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

Abstract

The invention discloses a monolithic integrated external cold cavity type self-focusing edge-emitting laser array and a preparation method thereof. The monolithic integrated external cold cavity type self-focusing edge-emitting laser array is characterized in that an inclined waveguide region, an electrical isolation channel and a fractional order Talbot cold cavity region are sequentially arranged on the upper surface of a semiconductor epitaxial layer; the inclined waveguide area comprises a central waveguide and a plurality of inclined waveguides symmetrically distributed on the left side and the right side of the central waveguide, and the inclined angle of each inclined waveguide is larger when being farther away from the central waveguide; the length of the fractional order Talbot cold cavity area meets the fractional order Talbot distance, and no gain and no loss are generated for passing light; a high-reflectivity DBR grating is arranged on one side of the upper surface of the inclined waveguide region; and one side of the upper surface of the fractional order Talbot cold cavity area is provided with a semi-reflection and semi-transmission DBR grating. According to the invention, the coherence of the laser array is effectively improved, the loss of the fractional order Talbot array in the super-mode identification process is reduced, and high-efficiency and high-beam-quality output of the laser array is realized.

Description

Technical Field

[0001] The invention relates to the technical field of edge-emitting semiconductor lasers, and in particular to a monolithic integrated external cooling cavity type self-focusing edge-emitting laser array and a preparation method thereof. Background Art

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

[0003] In recent years, various monolithic integrated Talbot cavity edge-emitting laser array solutions have been proposed. This structure takes into account the small size and easy integration of traditional edge-emitting lasers, and is based on the Talbot diffraction strong coupling method, which 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 not being able to achieve good supermode recognition under low loss conditions, which is also one of the reasons why such devices cannot be successfully commercialized. Therefore, the development of efficient, high-power, and high-beam quality laser light sources is still an urgent problem to be solved. Summary of the invention

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

[0006] The present invention 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 region, an electrical isolation channel, a fractional-order Talbot cold cavity region and a semi-reflective and 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, wherein the inclination angle of each inclined waveguide is symmetrical about the central waveguide, and the farther away from the central waveguide, the larger the inclination angle is, so that the light field is focused on the center of the array;

[0010] The electrical isolation channel is formed between the inclined waveguide region and the fractional-order Talbot cold cavity region, the length of the fractional-order Talbot cold cavity region satisfies the fractional-order Talbot distance, and has neither gain nor loss for the light passing therethrough;

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

[0012] The upper surfaces of the inclined waveguide region and the fractional-order Talbot cold cavity region are provided with electrode windows and P metal electrodes in sequence from bottom to top;

[0013] An N metal electrode is provided on the lower surface of the semiconductor substrate.

[0014] As a further improvement of the present invention, the semiconductor epitaxial layers are, from bottom to top, N limiting layer, N waveguide layer, active layer, P waveguide layer, transition layer, barrier layer, P limiting layer and P high-doped 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 fundamental transverse mode cutoff condition:

[0015]

[0016] Where D is the total thickness of the N waveguide layer and the P waveguide layer, λ is the wavelength of free space light, 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.

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

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

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

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

[0021] As a further improvement of the present invention, the central waveguide cross section of the inclined waveguide area is a rectangle, and the remaining inclined waveguide cross sections are parallelograms.

[0022] As a further improvement of the present invention, the number of central waveguides in the inclined waveguide area 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 side mode cutoff condition must be met:

[0023]

[0024] Where W is the width perpendicular to the waveguide 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;

[0025] The tilt angle of the tilted waveguide satisfies the formula:

[0026] θ j =arctan(id / jZ t )

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

[0028] As a further improvement of the present invention, the width of the fractional-order Talbot cold cavity zone is 10 μm to 1000 μm.

[0029] Length meets:

[0030] JZ t =2n eff3 d 2 / m

[0031] In the formula, Z t represents the Talbot distance, j represents the j-order 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 wavelength of free space light, and d represents the array period at the center of the tilted waveguide.

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

[0033] The high reflectivity DBR grating has an etching depth of 0.5 μm to 1 μm, a width of 2 μm to 3 μm, a period of 70 nm to 100 nm, a duty cycle of 0.5, and a total of 30 to 40 pairs;

[0034] The high-reflectivity and high-transmittance DBR grating has an etching depth of 0.5 μm to 1 μm, a width of 2 μm to 3 μm, a period of 70 nm to 100 nm, a duty cycle of 0.5, and a total of 6 to 10 pairs.

[0035] As a further improvement of the present invention, the etching depth of the electrical isolation channel is greater than the thickness of the P high-doped layer but cannot penetrate the barrier 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 invention, the electrode window is divided into two parts, one part is an electrode window formed on the upper surface of the inclined waveguide and the central waveguide in the inclined waveguide area, with a length of 990 μm to 3990 μm and a width of 1 μm to 2 μm, and the other part is an electrode window formed on the upper surface of the fractional-order Talbot cold cavity area, with a width of 9 μm to 990 μm and a length shorter than that of the fractional-order Talbot cold cavity area by 5 μm to 10 μm;

[0037] The electrode window is filled with the P metal electrode material, and both sides are electrical insulation layers; the electrical insulation layer is formed of silicon oxide or silicon nitride material, and has a thickness of 200nm to 500nm.

[0038] The present invention also discloses a method for preparing a monolithic integrated external cold cavity type self-focusing edge emitting laser array, comprising:

[0039] selecting a semiconductor substrate;

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

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

[0042] An electrical isolation channel is etched on the upper surface of the semiconductor epitaxial layer between the inclined waveguide region and the fractional-order Talbot cold cavity region;

[0043] Depositing an electrical insulating layer on the upper surface of the semiconductor epitaxial layer and etching the electrical insulating layer on the upper surface of the inclined waveguide region and the fractional-order Talbot cold cavity region to form an electrode window, and etching the electrical insulating layer above the region where the high-reflectivity DBR grating and the semi-reflective and semi-transmissive DBR grating are located;

[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 area where the electrical isolation channel, the high reflectivity DBR grating, and the semi-reflective and semi-transmissive DBR grating are located;

[0045] The high reflectivity DBR grating and the semi-reflective and semi-transmissive DBR grating are etched on the upper surface of the area where the high reflectivity DBR grating and the semi-reflective and semi-transmissive DBR grating are located to obtain the high reflectivity DBR grating and the semi-reflective and semi-transmissive DBR grating;

[0046] An N metal electrode is sputtered on the lower surface of the semiconductor substrate.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] The present invention sequentially provides an inclined waveguide region, an electrically isolated channel and a fractional-order Talbot cold cavity region on the upper surface of the epitaxial layer. By designing the inclination angle of the inclined waveguide in the inclined waveguide region, the feedback light field envelope and the central waveguide light field envelope after the waveguide goes back and forth to the fractional-order Talbot cold cavity region are almost completely overlapped, and the light field is focused at the center of the array, thereby greatly reducing the coupling loss, improving the supermode recognition capability, and significantly improving the coherence of the laser array; the design of the electrically isolated channel realizes the independent electrical control of the inclined waveguide region and the fractional-order Talbot cold cavity region, and the complementarity of the optical gain and absorption loss of the region is realized by regulating the injection current of the fractional-order Talbot cold cavity region, and the cavity is transformed into a cold cavity with neither gain nor loss to light, further improving the efficiency of the device. The present invention is not only simple in structure and low in cost, but also provides an innovative idea for obtaining high-efficiency, high-power and high-beam-quality lasers. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 A top view of the monolithic integrated external cooling cavity self-focusing edge emitting laser array disclosed in the present invention;

[0050] Figure 2 It is a side view of the monolithic integrated external cooling cavity type self-focusing edge emitting laser array disclosed in the present invention;

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

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

[0053] Figure 5 The figure is a schematic diagram of the working mechanism of the monolithic integrated external cooling cavity type self-focusing edge emitting laser array disclosed in the present invention.

[0054] In the figure:

[0055] 1. Inclined waveguide region (including: 2, 3, 4, 6, 7, 8 are inclined waveguides; 5 is a central waveguide); 9. High reflectivity DBR grating; 10. Electrical isolation channel; 11. Fractional-order Talbot cold cavity region; 12. Semi-reflective and 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 highly doped layer; 23. P metal electrode; 24. Electrical insulation layer; 25-26. Electrode window. DETAILED DESCRIPTION

[0056] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0057] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0058] like Figures 1 to 5 As shown, the present invention 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 invention is a semiconductor substrate 14 on which an N limiting 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 limiting layer 21 and a P high-doped layer 22 are sequentially grown; preferably, the semiconductor substrate 14 is a gallium arsenide substrate, the N limiting layer 15 is an N-type AlGaAs limiting 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 limiting layer 21 is an AlGaAs limiting 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 fundamental transverse mode cutoff condition:

[0060]

[0061] Where D is the total thickness of the N waveguide layer and the P waveguide layer, λ is the wavelength of free space light, 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 invention sequentially provides an inclined waveguide region 1, an electrical isolation channel 10 and a fractional-order Talbot cold cavity region 11 on the upper surface of the semiconductor epitaxial layer from the rear end to the front end.

[0063] Specific:

[0064] The inclined waveguide area 1 of the present invention includes a central waveguide and a plurality of inclined waveguides symmetrically distributed on the left and right sides of the central waveguide, and the number of the inclined waveguides is 2 to 100. Figure 1Six tilted waveguides are shown; the tilt angle of each tilted waveguide 2-4, 6-8 is symmetrical with respect to the central waveguide 5, and the tilt angle increases as it is farther away from the central waveguide 5, which is used to focus the light field at the center of the array.

[0065] The central waveguide 5 and the inclined waveguides 2-4, 6-8 in the inclined waveguide area 1 of the present invention have a length of 1000 μm to 4000 μm, a period of 4 μm to 10 μm, a width of 2 μm to 3 μm, and must meet the base side mode cutoff condition:

[0066]

[0067] Where W is the width perpendicular to the waveguide 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 tilt angle of the tilted waveguide of the present invention satisfies the formula:

[0069] θ j =arctan(id / jZ t )

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

[0071] The electrical isolation channel 10 of the present invention is formed between the inclined waveguide region 1 and the fractional-order Talbot cold cavity region 11. The length of the fractional-order Talbot cold cavity region 11 satisfies the fractional-order Talbot distance and has neither gain nor loss for the light passing therethrough. The width of the fractional-order Talbot cold cavity region 11 is 10 μm to 1000 μm.

[0072] Length meets:

[0073] JZ t =2n eff3 d 2 / m

[0074] In the formula, Z t represents the Talbot distance, j represents the j-order 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 wavelength of free space light, and d represents the array period at the center of the tilted waveguide.

[0075] A high-reflectivity DBR grating 9 is provided on the rear side of the upper surface of the inclined waveguide region 1 of the present invention, and a semi-reflective and semi-transmissive DBR grating 12 is provided on the front side of the upper surface of the fractional-order Talbot cold cavity region 11; the high-reflectivity DBR grating 9 of the present invention has an etching depth of 0.5 μm to 1 μm, a width of 2 μm to 3 μm, a period of 70 nm to 100 nm, a duty cycle of 0.5, and a total of 30 to 40 pairs; the high-reflectivity and high-transmittance DBR grating 12 has an etching depth of 0.5 μm to 1 μm, a width of 2 μm to 3 μm, a period of 70 nm to 100 nm, a duty cycle of 0.5, and a total of 6 to 10 pairs.

[0076] The etching depth of the electrical isolation channel 10 of the present invention is greater than the thickness of the P high-doped layer 22 but cannot penetrate the barrier layer 20, and the length is 2 μm to 3 μm and the width is 10 μm to 1000 μm.

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

[0078] The present invention provides a method for preparing a monolithic integrated external cooling cavity type self-focusing edge emitting laser array, comprising:

[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 the inclined waveguide region 1 on the upper surface of the semiconductor epitaxial layer to form a fractional-order Talbot cold cavity region 11;

[0082] Step 4, etching an electrical isolation channel 10 between the inclined waveguide region 1 and the fractional-order Talbot cold cavity region 11 on the upper surface of the semiconductor epitaxial layer;

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

[0084] Step 6, sputtering a P metal electrode 23 on the upper surface of the electrode windows 25-26, and peeling off the P metal electrode 23 above the area where the electrical isolation channel 10, the high reflectivity DBR grating 9 and the semi-reflective and semi-transmissive DBR grating 12 are located;

[0085] Step 7, etching the upper surface of the area where the high reflectivity DBR grating 9 and the semi-reflective and semi-transmissive DBR grating 12 are located to obtain the high reflectivity DBR grating 9 and the semi-reflective and semi-transmissive DBR grating 12;

[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 an operating wavelength of 980nm as an example, its preparation method includes:

[0088] S1. Select gallium arsenide substrate;

[0089] S2. On the GaAs substrate, an epitaxial layer is grown by metal organic compound vapor deposition (MOCVD) or molecular beam epitaxy (MBE), from bottom to top: N restriction layer 15 is an N-type restriction layer Al 0.28 GaAs, doping concentration 2.5e 18 ~3e 18 cm -3 , with a thickness of 1 μm to 2 μm; the N waveguide layer 16 is an N-type waveguide layer Al 0.23 GaAs, doping concentration 1e 17 ~2e 17 cm -3 , with a thickness of 0.8μm to 1.2μm; the active layer 17 is a single quantum well structure, in which the quantum well is In 0.15 GaAs material, thickness is 0.006μm~0.008μm, the barrier is GaAs material, thickness is 0.008μm~0.010μm; P waveguide layer 18 is P type waveguide layer Al 0.22 GaAs, doping concentration 1.5e 17 ~2e 17 cm -3 , with a thickness of 0.6μm to 0.8μm; the transition layer 19 is a P-type transition layer Al 0.22～0.38 GaAs, doping concentration 2e 17 ~3e 17 cm -3, with a thickness of 0.02μm to 0.05μm; the barrier layer 20 is a barrier layer GaAs with a doping concentration of 2e 17 ~3e 17 cm -3 , with a thickness of 0.02μm to 0.05μm; the P limiting layer 21 is a P-type limiting layer Al 0.27 GaAs, doping concentration 2.5e 18 ~3e 18 cm -3 , with a thickness of 0.8μm to 1μm; in order to form a good ohmic contact between the P metal electrode 23 and the epitaxial layer structure, a highly doped GaAs layer is grown above the P confinement layer 21, with a concentration of 3e 19 ~1e 20 cm -3 , with a thickness of 0.15 μm to 0.2 μm; 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 must be less than or equal to the fundamental transverse mode cutoff condition:

[0090]

[0091] Where D is the total thickness of the N waveguide layer and the P waveguide layer, λ is the wavelength of free space light, 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 epitaxial wafer is cleaned by a glue machine, and a positive photoresist mask pattern of the inclined waveguide area 1 and the fractional-order Talbot cold cavity area 11 is obtained on the upper surface of the epitaxial layer by ultraviolet lithography, and then the inclined waveguide area 1 and the fractional-order Talbot cold cavity area 11 are etched by an inductively coupled plasma method; wherein, the number of the central waveguide 5 in the inclined waveguide area 1 is 1, the number of the inclined waveguide 234678 is 2 to 100, the length is 1000μm to 4000μm, the period is 4μm to 10μm, the width is 2μm to 3μm, and the base side mode cutoff condition must be met:

[0093]

[0094] Where W is the width perpendicular to the waveguide 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.

[0095] The tilt angle satisfies the formula:

[0096] θ j =arctan(id / jZ t )

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

[0098] The width of the fractional-order Talbot cold cavity zone 11 is 10 μm to 1000 μm, and the length satisfies:

[0099] JZ t =2n eff2 d 2 / m

[0100] S4, clean the epitaxial wafer with acetone, ethanol and deionized water in turn, and use a nitrogen gun to dry the moisture on the surface of the epitaxial wafer, use ultraviolet photolithography to obtain a photoresist-free mask pattern of the electrical isolation channel 10 between the inclined waveguide area 1 and the fractional-order Talbot cold cavity area 11, and then use an inductively coupled plasma method to etch the electrical isolation channel 10, the etching depth is greater than the thickness of the P high-doped layer 22 but cannot penetrate the barrier layer 20, the length is 2μm~3μm, and the width is 10μm~1000μm.

[0101] S5. Clean the epitaxial wafer with acetone, ethanol and deionized water in turn, and use a nitrogen gun to dry the surface moisture of the epitaxial wafer. Use plasma chemical vapor deposition to deposit an electrical insulating layer 24, such as silicon oxide or silicon nitride material, with a thickness of 200nm to 500nm.

[0102] S6. Clean the epitaxial wafer with a glue sprayer, and obtain electrode windows 25-26 on the surface of the electrical insulation layer 24 on the upper surface of the inclined waveguide area 1 and the fractional-order Talbot cold cavity area 11 without a photoresist mask pattern by ultraviolet lithography, and then etch the electrode windows 25-26 by inductively coupled plasma method; wherein, one part is the electrode window 25 formed on the upper surface of the inclined waveguide 234678 and the central waveguide 5 in the inclined waveguide area 1, with a length of 990μm-3990μm and a width of 1μm-2μm, and the other part is the electrode window 26 formed on the upper surface of the fractional-order Talbot cold cavity area 11, with a width of 9μm-990μm and a length shorter than that of the fractional-order Talbot cold cavity area 11 by 5μm-10μm; at the same time, etch the electrical insulation layer 24 on the upper surface of the high-reflectivity DBR grating 9 and the semi-reflective and semi-transmissive DBR grating 12.

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

[0104] S8. Using electron beam lithography, a mask pattern is obtained on the upper surface of the area where the high reflectivity DBR grating 9 and the semi-reflective and semi-transmissive DBR grating 12 are located. Using inductively coupled plasma, a high reflectivity DBR grating 9 and a semi-reflective and semi-transmissive DBR grating 12 are etched. The etching depth is 0.5 μm to 1 μm, the width is 2 μm to 3 μm, the period is 70 nm to 100 nm, and the duty cycle is 0.5. Among them, there are 30 to 40 pairs of high reflectivity DBR gratings 9 and 6 to 10 pairs of semi-reflective and semi-transmissive DBR gratings 12.

[0105] S9, thinning and polishing the gallium arsenide substrate, and the remaining substrate thickness is 100 μm to 120 μm.

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

[0107] S11, performing alloy annealing treatment on the epitaxial wafer using an alloy annealing machine;

[0108] S12, using a cleaving machine to cleave the array unit;

[0109] S13, using a flip-chip method, encapsulate the array unit P face down on a heat sink with solder, and perform a device performance test.

[0110] The advantages of the present invention are:

[0111] The present invention sequentially provides an inclined waveguide region, an electrically isolated channel, and a fractional-order Talbot cold cavity region on the upper surface of the epitaxial layer. By designing the inclination angle of the inclined waveguide in the inclined waveguide region, the feedback light field envelope and the central waveguide light field envelope after the round trip to the fractional-order Talbot cold cavity region are almost completely overlapped, thereby realizing self-focusing of the light field, thereby improving the coupling efficiency and supermode recognition ability of the laser array, and significantly improving the coherence of the device. The design of the electrically isolated channel realizes independent electrical control of the inclined waveguide region and the fractional-order Talbot cold cavity region, and the transparency of the material in the fractional-order Talbot cold cavity region is realized by regulating the injection current of the fractional-order Talbot cold cavity region, turning the cavity into a cold cavity with neither gain nor loss for photons, further improving the efficiency of the device. The present invention is not only simple in structure and low in cost, but also provides an innovative idea for obtaining high-efficiency, high-power and high-beam quality lasers.

[0112] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A monolithic integrated external cooling cavity type self-focusing edge emitting laser array, characterized in that: include: Semiconductor substrate; A semiconductor epitaxial layer is formed on the upper surface of the semiconductor substrate; The upper surface of the semiconductor epitaxial layer is provided with an inclined waveguide region, an electrical isolation channel, a fractional-order Talbot cold cavity region and a semi-reflective and semi-transmissive DBR grating; 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, wherein the inclination angle of each inclined waveguide is symmetrical about the central waveguide, and the farther away from the central waveguide, the larger the inclination angle is, so that the light field is focused on the center of the array; The electrical isolation channel is formed between the inclined waveguide region and the fractional-order Talbot cold cavity region, the length of the fractional-order Talbot cold cavity region satisfies the fractional-order Talbot distance, and has neither gain nor loss for the light passing therethrough; A high-reflectivity DBR grating is disposed on the rear side of the upper surface of the inclined waveguide region, and a semi-reflective and semi-transmissive DBR grating is disposed on the front side of the upper surface of the fractional-order Talbot cold cavity region; The upper surfaces of the inclined waveguide region and the fractional-order Talbot cold cavity region are provided with electrode windows and P metal electrodes in sequence from bottom to top; An N metal electrode is provided on the lower surface of the semiconductor substrate.

2. The monolithic integrated external cooling cavity self-focusing edge emitting laser array according to claim 1, characterized in that: The semiconductor epitaxial layers are, from bottom to top, N limiting layer, N waveguide layer, active layer, P waveguide layer, transition layer, barrier layer, P limiting layer and P high-doped 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 fundamental transverse mode cutoff condition: Where D is the total thickness of the N waveguide layer and the P waveguide layer, λ is the wavelength of free space light, 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.

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

4. The monolithic integrated external cooling cavity type self-focusing edge emitting laser array according to claim 1, characterized in that: The central waveguide cross section of the inclined waveguide area is a rectangle, and the other inclined waveguide cross sections are parallelograms.

5. The monolithic integrated external cooling cavity type self-focusing edge emitting laser array according to claim 4, characterized in that: The number of central waveguides in the inclined waveguide area 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 side mode cutoff condition must be met: Where W is the width perpendicular to the waveguide 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; The tilt angle of the tilted waveguide satisfies the formula: θ j =arctan(id / jZ t ) Where 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-th fractional Talbot distance, j = 1 / m, 1 / 2, 1 / 3, ...; Z t represents the Talbot distance.

6. The monolithic integrated external cooling cavity type self-focusing edge emitting laser array according to claim 1, characterized in that: The width of the fractional-order Talbot cold cavity region is 10 μm to 1000 μm, and the length satisfies: jZ t =2n eff3 d 2 / mλ In the formula, Z t represents the Talbot distance, j represents the j-order 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 wavelength of free space light, and d represents the array period at the center of the tilted waveguide.

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

8. The monolithic integrated external cooling cavity type self-focusing edge emitting laser array according to claim 2, characterized in that: The etching depth of the electrical isolation channel is greater than the thickness of the P high-doped layer but cannot penetrate the barrier layer, the length is 2 μm to 3 μm, and the width is 10 μm to 1000 μm.

9. The monolithic integrated external cooling cavity type self-focusing edge emitting laser array according to claim 1, characterized in that: The electrode window is divided into two parts, one part is an electrode window formed on the upper surface of the inclined waveguide and the central waveguide in the inclined waveguide area, with a length of 990 μm to 3990 μm and a width of 1 μm to 2 μm, and the other part is an electrode window formed on the upper surface of the fractional-order Talbot cold cavity area, with a width of 9 μm to 990 μm and a length shorter than that of the fractional-order Talbot cold cavity area by 5 μm to 10 μm; The electrode window is filled with the P metal electrode material, and both sides are electrical insulation layers; the electrical insulation layer is formed of silicon oxide or silicon nitride material, and has a thickness of 200nm to 500nm.

10. A method for preparing a monolithically integrated externally cooled cavity self-focusing edge emitting laser array as claimed in any one of claims 1 to 9, characterized in that: include: selecting a semiconductor substrate; Growing a semiconductor epitaxial layer on the surface of a semiconductor substrate; Etching an inclined waveguide region on the upper surface of the semiconductor epitaxial layer and forming a fractional-order Talbot cold cavity region; An electrical isolation channel is etched on the upper surface of the semiconductor epitaxial layer between the inclined waveguide region and the fractional-order Talbot cold cavity region; Depositing an electrical insulating layer on the upper surface of the semiconductor epitaxial layer and etching the electrical insulating layer on the upper surface of the inclined waveguide region and the fractional-order Talbot cold cavity region to form an electrode window, and etching the electrical insulating layer above the region where the high-reflectivity DBR grating and the semi-reflective and semi-transmissive DBR grating are located; 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 area where the electrical isolation channel, the high reflectivity DBR grating, and the semi-reflective and semi-transmissive DBR grating are located; The high reflectivity DBR grating and the semi-reflective and semi-transmissive DBR grating are etched on the upper surface of the area where the high reflectivity DBR grating and the semi-reflective and semi-transmissive DBR grating are located to obtain the high reflectivity DBR grating and the semi-reflective and semi-transmissive DBR grating; An N metal electrode is sputtered on the lower surface of the semiconductor substrate.

Images