Anti-reflection semiconductor laser based on coupling of asymmetric grating and lateral microcavity

Abstract

The invention belongs to the technical field of semiconductor lasers, and discloses an asymmetric grating and lateral microcavity coupling-based anti-reflection semiconductor laser, which comprises a substrate layer (2), and a buffer layer (3), a lower limiting layer (4), a lower waveguide layer (5), a multi-quantum well layer (6), an upper waveguide layer (7), a grating layer (8), a cover layer (9) and a contact layer (10) which are sequentially formed on the substrate layer (2), the grating layer (8) is asymmetrically distributed, the refractive index modulation depth of the grating layer (8) varies non-uniformly along the cavity length direction, the front half section of grating close to the light output end of the front end of the laser has a relatively shallow modulation depth, and the rear half section of grating has a relatively deep modulation depth. A'light path irreversible 'structure is introduced into the laser, so that forward emergent light is efficiently output, and reverse reflected light is guided to a special'light trap' to be absorbed and dissipated instead of returning to an active area.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor laser technology and relates to an anti-reflection semiconductor laser based on coupling between an asymmetric grating and a lateral microcavity. Background Technology

[0002] In 10Gbps optical communication systems such as data center interconnects and 5G fronthaul, low-cost, small-package direct-modulation lasers are the core light source. Traditional solutions use a combination of distributed feedback lasers and optical isolators to suppress external reflected light, but this leads to problems such as high cost, complex packaging, and large module size.

[0003] Currently, achieving anti-reflection capabilities in optical chips has gradually become a key to reducing costs and enhancing chip competitiveness. The anti-reflection capability of a chip is related to both the stability of its resonant mode and the waveguides in the vertical and horizontal directions of the light-emitting end face. Major domestic optical chip manufacturers have some patents in this area. For example, CN 112072463 A discloses an anti-reflection laser using an absorbable grating, employing a double-layer diffraction grating structure to absorb reflected light and improve anti-reflection capability. CN118801210 A discloses a high-power anti-emission semiconductor laser using a non-overlapping upper and lower grating structure to enhance the laser's anti-reflection capability.

[0004] The aforementioned anti-reflection design schemes for semiconductor lasers each have their own advantages. However, existing anti-reflection designs for semiconductor lasers all suffer from more complex structures and difficult fabrication, resulting in high costs, low yields, and unsuitability for mass production. Summary of the Invention

[0005] (a) Purpose of the invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a 10Gbps laser with a novel structure, simple fabrication, and excellent anti-reflection performance. An "irreversible optical path" structure is introduced inside the laser to enable efficient output of forward-emitted light, while guiding the reflected light to a specially designed "optical trap" for absorption and dissipation, rather than returning to the active region.

[0007] (II) Technical Solution

[0008] To address the aforementioned technical problems, this invention provides an anti-reflection semiconductor laser based on asymmetric grating and lateral microcavity coupling, comprising a substrate layer 2 and, sequentially formed on it, a buffer layer 3, a lower confinement layer 4, a lower waveguide layer 5, a multiple quantum well layer 6, an upper waveguide layer 7, a grating layer 8, a capping layer 9, and a contact layer 10; an N-plane metal layer 1 is formed on the back side of the substrate layer 2 as an N-electrode, and a P-plane metal layer 11 is formed above the contact layer 10 as a P-electrode, i.e., the main electrode; the P-plane metal layer 11, the contact layer 10, and a portion of the capping layer 9 below the contact layer 10 together form a ridge waveguide 16; the grating layer 8 is asymmetrically distributed. Its refractive index modulation depth varies non-uniformly along the cavity length direction. The first half of the grating near the front end of the laser has a shallow modulation depth, referred to as the shallow grating region, while the second half of the grating has a deep modulation depth, referred to as the deep grating region. Near the rear end of the laser and adjacent to the deep grating region, a laterally passive laterally integrated absorption microcavity 14 is integrated through etching and regeneration processes. The laterally integrated absorption microcavity 14 is connected to the epitaxial structure under the ridge waveguide 16 through an adiabatic evanescent wave coupler 15. The main electrode covers more than half of the grating layer 8, and the laterally integrated absorption microcavity 14 is designed with independent floating or grounded electrodes.

[0009] Furthermore, an antireflection coating 13 is provided on the light output end face of the laser front end, and a high reflectivity coating 12 is provided on the rear end face.

[0010] Furthermore, substrate layer 2 is an n-type doped InP layer with a doping concentration of 2 × 10⁻⁶. 18 cm -3 .

[0011] Furthermore, the buffer layer 3 is an InP buffer layer with a thickness of 200 nm and a doping concentration of 1 × 10⁻⁶. 18 cm -3 .

[0012] Furthermore, the lower confinement layer 4 has a thickness of 1500 nm and a doping concentration of 5 × 10⁻⁶. 17 cm -3 The lower waveguide layer 5 has a thickness of 100 nm and is made of lattice-matched AlGaInAs or InGaAsP material.

[0013] Furthermore, the multi-quantum-well layer 6 employs strained AlGaInAs or InGaAsP multi-quantum-wells, with 6 quantum wells, where the well width is 7 nm, the barrier width is 10 nm, the lattice-matched material is used, the compressive strain is 1%, and the bandgap wavelength is 1.25 μm.

[0014] Furthermore, the upper waveguide layer 7 is made of lattice-matched AlGaInAs or InGaAsP material, with a thickness of 100nm and is undoped.

[0015] Furthermore, in grating layer 8, the etching depth of the deep grating region is 50-100nm, and the etching depth of the shallow grating region is 20-40nm. The etching depth of the deep grating region is more than twice that of the shallow grating region. The duty cycle of the shallow and deep grating regions is between 40% and 60%. The length of the deep grating region accounts for 3 / 10 to 1 / 2 of the total cavity length. The length of the shallow grating region accounts for 1 / 2 to 3 / 5 of the total cavity length. The grating depth gradually changes between the deep and shallow grating regions, with a gradient width of 30-80μm. The length of the deep grating region is 120μm, and the length of the shallow grating region is 150μm.

[0016] Furthermore, the capping layer 9 is a p-InP cladding layer grown on the grating layer 8 via secondary epitaxy, with a doping concentration of 5 × 10⁻⁶. 17 cm -3 The thickness is 1.5 μm; the contact layer 10 is an InGaAs contact layer with a thickness of 200 nm; a SiO2 passivation layer is deposited on the P-side metal layer 11, and the P-side electrode contact window is opened by photolithography and etching. When evaporating the P-side electrode, a mask is used to ensure that the metal only covers the ridge of the ridge waveguide and avoids the lateral absorption microcavity region.

[0017] Furthermore, the laterally integrated absorption microcavity 14 uses an undoped Fe:InP layer as the absorption material, with a length greater than the length of the deep grating region and a width of 3-5 μm, which is greater than the width of the ridge waveguide. Its thickness extends at least through the lower waveguide layer. A floating or grounded independent electrode is designed on the laterally integrated absorption microcavity to further deplete any residual carriers in the microcavity region.

[0018] Furthermore, the evanescent wave coupler 15 is filled with regrown undoped InP, with a width of 150-300 nm and a length of 50-130 μm, and its thickness is the same as that of the lateral integrated absorption microcavity 14.

[0019] (III) Beneficial Effects

[0020] The anti-reflection semiconductor laser based on asymmetric grating and lateral microcavity coupling provided by the above technical solution has the following beneficial effects:

[0021] (1) Since no additional losses are introduced in the core active region, it can maintain excellent high-speed performance;

[0022] (2) The main process steps (grating preparation, etching, and regeneration) are compatible with the existing DFB laser standard process, requiring no special materials or complex equipment, which is conducive to large-scale mass production and cost control;

[0023] (3) The lateral absorption microcavity dissipates the energy of reflected light in the form of heat, avoiding the direct impact of reflected light on the active region, which is expected to improve the long-term reliability of the device.

[0024] (4) The present invention has a novel structure and a simple fabrication process for a 10Gbps laser. The main process steps are compatible with the existing standard process of DFB lasers. No special materials or complex equipment are required, which is conducive to large-scale mass production and cost control. It can work stably without isolators, which significantly reduces the size and cost of optical modules. Attached Figure Description

[0025] Figure 1 This is a rear view of an anti-reflection semiconductor laser based on asymmetric grating and lateral microcavity coupling according to an embodiment of the present invention.

[0026] Figure 2 This is a side view of an anti-reflection semiconductor laser based on asymmetric grating and lateral microcavity coupling according to an embodiment of the present invention.

[0027] Figure 3 This is a three-dimensional view of an anti-reflection semiconductor laser based on asymmetric grating and lateral microcavity coupling according to an embodiment of the present invention.

[0028] Figure 4 This is an internal schematic diagram of an anti-reflection semiconductor laser based on asymmetric grating and lateral microcavity coupling according to an embodiment of the present invention. Detailed Implementation

[0029] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.

[0030] See Figures 1-4 As shown, this embodiment of an anti-reflection semiconductor laser based on asymmetric grating and lateral microcavity coupling includes a substrate layer 2 and a buffer layer 3, a lower confinement layer 4, a lower waveguide layer 5, a multiple quantum well layer 6, an upper waveguide layer 7, a grating layer 8, a capping layer 9, and a contact layer 10 sequentially formed thereon. An N-plane metal layer 1 is formed on the back side of the substrate layer 2 as an N-electrode, and a P-plane metal layer 11 is formed above the contact layer 10 as a P-electrode, i.e., the main electrode. The P-plane metal layer 11, the contact layer 10, and a portion of the capping layer 9 below the contact layer 10 together form a ridge waveguide 16. The grating layer 8 is asymmetrically distributed, and its refractive index is modulated. The depth varies non-uniformly along the cavity length. The first half of the grating near the front end of the laser has a shallower modulation depth, referred to as the shallow grating region, while the second half has a deeper modulation depth, referred to as the deep grating region. Near the rear end of the laser and adjacent to the deep grating region, a laterally passive laterally integrated absorption microcavity 14 is integrated through etching and regeneration processes. The laterally integrated absorption microcavity 14 is connected to the epitaxial structure under the ridge waveguide 16 through an adiabatic evanescent wave coupler 15. The main electrode covers more than half of the grating layer 8, and the laterally integrated absorption microcavity 14 is designed with independent floating or grounded electrodes.

[0031] An anti-reflection coating 13 is provided on the front end face of the laser's light output end, and a high-reflection coating 12 is provided on the rear end face.

[0032] In this embodiment, substrate layer 2 is an n-type doped InP layer with a doping concentration of 2 × 10⁻⁶. 18 cm -3 .

[0033] Buffer layer 3 is made of a III-V compound, specifically an InP buffer layer with a thickness of 200 nm and a doping concentration of 1 × 10⁻⁶. 18 cm -3 .

[0034] The lower confinement layer 4 has a thickness of 1500 nm and a doping concentration of 5 × 10⁻⁶. 17 cm -3 .

[0035] The lower waveguide layer 5 has a thickness of 100 nm and is made of lattice-matched AlGaInAs or InGaAsP material.

[0036] The multi-quantum-well layer 6 employs strained AlGaInAs or InGaAsP multi-quantum-wells, with 6 quantum wells, each with a well width of 7 nm and a barrier width of 10 nm. It uses lattice-matched materials, with a compressive strain of 1% and a bandgap wavelength of 1.25 μm.

[0037] The upper waveguide layer 7 is made of lattice-matched AlGaInAs or InGaAsP material, with a thickness of 100nm and is undoped.

[0038] In grating layer 8, the etching depth of the deep grating region is 50-100 nm, and the etching depth of the shallow grating region is 20-40 nm. The etching depth of the deep grating region is more than twice that of the shallow grating region. The duty cycle of the shallow and deep grating regions is between 40% and 60%. The length of the deep grating region accounts for 3 / 10 to 1 / 2 of the total cavity length. The length of the shallow grating region accounts for 1 / 2 to 3 / 5 of the total cavity length. The grating depth gradually changes between the deep and shallow grating regions, with a gradient width of 30-80 μm.

[0039] Preferably, in this embodiment, the length of the deep grating region is 120 μm, the length of the shallow grating region is 150 μm, and there is a gradient etching depth of 30~50 μm between the shallow grating region and the deep grating region.

[0040] In this embodiment, grating layer 8 employs a combination of holographic lithography and electron beam lithography. First, the entire layer is etched to the depth of the shallow grating region, followed by a second etching of the deep grating region. The deep grating region, located at the rear end of the laser, has a large modulation depth, providing strong distributed feedback for the forward laser, which is crucial for achieving single-mode lasing, narrow linewidth, and low noise. The shallow grating region, located near the output end, has a shallower modulation depth. It serves as a low-loss output window for the forward laser, but its coupling efficiency for reflected light is very low, causing most reflected light to "pass through" this region and continue propagating backward.

[0041] Cap layer 9 is a p-InP cladding layer grown on grating layer 8 via secondary epitaxy, with a doping concentration of 5 × 10⁻⁶. 17 cm -3 It has a thickness of approximately 1.5 μm.

[0042] Contact layer 10 is an InGaAs contact layer with a thickness of 200 nm.

[0043] SiO2 passivation layer is deposited on the P-side metal layer 11, and the P-side electrode contact window is opened by photolithography and etching. When depositing the P-side electrode, a mask is used to ensure that the metal only covers the ridge of the ridge waveguide and completely avoids the lateral absorption microcavity region.

[0044] The laterally integrated absorption microcavity 14 employs a regenerated long absorption layer, specifically using an undoped Fe:InP layer as the absorption material. Its length is greater than the length of the deep grating region, and its width is 3-5 μm, slightly larger than the width of the ridge waveguide. Its thickness extends at least through the lower waveguide layer. A floating or grounded independent electrode is designed on the laterally integrated absorption microcavity to further deplete any residual carriers in the microcavity region.

[0045] The evanescent wave coupler 15 is filled with regrown undoped InP, with a width of 150-300 nm and a length of 50-130 μm. Its thickness is the same as that of the lateral integrated absorption microcavity 14.

[0046] The ridge waveguide 16 is a ridge-shaped region composed of a P-plane metal layer 11, a contact layer 10, and a partial capping layer 09, used to confine the distribution of the light field in the lateral direction.

[0047] The fabrication process of the lateral integrated absorption microcavity 14 and the evanescent wave coupler 15 is as follows: First, SiO2 or SiN is deposited on the wafer using PECVD as a hard mask. Then, the contours of the ridge waveguide, the lateral integrated absorption microcavity, and the evanescent wave coupler are simultaneously etched using electron beam lithography. ICP deep etching is then performed, with the ridge waveguide ridge etched into the capping layer 09. The etching depth of the lateral integrated absorption microcavity and the evanescent wave coupler must reach the lower cladding layer to ensure optical and electrical isolation. Subsequently, the lateral integrated absorption microcavity and the evanescent wave coupler are selected for epitaxial growth. Fe-doped InP is grown as the absorption layer for the lateral integrated absorption microcavity, while undoped InP is used as the absorption layer for the evanescent wave coupler.

[0048] As can be seen from the above technical solution, the present invention has the following significant features:

[0049] (1) The asymmetric grating design of the present invention enables the laser to have different coupling efficiencies for reflected light returning from the output end. During forward lasing, the light obtains stronger feedback in the deep grating region to maintain single-mode characteristics and achieves efficient output in the shallow grating region; when the back-reflected light enters the shallow grating region, due to its low coupling efficiency, most of its energy will "pass through" the conventional Bragg reflection condition and continue to propagate backward.

[0050] (2) The reflected light returning from the front end and “passing through” the asymmetric grating in this invention has its propagation mode changed and is efficiently coupled into the lateral absorption microcavity. The microcavity is made of a wide bandgap material (such as Fe:InP or undoped InGaAsP), which can quickly convert the incident light energy into heat energy and dissipate it, forming an efficient “light trap” and reducing the interference of the reflected light on the original resonant light.

[0051] (3) The main electrode covers most of the asymmetric grating area to ensure sufficient modulation bandwidth. At the same time, independent floating or grounded electrodes are designed in the lateral absorption microcavity area to deplete the carriers in this area, reduce its capacitive load on the ridge waveguide, and ensure that the 10Gbps high-speed modulation performance is not affected.

[0052] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An anti-reflection semiconductor laser based on coupling of an asymmetric grating and a lateral microcavity, characterized in that, The structure includes a substrate layer (2) and, sequentially, a buffer layer (3), a lower confinement layer (4), a lower waveguide layer (5), a multiple quantum well layer (6), an upper waveguide layer (7), a grating layer (8), a capping layer (9), and a contact layer (10). An N-plane metal layer (1) is formed on the back side of the substrate layer (2) as the N-electrode, and a P-plane metal layer (11) is formed above the contact layer (10) as the P-electrode, i.e., the main electrode. The P-plane metal layer (11), the contact layer (10), and the corresponding portion of the capping layer (9) below the contact layer (10) together form a ridge waveguide (16). The grating layer (8) is asymmetrically distributed, and its refractive index modulation depth is along... The cavity length varies non-uniformly. The first half of the grating near the front end of the laser has a shallow modulation depth, referred to as the shallow grating region, while the second half has a deep modulation depth, referred to as the deep grating region. A laterally passive laterally integrated absorption microcavity (14) is integrated near the rear end of the laser and adjacent to the deep grating region through etching and regeneration processes. The laterally integrated absorption microcavity (14) is connected to the epitaxial structure under the ridge waveguide (16) through an adiabatic evanescent wave coupler (15). The main electrode covers more than half of the grating layer (8), and the laterally integrated absorption microcavity (14) is designed with independent floating or grounded electrodes.

2. The anti-reflection semiconductor laser based on asymmetric grating and lateral microcavity coupling as described in claim 1, characterized in that, An antireflection coating (13) is provided on the front end face of the laser's light output end, and a high reflectivity coating (12) is provided on the rear end face.

3. The anti-reflection semiconductor laser based on asymmetric grating and lateral microcavity coupling as described in claim 2, characterized in that, The substrate layer (2) is an n-type doped InP layer with a doping concentration of 2×10⁻⁶. 18 cm -3 ; Buffer layer (3) Material: InP buffer layer, thickness: 200nm, doping concentration: 1×10 18 cm -3 .

4. The anti-reflection semiconductor laser based on asymmetric grating and lateral microcavity coupling as described in claim 3, characterized in that, The lower confinement layer (4) has a thickness of 1500 nm and a doping concentration of 5 × 10⁻⁶. 17 cm -3 The lower waveguide layer (5) has a thickness of 100 nm and is made of lattice-matched AlGaInAs or InGaAsP material.

5. The anti-reflection semiconductor laser based on asymmetric grating and lateral microcavity coupling as described in claim 4, characterized in that, The multi-quantum well layer (6) adopts strained AlGaInAs or InGaAsP multi-quantum wells, with 6 quantum wells, where the well width is 7nm and the barrier width is 10nm. It adopts lattice-matched materials, compressive strain of 1%, and band gap wavelength of 1.25μm.

6. The anti-reflection semiconductor laser based on asymmetric grating and lateral microcavity coupling as described in claim 5, characterized in that, The upper waveguide layer (7) is made of lattice-matched AlGaInAs or InGaAsP material with a thickness of 100nm and is undoped.

7. The anti-reflection semiconductor laser based on asymmetric grating and lateral microcavity coupling as described in claim 6, characterized in that, In the grating layer (8), the etching depth of the deep grating region is 50-100nm, the etching depth of the shallow grating region is 20-40nm, and the etching depth of the deep grating region is more than 1 times that of the shallow grating region; the duty cycle of the shallow grating region and the deep grating region is between 40 and 60%; the length of the deep grating region accounts for 3 / 10 to 1 / 2 of the total cavity length; the length of the shallow grating region accounts for 1 / 2 to 3 / 5 of the total cavity length; the grating depth gradually changes between the deep grating region and the shallow grating region, and the gradient width is 30 to 80μm; the length of the deep grating region is 120μm, and the length of the shallow grating region is 150μm.

8. The anti-reflection semiconductor laser based on asymmetric grating and lateral microcavity coupling as described in claim 7, characterized in that, The capping layer (9) is a p-InP cladding layer grown on the grating layer (8) via secondary epitaxy, with a doping concentration of 5 × 10⁻⁶. 17 cm -3 The thickness is 1.5 μm; the contact layer (10) is an InGaAs contact layer with a thickness of 200 nm; a SiO2 passivation layer is deposited on the P-side metal layer (11), and the P-side electrode contact window is opened by photolithography and etching. When evaporating the P-side electrode, a mask is used to ensure that the metal only covers the ridge of the ridge waveguide and avoids the lateral absorption microcavity region.

9. The anti-reflection semiconductor laser based on asymmetric grating and lateral microcavity coupling as described in claim 8, characterized in that, The laterally integrated absorption microcavity (14) uses an undoped Fe:InP layer as the absorption material. Its length is greater than the length of the deep grating region, and its width is 3-5 μm, which is greater than the width of the ridge waveguide. Its thickness extends at least through the lower waveguide layer. A floating or grounded independent electrode is designed on the laterally integrated absorption microcavity to further deplete any residual carriers in the microcavity region.

10. The anti-reflection semiconductor laser based on asymmetric grating and lateral microcavity coupling as described in claim 9, characterized in that, The evanescent wave coupler (15) is filled with regrown undoped InP, with a width of 150-300 nm and a length of 50-130 μm. Its thickness is the same as that of the lateral integrated absorption microcavity (14).

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