JP2004128372A - Distribution feedback semiconductor laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a distribution feedback semiconductor laser device which has a long resonator length and is oscillated in the single mode, and wherein inter-mode transition is suppressed. <P>SOLUTION: In the distribution feedback semiconductor laser element 10 with the resonator whose length is 1200 μm, respective diffraction patterns 26 configuring a diffraction grating 15 are structured such that one of every three patterns is thinned out. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a distributed feedback semiconductor laser device, and more particularly to a distributed feedback semiconductor laser device having a large resonator length, oscillating in a single mode, and suppressing transition between modes.
[0002]
[Prior art]
A distributed feedback semiconductor laser device (DFB laser device) is a laser device having a structure in which a real part or an imaginary part of a refractive index periodically changes (hereinafter referred to as a diffraction grating) inside a resonator. Since only the light of a specific wavelength is fed back by the diffraction grating, the DFB laser element has wavelength selectivity and can oscillate in a single mode (single wavelength).
[0003]
The DFB laser element can be suitably used as a signal light source for optical communication because of its high single mode property. There are various types of DFB laser elements as signal light sources for optical communication, such as continuous wave (CW), direct modulation (DM), electroabsorption type optical modulator / built-in type (EA-DFB), depending on the application. Among these, the CW type DFB laser element (CW-DFB laser) is used in combination with an external modulator, and is used for, for example, a backbone signal light source for WDM or analog transmission such as CATV. Laser oscillation is required at the output.
[0004]
In a high-power CW-DFB laser, a low-reflectance film is usually provided on one end face (hereinafter, referred to as a front end face) on the light emission side, and a high-reflectance film is provided on the other end face (hereinafter, referred to as a rear end face). An asymmetric reflective film structure to be formed is adopted. In this case, most of the laser light can be extracted from the front end face side of the resonator, and a laser output can be obtained with high efficiency.
[0005]
In a CW-DFB laser, the coupling coefficient κ is usually optimized in consideration of single mode characteristics, efficiency, and the like. That is, if κ is too large, a high output cannot be obtained, and if κ is too small, a single mode property cannot be obtained. For this reason, it is necessary to control κ in an appropriate range, and from the viewpoint of the yield such as the above-mentioned single mode characteristics and efficiency, a value of about 1 is considered to be the best as the product κL of κ and the resonator length L. Have been. In the case of a DFB laser element having refractive index coupling, the coupling coefficient κ is a film thickness and composition of a diffraction grating, a duty ratio which is a ratio of a width between a large refractive index portion and a small refractive index portion, and a diffraction grating and an active layer. It can be set to a predetermined value by adjusting various parameters such as the distance to the camera.
[0006]
To increase the output, it is effective to increase the resonator length L. In this case, a high output can be obtained while suppressing heat saturation caused by heat generated by a large drive current. At this time, since it is necessary to control κL = 1 as described above, it is necessary to decrease the coupling coefficient κ as L increases.
[0007]
[Problems to be solved by the invention]
However, for example, when a very large resonator length L such that L = 1000 μm is adopted, when trying to realize the above κL = 1, κ = 10 cm^-1It is necessary to realize a very small coupling coefficient κ such that However, it is not easy to realize such a very small κ. Here, in order to realize a small κ, for example, a method of reducing the thickness of the diffraction grating or a method of reducing the difference in the refractive index between the diffraction grating and the waveguide layer in which the diffraction grating is embedded can be considered. However, since extremely high manufacturing accuracy is required in all cases, it is difficult to stably manufacture a laser element having a constant coupling coefficient κ, and it is possible to stably obtain a laser element having a high single mode property. There was a problem that I could not do it.
[0008]
As a method for realizing a small κ, a partial diffraction grating that forms a diffraction grating only in a part of the resonator can be adopted. In the partial diffraction grating, the effective coupling coefficient κ can be reduced by the ratio of the length of the partial diffraction grating to the length of the resonator. However, in this structure, the electric field intensity distribution is discontinuous at the boundary between the region where the partial diffraction grating is formed and the region where the partial diffraction grating is not formed, and the carrier concentration tends to be non-uniform at the time of current injection. For this reason, there is a problem that the oscillation gain difference between the modes becomes small, the transition between the modes occurs under a high output, and the current dependency of the optical output causes a kink.
[0009]
Accordingly, an object of the present invention is to provide a DFB laser device having a large resonator length, oscillating in a single mode, and suppressing transition between modes.
[0010]
[Means for Solving the Problems]
The present inventor has conceived of a structure in which the diffraction pattern constituting the diffraction grating is periodically thinned out in the course of research for solving the above-mentioned problem, and thought that this structure is effective in solving the above-mentioned problem. went. That is, by periodically thinning out the diffraction pattern, a DFB laser element having a large resonator length L can effectively reduce the effective coupling coefficient κ, and stably produce a laser element having high single mode property. it can. Here, by setting the length of the period in which the diffraction pattern is thinned to a small value in, for example, a submicron unit, the discontinuity of the electric field intensity distribution as generated in a DFB laser device having a partial diffraction grating is obtained. It was thought that the occurrence of the transition between modes could be suppressed. The present invention has been completed through various experiments.
[0011]
That is, a DFB laser device according to the present invention that achieves the above object is a distributed feedback semiconductor laser device including a diffraction grating including a plurality of diffraction patterns arranged adjacent to a resonator and arranged in the resonator direction.
The diffraction grating includes a plurality of diffraction pattern groups, and in the diffraction pattern group, a predetermined number of diffraction patterns among the diffraction patterns arranged at a predetermined pitch are thinned out.
[0012]
In the diffraction pattern group, a predetermined number of diffraction patterns among the diffraction patterns arranged at a predetermined pitch are thinned out, whereby the effective coupling coefficient κ can be reduced. Therefore, a laser element having a small coupling coefficient κ can be manufactured stably, and a laser element having a high single mode property can be obtained stably. In addition, by appropriately adjusting the length of the plurality of diffraction pattern groups constituting the diffraction grating, discontinuity of the electric field intensity distribution inside the resonator is suppressed, and occurrence of transition between modes under high output is suppressed. be able to.
[0013]
In a preferred embodiment of the present invention, in the diffraction pattern group, diffraction patterns at corresponding positions are thinned out. Thereby, discontinuity of the electric field intensity distribution inside the resonator can be effectively suppressed, and occurrence of transition between modes under high output can be effectively suppressed.
[0014]
In a preferred embodiment of the present invention, the diffraction pattern group has a length of 30 μm or less in a resonator direction. As a result, discontinuity of the electric field intensity distribution inside the resonator can be sufficiently suppressed, and occurrence of transition between modes under high output can be effectively suppressed. In a preferred embodiment of the present invention, the diffraction pattern group has a length of 3 μm or less in a resonator direction. The occurrence of transition between modes under high output can be suppressed more effectively.
[0015]
In the present invention, preferably, the predetermined number is ５〜 to の of the number of diffraction patterns included in each diffraction pattern group. If the predetermined number is not more than 1/5 of the number of the diffraction patterns, it is difficult to stably manufacture a laser element having a large resonator length and a constant small coupling coefficient κ, and a high single mode A stable laser element cannot be obtained. On the other hand, if the predetermined number is not less than の of the number of the diffraction patterns, the rate of thinning out the diffraction patterns is too large, which adversely affects the laser characteristics such as the single mode property.
[0016]
The present invention is intended to stably manufacture a DFB laser device having a long resonator length and a laser device having a constant small coupling coefficient κ by applying the invention to a DFB laser device having a resonator length of 500 μm or more. Is solved, and a laser element having a high single mode property can be stably obtained.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described specifically and in detail with reference to the accompanying drawings by way of example embodiments.
Embodiment 1
FIG. 1 is a perspective view showing a part of the DFB laser device of the present embodiment in a cross section, and FIG. 2 is a cross sectional view showing a II-II cross section of FIG. This DFB laser device is a buried hetero DFB laser device having an oscillation wavelength set to 1550 nm and a cavity length of 1200 μm. The present DFB laser device 10 includes an n-InP buffer layer 12, an MQW-SCH (not shown) formed on an n-InP substrate 11 having a thickness of about 120 μm.SeparateConfinementHIt has a laminated structure including an active layer 13, a p-InP spacer layer 14, a 10-nm-thick diffraction grating 15, a p-InP buried layer 16 in which the diffraction grating 15 is embedded, and a p-InP clad layer 17. The MQW-SCH active layer 13 includes six quantum well layers in a quantum well active layer (MQW).
[0018]
The diffraction grating 15 is made of InGaAsP made of a quaternary material and having a band gap wavelength λg of 1100 nm. As shown in FIG. 2, the diffraction grating 15 has a pattern period of 240 nm, and each diffraction pattern 26 constituting the diffraction grating 15 has a configuration in which one out of every three diffraction patterns is thinned out. I have. Further, the ratio between the width of the diffraction pattern 26 and the distance between the adjacent diffraction patterns 26 is 3: 7. With such a configuration of the diffraction grating 15, about 10 cm^-1Can be obtained.
[0019]
In the present embodiment, since the diffraction pattern 26 has a configuration in which one out of every three diffraction patterns is thinned out as described above, a uniform diffraction pattern is formed over the entire region of the resonator under the same conditions. Compared with a diffraction grating, the magnitude of the effective coupling coefficient κ can be reduced to 2/3. In addition, since the period at which the diffraction pattern 26 is thinned out is on the order of submicron, it is possible to suppress discontinuity in the electric field intensity distribution, which has conventionally been a problem in a DFB laser device having a partial diffraction grating. it can.
[0020]
In the laminated structure, the upper portions of the p-InP cladding layer 17, the p-InP buried layer 16, the diffraction grating 15, the p-InP spacer layer 14, the MQW-SCH active layer 13, and the n-InP buffer layer 12 are formed of MQW. The SCH active layer 13 is processed in a mesa stripe shape so as to have a width of about 1.8 μm. Both sides of the mesa stripe are filled with a carrier block layer having a stacked structure of a p-InP layer 20 and an n-InP layer 21.
[0021]
On the p-InP cladding layer 17 and the n-InP layers 21 on both sides thereof, a p-InP cladding layer 18 having a thickness of about 2 μm and a highly-doped GaInAs contact layer 19 are sequentially laminated. The highly doped GaInAs contact layer 19 is heavily doped with a p-type dopant in order to make ohmic contact with a p-side electrode 22 described later.
[0022]
On the highly doped GaInAs contact layer 19, a Ti / Pt / Au multilayer metal film is provided as the p-side electrode 22, and on the back surface of the n-InP substrate 11, an AuGeNi film is provided as the n-side electrode 23. The front end face 24 of the DFB laser element 30 is provided with an anti-reflection coating, and the rear end face 25 is provided with an HR (High Reflective) coating having a reflectivity of about 90%.
[0023]
In manufacturing the DFB laser device 10 of this embodiment, first, an n-InP buffer layer 12, an MQW-SCH active layer 13, an n-InP buffer layer 12 are formed on an n-InP substrate 11 at a growth temperature of 600 ° C. by using a MOCVD apparatus. The p-InP spacer layer 14 and the diffraction grating forming layer 15a are grown. In growing the diffraction grating forming layer 15a, InGaAsP having a band gap wavelength λg of 1100 nm is grown. In growing the MQW-SCH active layer 13, the quantum well active layer (MQW) is grown so as to include six quantum well layers.
[0024]
Next, a resist for electron beam (EB) drawing is applied on the diffraction grating forming layer 15a to a thickness of about 100 nm, and EB drawing is performed using an EB drawing apparatus, thereby forming a diffraction grating forming mask 27 as shown in FIG. Form. The diffraction grating forming mask 27 has a pattern period of 240 nm, and each rectangular pattern 28 forming the diffraction grating forming mask 27 is formed in a shape in which one of three rectangular patterns is thinned out. Further, the ratio between the width of each rectangular pattern 28 and the distance between adjacent rectangular patterns 28 is 3: 7.
[0025]
Next, the diffraction grating 15 is formed by methane / hydrogen dry etching so as to penetrate the diffraction grating forming layer 15a from above the diffraction grating forming mask 27. Subsequently, the p-InP buried layer 16 and the p-InP clad layer 17 are grown by using the MOCVD apparatus, and the diffraction grating 15 is buried and regrown.
[0026]
As described above, the DFB laser element 10 employs the diffraction grating 15 having a configuration in which one out of every three diffraction patterns 26 is thinned out. As compared with a diffraction grating having a simple diffraction pattern, the magnitude of the effective coupling coefficient κ can be reduced to 2/3. For this reason, when forming the diffraction grating 15, very high manufacturing accuracy is not required, and 10 cm as in the present embodiment.^-1A laser element having a small coupling coefficient κ can be manufactured stably.
[0027]
Next, a SiNx film is formed on the entire surface of the substrate by using a plasma CVD apparatus, and the SiNx film is etched in a stripe shape extending in the periodic direction of the diffraction grating 15 by photolithography and reactive ion etching (RIE: Reactive Ion Etching). Thus, a SiNx film mask (not shown) was formed. Subsequently, the p-InP cladding layer 17, the p-InP buried layer 16, the diffraction grating 15, the p-InP spacer layer 14, the MQW-SCH active layer 13, and the n-type SiNx film mask are used as an etching mask. -The upper portion of the InP buffer layer 12 was etched and processed into a mesa stripe shape so that the MQW-SCH active layer 13 had a width of about 1.8 m.
[0028]
Next, using the SiNx film mask as a selective growth mask, the p-InP layer 20 and the n-InP layer 21 were selectively grown sequentially, and both sides of the mesa stripe were buried to form a carrier block layer. Subsequently, after removing the SiNx film mask, a p-InP cladding layer 18 having a thickness of about 2 μm and a highly doped InGaAs contact layer 19 were sequentially grown.
[0029]
Next, a Ti / Pt / Au multilayer metal film was formed as a p-side electrode 22 on the highly doped InGaAs contact layer 19. The back surface of the n-InP substrate 11 was polished so that the thickness of the n-InP substrate 11 was about 120 μm, and an AuGeNi film was provided as the n-side electrode 23 on the back surface of the n-InP substrate 11.
[0030]
Next, the obtained wafer was cleaved at the front end face 24 and the rear end face 25 such that the cavity length L of the laser element was 1200 μm. Subsequently, a non-reflective coating was applied to each front end face 24, and an HR coating having a reflectivity of about 90% was applied to each rear end face 25. Further, each laser element was divided into individual laser elements, and then formed into chips and bonded.
[0031]
In this embodiment, as described above, the diffraction grating 15 having a configuration in which one out of every three diffraction patterns 26 is thinned out is employed. A laser element having a small coupling coefficient κ can be obtained without requiring accuracy. Therefore, it is possible to stably provide a laser element having a high single mode property. Further, since the period at which the diffraction pattern 26 is thinned out is on the order of submicron, discontinuity of the electric field intensity distribution, which has conventionally been a problem in a DFB laser device having a partial diffraction grating, is suppressed. Since the occurrence of transition is suppressed, the occurrence of kink can be prevented.
[0032]
Comparative example
In order to evaluate the performance of the DFB laser device of the above embodiment, a DFB laser device of a comparative example was prototyped as the DFB laser device 10 and a conventional DFB laser device. The DFB laser device of the comparative example has a configuration similar to that of the DFB laser device 10 except that the diffraction pattern is formed uniformly in the entire region of the resonator and the oscillation wavelength is set to 1551 nm. With such a diffraction grating 15, about 15 cm^-1Is obtained. The DFB laser device of the comparative example can be manufactured in the same manner as the DFB laser device 10 except that the diffraction pattern is formed uniformly over the entire region of the resonator and the oscillation wavelength is set to 1551 nm.
[0033]
For the DFB laser device 10 of the present embodiment and the DFB laser device of the comparative example, the oscillation wavelength λ_DFBWhen the characteristics of the light output efficiency SE (Slope @ Efficiency) with respect to were examined, the graph shown in FIG. 4A was obtained. The light output efficiency SE refers to the gradient of the light output with respect to the injection current of the laser device. In the figure, (i) shows the characteristics of the DFB laser device 10 of the present embodiment, and (ii) shows the characteristics of the DFB laser device of the comparative example. Since the light output efficiency SE is affected by the phase position θ of the rear end face with respect to the diffraction grating, each has a spread centering on the oscillation wavelength. Θ = 0 at the oscillation wavelength, and θ = −π, π at both ends.
[0034]
As shown in the drawing, the maximum value of the light output efficiency SE is about 0.35 mW / mA in the DFB laser element 10 of the present embodiment, and the maximum value of the light output efficiency SE is about 0 in the DFB laser element of the comparative example. .28 mW / mA. Therefore, in the DFB laser device 10 of the present embodiment, the maximum value of the light output efficiency SE increases about 1.25 times as compared with the DFB laser device of the comparative example, and the characteristics of the good light output efficiency SE are improved. It can be evaluated as obtained.
[0035]
With respect to the DFB laser device 10 of the present embodiment and the DFB laser device having the configuration of the comparative example, the oscillation wavelength λ_DFBGain difference Δα_thSimulation was performed on the characteristic of L, and the result shown in FIG. 4B was obtained. In the figure, (i) shows the characteristics of the DFB laser device 10 of the present embodiment, and (ii) shows the characteristics of the DFB laser device of the comparative example. Threshold gain difference Δα_thL is the oscillation threshold gain difference between the main mode and the sub mode, and is a parameter representing the single mode property of the DFB laser device. Threshold gain difference Δα_thSince L is affected by the phase position θ of the rear end face with respect to the diffraction grating, each has a spread around the oscillation wavelength. Θ = 0 at the oscillation wavelength, and θ = −π, π at both ends.
[0036]
As can be seen from the figure, there is no significant difference between the graph of (i) and the graph of (ii), and the DFB laser device 10 of the present embodiment is compared with the DFB laser device of the comparative example in a single mode. It can be evaluated as having the same performance in terms of performance.
[0037]
Embodiment 2
FIG. 5A is a plan view illustrating the configuration of the DFB laser device according to the present embodiment. The DFB laser device of the present embodiment is a laser device having a configuration in which partial diffraction gratings are periodically repeated. Diffraction gratings are formed in the four zones set in the resonator direction from the rear end face 25 side. The partial diffraction grating regions 29 and the Fabry-Perot regions 30 where no diffraction grating is formed are provided alternately. The length ratio between the partial diffraction grating 29 and the Fabry-Perot region 30 is 2: 1. In the partial diffraction grating region 29, a diffraction pattern having the same configuration as the diffraction pattern 26 of the DFB laser device 10 of the first embodiment shown in FIG. 2 is formed uniformly without being thinned out. With such a diffraction grating configuration, about 10 cm^-1Can be obtained. Other configurations are the same as those of the DFB laser device 10 of the first embodiment.
[0038]
In the method of manufacturing a DFB laser device according to the present embodiment, when forming a diffraction grating forming mask by EB lithography, four zones are set in the cavity direction, and a region where the diffraction grating mask is formed from the rear end face 25 side. (Not shown) and regions (not shown) where no diffraction grating mask is formed are provided alternately. The length ratio between the region where the diffraction grating mask is formed and the region where the diffraction grating mask is not formed is 2: 1. In the region where the diffraction grating mask is formed, a rectangular pattern having the same configuration as the rectangular pattern 28 of the DFB laser device of the first embodiment shown in FIG. 3 is formed uniformly without thinning. Other manufacturing methods are the same as the manufacturing method of the DFB laser element 10 of the first embodiment.
[0039]
In the DFB laser device of the present embodiment, the ratio of the length of the partial diffraction grating 29 to the Fabry-Perot region 30 is set to 2: 1 so that the diffraction grating can be uniformly formed over the entire region of the resonator under the same conditions. It is possible to reduce the magnitude of the effective coupling coefficient κ to ／, as compared with the case where it is formed. For this reason, in forming a diffraction grating, a laser element having a small coupling coefficient κ can be obtained without requiring extremely high manufacturing accuracy, and a laser element having a high single-mode property can be stably provided. Further, by providing the partial diffraction grating regions 29 and the Fabry-Perot regions 30 alternately in the four zones set in the resonator direction, the electric field intensity distribution is not as high as that of the DFB laser device of the first embodiment. Discontinuity can be suppressed, and occurrence of transition between modes and kink can be suppressed.
[0040]
Embodiment 3
FIG. 5B is a plan view showing the configuration of the DFB laser device of the present embodiment. In the DFB laser device of the present embodiment, a partial diffraction grating region 29 where a diffraction grating is formed from the rear end face 25 side and a Fabry-Perot region 30 where no diffraction grating is formed are arranged in eight zones set in the cavity direction. Except that they are provided alternately, they have the same configuration as the DFB laser device of the second embodiment. In the method of manufacturing a DFB laser device according to the present embodiment, when forming a diffraction grating forming mask by EB drawing, eight zones are set in the resonator direction, and the diffraction grating mask is formed from the rear end face 25 side. The method is the same as the method of manufacturing the DFB laser device of the second embodiment, except that regions (not shown) and regions where a diffraction grating mask is not formed (not shown) are alternately provided.
[0041]
In the DFB laser device of the present embodiment, the length ratio between the partial diffraction grating 29 and the Fabry-Perot region 30 is set to 2: 1. A laser element having a small coupling coefficient κ can be obtained without requiring high manufacturing accuracy, and a laser element having a high single-mode property can be stably provided. Further, the DFB laser device of the first embodiment is configured such that the partial diffraction grating regions 29 and the Fabry-Perot regions 30 are provided alternately in eight zones set in the resonator direction, thereby providing the DFB laser device of the first embodiment. Although not as large as the element, the discontinuity of the electric field intensity distribution can be suppressed more effectively than the DFB laser element of Embodiment 2, and the occurrence of transition between modes and kink can be suppressed.
[0042]
Embodiment 4
FIG. 5C is a plan view showing the configuration of the DFB laser device according to the present embodiment. In the DFB laser device of the present embodiment, the 16 zones set in the resonator direction include a partial diffraction grating region 29 where a diffraction grating is formed from the rear end face 25 side and a Fabry-Perot region 30 where no diffraction grating is formed. Except that they are provided alternately, they have the same configuration as the DFB laser device of the second embodiment. In the method of manufacturing a DFB laser device according to the present embodiment, when forming a diffraction grating forming mask by EB drawing, 16 zones are set in the resonator direction, and the diffraction grating mask is formed from the rear end face 25 side. The method is the same as the method of manufacturing the DFB laser device of the second embodiment, except that regions (not shown) and regions where a diffraction grating mask is not formed (not shown) are alternately provided.
[0043]
In the DFB laser device of the present embodiment, the length ratio between the partial diffraction grating 29 and the Fabry-Perot region 30 is set to 2: 1. A laser element having a small coupling coefficient κ can be obtained without requiring high manufacturing accuracy, and a laser element having a high single-mode property can be stably provided. Further, the DFB laser device of the first embodiment is configured such that the partial diffraction grating regions 29 and the Fabry-Perot regions 30 are alternately provided in 16 zones set in the resonator direction, whereby the DFB laser device of the first embodiment is provided. Although not as large as the element, the discontinuity of the electric field intensity distribution can be suppressed more effectively than the DFB laser element of the third embodiment, and the occurrence of transition between modes and kink can be suppressed.
[0044]
Embodiment 5
FIG. 5D is a plan view illustrating the configuration of the DFB laser device according to the present embodiment. In the DFB laser device according to the present embodiment, in 32 zones set in the resonator direction, a partial diffraction grating region 29 where a diffraction grating is formed from the rear end face 25 side and a Fabry-Perot region 30 where no diffraction grating is formed are provided. Except that they are provided alternately, they have the same configuration as the DFB laser device of the second embodiment. In the method of manufacturing a DFB laser device according to the present embodiment, when forming a diffraction grating forming mask by EB drawing, 32 zones are set in the resonator direction, and the diffraction grating mask is formed from the rear end face 25 side. The method is the same as the method of manufacturing the DFB laser device of the second embodiment, except that regions (not shown) and regions where a diffraction grating mask is not formed (not shown) are alternately provided.
[0045]
In the DFB laser device of the present embodiment, the length ratio between the partial diffraction grating 29 and the Fabry-Perot region 30 is set to 2: 1. A laser element having a small coupling coefficient κ can be obtained without requiring high manufacturing accuracy, and a laser element having a high single-mode property can be stably provided. Further, the DFB laser device of the first embodiment is provided with the partial diffraction grating regions 29 and the Fabry-Perot regions 30 alternately provided in 32 zones set in the resonator direction. Although not as large as the element, the discontinuity of the electric field intensity distribution can be suppressed more effectively than the DFB laser element of the fourth embodiment, and the occurrence of transition between modes and kink can be suppressed.
[0046]
Simulation of the electric field intensity distribution inside the resonator was performed on the DFB laser devices having the configurations of Embodiments 1 to 5, and the graph shown in FIG. 6 was obtained. In the figure, (i) to (v) show the characteristics of the DFB laser devices of the first to fifth embodiments, respectively. From the figure, it can be seen that in the DFB laser elements of the second to fifth embodiments, the discontinuity of the electric field intensity distribution is more effectively suppressed as the number of zones is increased. Further, in the DFB laser device 10 of the first embodiment, the discontinuity of the electric field intensity distribution inside the resonator is greatly reduced by controlling the period of thinning out the diffraction pattern in the unit of submicron, so that the high-power It can be evaluated as having a structure in which the transition between modes is the least likely to occur among these.
[0047]
According to the manufacturing method of the present invention, the effective coupling coefficient κ of the laser element can be adjusted only by setting the method of thinning out the diffraction pattern. Therefore, not only laser devices having a large cavity length but also laser devices having various coupling coefficients κ on a single wafer can be manufactured simultaneously and in the same number of steps as in the related art, thereby improving manufacturing efficiency. It is possible to achieve.
[0048]
As described above, the present invention has been described based on the preferred embodiments. However, the DFB laser device of the present invention is not limited only to the configuration of the above-described embodiment, but may be variously changed from the configuration of the above-described embodiment. Modified and changed DFB laser elements are also included in the scope of the present invention.
[0049]
【The invention's effect】
According to the present invention, the effective coupling coefficient κ can be reduced by thinning out a predetermined number of diffraction patterns among the diffraction patterns arranged at a predetermined pitch in the diffraction pattern group. Therefore, a laser element having a small coupling coefficient κ can be stably manufactured, and a laser element having a high single mode property can be stably obtained. In addition, by appropriately adjusting the length of the plurality of diffraction pattern groups constituting the diffraction grating, discontinuity of the electric field intensity distribution inside the resonator is suppressed, and occurrence of transition between modes under high output is suppressed. be able to.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a cross section of a part of a DFB laser device according to a first embodiment.
FIG. 2 is a sectional view showing a II-II section of FIG. 1;
FIG. 3 is a plan view related to one manufacturing process step of the DFB laser element of the first embodiment.
FIG. 4A shows an oscillation wavelength λ in the DFB laser devices of Embodiment 1 and Comparative Example._DFB6A and 6B are graphs respectively showing a relationship between the laser output power SE and the light output efficiency SE. FIG._DFBAnd threshold gain difference Δα_thIt is a graph which shows the relationship with L respectively.
FIGS. 5A to 5D are plan views showing the configurations of DFB laser elements according to Embodiments 2 to 5, respectively.
FIG. 6 is a graph showing an electric field intensity distribution inside a resonator in each of the DFB laser devices according to the first to fifth embodiments.
[Explanation of symbols]
10 ° DFB Laser Device of First Embodiment
11 n-InP substrate
12 n-InP buffer layer
13 MQW-SCH active layer
14 p-InP spacer layer
15 ° diffraction grating
Forming layer of 15a 格子 diffraction grating
16 p-InP buried layer
17 p-InP cladding layer
18 p-InP cladding layer
19% InGaAs contact layer
20 p-InP layer
21 n-InP layer
22 p side electrode
23 n side electrode
24 ° exit surface
25 rear end face
26 ° diffraction pattern
27 ° diffraction grating forming mask
28 rectangular pattern
29 ° partial diffraction grating area
30 Fabry-Perot region

Claims (6)

In a distributed feedback semiconductor laser device including a diffraction grating composed of a plurality of diffraction patterns arranged in the resonator direction adjacent to the resonator,
The diffraction grating is composed of a plurality of diffraction pattern groups, and in the diffraction pattern group, a predetermined number of diffraction patterns among the diffraction patterns arranged at a predetermined pitch are respectively thinned out. Semiconductor laser device. The distributed feedback semiconductor laser device according to claim 1, wherein in the diffraction pattern group, diffraction patterns at corresponding positions are thinned out. The distributed feedback semiconductor laser device according to claim 1, wherein the diffraction pattern group has a length of 30 μm or less in a cavity direction. The distributed feedback semiconductor laser device according to claim 1, wherein the diffraction pattern group has a length of 3 μm or less in a resonator direction. The distributed feedback semiconductor laser device according to claim 1, wherein the predetermined number is ５〜 to の of the number of diffraction patterns included in each diffraction pattern group. The distributed feedback semiconductor laser device according to claim 1, wherein the length of the resonator is at least 500 μm.

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