Monolithic integrated external cavity type self-focusing edge-emitting laser array and preparation method thereof

Abstract

The application discloses a kind of monolithic integrated outer cold cavity type self-focusing edge-emitting laser array and preparation method, comprising: on the surface of semiconductor epitaxial layer, there are in turn inclined waveguide area, electrically isolated channel and fractional order Talbot cold cavity area;Inclined waveguide area includes a central waveguide and a plurality of inclined waveguides distributed symmetrically on the left and right sides of central waveguide, and the inclination angle of each inclined waveguide is greater than the inclination angle of central waveguide;Fractional order Talbot cold cavity area length meets fractional order Talbot distance, and there is no gain and no loss for the light passing through;One side of the upper surface of inclined waveguide area is provided with high reflectivity DBR grating;One side of the upper surface of fractional order Talbot cold cavity area is provided with semi-reflective semi-transmissive DBR grating.The application effectively improves the coherence of laser array, reduces the loss of fractional order Talbot array in supermode identification process, and realizes high-efficiency high-beam-quality output of laser array.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of edge-emitting semiconductor lasers, in particular to a monolithic integrated external cold cavity type self-focusing edge-emitting laser array and a preparation method. BACKGROUND

[0002] Talbot optical effect is widely studied due to its famous optical "self-reproduction" phenomenon, but it is mostly in the field of passive coherent laser. With further research, it is applied to the phase-locked field of edge-emitting laser array as an external cavity mirror structure, which has the characteristics of simple structure, high stability and strong robustness.

[0003] In recent years, various monolithic integrated Talbot cavity edge-emitting laser array schemes have been proposed. This structure takes into account the small size and easy integration of traditional edge-emitting lasers, and based on the strong coupling mode of Talbot diffraction, greatly improves the beam quality of the laser array.

[0004] Although this method has many advantages, it is still difficult to overcome the problem of realizing good supermode recognition in low loss, which is also one of the problems that this type of device cannot be successfully commercialized at present. Therefore, the development of high-efficiency, high-power and high-beam-quality laser light source is still a problem that needs to be solved at present. SUMMARY

[0005] In view of the deficiencies in the prior art, the present application provides a monolithic integrated external cold cavity type self-focusing edge-emitting laser array and a preparation method. The laser array restructures the traditional Talbot optical field effect, focuses the optical field on the array center, realizes low-loss supermode recognition, and solves the problems of high-efficiency, high-power and high-beam-quality light source.

[0006] The present application discloses a monolithic integrated external cold cavity type self-focusing edge-emitting laser array, comprising: a semiconductor substrate;

[0007] A semiconductor epitaxial layer is formed on the upper surface of the semiconductor substrate;

[0008] The upper surface of the semiconductor epitaxial layer is provided with an inclined waveguide area, an electrical isolation channel, a fractional Talbot cold cavity area and a semi-reflective semi-transmissive DBR grating;

[0009] The inclined waveguide area includes a central waveguide and a plurality of inclined waveguides symmetrically distributed on the left and right sides of the central waveguide. The inclination angle of each inclined waveguide is symmetric to the center of the central waveguide, and the inclination angle increases with the distance from the central waveguide, so that the optical field is focused on the array center;

[0010] The electrically isolated channel is formed between the inclined waveguide region and the fractional Talbot cold cavity region, the length of the fractional Talbot cold cavity region satisfies the fractional Talbot distance, and the passing light has neither gain nor loss;

[0011] The rear side of the upper surface of the inclined waveguide region is provided with a high reflectivity DBR grating, and the front side of the upper surface of the fractional Talbot cold cavity region is provided with a semi-reflective and semi-transmissive DBR grating;

[0012] The upper surfaces of the inclined waveguide region and the fractional Talbot cold cavity region are sequentially provided with an electrode window and a P-metal electrode from bottom to top;

[0013] The lower surface of the semiconductor substrate is provided with an N-metal electrode.

[0014] As a further improvement of the present application, the semiconductor epitaxial layer is sequentially provided with an N-limiting layer, an N-waveguide layer, an active layer, a P-waveguide layer, a transition layer, a barrier layer, a P-limiting layer and a P-high-doping layer from bottom to top, wherein the thickness of the N-waveguide layer is greater than the thickness of the P-waveguide layer, and the total thickness of the N-waveguide layer and the P-waveguide layer is less than or equal to the base lateral mode cutoff condition:

[0015]

[0016] In the formula, D is the total thickness of the N-waveguide layer and the P-waveguide layer, λ is the free space optical wavelength, n2 is the equivalent refractive index of the total thickness of the N-waveguide layer and the P-waveguide layer, n1 is the equivalent refractive index of the N-limiting layer and the P-limiting layer, and m is a positive integer.

[0017] As a further improvement of the present application,

[0018] The semiconductor substrate is selected from gallium arsenide, indium phosphide or gallium nitride;

[0019] The P-metal electrode comprises one or more of titanium, platinum and gold, and has a thickness of 300 nm to 1000 nm;

[0020] The N-metal electrode comprises one or more of nickel, germanium and gold, and has a thickness of 300 nm to 500 nm.

[0021] As a further improvement of the present application, the central waveguide cross section of the inclined waveguide region is rectangular, and the remaining inclined waveguide cross sections are parallelograms.

[0022] As a further improvement of the present application, the number of central waveguides in the inclined waveguide region is 1, the number of inclined waveguides is 2 to 100, the length is 1000 μm to 4000 μm, the period is 4 μm to 10 μm, the width is 2 μm to 3 μm, and the base lateral mode cutoff condition is satisfied:

[0023]

[0024] wherein W is the width of the waveguide cross-section perpendicular to the waveguide, n eff1 is the equivalent refractive index at the waveguide spacing in the slanted waveguide region, n eff2 is the equivalent refractive index at the waveguide region in the slanted waveguide region;

[0025] The slant angle of the slanted waveguide satisfies the formula:

[0026] θ j = arctan (id / jZ t )

[0027] wherein i represents the i-th slanted waveguide, i = 1, 2, 3, …; d represents the array period of the slanted waveguide, j represents the j fractional Talbot distance, j = 1 / m, 1 / 2, 1 / 3, …; Z t represents the Talbot distance.

[0028] As a further improvement of the present application, the width of the fractional Talbot cold cavity region is 10 μm to 1000 μm,

[0029] The length satisfies:

[0030] jZ t = 2n eff3 d 2 / mλ

[0031] wherein Z t represents the Talbot distance, j represents the j fractional Talbot distance, j = 1 / m, 1 / 2, 1 / 3, …; n eff3 is the equivalent refractive index of the fractional Talbot cold cavity region, m is a positive integer, λ is the free space optical wavelength, and d represents the array period at the center of the slanted waveguide.

[0032] As a further improvement of the present application,

[0033] The etching depth of the high reflectivity DBR grating is 0.5 μm to 1 μm, the width is 2 μm to 3 μm, the period is 70 nm to 100 nm, the duty cycle is 0.5, and there are 30 to 40 pairs in total.

[0034] The etching depth of the high reflectivity high transmission DBR grating is 0.5 μm to 1 μm, the width is 2 μm to 3 μm, the period is 70 nm to 100 nm, the duty cycle is 0.5, and there are 6 to 10 pairs in total.

[0035] As a further improvement of the present application, the etching depth of the electrically isolated trench is greater than the thickness of the P high doping layer but cannot etch through the blocking layer, the length is 2 μm to 3 μm, and the width is 10 μm to 1000 μm.

[0036] As a further improvement of the present application, the electrode window is divided into two parts, one part is the electrode window formed on the upper surface of the tilted waveguide and the center waveguide in the tilted waveguide region, with a length of 990-3990 mu m and a width of 1-2 mu m, and the other part is the electrode window formed on the upper surface of the fractional Talbot cold cavity region, with a width of 9-990 mu m and a length of 5-10 mu m shorter than that of the fractional Talbot cold cavity region.

[0037] The electrode window is filled with the P metal electrode material, and both sides are electrically insulated layers; the electrically insulated layer is formed by selecting silicon oxide or silicon nitride material, and the thickness is 200-500 nm.

[0038] The application also discloses a preparation method of the monolithic integrated outer cold cavity type self-focusing edge-emitting laser array.

[0039] Selecting a semiconductor substrate;

[0040] Growing a semiconductor epitaxial layer on the upper surface of the semiconductor substrate;

[0041] Etching a tilted waveguide region and forming a fractional Talbot cold cavity region on the upper surface of the semiconductor epitaxial layer;

[0042] Etching an electrically isolated channel between the tilted waveguide region and the fractional Talbot cold cavity region on the upper surface of the semiconductor epitaxial layer;

[0043] Depositing an electrically insulated layer on the upper surface of the semiconductor epitaxial layer and etching the electrically insulated layer on the upper surface of the tilted waveguide region and the fractional Talbot cold cavity region to form an electrode window, and etching the electrically insulated layer above the high reflectivity DBR grating and the semi-reflective semi-transmissive DBR grating region;

[0044] Sputtering a P metal electrode on the upper surface of the electrode window, and stripping the P metal electrode on the upper surface of the electrically isolated channel, the high reflectivity DBR grating and the semi-reflective semi-transmissive DBR grating region;

[0045] Etching the high reflectivity DBR grating and the semi-reflective semi-transmissive DBR grating on the upper surface of the high reflectivity DBR grating and the semi-reflective semi-transmissive DBR grating region;

[0046] Sputtering an N metal electrode on the lower surface of the semiconductor substrate.

[0047] Compared with the prior art, the present application has the following advantages:

[0048] The application is provided with a tilted waveguide area, an electrically isolated channel and a fractional Talbot cold cavity area on the surface of the epitaxial layer in sequence, the tilted angle of the tilted waveguide in the tilted waveguide area is designed to realize the nearly complete coincidence of the feedback light field envelope and the central waveguide light field envelope after the light field returns to the fractional Talbot cold cavity area, the light field is focused on the array center, the coupling loss is greatly reduced, the supermode recognition ability is improved, and the coherence of the laser array is also significantly improved; the design of the electrically isolated channel realizes the independent electric regulation and control of the tilted waveguide area and the fractional Talbot cold cavity area, the complement of the optical gain and the absorption loss of the fractional Talbot cold cavity area is realized by regulating and controlling the injection current of the fractional Talbot cold cavity area, the cavity is changed into a cold cavity without gain and loss for light, and the device efficiency is further improved. The application has simple structure, low cost, and provides an innovative idea for obtaining high-efficiency, high-power and high-beam-quality laser. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 It is a top view of the monolithic integrated external cold cavity type self-focusing edge-emitting laser array disclosed by the application;

[0050] Figure 2 It is a side view of the monolithic integrated external cold cavity type self-focusing edge-emitting laser array disclosed by the application;

[0051] Figure 3 It is a rear cavity surface structure schematic diagram of the monolithic integrated external cold cavity type self-focusing edge-emitting laser array disclosed by the application;

[0052] Figure 4 It is a front cavity surface structure schematic diagram of the monolithic integrated external cold cavity type self-focusing edge-emitting laser array disclosed by the application;

[0053] Figure 5 It is a working mechanism schematic diagram of the monolithic integrated external cold cavity type self-focusing edge-emitting laser array disclosed by the application.

[0054] In the figure:

[0055] 1, tilted waveguide area (including: 2, 3, 4, 6, 7, 8 are tilted waveguides; 5 is a central waveguide); 9, high reflectivity DBR grating; 10, electrically isolated channel; 11, fractional Talbot cold cavity area; 12, semi-reflective semi-transmissive DBR grating; 13, N metal electrode; 14, semiconductor substrate; 15, N confinement layer; 16, N waveguide layer; 17, active layer; 18, P waveguide layer; 19, transition layer; 20, barrier layer; 21, P confinement layer; 22, P high-doped layer; 23, P metal electrode; 24, electrically insulating layer; 25-26, electrode window. DETAILED DESCRIPTION

[0056] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0057] The present application will be described in further detail below with reference to the drawings:

[0058] As shown in the drawings, Figures 1-5 The present application provides a monolithic integrated external cold cavity type self-focusing edge-emitting laser array, comprising: a semiconductor substrate 14 and a semiconductor epitaxial layer formed on the upper surface of the semiconductor substrate 14; wherein,

[0059] The semiconductor epitaxial layer of the present application is sequentially grown on the upper surface of the semiconductor substrate 14, including an N confinement layer 15, an N waveguide layer 16, an active layer 17, a P waveguide layer 18, a transition layer 19, a barrier layer 20, a P confinement layer 21 and a P high-doped layer 22; preferably, the semiconductor substrate 14 is a gallium arsenide substrate, the N confinement layer 15 is an N-type AlGaAs confinement layer, the N waveguide layer 16 is an N-type AlGaAs waveguide layer, the active layer 17 is an InGaAs / GaAs single quantum well active region, the P waveguide layer 18 is a P-type AlGaAs waveguide layer, the transition layer 19 is a P-type AlGaAs transition layer, the barrier layer 20 is a GaAs barrier layer, the P confinement layer 21 is an AlGaAs confinement layer, and the P high-doped layer 22 is a GaAs high-doped layer; wherein, the thickness of the N waveguide layer 16 is greater than that of the P waveguide layer 18, and the total thickness of the two waveguide layers needs to be less than or equal to the base transverse mode cutoff condition:

[0060]

[0061] In the formula, D is the total thickness of the N waveguide layer and the P waveguide layer, λ is the free space optical wavelength, n2 is the equivalent refractive index of the total thickness of the N waveguide layer and the P waveguide layer, n1 is the equivalent refractive index of the N confinement layer and the P confinement layer, and m is a positive integer.

[0062] The present application is sequentially provided with a tilted waveguide region 1, an electrical isolation channel 10 and a fractional Talbot cold cavity region 11 on the upper surface of the semiconductor epitaxial layer from the rear end to the front end.

[0063] Specifically:

[0064] The tilted waveguide region 1 of the present application includes a central waveguide and a plurality of tilted waveguides symmetrically distributed on the left and right sides of the central waveguide, and the number of tilted waveguides is 2-100, such as Figure 1Six inclined waveguides are shown; the inclination angles of each inclined waveguide 2-4, 6-8 are symmetric to the center waveguide 5, and the inclination angle is larger as it is farther away from the center waveguide 5, which is used to focus the light field to the center of the array.

[0065] The length of the center waveguide 5 and the inclined waveguides 2-4, 6-8 in the inclined waveguide region 1 of the present application is 1000 μm-4000 μm, the period is 4 μm-10 μm, the width is 2 μm-3 μm, and the base side mode cutoff condition is met:

[0066]

[0067] In the formula, W is the width perpendicular to the waveguide cross section, n eff1 is the equivalent refractive index at the waveguide interval in the inclined waveguide region, n eff2 is the equivalent refractive index at the waveguide region in the inclined waveguide region.

[0068] The inclination angle of the inclined waveguide of the present application meets the formula:

[0069] θ j =arctan(id / jZ t )

[0070] In the formula, i represents the i-th inclined waveguide (i=1, 2, 3, …), d represents the array period of the inclined waveguide, j represents the j fractional Talbot distance (j=1 / m, 1 / 2, 1 / 3, …), and Z t represents the Talbot distance.

[0071] The electrically isolated channel 10 of the present application is formed between the inclined waveguide region 1 and the fractional Talbot cold cavity region 11, the length of the fractional Talbot cold cavity region 11 meets the fractional Talbot distance, and the passing light has neither gain nor loss; wherein the width of the fractional Talbot cold cavity region 11 is 10 μm-1000 μm,

[0072] The length meets:

[0073] jZ t =2n eff3 d 2 / mλ

[0074] In the formula, Z t represents the Talbot distance, j represents the j fractional Talbot distance, j=1 / m, 1 / 2, 1 / 3, …; n eff3 is the equivalent refractive index of the fractional Talbot cold cavity region, m is a positive integer, λ is the free space light wavelength, and d represents the array period at the center of the inclined waveguide.

[0075] The rear side of the upper surface of the inclined waveguide area 1 is provided with a high reflectivity DBR grating 9, and the front side of the upper surface of the fractional Talbot cold cavity area 11 is provided with a half-reflective and half-transmissive DBR grating 12; the etching depth of the high reflectivity DBR grating 9 is 0.5-1 μm, the width is 2-3 μm, the period is 70-100 nm, the duty cycle is 0.5, and there are 30-40 pairs in total; the etching depth of the high reflectivity and high transmission DBR grating 12 is 0.5-1 μm, the width is 2-3 μm, the period is 70-100 nm, the duty cycle is 0.5, and there are 6-10 pairs in total.

[0076] The etching depth of the electrically isolated channel 10 is greater than the thickness of the P high-doped layer 22 but cannot etch through the blocking layer 20, and the length is 2-3 μm and the width is 10-1000 μm.

[0077] The upper surfaces of the inclined waveguide area 1 and the fractional Talbot cold cavity area 11 are sequentially provided with an electrode window and a P metal electrode 23 from bottom to top, and the lower surface of the semiconductor substrate 14 is provided with an N metal electrode 13; wherein the electrode window 25-26 is divided into two parts, one part is the electrode window 25 formed on the upper surface of the inclined waveguide area 1, the length is 990-3990 μm and the width is 1-2 μm, and the other part is the electrode window 26 formed on the upper surface of the fractional Talbot cold cavity area 11, the width is 9-990 μm and the length is 5-10 μm shorter than that of the fractional Talbot cold cavity area 11. The electrode window 25-26 is filled with P metal electrode 23 material, and the two sides are electrically insulating layers 24; wherein the electrically insulating layer 24 is formed by selecting silicon oxide or silicon nitride material, and the thickness is 200-500 nm. The P metal electrode 23 includes one or more of titanium, platinum and gold, and the thickness is 300-1000 nm; the N metal electrode 13 includes one or more of nickel, germanium and gold, and the thickness is 300-500 nm.

[0078] The application provides a preparation method of a monolithic integrated external cold cavity type self-focusing edge-emitting laser array, which comprises the following steps:

[0079] Step 1, selecting a semiconductor substrate 14;

[0080] Step 2, growing a semiconductor epitaxial layer on the upper surface of the semiconductor substrate 14;

[0081] Step 3, etching an inclined waveguide area 1 on the upper surface of the semiconductor epitaxial layer and forming a fractional Talbot cold cavity area 11;

[0082] Step 4, etching an electrically isolated channel 10 on the upper surface of the semiconductor epitaxial layer between the inclined waveguide area 1 and the fractional Talbot cold cavity area 11;

[0083] Step 5, depositing an electrically insulating layer 24 on the surface of the semiconductor epitaxial layer and etching the electrically insulating layer 24 to form electrode windows 25-26, and etching the electrically insulating layer 24 above the region where the high-reflection DBR grating 9 and the semi-reflective semi-transmissive DBR grating 12 are located;

[0084] Step 6, sputtering a P-metal electrode 23 on the surface of the electrode windows 25-26, and stripping the P-metal electrode 23 above the region where the electrically isolated channel 10, the high-reflection DBR grating 9 and the semi-reflective semi-transmissive DBR grating 12 are located;

[0085] Step 7, etching the high-reflection DBR grating 9 and the semi-reflective semi-transmissive DBR grating 12 on the surface of the region where the high-reflection DBR grating 9 and the semi-reflective semi-transmissive DBR grating 12 are located;

[0086] Step 8, sputtering an N-metal electrode 13 on the lower surface of the semiconductor substrate 14;

[0087] Taking a gallium arsenide semiconductor laser with a working wavelength of 980 nm as an example, a preparation method thereof comprises the following steps:

[0088] S1, selecting a gallium arsenide substrate;

[0089] S2, growing an epitaxial layer on the gallium arsenide substrate by using a metal organic compound vapor deposition method (MOCVD) or a molecular beam epitaxy (MBE) method, from bottom to top in sequence: an N confinement layer 15 is an N-type confinement layer Al 0.28 GaAs, with a doping concentration of 2.5e 18 -3e 18 cm -3 , and a thickness of 1-2 μm; an N waveguide layer 16 is an N-type waveguide layer Al 0.23 GaAs, with a doping concentration of 1e 17 -2e 17 cm -3 , and a thickness of 0.8-1.2 μm; an active layer 17 is a single quantum well structure, wherein the quantum well is In 0.15 GaAs material, with a thickness of 0.006-0.008 μm, and the barrier is GaAs material, with a thickness of 0.008-0.010 μm; a P waveguide layer 18 is a P-type waveguide layer Al 0.22 GaAs, with a doping concentration of 1.5e 17 -2e 17 cm -3 , and a thickness of 0.6-0.8 μm; a transition layer 19 is a P-type transition layer Al 0.22～0.38 GaAs, with a doping concentration of 2e 17 -3e 17 cm -3, thickness is 0.02-0.05 μm; the barrier layer 20 is a barrier layer GaAs, doping concentration is 2e 17 -3e 17 cm -3 -3e 0.27 cm 18 , thickness is 0.02-0.05 μm; the P confinement layer 21 is a P-type confinement layer Al 18 GaAs, doping concentration is 2.5e -3 -3e 19 cm 20 , thickness is 0.8-1 μm; in order to form a good ohmic contact between the P metal electrode 23 and the epitaxial layer structure, a high-doped layer GaAs is grown above the P confinement layer 21, concentration is 3e -3 -1e eff1 cm eff2 , thickness is 0.15-0.2 μm; wherein the N waveguide layer 16 is thicker than the P waveguide layer 18, and the total thickness of the two waveguide layers needs to be less than or equal to the base lateral mode cutoff condition:

[0090]

[0091] wherein D is the total thickness of the N waveguide layer and the P waveguide layer, λ is the free space optical wavelength, n2 is the equivalent refractive index of the total thickness of the N waveguide layer and the P waveguide layer, n1 is the equivalent refractive index of the N confinement layer and the P confinement layer, and m is a positive integer.

[0092] S3, the glue machine cleans the epitaxial wafer, adopts the method of ultraviolet lithography to obtain the inclined waveguide area 1 and the positive photoresist mask pattern of the fractional Talbot cold cavity area 11 on the upper surface of the epitaxial layer, and then etches to obtain the inclined waveguide area 1 and the fractional Talbot cold cavity area 11 by using inductively coupled plasma; wherein the number of the central waveguide in the inclined waveguide area 1 is 1, the number of the inclined waveguide 234678 is 2-100, the length is 1000-4000 μm, the period is 4-10 μm, the width is 2-3 μm, and the base lateral mode cutoff condition needs to be met:

[0093]

[0094] wherein W is the width perpendicular to the waveguide cross section, n eff2 is the equivalent refractive index at the waveguide interval in the inclined waveguide area, and n eff1 is the equivalent refractive index at the waveguide region in the inclined waveguide area.

[0095] The inclination angle satisfies the formula:

[0096] θ j = arctan(id / jZ t )

[0097] wherein i represents the ith tilted waveguide (i = 1, 2, 3,...), d represents the tilted waveguide array period, j represents the j fractional Talbot distance (j = 1 / m, 1 / 2, 1 / 3,...), Z t represents the Talbot distance;

[0098] The fractional Talbot cold cavity region 11 has a width of 10 μm to 1000 μm and a length satisfying:

[0099] jZ t = 2n eff2 d 2 / mλ

[0100] S4, acetone, ethanol, deionized water are used to clean the epitaxial wafer in sequence, and the surface moisture of the epitaxial wafer is blown dry by a nitrogen gun. A photoresist mask pattern is obtained between the tilted waveguide region 1 and the fractional Talbot cold cavity region 11 by using the ultraviolet lithography method, and the electrically isolated channel 10 is obtained by using the inductively coupled plasma method. The etching depth is greater than the thickness of the P high-doped layer 22 but cannot etch through the barrier layer 20. The length is 2 μm to 3 μm, and the width is 10 μm to 1000 μm.

[0101] S5, acetone, ethanol, deionized water are used to clean the epitaxial wafer in sequence, and the surface moisture of the epitaxial wafer is blown dry by a nitrogen gun. The electrically insulating layer 24 such as silicon oxide or silicon nitride material is deposited by using the plasma chemical vapor deposition method. The thickness is 200 nm to 500 nm.

[0102] S6, the epitaxial wafer is cleaned by a glue machine. A photoresist mask pattern is obtained on the surface of the electrically insulating layer 24 on the upper surface of the tilted waveguide region 1 and the fractional Talbot cold cavity region 11 by using the ultraviolet lithography method. The electrode window 25-26 is obtained by using the inductively coupled plasma method. Part of the electrode window 25 is formed on the upper surface of the tilted waveguide 234678 and the center waveguide 5 in the tilted waveguide region 1. The length is 990 μm to 3990 μm, and the width is 1 μm to 2 μm. The other part of the electrode window 26 is formed on the upper surface of the fractional Talbot cold cavity region 11. The width is 9 μm to 990 μm, and the length is 5 μm to 10 μm shorter than the fractional Talbot cold cavity region 11. At the same time, the electrically insulating layer 24 on the upper surface of the region where the high-reflectivity DBR grating 9 and the semi-reflective semi-transmissive DBR grating 12 are located is etched.

[0103] S7, sputtering or evaporating P metal electrode 23 on the top surface of the epitaxial wafer by using the method of magnetron sputtering or electron beam evaporation, sputtering titanium metal 30-50nm, platinum metal 30-50nm, gold metal 300-500nm in sequence, and stripping P metal electrode 23 above the region where electric isolation channel 10, high reflectivity DBR grating 9 and semi-reflective semi-transmissive DBR grating 12 are located;

[0104] S8, obtaining mask pattern on the top surface of the region where high reflectivity DBR grating 9 and semi-reflective semi-transmissive DBR grating 12 are located by using the method of electron beam lithography, and etching high reflectivity DBR grating 9 and semi-reflective semi-transmissive DBR grating 12 by using the method of inductively coupled plasma, etching depth 0.5-1um, width 2-3um, period 70-100nm, duty cycle 0.5; wherein, high reflectivity DBR grating 9 has 30-40 pairs, and semi-reflective semi-transmissive DBR grating 12 has 6-10 pairs

[0105] S9, thinning and polishing gallium arsenide substrate, remaining substrate thickness 100-120um.

[0106] S10, sputtering N face electrode 13 on the lower surface of gallium arsenide substrate 14 by using the method of magnetron sputtering, sputtering nickel metal 20-30nm, germanium gold alloy 30-50nm, gold metal 200-300nm in sequence;

[0107] S11, alloy annealing the epitaxial wafer by using alloy annealing machine;

[0108] S12, cleaving array units by using cleaving machine;

[0109] S13, packaging array units with P face downward on the heat sink with solder by using flip-chip method, and testing device performance.

[0110] The advantages of the present application are:

[0111] The present application is provided with a tilted waveguide area, an electrically isolated channel and a fractional Talbot cold cavity area on the surface of the epitaxial layer in turn. By designing the tilt angle of the tilted waveguide in the tilted waveguide area, the feedback light field envelope and the central waveguide light field envelope after the return of the fractional Talbot cold cavity area are nearly completely overlapped, the light field self-focusing is realized, and the coupling efficiency and supermode recognition ability of the laser array are improved, and the coherence of the device is also significantly improved. The design of the electrically isolated channel realizes the independent electric regulation and control of the tilted waveguide area and the fractional Talbot cold cavity area, the material in the fractional Talbot cold cavity area is transparentized by regulating the injection current of the fractional Talbot cold cavity area, the cavity is changed into a cold cavity without gain and loss for photons, and the efficiency of the device is further improved. The present application not only has simple structure and low cost, but also provides an innovative idea for obtaining high-efficiency, high-power and high-beam-quality laser.

[0112] The above is only the preferred embodiment of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A monolithic integrated external cold cavity type self-focusing edge emitting laser array, characterized by, It comprises: a semiconductor substrate; a semiconductor epitaxial layer is formed on the upper surface of the semiconductor substrate; a tilted waveguide area, an electrical isolation channel, a fractional Talbot cold cavity area and a semi-reflective semi-transmissive DBR grating are arranged on the upper surface of the semiconductor epitaxial layer; the tilted waveguide area comprises a central waveguide and a plurality of tilted waveguides symmetrically distributed on both sides of the central waveguide, the tilt angle of each tilted waveguide is symmetric to the center of the central waveguide, and the tilt angle increases with the distance from the central waveguide, so that the light field is focused on the array center; the electrical isolation channel is formed between the tilted waveguide area and the fractional Talbot cold cavity area, the length of the fractional Talbot cold cavity area satisfies the fractional Talbot distance, and the passing light has neither gain nor loss; the rear side of the upper surface of the tilted waveguide area is provided with a high reflectivity DBR grating, and the front side of the upper surface of the fractional Talbot cold cavity area is provided with a semi-reflective semi-transmissive DBR grating; the upper surfaces of the tilted waveguide area and the fractional Talbot cold cavity area are sequentially provided with an electrode window and a P-metal electrode from bottom to top; the lower surface of the semiconductor substrate is provided with an N-metal electrode.

2. The monolithic integrated, external-cavity, type self-focused edge emitting laser array of claim 1, wherein, The semiconductor epitaxial layer sequentially comprises an N-limiting layer, an N-waveguide layer, an active layer, a P-waveguide layer, a transition layer, a barrier layer, a P-limiting layer and a P-high-doping layer, wherein the thickness of the N-waveguide layer is greater than the thickness of the P-waveguide layer, and the total thickness of the N-waveguide layer and the P-waveguide layer is less than or equal to the base transverse mode cutoff condition: wherein D is the total thickness of the N-waveguide layer and the P-waveguide layer, λ is the free space optical wavelength, n2 is the equivalent refractive index of the total thickness of the N-waveguide layer and the P-waveguide layer, n1 is the equivalent refractive index of the N-limiting layer and the P-limiting layer, and m is a positive integer.

3. The monolithic integrated external cold cavity type self-focusing edge emitting laser array according to claim 1 or 2, wherein: the semiconductor substrate is selected from gallium arsenide, indium phosphide or gallium nitride; the P-metal electrode comprises one or more of titanium, platinum and gold, and has a thickness of 300 nm to 1000 nm; the N-metal electrode comprises one or more of nickel, germanium and gold, and has a thickness of 300 nm to 500 nm.

4. The monolithically integrated, external-cavity, self-aligned edge-emitting laser array of claim 1, wherein, The cross section of the central waveguide of the tilted waveguide area is rectangular, and the cross sections of the remaining tilted waveguides are parallelograms.

5. The monolithically integrated, external-cavity, type-II self-focusing edge- emitting laser array of claim 4, wherein, The number of central waveguides in the tilted waveguide area is 1, the number of tilted waveguides is 2 to 100, the length is 1000 μm to 4000 μm, the period is 4 μm to 10 μm, the width is 2 μm to 3 μm, and the base lateral mode cutoff condition is satisfied: where W is the width of the waveguide cross-section normal to the direction of propagation, n eff1 is the equivalent refractive index at the waveguide spacing within the tilted waveguide region, n eff2 is the equivalent refractive index at the waveguide region within the tilted waveguide region. The tilt angle of the tilted waveguide satisfies the formula: θ j = arctan(id / jz t ) In the formula, i represents the i-th tilted waveguide, i = 1, 2, 3, …; d represents the array period at the center of the tilted waveguide, j represents the j fractional Talbot distance, j = 1 / m, 1 / 2, 1 / 3, …; Z t represents the Talbot distance.

6. The monolithically integrated, external-cavity, self-aligned edge-emitting laser array of claim 1, wherein, The width of the fractional Talbot cold cavity area is 10 μm to 1000 μm, and the length satisfies: jZ t = 2n eff3 d 2 / mλ In the formula, Z t Talbot distance, j represents j fractional order Talbot distance, j = 1 / m, 1 / 2, 1 / 3,...; n eff3 Fractional Talbot cold cavity region equivalent refractive index, m is a positive integer, λ is a free space optical wavelength, and d represents an array period at the center of the inclined waveguide.

7. The monolithic integrated external cold cavity type self-focusing edge emitting laser array according to claim 1, wherein: the etching depth of the high reflectivity DBR grating is 0.5 μm to 1 μm, the width is 2 μm to 3 μm, the period is 70 nm to 100 nm, the duty cycle is 0.5, and there are 30 to 40 pairs. The high reflectivity high transmission DBR grating has an etching depth of 0.5-1 μm, a width of 2-3 μm, a period of 70-100 nm, a duty cycle of 0.5, and 6-10 pairs in total.

8. The monolithically integrated, external-cavity, type self-focusing edge- emitting laser array of claim 2, wherein, The etching depth of the electrically isolated channel is greater than the thickness of the P high doping layer but cannot etch through the blocking layer, the length is 2-3 μm, and the width is 10-1000 μm.

9. The monolithically integrated, external-cavity, self-aligned edge-emitting laser array of claim 1, wherein, The electrode window is divided into two parts, one part is the electrode window formed on the upper surface of the tilted waveguide and the central waveguide in the tilted waveguide region, with a length of 990-3990 μm and a width of 1-2 μm, and the other part is the electrode window formed on the upper surface of the fractional Talbot cold cavity region, with a width of 9-990 μm and a length of 5-10 μm shorter than the fractional Talbot cold cavity region. The electrode window is filled with the P metal electrode material, and the two sides are electrically insulated layers; the electrically insulated layers are formed by selecting silicon oxide or silicon nitride material, and the thickness is 200-500 nm.

10. A method of fabricating a monolithic integrated external-cavity type self- focused edge-emitting laser array as claimed in any one of claims 1 to 9, characterized in that, The method comprises the following steps: selecting a semiconductor substrate; growing a semiconductor epitaxial layer on the upper surface of the semiconductor substrate; etching a tilted waveguide region and forming a fractional Talbot cold cavity region on the upper surface of the semiconductor epitaxial layer; etching an electrically isolated channel between the tilted waveguide region and the fractional Talbot cold cavity region on the upper surface of the semiconductor epitaxial layer; depositing an electrically insulated layer on the upper surface of the semiconductor epitaxial layer, etching the electrically insulated layer on the upper surface of the tilted waveguide region and the fractional Talbot cold cavity region to form an electrode window, and etching the electrically insulated layer above the high reflectivity DBR grating and the semi-reflective semi-transmissive DBR grating region; sputtering a P metal electrode on the upper surface of the electrode window, and stripping the P metal electrode on the upper surface of the electrically isolated channel, the high reflectivity DBR grating and the semi-reflective semi-transmissive DBR grating region; etching the high reflectivity DBR grating and the semi-reflective semi-transmissive DBR grating on the upper surface of the high reflectivity DBR grating and the semi-reflective semi-transmissive DBR grating region; sputtering an N metal electrode on the lower surface of the semiconductor substrate.

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