Semiconductor laser with mode expansion layer and method for manufacturing the same

Abstract

A semiconductor laser comprises: a substrate; a first cladding layer arranged above the substrate; a second cladding layer arranged above the first cladding layer so that the first cladding layer is located between the substrate and the second cladding layer; and a first mode expansion layer in the first cladding layer, a second mode expansion layer in the second cladding layer, or both the first mode expansion layer in the first cladding layer and the second mode expansion layer in the second cladding layer.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. provisional patent application number 62 / 865,821 filed by Futurewei Technology Co., Ltd. on June 24, 2019, and entitled “Far Field Angle Reduction for High-Speed ​​Semiconductor Lasers,” which is incorporated by reference. Technical Field

[0003] The disclosed embodiments relate generally to optical devices, and more particularly to semiconductor lasers having mode spreading layers. Background Art

[0004] Semiconductor lasers or diode lasers are widely used as transmitter light sources in optical communication applications such as PON. Semiconductor lasers are used because of their small size, high efficiency, high-speed modulation, low cost, and ability to be easily coupled to optical fibers. User demand for increased bandwidth continues to increase, and it is therefore desirable to increase the modulation speed of semiconductor lasers to meet this demand. Summary of the invention

[0005] In a first aspect, a semiconductor laser comprises: a substrate; a first cladding layer disposed above the substrate; a second cladding layer disposed above the first cladding layer so that the first cladding layer is located between the substrate and the second cladding layer; and a first mode expansion layer within the first cladding layer, a second mode expansion layer within the second cladding layer, or both the first mode expansion layer within the first cladding layer and the second mode expansion layer within the second cladding layer.

[0006] In a first portion of a semiconductor laser including a mode expansion layer, the mode expansion layer reduces the far field angle of the semiconductor laser without significantly reducing the average optical confinement factor of the semiconductor laser, and thereby not significantly reducing the frequency response and modulation speed of the semiconductor laser. Specifically, the mode expansion layer can reduce the vertical far field angle of the semiconductor laser from about 30.2° to about 24.4°. In a second portion of the semiconductor laser not including the mode expansion layer, the absence of the mode expansion layer maintains the average optical confinement factor of the semiconductor laser, and thereby maintains the frequency response and modulation speed of the semiconductor laser. The manufacturer can form the mode expansion layer without using external manufacturing. For example, the manufacturer can use available epitaxial growth, etching and regrowth processes.

[0007] In a first implementation manner of the first aspect, the first cladding layer has a first refractive index, and the first mode expansion layer has a second refractive index higher than the first refractive index.

[0008] In a second implementation of the first aspect or a prior implementation of the first aspect, the second cladding layer has a first refractive index, and the second mode expansion layer has a second refractive index higher than the first refractive index.

[0009] In a third implementation of the first aspect or a previous implementation of the first aspect, the semiconductor laser has a first length, and the first mode expansion layer has a second length that is smaller than the first length.

[0010] In a fourth implementation of the first aspect or a previous implementation of the first aspect, the semiconductor laser has a first length, and the second mode expansion layer has a second length that is smaller than the first length.

[0011] In a fifth implementation of the first aspect or a prior implementation of the first aspect, the semiconductor laser further includes a first confinement layer, and the first confinement layer is disposed above the first cladding layer so that the first cladding layer is located between the substrate and the first confinement layer.

[0012] In a sixth implementation of the first aspect or a prior implementation of the first aspect, the semiconductor laser further includes a quantum well layer, and the quantum well layer is disposed above the first confinement layer so that the first confinement layer is located between the first cladding layer and the quantum well layer.

[0013] In a seventh implementation of the first aspect or a prior implementation of the first aspect, the semiconductor laser further comprises a second confinement layer, wherein the second confinement layer is disposed above the quantum well layer, such that the quantum well layer is located between the first confinement layer and the second confinement layer, and such that the second confinement layer is located between the quantum well layer and the second cladding layer.

[0014] In an eighth implementation of the first aspect or any prior implementation of the first aspect, the second coating layer includes vertically extending ridges.

[0015] In a ninth implementation of the first aspect or a previous implementation of the first aspect, the semiconductor laser further includes a contact layer disposed above the ridge.

[0016] In a second aspect, a method for manufacturing a semiconductor laser includes: epitaxially growing a first cladding layer over a substrate; epitaxially growing a first confinement layer over the first cladding layer; epitaxially growing a quantum well layer over the first confinement layer; epitaxially growing a second confinement layer over the quantum well layer; epitaxially growing a second cladding layer over the second confinement layer; and epitaxially growing a first mode extension layer in the first cladding layer, epitaxially growing a second mode extension layer in the second cladding layer, or epitaxially growing the first mode extension layer in the first cladding layer and the second mode extension layer in the second cladding layer.

[0017] In a first implementation manner of the second aspect, the method further includes: after epitaxially growing the second mode extension layer, etching away a first portion of the second cladding layer and a second portion of the second mode extension layer to form a gap.

[0018] In a second implementation of the second aspect or a prior implementation of the second aspect, the method further includes: after etching away the first portion and the second portion, regrowing the second cladding layer to fill the gap; and after the regrowth, epitaxially growing a contact layer above the second cladding layer.

[0019] In a third implementation of the second aspect or a prior implementation of the second aspect, the method further includes: after epitaxially growing the contact layer, etching away a third portion of the second cladding layer, a fourth portion of the contact layer, a fifth portion of the second cladding layer, and a sixth portion of the contact layer to form a ridge of the second cladding layer.

[0020] In a fourth implementation of the second aspect or a prior implementation of the second aspect, the method further includes: after epitaxially growing the first cladding layer and before epitaxially growing the first confinement layer, etching away a first portion of the first cladding layer and a second portion of the first mode extension layer to form a gap.

[0021] In a fifth implementation of the second aspect or a prior implementation of the second aspect, the method further includes: after etching away the first portion and the second portion, regrowing the first cladding layer to fill the gap; and after growing the second cladding layer, epitaxially growing a contact layer above the second cladding layer.

[0022] In a sixth implementation of the second aspect or a prior implementation of the second aspect, the method further includes: after epitaxially growing the contact layer, etching away the third portion of the second cladding layer, the fourth portion of the contact layer, the fifth portion of the second cladding layer, and the sixth portion of the contact layer to form a ridge of the second cladding layer.

[0023] In a seventh implementation manner of the second aspect or a previous implementation manner of the second aspect, the method further includes etching the first mode extension layer to form a tapered structure.

[0024] In an eighth implementation manner of the second aspect or any previous implementation manner of the second aspect, the method further includes etching the second mode extension layer to form a tapered structure.

[0025] In a third aspect, a semiconductor laser comprises: a first cladding layer epitaxially grown over a substrate; a first confinement layer epitaxially grown over the first cladding layer; a quantum well layer epitaxially grown over the first confinement layer; a second confinement layer epitaxially grown over the quantum well layer; a second cladding layer epitaxially grown over the second confinement layer; and a first mode extension layer epitaxially grown in the first cladding layer, a second mode extension layer epitaxially grown in the second cladding layer, or both the first mode extension layer epitaxially grown in the first cladding layer and the second mode extension layer epitaxially grown in the second cladding layer.

[0026] Any of the above-mentioned embodiments can be combined with any of the other above-mentioned embodiments to produce new embodiments. These and other features will be more clearly understood from the following detailed description in conjunction with the accompanying drawings and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] For a more complete understanding of the present disclosure, reference is now made to the following brief description taken in conjunction with the accompanying drawings and detailed description, wherein like reference numerals refer to like parts throughout the drawings.

[0028] Figure 1 is a schematic diagram of a semiconductor laser according to an embodiment.

[0029] Figure 2A-2D Shows Figure 1 The manufacturing process of semiconductor lasers.

[0030] Figure 3 is a schematic diagram of a semiconductor laser according to another embodiment.

[0031] Figure 4A-4F Shows Figure 3 The manufacturing process of semiconductor lasers.

[0032] Figure 5 is a schematic diagram of a semiconductor laser according to yet another embodiment.

[0033] Figure 6A-6D Shows Figure 5 The manufacturing process of semiconductor lasers.

[0034] Figure 7is a top view of a portion of a semiconductor laser according to an embodiment.

[0035] Figure 8 is a flowchart illustrating a method for manufacturing a semiconductor laser according to an embodiment. DETAILED DESCRIPTION

[0036] First, it should be understood that although illustrative implementations of one or more embodiments are provided below, the disclosed systems and / or methods can be implemented using any number of techniques, whether currently known or existing. The present disclosure should in no way be limited to the illustrative implementations, drawings, and techniques described below, including the exemplary designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims, along with their full scope of equivalents.

[0037] The following abbreviations are used:

[0038] AlGaInAs:aluminum gallium indium arsenic

[0039] DFB: distributed feedback

[0040] FP stands for Fabry-Perot

[0041] GaAs: Gallium arsenide

[0042] Gb / s: gigabit per second

[0043] GRIN-SCH: graded index separate confinement heterostructure

[0044] InGaAs: indium gallium arsenide

[0045] InGaAsP: indium gallium arsenide phosphide

[0046] InP:Indium phosphide

[0047] PON: passive optical network

[0048] μm:micrometer(s)

[0049] °: degree(s).

[0050] The frequency response of a semiconductor laser determines the modulation speed of the semiconductor laser. The frequency response R(f) can be expressed as follows:

[0051]

[0052] Among them, f r is the relaxation oscillation frequency, f is the frequency, γ is the damping coefficient, and RC is the RC time constant of the semiconductor laser. It can be seen that increasing f r The magnitude of R(f) increases. The term f r It can be expressed as follows:

[0053]

[0054] Where Γ is the optical confinement factor, dg / dn is the differential gain, L is the active region length, W is the active region width, and N w is the number of quantum wells, d w is the well thickness of the quantum well, I is the injection current, and I th is the threshold current. Specifically, Γ is the optical confinement factor at a specific location or section of the waveguide. The average optical confinement factor calculates the average Γ at multiple locations. It can be seen that increasing Γ makes f r Increase.

[0055] In order to increase the optical confinement factor Γ, the thickness of the gain material or the separation confinement structure of the semiconductor laser can be increased. However, the increase in the confinement factor causes an undesirable increase in the far field angle or the divergence angle. The far field angle includes the horizontal far field angle and the vertical far field angle. The increase in the far field angle makes it difficult for the semiconductor laser to be coupled to the optical fiber. Various methods either undesirably increase the far field angle while increasing the confinement factor, or undesirably reduce the confinement factor while reducing the far field angle. In addition, these complex methods are often accompanied by an increase in manufacturing costs. Therefore, it is desirable to increase the confinement factor while reducing or maintaining the far field angle and also limiting manufacturing costs.

[0056] Embodiments of semiconductor lasers with mode expansion layers are disclosed herein. The mode expansion layer is in the first cladding layer, in the second cladding layer, or in both the first cladding layer and the second cladding layer. The refractive index of the mode expansion layer is higher than the refractive index of the first cladding layer or the second cladding layer. In addition, the length of the mode expansion layer is less than the length of the semiconductor laser. In the first portion of the semiconductor laser including the mode expansion layer, the mode expansion layer reduces the far field angle of the semiconductor laser without significantly reducing the average optical confinement factor of the semiconductor laser, and thus does not significantly reduce the frequency response and modulation speed of the semiconductor laser. Specifically, the mode expansion layer can reduce the vertical far field angle of the semiconductor laser from about 30.2° to about 24.4°. In the second portion of the semiconductor laser not including the mode expansion layer, the absence of the mode expansion layer maintains the average optical confinement factor of the semiconductor laser, and thus maintains the frequency response and modulation speed of the semiconductor laser. The manufacturer can form the mode expansion layer without using external manufacturing. For example, the manufacturer can use available epitaxial growth, etching and regrowth processes. Although the semiconductor laser is shown and described as a FP laser, the semiconductor laser may also be a DFB laser having a grating layer below the bottom cladding layer or above the top cladding layer.

[0057] Figure 1 is a schematic diagram of a semiconductor laser 100 according to an embodiment. The semiconductor laser 100 includes a back side 105 that generally faces the left side of the page and is not visible, a side 110 that faces the front of the page, a side 115 that faces the back of the page and is not visible, and a front side 120 that generally faces the right side of the page and is visible. The semiconductor laser 100 also includes a substrate 125, a cladding layer 130, a confinement layer 135, a quantum well layer 140, a confinement layer 145, a cladding layer 150, a mode expansion layer 155, a ridge 160, and a contact layer 165. In response to an electric current, the semiconductor laser 100 emits a light beam away from the front face 120 in a direction approximately perpendicular to the front face 120.

[0058] The semiconductor laser 100 and its components have a length in the x direction, a width in the y direction, and a height in the z direction. The length of the semiconductor laser 100 may be about 150 μm-1,500 μm. The width of the semiconductor laser 100 may be about 150 μm-1,000 μm. The height of the semiconductor laser 100 may be about 100 μm-200 μm.

[0059] Substrate 125 is n+ doped; includes InP, GaAs or other suitable materials; and provides a structure to support other layers and for the growth of other layers. Cladding layer 130 is n doped, includes InP or other suitable materials, and has a lower refractive index than other non-cladding layers to provide optical confinement. Confinement layer 135 includes InGaAsP, AlGaInAs or other suitable materials; includes GRIN-SCH that provides electrical confinement and further optical confinement; and can have a height of about 20μm-120μm.

[0060] The quantum well layer 140 is an active layer; includes InGaAsP, AlGaInAs or other suitable materials; and includes quantum wells that provide optical gain. The confinement layer 145 includes InGaAsP, AlGaInAs or other suitable materials; includes GRIN-SCH; and may have a height of about 20 μm-120 μm. The cladding layer 150 is p-doped, includes InP or other suitable materials, and has a lower refractive index than other non-cladding layers to provide optical confinement. The refractive index of the cladding layer 150 may be about 3.3-3.5. The mode expansion layer 155 is described below.

[0061] The ridge 160 is a portion of the cladding layer 150 that extends vertically in the z direction, defines a waveguide for the light beam, and may have a width of about 1 μm-2 μm. Thus, the semiconductor laser 100 may be referred to as a ridge waveguide semiconductor laser. Alternatively, the semiconductor laser 100 is a buried heterostructure semiconductor laser. The contact layer 165 is p+ doped, includes InGaAs or other suitable materials, receives an electrical signal from an external source, and modulates the light to generate a light beam.

[0062] The mode expansion layer 155 is disposed within the cladding layer 150 so that the cladding layer 150 is both below and above the mode expansion layer 155 in the z direction. The mode expansion layer 155 is a passive layer, is p-doped, includes InGaAsP or other suitable materials, has a refractive index higher than that of the cladding layer 150, expands the optical mode of the light beam, and shapes the far field angle of the semiconductor laser 100. The refractive index of the mode expansion layer 155 may be about 3.4-3.6. The manufacturer forms the mode expansion layer 155 using planar manufacturing technology, so the manufacture of the mode expansion layer 155 is relatively simple and inexpensive.

[0063] like Figure 1As shown, the mode expansion layer 155 extends completely across the width of the semiconductor laser 100. The mode expansion layer 155 does not extend completely across the length of the semiconductor laser 100. Specifically, the mode expansion layer 155 extends from the front face 120 across a first length 175 of the semiconductor laser 100 toward the back face 105 but does not extend to the back face 105; and the mode expansion layer 155 does not extend from the back face 105 across a second length 170 of the semiconductor laser 100 toward the front face 120 but does not extend to the front face 120.

[0064] In a first portion of the semiconductor laser 100 corresponding to the first length 175, the mode expansion layer 155 reduces the far field angle of the semiconductor laser 100 without significantly reducing the average optical confinement factor of the semiconductor laser 100, and thereby does not significantly reduce the frequency response and modulation speed of the semiconductor laser 100. The mode expansion layer 155 can particularly reduce the vertical far field angle of the semiconductor laser 100, which is generally larger and more problematic than the horizontal far field angle of the semiconductor laser 100. For example, the mode expansion layer 155 can reduce the vertical far field angle of the semiconductor laser 100 from about 30.2° to about 24.4°. In a second portion of the semiconductor laser 100 corresponding to the second length 170, the mode expansion layer 155 is not present, and the absence of the mode expansion layer maintains the average optical confinement factor of the semiconductor laser 100, and thereby maintains the frequency response and modulation speed of the semiconductor laser 100.

[0065] Increasing the length of the mode expansion layer 155 (which is the same as the first length 175 of the semiconductor laser 100) and the height of the mode expansion layer 155 reduces the far field angle of the semiconductor laser 100. The length of the mode expansion layer 155 may be about 30 μm-50 μm or about 30 μm-80 μm. The height of the mode expansion layer 155 may be about 30 μm-100 μm.

[0066] The manufacturer can design the dimensions of the components of the semiconductor laser 100 based on various metrics, including the length of the mode expansion layer 155, the height of the mode expansion layer 155, the height of the confinement layer 135 and the confinement layer 145, and the width of the ridge 160. These metrics include the far field angle, optical confinement factor or average optical confinement factor, frequency response, and modulation speed of the semiconductor laser 100. The manufacturer can seek the desired value or range of any combination of these metrics. For example, the manufacturer designs the length of the mode expansion layer 155 and the height of the mode expansion layer 155 to achieve the desired frequency response and the desired far field angle of the semiconductor laser 100. In one example, the length of the mode expansion layer 155 is about 50 μm, and the height of the mode expansion layer 155 is about 40 μm. In addition, the height of the confinement layers 135, 145 is about 30 μm; and the width of the ridge 160 is about 2 μm.

[0067] Figure 2A-2D Shows Figure 1 1. The manufacturing process of the semiconductor laser 100 is shown in FIG. Figure 2A 2 is a schematic diagram 200 of semiconductor laser 100 after epitaxial growth. The fabricator starts with substrate 125. The fabricator epitaxially grows cladding layer 130 on top of substrate 125, epitaxially grows confinement layer 135 on top of cladding layer 130, epitaxially grows quantum well layer 140 on top of confinement layer 135, epitaxially grows confinement layer 145 on top of quantum well layer 140, and epitaxially grows cladding layer 150 on top of confinement layer 145. The fabricator epitaxially grows mode extension layer 155 in cladding layer 150.

[0068] Figure 2B 210 is a schematic diagram of semiconductor laser 100 after a first etch. The manufacturer etches away a portion of cladding layer 150 and mode expansion layer 155 to form void 240. Void 240 extends across the width of semiconductor laser 100 and extends across a second length 170 from back side 105 toward front side 120. Void 240 further extends from the top of semiconductor laser 100 toward confinement layer 145, but does not extend to confinement layer 145, thereby leaving a sublayer 250 of cladding layer 150 below void 240. Sublayer 250 is relatively thin and may have a height of about 20 μm-40 μm. Etching is either wet etching or dry etching.

[0069] Figure 2C 220 is a schematic diagram of semiconductor laser 100 after regrowth. The manufacturer re-grows cladding layer 150 to fill voids 240. After regrowth, cladding layer 150 does not include mode expansion layer 155 where voids 240 existed. In addition, the manufacturer epitaxially grows contact layer 165 on top of cladding layer 150.

[0070] Figure 2D 230 is a schematic diagram of semiconductor laser 100 after a second etch. The manufacturer etches away a portion of cladding layer 150 and a portion of contact layer 165 to form a first void 260 extending from side 110 toward the middle of semiconductor laser 100 across width 280; and the manufacturer etches away a portion of cladding layer 150 and a portion of contact layer 165 to form a second void 270 extending from side 115 to the middle of semiconductor laser 100 across width 290. By doing so, the manufacturer forms ridge 160.

[0071] Figure 3is a schematic diagram of a semiconductor laser 300 according to another embodiment. The semiconductor laser 300 is similar to the semiconductor laser 100. Specifically, the semiconductor laser 300 includes a back surface 305 similar to the back surface 105, a side surface 310 similar to the side surface 110, a side surface 315 similar to the side surface 115, and a front surface 320 similar to the front surface 120. In addition, the semiconductor laser 300 also includes a substrate 325 similar to the substrate 125, a cladding layer 330 similar to the cladding layer 130, a confinement layer 335 similar to the confinement layer 135, a quantum well layer 340 similar to the quantum well layer 140, a confinement layer 345 similar to the confinement layer 145, a cladding layer 350 similar to the cladding layer 150, a mode expansion layer 355 similar to the mode expansion layer 155, a ridge 360 ​​similar to the ridge 160, and a contact layer 365 similar to the contact layer 165.

[0072] However, unlike the semiconductor laser 100, the semiconductor laser 300 includes a mode expansion layer 380 within the cladding layer 330. The mode expansion layer 380 has a composition, function, and size similar to the mode expansion layer 355, and thus similar to the mode expansion layer 155. The refractive index of the mode expansion layer 380 is higher than the refractive index of the cladding layer 330. The refractive index of the cladding layer 330 may be about 3.3-3.5, and the refractive index of the mode expansion layer 380 may be about 3.4-3.6. The mode expansion layers 355, 380 together reduce the far field angle of the semiconductor laser 300 without significantly reducing the average optical confinement factor of the semiconductor laser 300, and thus without significantly reducing the frequency response and modulation speed of the semiconductor laser 300. Although the mode expansion layers 355, 380 are shown to have the same length, which extends across the first length 375 of the semiconductor laser 300, but does not extend across the second length 370 of the semiconductor laser 300, the mode expansion layers 355, 380 may have different lengths. The manufacturer can design these lengths based on the above metrics, for example, to achieve a desired frequency response and a desired far-field angle.

[0073] Figure 4A-4F Shows Figure 3 1. The manufacturing process of the semiconductor laser 300 is shown in FIG. Figure 4A 400 is a schematic diagram of semiconductor laser 300 after epitaxial growth. The fabricator starts with substrate 325. The fabricator epitaxially grows cladding layer 330 on top of substrate 325. The fabricator epitaxially grows mode extension layer 380 within cladding layer 330.

[0074] Figure 4B405 is a schematic diagram of semiconductor laser 300 after a first etch. The manufacturer etches away a portion of cladding layer 330 and mode expansion layer 380 to form void 430. Void 430 extends across the width of semiconductor laser 300 and extends across second length 370 from back side 305 toward front side 320. Void 430 further extends from the top of semiconductor laser 300 toward substrate 325, but not to substrate 325, thereby leaving a sublayer 435 of cladding layer 330 below void 430. Sublayer 435 is relatively thin and may have a height of about 20 μm-40 μm. Etching is either wet etching or dry etching.

[0075] Figure 4C 410 is a schematic diagram of semiconductor laser 300 after a first regrowth. The manufacturer regrows cladding layer 330 to fill voids 430. After regrowth, cladding layer 330 does not include mode expansion layer 380 where voids 430 existed. In addition, the manufacturer epitaxially grows confinement layer 335 on top of cladding layer 330, epitaxially grows quantum well layer 340 on top of confinement layer 335, epitaxially grows confinement layer 345 on top of quantum well layer 340, and epitaxially grows cladding layer 350 on top of confinement layer 345. The manufacturer epitaxially grows mode expansion layer 355 on cladding layer 350.

[0076] Figure 4D 415 is a schematic diagram of semiconductor laser 300 after a second etch. The manufacturer etches away a portion of cladding layer 350 and mode expansion layer 355 to form void 440. Void 440 extends across the width of semiconductor laser 300 and extends across a second length 370 from back side 305 toward front side 320. Void 440 further extends from the top of semiconductor laser 300 toward confinement layer 345, but does not extend to confinement layer 345, thereby leaving a sublayer 445 of cladding layer 350 below void 440. Sublayer 445 is relatively thin and may have a height of about 20 μm-40 μm. Etching is either wet etching or dry etching.

[0077] Figure 4E 420 is a schematic diagram of semiconductor laser 300 after the second regrowth. The manufacturer re-grows cladding layer 350 to fill voids 440. After regrowth, cladding layer 350 does not include mode expansion layer 355 where voids 440 existed. In addition, the manufacturer epitaxially grows contact layer 365 on top of cladding layer 350.

[0078] Figure 4F425 is a schematic diagram of semiconductor laser 300 after the third etch. The manufacturer etches away a portion of cladding layer 350 and a portion of contact layer 365 to form a first void 450 extending from side 310 toward the middle of semiconductor laser 300 across width 460; and the manufacturer etches away a portion of cladding layer 350 and a portion of contact layer 365 to form a second void 455 extending from side 315 to the middle of semiconductor laser 300 across width 465. By doing so, the manufacturer forms ridge 360.

[0079] Figure 5 is a schematic diagram of a semiconductor laser 500 according to yet another embodiment. Semiconductor laser 500 is similar to semiconductor laser 100. Specifically, semiconductor laser 500 includes a back surface 505 similar to back surface 105, a side surface 510 similar to side surface 110, a side surface 515 similar to side surface 115, and a front surface 520 similar to front surface 120. In addition, semiconductor laser 500 also includes a substrate 525 similar to substrate 125, a cladding layer 530 similar to cladding layer 130, a confinement layer 535 similar to confinement layer 135, a quantum well layer 540 similar to quantum well layer 140, a confinement layer 545 similar to confinement layer 145, a cladding layer 550 similar to cladding layer 150, a ridge 560 similar to ridge 160, and a contact layer 565 similar to contact layer 165.

[0080] However, unlike the semiconductor laser 100 in which the cladding layer 150 includes the mode expansion layer 155, the semiconductor laser 500 includes a mode expansion layer 580 within the cladding layer 530. The mode expansion layer 580 has a composition, function, and size similar to the mode expansion layer 155. The refractive index of the mode expansion layer 580 is higher than the refractive index of the cladding layer 530. The refractive index of the cladding layer 530 may be about 3.3-3.5, and the refractive index of the mode expansion layer 580 may be about 3.4-3.6. The mode expansion layer 580 reduces the far field angle of the semiconductor laser 500 without significantly reducing the average optical confinement factor of the semiconductor laser 500, and thereby without significantly reducing the frequency response and modulation speed of the semiconductor laser 500. The manufacturer can design the length of the mode expansion layer 580 based on the above metrics, for example, to achieve a desired frequency response and a desired far field angle.

[0081] Figure 6A-6D Shows Figure 5 1. The manufacturing process of the semiconductor laser 500 is shown in FIG. Fig. 6A 600 is a schematic diagram of semiconductor laser 500 after epitaxial growth. The fabricator starts with substrate 525. The fabricator epitaxially grows cladding layer 530 on top of substrate 525. The fabricator epitaxially grows mode extension layer 580 within cladding layer 530.

[0082] Figure 6B 610 is a schematic diagram of semiconductor laser 500 after a first etch. The manufacturer etches away a portion of cladding layer 530 and mode expansion layer 580 to form a void 640. Void 640 extends across the width of semiconductor laser 500 and extends across a second length 570 from back side 505 toward front side 520. Void 640 further extends from the top of semiconductor laser 500 toward substrate 525, but does not extend to substrate 525, thereby leaving a sublayer 650 of cladding layer 530 below void 640. Sublayer 650 is relatively thin and may have a height of about 20 μm-40 μm. Etching is either wet etching or dry etching.

[0083] Figure 6C 620 is a schematic diagram of semiconductor laser 500 after regrowth. The manufacturer re-grows cladding layer 530 to fill voids 640. After regrowth, cladding layer 530 does not include mode expansion layer 580 where voids 640 existed. In addition, the manufacturer epitaxially grows confinement layer 535 on top of cladding layer 530, epitaxially grows quantum well layer 540 on top of confinement layer 535, epitaxially grows confinement layer 545 on top of quantum well layer 540, epitaxially grows cladding layer 550 on top of confinement layer 545, and epitaxially grows contact layer 565 on top of cladding layer 550.

[0084] Fig.6D 630 is a schematic diagram of semiconductor laser 500 after a second etch. The manufacturer etches away a portion of cladding layer 550 and a portion of contact layer 565 to form a first void 660 extending from side 510 toward the middle of semiconductor laser 500 across width 680; and the manufacturer etches away a portion of cladding layer 550 and a portion of contact layer 565 to form a second void 670 extending from side 515 to the middle of semiconductor laser 500 across width 690. By doing so, the manufacturer forms ridge 560.

[0085] Figure 7 7 is a top view of a portion 700 of a semiconductor laser according to an embodiment. Portion 700 includes a ridge 710 and a mode expansion layer 760. Ridge 710 may be ridge 160, 360, or 560, and mode expansion layer 760 may be mode expansion layer 155, 380, 555, or 580. Ridge 710 is substantially rectangular and is located above mode expansion layer 760.

[0086] The mode expansion layer 760 includes a first portion 720 across a first length 780 and a second portion 770 across a second length 790. The first portion 720 is substantially triangular or trapezoidal and includes a tapered portion 730, a tip 740, and a tapered portion 750. The tapered portion 730, the tip 740, and the tapered portion 750 form a tapered structure that reduces coupling loss and beam reflection. The manufacturer can use wet etching or dry etching to form the tapered structure. The second portion 770 is substantially rectangular.

[0087] Figure 8 8 is a flow chart illustrating a method 800 for manufacturing a semiconductor laser according to an embodiment. A manufacturer may implement the method 800 to manufacture the semiconductor laser 100, 300, or 500. In step 810, a substrate is obtained. For example, the manufacturer obtains the substrate 125, 325, or 525.

[0088] In step 820, a first cladding layer is epitaxially grown over the substrate. For example, the manufacturer epitaxially grows cladding layer 130, 330, or 530. In step 830, a first confinement layer is epitaxially grown over the first cladding layer. For example, the manufacturer epitaxially grows confinement layer 135, 335, or 535.

[0089] In step 840, a quantum well layer is epitaxially grown over the first confinement layer. For example, the manufacturer epitaxially grows quantum well layer 140, 340, or 540. In step 850, a second confinement layer is epitaxially grown over the quantum well layer. For example, the manufacturer epitaxially grows confinement layer 145, 345, or 545.

[0090] In step 860, a second cladding layer is epitaxially grown over the second confinement layer. For example, the manufacturer epitaxially grows cladding layer 150, 350, or 550. Finally, in step 870, a first mode extension layer is epitaxially grown in the first cladding layer, a second mode extension layer is epitaxially grown in the second cladding layer, or both the first mode extension layer and the second mode extension layer are epitaxially grown in the first cladding layer. For example, the manufacturer epitaxially grows mode extension layer 580 in cladding layer 530, epitaxially grows mode extension layer 155 in cladding layer 150, or epitaxially grows mode extension layer 380 in cladding layer 330 and epitaxially grows mode extension layer 355 in cladding layer 350.

[0091] Method 800 may include additional steps. In a first embodiment, after epitaxially growing the second mode extension layer, a first portion of the second cladding layer and a second portion of the second mode extension layer are etched away to form a gap. For example, the manufacturer etches away the cladding layer 150 and the mode extension layer 155 to form the gap 240. After etching away the first portion and the second portion, the second cladding layer is regrown to fill the gap. For example, the manufacturer regrows the cladding layer 150 to fill the gap 240. After the regrowth, a contact layer is epitaxially grown over the second cladding layer. For example, the manufacturer epitaxially grows the contact layer 165. Finally, after epitaxially growing the contact layer, a third portion of the second cladding layer, a fourth portion of the contact layer, a fifth portion of the second cladding layer, and a sixth portion of the contact layer are etched away to form a ridge of the second cladding layer. For example, the manufacturer etches away a portion of the cladding layer 150 and a portion of the contact layer 165 to form the first gap 260 , and etches away a portion of the cladding layer 150 and a portion of the contact layer 165 to form the second gap 270 , thereby forming the ridge 160 .

[0092] In a second embodiment, after epitaxially growing the first cladding layer and before epitaxially growing the first confinement layer, a first portion of the first cladding layer and a second portion of the first mode expansion layer are etched away to form a void. For example, the manufacturer etches away the cladding layer 530 and the mode expansion layer 580 to form a void 640. After etching away the first portion and the second portion, the first cladding layer is regrown to fill the void. For example, the manufacturer regrows the cladding layer 530 to fill the void 640. After growing the second cladding layer, a contact layer is epitaxially grown over the second cladding layer. For example, the manufacturer epitaxially grows the contact layer 565. Finally, after epitaxially growing the contact layer, a third portion of the second cladding layer, a fourth portion of the contact layer, a fifth portion of the second cladding layer, and a sixth portion of the contact layer are etched away to form a ridge of the second cladding layer. For example, the manufacturer etches away a portion of the cladding layer 550 and a portion of the contact layer 565 to form the first gap 660, and etches away a portion of the cladding layer 550 and a portion of the contact layer 565 to form the second gap 670, thereby forming the ridge 560. The first embodiment and the second embodiment may be combined, such as Figure 3-4F shown.

[0093] In a third embodiment, the first mode extension layer is etched to form a tapered structure. For example, the manufacturer etches the mode extension layer 580 to form Figure 7 In the fourth embodiment, the second mode extension layer is etched to form a tapered structure. For example, the manufacturer etches the mode extension layer 155 to form Figure 7 The third embodiment and the fourth embodiment can be Figure 3 The semiconductor laser 300 is combined in the above embodiment.

[0094] Unless otherwise indicated, the term "approximately" means including a range of ±10% of the subsequent number. The term "substantially" means within ±10%. Although the present disclosure provides several embodiments, it is understood that the disclosed systems and methods may be embodied in a variety of other specific forms without departing from the spirit or scope of the present disclosure. This example should be considered illustrative rather than restrictive, and is not intended to be limited to the details given herein. For example, various elements or components may be combined or integrated in another system, or certain features may be omitted or not implemented.

[0095] In addition, without departing from the scope of the present disclosure, the techniques, systems, subsystems and methods described and illustrated as discrete or separate in the various embodiments may be combined or integrated with other systems, components, techniques or methods. Other items shown or described as coupled may be directly coupled, or may be indirectly coupled or communicated through an interface, device or intermediate component, whether electrically, mechanically or otherwise. Other examples of changes, substitutions and variants can be determined by those skilled in the art and may be made without departing from the spirit and scope of the present disclosure.

Claims

1. A semiconductor laser comprising: substrate; A first cladding layer is disposed above the substrate; A quantum well layer, disposed above the first cladding layer; A second cladding layer is disposed above the quantum well layer, and the first cladding layer is located between the substrate and the quantum well layer; wherein the semiconductor laser further comprises: a first mode expansion layer in the first cladding layer; or a second mode expansion layer in the second cladding layer; or both the first mode expansion layer in the first cladding layer and the second mode expansion layer in the second cladding layer; When the semiconductor laser includes the first mode expansion layer in the first cladding layer, the first mode expansion layer extends from the front side of the semiconductor laser across a certain length of the semiconductor laser toward the back side but does not extend to the back side, wherein the front side of the semiconductor laser is the light emitting surface of the semiconductor laser, and the refractive index of the first mode expansion layer is higher than the refractive index of the first cladding layer; When the semiconductor laser includes the second mode expansion layer in the second cladding layer, the second mode expansion layer extends from the front face of the semiconductor laser across a certain length of the semiconductor laser toward the back face but does not extend to the back face, wherein the front face of the semiconductor laser is the light emitting surface of the semiconductor laser, and the refractive index of the second mode expansion layer is higher than the refractive index of the second cladding layer.

2. The semiconductor laser according to claim 1, wherein Where the semiconductor laser comprises the first mode spreading layer, the first mode spreading layer extends completely across the width of the semiconductor laser.

3. The semiconductor laser according to claim 1, wherein Where the semiconductor laser comprises the second mode spreading layer, the second mode spreading layer extends completely across the width of the semiconductor laser. 4 . The semiconductor laser according to claim 2 , further comprising a first confinement layer, the first confinement layer being disposed above the first cladding layer such that the first cladding layer is located between the substrate and the first confinement layer. 5 . The semiconductor laser according to claim 4 , wherein the quantum well layer is disposed above the first confinement layer, so that the first confinement layer is located between the first cladding layer and the quantum well layer.

6. The semiconductor laser according to claim 5, further comprising a second confinement layer, the second confinement layer being disposed above the quantum well layer so that the quantum well layer is located between the first confinement layer and the second confinement layer, and so that the second confinement layer is located between the quantum well layer and the second cladding layer.

7. The semiconductor laser according to claim 6, wherein: The second coating layer includes vertically extending ridges. 8 . The semiconductor laser according to claim 7 , further comprising a contact layer disposed over the ridge.

9. A method for manufacturing a semiconductor laser, comprising: epitaxially growing a first cladding layer over the substrate; epitaxially growing a first confinement layer on the first cladding layer; epitaxially growing a quantum well layer on the first confinement layer; epitaxially growing a second confinement layer above the quantum well layer; epitaxially growing a second cladding layer on the second confinement layer; as well as epitaxially grow a first mode extension layer in the first cladding layer, epitaxially grow a second mode extension layer in the second cladding layer, or epitaxially grow the first mode extension layer in the first cladding layer and epitaxially grow the second mode extension layer in the second cladding layer; In the case where the method includes epitaxially growing the second mode expansion layer in the second cladding layer, the method further includes: after epitaxially growing the second mode expansion layer, etching away a first portion of the second cladding layer and a second portion of the second mode expansion layer opposite to the first portion of the second cladding layer to form a gap, so that the second mode expansion layer extends from the front side of the semiconductor laser across a certain length of the semiconductor laser toward the back side but does not extend to the back side, wherein the front side of the semiconductor laser is the light emitting surface of the semiconductor laser, and the refractive index of the second mode expansion layer is higher than the refractive index of the second cladding layer; In the case where the method includes epitaxially growing the first mode expansion layer in the first cladding layer, the method further includes: after epitaxially growing the first cladding layer and before epitaxially growing the first confinement layer, etching away a first portion of the first cladding layer and a second portion of the first mode expansion layer opposite to the first portion of the first cladding layer to form a gap, so that the first mode expansion layer extends from the front face of the semiconductor laser across a certain length of the semiconductor laser toward the back face but does not extend to the back face, wherein the front face of the semiconductor laser is the light emitting surface of the semiconductor laser, and the refractive index of the first mode expansion layer is higher than the refractive index of the first cladding layer.

10. The method of claim 9, wherein the gap formed by etching away the first portion of the second cladding layer and the second portion of the second mode extension layer opposite to the first portion of the second cladding layer completely extends across the width of the semiconductor laser.

11. The method according to claim 10, further comprising: After etching away a first portion of the second cladding layer and a second portion of the second mode extension layer opposite to the first portion of the second cladding layer, regrowing the second cladding layer to fill the gap; as well as After the regrowth, a contact layer is epitaxially grown over the second cladding layer.

12. The method according to claim 11 further includes, after epitaxially growing the contact layer, etching away a third portion of the second cladding layer, a fourth portion of the contact layer opposite to the third portion of the second cladding layer, a fifth portion of the second cladding layer, and a sixth portion of the contact layer opposite to the fifth portion of the second cladding layer to form a ridge of the second cladding layer.

13. The method of claim 9, wherein a gap formed by etching away the first portion of the first cladding layer and a second portion of the first mode extension layer opposite to the first portion of the first cladding layer completely extends across a width of the semiconductor laser.

14. The method according to claim 13, further comprising: After etching away a first portion of the first cladding layer and a second portion of the first mode extension layer opposite to the first portion of the first cladding layer, regrowing the first cladding layer to fill the gap; and After growing the second cladding layer, a contact layer is epitaxially grown on the second cladding layer.

15. The method according to claim 14 further includes, after epitaxially growing the contact layer, etching away a third portion of the second cladding layer, a fourth portion of the contact layer opposite to the third portion of the second cladding layer, a fifth portion of the second cladding layer, and a sixth portion of the contact layer opposite to the fifth portion of the second cladding layer to form a ridge of the second cladding layer. 16 . The method of claim 9 , further comprising etching the first mode extension layer to form a tapered structure. 17 . The method of claim 9 , further comprising etching the second mode extension layer to form a tapered structure.

18. A semiconductor laser comprising: a first cladding layer epitaxially grown over the substrate; a first confinement layer epitaxially grown over the first cladding layer; a quantum well layer epitaxially grown above the first confinement layer; a second confinement layer epitaxially grown above the quantum well layer; a second cladding layer epitaxially grown on the second confinement layer; wherein the semiconductor laser further comprises: a first mode extension layer epitaxially grown in the first cladding layer; or a second mode extension layer epitaxially grown in the second cladding layer; or both the first mode extension layer epitaxially grown in the first cladding layer and the second mode extension layer epitaxially grown in the second cladding layer; When the semiconductor laser includes the first mode expansion layer epitaxially grown in the first cladding layer, the first mode expansion layer extends from the front side of the semiconductor laser across a certain length of the semiconductor laser toward the back side but does not extend to the back side, wherein the front side of the semiconductor laser is the light emitting surface of the semiconductor laser, and the refractive index of the first mode expansion layer is higher than the refractive index of the first cladding layer; When the semiconductor laser includes the second mode expansion layer epitaxially grown in the second cladding layer, the second mode expansion layer extends from the front side of the semiconductor laser across a certain length of the semiconductor laser toward the back side but does not extend to the back side, wherein the front side of the semiconductor laser is the light emitting surface of the semiconductor laser, and the refractive index of the second mode expansion layer is higher than the refractive index of the second cladding layer.

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