CN106961071B - Semiconductor optical amplifier based on ridge active region weak waveguide - Google Patents

Semiconductor optical amplifier based on ridge active region weak waveguide Download PDF

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CN106961071B
CN106961071B CN201710287611.2A CN201710287611A CN106961071B CN 106961071 B CN106961071 B CN 106961071B CN 201710287611 A CN201710287611 A CN 201710287611A CN 106961071 B CN106961071 B CN 106961071B
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layer
waveguide
optical amplifier
ridge
semiconductor optical
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CN106961071A (en
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梁磊
张建
张星
秦莉
曾玉刚
宁永强
王立军
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Changchun Institute of Optics Fine Mechanics and Physics of CAS
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Changchun Institute of Optics Fine Mechanics and Physics of CAS
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/30—Structure or shape of the active region; Materials used for the active region
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
    • H01S5/2054—Methods of obtaining the confinement

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  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Optics & Photonics (AREA)
  • Geometry (AREA)
  • Semiconductor Lasers (AREA)
  • Led Devices (AREA)

Abstract

The invention discloses a semiconductor optical amplifier based on ridge active region weak waveguide, which comprises an active layer, an upper waveguide layer and a lower waveguide layer, wherein the upper waveguide layer and the lower waveguide layer are respectively grown on the upper surface and the lower surface of the active layer, and the difference value between the refractive index of the active layer and the refractive index of the upper waveguide layer or the lower waveguide layer is smaller than or equal to a threshold value, so that a fundamental mode strong optical field is diffused to the lower waveguide layer from the active layer. The difference between the refractive indexes of the active region and the waveguide region has a limiting effect on an optical field and influences the optical field distribution, so that the size of an optical field limiting factor of the active layer is limited by limiting the difference between the refractive index of the active layer and the refractive index of the upper waveguide layer or the lower waveguide layer within a threshold value, a weak waveguide is formed, the intensity distribution of the optical field of the active layer is no longer the maximum value, the fundamental mode high optical field distribution is diffused to the upper waveguide layer and the lower waveguide layer from the original active layer, a large-size fundamental mode light spot is formed, the saturated output power and the light beam quality are improved, and the large-size fundamental mode light spot has the advantages of simple process.

Description

Semiconductor optical amplifier based on ridge active region weak waveguide
Technical Field
The invention relates to the technical field of semiconductor optical amplifiers, in particular to a ridge active region weak waveguide-based semiconductor optical amplifier.
Background
The semiconductor optical amplifier is composed of an active region and a passive region, wherein the active region is a gain region and is made of semiconductor materials, and the principle of the semiconductor optical amplifier mainly depends on the medium characteristics of an active layer and the characteristics of a laser cavity. Specifically, the active region is stimulated to emit radiation under the action of incident photons to produce optical amplification. In recent years, with the development of science and technology, semiconductor optical amplifiers have a series of advantages, such as low power consumption, large wavelength flexibility, small size, light weight, high electro-optical conversion efficiency, convenience for monolithic integration with other semiconductor optoelectronic devices, and the like. At present, a semiconductor optical amplifier with the saturation output power of more than 1W at a 1.55 mu m waveband is urgently needed in the fields of free space optical communication, eye safety laser ranging and imaging, low-jitter film-locked lasers for sampling and the like.
However, the conventional single-mode ridge waveguide semiconductor optical amplifier has a small size, a large optical confinement factor of an active region, and limits its output power to about 100mW, and the small mode size requires a lens to match an input-output single-mode optical fiber, which increases the complexity of packaging. In order to increase the saturation output power of the semiconductor optical amplifier, the mode volume needs to be increased, the differential gain needs to be reduced, the carrier lifetime needs to be reduced, the waveguide loss needs to be reduced, and the optical field limiting factor needs to be reduced by optimizing the active region structure. Therefore, in the prior art, it is proposed to make the semiconductor optical amplifier into a tapered amplification region, and increase the width of the active region to obtain high saturation output power, but this structure will parasitize a high-order mode, so that a single mode cannot be realized, and the spot mode still cannot be matched with the size of a single-mode optical fiber.
Therefore, how to develop a semiconductor optical amplifier with high saturation output power, large-size single-mode light spot, high light beam quality, simple manufacturing process, stable performance and low cost is a technical problem that needs to be solved urgently by those skilled in the art.
Disclosure of Invention
The invention aims to provide a ridge active region weak waveguide-based semiconductor optical amplifier which has the characteristics of high saturated output power, large-size single-mode light spots, high light beam quality, simple manufacturing process, stable performance and low cost.
In order to solve the above technical problems, the present invention provides a ridge active region weak waveguide-based semiconductor optical amplifier, including an active layer, and an upper waveguide layer and a lower waveguide layer respectively grown on an upper surface and a lower surface of the active layer, wherein a difference between a refractive index of the active layer and a refractive index of the upper waveguide layer or the lower waveguide layer is less than or equal to a threshold value, so that a fundamental mode strong optical field is diffused from the active layer to the upper waveguide layer and the lower waveguide layer.
Preferably, in the above semiconductor optical amplifier based on the ridge active region weak waveguide, the threshold value is in the range of 0 to 3%.
Preferably, in the above ridge active region weak waveguide-based semiconductor optical amplifier, the active layer includes:
multiple quantum wells formed by periodically and alternately growing undoped potential wells and undoped potential barriers;
and undoped boundary layers grown on the upper surface and the lower surface of the multiple quantum well.
Preferably, in the above semiconductor optical amplifier based on ridge active region weak waveguide, the thickness of the undoped boundary layer is in the range of 5nm to 50 nm.
Preferably, in the semiconductor optical amplifier based on the ridge active region weak waveguide, the semiconductor optical amplifier further includes:
the waveguide upper cladding comprises a P-type doped upper limiting layer growing on the upper surface of the upper waveguide layer and a P-type doped upper buffer layer growing on the upper surface of the upper limiting layer, and the refractive index of the P-type doped upper buffer layer is smaller than or equal to that of the P-type doped upper limiting layer.
Preferably, in the semiconductor optical amplifier based on the ridge active region weak waveguide, the semiconductor optical amplifier further includes:
the waveguide lower cladding layer comprises an N-type doping lower limiting layer growing on the lower surface of the lower waveguide layer and an N-type doping lower buffer layer growing on the lower surface of the lower limiting layer, and the refractive index of the N-type doping lower buffer layer is smaller than or equal to that of the N-type doping lower limiting layer.
Preferably, in the semiconductor optical amplifier based on the ridge active region weak waveguide, the semiconductor optical amplifier further includes:
and the P-type heavily doped electrode contact layer is arranged between the upper surface of the waveguide upper cladding layer and the lower surface of the P-surface metal upper electrode.
Preferably, in the semiconductor optical amplifier based on the ridge active region weak waveguide, the semiconductor optical amplifier further includes:
and the insulating layer covers the upper surface of a plane region formed by the upper waveguide layer and the upper surface of a ridge region formed by the upper waveguide layer cladding layer and the electrode contact layer part, and the thickness of the insulating layer ranges from 100nm to 300 nm.
Preferably, in the semiconductor optical amplifier based on the ridge active region weak waveguide, the semiconductor optical amplifier further includes:
the waveguide device comprises an N-type highly doped substrate arranged on the lower surface of the waveguide lower cladding layer and an N-surface metal lower electrode arranged on the lower surface of the N-type highly doped substrate.
Preferably, in the semiconductor optical amplifier based on the ridge active region weak waveguide, the front and rear end faces are plated with antireflection films with reflectivity less than 0.01%.
The invention provides a semiconductor optical amplifier based on a ridge active region weak waveguide, which comprises an active layer, an upper waveguide layer and a lower waveguide layer, wherein the upper waveguide layer and the lower waveguide layer are respectively grown on the upper surface and the lower surface of the active layer, and the difference value between the refractive index of the active layer and the refractive index of the upper waveguide layer or the lower waveguide layer is smaller than or equal to a threshold value, so that a fundamental mode intensity optical field is diffused to the upper waveguide layer and the lower waveguide layer from the active layer. Because the difference between the refractive indexes of the active region and the waveguide region has a limiting effect on an optical field and influences the distribution of the optical field, the size of an optical field limiting factor of the active layer is limited by limiting the difference between the refractive index of the active layer and the refractive index of the upper waveguide layer or the refractive index of the lower waveguide layer within a threshold value to form a weak waveguide, a fundamental mode strong optical field is diffused to the lower waveguide layer from the original active layer to form a large-size fundamental mode light spot, the saturated output power and the light beam quality are improved at the same time, and the method has the advantages of simple process, stable performance and low cost.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
Fig. 1 is a schematic structural diagram of a semiconductor optical amplifier based on a ridge active region weak waveguide according to an embodiment of the present invention;
fig. 2 is an N-N' cross-sectional view of a semiconductor optical amplifier based on a ridge active region weak waveguide according to an embodiment of the present invention;
fig. 3 is a cross-sectional view of an M-M' of a semiconductor optical amplifier based on a ridge active region weak waveguide according to an embodiment of the present invention;
FIG. 4 shows ridge waveguide single mode conditions at different refractive index differences between the active layer and the waveguide layer provided by embodiments of the present invention;
FIG. 5(a) is a diagram illustrating a fundamental mode optical field distribution with a 9% difference in the refractive index between the active layer and the waveguide layer provided by an embodiment of the present invention;
fig. 5(b) shows the fundamental mode optical field distribution when the difference between the refractive indices of the active layer and the waveguide layer is 1% according to the embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1, 2 and 3, fig. 1 is a schematic structural diagram of a semiconductor optical amplifier based on a ridge active region weak waveguide according to an embodiment of the present invention; fig. 2 is an N-N' cross-sectional view of a semiconductor optical amplifier based on a ridge active region weak waveguide according to an embodiment of the present invention; fig. 3 is a cross-sectional view of an M-M' of a semiconductor optical amplifier based on a ridge active region weak waveguide according to an embodiment of the present invention.
In a specific embodiment, the present invention provides a ridge active region weak waveguide-based semiconductor optical amplifier, comprising an active layer 4b, and an upper waveguide layer 4c and a lower waveguide layer 4a grown on the upper surface and the lower surface of the active layer 4b, respectively, the difference between the refractive index of the active layer 4b and the refractive index of the upper waveguide layer 4c or the lower waveguide layer 4a being less than or equal to a threshold value, so that a fundamental mode strong optical field distribution is diffused from the active layer 4b to the upper waveguide layer 4c and the lower waveguide layer 4 a.
Specifically, as shown in fig. 1, the structure of the semiconductor optical amplifier based on the ridge active region weak waveguide provided in this embodiment is as follows: the N-surface metal lower electrode 1, the substrate 2, the waveguide lower cladding 3, the waveguide core layer 4, the waveguide upper cladding 5, the electrode contact layer 6, the insulating layer 7 and the P-surface metal upper electrode 8 are arranged from bottom to top in sequence; an N-side metal lower electrode 1 grows on the back of the thinned substrate 2 to realize the electrical connection with the substrate 2, and a P-side metal upper electrode 8 grows on the P-type electrode contact layer 6 and the insulating layer 7 to form a P-side current injection window 9 to realize the electrical connection with the P-type electrode contact layer 6; the waveguide core layer 4 is positioned between the waveguide upper cladding layer 5 and the waveguide lower cladding layer 3, comprises a lower waveguide layer 4a, an active layer 4b and an upper waveguide layer 4c, and sequentially grows on the waveguide lower cladding layer 3; the waveguide upper cladding layer 5 comprises an upper limiting layer 5a and an upper buffer layer 5b, which are grown on the active layer 4b in sequence; the waveguide lower cladding layer 3 includes a lower buffer layer 3a and a lower confinement layer 3b, which are grown in sequence on the substrate 2.
As shown in fig. 2 and 3, the waveguide core layer 4: the lower waveguide layer 4a has a thickness h2Having an effective refractive index n2The thickness of the active layer 4b is h3Having an effective refractive index n1effThe upper waveguide layer 4c has a thickness h4Having an effective refractive index n3(ii) a Waveguide lower cladding 3: the thickness of the waveguide lower cladding 3 is h1The effective refractive index of the lower confinement layer 3b is n41The effective refractive index of the lower buffer layer 3a is n42(ii) a Waveguide upper cladding 5: the upper limiting layer 5a and the upper buffer layer 5b each have a thickness h5And h6Effective refractive indices n51And n52. The structure is completed by one-time epitaxial growth, the cavity length of the whole structure is L, the mesa is etched by adopting an inductively coupled plasma etching (ICP) technology to obtain a plane area and a ridge area, and the etching depth of the epitaxial wafer is hetchEtching waveThe width of the guide strip is WribThen, a layer of insulating layer 7 is deposited by adopting a Plasma Enhanced Chemical Vapor Deposition (PECVD) technology, a P-surface metal electrode is prepared by adopting a magnetron sputtering system, an electrode contact layer 6 is arranged between the P-surface metal electrode and the waveguide upper cladding 5, and the thickness is h7Then, carrying out secondary photoetching, developing and etching to form a P-surface current window, wherein the width of the P-surface current injection window 9 is WwindowAnd thinning and polishing the substrate 2, and preparing N-surface metal electrodes and alloys on the back surface of the substrate 2 to finish the whole device preparation process.
The ridge semiconductor optical amplifier is divided into a slab region and a ridge region, and the number of supported modes is only equal to the thickness h of the lower waveguide layer 4a under the condition that the materials of all layers are certain from the analysis of an optical waveguide mode theory and a coupling mode theory2Thickness h of active layer 4b3Thickness h of upper waveguide layer 4c4Etching depth h of epitaxial waferetchAnd a waveguide width WribIt is related. The mesa is etched by inductively coupled plasma etching (ICP), the plate region is similar to a mode filter, and when the high-order mode is coupled to the continuous plate mode, the high-order mode is radiated from two ends of the plate region to filter the high-order mode, so that the width W of the ridge waveguide is controlledribAnd depth hetchThe single mode condition of the ridge waveguide of the optical amplifier is obtained, and the light field limiting factor of the active region and the size of the light spot of the fundamental mode can be adjusted within a certain range. In this embodiment, the difference between the refractive index of the active layer 4b and the refractive index of the upper waveguide layer 4c or the lower waveguide layer 4a is controlled to be within a threshold range, and the threshold is smaller, so that the optical field confinement factor of the active region is smaller, and a weak waveguide is formed, so that the penetration depth of the fundamental mode intensity optical field is increased, and the fundamental mode intensity optical field is diffused from the active layer 4b to the lower waveguide layer 4 a.
Further, in the above ridge active region weak waveguide-based semiconductor optical amplifier, the thickness h of the lower waveguide layer 4a2Is greater than the thickness h of the upper waveguide layer 4c4The heat dissipation of the flip-chip welding of the whole semiconductor optical amplifier is facilitated, and the mode leakage of a strong optical field at the upper waveguide layer 4c can be prevented.
Further, in the above semiconductor optical amplifier based on the ridge active region weak waveguide, the threshold value is in the range of 0 to 3%.
Wherein, when the difference between the refractive index of the active layer 4b and the refractive index of the upper waveguide layer 4c or the lower waveguide layer 4a is in the range of 0-3%, the optical field confinement factor of the active layer 4b is lower than 0.0327, and when the refractive index difference is reduced to below 1%, the optical field confinement factor of the active layer 4b is lower than 0.0157. The difference between the refractive indexes of the active layer 4b and the waveguide layer is within 0-3%, so that the basic mode intensity optical field is diffused to the upper waveguide layer 4c and the lower waveguide layer 4a, the single mode size of the optical field mode can be completely compared with the single mode optical fiber optical field mode size, and the semiconductor optical amplifier with high saturation output power, large-size single mode light spots and high light beam quality is realized. Of course, the threshold range includes, but is not limited to, the above ranges, and may be varied depending on the materials used, and is within the protection range.
Further, in the above ridge active region weak waveguide-based semiconductor optical amplifier, the active layer 4b includes:
multiple quantum wells formed by periodically and alternately growing undoped potential wells and undoped potential barriers;
and undoped boundary layers grown on the upper surface and the lower surface of the multiple quantum well.
Wherein the active layer 4b acts as a gain region of the amplifier, providing sufficient optical gain upon electrical injection. In this embodiment, the active layer 4b is formed by periodically and alternately growing undoped potential wells and undoped barriers in a multi-quantum well structure, such as InGaAsP/InP multi-quantum well structure, but the active layer 4b may be formed by alternately growing other P-type materials, which are within the protection range.
Further, in the above semiconductor optical amplifier based on ridge active region weak waveguide, the thickness of the undoped boundary layer is in the range of 5nm to 50 nm.
The reasonable boundary layer thickness can not only obtain the ideal weak light field limiting factor of the fundamental mode, realize large-size fundamental mode weak waveguide, but also avoid the waveguide in the waveguide. The thickness of the undoped boundary layer depends on the actual situation.
Further, in the above semiconductor optical amplifier based on a ridge active region weak waveguide, the optical amplifier further includes:
the waveguide upper cladding layer 5 comprises a P-type doped upper limiting layer 5a grown on the upper surface of the upper waveguide layer 4c and a P-type doped upper buffer layer 5b grown on the upper surface of the upper limiting layer 5a, and the refractive index of the P-type doped upper buffer layer 5b is greater than or equal to that of the P-type doped upper limiting layer 5 a.
In this embodiment, In is used as the upper waveguide layer 4cxIn GaAsPy, the upper confinement layer 5a may be made of a single P-type doped material, or may be made of a diluted waveguide in which two materials are alternately grown, and the upper buffer layer 5b may be made of a P-type highly doped material. The confinement of the transverse mode of the optical field can be realized by the refractive index of the P-type doped upper buffer layer 5b being greater than or equal to the refractive index of the P-type doped upper confinement layer 5 a.
Further, in the above semiconductor optical amplifier based on a ridge active region weak waveguide, the optical amplifier further includes:
the waveguide lower cladding layer 3 comprises an N-type doping lower limiting layer 3b grown on the lower surface of the lower waveguide layer 4a and an N-type doping lower buffer layer 3a grown on the lower surface of the lower limiting layer 3b, and the refractive index of the N-type doping lower buffer layer 3a is smaller than or equal to that of the N-type doping lower limiting layer 3 b.
The lower waveguide layer 4a may be a single N-type doped material, or may be a diluted waveguide formed by alternately growing two materials, where the diluted waveguide is usually formed by stacking a plurality of layers of periodically arranged undoped InP/InGaAsP combination layers. In this embodiment, the lower waveguide layer 4a is made of the same material In as the upper waveguide layer 4cxGaAsPy material.
The lower limiting layer 3b is an N-type doped material grown on the lower buffer layer 3a, and is usually made of the same material as the lower buffer layer 3a, the doping concentration is gradually changed, and the light field transverse mode diffusion can be effectively limited. The lower buffer layer 3a is an N-type highly doped material grown on the substrate 2, and is usually made of the same material as the substrate 2, so that defects of the substrate 2 can be modified, and subsequent material growth is facilitated. The limitation on the transverse mode of the optical field can be realized by the refractive index of the N-type doped lower buffer layer 3a being less than or equal to the refractive index of the N-type doped lower limiting layer 3 b.
In summary, the refractive index satisfies n1eff≥n2≈n3>n41≈n51≥n42≈n52The semiconductor optical amplifier can realize the distribution and diffusion of the fundamental mode high optical field to the lower waveguide layer 4a, limit the transverse mode of the optical field and realize high saturation output power, large-size single-mode light spots and high light beam quality.
Further, in the above semiconductor optical amplifier based on a ridge active region weak waveguide, the optical amplifier further includes:
and the P-type heavily doped electrode contact layer 6 is arranged between the upper surface of the waveguide upper cladding layer 5 and the lower surface of the P-surface metal upper electrode 8.
The electrode contact layer 6 is grown on the upper buffer layer 5b, and is heavily doped in a P-type manner, so that ohmic contact is facilitated.
Further, in the above semiconductor optical amplifier based on a ridge active region weak waveguide, the optical amplifier further includes:
and an insulating layer 7 covering the upper surface of the planar region formed by the upper waveguide layer 4c and the upper surface of the ridge region formed by the waveguide upper cladding layer 5 and the electrode contact layer 6, wherein the thickness of the insulating layer 7 is in the range of 100nm to 300 nm. The actual process usually uses two thicknesses of 200nm and 300nm to avoid electric leakage.
Wherein a silicon dioxide insulating layer 7 is deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) technique, which can be used as the insulating layer 7 of the etched portion and also as the low refractive index cladding of the ridge waveguide to limit the leakage of the optical mode. Since the sufficiently thick insulating layer 7 plays a role in restricting the optical field mode, the optical field is prevented from leaking to the metal layer, and current injection on both sides of the ridge waveguide is prevented.
Further, in the above semiconductor optical amplifier based on a ridge active region weak waveguide, the optical amplifier further includes:
the waveguide structure comprises an N-type highly doped substrate 2 arranged on the lower surface of the waveguide lower cladding layer 3, and an N-surface metal lower electrode 1 arranged on the lower surface of the N-type highly doped substrate 2.
The substrate 2 may be an N-type highly doped GaAs, InP, or other material, and the selection of the substrate 2 determines the lasing wavelength of the epitaxial chip according to the lattice matching principle, and the N-type highly doped InP substrate 2 is mainly used in this embodiment. The metal electrode is composed of a plurality of layers of metals, wherein the P-surface metal upper electrode 8 generally adopts Ti-Pt-Au, and the N-surface metal lower electrode 1 generally adopts Au-Ge-Ni.
Furthermore, in the semiconductor optical amplifier based on the ridge active region weak waveguide, the front end face and the rear end face are plated with the antireflection films 10 with the reflectivity of less than 0.01 percent.
The front and rear end faces mean that the mode reflection of input and output can be reduced to the maximum extent by coating the antireflection film 10 having a reflectance of less than 0.01% on both ends, i.e., the longitudinal section, of the entire semiconductor amplifier.
Fig. 4 shows ridge waveguide single mode conditions for different refractive index differences between the active layer 4b and the waveguide layer, according to an embodiment of the present invention.
The thick solid line SM1_ 0% represents a single mode boundary line when the difference between the refractive indices of the active region and the waveguide region is 0, and the lower region thereof represents the etching depth hetchAnd ridge waveguide width WribIn this region, the ridge waveguide is a single mode waveguide. Similarly, the thin solid line SM2_ 1%, the short broken line SM3_ 2%, the broken line SM4_ 3%, the dotted line SM5_ 9%, and the area contained below the broken line SM 3526 _ 3% represent a single-mode boundary line and a single-mode area when the difference in refractive index between the active region and the waveguide region is 1%, 2%, 3%, and 9%, respectively. It can be seen that the etching depth h increases with the difference in the refractive index between the active layer 4b and the waveguide layeretchAnd ridge waveguide width WribThe area that can satisfy the single mode condition becomes gradually smaller. In order to satisfy the mode matching with the single mode fiber, when WribWhen the thickness is 6 mu m, the SM1_ 0%, the SM2_ 1% and the SM3_ 2% satisfy a single mode condition, and the allowable etching depth hetchGradually reducing, comprehensively considering factors such as process error and the like, selecting SM2_ 1%, and etching depth hetch＝2.05μm。
FIG. 5(a) shows a fundamental mode optical field distribution with a 9% difference between the refractive indices of the active layer 4b and the waveguide layer provided by an embodiment of the present invention; fig. 5(b) shows the fundamental mode optical field distribution when the difference between the refractive indices of the active layer 4b and the waveguide layer is 1% according to the embodiment of the present invention. Their lower waveguide layer 4a is much thicker than the upper waveguide layer 4c and the central optical field distribution of the fundamental mode is transferred from the active layer 4b to the lower waveguide layer 4 a.
As can be seen from fig. 5(a), when the refractive index difference is 9%, the waveguide layer and the active layer 4b have formed a waveguide with the active layer 4b as a core layer, the upper waveguide layer 4c and the lower waveguide layer 4a as upper and lower cladding layers, and since the optical field confinement factor of the active layer 4b is high, 0.1243 is reached, such a strong waveguide is difficult to form large-sized single-mode optical field distribution, and the optical field intensity contour line region shown by the arrow contains 86.5% optical field intensity. As can be seen from fig. 5(b), when the refractive index difference is 1%, the upper waveguide layer 4c, the lower waveguide layer 4a and the active layer 4b form a weak waveguide, the optical field is redistributed to form the upper waveguide layer 4c, the lower waveguide layer 4a and the active layer 4b as core layers, the waveguide upper cladding layer 5 and the waveguide lower cladding layer 3 are ridge waveguides of the upper and lower cladding layers, at this time, the optical field limiting factor of the active layer 4b is only 0.0157, since the lower waveguide layer 4a is far thicker than the upper waveguide layer 4c, the central optical field distribution of the fundamental mode is transferred from the active layer 4b to the lower waveguide layer 4a, and the region with the same optical field intensity contour line shown by the arrow also contains 86.5% optical field intensity, it can be seen that the mode spot size is far larger than the mode size when the refractive index difference is 9%, and is completely comparable to the optical field mode size of the.
The semiconductor optical amplifier based on the ridge active region weak waveguide provided by the invention is easy to deal with thermal power consumption in the absence of thermal conduction, is expected to realize high saturated output power, high brightness and low-loss optical amplification output under the condition of large single-mode size, and the large mode size reduces the cavity surface power density, so that high-efficiency butt coupling with a single-mode optical fiber can be realized.
The embodiments are described in a progressive manner in the specification, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.
The principles and embodiments of the present invention are explained herein using specific examples, which are presented only to assist in understanding the method and its core concepts. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.

Claims (8)

1. A ridge active area weak waveguide based semiconductor optical amplifier comprising an active layer, and upper and lower waveguide layers grown on upper and lower surfaces of the active layer, respectively, the difference between the refractive index of the active layer and the refractive index of the upper or lower waveguide layer being less than or equal to a threshold value such that a fundamental mode optical field distribution is diffused from the active layer to the upper and lower waveguide layers, wherein the threshold value is in the range of 0-3%, the active layer comprising: multiple quantum wells formed by periodically and alternately growing undoped potential wells and undoped potential barriers; and undoped boundary layers grown on the upper surface and the lower surface of the multiple quantum well.
2. A ridge active region weak waveguide based semiconductor optical amplifier as defined in claim 1, wherein said undoped boundary layer has a thickness in the range of 5nm to 50 nm.
3. A ridge active region weak waveguide based semiconductor optical amplifier as defined in claim 2, further comprising:
the waveguide upper cladding comprises a P-type doped upper limiting layer growing on the upper surface of the upper waveguide layer and a P-type doped upper buffer layer growing on the upper surface of the upper limiting layer, and the refractive index of the P-type doped upper buffer layer is smaller than or equal to that of the P-type doped upper limiting layer.
4. A ridge active region weak waveguide based semiconductor optical amplifier as defined in claim 3, further comprising:
the waveguide lower cladding layer comprises an N-type doping lower limiting layer growing on the lower surface of the lower waveguide layer and an N-type doping lower buffer layer growing on the lower surface of the lower limiting layer, and the refractive index of the N-type doping lower buffer layer is smaller than or equal to that of the N-type doping lower limiting layer.
5. A ridge active region weak waveguide based semiconductor optical amplifier as defined in claim 4, further comprising:
and the P-type heavily doped electrode contact layer is arranged between the upper surface of the waveguide upper cladding layer and the lower surface of the P-surface metal upper electrode.
6. A ridge active region weak waveguide based semiconductor optical amplifier as defined in claim 5, further comprising:
and the insulating layer covers the upper surface of a plane region formed by the upper waveguide layer and the upper surface of a ridge region formed by the upper waveguide layer cladding layer and the electrode contact layer part, and the thickness of the insulating layer ranges from 100nm to 300 nm.
7. A ridge active region weak waveguide based semiconductor optical amplifier as defined in claim 6, further comprising:
the waveguide device comprises an N-type highly doped substrate arranged on the lower surface of the waveguide lower cladding layer and an N-surface metal lower electrode arranged on the lower surface of the N-type highly doped substrate.
8. A ridge active region weak waveguide-based semiconductor optical amplifier as claimed in claim 7, wherein front and rear end faces are coated with antireflection films having a reflectance of less than 0.01%.
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