JP4070196B2 - Wavelength stabilized laser - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wavelength stabilized laser whose oscillation wavelength and output are stabilized, and is useful when applied to a wavelength stabilized light source for optical communication.
[0002]
[Prior art]
With the explosive spread of the Internet, there is an urgent need to increase the capacity of communication networks and reduce communication costs. For this reason, communication systems are currently shifting to an optical high-density wavelength division multiplexing (DWDM) system that multiplexes different wavelengths in one optical fiber and increases the transmission capacity per optical fiber. A light source used for optical communication is required to be a low-cost device with stable oscillation wavelength and output. For this reason, a wavelength-stabilized light source using a semiconductor DFB-LD (Distributed Feedback Laser Diode) is currently used as a light source for optical communication.
[0003]
The grid of each wavelength of DWDM is determined at intervals of 100 GHz (0.8 nm), 50 GHz (0.4 nm), 25 GHz (0.2 nm), etc., centering on the anchor frequency 193.1 THz (1552.24 nm). . Since the wavelength control accuracy required for the light source used for optical communication is 1/10 of the wavelength interval, it is 0.08 nm, 0.04 nm, and 0.02 nm, respectively.
[0004]
On the other hand, since the oscillation wavelength of the semiconductor DFB laser (semiconductor DFB-LD) is shifted by about ± 1 nm from the target wavelength at the time of production, the oscillation wavelength is monitored and temperature control (0.1 nm / ° C.) The oscillation wavelength is controlled to a DWDM wavelength grid. At this time, it is necessary to make the optical output of the semiconductor DFB laser constant, but this is done by controlling the injection current to the semiconductor DFB laser.
[0005]
A module in which the above-mentioned parts are integrated is a wavelength-stabilized light source equipped with a wavelength locker, which has been commercialized by each company. Examples of such a DFB laser with a wavelength locker include the following Non-Patent Document 1. This wavelength stabilized light source is used for DWDM transmission with its oscillation wavelength controlled with high accuracy.
[0006]
[Non-Patent Document 1]
Yokoyama et al. "DFB-LD module with built-in wavelength locker", 2000 IEICE Electronics Society C-3-106, pp. 232
[0007]
FIG. 16 shows a top view of a wavelength-stabilized light source equipped with a wavelength locker manufactured using a conventional technique. As shown in the figure, the light emitted from the front end face of the semiconductor DFB laser 4 is output via a collimator lens 6. On the other hand, the light emitted from the rear end face of the semiconductor DFB laser 4 passes through the collimating lens 7 and then is branched into reflected light and transmitted light by the half mirror 5. The reflected light is incident on a monitor PD (Photo-Diode: photodiode) 2 to monitor the output of the semiconductor DFB laser 4 with the monitor PD 2, and the transmitted light is etalon (Fabry-Perot interferometer) 1. Is allowed to enter the monitor PD3, and the oscillation wavelength of the semiconductor DFB laser 4 is monitored by the monitor PD3.
[0008]
In the monitor PD2, a photocurrent proportional to the incident light intensity flows, and the intensity of incident light can be monitored. Therefore, the output power of the semiconductor DFB laser 4 can be controlled by monitoring the output of the semiconductor DFB laser 4 from the output of the monitor PD2 and feeding it back to the injection current of the semiconductor DFB laser 4. The light passing through the etalon 1 periodically intensifies against changes in wavelength as shown in FIG. 17, and therefore wavelength monitoring is possible by using an appropriate light output as a monitoring point. If the output of the monitor PD3 is fed back to the temperature of the semiconductor DFB laser 4, the oscillation wavelength of the semiconductor DFB laser 4 can be controlled. The temperature of the semiconductor DFB laser 4 is controlled by a Peltier element provided at the lower part of the semiconductor DFB laser 4.
[0009]
[Problems to be solved by the invention]
However, the wavelength-stabilized light source equipped with the wavelength locker manufactured by using the conventional technique is not integrated and is an assembly method of bulk parts, so that the mechanical and thermal stability is insufficient. In particular, in the wavelength-stabilized light source shown in FIG. 16, when used in a place where the environmental temperature changes, the etalon 1 is also temperature-dependent, and the wavelength transmission characteristic of the etalon 1 changes due to the temperature change. The thermal stability was insufficient.
[0010]
In order to solve this, it is necessary to stabilize the temperature of the etalon 1, and for that purpose, it is necessary to stabilize the temperature by using a Peltier element different from the Peltier element for the semiconductor DFB laser. This is because the Peltier device for the semiconductor DFB laser may stabilize the temperature at a place deviated by about ± 10 degrees from the room temperature in order to control the oscillation wavelength of the semiconductor DFB laser 4. This is because when the temperature adjustment of 1 is performed, the wavelength transmission characteristic of the etalon 1 (which adjusted the wavelength transmission characteristic at room temperature) is changed. Further, since the conventional wavelength stabilized light source is an assembly method of bulk parts, the number of parts increases and the cost increases. Therefore, there has been a demand for a wavelength-stabilized light source (wavelength-stabilized laser) that is integrated, has a stable oscillation wavelength and output, and is low in cost (small number of components).
[0011]
Accordingly, the present invention has been made to solve such problems, and an object thereof is to provide a wavelength-stabilized laser that is small, stable, and low in cost.
[0012]
[Means for Solving the Problems]
The wavelength-stabilized laser according to the first aspect of the present invention that achieves the above object is fabricated on the substrate, one semiconductor DFB-LD mounted on the substrate, two first semiconductor PDs and second semiconductor PDs. Quartz glass A wavelength-stabilized laser obtained by hybrid integration with an optical waveguide, wherein emitted light from the front or rear of the semiconductor DFB-LD Quartz glass A branch circuit composed of an optical waveguide branches to the first semiconductor PD side and the second semiconductor PD side, and the light branched to the first semiconductor PD side Quartz glass Light that has entered the first semiconductor PD after passing through a wavelength demultiplexing circuit composed of an optical waveguide and branched to the second semiconductor PD side directly does not pass through the wavelength demultiplexing circuit, but is directly in the second semiconductor PD. Configured to be incident on And means for controlling the oscillation wavelength of the semiconductor DFB-LD by changing the temperature of the substrate. It is characterized by that.
[0014]
The second 2 The wavelength-stabilized laser of the invention is the first 1 In the wavelength stabilized laser of the invention, the wavelength demultiplexing circuit is an MZ interferometer.
[0015]
The second 3 The wavelength-stabilized laser of the invention is the first 1 In the wavelength stabilized laser of the invention, the wavelength demultiplexing circuit is an AWG.
[0016]
The second 4 The wavelength-stabilized laser of the invention is the first 1 In the wavelength-stabilized laser of the invention, the wavelength demultiplexing circuit is formed by forming a grating in a core of the silica-based glass waveguide.
[0017]
The second 5 The wavelength-stabilized laser of the invention is the first 2 In the wavelength-stabilized laser according to the invention, a material having a refractive index temperature coefficient opposite to that of the silica glass waveguide is removed from a part of the silica glass waveguide constituting the MZ interferometer, and the upper clad and the core are removed. The MZ interferometer is made temperature-independent by inserting it into the part where the upper clad, core and lower clad are removed.
[0018]
The second 6 The wavelength-stabilized laser of the invention is the first 3 In the wavelength-stabilized laser of the invention, a part of the silica-based glass waveguide constituting the AWG, a material having a refractive index temperature coefficient opposite in sign to that of the silica-based glass waveguide, with the upper clad and core removed Alternatively, the AWG is made temperature-independent by inserting it in a portion where the upper cladding, the core, and the lower cladding are removed.
[0019]
The second 7 The wavelength-stabilized laser of the invention is the first 4 In the wavelength-stabilized laser of the invention, the grating is heated to a temperature by inserting a material having a refractive index temperature coefficient opposite to that of the silica-based glass waveguide into a portion where the upper clad on the upper portion of the grating is partially or entirely removed. It is characterized by having become independent.
[0020]
The second 8 The wavelength-stabilized laser of the invention is the first 1 In the wavelength-stabilized laser of the invention, a light absorber is inserted into a portion where the upper clad and the lower clad constituting the silica-based glass waveguide are removed or a portion where the upper clad, the core and the lower clad are removed. A feature is that a stray light from the semiconductor DFB-LD is prevented from entering the first semiconductor PD and the second semiconductor PD by an agent.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0022]
(First embodiment)
FIG. 1 shows a top view of the wavelength stabilized laser according to the first embodiment of the present invention. The wavelength stabilization laser of the first embodiment is obtained by hybridly integrating an LD and PD semiconductor chip and an optical waveguide (quartz glass waveguide) on a single substrate.
[0023]
Specifically, as shown in FIG. 1, the wavelength-stabilized laser according to the first embodiment has a monitor PD13 (first semiconductor PD) and a monitor PD12 (second semiconductor PD) which are semiconductor chips on a single Si substrate. ) And a semiconductor DFB laser 14 (semiconductor DFB-LD), a directional coupler 16 as a branch circuit, and an MZ (Mach-Zehnder) interferometer 17 as a wavelength demultiplexing circuit are hybrid-integrated. It has a configuration.
[0024]
The directional coupler 16 is composed of silica-based glass waveguides 18 and 19 fabricated on a Si substrate, and the MZ interferometer 17 is composed of silica-based glass waveguides 10 and 11 fabricated on a Si substrate. . That is, the wavelength-stabilized laser of the first embodiment has a single substrate (PLC (Planar) on which quartz glass waveguides 10, 11, 18, and 19 constituting the directional coupler 16 and the MZ interferometer 17 are fabricated. One semiconductor DFB laser 14 and two monitor PDs 12 and 13 are mounted on a lightguide circuit (chip) 15 and integrated in a hybrid manner.
[0025]
When the relative refractive index difference of the silica-based glass waveguide is 0.75% or less, the semiconductor DFB laser 14 increases the coupling ratio of light with the silica-based glass waveguide. A spot size conversion DFB-LD in which spot size conversion units for enlargement are integrated is desirable. Further, when the relative refractive index is higher than that, a DFB-LD in which the spot size converter is not integrated can be used as the semiconductor DFB laser 14.
[0026]
In the wavelength stabilization laser of the first embodiment, output light is emitted from the front of the semiconductor DFB laser 14. Then, the emitted light from behind the semiconductor DFB laser 14 is branched by the directional coupler 16 into the monitor PD 13 side and the monitor PD 12 side. The light branched to the monitor PD 13 side enters the monitor PD 13 after passing through the MZ interferometer 17 and is monitored by the monitor PD 13. On the other hand, the light branched to the monitor PD 12 side directly enters the monitor PD 12 without passing through the MZ interferometer 17 and is monitored by the monitor PD 12.
[0027]
As shown in FIG. 2, the MZ interferometer 17 changes its light transmission intensity with a period of FSR (free spectral range) according to the change of the wavelength of light. Therefore, the oscillation wavelength of the semiconductor DFB laser 14 can be monitored by monitoring the intensity of light that has passed through the MZ interferometer 17 with the monitor PD 13. Here, if the FSR of the MZ interferometer 17 is 400 GHz (3.2 nm), the target is within the same period as the oscillation wavelength of the semiconductor DFB laser 14 (when the semiconductor DFB laser 14 is oscillated as it is without control). Therefore, the oscillation wavelength of the semiconductor DFB laser 14 can be tuned to an appropriate wavelength by monitoring the output value of the monitor PD 13 (uniquely).
[0028]
Since the monitor PD 12 can monitor the light intensity proportional to the output of the semiconductor DFB laser 14, the monitor PD 13 and the monitor PD 12 can eventually monitor the wavelength and intensity of the output light of the semiconductor DFB laser 14. .
[0029]
Now, an actual operation example will be described here (see FIG. 15). When the semiconductor DFB laser 14 was oscillated and the oscillation wavelength was monitored by the monitor PD 13 at room temperature, the oscillation wavelength was shifted from the desired (target) wavelength by about 0.8 nm. Therefore, the temperature of the substrate (PLC chip) 15, that is, the temperature of the semiconductor DFB laser 14 is changed by about 8 degrees using a Peltier element so that the oscillation wavelength of the semiconductor DFB laser 14 becomes a target wavelength. While monitoring the optical output with the monitor PD12, the injection current to the semiconductor DFB laser 14 was changed to obtain the target output.
[0030]
About 100 wavelength-stabilized lasers (wavelength-stabilized light sources) were produced with the configuration of the first embodiment, but all the wavelength-stabilized lasers were within an output error of ± 0.5 dB and a wavelength error of ± 0.15 nm. .
[0031]
The wavelength stabilization laser of the first embodiment includes one semiconductor DFB laser 14 and two monitors PD12 and 13 mounted on a Si substrate, and a silica-based glass waveguide (direction) formed on the Si substrate. Since the optic coupler 16 and the MZ interferometer 10) have a hybrid integrated configuration, compared with a conventional wavelength stabilized laser of a bulk component assembly method, the number of components is small and the size is small. High mechanical and thermal stability, stable wavelength and output, and low cost production.
[0032]
The means for branching the light emitted from the semiconductor DFB laser 14 is not limited to the directional coupler 16, and any optical circuit having a function of branching light may be used. For example, a Y branch circuit or a 2 × 2 MMI coupler may be used. There may be.
[0033]
(Second embodiment)
FIG. 3 shows a top view of the wavelength stabilized laser according to the second embodiment of the present invention. The wavelength-stabilized laser of the second embodiment is also a hybrid integrated LD and PD semiconductor chip and optical waveguide (quartz glass waveguide) on a single substrate.
[0034]
Specifically, as shown in FIG. 3, the wavelength stabilization laser according to the second embodiment includes a monitor PD13, a monitor PD12, and a semiconductor DFB laser 14, which are semiconductor chips, on a single Si substrate, and a branch circuit. The directional coupler 16 and an arrayed waveguide grating (AWG (Array-Waveguide-Grating)) 21 as a wavelength demultiplexing circuit are hybrid-integrated. That is, the wavelength stabilization laser of the second embodiment has a configuration in which an AWG 21 is provided instead of the MZ interferometer 17 (see FIG. 1) of the first embodiment, and other configurations are the same as those of the first embodiment. It is the same as the wavelength stabilization laser.
[0035]
The AWG 21 is configured as shown in the figure by a plurality of quartz glass waveguides fabricated on a Si substrate. Specifically, the AWG 21 has one input and N outputs (1 × N), and is provided between one input waveguide 25, slab waveguides 22 and 23, and these slab waveguides 22 and 23. .., 24-M and N output waveguides 26-1, 26-2,..., 26-N.
[0036]
In the wavelength stabilization laser of the second embodiment, the emitted light from the rear of the semiconductor DFB laser 14 is branched by the directional coupler 16 into the monitor PD 13 side and the monitor PD 12 side. Then, the light branched to the monitor PD 13 side enters the monitor PD 13 after passing through the AWG 21 and is monitored by the monitor PD 13. That is, of the light that has passed through the AWG 21 with 1 input and N outputs (1 × N), the light at an appropriate output port (output waveguide 26-1 in the illustrated example) is monitored by the monitor PD 13. The light branched to the monitor PD 12 side enters the monitor PD 12 directly without passing through the AWG 21 and is monitored by the monitor PD 12.
[0037]
FIG. 4 shows the wavelength dependence (transmission spectrum) of the transmittance from the AWG 21 of the light incident on the monitor PD 13. Here, the FSR of the AWG 21 is designed to be one digit or more wider than the wavelength error ± 1 nm of the semiconductor DFB laser 14, and the range of the horizontal axis is sufficiently smaller than the FSR of the AWG. The vertical axis is a linear scale. As shown in FIG. 4, the transmittance is high near the center wavelength λc, and the transmittance is highest at the center wavelength λc. Since the current due to light reception by the monitor PD 13 depends on the light intensity, the oscillation wavelength of the semiconductor DFB laser 14 can be monitored by monitoring the current of the monitor PD 13 for light having a wavelength near the center wavelength λc. Therefore, for example, when the center wavelength λc is controlled to the target wavelength, the oscillation value of the semiconductor DFB laser 14 can be tuned to an appropriate (target) wavelength by monitoring the output value of the monitor PD 13 (uniquely). become able to.
[0038]
As a method for controlling the transmission center wavelength from the AWG to each port, for example, there is a method using ultraviolet irradiation. This method is described in Abe et al., 2000 Annual Conference of the Institute of Electronics, Information and Communication Engineers, C-3-75, “Controlling the central wavelength of temperature-independent silica-based AWG by laser light irradiation” and the like. As shown in FIG. 3, the transmission center wavelength of the output light from the monitor waveguide (in the illustrated example, the output waveguide 26-N) can be monitored by inputting the light of the broadband light source from the waveguide 18, and from this monitor waveguide From the transmission center wavelength of the output light, the transmission center wavelength of the output light from the port (output waveguide 26-1 in the illustrated example) input to the monitor PD 13 can be calculated. Accordingly, since the transmission center wavelength of the AWG 21 can be monitored while irradiating the AWG 21 with UV light (ultraviolet light), the transmission center wavelength of the AWG 21 can be controlled to a target wavelength.
[0039]
Since the monitor PD 12 can monitor the light intensity proportional to the output of the semiconductor DFB laser 14, the monitor PD 13 and the monitor PD 12 can eventually monitor the wavelength and intensity of the output light of the semiconductor DFB laser 14. .
[0040]
Now, an actual operation example will be described here (see FIG. 15). When the semiconductor DFB laser 14 was oscillated and this oscillation wavelength was monitored by the monitor PD 13 at room temperature, the oscillation wavelength was shifted from the desired (target) wavelength by about 0.5 nm. Therefore, the temperature of the substrate (PLC chip) 15, that is, the temperature of the semiconductor DFB laser 14 is changed by about 5 degrees to control the oscillation wavelength of the semiconductor DFB laser 14 to a target wavelength, and the monitor PD 12 outputs the light. In order to obtain the target output, the injection current to the semiconductor DFB laser 14 was changed.
[0041]
About 100 wavelength-stabilized lasers (wavelength-stabilized light sources) were produced with the configuration of the second embodiment. However, all the wavelength-stabilized lasers had an output error of ± 0.5 dB and a wavelength error of ± 0.15 nm. It was.
[0042]
The wavelength stabilization laser of the second embodiment includes one semiconductor DFB laser 14 and two monitors PD 12 and 13 mounted on a Si substrate, and a silica-based glass waveguide (direction) formed on the Si substrate. Since the coupler 16 and the AWG 21) have a hybrid integrated configuration, compared with the conventional wavelength stabilized laser of the bulk component assembly method, the number of components is small, the size is small, the mechanical and High thermal stability, stable wavelength and output, and low cost production.
[0043]
The means for branching the light emitted from the semiconductor DFB laser 14 is not limited to the directional coupler 16, and any optical circuit having a function of branching light may be used. For example, a Y branch circuit or a 2 × 2 MMI coupler may be used. There may be.
[0044]
(Embodiment 3)
FIG. 5 shows a top view of a wavelength stabilized laser according to the third embodiment of the present invention. The wavelength-stabilized laser of the third embodiment is also a hybrid integrated LD and PD semiconductor chip and optical waveguide (quartz glass waveguide) on a single substrate.
[0045]
Specifically, as shown in FIG. 5, the wavelength stabilization laser of the third embodiment includes a monitor PD13, a monitor PD12, and a semiconductor DFB laser 14, which are semiconductor chips, on a single Si substrate, and a branch circuit. The directional coupler 6 and the grating 31 as a wavelength demultiplexing circuit are hybrid-integrated. That is, the wavelength stabilized laser of the third embodiment has a configuration in which a grating 31 is provided instead of the MZ interferometer 17 (see FIG. 1) of the first embodiment, and the other configurations are the first embodiment. This is the same as the wavelength stabilized laser. The grating 31 is a refractive index modulation section formed in the core of a silica glass waveguide 32 fabricated on a Si substrate (see FIG. 11).
[0046]
In the wavelength stabilized laser of the third embodiment, the emitted light from the rear of the semiconductor DFB laser 14 is branched by the directional coupler 16 into the monitor PD 13 side and the monitor PD 12 side. The light branched to the monitor PD 13 side enters the monitor PD 13 after passing through the grating 31 and is monitored by the monitor PD 13. The light branched to the monitor PD 12 side directly enters the monitor PD 12 without passing through the grating 31 and is monitored by the monitor PD 12.
[0047]
The pass spectrum of the grating 31 is expressed as shown in FIG. The transmittance decreases at a wavelength close to the center wavelength λc, and the transmittance decreases at the center wavelength λc. When the grating 31 is a λ / 4 phase shift grating (J. Canning, et al, Electron. Lett., Vol30, No.16, pp1344-1345), the transmission spectrum of the grating 31 is as shown in FIG. The transmittance at the wavelength λc is maximized.
[0048]
Since the transmittance changes with respect to the center wavelength λc in this way, the oscillation wavelength of the semiconductor DFB laser 14 can be monitored by monitoring the output current from the monitor FD13. Since the monitor PD 12 can monitor the light intensity proportional to the output of the semiconductor DFB laser 14, the monitor PD 13 and the monitor PD 12 can eventually monitor the wavelength and intensity of the output light of the semiconductor DFB laser 14. .
[0049]
Now, an actual operation example will be described here (see FIG. 15). When the semiconductor DFB laser 14 was oscillated and this oscillation wavelength was monitored by the monitor PD 13 at room temperature, the oscillation wavelength was shifted from the desired (target) wavelength by about 0.3 nm. Therefore, the temperature of the substrate (PLC chip) 15, that is, the temperature of the semiconductor DFB laser 14 is changed by about 3 degrees so that the oscillation wavelength of the semiconductor DFB laser 14 becomes the target wavelength, and the monitor PD 12 While monitoring the output, the injection current was varied to obtain the target output.
[0050]
About 100 wavelength-stabilized lasers (wavelength-stabilized light sources) were produced with the configuration of the third embodiment. All wavelength-stabilized lasers had an output error of ± 0.5 dB and a wavelength error of ± 0.15 nm. It was.
[0051]
The wavelength stabilization laser of the third embodiment includes one semiconductor DFB laser 14 and two monitors PD12 and 13 mounted on a Si substrate, and a silica-based glass waveguide (direction) formed on the Si substrate. Since the coupler 16 and the grating 31) have a hybrid integrated configuration, compared with a conventional wavelength stabilization laser of a bulk component assembly method, the configuration is simple, the number of components is small, and the size is small. In addition, the thermal stability is high, the wavelength and output are stable, and it can be produced at low cost.
[0052]
The means for branching the light emitted from the semiconductor DFB laser 14 is not limited to the directional coupler 16, and any optical circuit having a function of branching light may be used. For example, a Y branch circuit or a 2 × 2 MMI coupler may be used. There may be.
[0053]
(Fourth embodiment)
FIG. 8 shows a top view of a wavelength stabilized laser according to the fourth embodiment of the present invention. The wavelength-stabilized laser of the fourth embodiment is also a hybrid integration of LD and PD semiconductor chips and an optical waveguide (quartz glass waveguide) on a single substrate.
[0054]
Specifically, as shown in FIG. 8, the wavelength stabilization laser of the fourth embodiment includes a monitor PD13, a monitor PD12, and a semiconductor DFB laser 14, which are semiconductor chips, on a single Si substrate, and a branch circuit. The directional coupler 6 and the MZ interferometer 41 as the wavelength demultiplexing circuit are hybrid-integrated, and the MZ interferometer 41 is temperature independent. That is, the wavelength stabilized laser of the fourth embodiment is a temperature-independent MZ interferometer instead of the MZ interferometer 17 (see FIG. 1) made of the normal silica glass waveguide in the first embodiment. The other components are the same as those of the wavelength stabilized laser of the first embodiment. In the fourth embodiment, the light emitted from the rear of the semiconductor DFB laser 14 is branched by the directional coupler 16, the light that has passed through the MZ interferometer 41 is monitored by the monitor PD 13, and passes through the MZ interferometer 41. No light is monitored by the monitor PD12.
[0055]
The MZ interferometer 41 is made temperature-independent by inserting the polymer 42 into the divided groove (s). More specifically, the MZ interferometer 41 is composed of silica-based glass waveguides 10 and 11 manufactured on a Si substrate, and the polymer 42 is part of the silica-based glass waveguide 10 constituting the MZ interferometer 41. The upper clad and the core are removed (groove) or the upper clad, the core and the lower clad are removed (groove). The polymer 42 may be a material having a reverse sign to the temperature coefficient of the refractive index of the silica glass waveguide, that is, a material having a negative temperature coefficient.
[0056]
For example, a silicone resin can be used as the polymer 42. By inserting a silicone resin in a region having an appropriate length, the optical path length difference between the quartz glass waveguides 10 and 11 of the MZ interferometer 41 can be prevented from changing with temperature. That is, the temperature dependence (transmission spectrum) of the MZ interferometer 41 can be eliminated. The temperature coefficient of the MZ interferometer manufactured with a normal silica-based glass waveguide was 0.01 nm / ° C. However, the temperature coefficient of the MZ interferometer is reduced to 0.001 nm / ° C. or less by inserting a silicone resin. be able to. The temperature independence technique is described in detail in Inoue et al., “Optical Waveguide Circuit” Japanese Patent Application No. 9-30251. Here, the polymer 42 may be inserted not only in the silica-based glass waveguide 10 but also in a part of the silica-based glass waveguide 11.
[0057]
Even in the wavelength stabilized laser of the fourth embodiment, the monitor PD 13 can monitor the light intensity corresponding to the oscillation wavelength of the semiconductor DFB laser 14 as in the first embodiment, and the monitor PD 12 can monitor the light proportional to the output of the semiconductor DFB laser 14. Since the intensity can be monitored, the wavelength and intensity of the output light of the semiconductor DFB laser 14 can be monitored by the monitor PD 13 and the monitor PD 12 after all.
[0058]
The actual operation will now be described (see FIG. 15). When the semiconductor DFB laser 14 was oscillated and the oscillation wavelength was monitored by the monitor PD 13 at room temperature, the oscillation wavelength was shifted from the desired (target) wavelength by about 0.8 nm. Therefore, the temperature of the substrate (PLC chip) 15, that is, the temperature of the semiconductor DFB laser 14 is changed by about 8 degrees using a Peltier element so that the oscillation wavelength of the semiconductor DFB laser 14 becomes a target wavelength. While monitoring the optical output with the monitor PD12, the injection current to the semiconductor DFB laser 14 was changed to obtain the target output.
[0059]
About 100 wavelength-stabilized lasers (wavelength-stabilized light sources) were produced with the configuration of the fourth embodiment, but all the wavelength-stabilized lasers were within an output error of ± 0.5 dB and a wavelength error of ± 0.015 nm. . The wavelength error is one digit smaller than that in the first embodiment. This is because even if the temperature of the substrate is changed in order to change the oscillation wavelength of the wavelength stabilizing laser 14, the transmission spectrum of the MZ interferometer 41 does not change. This is a result of using the polymer 42 to make the transmission spectrum of the MZ interferometer 12 temperature independent.
[0060]
The means for branching the light emitted from the semiconductor DFB laser 14 is not limited to the directional coupler 16, and any optical circuit having a function of branching light may be used. For example, a Y branch circuit or a 2 × 2 MMI coupler may be used. There may be.
[0061]
(5th Example)
FIG. 9 shows a top view of the wavelength stabilized laser according to the fifth embodiment of the present invention. The wavelength-stabilized laser of the fifth embodiment is also a hybrid integrated LD and PD semiconductor chip and optical waveguide (quartz glass waveguide) on a single substrate.
[0062]
Specifically, as shown in FIG. 9, the wavelength stabilization laser of the fifth embodiment has a monitor PD13, a monitor PD12, and a semiconductor DFB laser 14 as semiconductor chips on one Si substrate, and a branch circuit. The directional coupler 16 and the AWG 51 as the wavelength demultiplexing circuit are hybrid-integrated, and the AWG 51 is temperature independent. That is, the wavelength stabilized laser of the fifth embodiment has a configuration in which an AWG 51 that is temperature-independent is provided in place of the AWG 21 in the second embodiment, and the other configurations are the wavelength stabilized laser of the second embodiment. This is the same as the laser. In the fifth embodiment, the emitted light from behind the semiconductor DFB laser 14 is branched by the directional coupler 16, the light that has passed through the AWG 51 is monitored by the monitor PD 13, and the light that has not passed through the AWG 51 is monitored by the monitor PD 12. Monitor.
[0063]
The AWG 51 is provided between a plurality of quartz-based glass waveguides fabricated on a Si substrate, that is, one input waveguide 25, slab waveguides 22 and 23, and these slab waveguides 22 and 23. 1-input N-output (1 × N) composed of M arrayed waveguides 24-1, 24-2... 24-M and N output waveguides 26-1, 26-2. belongs to. Then, in a part of the M arrayed waveguides 24-1, 24-2... 24-M constituting the AWG 51, the upper clad and the core are removed or the upper clad, the core and the lower clad are removed. By inserting the silicone resin 52 into the portion, the transmission spectrum of the AWG 51 is made temperature-independent.
[0064]
Also in this case, similarly to the fourth embodiment, the temperature coefficient of the silica-based glass waveguide can be canceled by inserting a silicone resin 52 opposite to the temperature coefficient of the silica-based glass waveguide into a region having an appropriate length. . The AWG 51 demultiplexes the wavelength by multi-speed interference from the arm waveguides (array waveguides 24-1, 24-2,..., 24-M) (different in length). If the silicone resin 52 is inserted so that the difference in temperature does not depend on the temperature, the transmission center wavelength of the AWG 51 can be made temperature-independent.
[0065]
The temperature independence technique is described in detail in Inoue et al., “Optical Waveguide Circuit” Japanese Patent Application No. 9-30251. By making this temperature independence, the temperature coefficient of the center wavelength can be reduced to 0.001 nm / ° C. (what was conventionally 0.01 nm / ° C.). Further, as a method for controlling the transmission center wavelength from the AWG 51 to each port, there is a method using ultraviolet irradiation as described in the second embodiment.
[0066]
As described in the second embodiment, since the light transmitted through the AWG 51 and input to the monitor PD 13 has wavelength dependency, the oscillation wavelength of the semiconductor DFB laser 14 is monitored by monitoring the light intensity with the monitor PD 13. be able to. Since the monitor PD 12 can monitor the light intensity proportional to the output of the semiconductor DFB laser 14, the monitor PD 13 and the monitor PD 12 can eventually monitor the wavelength and intensity of the output light of the semiconductor DFB laser 14. .
[0067]
Now, an actual operation example will be described here (see FIG. 15). When the semiconductor DFB laser 14 was oscillated and this oscillation wavelength was monitored by the monitor PD 13 at room temperature, the oscillation wavelength was shifted from the desired (target) wavelength by about 0.5 nm. Therefore, the temperature of the substrate (PLC chip) 15, that is, the temperature of the semiconductor DFB laser 14 is changed by about 5 degrees to control the oscillation wavelength of the semiconductor DFB laser 14 to a target wavelength, and the monitor PD 12 outputs the light. In order to obtain the target output, the injection current to the semiconductor DFB laser 14 was changed.
[0068]
About 100 wavelength-stabilized lasers (wavelength-stabilized light sources) were produced with the configuration of the fifth embodiment, but all the wavelength-stabilized lasers were within an output error of ± 0.5 dB and a wavelength error of ± 0.015 nm. . The wavelength error is an order of magnitude smaller than that of the second embodiment due to the effect of making the AWG 51 temperature independent.
[0069]
The means for branching the light emitted from the semiconductor DFB laser 14 is not limited to the directional coupler 16, and any optical circuit having a function of branching light may be used. For example, a Y branch circuit or a 2 × 2 MMI coupler may be used. There may be.
[0070]
(Sixth embodiment)
FIG. 10 shows a top view of a wavelength stabilized laser according to the sixth embodiment of the present invention. The wavelength-stabilized laser of the sixth embodiment is also a hybrid integrated LD and PD semiconductor chip and optical waveguide (quartz glass waveguide) on a single substrate.
[0071]
Specifically, as shown in FIG. 10, the wavelength stabilization laser according to the sixth embodiment includes a monitor PD13, a monitor PD12, and a semiconductor DFB laser 14, which are semiconductor chips, on a single Si substrate, and a branch circuit. The directional coupler 6 and a grating 67 as a wavelength demultiplexing circuit are integrated, and the grating 67 is made temperature independent by the silicone resin 62. That is, the wavelength stabilization laser of the sixth embodiment has a configuration in which a grating 67 that is temperature-independent is provided instead of the grating 31 in the third embodiment, and other configurations are the same as those of the third embodiment. It is the same as the wavelength stabilization laser.
[0072]
The grating 67 is a refractive index modulation part formed in the core of the silica-based glass waveguide 32 manufactured on the Si substrate. In the sixth embodiment, the emitted light from behind the semiconductor DFB laser 14 is branched by the directional coupler 16, the light passing through the grating 67 is monitored by the monitor PD 13, and the light not passing through the grating 67 is monitored. Monitor with PD12.
[0073]
The grating 67 is independent of temperature in the configuration described below.
[0074]
FIG. 11 is a cross-sectional view of the grating forming portion 61 shown in FIG. In FIG. 11, 63 is an upper clad, 64 is a core, 65 is a lower clad, 66 is a Si substrate, and 67 is a portion (grating) in which the refractive index is modulated in the core 64. A part of the energy of the light guided through the core 64 oozes out into the clads 63 and 65. Therefore, since light senses both the refractive index of the core 64 and the refractive indexes of the clads 63 and 65, the effective refractive index is an intermediate value between the refractive indexes of the two. Therefore, for example, a silicone resin 62 is inserted as a temperature coefficient adjusting material into a portion where the upper clad 63 on the grating 67 is partially or entirely removed, and the temperature coefficient is opposite to that of the quartz glass waveguide (particularly the core). If so, the temperature coefficient of the effective refractive index can be adjusted. With the above configuration, the temperature coefficient of the reflection center wavelength of the grating 67 can be reduced to 0.001 / ° C. (what was conventionally 0.01 nm / ° C.).
[0075]
For details of the temperature-independent grating configuration, see Kokubun, et al., “Temperature-independent narrowband optical filter at 1.3 um wavelength by an athermal waveguide”, Election, Lett, vol. 32, no. 21, pp. 1998. -1999,1996 and Bosc, et al., "Temperature and polarization insensitive Bragg gratings realised on silica waveguide on silicon", Electron.Lett.vol.33, no.2, pp.134-136,1997 and Yoneda et al. Design of athermal optical waveguide system ", Proceedings of the IEICE Spring Conference C-3-2, p.187, 1997.
[0076]
In the pass spectrum of the grating 67, the transmittance changes in the vicinity of the center wavelength as in the case of the grating 31 shown in the third embodiment. Therefore, the oscillation wavelength of the semiconductor DFB laser 14 is monitored by monitoring the output current from the monitor PD13. Can be monitored. Since the monitor PD 12 can monitor the light intensity proportional to the output of the semiconductor DFB laser 14, the monitor PD 13 and the monitor PD 12 can eventually monitor the wavelength and intensity of the output light of the semiconductor DFB laser 14. .
[0077]
Now, an actual operation example will be described here (see FIG. 15). When the semiconductor DFB laser 14 was oscillated and this oscillation wavelength was monitored by the monitor PD 13 at room temperature, the oscillation wavelength was shifted from the desired (target) wavelength by about 0.3 nm. Therefore, the temperature of the substrate (PLC chip) 15, that is, the temperature of the semiconductor DFB laser 14 is changed by about 3 degrees to control the oscillation wavelength of the semiconductor DFB laser 14 to a target wavelength, and the monitor PD 12 outputs light. In order to obtain the target output, the injection current to the semiconductor DFB laser 14 was changed.
[0078]
About 100 wavelength-stabilized lasers (wavelength-stabilized light sources) were produced with the configuration of the sixth embodiment, but all the wavelength-stabilized lasers were within an output error of ± 0.5 dB and a wavelength error of ± 0.015 nm. . The wavelength error is one digit smaller than that of the third embodiment due to the effect of making the grating 67 temperature independent.
[0079]
The means for branching the light emitted from the semiconductor DFB laser 14 is not limited to the directional coupler 16, and any optical circuit having a function of branching light may be used. For example, a Y branch circuit or a 2 × 2 MMI coupler may be used. There may be.
[0080]
(Seventh embodiment)
FIG. 12 shows a top view of the wavelength stabilized laser according to the seventh embodiment of the present invention. The wavelength stabilized laser of the seventh embodiment is also a hybrid integrated LD and PD semiconductor chip and optical waveguide (quartz glass waveguide) on a single substrate.
[0081]
Specifically, as shown in FIG. 12, the wavelength-stabilized laser of the seventh embodiment is the same as the wavelength-stabilized laser of the second embodiment (see FIG. 3), and a semiconductor chip is formed on one Si substrate. The monitor PD 13, the monitor PD 12, and the semiconductor DFB laser 14, the directional coupler 16 as a branch circuit, and the AWG 21 as a wavelength demultiplexing circuit are hybridly integrated.
[0082]
In the wavelength stabilization laser of the seventh embodiment, in the vicinity of the semiconductor DFB laser 14, a portion where the upper cladding and the lower cladding of the silica-based glass waveguide are removed (a portion where a portion of the cladding layer in the PLC chip 15 is removed). ) Is inserted with a light-absorbing agent 71.
[0083]
Although the operating principle is the same as that of the second embodiment, in the seventh embodiment, stray light from the semiconductor DFB laser 14 (PLC chip cladding layer (upper cladding and lower cladding) is absorbed by the light absorber 71 inserted in the cladding removal portion. ) Is prevented from entering the monitor PD 12 and the monitor PD 13. When the stray light is incident on the monitor PDs 12 and 13, the monitor PD 12 and the monitor PD 13 monitor the light intensity that is larger than the light intensity to be actually measured, and accordingly, the oscillation wavelength and output of the present wavelength stabilized laser are increased. It was out of the target value. Therefore, in the seventh embodiment, the light absorber 71 is inserted into the clad removal portion as described above.
[0084]
About 100 wavelength-stabilized lasers (wavelength-stabilized light sources) were produced with the configuration of the seventh embodiment, but all the wavelength-stabilized lasers were within an output error of ± 0.05 dB and a wavelength error of ± 0.010 nm. . The output error and the wavelength error are smaller than in the second embodiment due to the effect of the light absorber 71.
[0085]
In FIG. 12, the portion where the light absorber 41 is inserted is made not only to cross the quartz glass waveguide 19 but also to not cross the quartz glass waveguide 18. That is, the core portion is not removed, only the clad portion is removed, and the light absorber 41 is inserted here. However, the present invention is not limited to this, and the silica-based glass waveguide 18 may be crossed by the light absorber 41. In this case, the light absorber 71 is inserted into the portion where the upper clad, the core (the core portion of the silica glass waveguide 18) and the lower clad are removed. However, in the case of FIG. 12, it is necessary to adjust the transmission center wavelength of the AWG 21 to the target wavelength by inputting the light of the broadband light source from the silica-based glass waveguide 18 as described above. 71 may be inserted.
[0086]
Further, by combining the configuration of the seventh embodiment (the configuration in which the light absorber 71 is inserted) with the configurations of the first embodiment, the third embodiment to the sixth embodiment, the effect of the light absorber 71 is reduced to the first. It goes without saying that a semiconductor DFB laser (wavelength-stabilized light source) with less wavelength error as well as output error can be manufactured as compared with the examples and the third to sixth examples. As an example, FIG. 13 shows an example in which the configuration of the seventh embodiment is combined with the configuration of the first embodiment, and FIG. 14 shows an example in which the configuration of the seventh embodiment is combined with the configuration of the fourth embodiment. .
[0087]
Needless to say, an EA (electron-absorption) modulator integrated semiconductor DFB laser can be used for the semiconductor DFB lasers 14 of the first to seventh embodiments. In this case, since modulation can be performed by an integrated EA modulator, it is possible to realize modulated light with less chirp than direct modulation of the semiconductor DFB laser itself.
[0088]
In the first to seventh embodiments, the light emitted from the rear side of the semiconductor DFB laser is branched and monitored. However, the present invention is not limited to this. A configuration may be adopted in which the emitted light is branched and monitored.
[0089]
(Eighth embodiment)
FIG. 15 shows a wavelength-stabilized laser module using the wavelength-stabilized laser chip described in the first to seventh embodiments.
[0090]
As shown in FIG. 15, this wavelength stabilized laser module is placed on a Peltier element 82 and a Peltier element 82 in a casing 81 (for convenience of explanation), and is in thermal contact with the Peltier element 82. A soaking plate 83 made of an aluminum plate, a thermistor 84 in thermal contact with the soaking plate 83, and a first embodiment installed on the soaking plate 83 and in thermal contact with the soaking plate 83 The wavelength-stabilized laser chip 85 of any one of the examples to the seventh embodiment is provided. In this wavelength stabilized laser module, the temperature of the semiconductor DFB laser 14 is controlled by heat generation or heat absorption of the Peltier element 82. At this time, the temperature of the semiconductor DFB laser 14 is measured by setting the substrate (PLC chip) 15 as a whole to a uniform temperature in the soaking plate 83 and measuring the temperature of the soaking plate 83 in the thermistor 84.
[0091]
An optical fiber 87 is connected to the front end face of the wavelength stabilization laser chip 85 by a fiber block (glass block) 86, and a fiber connector 88 is provided at the tip of the optical fiber 87. Accordingly, the light emitted from the semiconductor DFB laser 14 is output via the optical fiber 87 and the fiber connector 88.
[0092]
A plurality of electrical terminals 89 extend from the housing 81 to the outside in a butterfly shape. The monitor PD 12, the monitor PD 13 and the semiconductor DFB laser 14 mounted on the PLC chip 15, the Peltier element 82 and the thermistor 84 are connected to the PLC chip 15 through the electrical terminals 89 and the printed wiring board 90 provided in the housing 81. Are connected to a PD voltage monitor 91, a PD voltage monitor 92, an LD driver 93, and a temperature control circuit 94 provided outside the housing, respectively, and are controlled by an APC (Auto Power Control) control circuit 95 that generalizes them. By doing so, the oscillation wavelength and output of the wavelength stabilization laser chip 85 (semiconductor DFB laser 14) are stabilized.
[0093]
In a conventional laser with a wavelength locker (FIG. 13), the laser light in the laser module propagates through space, and a collimator lens or the like is required as shown in FIG. In addition, since light propagates through the space, it is very difficult to align the etalon, the half mirror, and the two PDs. On the other hand, in the present wavelength stabilized laser module, the laser light propagates in the silica glass waveguide, so there is no such disadvantage as described above, no collimating lens is required, and the light emitted from the semiconductor DFB laser 14 is also direct light. Since it can be introduced into the fiber 87, a complicated lens configuration is unnecessary. Accordingly, the number of component parts can be reduced, and there are effects of cost reduction and yield improvement.
[0094]
【The invention's effect】
As described above, the wavelength-stabilized laser according to the present invention is fabricated on the substrate with one semiconductor DFB-LD, two first semiconductor PDs and second semiconductor PDs mounted on the substrate. Quartz glass A wavelength-stabilized laser obtained by hybrid integration with an optical waveguide, wherein emitted light from the front or rear of the semiconductor DFB-LD Quartz glass A branch circuit composed of an optical waveguide branches to the first semiconductor PD side and the second semiconductor PD side, and the light branched to the first semiconductor PD side Quartz glass Light that has entered the first semiconductor PD after passing through a wavelength demultiplexing circuit composed of an optical waveguide and branched to the second semiconductor PD side directly does not pass through the wavelength demultiplexing circuit, but is directly in the second semiconductor PD. Configured to be incident on And means for controlling the oscillation wavelength of the semiconductor DFB-LD by changing the temperature of the substrate. It is characterized by that. Therefore, according to the present invention, compared with the conventional wavelength stabilized laser of the bulk component assembling method, the number of components is small, the size is small, the mechanical and thermal stability is high, the wavelength and the output are high. However, a stable and inexpensive wavelength-stabilized laser can be realized.
[0095]
Also, according to the wavelength stabilized laser of the present invention, a material having a refractive index temperature coefficient opposite to that of the silica-based glass waveguide is inserted, and the wavelength demultiplexing circuit MZ interferometer, AWG or grating is temperature independent. Therefore, the wavelength error can be further reduced.
[0096]
Further, according to the wavelength stabilized laser of the present invention, the stray light from the semiconductor DFB-LD is prevented from entering the first semiconductor PD and the second semiconductor PD by the light absorber, thereby reducing the output error and the wavelength error. It can be further reduced.
[Brief description of the drawings]
FIG. 1 is a top view showing a configuration of a wavelength stabilized laser according to a first embodiment of the present invention.
FIG. 2 is a diagram showing a transmission spectrum from an MZ interferometer.
FIG. 3 is a top view showing a configuration of a wavelength stabilized laser according to a second embodiment of the present invention.
FIG. 4 is a diagram showing a transmission spectrum from an AWG to an output port connected to a monitor PD.
FIG. 5 is a top view showing a configuration of a wavelength stabilized laser according to a third embodiment of the present invention.
FIG. 6 is a diagram showing a transmission spectrum of a grating.
FIG. 7 is a diagram showing a transmission spectrum of a λ / 4 phase shift grating.
FIG. 8 is a top view showing a configuration of a wavelength stabilized laser according to a fourth embodiment of the present invention.
FIG. 9 is a top view showing a configuration of a wavelength stabilized laser according to a fifth embodiment of the present invention.
FIG. 10 is a top view showing a configuration of a wavelength stabilized laser according to a sixth embodiment of the present invention.
FIG. 11 is a cross-sectional view showing a configuration of a temperature-independent grating.
FIG. 12 is a top view showing a configuration of a wavelength stabilized laser according to a seventh embodiment of the present invention.
FIG. 13 is a top view showing another configuration of the wavelength stabilized laser according to the seventh embodiment of the present invention.
FIG. 14 is a top view showing another configuration of the wavelength stabilized laser according to the seventh embodiment of the present invention.
FIG. 15 is a perspective view showing a configuration of a wavelength stabilized laser module using the wavelength stabilized laser chip shown in the first to seventh embodiments.
FIG. 16 is a top view showing a configuration of a conventional wavelength stabilized laser (wavelength stabilized light source).
FIG. 17 shows a transmission spectrum of etalon.
[Explanation of symbols]
10, 11 Silica-based glass waveguide constituting MZ interferometer
12, 13 Monitor PD
14 Semiconductor DFB laser
15 PLC chip
16 Directional coupler
17 MZ interferometer
18, 19 Silica-based glass waveguide constituting directional coupler
21 AWG
22 and 23 slab waveguide constituting AWG
24-1, 24-2 ... 24-M array waveguides constituting AWG
26-1, 26-2 ... 26-N AWG output waveguide
31 grating (refractive index modulation part)
32 Silica-based glass waveguide with grating
41 Temperature independent MZ interferometer
42 Polymer (silicone resin)
51 Temperature independent AWG
52 Silicone resin
61 Grating forming part
62 Silicone resin
63 Upper cladding
64 core
65 Lower cladding
66 Si substrate
67 Temperature independent grating (refractive index modulation part)
71 Absorber
81 body
82 Peltier element
83 Soaking plate
84 Thermistor
85 Semiconductor DFB laser chip
86 Fiber block
87 Optical fiber
88 Fiber connector
89 Electrical terminal
90 Printed circuit board
91,92 PD voltage monitor
93 LD driver
94 Temperature control circuit
95 APC control circuit

Claims (8)

A wavelength-stabilized laser in which one semiconductor DFB-LD mounted on a substrate, two first semiconductor PDs and second semiconductor PDs, and a silica-based glass optical waveguide fabricated on the substrate are hybrid-integrated. There,
The outgoing light from the front or rear of the semiconductor DFB-LD is branched into the first semiconductor PD side and the second semiconductor PD side by a branch circuit composed of the silica-based glass optical waveguide, and the first semiconductor PD The light branched to the side passes through the wavelength demultiplexing circuit composed of the silica glass optical waveguide and then enters the first semiconductor PD, and the light branched to the second semiconductor PD side is the wavelength demultiplexing circuit configured to be incident directly on the second semiconductor PD without passing through the,
A wavelength stabilized laser comprising means for controlling an oscillation wavelength of the semiconductor DFB-LD by changing a temperature of the substrate . The wavelength stabilized laser according to claim 1 , wherein
The wavelength stabilization laser, wherein the wavelength demultiplexing circuit is an MZ interferometer. The wavelength stabilized laser according to claim 1 , wherein
The wavelength stabilizing laser, wherein the wavelength demultiplexing circuit is an AWG. The wavelength stabilized laser according to claim 1 , wherein
2. A wavelength-stabilized laser, wherein the wavelength demultiplexing circuit is formed by forming a grating in the core of the silica-based glass waveguide. The wavelength-stabilized laser according to claim 2 ,
In a part of the silica glass waveguide constituting the MZ interferometer, a material having a refractive index temperature coefficient opposite in sign to that of the silica glass waveguide is obtained by removing the upper clad and the core, or the upper clad and the core, A wavelength-stabilized laser characterized in that the MZ interferometer is made temperature-independent by inserting it in a portion where the lower cladding is removed. The wavelength-stabilized laser according to claim 3 ,
In a part of the silica-based glass waveguide constituting the AWG, a material having a refractive index temperature coefficient opposite to that of the silica-based glass waveguide is removed from the upper clad and the core, or the upper clad, the core, and the lower clad. A wavelength-stabilized laser characterized in that the AWG is made temperature-independent by inserting it in a portion from which the above are removed. The wavelength stabilized laser according to claim 4 , wherein
The grating is made temperature-independent by inserting a material having a refractive index temperature coefficient opposite to that of the silica-based glass waveguide into a portion where the upper cladding of the upper part of the grating is partially or entirely removed. Wavelength stabilized laser. The wavelength stabilized laser according to claim 1 , wherein
A light-absorbing agent is inserted into a portion where the upper clad and lower clad constituting the silica-based glass waveguide are removed, or a portion where the upper clad, the core and the lower clad are removed, and the semiconductor DFB-LD is obtained by using this light-absorbing agent. A wavelength-stabilized laser characterized in that stray light from the laser beam is prevented from entering the first semiconductor PD and the second semiconductor PD.

Images