U.S. patent application number 15/146215 was filed with the patent office on 2017-01-05 for modulated light source.
This patent application is currently assigned to FUJITSU LIMITED. The applicant listed for this patent is FUJITSU LIMITED, Photonics Electronics Technology Research Association. Invention is credited to Tomoyuki Akiyama.
Application Number | 20170005454 15/146215 |
Document ID | / |
Family ID | 57682462 |
Filed Date | 2017-01-05 |
United States Patent
Application |
20170005454 |
Kind Code |
A1 |
Akiyama; Tomoyuki |
January 5, 2017 |
MODULATED LIGHT SOURCE
Abstract
A modulated light source includes a ring modulator, a first
optical waveguide and a second optical waveguide that are optically
connected to the ring modulator, and a third optical waveguide that
optically connects an end of the first optical waveguide and an end
of the second optical waveguide. At least part of the third optical
waveguide has optical gain, and an optical waveguide loop including
the ring modulator, the first optical waveguide, the second optical
waveguide, and the third optical waveguide is used as a resonator
to cause laser oscillation.
Inventors: |
Akiyama; Tomoyuki;
(Yokohama, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJITSU LIMITED
Photonics Electronics Technology Research Association |
Kawasaki-shi
Tokyo |
|
JP
JP |
|
|
Assignee: |
FUJITSU LIMITED
Kawasaki-shi
JP
Photonics Electronics Technology Research Association
Tokyo
JP
|
Family ID: |
57682462 |
Appl. No.: |
15/146215 |
Filed: |
May 4, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01S 5/0265 20130101;
H01S 5/06837 20130101; H01S 5/06832 20130101; H01S 5/142 20130101;
H01S 5/021 20130101; H01S 5/125 20130101; H01S 5/0262 20130101;
H01S 5/0261 20130101 |
International
Class: |
H01S 5/14 20060101
H01S005/14; H01S 5/026 20060101 H01S005/026; H01S 5/0683 20060101
H01S005/0683; H01S 5/125 20060101 H01S005/125 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 2015 |
JP |
2015-131771 |
Claims
1. A modulated light source comprising: a ring modulator; a first
optical waveguide and a second optical waveguide that are optically
connected to the ring modulator; and a third optical waveguide that
optically connects an end of the first optical waveguide and an end
of the second optical waveguide, wherein at least part of the third
optical waveguide has optical gain, and an optical waveguide loop
including the ring modulator, the first optical waveguide, the
second optical waveguide, and the third optical waveguide is used
as a resonator to cause laser oscillation.
2. The modulated light source according to claim 1, wherein a
transmission wavelength band between the end of the first optical
waveguide and the end of the second optical waveguide has a size
that allows selecting one of a plurality of longitudinal modes in
which laser oscillation is possible to occur, and the laser
oscillation occurs in a single longitudinal mode.
3. The modulated light source according to claim 1, wherein the
first optical waveguide has another end having a mirror, and the
second optical waveguide has another end serving as a light output
port.
4. The modulated light source according to claim 1, including a
plurality of optical waveguide loops each identical to the optical
waveguide loop, wherein in two adjacent optical waveguide loops out
of the optical waveguide loops, another end of the second optical
waveguide of one of the two adjacent optical waveguide loops and an
end of the first optical waveguide of the other of the two adjacent
optical waveguide loops are connected directly to each other.
5. The modulated light source according to claim 4, wherein the
first optical waveguide has another end having a mirror and not
being connected directly to any end of another optical waveguide,
and the second optical waveguide has another end serving as a light
output port and not being connected directly to any end of another
optical waveguide.
6. The modulated light source according to claim 1, wherein the
optical waveguide loop has a plurality of ring modulators each
identical to the ring modulator, and the first optical waveguide
and the second optical waveguide are optically connected to the
plurality of ring modulators.
7. The modulated light source according to claim 1, further
comprising a heater unit that heats the ring modulator.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based upon and claims the benefit of
priority of the prior Japanese Patent Application No. 2015-131771,
filed on Jun. 30, 2015, the entire contents of which are
incorporated herein by reference.
FIELD
[0002] The embodiments discussed herein relate to a modulated light
source.
BACKGROUND
[0003] It has been desired to develop a modulated light source that
is compact and consumes a low power. In such a modulated light
source, using a minute ring modulator with a silicon sub-micron
optical waveguide has been studied.
[0004] FIG. 8 is a diagrammatic view depicting a schematic
configuration of a modulated light source of related art using a
ring modulator.
[0005] The modulated light source includes a distributed feedback
(DFB) laser 101, a ring modulator 102, a PD 103, a wavelength
controller 104, and a heater 105.
[0006] The PD 103 senses power of light having passed through the
ring modulator 102. The wavelength controller 104 outputs a signal
that controls the wavelength of the ring resonance based on the
optical power sensed with the PD 103. The heater 105 heats the ring
modulator 102 in accordance with the control signal from the
wavelength controller 104 to adjust the wavelength of the ring
modulator to match the laser wavelength.
[0007] In the modulated light source, the DFB laser 101 outputs
laser light in a continuous emission mode. The outputted laser
light passes through an optical waveguide and then is guided to the
ring modulator 102, which modulates the transmissivity at the laser
light wavelength transmissivity.
[0008] The ring modulator 102 has a Lorentzian spectrum centered at
a resonance wavelength. The ring modulator 102 changes the
resonance wavelength in accordance with a change in a modulation
signal between voltages V.sub.0 and V.sub.1. The transmissivity is
thus modulated, whereby intensity-modulated output light is
produced.
[0009] The resonance wavelength of the ring modulator 102 changes
as a circumference optical path length of the ring modulator 102
changes due to a manufacturing error and/or a temperature change,
resulting in a discrepancy between the resonance wavelength and the
wavelength of the laser light being emitted. As depicted in FIG. 9,
to compensate for the discrepancy, the heater 105 heats the ring
modulator 102 to raise the temperature of it for adjustment of the
resonance wavelength.
[0010] In this case, however, it is undesirably difficult not only
to ensure reliability of the modulated light source but also to
improve power efficiency in the modulation or the like (decrease in
electric power necessary for heater and modulation operation). The
reason for this is as follows.
[0011] The case where the ring modulator has a small radius as
depicted in FIG. 10A will be considered. In this case, the volume
of the ring modulator is small, whereby electric power consumed by
the heater that is required to compensate for the wavelength shift
resulting from variation in temperature is decreased. Furthermore,
the small radius of the ring modulator reduces a capacitance that
serves as a load on a drive circuit of the ring modulator, whereby
the modulation power is deceased. On the other hand, because the
difference between the laser and the ring modulator wavelength
amounts up to the free spectral range (FSR), an increased FSR
increases the amount of required wavelength compensation, resulting
in an increase in the amount of increase in the temperature of the
ring modulator and hence a decrease in reliability of the ring
modulator.
[0012] The case where the ring modulator 102 has a large radius as
depicted in FIG. 10B will be considered. In this case, the FSR is
small, resulting in a decrease in the amount of wavelength
compensation, which reduces the amount of increase in the
temperature of the ring modulator, whereby reliability of the ring
modulator is ensured. On the other hand, the volume of the ring
modulator increases, resulting in increases in modulation power,
and electric power consumed by the heater that is required to
compensate for the wavelength shift due to variation in
temperature.
[0013] Furthermore, a problem caused by use of the DFB laser 101 is
not negligible. That is, DFB lasers without a phase shift in the
diffraction grating for improvement of power efficiency reduces a
yield thereof. Conversely, introduction of a phase shift for
improvement in the yield lowers the power efficiency.
[0014] Patent Document 1: Japanese Laid-open Patent Publication No.
2012-64862
[0015] Patent Document 2: Japanese Laid-open Patent Publication No.
2009-59729
SUMMARY
[0016] An aspect of a modulated light source includes a ring
modulator, a first optical waveguide and a second optical waveguide
that are optically connected to the ring modulator, and a third
optical waveguide that optically connects one end of the first
optical waveguide and one end of the second optical waveguide,
wherein at least part of the third optical waveguide has optical
gain, and an optical waveguide loop including the ring modulator,
the first optical waveguide, the second optical waveguide, and the
third optical waveguide is used as a resonator to cause laser
oscillation.
[0017] The object and advantages of the invention will be realized
and attained by means of the elements and combinations particularly
pointed out in the claims.
[0018] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory and are not restrictive of the invention.
BRIEF DESCRIPTION OF DRAWINGS
[0019] FIG. 1 is a diagrammatic view depicting a schematic
configuration of a modulated light source according to a first
embodiment;
[0020] FIG. 2 is a diagrammatical view depicting in enlargement an
optical waveguide loop of FIG. 1;
[0021] FIGS. 3A to 3D are diagrams depicting operation when a
wavelength is adjusted in the optical device according to the
present embodiment;
[0022] FIG. 4 is a table depicting the amount of wavelength shift
and the amount of temperature increase required for wavelength
matching between the laser and the ring modulator;
[0023] FIGS. 5A and 5B are diagrammatic views describing a
mechanism for selecting an oscillation mode in a ring laser
resonator;
[0024] FIG. 6 is a diagrammatic view depicting a schematic
configuration of a modulated light source according to a second
embodiment;
[0025] FIG. 7 is a diagrammatic view depicting a schematic
configuration of a modulated light source according to a third
embodiment;
[0026] FIG. 8 is a diagrammatic view depicting a schematic
configuration of a modulated light source of related art using a
ring modulator;
[0027] FIG. 9 is a diagram depicting how the modulated light source
of related art adjusts the resonance wavelength; and
[0028] FIGS. 10A and 10B are diagrammatic views describing problems
in the modulated light source of related art.
DESCRIPTION OF EMBODIMENTS
[0029] Preferable embodiments of a modulated light source will be
described below in detail with reference to the drawings.
First Embodiment
[0030] FIG. 1 is a diagrammatic view depicting a schematic
configuration of a modulated light source according to a first
embodiment.
[0031] The modulated light source includes an optical waveguide
loop 1, a photodiode (PD) 2, a wavelength controller 3, and a
heater 4.
[0032] The optical waveguide loop 1 has a ring modulator 11, which
is a band-pass filter, a first optical waveguide 12, a second
optical waveguide 13, and a third optical waveguide 14. The first
optical waveguide 12 and the second optical waveguide 13 are bus
waveguides of the ring modulator 11. The third optical waveguide 14
is a U-shaped optical waveguide optically connecting a port on one
end of the first optical waveguide 12 and a port on one end of the
second optical waveguide 13, and at least a portion of the third
optical waveguide 14 has optical gain. The optical waveguide loop 1
as a resonator causes laser oscillation.
[0033] The ring modulator 11 is a band-pass filter and is formed,
for example, of a silicon wire. In the ring modulator 11, a P-type
doped region and an N-type doped region are provided to form a PN
junction (or PIN junction) in a ring-shaped optical waveguide
formed of a silicon wire having a radius of, for example, about 5
.mu.m. In the ring modulator 11, electrodes 11a and 11b and an
electrode in a center part of the ring modulator 11 are disposed
for modulating the resonance wavelength based on the modulation
signal and in accordance with the intensity thereof. The electrodes
11a, 11b have the same polarity, and are conductive to each other.
The electrode in the center part of the ring modulator 11 has
different polarity from the electrodes 11a, 11b. These electrodes
form a group of electrodes. The ring modulator 11 changes the
refractive index of the optical waveguide to modulate the resonance
wavelength by a reverse bias voltage or a forward bias voltage
applied by the group of electrodes between the P-type doped region
and the N-type doped region.
[0034] The first optical waveguide 12, the second optical waveguide
13, and the third optical waveguide 14 optically connected to the
ring modulator 11 are formed of a silicon wire which is formed by
processing, for example, an SOI layer of an SOI substrate. In the
third optical waveguide 14, for example, GeSn is formed as an
optical gain medium 14a in a region to which the optical gain is
given. Among four ports of the first optical waveguide 12 and the
second optical waveguide 13, which are bus waveguides of the ring
modulator 11, for example, at a port on the other end of the first
optical waveguide 12, a DBR mirror 12a having a reflectivity, for
example, of 97% is formed of a diffraction grating. In the port on
the other end of the second optical waveguide 13, a tap 13a guiding
part of output light is provided, and the PD 2 is disposed on the
tap 13a.
[0035] The PD 2 senses the power of the light having been guided to
an output port.
[0036] The wavelength controller 3 outputs a signal that controls
the wavelength of the ring modulator based on the optical power
sensed with the PD 2.
[0037] The heater 4 heats the ring modulator 11 in accordance with
the signal from the wavelength controller 3 to adjust the ring
resonance wavelength.
[0038] FIG. 2 is a diagrammatical view depicting in enlargement an
optical waveguide loop of FIG. 1.
[0039] In the modulated light source according to the present
embodiment, the optical waveguide loop 1 has optical bus waveguides
(the first optical waveguide 12 and the second optical waveguide
13) of the ring modulator 11 optically connected to each other by
the third optical waveguide 14, and the third optical waveguide 14
has optical gain. A ring laser resonator having the ring modulator
11 is thus formed. This ring laser resonator has optical gain, and
a transmission wavelength band between the one end of the first
optical waveguide 12 and the one end of the second optical
waveguide 13 has a size that allows selecting one of a plurality of
longitudinal modes in which laser oscillation is possible to occur.
This enables the ring laser resonator to oscillate in a ring laser
mode which is a single longitudinal mode existing within the
transmission wavelength band of the transmission spectrum between
the bus waveguides of the ring modulator 11. Adjusting the
transmission wavelength band of the ring modulator 11 allows
selectively oscillating in one predetermined ring laser mode.
[0040] Applying a digital modulation signal that changes between
voltages V.sub.0 and V.sub.1 to the group of electrodes of the ring
modulator 11 allows the resonance wavelength to be modulated in
accordance with the intensity of the modulation signal.
Transmissivity, T.sub.out to the output port at the wavelength of
the emitted light can thus be modulated. The power P.sub.out of the
output light is equal to the product P.sub.rP.sub.out of the
optical power P.sub.r in the optical resonator and the
transmissivity T.sub.out, and thus a design of the optical
resonator with reduced variation in P.sub.r allows the power
P.sub.out to be modulated in correspondence with the modulation
signal.
[0041] FIGS. 3A to 3D are diagrams depicting operation when a
wavelength is adjusted in the modulated light source according to
the present embodiment. FIG. 3A depicts a state before the
wavelength is adjusted, and FIG. 3D depicts a state after the
wavelength is adjusted.
[0042] As depicted with an arrow in FIG. 3A, there are ring laser
modes at equal intervals that can be oscillated by the ring laser
resonator having the optical gain medium. The interval between the
ring laser modes is proportional to the reciprocal of a
circumference optical path length of the ring laser resonator. The
transmission peak of the ring modulator 11 does not necessarily
coincide with the wavelength of the ring laser modes in the state
before adjustment. At this time, one among the ring laser modes
that is closest to the transmission peak of the ring modulator 11
is oscillated with priority.
[0043] Turning on the heater 4 causes the transmission peak of the
ring modulator 11 to shift to the long wavelength side.
Accompanying this, as depicted in FIGS. 3B and 3C, the ring laser
mode closest to the transmission peak wavelength of the ring
modulator 11 is switched to the next ring laser mode on the long
wavelength side. At this time, as depicted in FIG. 3C, the ring
laser mode to be oscillated is also switched. The timing of this
switching is before the transmission peak wavelength of the ring
modulator 11 reaches the ring laser mode on the long wavelength
side, as depicted in FIG. 3C. Because of this, increasing the power
of the heater 4 to adjust the transmission peak wavelength of the
ring modulator 11 to the long wavelength side can make the
transmission peak wavelength of the ring modulator 11 finally
coincide with the ring laser mode, as depicted in FIG. 3D. When the
laser oscillation wavelength and the transmission peak wavelength
of the ring modulator 11 are made to coincide in this manner, the
range of adjusting the transmission peak wavelength of the ring
modulator 11 with the heater 4 can be reduced to be equal to or
lower than the interval between the ring laser modes. As will be
described later, in the related art, a free spectral range (FSR) is
required at the maximum as the amount of adjustment of a wavelength
shift of the ring modulator. In the present embodiment, the
interval between the ring laser modes can be made much smaller than
the FSR.
[0044] In the ring modulator using optical waveguides each formed
of a silicon wire, the ring radius can be reduced to about 5 .mu.m
without a significant increase in the bending loss, and the
electric power necessary for the modulation and the electric power
consumed by the heater can be lowered as the ring radius decreases.
In the case that the ring radius is 5 .mu.m, the free spectral
range (FSR) becomes about 19 nm. In this case, a wavelength shift
of about 19 nm is required at the maximum in the related art. On
the other hand, in the present embodiment, in which the
circumference optical path length of the ring laser resonator is
set at about 800 .mu.m, the interval between the ring laser modes
becomes about 0.8 nm. In this case, as depicted in FIG. 4, the
amount of wavelength shift compensation is only 0.8 nm at the
maximum. When the amount of wavelength shift compensation is
converted into temperature by using a wavelength-temperature
coefficient of 0.07 nm/K, it is necessary to increase the
temperature by approximately 271.degree. C. in related art. In
contrast, in the present embodiment, an increase in temperature is
only 11.4.degree. C., resulting in a significant improvement in
reliability. The power consumed by the heater can also be reduced
to about 0.8 nm/19 nm.times.100.apprxeq.4.2%.
[0045] The ring laser resonator has two types of oscillation modes,
a clockwise (CW) mode and a counterclockwise (CCW) mode. Although
the modulation operation is possible even when the CW mode and the
CCW mode are oscillated simultaneously, the output light is
dispersed to two ports, and thus it is preferred to oscillate in
one of the CW mode and the CCW mode. In order to cause oscillation
in one mode, as depicted in FIG. 5A, the DBR mirror 12a is provided
on the port on the other end of the first optical waveguide 12. The
DBR mirror 12a can change part of the emitted light in the CW mode
to the CCW mode. The phase of oscillation in the CCW mode is
synchronous with the phase of the CW mode by injecting the emitted
light in the CW mode. As a result, when the light changes from the
CW mode to the CCW mode, a change with a phase satisfying
predetermined interference conditions is always achieved.
Consequently, as illustrated in FIG. 5B, the power of the emitted
light in the CCW mode becomes higher than the power of the emitted
light in the CW mode, and the oscillation in the CW mode finally
stops.
[0046] In the present embodiment, by setting the circumference
optical path length of the ring laser resonator to about 800 .mu.m
for example, the interval between the ring laser modes becomes 100
GHz (=0.8 nm). In this case, when the full width at the half
maximum (FWHM) of the ring modulator 11 is set at 50 GHz for
example, only one of the ring laser modes can be selectively
oscillated, and moreover, the ring modulator 11 can provide a
modulation band up to about 50 GHz.
[0047] In the present embodiment, a DBR mirror formed of a
diffraction grating is exemplified as the light reflector provided
in one port of the bus waveguides of the ring modulator 11, but the
light reflector is not limited to a DBR mirror. The light reflector
may be any component having reflectivity over a wavelength range
wide enough to tolerate variation in the resonance wavelength of
the ring modulator 11. For example, the light reflector may instead
be a loop mirror, a mirror using an optical waveguide end surface,
or a mirror using an optical waveguide end surface on which a metal
film or a dielectric multilayer film is formed for enhanced
reflectivity.
[0048] Further, a heater 4 is exemplified as part of the wavelength
adjustment mechanism of the ring modulator 11, but the wavelength
adjustment mechanism does not necessarily include a heater, and
methods of applying current to the forward direction through a PN
or PIN junction may be employed. In this case, the ring modulator
has two portions. One of the portions is used as an intensity
modulation region including a pair of first electrodes that
modulates the resonance wavelength based on a modulation signal and
in accordance with the intensity thereof. The other portion is used
as a wavelength adjustment region including a pair of second
electrodes to which a wavelength modulation control signal is
inputted.
[0049] Further, GeSn is used as the optical gain medium 14a
provided in the third optical waveguide 14, but the optical gain
medium is not necessarily be GeSn. For example, another type of an
optical gain medium using Ge may be used, or a III-V semiconductor
or the like mounted on a silicon optical waveguide by wafer bonding
or using an adhesive may be used. A gain chip formed of a III-V
semiconductor that is flip-chip bonded to an end of a silicon
optical waveguide may also be used.
[0050] In the present embodiment, power consumption required for
correcting variation in wavelength of the ring modulator 11 can be
suppressed largely. Further, increase in temperature when the
wavelength adjustment is carried out with the heater 4 can be
suppressed largely. In the present embodiment, a ring modulator
with a small radius can be used. In the related art, when this ring
modulator with a small radius is used, a temperature increase of,
for example, 271.degree. C. is required, which significantly
exceeds the temperature for assuring reliability in the silicon
process (about 140.degree. C.). On the other hand, in the present
embodiment, a temperature increase of only about 11.4.degree. C. is
required for the ring modulator with a small radius. Therefore,
electric power necessary for the modulation and electric power
necessary for heating by the heater can be decreased while the
reliability is ensured.
[0051] According to the aspects described above, an excellent,
minute multi-wavelength modulated light source meets the two
requirements at the same time, one of which is to ensure the
reliability of the modulated light source and the other of which is
to improve power efficiency in modulation operation and/or the
like.
Second Embodiment
[0052] In the second embodiment, a modulated light source is
disclosed as in the first embodiment, but the disclosed modulated
light source differs from the modulated light source according to
the first embodiment in that it is a multi-wavelength modulated
light source.
[0053] FIG. 6 is a diagrammatic view depicting a schematic
configuration of the modulated light source according to the second
embodiment. The constituent members and other components
corresponding to those in the first embodiment have the same
reference characters as those in FIG. 1 and will not be described
in detail.
[0054] The modulated light source includes a plurality of light
modulation units 21.sub.1 to 21.sub.N (N.gtoreq.2).
[0055] Each light modulation unit includes an optical waveguide
loop 1, a photodiode (PD) 2, a wavelength controller 3, and a
heater 4, similarly to the first embodiment in FIG. 1. In FIG. 6,
the PD 4 and the wavelength controller 3 are omitted. The optical
waveguide loop 1 has a ring modulator 11, a first optical waveguide
12, a second optical waveguide 13, and a third optical waveguide
14, similarly to the first embodiment in FIG. 1. In a light
modulation unit 21.sub.k (1.ltoreq.k.ltoreq.N) and a light
modulation unit 21.sub.k+1 which are adjacent to each other, the
port on the other end of the second optical waveguide 13 of the
light modulation unit 21.sub.k and the port on one end of the first
optical waveguide 12 of the light modulation unit 21.sub.k+1 are
connected directly to each other. A DBR mirror 12a is formed at the
other end of the first optical waveguide 12 of the light modulation
unit 21.sub.1 and this other end is not connected directly to any
other port, and the other end of the second optical waveguide 13 of
the light modulation unit 21.sub.N is not connected directly to any
other port and serves as a light output port.
[0056] The emitted light outputted through the plurality of optical
waveguide loops 1, which are ring laser resonators, is guided to
one light output port. By changing the resonance wavelength of each
ring modulator 11, the oscillation wavelength of the laser can be
changed. A multi-wavelength modulated light source capable of
combining lights can thus be achieved.
[0057] As described above, according to the aspects described
above, an excellent, minute multi-wavelength modulated light source
meets the two requirements at the same time, one of which is to
ensure the reliability of the modulated light source and the other
of which is to improve power efficiency in modulation operation
and/or the like.
Third Embodiment
[0058] In the third embodiment, a modulated light source is
disclosed as in the first embodiment, but the disclosed modulated
light source differs from the modulated light source according to
the first embodiment in that it is a multi-wavelength modulated
light source.
[0059] FIG. 7 depicts a configuration of the modulated light source
according to the third embodiment. The constituent members and
other components corresponding to those in the first embodiment
have the same reference characters as those in FIG. 1 and will not
be described in detail.
[0060] The modulated light source includes a plurality of light
modulation units 31.sub.1 to 31.sub.N (N.gtoreq.2).
[0061] Each light modulation unit includes a ring modulator 11, a
photodiode (PD) 2, a wavelength controller 3, and a heater 4. In
FIG. 7, the PD 2 and the wavelength controller 3 are omitted. A
first optical waveguide 12, a second optical waveguide 13, and a
third optical waveguide 14 are provided in common for the light
modulation units 31.sub.1 to 31.sub.N, so as to form an optical
waveguide loop having a plurality of ring modulators 11, the first
optical waveguide 12, the second optical waveguide 13, and the
third optical waveguide 14.
[0062] In the present embodiment, a multi-wavelength modulated
light source can guide emitted lights of a plurality of wavelengths
to one output port and is capable of combining lights, similarly to
the second embodiment. By sharing one optical gain medium 14a among
the plurality of ring laser resonators each having the ring
modulator 11, the number of optical gain media is decreased,
reducing a load imposed on the manufacturing process thereof.
[0063] According to the aspects described above, an excellent,
minute multi-wavelength modulated light source meets the two
requirements at the same time, one of which is to ensure the
reliability of the modulated light source and the other of which is
to improve power efficiency in modulation operation and/or the
like.
[0064] All examples and conditional language provided herein are
intended for the pedagogical purposes of aiding the reader in
understanding the invention and the concepts contributed by the
inventor to further the art, and are not to be construed as
limitations to such specifically recited examples and conditions,
nor does the organization of such examples in the specification
relate to a showing of the superiority and inferiority of the
invention. Although one or more embodiments of the present
invention have been described in detail, it should be understood
that the various changes, substitutions, and alterations could be
made hereto without departing from the spirit and scope of the
invention.
* * * * *