
lasing cavity that passes through the optical gain material and the
NTOC material is substantially the same as the TOC of silicon.
13. The system of claim 11, wherein the silicon mirror comprises
one of: a microring mirror, and a distributed Bragg reflector
(DBR).
14. The system of claim 11, wherein the silicon mirror is a tunable
silicon mirror, which includes a thermal-tuning mechanism.
15. The system of claim 11, wherein the silicon mirror is an
athermal silicon mirror, which includes a cladding of the NTOC
material.
16. The system of claim 11, wherein a bottom surface of the NTOC,
which is in contact with the SSC, is clad with a low-index
dielectric material; and wherein a top surface of the NTOC is
covered by one of the following: air, a low-index dielectric
material, and a polymer.
17. The system of claim 11, wherein the RGM in located on a gain
chip, which is separate from a silicon photonic chip that includes
the silicon waveguide, and the silicon mirror.
18. The system of claim 11, wherein the NTOC material comprises
titanium dioxide (TiO.sub.2).
19. The system of claim 11, wherein the spot-size converter is
comprised of one of the following: silicon oxynitride (SiON),
wherein the nitrogen-to-oxygen ratio may vary; and stoichiometric
or low-stress silicon nitride (SiNx).
20. A method for operating an athermal laser, comprising:
generating an optical signal by powering a reflective gain medium
(RGM) comprising an optical gain material coupled with an
associated reflector; channeling the optical signal through a
spot-size converter (SSC) and into a silicon waveguide, wherein the
SSC converts an optical mode-field size of the RGM to an optical
mode-field size of the silicon waveguide; wherein a negative
thermo-optic coefficient (NTOC) waveguide comprised of an NTOC
material is fabricated on top of the SSC, whereby the optical
signal, which originates from the RGM, passes into the SSC, is
coupled into the NTOC waveguide, passes through the NTOC waveguide,
and is coupled back into the SSC before passing into the silicon
waveguide; channeling an optical signal from the silicon waveguide
into a silicon mirror; and optically coupling light from a lasing
cavity, which is formed by the RGM, the SSC, the NTOC waveguide,
the optical waveguide, and the silicon mirror, into a laser output.
Description
RELATED APPLICATION
[0001] This application claims priority under 35 U.S.C. .sctn. 119
to U.S. Provisional Application No. 62/398,366, entitled "Thermally
Compensating Spot-size Converter in Athermal Laser" by the same
inventors as the instant application, filed on 22 Sep. 2016 (Atty.
Docket No.: ORA17-0220-US-PSP), the contents of which are
incorporated by reference herein in their entirety.
FIELD
[0003] The disclosed embodiments generally relate to the design of
optoelectronic circuits. More specifically, the disclosed
embodiments relate to the design of a thermally compensating
spot-size converter to facilitate implementation of an athermal
laser.
RELATED ART
[0004] Silicon photonics is a promising new technology that can
potentially provide large communication bandwidth, low latency and
low power consumption for inter-chip and intra-chip connections. In
order to achieve low-latency, high-bandwidth optical connectivity,
a number of optical components are required, including: optical
transmitters, optical detectors, optical multiplexers, optical
demultiplexers and lasers.
[0005] The operating wavelength of many silicon photonic devices
depends on the refractive index of a silicon waveguide core, which
is a function of ambient temperature. Providing wavelength
stability for these optical components presents challenges, which
are typically solved by using some type of temperature-control. For
dense wavelength-divisional multiplexing (DWDM) links, it is
possible to regulate the temperature of thermally sensitive optical
components by using heating elements and/or thermoelectric coolers
(TECs). It is alternatively possible to loosen the
wavelength-spacing requirements for WDM links to allow for natural
wavelength drift of the optical components.
[0006] Researchers have also investigated designs for thermally
insensitive lasers, which can operate without heating elements or
TECs. For example, some researchers have investigated the
possibility of using the stress-optic effect to compensate for
thermal drift. (See D. A. Cohen, M. E. Heimbuch, and L. A. Coldren,
"Reduced temperature sensitivity of the wavelength of a diode laser
in a stress-engineered hydrostatic package," Appl. Phys. Lett.,
vol. 69, no. 4, p. 455, 1996.) Other researchers have investigated
the possibility of integrating negative thermo-optic coefficient
(NTOC) materials into waveguides in a lasing cavity. (See J.
Bovington, S. Srinivasan, and J. E. Bowers, "Athermal laser
design," Opt. Express, vol. 22, no. 16, pp. 19357-64, August
2014.)
[0007] In spite of these promising research efforts, no one has
successfully demonstrated an athermal laser that operates without
some type of heating element inside the lasing cavity. The reason
for this is that hybrid lasers that make use of a III-V gain
material, which has a wavelength drift of .about.80 pm/K, cannot be
easily integrated with NTOC waveguides. It is possible to build
external cavity lasers, which have large sections of air in the
lasing cavity. This can potentially reduce thermal drift by the
ratio of the optical path lengths through the III-V gain material
and through the air segments. This ratio can be expressed as nl/L,
where n is the effective index of the III-V gain material, l is its
length and L is the length of the external segment of the lasing
cavity. (Note that the refractive index of air in the external
segment is 1, so it is dropped from this ratio.) However,
commercial systems have not used such external cavity lasers due to
their size, reduced efficiency and additional stabilization
requirements.
[0008] Hence, what is needed is an athermal laser, which does not
suffer from the above-described drawbacks of existing athermal
lasers.
SUMMARY
[0009] The disclosed embodiments relate to a system that implements
an athermal laser. This system includes a reflective gain medium
(RGM) comprising an optical gain material coupled to a mirror. This
RGM is coupled to a spot-size converter (SSC), which optically
couples the RGM to an optical reflector through a silicon
waveguide. The SSC converts an optical mode-field size of the RGM
to an optical mode-field size of the silicon waveguide. Moreover, a
negative thermo-optic coefficient (NTOC) waveguide comprised of an
NTOC material is fabricated on top of the SSC. In this way, an
optical signal, which originates from the RGM, passes into the SSC,
is coupled into the NTOC waveguide, passes through the NTOC
waveguide, and is coupled back into the SSC before passing through
the silicon waveguide to the silicon mirror. During operation, the
RGM, the spot-size converter, the NTOC waveguide, the silicon
waveguide and the silicon mirror collectively form a lasing cavity.
Finally, a laser output is optically coupled out of the lasing
cavity.
[0010] In some embodiments, the lasing cavity includes a length
l.sub.Si through silicon, a length l.sub.NTOC through the NTOC
material, a length l.sub.OGM through the optical gain material and
a negligible length through the SSC, wherein the effective
refractive index of silicon is n.sub.Si, the effective refractive
index of the NTOC material is n.sub.NTOC, and the effective
refractive index of the optical gain material is n.sub.OGM.
Moreover, the effective thermo-optic coefficient (TOC) of silicon
is dn.sub.Si/dT, the effective TOC of the NTOC material is
dn.sub.NTOC/dT, and the effective TOC of the optical gain material
is dn.sub.OGM/dT. Finally,
l.sub.NTOC.apprxeq.l.sub.OGM*(dn.sub.OGM/dT-dn.sub.Si/dT)/(dn.sub.Si/dT-d-
n.sub.NTOC/dT), whereby the effective TOC of the portion of the
lasing cavity that passes through the optical gain material and the
NTOC material is substantially the same as the TOC of silicon.
[0011] In some embodiments, the silicon mirror comprises a
microring mirror.
[0012] In some embodiments, the silicon mirror comprises a
distributed Bragg reflector (DBR).
[0013] In some embodiments, the silicon mirror is a tunable silicon
mirror, which includes a thermal-tuning mechanism.
[0014] In some embodiments, the silicon mirror is an athermal
silicon mirror, which includes a cladding of the NTOC material.
[0015] In some embodiments, a bottom surface of the NTOC, which is
in contact with the SSC, is clad with a low-index dielectric
material. Moreover, a top surface of the NTOC is covered by one of
the following: air, a low-index dielectric material, and a
polymer.
[0016] In some embodiments, the RGM in located on a gain chip,
which is separate from a silicon photonic chip, which includes the
silicon waveguide and the silicon mirror.
[0017] In some embodiments, the NTOC material comprises titanium
dioxide (TiO.sub.2).
[0018] In some embodiments, the spot-size converter is comprised of
silicon oxynitride (SiON), where the nitrogen-to-oxygen ratio may
vary.
[0019] In some embodiments, the spot-size converter is comprised of
stoichiometric or low-stress silicon nitride (SiNx).
[0020] In some embodiments, the optical gain material is comprised
of a III-V semiconductor.
BRIEF DESCRIPTION OF THE FIGURES
[0021] The patent or application file contains at least one drawing
executed in color. Copies of this patent or patent application
publication with color drawing(s) will be provided by the Office
upon request and payment of the necessary fee.
[0022] FIG. 1 illustrates an exemplary configuration for an
athermal tunable laser in accordance with the disclosed
embodiments.
[0023] FIG. 2 presents a graph of thermo-optic coefficient versus
thermal expansion coefficient for materials that can be used to
construct a III-V/Si hybrid laser in accordance with the disclosed
embodiments.
[0024] FIG. 3A illustrates an exemplary configuration for a trimmed
and athermalized hybrid laser in accordance with the disclosed
embodiments.
[0025] FIG. 3B illustrates another configuration for a trimmed and
athermalized hybrid laser in accordance with the disclosed
embodiments.
[0026] FIG. 4A presents a graph illustrating gain versus wavelength
for an in-plane DBR laser in accordance with the disclosed
embodiments.
[0027] FIG. 4B presents a graph illustrating gain versus wavelength
for an athermal ring filtered laser in accordance with the
disclosed embodiments.
[0028] FIG. 5 presents a flow chart describing an optical path
through an athermalized hybrid laser in accordance with the
disclosed embodiments.
[0029] FIG. 6 illustrates a system that incorporates optical
components with semiconductor chips in accordance with an
embodiment of the present disclosure.
DETAILED DESCRIPTION
[0030] The following description is presented to enable any person
skilled in the art to make and use the present embodiments, and is
provided in the context of a particular application and its
requirements. Various modifications to the disclosed embodiments
will be readily apparent to those skilled in the art, and the
general principles defined herein may be applied to other
embodiments and applications without departing from the spirit and
scope of the present embodiments. Thus, the present embodiments are
not limited to the embodiments shown, but are to be accorded the
widest scope consistent with the principles and features disclosed
herein.
[0031] The data structures and code described in this detailed
description are typically stored on a computer-readable storage
medium, which may be any device or medium that can store code
and/or data for use by a computer system. The computer-readable
storage medium includes, but is not limited to, volatile memory,
non-volatile memory, magnetic and optical storage devices such as
disk drives, magnetic tape, CDs (compact discs), DVDs (digital
versatile discs or digital video discs), or other media capable of
storing computer-readable media now known or later developed.
[0032] The methods and processes described in the detailed
description section can be embodied as code and/or data, which can
be stored in a computer-readable storage medium as described above.
When a computer system reads and executes the code and/or data
stored on the computer-readable storage medium, the computer system
performs the methods and processes embodied as data structures and
code and stored within the computer-readable storage medium.
Furthermore, the methods and processes described below can be
included in hardware modules. For example, the hardware modules can
include, but are not limited to, application-specific integrated
circuit (ASIC) chips, field-programmable gate arrays (FPGAs), and
other programmable-logic devices now known or later developed. When
the hardware modules are activated, the hardware modules perform
the methods and processes included within the hardware modules.
[0033] Throughout this specification, and in the appended claims,
we use the term "gain medium" (GM) to refer to any device, which
contains active gain material and can be used to power a laser.
This can include, but is not limited to: a semiconductor optical
amplifier (SOA), an active device fabricated using a quantum-dot
gain material, and an active device fabricated in a nonlinear fiber
gain medium. We also use the term "reflective gain medium" (RGM) to
refer to any type of active gain material, which is coupled to an
associated reflector. This can include, but is not limited to: a
reflective semiconductor optical amplifier (RSOA), and an SOA that
can be accessed through both ends and looped either as: (1) a loop
mirror coupled to a reflective end of the SOA, or (2) a loop
containing the SOA before the SOA. (This geometry changes the
structure to the extent that light passes in a single pass through
both directions in the SOA, just like a double pass through an
RSOA, and provides gain.) Note that the loop mirror recited above
can alternatively be replaced with a distributed Bragg reflector
(DBR).
[0034] Various modifications to the disclosed embodiments will be
readily apparent to those skilled in the art, and the general
principles defined herein may be applied to other embodiments and
applications without departing from the spirit and scope of the
present invention. Thus, the present invention is not limited to
the embodiments shown, but is to be accorded the widest scope
consistent with the principles and features disclosed herein.
Overview
[0035] We present a new design for a III-V/Si hybrid laser, which
includes a thermally compensating element that makes the laser's
output wavelength stable during temperature variations without the
need for a heating element or a thermoelectric cooler (TEC). This
thermally compensating element can be implemented as a waveguide
comprised of a negative thermo-optic coefficient (NTOC) material,
such as TiO.sub.2, which is integrated onto a dielectric spot-size
converter (SSC) that converts an optical mode-field size of a III-V
gain medium to an optical mode-field size of a silicon waveguide in
the laser. Note that this new hybrid laser reduces the energy
required to maintain wavelength stability, and also decreases the
wavelength spacing of associated WDM links.
Details
[0036] Recently developed silicon photonic technologies can provide
significant advantages for optoelectronic systems, wherein the
advantages include lower cost, increased reliability and
scalability. For example, a hybrid III-V silicon laser combines
energy-efficient compound III-V semiconductor materials with
low-cost and reliable silicon-photonic (SiP) mirrors to provide an
efficient light source for optical communications. To this end, we
have developed a new hybrid III-V silicon laser having an
edge-coupled configuration, which includes a spot-size converter
(SSC) between III-V material on a gain chip and a silicon waveguide
on an SiP chip. This SSC comprises a dielectric material, such as
SiNx or SiON, which provides some reduction in the total thermal
drift, but cannot totally eliminate the thermal drift.
[0037] This thermal drift d.lamda..sub.C/dT can be expressed as
specified in equation (1) below as a function of a thermal
expansion coefficient .alpha., a group index n.sub.g, an effective
index n.sub.eff and a change in the effective index with
temperature dn.sub.eff/dT of all segments of the lasing cavity.
d .lamda. C dT = .lamda. C .intg. L C n 8 dL ( .alpha. sub .intg. L
C n eff dL + .intg. L C dn eff dT dL ) ( 1 ) ##EQU00001##
[0038] FIG. 1 illustrates an exemplary configuration for this new
hybrid athermal laser 100 in accordance with the disclosed
embodiments. As illustrated in FIG. 1, this new athermal laser 100
includes a III-V gain chip 102, which contains a reflective
semiconductor optical amplifier (RSOA) 104. The III-V gain chip 102
is attached to a silicon photonic chip 106, which includes a
silicon waveguide 112 that is coupled to a silicon (Si) mirror 114.
Light generated by RSOA 104 is directed into silicon waveguide 112
through a spot-size converter (SSC) 108, which converts the optical
mode-field size of RSOA 104 to the optical mode-field size of
silicon waveguide 112. SSC 108 is comprised of a material such as
SiON or SiNx, which (as mentioned above) provides some reduction in
total thermal drift, but cannot completely eliminate thermal drift.
In order to eliminate this thermal drift, the new laser design
integrates an NTOC waveguide 109 on top of SSC 108. More
specifically, NTOC waveguide 109 can comprise a TiO.sub.2 core,
clad on the bottom by a low-index dielectric and on top either by
air or another low-index dielectric or polymer. Also note that a
laser output (not shown) is optically coupled to this lasing
cavity.
[0039] Equation (1) (specified above) can be used to select the
length of NTOC waveguide 109, which is comprised of TiO.sub.2, as a
function of the length of the other segments in the lasing cavity.
The longer the RSOA 104 in III-V gain chip 102, the longer the NTOC
waveguide 109. Also, the longer the effective length of silicon
mirror 114, the longer the length of NTOC waveguide 109. However,
in a design where negligible length is given to silicon, which is
not athermalized by the TiO.sub.2 in NTOC waveguide 109, there is a
direct relationship between the length of NTOC waveguide 109 and
RSOA 104 in III-V gain chip 102. To a first order, the length of
the TiO.sub.2 in NTOC waveguide 109 and the length of any silicon
or III-V material should be nearly equal owing to their common
dn/dT coefficients.
[0040] Also note that a number of different materials (instead of a
III-V semiconductor, SiON or SiNx and TiO.sub.2) can be used to
implement RSOA 104, SSC 108 and NTOC waveguide 109, respectively.
For example, FIG. 2 presents a graph of thermo-optic coefficients
versus thermal expansion coefficients for various alternative
materials that can be used to implement a III-V/Si hybrid laser in
accordance with the disclosed embodiments.
[0041] Note that RSOA 104, SSC 108, NTOC waveguide 109, silicon
waveguide 112 and silicon mirror 114 collectively form a lasing
cavity for the laser 100. During operation of this laser 100, light
which is generated by RSOA 104 is directed into SSC 108, which is
shaped to receive the mode of RSOA 104. Next, the mode is coupled
into NTOC waveguide 109. After passing through NTOC waveguide 109,
the mode is converted back to SSC 108 again before coupling to
silicon waveguide 112 via a tapered mode converter 110, which
provides an inverse taper.
[0042] The embodiment of hybrid external laser 100 illustrated in
FIG. 1 uses a tunable microring mirror to implement silicon mirror
114. It is advantageous to use such a "tunable" microring mirror
114 because there will be manufacturing variations, which need to
be resolved through tuning, and there is also a requirement for
mode stability, which can best be solved by locking the microring
mirror 114 through continuous tuning to a single cavity mode in a
feedback loop.
[0043] It is also possible to implement silicon mirror 114 using an
"athermal mirror," which is not tunable as is illustrated in FIGS.
3A and 3B. More specifically, FIG. 3A illustrates an athermal
silicon mirror comprising a ring filter clad with an NTOC material
such as TiO.sub.2, and FIG. 3B illustrates an athermal silicon
mirror comprised of a distributed Bragg reflector (DBR), which is
also clad with an NTOC material. In the embodiments illustrated in
FIGS. 3A and 3B, instead of making silicon mirror 114 tunable, the
lasing cavity is designed to achieve an athermal character, either
by manufacturing tolerance improvements, or through a trimming
process, followed by cladding silicon mirror 114 with an NTOC
material to facilitate athermalization. Note that making silicon
mirror 114 athermal is desirable for a passively athermal design
because the drift of the mirror filter and the cavity modes must
both be insensitive to temperature to lock the laser wavelength
during temperature variations. Admittedly, this does not solve the
gain drift issue, but as illustrated by the graphs that appear in
FIGS. 4A and 4B, the gain can be designed to drift into the
resonance to compensate for the decrease in gain which also
accompanies raising temperatures. (Note that FIG. 4A illustrates
the gain for the embodiment illustrated in FIG. 3B, which uses a
DBR as a silicon mirror. Similarly, FIG. 4B illustrates the gain
for the embodiment illustrated in FIG. 3A, which uses a ring filter
as a silicon mirror.)
Operation
[0044] During operation, the athermal laser system described above
operates as illustrated in the flow chart that appears in FIG. 5.
The system first generates an optical signal by powering a
reflective gain medium (RGM) comprising an optical gain material
coupled to an associated reflector (step 502). Next, the system
channels the optical signal through a spot-size converter (SSC)
into a silicon waveguide, wherein the SSC converts an optical
mode-field size of the RGM to an optical mode-field size of the
silicon waveguide. A negative thermo-optic coefficient (NTOC)
waveguide comprised of an NTOC material is fabricated on top of the
SSC, whereby the optical signal, which originates from the RGM and
passes into the SSC, is coupled into the NTOC waveguide, passes
through the NTOC waveguide, and is coupled back into the SSC before
passing into the silicon waveguide (step 504). The system then
channels the optical signal from the silicon waveguide into a
silicon mirror (step 506). Finally, the system optically couples
light from a lasing cavity, which is formed by the RGM, the SSC,
the NTOC waveguide, the optical waveguide, and the silicon mirror,
into a laser output (step 508).
System
[0045] One or more of the preceding embodiments may be included in
a system or device. More specifically, FIG. 6 illustrates a system
600 that includes optoelectrical components 602 including one or
more hybrid lasers. System 600 also includes a processing subsystem
606 (with one or more processors) and a memory subsystem 608 (with
memory).
[0046] In general, system 600 may be implemented using a
combination of hardware and/or software. Thus, system 600 may
include one or more program modules or sets of instructions stored
in a memory subsystem 608 (such as DRAM or another type of volatile
or non-volatile computer-readable memory), which, during operation,
may be executed by processing subsystem 606. Furthermore,
instructions in the various modules in memory subsystem 608 may be
implemented in: a high-level procedural language, an
object-oriented programming language, and/or in an assembly or
machine language. Note that the programming language may be
compiled or interpreted, e.g., configurable or configured, to be
executed by the processing subsystem.
[0047] Components in system 600 may be coupled by signal lines,
links or buses, for example bus 604. These connections may include
electrical, optical, or electro-optical communication of signals
and/or data. Furthermore, in the preceding embodiments, some
components are shown directly connected to one another, while
others are shown connected via intermediate components. In each
instance, the method of interconnection, or "coupling," establishes
some desired communication between two or more circuit nodes, or
terminals. Such coupling may often be accomplished using a number
of photonic or circuit configurations, as will be understood by
those of skill in the art; for example, photonic coupling, AC
coupling and/or DC coupling may be used.
[0048] In some embodiments, functionality in these circuits,
components and devices may be implemented in one or more:
application-specific integrated circuits (ASICs),
field-programmable gate arrays (FPGAs), and/or one or more digital
signal processors (DSPs). Furthermore, functionality in the
preceding embodiments may be implemented more in hardware and less
in software, or less in hardware and more in software, as is known
in the art. In general, system 600 may be at one location or may be
distributed over multiple, geographically dispersed locations.
[0049] System 600 may include: a switch, a hub, a bridge, a router,
a communication system (such as a wavelength-division-multiplexing
communication system), a storage area network, a data center, a
network (such as a local area network), and/or a computer system
(such as a multiple-core processor computer system). Furthermore,
the computer system may include, but is not limited to: a server
(such as a multi-socket, multi-rack server), a laptop computer, a
communication device or system, a personal computer, a work
station, a mainframe computer, a blade, an enterprise computer, a
data center, a tablet computer, a supercomputer, a
network-attached-storage (NAS) system, a storage-area-network (SAN)
system, a media player (such as an MP3 player), an appliance, a
subnotebook/netbook, a tablet computer, a smartphone, a cellular
telephone, a network appliance, a set-top box, a personal digital
assistant (PDA), a toy, a controller, a digital signal processor, a
game console, a device controller, a computational engine within an
appliance, a consumer-electronic device, a portable computing
device or a portable electronic device, a personal organizer,
and/or another electronic device.
[0050] Moreover, the optoelectrical components 602 can be used in a
wide variety of applications, such as: communications (for example,
in a transceiver, an optical interconnect or an optical link, such
as for intra-chip or inter-chip communication), a radio-frequency
filter, a bio-sensor, data storage (such as an optical-storage
device or system), medicine (such as a diagnostic technique or
surgery), a barcode scanner, metrology (such as precision
measurements of distance), manufacturing (cutting or welding), a
lithographic process, data storage (such as an optical-storage
device or system) and/or entertainment (a laser light show).
[0051] The foregoing descriptions of embodiments have been
presented for purposes of illustration and description only. They
are not intended to be exhaustive or to limit the present
description to the forms disclosed. Accordingly, many modifications
and variations will be apparent to practitioners skilled in the
art. Additionally, the above disclosure is not intended to limit
the present description. The scope of the present description is
defined by the appended claims.
* * * * *