JP2006332375A - Semiconductor laser apparatus and wavelength control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser apparatus and a wavelength control method for improving the stability of the oscillation wavelength against temperature change without developing a new material or combining with a material other than a semiconductor. <P>SOLUTION: This semiconductor laser apparatus comprises a wavelength variable semiconductor laser device 1 having two DFB regions with electrodes 107a and 107b formed therein, and a wavelength control region with an electrode 108 formed therein for generating a wavelength which is changed by injecting a current I<SB>Phase</SB>into the wavelength control region; a photodiode 2 for receiving the optical output of the semiconductor laser device 1; an optical output control circuit 3 for determining the value of the current injected into the semiconductor laser device 1, in accordance with the optical output received by the photodiode 2 so that the optical output of the semiconductor laser device 1 is kept constant; and a current distribution circuit 4 for distributing the current value of the injected current and determining the current values output to the electrodes 107a and 107b formed in the gain regions and the electrode 108 formed in the phase control region respectively. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor laser device and a wavelength control method, and more particularly to a semiconductor laser device and a wavelength control method applicable to adjustment of the amount of change in the oscillation wavelength of a laser depending on the temperature.

In general, the oscillation wavelength, threshold current, and output efficiency of a semiconductor laser vary depending on the ambient temperature and element temperature. For example, the temperature dependence of the oscillation wavelength of a general distributed feedback (DFB) laser is about 0.1 nm / K. This is because the refractive index (n) of the semiconductor constituting the DFB laser is temperature-dependent, so that the Bragg wavelength (λ _B ) of the diffraction grating is mλ _B = 2nΛ (1)
It is because it changes according to. Here, m is the order of diffraction, and Λ is the period of the diffraction grating. InP and GaAs semiconductors currently used as laser materials have a refractive index that increases with increasing temperature. For this reason, in a laser using an InP-based or GaAs-based semiconductor, the oscillation wavelength changes to the longer wavelength side as the temperature rises. In addition, the threshold current increases as the normal temperature rises, and the output efficiency decreases. Therefore, in order to obtain a certain output, the necessary current value increases as the temperature rises.

  For example, when using a semiconductor laser as a light source for optical fiber communication, particularly when performing wavelength division multiplexing (WDM) in which several different wavelength light signals are multiplexed and transmitted on a single fiber, the accuracy of the signal light wavelength When is important, it is essential to stabilize the oscillation wavelength of the semiconductor laser, which is the light source, without depending on temperature. For this reason, for example, it is necessary to perform temperature control using a Peltier element, but there are problems such as a complicated element structure and control, and an increase in power consumption.

  The methods for stabilizing the temperature dependence of the oscillation wavelength without using temperature control by a Peltier element or the like can be roughly classified into two methods. As one of the above-described methods, for example, Patent Document 1 describes the development of a semiconductor material having a refractive index with a small temperature dependence, which is different from conventional ones. That is, the method described in Patent Document 1 is a method of reducing temperature dependency by a configuration of only a semiconductor.

  As another method of the above method, for example, Patent Document 2 describes a laser in which a semiconductor laser and an external waveguide made of a material other than a semiconductor are combined. Further, Patent Document 3 describes a configuration in which a semiconductor and a material other than a semiconductor having a refractive index temperature dependency opposite to that of the semiconductor are alternately connected in cascade. In other words, the methods described in Patent Documents 2 and 3 are methods for reducing temperature dependency by a composite configuration using a semiconductor and a material other than the semiconductor.

  On the other hand, the refractive index of a semiconductor changes due to current injection even at a temperature other than temperature. Many tunable lasers using this have been developed. For example, according to Patent Document 4, the refractive index of the waveguide core in the phase adjustment region is changed by injecting a current into the phase adjustment region sandwiched between two reflection regions, at least one of which has gain and wavelength selectivity. The wavelength is changed. When current is injected into a commonly used semiconductor such as InP or GaAs, the refractive index changes in a decreasing direction. As a result, the optical length (optical path length) is shortened and the resonator length is shortened, so that the oscillation wavelength is changed to the short wavelength side.

  Various types of such wavelength tunable lasers have been reported. As lasers whose wavelengths change continuously, lasers using distributed Bragg reflection (DBR), which will be described later, and twin- There is a tunable laser such as a guide (TTG) distributed feedback (DFB) laser.

Japanese Patent Laid-Open No. 11-8432 JP 2002-190643 A JP 2002-14247 A JP 2004-273644 A T. Wolf et al, “Tunable twin-guide (TTG) distributed feedback (DFB) laser with over 10 nm continuous tuning range” Electron. Lett., Vol. 29, No. 24, pp. 2124-2125, Nov. 1993

  However, there are no reports of new materials that have been put into practical use so far, and it can be said that it is very difficult to develop a new semiconductor in terms of crystal growth and device formation.

  On the other hand, when a semiconductor laser is combined with a material other than a semiconductor, there is a problem in simplicity, such as the need for optical axis adjustment. Even if it is a simple production method such as spin coating an organic material on a semiconductor substrate, for example, when a distributed reflector is formed by alternately cascading a semiconductor and an organic material, it has excellent characteristics. In order to produce the obtained primary diffraction grating, it is necessary to alternately arrange the semiconductor and the organic material with a length of about ¼ wavelength. Therefore, a big problem remains in the difficulty of processing and reliability. In addition, even if the method is easy to combine, the process becomes more complicated than the laser manufactured only by the semiconductor because the different materials are combined.

  The present invention has been made in view of these problems, and a semiconductor laser device and a wavelength for improving the stability of an oscillation wavelength against a temperature change without developing a new material or combining with a material other than a semiconductor. It is to provide a control method.

  In order to achieve the above object, according to the present invention, a first electrode is formed, a gain region for adjusting a gain, and a second electrode are formed and passed therethrough. A wavelength tunable laser that has at least one wavelength control region that adjusts the wavelength of light and that changes its wavelength by injecting a first current into the wavelength control region via the second electrode; A light receiving unit that receives the light output of the wavelength tunable laser, and injecting the light into the wavelength tunable laser according to the light output received by the light receiving unit so as to keep the light output of the wavelength tunable laser substantially constant. A light output control circuit for determining a value of the second current and outputting a current related to the value of the second current; and when a current related to the value of the second current is input, the light output Based on the value of the second current determined by the control circuit. And distributing the value of the second current, and outputting from the distributed current value to the first electrode formed in the gain region and the second electrode formed in the phase control region And a current distribution circuit for determining each of the values.

  According to a second aspect of the present invention, in the first aspect of the present invention, the current related to the value of the second current is an electric signal related to the value of the second current.

  According to a third aspect of the present invention, in the first aspect of the present invention, the current related to the value of the second current is the second current itself.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the current distribution circuit is configured to reduce the wavelength change caused by a temperature increase of the wavelength tunable laser. A value is distributed, and a current value to be output to the gain region and the phase control region is determined based on the distributed current value.

  According to a fifth aspect of the present invention, in the invention according to any one of the first to third aspects, the current distribution circuit is configured to increase the wavelength change due to a temperature rise of the wavelength tunable laser. A value is distributed, and a current value to be output to the gain region and the phase control region is determined based on the distributed current value.

  According to a sixth aspect of the present invention, in any of the first to fifth aspects of the present invention, either the gain region or the wavelength control region has a diffraction grating.

The invention according to claim 7 is the invention according to claim 6, wherein a coupling coefficient of the diffraction grating is 150 cm ⁻¹ or more.

  According to an eighth aspect of the present invention, in the invention according to any one of the first to seventh aspects, the current distribution circuit includes a resistance element having a resistance of 10 times or more of an element resistance of the wavelength tunable laser. And

  According to a ninth aspect of the present invention, at least one gain region in which the first electrode is formed and the gain is adjusted and at least one wavelength control region in which the second electrode is formed and the wavelength of light passing therethrough is adjusted. A light receiving step for receiving a light output of a wavelength tunable laser whose wavelength is changed by injecting a first current into the wavelength control region via the second electrode; and A second current value to be injected into the wavelength tunable laser is determined according to the received light output so as to keep the light output substantially constant, and a current related to the second current value is output. When a current relating to the first current value and the second current value is input, the second current value is distributed based on the determined second current value; From the distributed current value to the gain region and the phase control region And having a second determination step of determining the value of the current output, respectively.

  As described above, according to the present invention, it is possible to observe the oscillation wavelength and the temperature using only a semiconductor having a processing technology established so far, without combining with a new semiconductor material or a material other than a semiconductor. Therefore, it is possible to provide a semiconductor laser whose oscillation wavelength is stable with respect to a temperature change and a semiconductor laser capable of controlling the temperature change of the oscillation wavelength.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is a cross-sectional view along the optical waveguide direction of the semiconductor laser device according to the first embodiment of the present invention. In the first and second distributed feedback (DFB) regions on both sides of the element, a GaInAsP lower guide layer 102, a GaInAsP active layer 103, a GaInAsP upper guide layer 104, and an InP cladding 105 are sequentially stacked on the InP semiconductor substrate 101. ing. A diffraction grating is provided between the upper guide layer 104 and the clad 105. In the phase control region (also referred to as a phase shift region) in the central portion of the element, a GaInAsP core layer 106 and a clad 105 are stacked on the semiconductor substrate 101. In the present embodiment, the phase control region is formed so as to be sandwiched between the first and second DFB regions, and the phase control region and the first and second DFB regions are formed continuously. On the element surface, as an electrode of each region, an electrode 107a is formed on the first DFB region, 107b is formed on the second DFB region, and an electrode 108 is formed on the phase control region. ing. A lower electrode 109 is formed below the InP semiconductor substrate 101, and the lower electrode 109 is common in each region.

  The semiconductor material is not limited to the combination of InP and GaInAsP. There is no particular restriction, and any material such as InP, GaInAsP, GaInAs, GaAs, AlGaAs, and GaInNAs can be applied. There are no particular restrictions on the semiconductor crystal growth method, that is, the stacking method. For example, MBE (Molecular Beam Epitaxy), MOCVD (metal organic chemical vapor deposition), or the like can be used. The shape of the active layer 103 may be any shape such as bulk, MQW (multiple quantum well), quantum wire, or quantum dot. The guide layers 102 and 104 are generally also referred to as a separate confinement heterostructure (SCH), an optical confinement layer, or the like. Depending on the required laser characteristics, for example, the refractive index may be stepped or stepwise. The gradient refractive index (GI-) SCH may be changed. As for the waveguide structure, commonly used waveguide shapes such as a pn buried structure, a semi-insulating buried structure, a ridge structure, and a high mesa structure can be applied.

  There is no particular restriction on the formation of the core layer in the phase control region, so that the DFB region grows one of the phase control regions, and then the so-called bad joint method in which etching is performed to re-grow into the groove, or the growth region is formed by using a mask. A regulated selective growth method or the like can be used.

  In FIG. 1, the diffraction grating position is formed in the guide layer 104 above the active layer 103, but may be formed at the boundary between the guide layer 102 below the active layer 103 and the semiconductor substrate 101. It may be processed periodically. That is, it is sufficient that the reflection region has wavelength selectivity.

In the semiconductor laser of FIG. 1, by injecting a current I _DFB into the DFB region, a gain is generated in the active layer and an oscillation state is reached. Since a diffraction grating is formed in the DFB region, strong reflection occurs only in light in a specific wavelength region, and oscillation occurs because the light is intensified at a wavelength that matches the phase of the light reflected in the DFB regions on both sides. It is called a stop band in the sense that it cannot transmit the wavelength range where strong reflection occurs.

That is, in FIG. 1, the first light having the stopband wavelength region from the first DFB region and the second light having the stopband wavelength region from the second DFB region are in phase. Interference occurs in the control region, and among these lights, light of intensifying wavelengths oscillates. At this time, the wavelength of the intensifying light (oscillation wavelength) can be controlled by the length of the phase control region, that is, the optical path length of the GaInAsP core layer 106. This optical path length can be controlled by the refractive index of the GaInAsP core layer 106. Therefore, in the semiconductor laser device of FIG. 1, the refractive index of the phase control region is changed by adjusting the control current I _Phase injected into the phase control region as shown in the schematic diagram of the spectrum shown in FIG. The oscillation wavelength can be adjusted.

  Next, the operating principle of athermalization will be described. When the operating temperature of the element rises due to changes in the surrounding environment and heat generation of the element, the refractive index rises in a semiconductor generally used in a normal optical device such as InP or GaAs. Therefore, the wavelength selected by the diffraction grating, that is, the Bragg wavelength also changes to a long wavelength. In the case of an InP-based DFB laser used in optical fiber communication, a wavelength change due to a temperature change is about 0.1 nm / ° C. That is, the Bragg wavelength selected by the diffraction grating has a temperature dependency of 0.1 nm / ° C. In the first embodiment shown in FIG. 1, the high reflection wavelength region, that is, the stop band in the DFB region moves to the long wavelength side due to the temperature rise.

On the other hand, it is known that as the temperature rises, the threshold current of the semiconductor laser increases and the output efficiency decreases. Therefore, in the case of a so-called APC (Auto power control) operation in which a constant light output is obtained at any operating temperature as in the current and light output characteristics shown in FIG. 3, T ₀ , T ₁ , T _{As the} temperature rises to ₂ , the necessary current values increase to I ₀ , I ₁ , and I ₂ .

  FIG. 4 shows a schematic diagram of a system configuration according to the present embodiment. In FIG. 4, reference numeral 1 denotes the wavelength-variable semiconductor laser element shown in FIG. A photodiode 2 is disposed at a predetermined distance from the output end of the semiconductor laser element 1, and the photodiode 2 detects the light output from the semiconductor laser element 1.

  In the present embodiment, the photodiode 2 is disposed so as to directly receive the light output from the semiconductor laser element 1, but the present invention is not limited to this. What is important in this embodiment is that the optical output from the semiconductor laser element 1 is measured. Therefore, any arrangement can be used as long as the optical output from the semiconductor laser element 1 can enter the photodiode 2. Also good. For example, a half mirror as a means for branching light is arranged on the optical axis of the light output from the semiconductor laser element 1, and the photodiode 2 is received so that a part of the output is branched by the half mirror and a part thereof is received It may be arranged.

  The photodiode 2 is electrically connected to an optical output control circuit 3 (also referred to as an APC circuit) that performs control to keep the optical output of the semiconductor laser element 1 substantially constant. A current distribution circuit 4 that distributes the current value from the light output control circuit 3 to the gain region and the wavelength control region of the semiconductor laser device 1 is electrically connected to the light output control circuit 3.

  In the present specification, the “gain region” is a region for adjusting the gain, and in FIG. 1, indicates the first and second DFB regions. The “phase control region (phase shift region)” is a region for adjusting the wavelength of light passing through the region.

In FIG. 4, in the case of the APC operation, the optical output from the semiconductor laser element 1 is monitored by a photodiode (PD) or the like, and the optical output control circuit 3 (APC) increases the optical output when the optical output decreases due to temperature rise. Circuit) to increase the injection current to the semiconductor laser device 1. That is, feedback is applied to the current flowing through the semiconductor laser element 1 so that the set light output is obtained again. At this time, the current injected into the semiconductor laser element 1 is distributed by the current distribution circuit 4 to the current I _DFB flowing through the DFB region and the phase control region I _Phase at a certain rate, thereby the phase shift amount. Changes, and the oscillation wavelength moves in the stop band to the short wavelength side. Accordingly, if the distribution amount of the current flowing between the DFB region and the phase control region is appropriately set, the Bragg wavelength and the stopband lengthening due to the temperature rise are offset by the shortening of the wavelength due to the phase shift amount variation. It becomes possible to suppress the temperature change.

  Hereinafter, the phase control method according to the present embodiment will be described in detail.

When the photodiode 2 receives the light output from the semiconductor laser element 1, the photodiode 2 outputs a light output electric signal related to the light output to the light output control circuit 3. When an optical output electrical signal is input, the optical output control circuit 3 outputs the optical output from the semiconductor laser element 1 to the semiconductor laser element 1 so that the optical output from the semiconductor laser element 1 becomes substantially constant according to the input optical output electrical signal. Sets the current value of the injected current. Next, the light output control circuit 3 outputs an injection current electric signal related to the injection current having a set current value to the current distribution circuit 4. When the injection current electrical signal is input, the current distribution circuit 4 distributes the current value of the injection current at a constant rate, and determines the current values related to the current I _DFB and the current I _Phase from the distributed current values. decide. When an electric signal relating to the current value related to the current I _DFB and the current I _Phase is output to a power source (not shown), the power source controls the current I _DFB to the first and second DFB regions and also controls the phase of the current I _Phase. Output to area.

Further, although the current distribution circuit 4 and the power source are used separately, the power source may be incorporated in the current distribution circuit 4. At this time, the current distribution circuit 4 converts the current I _DFB to the first and second DFB regions and the current I _Phase to the phase control region based on the current values related to the distributed current I _DFB and current I _Phase. To output.

In this embodiment, the light output control circuit 3 outputs an electrical signal related to the injection current, but an injection current having a set current value may be output to the current distribution circuit 4. In this case, the injection current is directly output from the light output control circuit 3 to the current distribution circuit 4. When this injection current is input, the current distribution circuit 4 distributes the injection current at a constant rate and outputs the current I _DFB and the current I _Phase to the semiconductor laser element 1. Therefore, in this case, the current distribution circuit 4 only distributes the injection current. With this configuration, it is only necessary to provide a power source only for the light output control circuit 3, so that the apparatus can be further simplified.

If the wavelength control is performed in this way, even if the Bragg wavelength and the stop band shift to the long wavelength side in the DFB region due to the temperature rise of the element, the current I _Phase set according to the temperature rise causes the phase control region. By reducing the refractive index, the wavelength causing constructive interference in the phase control region can be kept substantially constant. In other words, light having a wavelength within the stop band shifted to the long wavelength side is incident on the wavelength control region, but variations in wavelengths that cause constructive interference are suppressed. Therefore, even if the temperature of the oscillation wavelength element rises, variations in oscillation wavelength can be suppressed.

In this embodiment, the injection current determined by the light output control circuit 3 is distributed to the currents I _DFB and I _Phase by the current distribution circuit 4, but the purpose here is that the temperature of the element is Even if it changes, the light output is made constant and the stability of the oscillation wavelength is improved. In the configuration of FIG. 4, the received light intensity of the photodiode 2 changes according to the temperature change of the semiconductor laser element 1. The light output control circuit 3 determines the injection current value according to the received light intensity, that is, the change in the light output of the semiconductor laser element 1. Therefore, the photodiode 2 and the light output control circuit 3 play a role of detecting whether there is a temperature change and detecting the amount of temperature change. This is because when the temperature of the element changes, the intensity of light received by the photodiode 2 changes, so the value of the injected current from the light output control circuit 3 changes. When this change occurs, the temperature of the element changes. This is because the degree of change in the injection current value is reflected in the degree of change in the element temperature.

By combining the light output control circuit 3 and the current distribution circuit 4 as in this embodiment, the temperature change of the element can be reflected in the current I _DFB and the current I _Phase . Therefore, the light output can be kept substantially constant by the current _IDFB even if the temperature changes. Moreover, the phase shift of the amount according to the above-mentioned temperature change can be performed in the phase control region by the current I _Phase . Therefore, it is possible to improve the stability of the oscillation wavelength even if the temperature changes.

That is, by combining the optical output control circuit 3 and the current distribution circuit 4, the current I _DFB and the current I _Phase are distributed based on the injection current determined according to the temperature change, that is, the injection current is distributed. Therefore, the light output can be kept substantially constant without performing control for keeping the temperature of the element constant, and variations in the oscillation wavelength can be suppressed.

  In the present embodiment, the current distribution circuit 4 distributes the injection current determined by the light output control circuit 3 at a constant rate, but the present invention is not limited to this. For example, by incorporating a non-linear element in the current distribution circuit, the distribution ratio may be increased as the temperature rises, that is, as the injection current determined by the light output control circuit 3 increases.

  That is, in this embodiment, the current distribution circuit can be designed from the temperature dependency of the current-light output of the element and the current amount dependency of the phase shift amount. When complete compensation is performed, the circuit configuration becomes complicated. For example, in the case of simple distribution using resistors, even if complete temperature dependence cannot be compensated, the temperature dependence is smaller than that of a conventional semiconductor laser. It is effective to suppress the wavelength change width due to temperature within a certain range. In addition, since a simple distribution circuit can be incorporated into the laser module, it can be handled as a one-terminal element and is easy to handle. Furthermore, in addition to the difference in structure between the DFB region and the phase control region, current flowing between the regions may also occur depending on the applied voltage, so the device resistance in each region may be different. By configuring the current distribution circuit using a sufficiently large resistance value, the element resistance can be ignored. Normally, the element resistance is about several ohms, so it should be 10 times or more and several tens of ohms or more. By setting it to one hundred times or more, about several hundred ohms, the influence of current distribution on the change in element resistance is less. Become.

  In the conventional semiconductor laser, in order to stabilize the oscillation wavelength, it was necessary to monitor and control the temperature, such as keeping the temperature constant by using a Peltier element or the like. Disappear. The feedback can be performed only by the APC operation, and the temperature control is not necessary, so that the system can be greatly simplified. Since monitoring and controlling the optical output is often performed when using a semiconductor laser, it is often unnecessary to newly install an APC operation circuit. In that case, since only the current distribution circuit needs to be newly added, the system of this embodiment can be configured easily.

  In order to compensate for the increase in the oscillation wavelength due to the temperature rise by the wavelength variable mechanism, it is necessary that the wavelength variable width is wide. Since the change due to the temperature of the wavelength in a normal DFB laser is about 0.1 nm / ° C., 6 nm compensation is required to stabilize the wavelength in the range of 20 to 80 ° C. That is, the continuous variable width of the wavelength in the wavelength tunable laser needs to be 6 nm or more. In the DFB type tunable laser used in the desperate form, the wavelength changes in the stop band, so the width of the stop band needs to be 6 nm or more.

FIG. 5 is a diagram showing the stop band width and the reflectance at the Bragg wavelength with respect to the product κL of the diffraction grating coupling coefficient κ and the diffraction grating length L. From FIG. 5, it can be seen that in order to widen the stop band width, it is sufficient to increase κ or shorten L. However, if L is made too short, the reflectivity becomes small. Therefore, there is a case where the threshold current increases or the laser oscillation does not occur in the worst case. Since the reflectance is a parameter related to the output efficiency, it should be determined by characteristics to be obtained from the relationship between the threshold current and the output efficiency. For example, in order to obtain a reflectance of 90% or more, κL Must be 1.8 or more, and in order to obtain a reflectance of 95% or more, κL must be 2.2 or more. For this reason, in order to make the stop band 6 nm or more and the reflectance 90% or more, κ must be 150 cm ⁻¹ or more. In order to set the stop band to 6 nm or more and the reflectance to 95% or more, 150 cm ⁻¹ is not sufficient, and about 200 cm ⁻¹ is sufficient.

In order to widen the temperature compensation range or provide a margin in the operation range, the stop band may be further widened to about 10 nm. In order to set the stop band to 10 nm or more and reflectivity to 90% or more, κ must be 250 cm ⁻¹ or more. In order to set the stop band to 10 nm or more and reflectivity to 95% or more, 250 cm ⁻¹ is not sufficient, and about 300 cm ⁻¹ is sufficient.

(Second Embodiment)
In the first embodiment, a tunable laser having a structure in which a phase control region is sandwiched between two DFB regions is used. However, as long as the tunable laser has a wavelength that continuously changes by current injection, the principle of the present invention is used. Can be used as an athermal laser. In addition, if the objective is not to achieve complete athermalization, for example, it is sufficient if the wavelength changes within a certain range, the wavelength changes due to current injection even if the wavelength is not a tunable laser that changes continuously. The principle of the present invention can be used as long as the direction of the laser is always the same in a range in which the temperature change of the wavelength is compensated.

  As shown in FIG. 6, a structure in which the DFB region on one side of the wavelength tunable laser used in the first embodiment is replaced with a high-reflectivity dielectric film (HR film) 210 may be used. A GaInAsP lower guide layer 202, a GaInAsP active layer 203, a GaInAsP upper guide layer 204, and an InP clad 205 are sequentially stacked on an InP semiconductor substrate 201, and a diffraction grating is provided between the upper guide layer 204 and the clad 205. Yes. In the phase control region formed continuously with the DFB region, a GaInAsP core layer 206 and a clad 205 are stacked on the semiconductor substrate 201. On the element surface, an electrode 207 is formed on the DFB region, and an electrode 208 is formed on the phase control region as electrodes in the respective regions. A lower electrode 209 is formed below the InP semiconductor substrate 201, and the lower electrode 209 is common in each region. The semiconductor material to be used, the shape of the active region, the waveguide structure and the like are not particularly limited as in the first embodiment.

  Further, for example, as shown in FIG. 7, at least one of the two regions not having a gain having wavelength selectivity, that is, in the example shown in FIG. 7, an active region having a gain is formed by a distributed Bragg reflection type (DBR) region. Even a sandwiched so-called distributed Bragg reflection (DBR) laser can realize an athermal laser by appropriately distributing the APC control current. In the active region at the center of the element, a GaInAsP lower guide layer 302, a GaInAsP active layer 303, a GaInAsP upper guide layer 304, and an InP clad 305 are sequentially stacked on an InP semiconductor substrate 301. In the DBR regions on both sides, the core layer 306 and the clad 305 are sequentially stacked on the InP semiconductor substrate 301, and a diffraction grating is provided between the core layer 306 and the clad 305. On the element surface, as an electrode of each region, an electrode 307 is formed on the active region, and electrodes 308a and 308b are formed on the DBR region. A lower electrode 309 is formed below the InP semiconductor substrate 301, and the lower electrode 309 is common in each region.

The semiconductor material to be used, the shape of the active region, the waveguide structure and the like are not particularly limited as in the first embodiment. In the case of a DBR type wavelength tunable laser, the optical output changes with I _act flowing in the active region, and the wavelength changes with I _DBR . Therefore, when the DFB type tunable laser described in the first embodiment is replaced with a DBR type tunable laser, I _DFB may be replaced with I _act and I _Phase may be replaced with I _DBR .

  If the semiconductor laser element having the configuration shown in FIGS. 6 and 7 is used as the semiconductor laser element shown in FIG. 4, the semiconductor laser element can be operated in the same manner as in the first embodiment.

  Further, the TTG-DFB laser described in the section of the prior art can also be used as the wavelength tunable laser of the present invention.

(Third embodiment)
In the first and second embodiments, the current is distributed in a direction that cancels the temperature change of the wavelength, that is, the current is distributed so as to reduce the wavelength change due to the temperature rise of the element. In the present embodiment, the present invention is not limited to this, and the current may be distributed so as to increase the temperature change of the wavelength, that is, to increase the wavelength change due to the temperature rise of the element.

  For this purpose, the wavelength may be changed to the longer wavelength side with respect to the wavelength control current of the wavelength tunable laser, or the current may be reduced when the voltage increases by a current distribution circuit. In order to change the current value in the opposite direction as the voltage rises, for example, a resonant tunnel diode may be included in the circuit, and a negative resistance may be used.

  For example, the gain temperature change has a larger change rate than the refractive index temperature change. Although it is most efficient to oscillate at the wavelength with the largest gain, the difference between the oscillation wavelength determined by the refractive index and the peak wavelength of the gain changes due to temperature change. Therefore, single-mode semiconductor lasers such as DFB lasers are designed based on the fact that the difference from the gain peak changes when the temperature changes, such as by shifting the oscillation wavelength at room temperature from the peak wavelength of the gain. . Therefore, by using this embodiment, by further increasing the wavelength change due to temperature, the temperature change of the oscillation wavelength and the temperature change of the gain are made the same, and the oscillation is always set to the gain peak wavelength, or constant. If it is set to operate in a state where the difference is maintained, stable and efficient operation can be obtained.

  By using the above-described temperature independence method of the oscillation wavelength of a semiconductor laser according to an embodiment of the present invention, a processing technique has been established so far without combining with a new semiconductor material or a material other than a semiconductor. It is possible to provide a semiconductor laser in which the oscillation wavelength is stable with respect to temperature change using only the semiconductor and without measuring the oscillation wavelength or temperature. In addition, a semiconductor laser device that does not require a temperature adjustment mechanism can be obtained even when the oscillation wavelength of an optical communication light source or the like needs to be stable. Furthermore, the temperature dependence of the oscillation wavelength can be changed arbitrarily by changing the current distribution amount, etc. Can be obtained.

It is sectional drawing of the wavelength tunable laser which concerns on one Embodiment of this invention. It is a figure explaining operation | movement of the wavelength variable laser which concerns on one Embodiment of this invention. It is a figure explaining APC operation concerning one embodiment of the present invention. It is a figure explaining the system for wavelength stabilization based on one Embodiment of this invention. It is a figure explaining the stop band width and reflectance with respect to a coupling coefficient based on one Embodiment of this invention. It is sectional drawing of the wavelength tunable laser which concerns on one Embodiment of this invention. It is sectional drawing of the wavelength tunable laser which concerns on one Embodiment of this invention.

Explanation of symbols

101, 201, 301 Semiconductor substrate 102, 202, 302 Lower guide layer 103, 203, 303 Active layer 104, 204, 304 Upper guide layer 105, 205, 305 Clad 106, 206, 306 Core layer 107a, 107b, 207 DFB region Electrode 108, 208 Phase control region electrode 307 Active region current 307a, 307b DFB region electrode 109, 209, 309 Lower electrode 210 High reflection film (HR film)

Claims (9)

The first electrode is formed and has at least one gain region for adjusting the gain, and the second electrode is formed, and has at least one wavelength control region for adjusting the wavelength of light passing therethrough. A wavelength tunable laser whose wavelength is changed by injecting a first current into the wavelength control region via the electrode;
A light receiving unit for receiving the optical output of the wavelength tunable laser;
In order to keep the optical output of the wavelength tunable laser substantially constant, a value of a second current injected into the wavelength tunable laser is determined according to the optical output received by the light receiving unit, and the second current A light output control circuit that outputs a current related to the value of
When a current related to the second current value is input, the second current value is distributed based on the second current value determined by the light output control circuit. A current distribution circuit that determines a value of a current to be output to the first electrode formed in the gain region and the second electrode formed in the phase control region from the value of the measured current, respectively. Semiconductor laser device.   2. The semiconductor laser device according to claim 1, wherein the current related to the value of the second current is an electric signal related to the value of the second current.   2. The semiconductor laser device according to claim 1, wherein the current related to the value of the second current is the second current itself.   The current distribution circuit distributes the value of the second current so as to reduce a wavelength change due to a temperature rise of the wavelength tunable laser, and from the distributed current value to the gain region and the phase control region. 4. The semiconductor laser device according to claim 1, wherein values of output currents are respectively determined.   The current distribution circuit distributes the value of the second current so as to increase a wavelength change due to a temperature rise of the wavelength tunable laser, and the value of the distributed current is applied to the gain region and the phase control region. 4. The semiconductor laser device according to claim 1, wherein values of output currents are respectively determined.   6. The semiconductor laser device according to claim 1, wherein one of the gain region and the wavelength control region has a diffraction grating. The semiconductor laser device according to claim 6, wherein a coupling coefficient of the diffraction grating is 150 cm ⁻¹ or more.   8. The semiconductor laser device according to claim 1, wherein the current distribution circuit includes a resistance element having a resistance of 10 times or more of an element resistance of the wavelength tunable laser. The first electrode is formed and has at least one gain region for adjusting the gain, and the second electrode is formed, and has at least one wavelength control region for adjusting the wavelength of light passing therethrough. Receiving a light output of a wavelength tunable laser whose wavelength is changed by injecting a first current into the wavelength control region via the electrode;
A second current value to be injected into the wavelength tunable laser is determined according to the received light output so as to keep the optical output of the wavelength tunable laser substantially constant, and the second current value is set to the second current value. A first determining step of outputting an associated current;
When a current related to the second current value is input, the second current value is distributed based on the determined second current value, and the second current value is calculated based on the distributed current value. And a second determining step of determining a value of a current to be output to the gain region and the phase control region.

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