JP2007220692A - Semiconductor laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high output power semiconductor laser for communication capable of realizing a high optical output power with a low operating current, high optical fiber coupling efficiency, and excellent high-temperature characteristics without impairing mass productivity. <P>SOLUTION: An n-type InGaAsP mode-expansion layer 102 is provided between an n-type InP substrate 101 and an n-type InP clad layer 103. An n-side optical guiding layer 104 and a p-side optical guiding layer 106 are different from each other in composition or layer thickness, or in the both. The mode-expansion layer 102 is a high refractive index layer consisting of one or more layers having a different refractive index from that of the n-type clad layer 103, and its effective refractive index is higher than that of a p-type clad layer 107. The distance is 0.2 μm or more between the n-side optical guiding layer 104 and the mode-expansion layer 102. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor laser, and more particularly to a communication semiconductor laser that realizes a high optical output with a low operating current.

  In high-power semiconductor lasers for communication, for example, semiconductor lasers for pumping optical fiber amplifiers, in order to obtain a high optical output, the device is designed to suppress heat generation and improve heat dissipation by increasing the resonator length. .

   However, since the conventional semiconductor laser has a large internal loss (light absorption) with respect to the laser beam, there is a problem that the quantum efficiency (electric-to-optical conversion efficiency) is greatly lowered and the operating current is increased with the increase in the length of the resonator. It was. Therefore, it is important to reduce the internal loss in order to achieve a high optical output with a low operating current.

  As a semiconductor laser using a compound semiconductor such as GaAs, a semiconductor having a so-called double heterostructure (hereinafter referred to as “DH”) in which an active layer is sandwiched between semiconductors (clad layers) having a band gap larger than that of the active layer. Lasers are known, and are excellent in the recombination of electrons and holes and the light confinement effect in the light emitting region. Furthermore, in response to a demand for a low threshold current, an SCH (Separate Confinement Heterostructure) in which a light guide layer having a refractive index higher than that of the cladding layer and lower than that of the active layer is formed between the active layer and the cladding layer. And a GRIN-SCH (Graded Index Separate Confinement Heterostructure) structure in which the refractive index of the light guide layer is continuously changed.

  FIG. 6 shows a layer structure of a semiconductor laser that is devised to reduce internal loss in a communication semiconductor laser having a DH structure. Usually, an n-type cladding layer composed of InP (refractive index≈3.18) is composed of InGaAsP602 (refractive index≈3.20) having a slightly higher refractive index than InP, and an active layer 603 is formed thereon. The p-type InP cladding layer 604 is provided in this order. In this semiconductor laser, since the refractive index of the n-type InGaAsP clad layer 602 is slightly higher than that of the p-type InP clad layer 604, the laser light distribution is shifted to the n side. As a result, absorption between valence bands (light absorption in the p-type InP cladding layer), which is a main cause of internal loss, is suppressed, and internal loss can be reduced (see Non-Patent Document 1).

On the other hand, an AlGaInP-based visible semiconductor laser having an oscillation wavelength in the 0.6 μm band is known as a semiconductor laser such as an optical disk light source. For example, in Patent Document 1, in an SCH structure in which light guide layers are provided on both sides of an AlGaInP active layer, an asymmetric SCH structure in which the film thickness of the n-side light guide layer is larger than the film thickness of the p-side light guide layer, A high refractive index layer made of AlGaInP having a higher refractive index than the cladding layer is provided in the n cladding layer, and the refractive index of the high refractive index layer is the average refractive index of the SCH structure (waveguide layer) consisting of the active layer and the light guide layer. A semiconductor laser having the same level as that of the semiconductor laser is disclosed. With this structure, the center of the waveguide mode inside the laser is shifted to the n-cladding layer side, so that the light absorption near the laser end face is reduced, the optical damage level is increased, and the output of the laser can be increased. Also, by shifting the waveguide mode to the n-cladding layer side, most of the light is concentrated on the n-cladding layer side and light leakage to the p-cladding layer is reduced. The device resistance can be reduced by reducing the thickness of the p-type AlGaInP cladding layer that can be made thinner and has a relatively high resistivity.
Journals and papers (publications) listed by author Anritsu Co., Ltd. Title of publication News release (published on the web) Date of publication December 9, 2002 Description page / line / drawing http://www.anritsu.co. jp / J / news_events / PressRelease / 021209.asp JP-A-5-243669

  However, in the case of the semiconductor laser of Non-Patent Document 1, since the refractive index of the n-type InGaAsP cladding layer 602 is not so high, the n-type InGaAsP cladding layer 602 has a thickness of 7 μm or more in order to sufficiently shift the laser beam to the n side. It needs to be quite thick. Therefore, the mass productivity is remarkably lowered such that the epitaxial growth time takes twice or more as compared with the conventional case.

  In the case of this semiconductor laser, if the refractive index of the n-type cladding layer is changed, the horizontal and horizontal refraction distribution of the element changes, so that it is possible to obtain an output beam shape suitable for high-efficiency coupling with an optical fiber. There is a drawback in that the waveguide design and manufacturing process are restricted, such as the need to change the waveguide width.

  On the other hand, Patent Document 1 is an AlGaInP-based semiconductor laser different from the InGaAsP-based or InGaAlAs-based semiconductor that is the object of the present invention, and the configuration cannot be applied to an InGaAsP-based or InGaAlAs-based semiconductor laser as it is. In Patent Document 1, it is disclosed in claim 7 that the film thickness of the low refractive index barrier layer provided between the high refractive index layer and the light guide layer is 5 nm to 40 nm. Nothing is stated.

  The present invention is a high-power semiconductor laser for communication, particularly a semiconductor laser for pumping an optical fiber amplifier, which can realize a high optical output with a low operating current without impairing mass productivity, and has a high optical fiber coupling efficiency and an excellent high temperature. An object of the present invention is to provide a semiconductor laser structure capable of realizing the characteristics.

  The present invention for solving the above problems comprises the following (1) to (10).

  (1) An active layer made of an InGaAsP-based or InGaAlAs-based compound semiconductor is provided on a semiconductor substrate, and an n-type cladding layer, an n-side light guide layer, an active layer, a p-side light guide layer, and a p-type cladding layer are arranged in this order. The high-refractive index layer composed of one or more layers having a refractive index different from that of the n-type cladding layer is provided in a part of the n-type cladding layer. The refractive index is higher than the effective refractive index of the p-type cladding layer, and the effective refractive index of the active layer and the effective refractive index of the high refractive index layer are between the n-side light guide layer and the high refractive index layer. An n-type cladding layer having a lower effective refractive index is interposed, and the thickness of the interposed n-type cladding layer is 0.2 μm or more.

  (2) The high refractive index layer has a layer thickness of 0.01 μm or more and 1 μm or less, and the intervening n-type cladding layer has a layer thickness of 2 μm or less. Semiconductor laser.

  (3) The semiconductor laser according to (1) or (2), wherein an effective refractive index of the high refractive index layer is 1.5% or more higher than an effective refractive index of the p-type cladding layer. .

  (4) The semiconductor according to any one of (1) to (3), wherein a refractive index of the p-type cladding layer is uniform or monotonously changes in a layer thickness direction. laser.

  (5) Any one of (1) to (4), wherein the n-side light guide layer and the p-side light guide layer are different in effective refractive index and / or layer thickness. 2. The semiconductor laser according to item 1.

  (6) Any one of (1) to (5), wherein the n-type cladding layer, the n-side light guide layer, the active layer, the p-side light guide layer, and the p-type cladding layer have a mesa structure. The semiconductor laser according to item.

  (7) The layer thickness of the n-side light guide layer is 0.01 μm or more and 0.5 μm or less, and the layer thickness of the p-side light guide layer is 0.01 μm or more and 0.1 μm or less. The semiconductor laser according to any one of (1) to (6).

  (8) The semiconductor laser as set forth in any one of (1) to (7), wherein the refractive index distribution of the high refractive index layer changes in the layer thickness direction.

  (9) One or both of the n-side light guide layer and the p-side light guide layer are composed of a plurality of layers having different refractive indexes, (1) to (8) The semiconductor laser according to any one of claims.

  (10) The refractive index distribution of one or both of the n-side light guide layer and the p-side light guide layer is changed in the layer thickness direction, and any one of (1) to (9) The semiconductor laser according to claim 1.

  According to the present invention, a semiconductor laser with low internal loss and capable of realizing high optical output with low operating current can be realized without impairing mass productivity. In addition, the optical fiber coupling efficiency and the temperature characteristics can be improved at the same time.

  The structure of the semiconductor laser according to the present invention is a semiconductor laser having an active layer made of an InGaAsP-based or InGaAlAs-based compound semiconductor on a semiconductor substrate, and a high refractive index layer having an effective refractive index sufficiently higher than that of a p-type InP cladding layer. Is provided in the n-type InP clad layer. In addition, one or both of the effective refractive index and the layer thickness of the light guide layer (SCH: Separate Confinement Heterostructure) are different between the n side and the p side. For convenience, in the present invention, the high refractive index layer in the n-type InP cladding layer is referred to as a “mode expansion layer”. The mode expansion layer is made of, for example, InGaAsP or InGaAlAs having a composition wavelength of 1 μm or more. Hereinafter, an InGaAsP mode expansion layer will be described as an example.

  By inserting a mode expansion layer having a high effective refractive index in the n-side InP cladding layer, the laser beam can be sufficiently shifted to the n-side even with a relatively thin InGaAsP layer thickness. Therefore, the internal loss can be sufficiently reduced while the structure in which the increase in the epitaxial growth time is suppressed as much as possible.

  Furthermore, the semiconductor laser of the present invention enables high-efficiency coupling with an optical fiber without changing the design or manufacturing process of the waveguide. The reason for this will be described below based on the inventors' simulation studies and experimental results.

  The laser light distribution in the vertical transverse direction is substantially determined by the effective refractive index, the layer thickness, and the distance from the light guide layer of the mode expanding layer, and is hardly affected by the effective refractive index and the layer thickness of the light guide layer. On the other hand, since the horizontal and horizontal laser light distribution largely depends on the horizontal and horizontal refractive index distribution of the device, the mode expansion layer (effective refractive index, layer thickness, distance) and the light guide layer (effective refractive index, layer thickness) ) Determined from both. Therefore, by designing the beam shape in the vertical and transverse directions with the mode expansion layer and then designing the beam shape in the horizontal and transverse directions with the light guide layer, both can be optimized independently. Thereby, high-efficiency optical fiber coupling can be realized without changing the waveguide width.

  Furthermore, the semiconductor laser of the present invention can improve high temperature characteristics in addition to the above effects. The reason for this will be described below based on the inventors' simulation studies and experimental results.

  Since the p-side light guide layer has a role of a potential barrier against electrons having a small effective mass, the overflow of electrons greatly changes when the composition and layer thickness thereof are changed. On the other hand, the n-side light guide layer becomes a potential barrier against holes having a large effective mass, and therefore, even if the composition and layer thickness are changed, the electrical characteristics of the device are hardly affected. Therefore, the beam shape in the vertical and lateral directions is controlled by optimizing the mode expansion layer, the electron overflow is minimized by optimizing the p-side light guide layer, and the horizontal and horizontal beam shape is optimized by optimizing the n-side light guide layer. By controlling, it is possible to simultaneously realize reduction of internal loss, improvement of optical fiber coupling efficiency, and improvement of temperature characteristics.

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

  FIG. 1 is a view showing a cross section of a semiconductor laser according to a first embodiment of the present invention. An n-type InGaAsP mode expansion layer 102, an n-type InP cladding layer 103, an n-side light guide layer 104, an active layer 105, a p-side light guide layer 106, and a p-type InP cladding layer 107 are formed on the n-type InP substrate 101. The mesa 108 made of is embedded with the p-type InP current blocking layer 109 and the n-type InP current blocking layer 110, and the upper surfaces of the mesa 108 and the n-type InP current blocking layer 110 are covered with the p-type InP cladding layer 111. This is a so-called BH (Buried Heterostructure) laser.

  FIG. 2 is a diagram showing the refractive index distribution in the vertical direction in the mesa of the semiconductor laser according to the first embodiment of the present invention. A feature of the present invention is that an n-type InGaAsP mode expansion layer 202 is inserted between the n-type InP substrate 201 and the n-type InP cladding layer 203. Alternatively, an n-type InP cladding layer 203 is provided between the n-type InGaAsP mode expansion layer 202 and the active layer 205. In addition, the n-side light guide layer 204 and the p-side light guide layer 206 are different in the effective refractive index, the layer thickness, or both.

  FIG. 7 is a simulation example in the first embodiment of the present invention, and is a graph showing the dependence of the internal loss on the mode expansion layer refractive index. Calculations show that as the refractive index of the mode expansion layer increases, the amount of shift of the laser light toward the n side increases and the internal loss can be reduced. According to our calculation, it was found that if the refractive index of the mode expanding layer is higher than the effective refractive index of the p-type InP cladding layer by 1.5% or more, the effect of reducing the internal loss can be sufficiently obtained. On the other hand, if the refractive index of the mode expansion layer is higher than the effective refractive index of the active layer, the optical confinement ratio in the active layer becomes too small and the device characteristics deteriorate, so the effective refractive index of the mode expansion layer is the effective refractive index of the active layer. It is desirable that the refractive index be equal to or lower than the refractive index.

  FIG. 8 is a simulation example in the first embodiment of the present invention, and is a graph showing the dependence of the internal loss on the mode expansion layer thickness. Calculations show that as the mode expansion layer thickness increases, the shift amount of the laser light toward the n side increases, and the internal loss can be reduced. According to our calculation, it was found that if the thickness of the mode expansion layer is 10 nm or more, the effect of reducing the internal loss can be sufficiently obtained. If the thickness of the mode expansion layer is greater than 1 μm, the optical confinement ratio of the active layer becomes too small and the device characteristics deteriorate, and as the thickness increases, the epitaxial growth time increases and the mass productivity decreases. Is preferably 1 μm or less.

  FIG. 9 is a simulation example in the first embodiment of the present invention, which is a graph showing an example of the dependence of internal loss on the n-side light guide layer to the mode expansion interlayer distance, and a mode having a layer thickness of 0.15 μm. In the enlarged layer, the refractive index is 3.25 (displayed as “low”) and the refractive index is 3.4 (displayed as “high”). As the mode expansion layer moves away from the light guide layer, that is, as the layer thickness of the low refractive index n-type cladding layer provided therebetween increases, the amount of shift of laser light to the n side increases, reducing internal loss. Calculations have shown that this is possible. However, it has been found that if the mode expansion layer is too far from the light guide layer, the optical confinement ratio of the mode expansion layer is reduced, so that the shift amount of the laser light to the n side is reduced and the internal loss is increased. As a result of examining various mode expansion layers having different refractive indexes and layer thicknesses, it is possible to sufficiently reduce the internal loss when the distance from the light guide layer of the mode expansion layer is 0.2 μm or more and 2 μm or less. all right.

  As described above, the n-type InGaAsP mode expansion layer 202 has a refractive index higher than the effective refractive index of the p-type InP cladding layer 207 by 1.5% or more and below the effective refractive index of the active layer. Optimum design with the layer 202 having a thickness of 0.01 μm or more and 1 μm or less and a distance from the n-side light guide layer of 0.2 μm or more and 2 μm or less greatly reduces internal loss without sacrificing mass productivity. Can be reduced.

  More specifically, for example, when the refractive index of the n-type InGaAsP mode expansion layer 202 is 3.3, the layer thickness is 0.2 μm, and the distance from the n-side light guide layer is 0.5 μm, the mode expansion layer is The internal loss can be reduced by 30% or more compared to a structure having no structure. At this time, the increase in the thickness of the epitaxial layer is at most 0.7 μm as compared with the structure without the n-type InGaAsP mode expansion layer 202. Thus, according to the present invention, compared with the conventional structure shown in FIG. 6, an internal loss reduction effect equal to or higher than that of the conventional structure shown in FIG.

  Further, the mode expansion layer can obtain the same effect even when other compositions, layer thicknesses, and distances are combined. For example, even if the refractive index of the mode expansion layer is 3.35, the layer thickness is 0.1 μm, and the distance from the n-side light guide layer is 0.6 μm, the internal loss can be reduced by 30% or more. Accordingly, it is possible to optimize the design so that the internal loss is reduced and other characteristics are improved, for example, the laser light distribution in the vertical and lateral directions is a shape suitable for high-efficiency optical fiber coupling.

  FIG. 10 is a simulation example in the first embodiment of the present invention, and is a graph showing the dependence of electron overflow on the p-side guide layer thickness. Since the p-side SCH structure has a role of a potential barrier for electrons with a small effective mass, it has been calculated by optimizing the p-side guide layer thickness to minimize the electron overflow. Similarly, the refractive index of the p-side guide layer can be optimized.

  As described above, the p-side light guide layer 206 has an effective refractive index that is greater than or equal to the effective refractive index of the p-type InP cladding layer 207 and less than or equal to the effective refractive index of the active layer, and a thickness of 0.01 μm to 0.1 μm. By optimizing the design, the overflow of electrons can be effectively suppressed. Specifically, for example, by setting the effective refractive index of the p-side light guide layer 206 to 3.35 and the layer thickness to 0.03 μm, the overflow of electrons becomes a minimum value. At this time, the laser beam distribution in the vertical and lateral directions of the semiconductor laser according to the present invention is substantially determined by the active layer 205 and the mode expansion layer 202, and therefore changes substantially even if the composition and layer thickness of the p-side light guide layer 206 are changed. do not do. Therefore, by appropriately designing the p-side light guide layer 206, the high temperature characteristics can be improved without deteriorating internal loss and optical fiber coupling efficiency.

  In addition, the p-side light guide layer can achieve the same effect even when other compositions and layer thickness combinations are used. For example, even if the p-side light guide layer is composed of two stages having a refractive index of 3.3 and 3.4, and the thickness of each layer is 0.02 μm, the overflow of electrons can be minimized. Similarly, a multistage structure having three or more stages may be used. Moreover, it is good also as what is called GRIN-SCH (Graded Index Separate Confinement Heterostructure) from which a composition changes gradually in the layer thickness direction.

  FIG. 11 is a simulation example according to the first embodiment of the present invention, and is a graph showing the dependence of the fiber coupling efficiency on the n-side guide layer thickness. In this example, as the n-side light guide layer thickness increases, the refractive index distribution in the horizontal direction of the element increases and the beam shape in the horizontal transverse mode approaches that suitable for fiber coupling, thus improving fiber coupling efficiency. Calculations have shown that this is possible. According to our calculation, it was found that if the n-side light guide layer thickness is 10 nm or more, the effect of improving the fiber coupling efficiency can be sufficiently obtained. It was also found that when the n-side light guide layer thickness is greater than 0.5 μm, the equivalent refractive index of the element becomes too large to satisfy the fundamental mode cutoff condition.

  As described above, the n-side light guide layer 204 has an effective refractive index that is greater than or equal to the effective refractive index of the n-type InP cladding layer 203 and less than or equal to the effective refractive index of the active layer, and a layer thickness of 0.01 μm to 0.5 μm. By designing optimally, it is possible to control the horizontal and horizontal laser light distribution so as to have a shape suitable for high-efficiency optical fiber coupling. Specifically, for example, by setting the effective refractive index of the n-side light guide layer 204 to 3.35 and the layer thickness to 0.1 μm, an optical fiber coupling efficiency of 90% or more is achieved without changing the waveguide width. it can. At this time, even if the composition and the layer thickness of the n-side light guide layer 204 are changed, the laser light distribution in the vertical transverse direction and the hole overflow are hardly affected. Therefore, by designing the n-side light guide layer 204 optimally, high-efficiency optical fiber coupling can be realized without deteriorating internal loss and high temperature characteristics.

  In addition, the n-side light guide layer can obtain the same effect even when other compositions and layer thicknesses are combined. For example, the n-side light guide layer is composed of two stages with refractive indexes of 3.3 and 3.4, and the optical fiber coupling efficiency of 90% or more is realized even when the respective layer thicknesses are 0.04 μm and 0.06 μm. it can. Similarly, a multistage structure having three or more stages may be used. Moreover, it is good also as what is called GRIN-SCH from which a composition changes gradually in the layer thickness direction.

  Note that the composition and the layer thickness of the p-side light guide layer and the n-side light guide layer may be arbitrary as long as the results are optimally designed within the above range.

  The refractive index can be arbitrarily adjusted by adjusting the composition ratio of Ga or As in the InGaAsP or InGaAlAs semiconductor. Specifically, when the composition ratio of at least one of Ga or As is increased, the refractive index tends to increase.

  FIG. 3 is a view showing the refractive index distribution in the vertical direction in the mesa of the semiconductor laser according to the second embodiment of the present invention. The difference from the first embodiment is that the mode expansion layer 302 has a multiple structure (referred to as “multimode expansion layer”) in which a low refractive index layer is sandwiched between a plurality of high refractive index layers having different refractive indexes. . In this case, the laser light distribution in the vertical and lateral directions can be controlled more precisely, so that the optical fiber coupling efficiency can be further increased. FIG. 3 shows a case where the refractive index decreases, the layer thickness increases, and the interval increases as the mode expansion layer 302 moves away from the active layer 305. However, the vertical laser beam distribution is changed to high-efficiency optical fiber coupling. The mode expansion layer 302 may have any composition, layer thickness, and spacing in terms of controlling the shape suitable for the above. For example, any or all of the composition, the layer thickness, and the interval may be the same. The number of mode expansion layers 302 is not limited to three, but may be two layers or a multi-layer structure of four or more layers.

  FIG. 4 is a diagram showing the refractive index distribution in the vertical direction in the mesa of the semiconductor laser according to the third embodiment of the present invention. The difference from the first embodiment is that the mode expansion layer 402 is multistage (referred to as “multistage mode expansion layer”). In this case, the laser light distribution in the vertical and lateral directions can be controlled more precisely, so that the optical fiber coupling efficiency can be further increased. FIG. 4 shows a case where one layer having the highest refractive index in the mode expansion layer 402 is provided, and the composition and thickness of the low refractive index layers on both sides thereof are different, but the laser beam distribution in the vertical direction is shown. Is controlled to a shape suitable for high-efficiency optical fiber coupling, the composition, layer thickness, and spacing of the layers constituting the mode expansion layer 402 may be arbitrary. For example, the composition and layer thickness of the low refractive index layers provided on both sides of the highest refractive index layer in the mode expansion layer 402 may be the same. Further, a structure having a low refractive index layer only on one side of the layer having the highest refractive index in the mode expanding layer 402 may be used. In combination with the second embodiment of the present invention, a plurality of layers having a high refractive index may be provided in the mode expansion layer 402. Similarly, each layer of the mode expansion layer 302 shown in the second embodiment may be configured in multiple stages.

  FIG. 5 is a view showing the refractive index distribution in the vertical direction in the mesa of the semiconductor laser according to the fourth embodiment of the present invention. The difference from the first embodiment is that the composition of the mode expansion layer 502 gradually changes in the layer thickness direction (referred to as “gradient mode expansion layer”). In this case, the laser light distribution in the vertical and lateral directions can be controlled more precisely, so that the optical fiber coupling efficiency can be further increased. FIG. 5 shows a case where the refractive index distribution of the mode expansion layer 502 is asymmetric. However, the mode expansion layer 502 is controlled in that the laser light distribution in the vertical direction is controlled to a shape suitable for high-efficiency optical fiber coupling. Any change in the composition with respect to the thickness direction of the film may be used. For example, the refractive index distribution of the mode expansion layer 502 may be symmetric. Further, the change in the composition of the mode expansion layer 502 may be linear. Moreover, the structure combined with the 2nd Embodiment of this invention, 3rd Embodiment, or both may be sufficient.

  Note that the mode expansion layer is not limited to an InGaAsP or InGaAlAs-based compound semiconductor, and may be composed of another material having a higher effective refractive index than the p-type cladding layer.

  Further, the n-type cladding layer and the p-type cladding layer are not limited to InP, and can be applied to semiconductor lasers composed of other compositions or other materials. The present invention can also be applied to a semiconductor laser in which the n-type cladding layer and the p-type cladding layer are made of different compositions and materials. Also in this case, the mode expansion layer may be made of a composition or material having a higher effective refractive index than the p-type cladding layer.

  Since electrons which are majority carriers in the n-type cladding layer have a small effective mass, even if a layer having a relatively large potential barrier such as a mode expansion layer exists in the n-type cladding layer, the current-voltage characteristics, etc. The device characteristics are hardly deteriorated. However, since holes that are majority carriers in the p-type cladding layer have a large effective mass, and the presence of the potential barrier has a large influence on the device characteristics, the p-type cladding layer has no potential barrier or is in the layer thickness direction. It is desirable to change monotonously. Alternatively, it is desirable that the refractive index of the p-type cladding layer is uniform or changes monotonously in the layer thickness direction.

  The active layer can be applied to any structure such as a bulk, a single quantum well, and a multiple quantum well.

  Further, the present invention can be applied not only to the BH laser but also to a semiconductor laser having another structure. For example, the present invention can be applied to a DC-PBH (Double Channel Planar Buried Heterostructure) laser.

It is sectional drawing of the semiconductor laser of the 1st Embodiment of this invention. It is the figure which showed the refractive index distribution of the perpendicular direction in the mesa of the semiconductor laser of the 1st Embodiment of this invention. It is the figure which showed the refractive index distribution of the perpendicular direction in the mesa of the semiconductor laser of the 2nd Embodiment of this invention. It is the figure which showed the refractive index distribution of the perpendicular direction in the mesa of the semiconductor laser of the 3rd Embodiment of this invention. It is the figure which showed the refractive index distribution of the perpendicular direction in the mesa of the semiconductor laser of the 4th Embodiment of this invention. It is sectional drawing of the conventional semiconductor laser. It is a graph which shows the example of a simulation (mode expansion layer refractive index dependence of internal loss) in the 1st Embodiment of this invention. It is a graph which shows the example of a simulation (mode expansion layer thickness dependence of an internal loss) in the 1st Embodiment of this invention. It is a graph which shows the example of a simulation in the 1st Embodiment of this invention (The n side light guide layer-mode expansion interlayer distance dependence of an internal loss). It is a graph which shows the example of a simulation in the 1st Embodiment of this invention (the p side light guide layer thickness dependence of an electronic overflow). It is a graph which shows the example of a simulation in the 1st Embodiment of this invention (The n side light guide layer thickness dependence of fiber coupling efficiency).

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... n-type InP substrate 102 ... n-type InGaAsP mode expansion layer 103 ... n-type InP clad layer 104 ... n-side light guide layer 105 ... active layer 106 ... p-side light guide Layer 107 ... p-type InP cladding layer 108 ... mesa 109 ... p-type InP current blocking layer 110 ... n-type InP current blocking layer 111 ... p-type InP cladding layer 201 ... n-type InP substrate 202 ... n-type InGaAsP mode expansion layer 203 ... n-type InP cladding layer 204 ... n-side light guide layer 205 ... active layer 206 ... p-side light guide layer 207 ... p Type InP cladding layer 301... N type InP substrate 302... Multi-mode expansion layer 303... N type InP cladding layer 304... N-side light guide layer 305. Side light guide layer 307... P-type InP cladding layer 401... N-type InP substrate 402... Multistage mode expansion layer 403... N-type InP cladding layer 404. Active layer 406... P-side light guide layer 407... P-type InP cladding layer 501... N-type InP substrate 502... Inclined mode expansion layer 503. n-side light guide layer 505 ... active layer 506 ... p-side light guide layer 507 ... p-type InP clad layer 601 ... n-type InP substrate 602 ... n-type InGaAsP clad layer 603 ... Active layer 604... P-type InP cladding layer 605... P-type InP current blocking layer 606... N-type InP current blocking layer 607.

Claims (11)

  A semiconductor having an active layer made of an InGaAsP-based or InGaAlAs-based compound semiconductor on a semiconductor substrate, and an n-type cladding layer, an n-side light guide layer, an active layer, a p-side light guide layer, and a p-type cladding layer in this order. In the laser, a part of the n-type cladding layer is provided with a high refractive index layer composed of one or more layers having a refractive index different from that of the n-type cladding layer, and the effective refractive index of the high refractive index layer is An effective refractive index that is higher than the effective refractive index of the p-type cladding layer and lower than the effective refractive index of the active layer and the effective refractive index of the high refractive index layer between the n-side light guide layer and the high refractive index layer. A semiconductor laser, wherein an n-type cladding layer having a refractive index is interposed, and the thickness of the interposed n-type cladding layer is 0.2 μm or more.   2. The semiconductor laser according to claim 1, wherein the high refractive index layer has a layer thickness of 0.01 μm or more and 1 μm or less, and a thickness of the intervening n-type cladding layer is 2 μm or less. .   3. The semiconductor laser according to claim 1, wherein an effective refractive index of the high refractive index layer is 1.5% or more higher than an effective refractive index of the p-type cladding layer.   4. The semiconductor laser according to claim 1, wherein a refractive index of the p-type cladding layer is uniform or monotonously changes in a layer thickness direction. 5.   The n-side light guide layer and the p-side light guide layer are different from each other in effective refractive index, layer thickness, or both, according to any one of claims 1 to 4. Semiconductor laser.   The n-type cladding layer, the n-side light guide layer, the active layer, the p-side light guide layer, and the p-type cladding layer are formed in a mesa structure, according to any one of claims 1 to 5. The semiconductor laser described.   The layer thickness of the n-side light guide layer is 0.01 μm or more and 0.5 μm or less, and the layer thickness of the p-side light guide layer is 0.01 μm or more and 0.1 μm or less. Item 7. The semiconductor laser according to any one of Items 1 to 6.   8. The semiconductor laser according to claim 1, wherein a refractive index distribution of the high refractive index layer changes in a layer thickness direction. 9.   9. The device according to claim 1, wherein one or both of the n-side light guide layer and the p-side light guide layer is composed of a plurality of layers having different refractive indexes. The semiconductor laser described.   10. The refractive index distribution of one or both of the n-side light guide layer and the p-side light guide layer changes in the layer thickness direction, according to claim 1. Semiconductor laser.   A semiconductor laser having an n-type InP cladding layer, an n-side light guide layer, an active layer made of an InGaAsP-based or InGaAlAs-based compound semiconductor, a p-side light guide layer, and a p-type InP cladding layer in this order on an n-type InP semiconductor substrate In the n-type InP cladding layer, an n-type InGaAsP or n-type InGaAlAs high refractive index layer composed of one or more layers is provided in a part of the n-type InP cladding layer, and the effective refractive index of the high refractive index layer is A semiconductor laser having an effective refractive index or lower and higher than an effective refractive index of a p-type InP cladding layer.

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