JP2003023208A - Variable wavelength semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a variable wavelength semiconductor laser capable of suppressing a temperature distribution unevenness in a direction of an optical waveguide at the time of heating heater electrodes and enlarging a temperature varying range in a heater electrode integrated type variable wavelength semiconductor laser, and to provide a wavelength selective light source capable of obtaining good optical output characteristics without depending upon a selecting oscillation wavelength while realizing a simple process not requiring for a butt coupling process. SOLUTION: The variable wavelength semiconductor laser comprises heater electrodes changing in a direction of a semiconductor optical waveguide, so that a resistivity (Ω/m) of the electrodes become uniform in the waveguide by heating the waveguide and a distribution of a refractive index change by heating in a direction of the waveguide becomes uniform. Further, the wavelength selective light source in which a plurality of heater heating type variable wavelength semiconductor laser, a semiconductor optical coupler and a semiconductor optical amplifier are integrated, is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength tunable semiconductor laser, and more particularly to a wavelength that has a heater electrode for heating a semiconductor optical waveguide, suppresses nonuniform heat distribution generated in the axial direction, and maintains a stable oscillation mode. The present invention relates to a heater-integrated wavelength selection light source that can obtain a sufficient light output with a variable semiconductor laser.

[0002]

2. Description of the Related Art In recent years, with the rapid spread of the Internet, wavelength division multiplexing (Wavelength D
ivision Multiplexing, abbreviated as WDM) The communication market is exploding. In this WDM optical fiber communication,
Since as many wavelengths as the number of channels are used, many light sources having different wavelengths are required. This means that it is necessary to handle various types of light sources that differ in number depending on the number of wavelengths, which increases the inventory cost of light sources,
There is also a problem that a large number of backup light sources must be prepared when each light source fails. In order to cope with these problems, demand for a wavelength tunable light source (wavelength selective light source) capable of handling a plurality of wavelengths with one light source (one type) is rapidly increasing.

Hitherto, variable wavelength light sources (wavelength selective light sources)
Various methods (structures) for realizing the above have been reported. For example, a current is injected into the DBR region of a three-electrode distributed Bragg reflector (DBR for short) laser, and the change in the refractive index (that is, Bragg wavelength) due to the plasma effect is used to change the wavelength. Wavelength tuning using the refractive index change due to the same current injection.
Feedback, abbreviated as DFB) A tunable twin guide type DFB laser made possible by laser, a method of tuning the wavelength by changing the temperature of the DFB laser with a Peltier element mounted in the module, a heater electrode on the DFB laser. A method of integrating and tuning the wavelength by changing the temperature of the laser and the like. Among them, the light source based on the DFB laser, which is particularly excellent in wavelength stability and reliability, is considered to be promising for the basic structure of the wavelength tunable semiconductor laser. As a wavelength tunable semiconductor laser based on this DFB laser, a heater electrode integrated wavelength tunable DFB laser, which has low power consumption and is capable of expanding a variable temperature range (= variable wavelength range), is considered promising.

FIG. 7 shows a conventional heater electrode integrated type wavelength tunable device.
Schematic diagram of DFB laser structure (perspective view and axial cross-section)
Indicates. The DFB laser has a diffraction grating 6 formed on an InP substrate 1 and is composed of a semiconductor optical waveguide 2 including an active layer that generates light by current injection. It has a double electrode structure, that is, a laminated structure of a current injection electrode 3, a dielectric insulating film 4, and a heater electrode 5. In order to inject a current into the current injection electrode, the dielectric insulating film 4 is partially covered. The current injection window 7 is opened. This wavelength tunable DFB laser oscillates at the initial wavelength λ0 by injecting a current into the semiconductor optical waveguide 2 using the current injection electrode. At this time, the entire DFB laser is controlled at a constant temperature by a Peltier element or the like. Next, when a current is supplied to the heater electrode 5 to heat the heater electrode 5, the temperature of the semiconductor optical waveguide 2 located near the heater electrode 5 locally rises, and the refractive index of the optical waveguide 2 changes. The direction of the refractive index change is the direction in which the refractive index increases, and as a result, the oscillation wavelength shifts to the long wavelength side, and the wavelength can be tuned. This is the wavelength tuning mechanism of the tunable DFB laser with integrated heater electrode. The wavelength shift is about 1n per 10 ° C temperature change.
m, and the upper limit temperature is limited by the stability of the oscillation mode, the reduction of the optical output, and the upper limit value of the allowable power consumption.

[0005]

Among these limiting factors, in the conventional heater electrode integrated type wavelength tunable DFB laser (FIG. 7), especially when an attempt is made to change the temperature in a wide range by the heater, the optical wavelength of the DFB laser is increased. The temperature distribution in the waveguide direction becomes non-uniform (it becomes remarkable when the temperature change amount ΔT> 30 ° C),
There was a problem that the oscillation mode became unstable. Figure 8
3 shows the axial temperature distribution in the optical waveguide 2 when the optical waveguide temperature is changed by about 30 to 40 ° C. There is a temperature difference of about 10 ° C. between the central part and the end part of the laser resonator, which corresponds to a difference of about 1 nm when converted to the oscillation wavelength. Due to the influence of this temperature distribution, the refractive index distribution of the optical waveguide 2 becomes non-uniform, resulting in the problem that the oscillation mode becomes unstable during wavelength tuning. In addition, the unevenness of the heater temperature in the optical waveguide is also a problem from the viewpoint of the reliability of the heater.
Easy to break.

On the other hand, the expansion of the variable temperature range ΔT is as follows.
Not only the problem of non-uniform temperature distribution in the optical waveguide 2 but also the problem of reduction of the optical output of the semiconductor laser arises. As a result, the upper limit of ΔT is limited to about 50 ° C., and the maximum tunable range of the tunable laser is about There was a problem of being limited to about 5 nm.

That is, due to the problem of uneven temperature distribution in the optical waveguide, it is limited to ΔT <30 ° C. Even if the problem of uneven temperature distribution is solved, it is limited to ΔT <50 ° C. due to the problem of reduced optical output. Is done.

An object of the present invention is to provide a wavelength tunable semiconductor laser of a heater electrode integrated type, which can suppress uneven temperature distribution in the optical waveguide direction at the time of heating the heater electrode and expand the temperature variable range. A tunable semiconductor laser is provided. Further, an object of the present invention is to provide a wavelength selective light source that can obtain a good light output characteristic regardless of an oscillation wavelength to be selected while realizing a simple process that does not require a bat couple process in an array structure wavelength selective light source. That is.

[0009]

The present invention has been completed as a result of various studies in order to solve the above problems.

That is, the present invention has a diffraction grating,
In a wavelength tunable semiconductor laser having an electrode for injecting current and a heater electrode for heating the semiconductor optical waveguide in a semiconductor optical waveguide including an active layer composed of a bulk or multiple quantum wells, the resistivity of the heater electrode ( Ω / m) is a wavelength tunable semiconductor laser whose wavelength varies in the optical waveguide direction. Specifically, the heater electrode is composed of a single-layer metal thin film or a metal multi-layer thin film, and the width and thickness of the heater electrode are At least one of the material and the layer structure is a wavelength tunable semiconductor laser that changes in the optical waveguide direction, and the heating of the semiconductor optical waveguide by the heater electrode becomes uniform in the optical waveguide, and the change in the refractive index due to the heating The width, thickness, and material of the heater electrode are set so that the resistivity (Ω / m) of the heater electrode changes in the optical waveguide direction so that the distribution in the optical waveguide direction becomes uniform.
At least one of the layered structures is a wavelength tunable semiconductor laser that changes in the optical waveguide direction.

The heater electrode material and electrode wiring will be described in more detail below.

In the present invention, as a means for controlling the temperature of the semiconductor optical waveguide of the semiconductor laser, a heater electrode (resistive heating wire) made of a single metal thin film or a metal multilayer thin film is arranged in the vicinity of the semiconductor optical waveguide. Therefore, it is desirable to use a thermally stable metal thin film containing Pt as the material of the heater electrode.

As a method of arranging the electrodes, a current injection electrode is arranged immediately above the semiconductor optical waveguide, and further immediately above that,
A heater electrode is arranged via a dielectric insulating film such as SiO2 or SiNx. By arranging such that the distance between the optical waveguide of the semiconductor laser and the heater electrode is the shortest, the temperature of the semiconductor optical waveguide rises when current is applied to the heater electrode and constant power is applied (hereinafter referred to as heater The thermal efficiency Rth of the electrode) can be increased. Moreover, since the distance between the active layer of the semiconductor laser and the current injection electrode is shortest, it is possible to avoid an increase in extra element resistance.

As another electrode placement method, a current injection electrode is placed directly above the semiconductor optical waveguide, and a heater electrode is placed next to the current injection electrode. Alternatively, a heater electrode is arranged directly above the semiconductor optical waveguide via an insulating film, and a current injection electrode is arranged next to this heater electrode. In this way, if the heater electrode and the current injection electrode are separated and wired, the heater electrode does not directly heat the current injection electrode. Therefore, the influence of the low thermal resistance of the current injection electrode and the current injection electrode are prevented. It is effective from the viewpoints of suppressing deterioration of the electrode for use in electrodes, eroding the current injection electrode material into the semiconductor layer due to the annealing effect, suppressing dopant diffusion, and the like, and can prolong the life of the device. Whether to arrange the heater electrode or the current injection electrode directly above the semiconductor optical waveguide depends on the element structure (ridge structure, embedded structure, selective growth type, etc.) to be used, the simplification of the manufacturing process, etc. , You will choose the best one.

In the present invention, the semiconductor laser is DF
B laser is the most desirable from the viewpoint of wavelength stability, but D
Either a BR laser or a distributed reflection (DR) type laser may be used. The present invention is also effective when a gain-coupled (complex-coupled) laser is used.

As described above, according to the present invention, in the wavelength tunable semiconductor laser of the heater electrode integrated type, it is possible to suppress the uneven temperature distribution in the optical waveguide direction when the heater electrode is heated, and the temperature variable range ΔT> 30 ° C. It will be possible. For example, ΔT =
By setting the temperature to 40 ° C., it becomes possible to realize the variable wavelength range Δλ = about 4 nm of the wavelength tunable semiconductor laser. However, ΔT
At> 50 ° C., the decrease in light output becomes remarkable, and ΔT cannot be increased further.

Therefore, in the present invention, a plurality of semiconductor lasers, a semiconductor optical multiplexer, and a semiconductor optical amplifier (Semiconducto
r Optical Amplifier, SOA) integrated wavelength selective light source, wherein the plurality of semiconductor lasers are the wavelength tunable semiconductor lasers, and the wavelength tunable light source includes at least two arrays in which the wavelength tunable semiconductor lasers are arranged in parallel. did.

When the wavelength selective light source is required to have high-speed modulation characteristics, the semiconductor optical modulator is integrated in the wavelength selective light source.

Further, in the present invention, in the case where each of the plurality of wavelength tunable semiconductor lasers, the semiconductor optical multiplexer, the semiconductor optical amplifier, and the semiconductor optical waveguide layers of the semiconductor optical modulator is composed of layers continuous in the axial direction. In addition, since the butt-couple process for forming the optical waveguide layer of the semiconductor optical multiplexer or the semiconductor optical modulator is not necessary, the process becomes very simple,
It is effective.

The wavelength control method of the above wavelength selective light source according to the present invention is a temperature sufficiently low to maintain the high gain characteristics of the temperature of the semiconductor optical amplifier (SOA) by the Peltier element, for example, a temperature of 10 ° C. or higher and 30 ° C. or lower. The oscillation wavelength is selected by maintaining a constant temperature within the range and independently of this by controlling the temperatures of the plurality of semiconductor lasers by heater electrodes. That is, in the present invention, since the temperatures of the semiconductor laser and the SOA can be independently controlled (one is a heater and the other is a Peltier element), even if the semiconductor laser temperature is raised by the heater electrode (ΔT> 50 ° C.). ), The SOA temperature can be maintained at a sufficiently low temperature, and the decrease in the SOA gain can be prevented. Therefore, the decrease in the optical output of the semiconductor laser can be compensated by the SOA gain, and a large Δλ can be covered while maintaining good optical output characteristics. The resulting wavelength selective light source can be provided.

The present invention is most effective especially when the number of wavelength tunable semiconductor laser arrays is two. This is from the viewpoint of “minimizing the required element size with respect to the obtained Δλ (that is, maximizing the element yield from one wafer and reducing the element cost)”. The details will be described below.

In a wavelength tunable semiconductor laser having integrated heater electrodes, when the number of arrays is 1 (that is, a single stripe), there is a problem in that the heater electrodes and the current injection electrodes are arranged on the chip (the wiring between the two electrodes is a space). The problem of whether it is possible) does not occur. Further, even when the number of arrays is two, the heater electrodes and the current injection electrodes can be arranged on both sides of the semiconductor array optical waveguide, so that the semiconductor laser array interval can be sufficiently narrowed and the element can be miniaturized. It is possible to satisfy both of the two characteristics of large Δλ and However, when the number of arrays is three or more, it is necessary to secure an area for wiring the electrodes, and therefore the array interval cannot be sufficiently narrowed, resulting in a problem that the element size is unnecessarily increased.

For example, Proceedings of the Electronics Society Conference of the Institute of Electronics, Information and Communication Engineers, Autumn 2000, C-4-
In the four-array wavelength selective light source as reported in “23.”, it is extremely difficult to dispose a heater electrode or a current injection electrode on each semiconductor laser because the array interval is as narrow as 10 μm.

FIG. 3B shows the calculation result of the wavelength tuning efficiency (Δλ / chip area) with respect to the number of arrays in the wavelength selective light source. The analytical model is shown in FIG.
The wavelength selective light source includes a DFB laser array area 11, a curved waveguide area 12, an MMI optical multiplexer area 13, and an SOA area 1.
4 and the window region 10. The analysis shows that the length of the window region is 25 μm at each end and the radius of curvature of the curved waveguide region is 300 μm.
μm, the interval of the incident optical waveguide to the MMI optical multiplexer is 5 μm, the interval of the DFB laser array is 7 μm when the number of arrays is 2, and the DFB laser array interval is the electrode installation area when the number of arrays is 3 or more. It was performed at 200 μm. The other parameters are as shown in Table 1. As can be seen from the graph of FIG. 3 (b), the wavelength tuning efficiency shows the maximum value when the number of arrays is 2, and the result is that the efficiency is the highest.

[0025]

[Table 1]

However, even when the number of arrays exceeds 2, the configuration of the present invention can be implemented, and in that case, the present invention is effective in obtaining high output characteristics.

In addition, in the structure of the present invention, the optical multiplexer area (areas 12 and 13 in FIG. 3 (a)) arranged between the SOA and the semiconductor laser is separated from each semiconductor laser. In addition to the function of guiding light to the SOA, a thermal buffer function of suppressing the interference of the heat generated by the heater electrode in the semiconductor laser region with the SOA region can be provided. As a result, the independent temperature control effect of the wavelength tunable semiconductor laser and the SOA can be maximized, and a wavelength selection light source with extremely good characteristics can be realized.

For example, in a DFB laser in which an optical modulator is integrated, temperature control of the DFB laser is performed by a heater electrode arranged near the active layer, and temperature control of the optical modulator adjacent to the laser is performed by a Peltier element. The configuration is reported in the document “Autumn 2000 IEICE Electronics Society Conference Proceedings C-4-25”. However, in this modulator-integrated wavelength tunable DFB laser, the effect of heat generated at the heater electrode of the DFB laser section reaches the optical modulator, and therefore sufficient transmission characteristics cannot be obtained. Also, with this configuration, if a passive area for suppressing mutual thermal buffering is inserted between the DFB laser and the optical modulator, the device length will be unnecessarily lengthened and the device yield from the wafer will decrease. The problem of output reduction also occurs at the same time, which is not desirable. (in this case,
The efficiency is further deteriorated as compared with the case where the number of arrays is 1 in FIG. In other words, it is the first time that the structure of the wavelength selective light source of the present invention using at least two or more arrays can expand Δλ, reduce the element size, suppress thermal buffering between the semiconductor laser and the SOA, and maximize the element characteristics. The characteristic can be improved.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to FIGS. 1 and 2 and FIGS.

[Embodiment 1] First, regarding the first embodiment of the present invention, a variable wavelength D that covers a variable wavelength range of 4 nm.
An FB laser will be described as an example with reference to FIGS. 1 and 2.

FIG. 1 shows a structural perspective view and an axial sectional view of the laser. The tunable DFB laser is a semiconductor optical waveguide having a multiple quantum well (MQW) active layer that has a diffraction grating 6 formed on an n-InP substrate 1 and has a period of 239.198 nm and a depth of 30 nm and that generates light by current injection. It consists of two. Further, it has a p-InP layer 8 and an n-InP layer 9 as current blocking layers. The electrodes are the current injection electrode 3, the dielectric insulating film 4, and the heater electrode 5.
In order to inject a current into the current injection electrode, the dielectric insulating film 4 is partially provided with a current injection window 7.
Has been opened. The cavity length of the laser is 600 μm,
AR (reflectance 0.01%) / HR (reflectance 90%) coating is applied to both ends of the chip. The electrode width of the heater electrode 5 in the resonator direction is 7 μm at the resonator end and 15 μm at the resonator center (minimum resistivity), and the width expansion is optimized so that the temperature distribution in the axial direction is uniform. did. FIG. 2 shows the temperature distribution in the axial direction of the resonator estimated by the designed electrode structure. A uniform temperature distribution was estimated. When a current was actually injected into the semiconductor optical waveguide 2 using the current injection electrode 3, it oscillated with a threshold current of 10 mA and an initial wavelength of 1550 nm under the condition that the temperature was controlled at 25 ° C. by a Peltier element. Next, when a current of 100 mA was applied to the heater electrode 5 to heat the heater electrode 5, an oscillation wavelength shift of 4 nm could be obtained. At this time, a good value of 40 dB or more was obtained for the submode suppression ratio, demonstrating the effectiveness of the resistivity distribution type heater electrode.
The optical output was 25 mW when the current injection to the heater electrode was 0, and 10 mW was obtained when the current injection to the heater electrode was 100 mA (corresponding to Δλ = 4 nm) when the DFB laser drive current was 100 mA.

In the description of the present embodiment, the technique of changing the width of the heater electrode is used to change the resistivity of the heater electrode in the axial direction. However, the present invention is not limited to this. It is possible to obtain the same effect by changing the number of electrodes (the resistance decreases as the thickness increases), by using electrodes of different materials, or by using a multi-layer structure electrode and changing the number of layers in the axial direction. .

[Second Embodiment] Next, a second embodiment of the present invention will be described with reference to FIG. 4 by taking a wavelength selective light source covering a wavelength range of 10 nm as an example. FIG. 4 (a) is a perspective view of the wavelength selective light source according to this embodiment, FIG. 4 (b) is a top view, and FIG. 4 (c) is a schematic cross-sectional view of the DFB laser array region.

The wavelength selective light source comprises two DFB laser arrays in which a first DFB laser 15 having a diffraction grating with a period of 239.198 nm and a second DFB laser 16 having a diffraction grating with a period of 239.969 nm are arranged in parallel. The region 11, the MMI optical multiplexer 13 in the front stage thereof, the SOA 14 in the front stage thereof, and the window region 10 in the front stage thereof are monolithically integrated on the n-InP substrate 1. The optical waveguide layer in each of these regions is formed to be a layer continuous in the axial direction. An AR coating film 17 is formed on the front and rear emission end faces to suppress the end face reflectance to 0.1% or less (effective reflectance of 0.0 on the window region side).
The distance between the two DFB laser arrays must be as narrow as possible in order to shorten the total device length, but on the other hand, the manufacturing tolerance for forming the current injection electrode and the heater electrode separately is required. It is necessary to secure it. Here, the distance between the two DFB laser arrays was 7.5 μm. In order to control the DFB laser array and the SOA at different temperatures, the heater electrode 5 made of a Pt metal thin film is arranged on the current injection electrode 3 of the DFB laser via the SiO2 film 18 (see FIG. 4 (c )reference). On the other hand, the entire device is mounted on the Lutier device so that the temperature can be controlled. On the back surface of the n-InP substrate 1, a back surface electrode 20 is formed as a common n electrode for the two DFB laser arrays and the SOA. In the wavelength selective light source of this embodiment, the MMI optical multiplexer 13 is directly connected to the DFB laser,
It plays the role of guiding the optical output emitted from the B laser to the SOA. In the case of a 2 × 1 MMI optical multiplexer, a branch loss of 3 dB is generated in principle, but this branch loss and the decrease in optical output of the DFB laser due to temperature rise are compensated by the SOA gain, and finally the desired optical output can be extracted. Has become.

The manufacturing procedure will be described below. First, n-InP
A DFB laser diffraction grating is formed on a substrate 1 (thickness 450 μm). The equivalent refractive index of the DFB laser at 20 ° C. is 3.24, and the diffraction grating period is determined by the formula represented by (diffraction grating period) = (oscillation wavelength) / (equivalent refractive index) / 2. Therefore, at the reference temperature of 25 ℃, the target oscillation wavelength of each DFB laser is 1550n.
Corresponding to m and 1555 nm, the grating period is 239.1 respectively.
It becomes 98nm and 239.969nm. The formation of such a high-precision diffraction grating is performed by the WAVE technique (Weighted-dose A) using electron beam exposure described in JP-A-8-227838.
llocation for Variable-pitch EB-corrugation). Next, on the diffraction grating, the atmospheric pressure selective MO
Using the VPE growth technology, two DFB laser arrays (stripe width 1.5 μm, length 400 μm, array spacing 7.5 μm) and MMI
An optical waveguide layer consisting of an optical multiplexer (15 μm effective width, 233 μm length) and SOA (stripe width 2.0 μm, length 600 μm) InGaAsP multiple quantum well layer is fabricated at once. The DFB laser array, the MMI optical multiplexer, and the SOA optical waveguide layer are composed of layers that are continuous in the axial direction, and the bat couple process that has been conventionally required is not necessary in this embodiment, and the process is drastically reduced. It has been simplified. The bandgap wavelength of the MQW active layer of the DFB laser array at 25 ° C is 155
5 nm and 1560 nm, which is determined by the pitch of the diffraction grating
Detuning 5n for each oscillation wavelength of the laser array
It is set to follow m. The band gap wavelengths of the MMI optical multiplexer and SOA are set to be 170 nm shorter and 20 nm longer than the DFB laser band gap wavelength, respectively. Then, again using MOVPE selective growth, p
-InP 19 (thickness 2 μm) is embedded and grown, and a p + -InGaAs 20 (thickness 200 nm) contact layer is formed on the uppermost layer.
A SiO2 film (thickness 300 nm) was formed on the entire surface of the device. And D
The SiO2 film just above the MQW active layer of the FB laser and the SOA is removed by wet etching in a stripe shape to form a current injection opening stripe (width 4 μm). Ti / Pt / Au (thickness 50nm / 100nm / 400nm) is used as a current injection electrode for the DFB laser and SOA on the opening stripe, and the electrode width of the DFB laser is 100μ.
Pattern so that the electrode width of m and SOA is 250 μm. Immediately above the current injection electrode of the DFB laser, a SiO2 film (200 nm thick) is formed and insulated, and then a Pt metal thin film (D
A heater electrode having a width of 6 μm at the FB axis end, a width of 16 μm at the central portion, and a thickness of 200 nm) is formed. The bonding electrode pads for the current injection electrode and the heater electrode are taken out and wired outside the DFB laser array. Since there are two DFB laser arrays, the space for wiring the electrode pads of the heater electrode and the current injection electrode could be secured sufficiently wide on both the left and right outer sides of the DFB laser array. The back surface of the n-InP substrate is polished to a thickness of about 125 μm, and Ti / Pt / Au (thickness 50 nm / 100 nm / 400 n
m) is deposited. Finally, after cleavage, an AR coating film was formed on the emission end face.

In the manufactured wavelength selection light source, the thermal efficiency Rth of the heater electrode was 100 ° C./W, and the resistance value of the heater electrode was about 50Ω. Any combination of the control temperature of the Peltier element and the current value of the heater electrode for obtaining the desired oscillation wavelength can be used. That is, the Peltier element defines the element temperature as the base, and the heater electrode raises the element temperature by the difference between the reference element temperature and the target temperature. This combination is determined from the viewpoint of the heating capacity of the heater and the power consumption. For example, DFB
For combinations that raise the laser temperature to 50 ° C,
1) Set the temperature of the Peltier element to 18 ° C, and then apply a current to the resistance heating wire to raise the temperature of the DFB laser to 50 ° C. 2) Set the temperature of the Peltier element to 25 ° C and then resistance heating. Apply a current to the wire to raise the temperature of the DFB laser to 50 ° C. 3) After setting the Peltier element temperature to 30 ° C, apply a current to the resistance heating wire to raise the temperature of the DFB laser to 50 ° C. Can be combined. However,
Considering the purpose of the present invention of not lowering the SOA gain, the temperature of SOA is within the control temperature range of the Peltier device,
It is necessary to maintain the proper temperature. Therefore, when the control temperature of the Peltier element was fixed at 20 ° C and the oscillation wavelength was controlled only by the value of the current flowing in the resistance heating wire, a maximum current of 80 mA was applied to the heater electrode, and the DFB laser By increasing the temperature from 20 ℃ to 70 ℃, the first DFB
The laser oscillation wavelength shift amount was about 5 nm, and the second DFB laser was also shifted by about 5 nm, and a variable wavelength range of Δλ = 10 nm could be obtained as a whole. On the other hand, since the SOA temperature was kept constant at 20 ° C by the Peltier element, it was possible to avoid a decrease in the SOA gain and obtain a sufficiently large SOA gain regardless of the selected oscillation wavelength. As a result, with an SOA drive current of 100 mA, an optical output of 40 mW or more could be obtained over the entire wavelength range.

[Third Embodiment] Next, a third embodiment of the present invention will be described with reference to FIG. The difference between the wavelength selective light source of the present embodiment and the wavelength selective light source of the second embodiment is the method of arranging the current injection electrode and the heater electrode of the DFB laser.
In the second embodiment, the current injection electrode is provided directly above the DFB laser array, and the heater electrode is provided directly above the current injection electrode via the insulating film. On the other hand, in this example, the heater electrode was wired directly above the DFB laser array, and the current injection electrode was wired next to the heater electrode. The advantages of the method of arranging the current injection electrode and the heater electrode in this embodiment are as follows. For example, in the electrode configuration of the second embodiment, when the temperature of the active layer is increased from 20 ° C. to 50 ° C. and the oscillation wavelength is shifted by 3.2 nm, the temperature of the current injection electrode of the DFB laser is up to about 100 ° C. The increase is estimated from thermal analysis calculation using the finite element method. When the oscillation wavelength is shifted by 3.2 nm, the characteristics of the current injection electrode are deteriorated due to the effect of temperature rise and the device life is shortened as compared with the case where the wavelength is not shifted. Therefore,
If the heater electrode and the current injection electrode are separated and wired as in the present embodiment, the current injection electrode is not directly heated by the heater electrode, so that the temperature rise of the current injection electrode is suppressed. Therefore, the life of the device can be extended. However,
Since the distance between the current injection electrode and the active layer is large, p-InP
It is necessary to sufficiently reduce the resistance value of the clad 19. Also in this embodiment, since the DFB laser array, the MMI optical multiplexer, and the SOA optical waveguide layer are collectively formed by one MOVPE selective growth, the butt couple process is not necessary. Since the heater electrode is located immediately above the DFB laser as in the second embodiment, the thermal efficiency Rt of the resistance heating wire is Rt.
h is 100 ° C./W, which is the same as in Example 2. Also in the wavelength selective light source having this configuration, by using the wavelength control method described in the second embodiment, the decrease in the SOA gain due to the temperature rise is avoided, and the high SOA gain independent of the selected oscillation wavelength, that is, the high optical output characteristic is obtained. Was obtained.

[Fourth Embodiment] Next, a fourth embodiment of the present invention will be described with reference to FIG. The difference between the wavelength selective light source of the present embodiment and the wavelength selective light source of the third embodiment is the method of disposing the current injection electrode and the heater electrode of the DFB laser.
In Example 3, a heater electrode was provided directly above the DFB laser array, and a current injection electrode was provided side by side next to the heater electrode. On the other hand, in the present example, the current injection electrode was wired immediately above the DFB laser array, and the heater electrode was wired next to the current injection electrode. Also in this embodiment, the advantage obtained in the third embodiment, that is, the current injection electrode is not directly heated by the heater electrode, suppresses the temperature rise of the current injection electrode and prolongs the life of the element. There is something you can do. However, since the distance between the heater electrode and the active layer is large, the thermal efficiency Rth of the resistance heating wire is several tens of percent lower than that of the third embodiment. However, regarding the current injection, the problem with respect to the resistance value of the p-InP cladding 19 which has been a concern in the third embodiment is eliminated. Also in this embodiment, the DFB laser array, the MMI optical multiplexer, and the SOA optical waveguide layer are formed by a single MOVP.
Since it is collectively formed by E selective growth, the bat couple process is not necessary. Also in the wavelength selective light source having this configuration, by using the wavelength control method described in the second embodiment, the decrease in the SOA gain due to the temperature rise is avoided, and the high SOA gain independent of the selected oscillation wavelength, that is, the high optical output characteristic is obtained. Was obtained.

As described above, in Examples 2 to 4, the wavelength selective light source of the present invention realizes 1) a simple process that does not require a bat-couple process, and 2) regardless of the selected oscillation wavelength, the SOA gain. It has been explained that it is possible to realize a wavelength selective light source which can prevent the deterioration of the above and obtain a good light output characteristic. Furthermore, it should be added at the end that the wavelength selective light source of the present invention has not only the above two advantages but also the following advantages. One is, for example, when a wavelength tunable range of about 8 nm is to be obtained, a wavelength selective light source of a type in which temperature is controlled only by a conventional Peltier element (since ΔT cannot be made large,
I needed 4 arrays. Proceedings of the IEICE Electronics Society Conference Autumn 2000 C
-4-23 "), a larger ΔT can be obtained per DFB laser element, so the number of arrays can be reduced from 4 to 2 and as a result, the MMI branch loss is reduced from 6 dB to 3 dB. . As a result, the optical output of the device is increased and the device yield is improved. Another advantage is that an increase in device yield from one wafer can be achieved mainly by shortening the optical multiplexer length and shortening the device length.

In the second to third embodiments of the present invention, an example in which a homo-embedded structure of p-InP is used as an embedded structure of the element has been shown. It is also applicable to structures and the like.

With respect to the number of arrays, an example of a two-array light source is shown as the most effective structure, but when the present invention is used, the variable temperature range for one semiconductor laser can be expanded, so that the number of arrays can be reduced. A large variable wavelength range can be obtained. Therefore, it is very effective in expanding the wavelength tunable range as compared with the conventional wavelength selective light source using only the Peltier element. In this case, the number of arrays is not limited to 2, and it can be said that the present invention can be applied to the number of arrays greater than 2, such as 3, 4, ...

As described above, in the present specification, Examples 1 to 4 are used.
Although the effects of the present invention have been described based on the above, the present invention is not limited to these examples. It is obvious that the contents of the embodiments can be changed appropriately within the scope of the technical idea of the present invention.

As described above, the wavelength selective light source of the present invention has various advantages in device production and device characteristics, and has an extremely great industrial utility value.

[0044]

According to the present invention, in the wavelength tunable semiconductor laser of the heater electrode integrated type, it is possible to suppress uneven temperature distribution in the optical waveguide direction during heating of the heater electrode, and it is possible to expand the temperature variable range. Become. Further according to the invention,
In the array structure wavelength selective light source, it is possible to provide a wavelength selective light source that realizes a simple process that does not require a butt-couple process and that can obtain good light output characteristics regardless of the oscillation wavelength to be selected.

[Brief description of drawings]

FIG. 1 is a wavelength tunable DF according to a first embodiment of the present invention.
FIG. 3 is a perspective view and an axial sectional view of a B laser.

FIG. 2 is a wavelength tunable DF according to the first embodiment of the present invention.
FIG. 6 is a temperature distribution diagram in the axial direction when the heater of the B laser is heated.

FIG. 3 is a diagram showing an analysis result of wavelength tuning efficiency with respect to the number of arrays of a wavelength selective light source in which a heater heating type wavelength tunable DFB laser is integrated, which is used for explaining an effect of the present invention.

FIG. 4 is a structural perspective view, a top view, and a sectional view of a DFB laser region of a wavelength selective light source according to a second embodiment of the present invention.

FIG. 5 is a cross-sectional view of a DFB laser region in a wavelength selective light source according to a third embodiment of the present invention.

FIG. 6 is a cross-sectional view of a DFB laser region in a wavelength selective light source according to a fourth embodiment of the present invention.

FIG. 7 is a perspective view and an axial sectional view of a conventional wavelength tunable DFB laser.

FIG. 8 is an axial temperature distribution chart when heating a heater of a conventional wavelength tunable DFB laser.

[Explanation of symbols]

1 n-InP substrate 2 Semiconductor optical waveguide 3 Current injection electrode 4 Dielectric insulation film 5 heater electrode 6 diffraction grating 7 Current injection window 8 p-InP 9 n-InP 10 window area 11 DFB laser area 12 Bent waveguide region 13 MMI multiplexer area 14 SOA area 15 First DFB laser 16 Second DFB laser 17 AR coating film 18 SiO2 19 p-InP 20 p + -InGaAs 21 Back electrode

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01S 5/343 H01S 5/343 5/50 610 5/50 610

Claims (11)

[Claims] 1. A wavelength tunable device having an electrode for injecting current into a semiconductor optical waveguide having a diffraction grating and including an active layer composed of a bulk or multiple quantum wells, and a heater electrode for heating the semiconductor optical waveguide. A wavelength tunable semiconductor laser which is a semiconductor laser in which the resistivity of the heater electrode changes in the direction of the optical waveguide, wherein heating of the semiconductor optical waveguide by the heater electrode becomes uniform in the optical waveguide, and the refractive index changes due to heating. A tunable semiconductor laser in which the resistivity of the heater electrode is changed in the optical waveguide direction so that the distribution in the optical waveguide direction becomes uniform. 2. The heater electrode is composed of a single-layer metal thin film or a metal multi-layer thin film, and at least one of the width, thickness, material and layer structure of the heater electrode changes in the optical waveguide direction. The wavelength tunable semiconductor laser according to claim 1, wherein 3. The wavelength tunable semiconductor laser according to claim 1, wherein the heater electrode is made of a metal thin film made of Pt alone or a metal multi-layered film containing at least Pt. 4. The current injection electrode is arranged directly above the semiconductor optical waveguide, and the heater electrode is arranged directly above the current injection electrode via an insulating film. The tunable semiconductor laser according to item 1. 5. The current injection electrode is arranged directly above the semiconductor optical waveguide, and the heater electrode is arranged side by side next to the current injection electrode.
A tunable semiconductor laser according to any one of 1. 6. The heater electrode is arranged directly above the semiconductor optical waveguide via an insulating film, and the current injection electrode is arranged side by side with the heater electrode. 4. The wavelength tunable semiconductor laser according to any one of 3 to 3. 7. The tunable semiconductor laser has a basic structure of a distributed feedback (DFB) type laser, a distributed Bragg reflection (DBR) type laser, or a distributed reflection (DR) type laser,
7. The wavelength tunable semiconductor laser according to claim 1, which is a semiconductor laser of any type of a gain coupled laser and a complex coupled laser. 8. A wavelength tunable semiconductor laser according to claim 1, wherein a plurality of semiconductor lasers, a semiconductor optical multiplexer, and a semiconductor optical amplifier are integrated in a wavelength selective light source. And a wavelength selective light source, wherein the wavelength tunable semiconductor laser has at least two arrays arranged in parallel. 9. The wavelength selective light source according to claim 8, further comprising a semiconductor optical modulator integrated therein. 10. In the wavelength selective light source, a plurality of semiconductor lasers, a semiconductor optical multiplexer, a semiconductor optical amplifier,
10. The wavelength selective light source according to claim 8 or 9, wherein each semiconductor optical waveguide layer of the semiconductor optical modulator comprises a layer continuous in the axial direction. 11. The temperature of the plurality of wavelength tunable semiconductor lasers is maintained independently of the temperature of the semiconductor optical amplifier by a Peltier element while maintaining the temperature within a temperature range sufficient to maintain high gain characteristics. 11. The method for controlling a wavelength selective light source according to claim 8, wherein the lasing wavelength is selected by controlling with the heater electrode.