RU2197047C1 - Semiconductor amplifying element and semiconductor optical amplifier - Google Patents

Abstract

FIELD: fiber-optic communication and data transmission systems, superhigh-speed optical computing and communication systems, medicine, laser engineering. SUBSTANCE: novelties are retrofitting of semiconductor amplifying element heterostructure, comprehensive approach to selection of composition and thickness of heterostructure layers ensuring operation in narrow transition region for organizing radiation emission from active layer of mentioned semiconductor amplifying element of proposed optical amplifier, and also same or similar heterostructure is proposed to be used for injection laser. All these novelties provide for enhancing output radiation power, efficiency, and reliability of amplifier at reduced output radiation divergence angles, minimizing deviation of its direction from normal to optical face plane, improving distribution of near and distant radiation fields and temperature dependencies of amplifying element output parameters, reducing ohmic and thermal resistances, and reducing mechanical stresses. EFFECT: facilitated manufacture, enlarged functional capabilities. 25 cl, 6 dwg

Description

 The invention relates to quantum electronic technology, namely to efficient, powerful and compact semiconductor optical amplifiers and its semiconductor amplifying elements.

State of the art
The semiconductor amplifier element (hereinafter “PUE”) is based on the heterostructure and is the main element of an efficient high-power and compact semiconductor optical amplifier (hereinafter “POE”).

 Traditionally, a POE consists of a driving source of input radiation, the output of which is optically coupled by the optical system to the input of the PUE [1,2,3].

The closest to the technical problem being solved is the PUE proposed in [4] with an inflow region and an unconventional medium for amplified radiation propagation. It includes a semiconductor-based heterostructure containing at least one active layer consisting of at least one sublayer and a laser leak-in region of radiation leak-in from at least one side of the active layer, at least one with at least one one layer of leak-in radiation, consisting of at least one sublayer. The heterostructure is characterized by the ratio of the effective refractive index n _{eff of the} heterostructure to the refractive index n _{VT of the} inflow layer. PUE also contains optical faces, reflectors, ohmic contacts, at least one antireflection coating on the optical face. During the operation of the known PUE, the medium of propagation of the amplified radiation is at least part of the leak-in region and at least part of the active layer. In [4], constructions of PUEs with many areas of leak-in radiation and multistage PUEs were also proposed.

 All methods for manufacturing PES are based on the methods of modern technology for manufacturing semiconductor injection radiation sources. At the same time, there are technological difficulties in their manufacture, especially in the manufacture of inclined optical faces. There are a number of limitations when using a substrate as a radiation leak-in region.

Closest to the technical problem being solved is the POE proposed in [4], which contains the optically coupled master input radiation source with a PUE, including the leak-in region and the non-traditional medium of amplified radiation propagation. The volume of the amplified radiation propagation medium includes not only the active volume of the amplification region with intense leaky amplification, but also the passive volume of the radiation leak-in region. PUE includes a semiconductor-based heterostructure containing at least one active layer, consisting of at least one sublayer, a region of radiation leak-in, transparent to laser radiation, on at least one side of the active layer, at least one with at least one with a radiation leak-in layer consisting of at least one sublayer, the heterostructure is characterized by the ratio of the effective refractive index n _{eff of the} heterostructure to the refractive index n of the _VT leak-in layer. The PUE also contains optical faces, reflectors, ohmic contacts, at least one antireflection coating on the optical face, and when the semiconductor amplifier element is in operation, the propagation medium of the amplified radiation is at least part of the leak-in region and at least part of the active layer.

 At the same time, the areas of the input and output apertures were significantly increased; for all POU designs, the amplified output radiation was oblique, including perpendicular to its longitudinal axis lying in the plane of the active layer. In [4], the design of the POE with multi-beam output radiation, multi-stage POEs were also proposed.

 The main advantages of these POCs are the possibility of increasing the area of the input and output apertures, obtaining small divergence angles, increasing the service life and reliability. At the same time, the extraction of radiation at an angle to the active layer and to the optical faces creates great difficulties in the operation of the POEs known from [4]. There are technological difficulties in their manufacture, especially in the manufacture of inclined optical faces. There are limitations when using a substrate as a radiation leak-in region.

Disclosure of Invention
The basis of the invention is the technical task of simplifying the design of a semiconductor amplifying element and the technological process of its manufacture, both growing its heterostructure and manufacturing the said element, with reduced ohmic and thermal resistances and a reduced level of mechanical resistances, with large areas of its input and output apertures to create high-power , highly efficient, highly reliable, low noise, high aperture, semiconductor optical amplifiers, with small angles of divergence of the output radiation directed at an approximately right angle to a flat (possibly chipped) optical face, with improved distribution of the near and far radiation fields, improved temperature dependences of the output parameters of semiconductor optical amplifiers.

 The basis of the invention is the technical task of increasing the output radiation power, efficiency, reliability of a semiconductor optical amplifier, including a single-mode, single-frequency (depending on the driving source of input radiation), with large areas of its input and output apertures, while reducing the divergence angles of the output radiation, with minimizing the deviation of the direction of the output radiation from the direction of the normal to the plane (possibly chipped) of the optical face, with reduced ohmic and thermal oprotivleniyami, reduced level of mechanical stresses, with improved distribution of the near and far-field emission, improved temperature dependences of output parameters with simplification of its manufacturing technology.

In accordance with the invention, the stated technical problem is solved by the fact that the proposed semiconductor amplifying element comprising a heterostructure based on semiconductor compounds containing at least one active layer, which consists of at least one sublayer, a region of radiation leak-in, transparent to laser radiation, is at least on one side of the active layer, at least one with at least one radiation leak-in layer, consisting of at least one sublayer, heterostructure x acterized ratio of the effective refractive index n _eff of the heterostructure to the refractive index n _BT leak-in layer and also optical facets, reflectors, ohmic contacts, at least one clarifying film on an optical facet, wherein during operation of the semiconductor amplifying medium of propagation of amplified emission element are at at least part of the inflow region, at least part of the active layer, and at least two reflecting layers are additionally placed in the heterostructure, at the edge at least one on each side of the active layer having refractive indices less than n _eff and formed from at least one sublayer, the inflow region is located between the active layer and the corresponding reflective layer, two additional layers are formed in it, namely, the adjacent to the surface of the active layer, a localizing layer of the inflow region, formed of at least one sublayer, made of a semiconductor with a band gap exceeding the band gap of the active layer, and adjoin s to the surface of the confining layer, adjusting layer of the leak-formed at least of one sublayer, hereinafter in the leak-in region located leak-in layer, the ratio of n _eff to n _BT defined from the range from one minus delta to one plus delta, where delta is determined by magnitude much lesser than units, moreover, when the semiconductor amplifier element is operating, the additional medium for amplified radiation propagation is at least a part of the reflecting layer, the intensity of the amplified radiation is localized in the active layer, determined by the selected compositions and thicknesses of the heterostructure layers and the reflection coefficients of the antireflection coatings, less than its value is selected for the threshold self-excitation current density.

 A significant difference between the proposed semiconductor amplifying elements (hereinafter referred to as the PUE) consists in the comprehensive modernization of heterostructures (hereinafter referred to as the GS), in which the selection of the compositions, thicknesses, and location of its layers ensures the operation of the PUEs in the vicinity of a narrow transition region where the radiation leakage condition begins to be satisfied from the active layer. This main difference provides a solution to the technical problem.

 The proposed PUE is based on a modernized HS. Such HSs do not require the commonly used waveguide and restrictive layers of a traditional laser heterostructure, on the basis of which a traditional PUE is usually made. In the general case, the HS of the proposed PUE consists of the following layers: the inner surfaces of the localizing layers are adjacent to the active layer on both sides, the inner surfaces of the adjustment layers are adjacent to the opposite outer sides of the adjustment layers, the inner surfaces of the inflow layers are adjacent to the opposite outer sides, and the opposite outer the sides of the leak-in layers are adjacent to the inner surfaces of the reflective layers. Further, as usual, a contact semiconductor layer and a buffer layer located on a substrate can be formed to the p-type side of the HS — the contact semiconductor layer. Hereinafter, by an active layer we mean that it can be made in the form of one or more active sublayers (including those having quantum-well thicknesses) and one or more barrier sublayers located both between the active sublayers and on its two outer sides.

When the proposed PUE operates in a semiconductor optical amplifier (hereinafter referred to as "POE"), which consists of some corresponding reference source of input optical radiation - hereinafter referred to as "ZI", PUE, an optical system that connects ZI with PUE):
- introduced localizing layers are necessary for localization of current carriers (electrons and holes) in active sublayers. The localizing layers are very thin. To improve the output parameters of semiconductor injection radiation sources (hereinafter "III"), namely, the proposed PUE, it is proposed that the localizing layers be made with a thickness of not more than 0.05 μm. The band gap E _{gL of} these layers significantly exceeds the band gap E _{gAC of the} active layer,
- specially introduced adjustment layers are necessary for the ability to control the ratio of n _eff to n _BT . They are performed quite thin. To improve the output parameters of the PES, the adjustment layers in most modifications can be made with a thickness of not more than 1.0 microns. Their location immediately behind the localizing layer, as well as the selected composition of the tuning layers grown (depending on the type of semiconductor compounds used in the HS) from a semiconductor with a band gap E _gH slightly exceeding the band gap E _gAC active layers, and / or from the same composition or close to the composition of the substrate, determines the high efficiency of their use and the improvement of the output parameters of the PES.

 For a working PUE (when the leakage condition is fulfilled), the emitted radiation from the active layer through the localizing and tuning layers falls into the leak-in layer, from where it leaves the PUE after a series of reflections and rereflections inside the GS.

In contrast, in [4], the outgoing radiation through the leak-in layer exits directly. This proposed and experimentally tested leakage mechanism was implemented by introducing a reflecting layer having a refractive index n _sp , smaller than the effective refractive index n _{eff of the} heterostructure, and adjacent to the outer (relative to the active layer) surface of the leak-in layer, as well as the appropriate choice of thickness leak-in layer, and the outflow angle φ, equal to the cosine ratio n _eff to n _BT, namely φ = cos (n _eff / n _BT), and therefore, the ratio n _eff and n _BT, selected in the range from one minus delta to uniqueness tzu plus delta, where delta is determined by a number much smaller than unity. Therefore, the compositions and thicknesses of the PUE layers are selected such that, during its operation, radiation from the active layer to the inflow region occurs, at least in the vicinity of its initial transition stage. The transition point of the leakage process is the condition of equality of n _eff and n _VT .

If n _{eff is} noticeably greater than n _VT , then leakage is practically absent, and we have the usual PUE without leakage, if n _{VT is} noticeably greater than n _eff , then there is a very strong leakage, and the sensitivity of the PUE in the region of low radiation power of the ZI will be unacceptably low. Note that the value of n _eff decreases with increasing current flowing through the PUE in the working device. In this regard, we introduced the universal parameter β equal to the ratio of n _eff to n _BT , namely β = (n _eff / n _BT ), which characterizes the suitability of using the proposed PUE. This range of β values that we estimated by calculation is very narrow, namely from unity minus delta to unity plus delta, where delta is determined by a number much less than unity.

 It is proposed that, at least for a part of the range of operating currents, the parameter β be determined from a range of less than one or more than one minus delta, to narrow the radiation pattern, increase efficiency, reduce radiation density at the output face and solve other problems (the leakage condition is fulfilled).

In some modifications, for at least part of the range of operating currents, the ratio of n _eff to n _VT , determined by the compositions and thicknesses of the heterostructure layers, is chosen to be less than unity and more than 0.99, or near unity, or equal to unity to obtain leakage in the PUE.

 To exclude self-excitation of the PUE, it is necessary that, during its operation, the intensity of amplified radiation localized in the active layer, determined by the selected compositions and thicknesses of the heterostructure layers and reflection coefficients of the antireflective coatings, be chosen less than its value at a threshold self-excitation current density. With sufficient leakage radiation intensity increasing with increasing current, the self-excitation threshold for the proposed SCEs can be obtained at significantly higher currents than in the conventional SCEs currently in use. At the same time, this leads to a significant simplification of the requirements for antireflection coatings. In the proposed PUEs, the input and output apertures can be formed, unlike conventional PUEs, matched with the aperture of the optical fiber. In this case, the input signal input and output output amplified radiation from the PUE can be carried out using optical fiber directly without the use of additional matching elements.

 During operation of the PUE due to the interference summation of the resulting rays, the output radiation will be directed perpendicular to the planes of the optical faces. This is ensured by the available layers and their sequence in the GS PUE, the choice of their compositions, thicknesses. The same makes it possible to reduce the thickness of the inflow layers, which made it possible to grow HS for PUE in one technological cycle.

 The stated technical problem is solved in that in the PUE optical faces are located almost perpendicular to the plane of the active layer. Therefore, it is possible to use simple and conventional cleavage of the HS plate, in which the chipped faces are perpendicular to the plane of the active layer, which greatly simplifies the manufacturing process of PUE and its further use.

 The problem is also solved by the fact that to reduce the internal non-resonant losses that determine the effectiveness of the proposed PUE, the leakage layer, localizing and tuning layers, are unalloyed. In addition, part of the reflective layer adjacent to the leakage layer is also non-alloyed.

The proposed PUE with the introduced localizing and adjustment layers makes it possible to choose the optimal composition for improving the laser parameters for the leak-in layer. Typically, the inflow layers of the inflow regions have the same composition. It must be transparent and can be made of a semiconductor having the same composition as the substrate or similar in composition to it. In some cases, it is advisable that the band gap E _{gBT of the leak-in} layer differs from the band gap E _{gP of the} substrate by no more than 0.25 eV. In this case, the ohmic and thermal resistances will be reduced, the level of elastic mechanical stresses in the structures will be reduced, and at the same time, the temperature dependences of the device parameters will be reduced, which leads to their greater efficiency, stability, power, to a longer resource of their work and reliability.

 The stated technical problem is also solved by the fact that in order to improve the output parameters of the PUE, it is proposed that the tuning layer be made of a semiconductor that is close or equal in composition to the substrate on which the heterostructure is grown.

 In the next version, allowing to solve the problem, it is proposed that at least one localizing layer and / or one adjustment layer be grown with compositions identical or close to the composition of the inflow layer.

In the following modification, in order to improve the radiation distribution in the near and far field, it is proposed to form at least one of the sublayers of the leak-in layer with a refractive index less than n _eff , while the thickness is much less than the total thickness of the leak-out layer.

To solve the same technical problem posed and to control the parameter β = (n _eff / n _BT ) in the initial current region, it was proposed that at least one of the sublayers of the reflecting layer be grown with the same composition as the inflow layer.

 To improve the parameters of the PUE in the visible red region of the spectrum based on HS from AlGaInP compounds, it was proposed that only a thin active layer and a localizing layer be made on the basis of AlGaInP compounds, and the leak-in, adjustment and reflective layers should be made on the basis of AlGaAs compounds.

 To increase the radiation power of the PUE, it is proposed to place at least two active layers, the planes of which are parallel to each other, and between them there are p- and n-type layers separating them of the required thicknesses and doping levels to ensure tunneling current flow from one active layer when the device is operating to another.

The stated technical problem is also solved by the fact that a semiconductor optical amplifier is proposed, including an optically coupled driving source of input radiation and a semiconductor amplifying element comprising a heterostructure based on semiconductor compounds containing at least one active layer consisting of at least one sublayer, transparent to laser radiation region of the influx of radiation from at least one side of the active layer, at least one with at least one layer percolation radiation, consisting at least of one sublayer, said heterostructure is characterized by the ratio of the effective refractive index n _eff of the heterostructure to the refractive index n _BT leak-in layer and also optical facets, reflectors, ohmic contacts, at least one clarifying film on an optical facet.

Moreover, during the operation of the semiconductor amplifier element, the medium of propagation of the amplified radiation is at least a part of the leak-in region, at least a part of the active layer, and at least two reflecting layers, at least one on each side of the active layer, having indicators refractions less than n _eff and formed from at least one sublayer, the leak-in region is located between the active layer and the corresponding reflective layer, in which Two additional layers, namely, a localizing layer adjacent to the surface of the active layer, formed from at least one sublayer, made of a semiconductor with a band gap greater than the width of the forbidden zone of the active layer, and an adjustment layer adjacent to the surface of the localizing layer, are introduced formed from at least one sublayer, then a leak-in layer is located in the inflow region, the ratio of n _eff to n _{W is} determined from the range from unity minus delta to unity p lus delta, where the delta is determined by a number much less than unity, and when the semiconductor amplifier element is operating, the additional propagation medium of the amplified radiation is at least part of the reflective layer, and the intensity of the amplified radiation localized in the active layer, determined by the selected compositions and thicknesses of the heterostructure layers and reflection coefficients antireflective coatings, less than its value is selected at a threshold current density of self-excitation.

 A significant difference between the proposed semiconductor optical amplifiers (hereinafter referred to as “POE”) consists in the comprehensive modernization of heterostructures (hereinafter referred to as “GS”), in which by selecting the compositions and thicknesses of its layers the POE is ensured in the vicinity of a narrow transition region, where the condition for radiation leakage from the active PUE layer. This main difference provides a solution to the technical problem.

 The proposed POE is based on a modernized PUE, its modernized GS. Such HSs do not require the commonly used waveguide and restrictive layers of a traditional laser heterostructure, on the basis of which a traditional POC is usually made. In the general case, the PUE of the proposed POC consists of the following layers: the inner surfaces of the localizing layers are adjacent to the active layer on both sides, the inner surfaces of the adjustment layers are adjacent to the opposite outer sides of the adjustment layers, the inner surfaces of the inflow layers are adjacent to the opposite outer sides, to the opposite outer the sides of the leak-in layers are adjacent to the inner surfaces of the reflective layers. Further, as usual, a contact semiconductor layer and a buffer layer located on a substrate can be formed to the p-type side of the HS — the contact semiconductor layer. Hereinafter, by an active layer we mean that it can be made in the form of one or more active sublayers (including those having quantum-well thicknesses) and one or more barrier sublayers located both between the active sublayers and on its two outer sides.

When the proposed POW works with the proposed PUE
- introduced localizing layers are necessary for localization of current carriers (electrons and holes) in active sublayers. The localizing layers are very thin (to improve the output parameters of the POC, it is proposed that the localizing layers be made with a thickness of not more than 0.05 μm) with the band gap E _{gL of} these layers significantly exceeding the band gap E _{gAC of the} active layer.

- specially introduced adjustment layers are necessary for the ability to control the ratio of n _eff to n _BT . They are performed quite thin. To improve the output parameters of the POC, the adjustment layers in most modifications can be made with a thickness of not more than 1.0 microns. Their location immediately behind the localizing layer, as well as the selected composition of the tuning layers grown (depending on the type of semiconductor compounds used in the HS) from a semiconductor with a band gap E _gH slightly exceeding the band gap E _gAC active layers, and / or from the composition, the same or close to the composition of the substrate, determines the high efficiency of their use and the improvement of the output parameters of the PES.

For the working proposed POC, when the leakage condition in the PUE is fulfilled, the effluent radiation from the active layer through the localizing and tuning layers enters the leak-in layer, from where it leaves the POC after a series of reflections and rereflections inside the GS. This proposed and experimentally tested leakage mechanism was implemented by introducing a reflective layer having a refractive index n _sp , smaller than the effective refractive index n _{eff of the} entire heterostructure and adjacent to the outer (with respect to the active layer) surface of the leak-in layer, as well as the appropriate choice the thickness of the inflow layer and the outflow angle φ equal to the cosine of the ratio of n _eff to n _BT , namely φ = cos (n _eff / n _BT ), and, therefore, the ratio of n _eff and n _VT , selected in the range from unity minus delta to units plus delta, where the delta is determined by a number much less than one. Therefore, the compositions and thicknesses of the layers of the heterostructure are selected so that during the operation of the POC, the radiation from the active layer of the PUE to the inflow region occurs at least in the vicinity of its initial transition stage. Note that the value of n _eff decreases with increasing current flowing through the PUE. The transition point of the leakage process is the condition of equality of n _eff and n _VT . In this regard, we proposed a universal parameter β equal to the ratio of n _eff to n _BT , namely β = (n _eff / n _BT ), which characterizes the suitability of using the proposed POE. This range of β values that we estimated by calculation is very narrow, namely, from unity minus delta to unity plus delta, where delta is determined by a number much less than unity.

It has been proposed that, at least for a part of the range of operating currents, the ratios of n _eff to n _{VT should} be determined from a range of less than one or more units minus delta, where the delta is determined by a number much less than unity (in this case, the condition for leakage in the PUE of the proposed POC is fulfilled). This leads to a narrowing of the radiation pattern, an increase in efficiency, a decrease in the radiation density at the output face, the practical absence of gain saturation up to the maximum values of operating currents, and to solving other problems.

In some modifications, for at least part of the range of operating currents, the ratios n _eff to n _W , determined by the compositions and thicknesses of the heterostructure layers, are selected to be less than unity and more than 0.99, or near unity, or equal to unity to obtain the proposed POE in the PUE.

 To exclude self-excitation of the PUE of the proposed POE, it is necessary that, during its operation, the intensity of amplified radiation localized in the active layer, determined by the selected compositions and thicknesses of the heterostructure layers and reflection coefficients of the antireflection coatings, be less than its value at the threshold self-excitation current density. With sufficient leakage radiation intensity increasing with increasing current, the self-excitation threshold for the proposed POCs can be obtained at significantly higher currents than in the conventional POCs currently used. At the same time, this leads to a significant simplification of the requirements for antireflection coatings.

 In the proposed POC, the input and output apertures can be formed, unlike conventional POCs, matched with the aperture of the optical fiber. In this case, the input signal and the output of the amplified radiation output from the PUE can be carried out using an optical fiber directly without the use of additional matching elements.

 When working with the proposed PUE PUE due to the interference addition of the resulting rays, the output radiation will be directed perpendicular to the planes of the optical faces. This is ensured by the available layers and their sequence in the HS, used in the POE for the manufacture of at least PUE, by the choice of compositions and thicknesses of the layers of the said HS. The same makes it possible to reduce the thickness of the leak-in layers, which makes it possible to grow the mentioned HS in one technological cycle.

  The stated technical problem is solved by the fact that in the POC optical faces are located almost perpendicular to the plane of the active layer. Therefore, it is possible to use simple and ordinary cleavage of the HS plate, in which the chipped faces are perpendicular to the plane of the active layer of the SC PUE, which greatly simplifies the manufacturing process of the PUE for the proposed POC and the further use of the POC.

 The problem is also solved by the fact that to reduce the internal non-resonant losses that determine the effectiveness of the proposed POC, the leakage layer, localizing, tuning layers of the PUE are unalloyed. In addition, part of the reflective layer adjacent to the leakage layer is also non-alloyed.

The proposed POC with the introduced localizing and training layers allows one to choose the optimal composition for improving the POC parameters for the inflow layer. Typically, the inflow layers of the inflow regions have the same composition. The leak-in layer must be transparent and may be made of a semiconductor having the same composition as the substrate or similar in composition to it. In some cases, it is advisable that the band gap E _{gBT of the leak-in} layer differs from the band gap E _{gP of the} substrate by no more than 0.25 eV. In this case, the ohmic and thermal resistances will be reduced, the level of elastic mechanical stresses in the structures will be reduced, and at the same time, the temperature dependences of the device parameters will be reduced, which leads to their greater efficiency, stability, power, to a longer resource of their work and reliability.

 The stated technical problem is also solved by the fact that in order to improve the output parameters of the POC, it is proposed that the tuning layer be made of a semiconductor that is close or equal in composition to the substrate on which the heterostructure is grown.

 In the next version, allowing to solve the problem, it is proposed that at least one localizing layer and / or one adjustment layer be grown with compositions identical or close to the composition of the inflow layer.

In the following modification, in order to improve the radiation distribution in the near and far field, it is proposed to form at least one of the sublayers of the leak-in layer with a refractive index less than n _eff , while the thickness is much less than the total thickness of the leak-out layer.

To solve the same technical problem posed and to control the parameter β = (n _eff / n _BT ) in the initial current region, it was proposed that at least one of the sublayers of the reflecting layer be grown with the same composition as the inflow layer.

 To improve the parameters of the POC in the visible red spectrum of the spectrum based on HS from AlGaInP compounds, it was proposed that only a thin active layer and a localizing layer be made on the basis of AlGaInP compounds, and the leak-in layer, the adjustment and reflective layers should be made on the basis of AlGaAs compounds.

 To increase the radiation power of the POC, it was proposed to place at least two active layers, the planes of which are parallel to each other, and between them arrange p- and n-type layers separating them of the required thicknesses and doping levels to ensure tunneling current flow from one active layer during operation of the device to another.

 Creating a high-power, including single-mode or single-frequency radiation source, is possible using a combination of a master laser with high quality radiation and high-power PUE, connected directly. For conventional lasers and amplifiers this is almost impossible due to the small size of their input and output apertures. In the proposed POC, the manufacture of this combination becomes possible, because the size of the aperture of the PUE is ten times larger than the size of the aperture of conventional amplifying elements of the POC

 For a number of cases, it is advisable to produce a source of input radiation in the form of an injection laser and a semiconductor amplifying element from the same heterostructure and place them on one longitudinal optical axis at the shortest distance between them.

 In another modification, it is proposed that the injection laser and the semiconductor amplifier element be made of similar heterostructures, wherein the thicknesses of the leak-in layers of the semiconductor amplifier element exceed the corresponding thicknesses of the leak-in layers of the injection laser.

 In other cases, the combination of ZI - PUE can be performed in such a way that the adjacent optical faces of the injection laser and the semiconductor amplifier element are optically connected using an optical matching element. Such an element may be, for example, a collimating lens or optical foclin.

 Modifications are possible when the width of the strip region of the current flow of the semiconductor amplifier element is greater than the width of the strip region of the current of the injection laser, or when the width of the strip region of the current flow of the semiconductor amplifier element is expandable.

 As an injection laser, it was proposed to choose an injection laser (hereinafter referred to as the “Laser”), which is similar in design to the PUE considered here, characterized by coatings on optical faces (for PUEs it is antireflective, and for the Laser it is reflective).

Such a laser includes a semiconductor-based heterostructure containing at least one active layer, consisting of at least one sublayer, a region of radiation leak-in, transparent to laser radiation, on at least one side of the active layer, at least one with at least one one layer of radiation leak-in, consisting of at least one sublayer, moreover, at least two reflecting layers are placed in the heterostructure, at least one on each side of the active layer, having refractive indices less than n _eff and formed from at least one sublayer.

The leak-in region is located between the active layer and the corresponding reflective layer, two additional layers are formed in it, namely, the localization layer of the leak-in region adjacent to the surface of the active layer, formed from at least one sublayer, made of a semiconductor with a band gap exceeding the band gap active layer, and a tuning layer adjacent to the surface of the localizing layer, the inflow region, formed from at least one sublayer, then in the inflow region leak-in layer is false. The heterostructure is characterized by the ratio of the effective refractive index n _{eff of the} heterostructure to the refractive index of n _{VT of the} leak-in layer, namely, the ratio of n _eff to n _{VT is} determined from the range from unity minus delta to unity plus delta, where the delta is determined by a number much smaller than unity. The laser also includes optical faces, reflectors, ohmic contacts, an optical resonator, in which at least part of its medium is made up of at least part of the leak-in region, at least part of the active layer, and at least part of the additional optical cavity medium is also reflective layer. In this case, when the injection laser is operating for specified values of suprathreshold currents, the intensity of the laser radiation localized in the active layer, determined by the compositions and thicknesses of the heterostructure layers, is chosen not less than its value necessary to maintain the laser generation threshold.

In various modifications of the Laser, it is assumed that during its operation
- the ratio of n _eff to n _{BT is} determined from the range from 0.99 to 1.01;
- at least for a part of the interval of values of suprathreshold currents, the ratios n _eff to n _{VT are} determined from the range of less than one and more than one minus delta;
- at least for a part of the interval of values of suprathreshold currents, the ratios n _eff to n _{VT are} determined from the range of less than unity and more than 0.99;
- for values of threshold current densities and less, the ratios n _eff to n _{VT are} determined from the range from one to one plus delta;
- for the values of the densities of threshold currents and less, the ratios n _eff to n _{VT are} determined from the range from unity to 1.01;
- for the values of the densities of threshold currents and less, the ratios n _eff to n _{VT are} determined from the range from one to one minus delta;
- for values of threshold current densities and less, the ratios n _eff to n _{VT are} determined from the range from 0.99 to unity;
- in a given interval of suprathreshold currents, leakage angles φ equal to the cosines of the ratios n _eff to n _VT do not exceed their values, above which the single-mode operation of the injection laser is destroyed;
- at least for a part of the interval of values above the threshold currents, the intensity of the laser radiation localized in the active layer does not exceed the value of the intensity above which the single-frequency mode of operation is destroyed.

In addition, in various modifications of the Laser, it is assumed that
- the leak-in layer is made of a thickness of not more than twice the length of the optical cavity, multiplied by the tangent of the leak-out angle equal to the cosine of the ratio of n _eff to n _W ;
- optical faces are perpendicular to the plane of the active layer;
- the localizing layer has a thickness of not more than 0.05 μm;
- the adjustment layer has a thickness of not more than 1.0 μm;
- leak-in layers of both leak-in regions have the same composition;
- leak-in layer, localizing and adjustment layers are made undoped;
- part of at least one reflective layer adjacent to the inflow layer is made unalloyed;
- at least one of the sublayers of the reflective layer has a composition identical to that of the inflow layer;
- the active layer and the localizing layer are made on the basis of AlGaInP type compounds, and the leak-in layer, the adjustment and reflective layers are made on the basis of AlGaAs type compounds;
- at least two active layers are placed, the planes of which are parallel to each other, and between them p-type and n-type layers are located that provide tunneling current flow from one active layer to another during operation of the device;
- the band gap of the leak-in layer differs from the band gap of the substrate on which the heterostructure is grown, by no more than 0.25 electron-volts;
- the adjustment layer has the same composition as the substrate on which the heterostructure is grown;
- at least one localizing layer has a composition identical to that of the inflow layer;
- at least one adjustment layer has a composition identical to that of the inflow layer.

 The essence of the present invention is the proposed new non-obvious PUE and, on its basis, a new non-obvious PUE, created on the basis of a new modernized HS, in which the selected compositions, thicknesses and location of its layers ensure the functioning of PUE and POE in the region of the transition regime of radiation leakage from the active layer. This makes it possible to control the output of radiation approximately normal to the cleaved optical faces, to obtain large input and output apertures, a small angle of divergence of radiation, the amplification mode of one spatial mode, one longitudinal frequency, high efficiency, low ohmic and thermal resistances, low level of mechanical stresses and as a consequence of this, high radiation power with its high quality and reliability. The technology for obtaining the proposed PUEs and POEs is also simplified, which is close to the technology for manufacturing modern injection lasers, primarily because of the possibility of epitaxial growth of the leak-in layer in the same process of manufacturing a heterostructure and due to the absence of the need to fabricate inclined optical faces, as well as for a significant reduction in the requirements for the reflection coefficient of antireflection coatings for them.

 The technological implementation of the invention is not difficult, based on well-known basic technological processes that are currently well developed and widely used in the manufacture of injection lasers and therefore the proposal meets the criterion of "industrial applicability". The main difference in their manufacture consists only in other compositions and thicknesses of the grown heterostructure layers.

Brief Description of the Drawings
The present invention is illustrated in FIG. 1-4.

 Figure 1 schematically shows a longitudinal section of the proposed PUE with antireflective coatings on the optical faces with two different thickness inflow regions located on both sides of the active layer.

 Figure 2 schematically shows a longitudinal section of the proposed PUE with antireflection coatings on the optical faces with symmetrically located two areas of inflow on both sides of the active layer.

 Figure 3 schematically shows a longitudinal section of the PUE with antireflection coatings on the optical faces with two optical fibers attached to them and with two equal-thickness inflow regions adjacent to the active layer.

 Figure 4 schematically shows a longitudinal section of the proposed PUE with antireflection coatings on the optical faces with one inflow region, in which the localizing, tuning and inflow layers are made of the same composition.

 Figure 5 schematically shows a longitudinal section of the proposed PUE with antireflective coatings on optical faces with one inflow region, in which the localizing, tuning and inflow layers are made of the same composition, and one of the reflective layers is made of three sublayers.

 Figure 6 schematically shows a longitudinal section of a POC with a master laser autonomously located on the same optical axis with reflective coatings on the optical faces and PUE with antireflective coatings on the optical faces made of the same HS with two equally thick inflow regions adjacent to the active layer .

Embodiments of the invention
The invention is further explained in the specific options for its implementation with reference to the accompanying drawings. The above examples of modifications of the PUE and POU are not unique and suggest the presence of other implementations, the features of which are reflected in the totality of the features of the claims.

The proposed PUE 1 (see Fig. 1), used mainly in POE, contains an active layer 2, to which two inflow areas 3 and 4 are adjacent on both sides. Into inflow regions 3 and 4 from both sides external to the active layer 2 two reflecting layers 5 and 6 are adjacent. The reflecting layer 6 is located on the side of the n-type substrate 7. The inflow regions 3 and 4 contain one localizing layer 8 and 9 adjacent to the active layer 2 on both opposite sides thereof, one adjustment layer 10 and 11 adjacent to the localizing layers 8 and 9, respectively, and one inflow layer 12 and 13 adjacent to the adjustment layers 10 and 11. Active layer 2 consisted of five sublayers (not shown): two active sublayers of InGaAs and three barrier layers of GaAs of standard thicknesses and compositions [5]. The radiation wavelength of the amplified PUE made of such a heterostructure is 980 nm. The localizing layers 8 and 9 had the same composition of Al _0.40 Ga _0.40 As and the same thickness 0.03 μm. The adjustment layers 10 and 11 were grown from GaAs, the thickness of layer 10 is 0.3 μm, and layer 11 is 0.15 μm. The leak-in layers 12 and 13 were grown from Al _0.05 Ga _0.95 As, while the thickness of layer 12 was 1.0 μm, and that of layer 13 was 5.0 μm. The reflective layers 5 and 6 had the same composition of Al _0.09 Ga _0.91 As and the same thickness of 1.0 μm. The selected compositions and layer thicknesses of the GS PUE 1 provided the calculated values of the parameter β equal to 1.00015 and 0.99971, respectively, at current densities j equal to 50 A / cm ² and 20,000 A / cm ² . The equality of n _eff and n _VT took place at current densities of 1100 A / cm ² . The calculated angle of divergence θ _⊥ in the vertical plane at a current density of 12,000 A / cm ² is equal to 9.3 ^o (at the level of 0.5).

From the grown HS, the proposed PUE 1 was made (see Fig. 1). In such a PUE 1, ohmic metallization layers not shown in the figures are applied to an n-type substrate 7 and a p-type contact layer (not shown). The length of the PUE 1 L _PUE selected equal to 1600 μm. The cleaved facets 14 of the HS are coated with antireflection coatings 15 and 16 with equal reflection coefficients R ₁ and R ₂ equal to 0.5%. Strip active regions of current flow had a strip width of 10 μm. To exclude self-excitation of PUE 1 at all current values, the intensity of amplified radiation localized in active layer 2, determined by the compositions and thicknesses of the heterostructure layers and the coefficients R ₁ and R ₂ , is chosen less than its threshold value of self-excitation up to current densities of 20,000 A / cm ² and more . The condition for leakage of radiation from the active layer 2 into the leak-in layers 12 and 13 begins to be satisfied when the value of j exceeds 1100 A / cm ² . The leakage angle φ in this case increases from 0 ^o for j equal to 1100 A / cm ² to 1.37 ^o for j equal to 20,000 A / cm ² . The input aperture of this PUE 1 is 6 • 10 μm ² , and the angular aperture in the vertical plane is 9.3 ^o . Such PUE 1 practically does not have gain saturation, up to its limiting currents, determined only by overheating of its faces.

The next modification of PUE 1 (see Fig. 2), used mainly in POE, differed from the previous one in that the thickness of the leak-in layers 12 and 13 were the same and equal to 5 μm, and the thickness of the adjustment layers 10 and 11 were the same and equal to 0, 23 microns. For this modification of PUE 1, the calculated values of the parameter β at current densities of 50 A / cm ² and 20,000 A / cm ² were respectively 1,00036 and 0.99973. The equality of n _eff and n _VT took place at a current density of 2800 A / cm ² . The calculated angle of divergence θ _⊥ in the vertical plane at a current density of 12,000 A / cm ² is equal to 3.9 ^o .

 The next modification of PUE 1 (see Fig. 3) used in the POE differed from the previous composition of the layers, calculated for a radiation wavelength of 1310 nm, and that optical fibers were connected to the optical faces with coated coatings 15 and 16: input 17 for inputting radiation through the input optical face 14 with coating 15 and output 18 for outputting radiation from the opposite optical face 14 with coating 16. Large areas of the input and output apertures with matched angular apertures of the optical fibers 17 and 18 and PUE 1 allow fibers 17 and 18 directly without additional connecting elements.

This modification can be used with great efficiency as power amplifiers (and possibly preamplifiers) in modern fiber-optic communication lines. Its main advantages - low radiation losses when it is introduced into PUE 1 determine its low noise - the noise factor can be lower than 2..3 dB, which is comparable with fiber amplifiers, a symmetric waveguide with an area of 10 • 10 μm ² sharply reduces its sensitivity to input polarization signal, low signal amplification of the signal can be achieved more than 45.. 55 dB, and the amplified power without saturation in PUE 1 can reach 1..2 W and is limited mainly by thermal overheating. The advantage of PUE 1 is also a small angle of divergence θ _⊥ in the vertical plane, decreasing with increasing current density from 11.7 ^o to 4.9 ^o .

The difference between the following modification of PUE 1 (see Fig. 4) used in the POC and the modification depicted in Fig. 1 is that it forms one leak-in region 4, which is made from the side of the substrate 7. It has a leak-in layer 13 is made of the same composition as the localizing layer 9 and the adjustment layer 11, namely from Al _0.21 Ga _0.79 As. In this modification, on the p-type side, the reflecting layer 5 directly borders on the active layer 2. For this modification of the PUE 1, the calculated values of the parameter β at current densities of 50 A / cm ² and 20,000 A / cm ² were respectively 0.999912 and 0, 999648. Leakage in such a structure was present at all current values, while the leakage angle increased with a current from 0.8 ^o to 1.5 ^o . The calculated angle of divergence θ _⊥ in the vertical plane at a current density of 12,000 A / cm ² is 11.7 ^o (at the level of 0.5).

The difference between the next modification of PUE 1 (see Fig. 5) from the previous one is that in it the reflective layer 5 is formed of three sublayers: the first sublayer 19, which does not differ in composition from the reflective layer 5 in the previous modification and adjacent to the active layer, the second sublayer 20, having the same composition as the leak-in layer 13, and the third sublayer 21, having a refractive index smaller and the band gap E _gOTP greater than in the first sublayer 19. For this modification, the angle θ _{⊥ is} reduced to 9.5 ^o . Another modification is possible in which a reflective layer, divided into three similar sublayers, adjoins with its sublayer 14 to the outer surface of the leak-in layer parallel to the plane of the active layer. A decrease in the calculated divergence angle θ _{⊥ is} also obtained here.

 The next modification of PUE 1 used in the POC, with a laser wavelength of 650 nm, differed from the modification schematically depicted in figure 1, in that a thin active layer 2 was grown from GaInP in it, and thin localizing layers 8 and 9 were grown from AlGaInP, a all other thick inflow layers 12, 13 with a thickness of 1.2 μm and 3.0 μm, respectively, reflective 5 and 6 and tuning 10 and 11 are grown from AlGaAs, transparent for a wavelength of 650 nm.

 The next modification of PUE 1 used in the POC differed from the modification schematically depicted in FIG. 1 in that it has two active layers 2, the planes of which are parallel to each other and to the surfaces of the compounds of these layers, namely the surfaces of adjacent barrier sublayers included in the composition of active layers 2. These sublayers are made in this case with heavily doped n- and p-type layers. The p-type sublayer is placed on the side of the n-type substrate 7, and the n-type layer is on the side of the reflective layer. Such sublayers provide tunneling current flow during operation of the device. It has high efficiency.

The proposed POC (see Fig. 6) includes a driving input radiation source made in the form of a Laser 22 optically coupled to the PUE 1. The laser 22 and the PUE 1 are made using the same HS modification described above in the description of the PUE 1 and schematically shown in FIG. 2, as part of the design of the PUE 1. In the manufacture of Laser 22, ohmic metallization layers not shown in the figures were formed on the p-type contact layer (not shown) and the substrate 7. The length of the optical resonator L _cut Laser 22 is selected equal to 1000 μm. Reflected coatings 24 and 25, respectively, with reflection coefficients R ₁ equal to 95% and R ₂ equal to 5% are applied to the cleaved faces 23. Strip active regions were made with a strip width of 10 μm. In this master laser, the threshold current density j _pores is 250 A / cm ² .

The calculated angle of divergence θ _⊥ (at the level of 0.5) in the vertical plane at a current density of 12000 A / cm ² is equal to 3.9 ^o . The differential efficiency η _d was 85%, and the radiation power in one spatial mode was 0.5 W.

 As the PUE selected PUE 1 of the second modification, shown schematically in figure 2. The implementation of PUE 1 was carried out in accordance with example 1.

The input aperture of this PUE 1 is 10 • 10 μm ² , and the angular aperture in the vertical plane is 3.9 ^o . Such a PUE 1 has practically no gain saturation, up to its limiting currents, determined only by overheating of the face. The large and identical output aperture of the master laser and the input aperture of PUE 1 make it possible to align the master laser and PUE 1 on the same longitudinal optical axis with the shortest distance between them with sufficient accuracy and small losses of radiation. Such a POC is a powerful source of high-quality both single-mode and single-frequency radiation. At the output of the POC, a radiation power of 5 W was obtained in one mode.

The next modification of the POC differed from the previous one in that in PUE 1 with a total thickness of the inflow layers 12 and 13 equal to 10 μm, the width of the strip for the current flow was expandable from 10 μm at the input to 50 μm at the output. In this case, in one mode, a radiation power of 12.5 W was obtained, while in the vertical plane the divergence angle θ _⊥ is 3.9 ^o , and in the horizontal plane the divergence angle θ _∥ is 1.2 ^o .

 Thus, the proposed effective high-aperture high-speed low-noise, with reduced sensitivity to the input signal polarization, with practically no saturation of the amplified emission of PUEs and high-power high-performance high-performance high-performance POC with small angles of divergence of the output radiation directed at an almost right angle to a flat optical face, with an improved distribution of the near and far radiation fields, improved temperature dependences of output parameters and simplified technological by the manufacturing process.

Industrial applicability
PUE and POE are used in fiber-optic communication and information transfer systems, in optical superhigh-speed computing and switching systems, when creating medical equipment, laser technological equipment, lasers with doubled frequency of generated radiation, and also for pumping solid-state and fiber amplifiers and lasers.

Sources of information
1. S. O'Brien et al., IEEE J. of Quant. Electr. (1993), vol. 29, No.6, pp. 2052-2057.

 2. J.P. Donnelly et al., IEEE Phot. and Techn. Letters (1996), vol. 8, pp. 1450-1452.

 3. L. Goldberg et al., IEEE J. of Quant. Electr. (1993), vol.29, No.6, pp.2028-2042.

 4. Patent 2134007 RU [State Unitary Enterprise Research Institute "POLE", V.I. Shveikin, RF] 03/12/1998, H 01 S 3/19.

 5. Patent 2142665 RU (D-LED, LTD, US) 10.08.1998, H 01 S 3/19.

Claims (25)

1. A semiconductor amplifying element comprising a heterostructure based on semiconductor compounds, containing at least one active layer, consisting of at least one sublayer, a region of radiation leak-in from at least one side of the active layer, transparent to laser radiation, at least one, at least one layer of radiation leak, consisting at least of one sublayer, said heterostructure is characterized by the ratio of the effective refractive index n _eff of the heterostructure to exponents w refraction n _Mo layer of the leak, as well as optical facets, reflectors, ohmic contacts, at least one clarifying film on an optical facet, wherein during operation of the semiconductor amplifying medium propagation member amplified emission is at least part of the leak-in region, at least part of the active layer, characterized in that the heterostructure is additionally placed at least two reflective layers, at least one on each side of the active layer having refractive indices smaller than n _eff and formed from at least one sublayer, the leak-in region is located between the active layer and the corresponding reflective layer, two additional layers are formed in it, namely, the localization layer of the leak-in region adjacent to the surface of the active layer, formed at least from one sublayer made of a semiconductor with a band gap exceeding the band gap of the active layer and adjacent to the surface of the localizing layer, the adjustment layer of the inflow region is formed nny at least of one sublayer, hereinafter in the leak-in region located leak-in layer, the ratio of n _eff to n _Mo determined within the range from one minus delta to one plus delta, where delta is determined by a number much lesser than one, and when the semiconductor amplifying additional element The propagation medium of the amplified radiation is at least part of the reflective layer, and the intensity of the amplified radiation localized in the active layer, determined by the compositions, thicknesses of the heterostructure layers and reflection coefficients antireflective coating is chosen less than its magnitude at the threshold density of self-excitation current. 2. The semiconductor amplifying element according to claim 1, characterized in that during its operation, the ratios n _eff to n _{W are} determined from the range from 0.99 to 1.01 and at least for a part of the range of operating currents of the ratio n _eff to n _W defined from a range of unity to 1.01. 3. The semiconductor amplifier element according to any one of paragraphs. 1 and 2, characterized in that during its operation, for at least part of the range of operating current values, the ratios n _eff to n _{watt are} determined from a range of less than one or more than one minus delta.  4. The semiconductor amplifier element according to any one of paragraphs. 1-3, characterized in that the opposite optical faces coated with antireflection coatings are optically connected to the optical fibers so that the longitudinal axis of the optical fibers and the semiconductor amplifier element are aligned.  5. The semiconductor amplifier element according to any one of paragraphs. 1-4, characterized in that the leak-in layer, the localizing layer, the adjustment layer and the part of at least one reflective layer adjacent to the leak-in layer are made unalloyed.  6. The semiconductor amplifier element according to any one of paragraphs. 1-5, characterized in that the inflow layers in the inflow areas are made identical in composition.  7. The semiconductor amplifier element according to any one of paragraphs. 1-6, characterized in that at least one of the sublayers of the reflective layer has a composition identical to that of the inflow layer.  8. The semiconductor amplifier element according to any one of paragraphs. 1-7, characterized in that the active layer and the localizing layer are made on the basis of AlGaInP compounds, and the leak-in layer, the adjustment and reflective layers are made on the basis of AlGaAs compounds.  9. The semiconductor amplifier element according to any one of paragraphs. 1-8, characterized in that at least two active layers are placed, the planes of which are parallel to one another, and between them are p- and n-type layers separating them, which ensure the tunneling current flow from one active layer to another when the device is operating.  10. The semiconductor amplifier element according to any one of paragraphs. 1-9, characterized in that at least one localizing layer has a composition identical to the composition of the inflow layer.  11. The semiconductor amplifier element according to any one of paragraphs. 1-10, characterized in that at least one training layer has a composition identical to the composition of the inflow layer.  12. A semiconductor optical amplifier, including an optically coupled driving source of input radiation and a semiconductor amplifier element, characterized in that the semiconductor amplifier element is made according to claim 1. 13. The semiconductor optical amplifier according to claim 12, characterized in that during its operation the ratios n _eff to n _{W are} determined from the range from 0.99 to 1.01 and at least for a part of the range of operating currents of the ratio n _eff to n _W defined from a range of unity to 1.01.  14. The semiconductor optical amplifier according to any one of paragraphs. 12 and 13, characterized in that the opposite optical faces of the semiconductor amplifier element with antireflective coatings deposited on them are optically connected to the optical fibers.  15. The semiconductor optical amplifier according to any one of paragraphs. 12-14, characterized in that the leak-in layer, localizing, adjusting layers and part of at least one reflective layer adjacent to the leak-in layer, are made unalloyed.  16. The semiconductor optical amplifier according to any one of paragraphs. 12-15, characterized in that at least one of the sublayers of the reflective layer has a composition identical to that of the inflow layer.  17. The semiconductor optical amplifier according to any one of paragraphs. 12-16, characterized in that the active layer and the localizing layer are made on the basis of AlGaInP compounds, and the leak-in layer, the adjustment and reflective layers are made on the basis of AlGaAs compounds.  18. The semiconductor optical amplifier according to any one of paragraphs. 12-17, characterized in that at least two active layers are placed, the planes of which are parallel to each other, and between them are p- and n-type layers separating them, which ensure the tunneling passage of current from one active layer to another during operation of the device.  19. The semiconductor optical amplifier according to any one of paragraphs. 12-18, characterized in that at least one localizing layer has a composition identical to that of the inflow layer.  20. The semiconductor optical amplifier according to any one of paragraphs. 12-19, characterized in that at least one training layer has a composition identical to that of the inflow layer.  21. The semiconductor optical amplifier according to any one of paragraphs. 12-20, characterized in that the driving source of the input radiation is made in the form of an injection laser.  22. The semiconductor optical amplifier according to claim 21, characterized in that the injection laser and the semiconductor amplifier element are made of the same heterostructure and are placed on the same longitudinal optical axis with the shortest distance between them.  23. The semiconductor optical amplifier according to claim 21, wherein the injection laser and the semiconductor amplifier element are made of similar heterostructures, wherein the thickness of the corresponding leak-in layer of the semiconductor amplifier element exceeds the thickness of the corresponding leak-in layer of the injection laser.  24. The semiconductor optical amplifier according to any one of paragraphs. 21-23, characterized in that the width of the strip region of the current flow of the semiconductor amplifier element is greater than the width of the strip region of the injection laser.  25. The semiconductor optical amplifier according to any one of paragraphs. 21-24, characterized in that the width of the strip region of the current flow of the semiconductor amplifying element is made expandable.

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