JP4615184B2 - Distributed feedback laser diode - Google Patents

Description

[0001]
BACKGROUND 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 element (DFB laser element) is a laser element having a structure (hereinafter referred to as a diffraction grating) in which a real part or an imaginary part of a refractive index periodically changes in a resonator. Since feedback is applied only to light of a specific wavelength 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), and electroabsorption optical modulator / built-in type (EA-DFB). Among these, the CW type DFB laser element (CW-DFB laser) is used in combination with an external modulator, and is used, for example, for a WDM basic signal light source or an analog transmission such as CATV. It is required to oscillate at the output.
[0004]
A high-power CW-DFB laser usually has a low reflectance film on one end face (hereinafter referred to as the front end face) on the light emitting side and a high reflectance film on the other end face (hereinafter referred to as the rear end face). Asymmetrical reflecting film structures formed respectively are employed. In this case, most of the laser light can be extracted from the front end face side of the resonator, and laser output can be obtained with high efficiency.
[0005]
In the 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 within an appropriate range, and from the viewpoint of the yield such as the above-mentioned single mode property and efficiency, a value of about 1 is considered to be the best as the product κL of κ and the resonator length L. It has been. In the case of a DFB laser element having a refractive index coupling, the coupling coefficient κ is the film thickness and composition of the diffraction grating, the duty ratio that is the ratio of the width between the large refractive index portion and the small refractive index portion, and the diffraction grating and active layer. It can be set to a predetermined value by adjusting various parameters such as
[0006]
In order to increase the output, it is effective to increase the resonator length L. In this case, a high output can be obtained while suppressing thermal saturation caused by heat generated by a large drive current. At this time, since it is necessary to control to 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, when a very large resonator length L such as L = 1000 μm is employed, for example, κ = 10 cm when the above-mentioned κL = 1 is to be realized.^-1It is necessary to realize such a very small coupling coefficient κ. 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 a difference in refractive index between the diffraction grating and the waveguide layer in which the diffraction grating is embedded can be considered. However, since both require extremely high manufacturing accuracy, it is difficult to stably manufacture a laser element having a certain coupling coefficient κ, and it is possible to stably obtain a laser element having high single mode characteristics. There was a problem that it could not be done.
[0008]
As a method for realizing a small κ, a partial diffraction grating in which a diffraction grating is formed only in a part of the resonator can be employed. 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 resonator length. However, with 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 it is not formed, and the carrier concentration is likely to be nonuniform during current injection. For this reason, there is a problem that an oscillation gain difference between modes is reduced, a transition between modes occurs under a high output, and a kink occurs in the current dependency of the optical output.
[0009]
Accordingly, an object of the present invention is to provide a DFB laser element having a large resonator length, oscillating in a single mode, and suppressing inter-mode transition.
[0010]
[Means for Solving the Problems]
In the course of research to solve the above problems, the present inventor has conceived a structure in which diffraction patterns constituting a diffraction grating are periodically thinned out, considers that this structure is effective in solving the above problems, and considers the following considerations. went. In other words, by periodically thinning out the diffraction pattern, the effective coupling coefficient κ can be made sufficiently small with a DFB laser element having a large resonator length L, and a laser element having high single mode characteristics can be manufactured stably. it can. Here, the discontinuity of the electric field intensity distribution, which is generated in a DFB laser element having a partial diffraction grating, by reducing the length of the period in which the diffraction pattern is thinned out to a small value, for example, in submicron units. We thought that we could suppress the occurrence of transition between modes. Through various experiments, the present invention has been completed.
[0011]
  That is, a DFB laser device according to the present invention that achieves the above object is a distributed feedback semiconductor laser device comprising a diffraction grating composed of a plurality of diffraction patterns adjacent to a resonator and arranged in the resonator direction.
  The diffraction caseChildIs a diffraction pattern arranged at a predetermined pitch.OneThe diffraction pattern ofPeriodicallyThinned outAnd
  The number of diffraction patterns to be thinned out is 1/5 to 1/2 of the total number of diffraction patterns in the diffraction grating.It is characterized by that.
[0012]
  diffractionlatticeThen, out of the diffraction patterns arranged at a predetermined pitchOneThe diffraction pattern ofPeriodicallyBy thinning out, the effective coupling coefficient κ can be reduced. Therefore, it is possible to stably manufacture a laser element having a small coupling coefficient κ, and it is possible to stably obtain a laser element having a high single mode property. In addition, by appropriately adjusting the length of the plurality of diffraction pattern groups constituting the diffraction grating, the discontinuity of the electric field strength distribution inside the resonator is suppressed, and the occurrence of transition between modes under high output is suppressed. be able to.
[0013]
In a preferred embodiment of the present invention, the diffraction patterns at the corresponding positions are thinned out in the diffraction pattern group. Thereby, the discontinuity of the electric field strength distribution inside the resonator can be effectively suppressed, and the occurrence of transition between modes under high output can be effectively suppressed.
[0014]
  In a preferred embodiment of the present invention,Thinned outDiffraction patternCycle ofIn the direction of the resonator240 nm or more,It has a length of 30 μm or less. Thereby, the discontinuity of the electric field strength distribution inside the resonator can be sufficiently suppressed, and the occurrence of transition between modes under high output can be effectively suppressed. In a preferred embodiment of the present invention,Thinned outDiffraction patternCycle ofIn the direction of the resonator240 nm or more,It has a length of 3 μm or less. Occurrence of transition between modes under high output can be more effectively suppressed.
[0015]
  In the present invention, preferably, the above-mentionedDiffraction pattern to be thinned outNumber,All in the diffraction grating1/5 to 1/2 of the number of diffraction patterns. the aboveThinned outNumber of diffraction patternsIs the number of all diffraction patterns in the diffraction gratingIf it is less than 1/5, it is difficult to stably manufacture a laser element having a large small resonator length and a constant small coupling coefficient κ, and a laser element having high single mode characteristics can be stably produced. Can't get. On the other hand, the aboveThinned outNumber of diffraction patternsIs the number of all diffraction patterns in the diffraction gratingIf it is 1/2 or more, the ratio of thinning out diffraction patterns is too large, which adversely affects laser characteristics such as single mode.
[0016]
  In the present invention, the length of the resonator is 500 μm or more.1200μm or lessTo solve the problem that it is difficult to stably manufacture a laser element having a small small coupling coefficient κ with a DFB laser element having a long cavity length by applying to a DFB laser element of Can be obtained stably.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below specifically and in detail with reference to the accompanying drawings.
Embodiment 1
FIG. 1 is a perspective view showing a part of the DFB laser device of this embodiment in section, and FIG. 2 is a cross-sectional view showing a II-II section in FIG. This DFB laser device is a buried hetero type DFB laser device having an oscillation wavelength set to 1550 nm and a resonator length of 1200 μm. The DFB laser device 10 includes an n-InP buffer layer 12, MQW-SCH (on a n-InP substrate 11 having a film thickness of about 120 μm.SeparateConfinementHetero-Structure) It has a laminated structure including an active layer 13, a p-InP spacer layer 14, a diffraction grating 15 having a thickness of 10 nm, a p-InP buried layer 16 in which the diffraction grating 15 is embedded, and a p-InP cladding layer 17. The MQW-SCH active layer 13 includes six quantum well layers in the 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 is thinned out of every three lines. Yes. Furthermore, the ratio of the width of the diffraction pattern 26 to the distance between adjacent diffraction patterns 26 is 3: 7. With such a configuration of the diffraction grating 15, about 10 cm^-1The coupling coefficient κ can be obtained.
[0019]
In the present embodiment example, as described above, the diffraction pattern 26 has a configuration in which one out of every three diffraction patterns 26 is thinned out, so that a uniform diffraction pattern is formed in the entire region of the resonator under the same conditions. Compared with the diffraction grating, the effective coupling coefficient κ can be reduced to 2/3. In addition, since the period in which the diffraction pattern 26 is thinned out is about a submicron, it is possible to suppress the discontinuity of the electric field intensity distribution, which has been a problem with conventional DFB laser elements having a partial diffraction grating. it can.
[0020]
Of the stacked structure, 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 upper portion of the n-InP buffer layer 12 are 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 buried 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 stacked. The highly doped GaInAs contact layer 19 is highly doped with a p-type dopant in order to make ohmic contact with a p-side electrode 22 described later.
[0022]
A Ti / Pt / Au multilayer metal film is provided as the p-side electrode 22 on the highly doped GaInAs contact layer 19, and an AuGeNi film is provided as the n-side electrode 23 on the back surface of the n-InP substrate 11. The front end face 24 of the DFB laser element 30 is provided with a non-reflective coating, and the rear end face 25 is provided with a HR (High Reflective) coating having a reflectivity of about 90%.
[0023]
In producing the DFB laser device 10 of the present embodiment, first, an n-InP buffer layer 12, an MQW-SCH active layer 13 is formed on the n-InP substrate 11 at a growth temperature of 600 ° C. using an MOCVD apparatus. A p-InP spacer layer 14 and a 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 the growth of the MQW-SCH active layer 13, the quantum well active layer (MQW) is grown so as to include six quantum well layers.
[0024]
Next, an electron beam (EB) drawing resist 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. 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 constituting the diffraction grating forming mask 27 is formed in a shape in which one is thinned out every three. Further, the ratio of the width of each rectangular pattern 28 to the distance between adjacent rectangular patterns 28 is set to 3: 7.
[0025]
Next, the diffraction grating 15 is formed by etching through the diffraction grating formation mask 27 so as to penetrate the diffraction grating formation layer 15 a by methane / hydrogen dry etching. Subsequently, the p-InP buried layer 16 and the p-InP clad layer 17 are grown using the MOCVD apparatus, and the burying regrowth of the diffraction grating 15 is performed.
[0026]
As described above, the DFB laser element 10 employs the diffraction grating 15 having a configuration in which one diffraction pattern 26 is thinned out for every three, so that it is uniform over the entire region of the resonator under the same conditions. As compared with a diffraction grating having a simple diffraction pattern, the effective coupling coefficient κ can be reduced to 2/3. For this reason, in forming the diffraction grating 15, very high manufacturing accuracy is not required, and 10 cm as in the present embodiment example.^-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 using a plasma CVD apparatus, and the SiNx film is etched in stripes extending in the periodic direction of the diffraction grating 15 by photolithography and reactive ion etching (RIE). Then, a SiNx film mask (not shown) was formed. Subsequently, using the striped SiNx film mask as an etching mask, 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 -The upper part 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 μm.
[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 to fill both sides of the mesa stripe to form a carrier block layer. Subsequently, after removing the SiNx film mask, a p-InP clad layer 18 having a film 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 the p-side electrode 22 on the highly doped InGaAs contact layer 19. Further, 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 an n-side electrode 23 on the back surface of the n-InP substrate 11.
[0030]
Next, the obtained wafer was opened at the front end face 24 and the rear end face 25 so that the resonator length L of the laser element was 1200 μm. Subsequently, each front end face 24 was coated with a non-reflective coating, and each rear end face 25 was coated with an HR coating having a reflectivity of about 90%, and further divided into individual laser elements, and then formed into chips and bonded.
[0031]
In this embodiment, as described above, since the diffraction grating 15 having a configuration in which one diffraction pattern 26 is thinned out every three is employed, the production of the diffraction grating 15 is extremely high. A laser element having a small coupling coefficient κ can be obtained without requiring accuracy. For this reason, it is possible to stably provide a laser element having a high single mode property. In addition, since the period in which the diffraction pattern 26 is thinned is about a submicron, the discontinuity of the electric field intensity distribution, which has been a problem in the DFB laser element having a partial diffraction grating, is suppressed, and the inter-mode is reduced. Since the occurrence of transition is suppressed, the occurrence of kinks 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 element of the comparative example has the same configuration as the DFB laser element 10 except that the diffraction pattern is uniformly formed in the entire region of the resonator and the oscillation wavelength is set to 1551 nm. With such a diffraction grating 15, approximately 15 cm^-1The coupling coefficient κ is obtained. The DFB laser element of the comparative example can be manufactured in the same manner as the DFB laser element 10 except that the diffraction pattern is uniformly formed in the entire region of the resonator and the oscillation wavelength is set to 1551 nm.
[0033]
For the DFB laser element 10 of the present embodiment example and the DFB laser element 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 light output with respect to the injection current of the laser element. 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 around the oscillation wavelength. At the oscillation wavelength, θ = 0, and at both ends, θ = −π, π.
[0034]
From the figure, 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 is increased by about 1.25 times compared to the DFB laser device of the comparative example, and the characteristics of the good light output efficiency SE are improved. It can be evaluated that it was obtained.
[0035]
For 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_DFBThreshold gain difference for α_thA simulation was performed on the characteristics of L, and the results shown in FIG. 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 an 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 element. 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 L has a spread around the oscillation wavelength. At the oscillation wavelength, θ = 0, and at both ends, θ = −π, π.
[0036]
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 example has a single mode compared to the DFB laser device of the comparative example. It can be evaluated that the performance is equivalent.
[0037]
Embodiment 2
FIG. 5A is a plan view showing the configuration of the DFB laser element of this embodiment.
The DFB laser element according to the present embodiment is a laser element having a configuration in which partial diffraction gratings are periodically repeated, and diffraction gratings are formed from the rear end face 25 side in four zones set in the cavity direction. Partial diffraction grating regions 29 and Fabry-Perot regions 30 where no diffraction grating is formed are alternately provided. 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 uniformly formed without being thinned out. Due to the configuration of such a diffraction grating, about 10 cm^-1The coupling coefficient κ can 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 the DFB laser device according to this embodiment, when forming a diffraction grating forming mask by EB drawing, four zones are set in the resonator direction, and the diffraction grating mask is formed from the rear end face 25 side. (Not shown) and regions (not shown) where the diffraction grating mask is not formed are alternately provided. The length ratio of the region where the diffraction grating mask is formed and the region where the diffraction mask is not formed is 2: 1. In the region where the diffraction grating mask is to be formed, a rectangular pattern having the same configuration as the rectangular pattern 28 of the DFB laser element of Embodiment 1 shown in FIG. 3 is uniformly formed without being thinned out. Other manufacturing methods are the same as the manufacturing method of the DFB laser device 10 of the first embodiment.
[0039]
In the DFB laser element of this embodiment, the length ratio of the partial diffraction grating 29 and the Fabry-Perot region 30 is set to 2: 1, so that the diffraction grating can be uniformly distributed in the entire region of the resonator under the same conditions. Compared to the case where it is formed, the effective coupling coefficient κ can be reduced to 2/3. Therefore, in forming the diffraction grating, a laser element having a small coupling coefficient κ can be obtained without requiring a very high manufacturing accuracy, and a laser element having a high single mode can be provided stably. In addition, the partial diffraction grating regions 29 and the Fabry-Perot regions 30 are alternately provided in the four zones set in the resonator direction, so that the electric field intensity distribution is not as high as that of the DFB laser device of the first embodiment. It is possible to suppress discontinuity and suppress the transition between modes and the occurrence of kinks.
[0040]
Embodiment 3
FIG. 5B is a plan view showing the configuration of the DFB laser element of this embodiment. In the DFB laser element of this 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 formed in eight zones set in the cavity direction. Except for being provided alternately, it has the same configuration as the DFB laser element of the second embodiment. Also, in the method of manufacturing the DFB laser device of this embodiment, when forming the 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 for manufacturing the DFB laser device of the second embodiment except that regions (not shown) to be formed and regions (not shown) where the diffraction grating mask is not formed are alternately provided.
[0041]
In the DFB laser element according to the present embodiment, the ratio of the lengths of the partial diffraction grating 29 and the Fabry-Perot region 30 is set to 2: 1. In addition, a laser element having a small coupling coefficient κ can be obtained without requiring high manufacturing accuracy, and a laser element having high single mode characteristics can be provided stably. Further, the DFB laser element according to the present embodiment has the DFB laser according to the first embodiment by alternately providing the partial diffraction grating regions 29 and the Fabry-Perot regions 30 in the eight zones set in the cavity direction. Although not as large as the element, the discontinuity of the electric field strength distribution can be suppressed more effectively than the DFB laser element of the second embodiment, and the transition between modes and the occurrence of kinks can be suppressed.
[0042]
Embodiment 4
FIG. 5C is a plan view showing the configuration of the DFB laser element of this embodiment.
In the DFB laser element of the present embodiment example, a 16-zone set in the resonator direction includes 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 for being provided alternately, it has the same configuration as the DFB laser element of the second embodiment. Further, in the method of manufacturing the DFB laser device of this embodiment, when forming the 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 for manufacturing the DFB laser device of the second embodiment except that regions (not shown) to be formed and regions (not shown) where the diffraction grating mask is not formed are alternately provided.
[0043]
In the DFB laser element according to the present embodiment, the ratio of the lengths of the partial diffraction grating 29 and the Fabry-Perot region 30 is set to 2: 1. In addition, a laser element having a small coupling coefficient κ can be obtained without requiring high manufacturing accuracy, and a laser element having high single mode characteristics can be provided stably. Further, the DFB laser element of the present embodiment example has the DFB laser of the embodiment example 1 by alternately providing the partial diffraction grating regions 29 and the Fabry-Perot regions 30 in 16 zones set in the cavity direction. Although not as large as the element, it is possible to suppress the discontinuity of the electric field intensity distribution more effectively than the DFB laser element of Embodiment 3, and to suppress the transition between modes and the occurrence of kinks.
[0044]
Embodiment 5
FIG. 5D is a plan view showing the configuration of the DFB laser element of this embodiment.
In the DFB laser element of this embodiment example, 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 formed in 32 zones set in the cavity direction. Except for being provided alternately, it has the same configuration as the DFB laser element of the second embodiment. Further, in the method of manufacturing the DFB laser device of this embodiment, when forming the 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 for manufacturing the DFB laser device of the second embodiment except that regions (not shown) to be formed and regions (not shown) where the diffraction grating mask is not formed are alternately provided.
[0045]
In the DFB laser element according to the present embodiment, the ratio of the lengths of the partial diffraction grating 29 and the Fabry-Perot region 30 is set to 2: 1. In addition, a laser element having a small coupling coefficient κ can be obtained without requiring high manufacturing accuracy, and a laser element having high single mode characteristics can be provided stably. In addition, the DFB laser element according to the present embodiment has the DFB laser according to the first embodiment by alternately providing the partial diffraction grating regions 29 and the Fabry-Perot regions 30 in 32 zones set in the cavity direction. Although not as large as the element, the discontinuity of the electric field strength distribution can be suppressed more effectively than the DFB laser element of the fourth embodiment, and the transition between modes and the occurrence of kinks can be suppressed.
[0046]
When the electric field intensity distribution inside the resonator was simulated for the DFB laser elements having the configurations of the first to fifth embodiments, a graph shown in FIG. 6 was obtained. In the figure, (i) to (v) show the characteristics of the DFB laser elements of Embodiments 1 to 5, respectively. From the figure, it can be seen that in the DFB laser elements of Embodiments 2 to 5, 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 strength distribution inside the resonator is greatly relaxed by controlling the period of thinning out the diffraction pattern to a submicron unit, and the high power output is achieved. It can be evaluated that the transition between the modes has the structure that is least likely to occur.
[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 thinning method of the diffraction pattern. For this reason, not only laser elements having a large resonator length, but also laser elements having various coupling coefficients κ can be manufactured on a single wafer at the same time and with the same number of steps as in the prior art, thereby improving manufacturing efficiency. Can be achieved.
[0048]
Although the present invention has been described based on the preferred embodiment thereof, the DFB laser element of the present invention is not limited to the configuration of the above embodiment example. 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 diffraction patterns arranged at a predetermined pitch in the diffraction pattern group. For this reason, it becomes possible to stably manufacture a laser element having a small coupling coefficient κ, and a laser element having 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, the discontinuity of the electric field strength distribution inside the resonator is suppressed, and the 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 part of a DFB laser element according to Embodiment 1 in section.
FIG. 2 is a cross-sectional view showing a II-II cross section of FIG.
3 is a plan view according to one manufacturing step of the DFB laser element of Embodiment 1; FIG.
FIG. 4A shows an oscillation wavelength λ in the DFB laser elements of the first embodiment and the comparative example._DFBAnd (b) shows the oscillation wavelength λ in the DFB laser elements of the first embodiment and the comparative example._DFBAnd threshold gain difference Δα_thIt is a graph which shows the relationship with L, respectively.
FIGS. 5A to 5D are plan views showing configurations of DFB laser elements according to Embodiments 2 to 5, respectively. FIGS.
FIG. 6 is a graph showing electric field strength distribution inside the resonator in the DFB laser elements of the first to fifth embodiments.
[Explanation of symbols]
10 DFB laser element of embodiment 1
11 n-InP substrate
12 n-InP buffer layer
13 MQW-SCH active layer
14 p-InP spacer layer
15 Diffraction grating
15a Diffraction grating formation layer
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 Outgoing surface
25 Rear end face
26 Diffraction pattern
27 Diffraction grating mask
28 Rectangular pattern
29 Partial diffraction grating region
30 Fabry-Perot area

Claims (1)

In a distributed feedback semiconductor laser device including a diffraction grating composed of a plurality of diffraction patterns arranged adjacent to a resonator and in the direction of the resonator,
In the diffraction grating, one diffraction pattern among the diffraction patterns arranged at a predetermined pitch is periodically thinned out,
The distributed feedback semiconductor laser device, wherein the number of diffraction patterns to be thinned out is 1/5 to 1/2 of the total number of diffraction patterns in the diffraction grating.

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