Optically pumped tunable vertical cavity surface emitting laser, mirror and applications thereof

Abstract

This invention discloses an optically pumped tunable vertical-cavity surface-emitting laser (VCSEL), a mirror, and their applications. The wavelength-selective mirror includes a phase-matching region and an optimization region arranged sequentially along the vertical direction. The phase-matching region is formed by periodically alternating stacks of x pairs of first high-refractive-index material layers and first low-refractive-index material layers along the vertical direction. The optimization region is formed by y pairs of second high-refractive-index material layers and z pairs of second low-refractive-index material layers, which are alternately stacked along the vertical direction, and the optical thicknesses of the second high-refractive-index material layers and the second low-refractive-index material layers are unequal. This invention breaks away from the traditional single optimization paradigm centered on lasing light in DBRs, significantly improving optical pumping efficiency while ensuring a wide tuning range and free spectral range, thereby realizing a highly efficient wide-tunable single-longitudinal-mode output MEMS-VCSEL, laying the foundation for next-generation high-performance tunable lasers.

Description

Technical Field

[0001] This invention specifically relates to an optically pumped tunable vertical cavity surface-emitting laser, a mirror, and their applications, belonging to the field of semiconductor device and micro / nano manufacturing technology. Background Technology

[0002] Vertical-cavity surface-emitting lasers (VCSELs) emit light perpendicular to the substrate. Due to their advantages such as low threshold voltage, low power consumption, high beam quality, and ease of two-dimensional integration, they have wide applications in optical communication, sensing, lidar, and consumer electronics. MEMS-VCSELs are a new type of laser that combines a VCSEL with microelectromechanical systems (MEMS). A mechanically movable MEMS mirror replaces the fixed mirror on top of a traditional VCSEL. Driven by electrostatic force, the MEMS mirror shifts, changing the cavity length and thus achieving continuous tuning of the laser wavelength.

[0003] Tunable light sources in the 1050nm band are of great significance in optical coherence tomography (OCT) retinal imaging. Compared with the commonly used 850nm and 1300nm bands, the 1050nm band exhibits less scattering in the retina and results in deeper imaging. Furthermore, the 1050nm band has a higher safe exposure threshold for the human eye, allowing for the use of higher incident light power within a safe range, thereby improving the signal-to-noise ratio of the imaging system.

[0004] Compared to electrically pumped MEMS-VCSELs, optically pumped MEMS-VCSELs offer a wider tuning range and simpler fabrication processes. 1050nm band electrically pumped MEMS-VCSELs utilize Al with different Al compositions. x Ga 1-x As a bottom distributed Bragg reflector (DBR), GaAs has a small refractive index difference and a limited high-reflection band width, which restricts the tuning range of the device. In contrast, 1050nm optically pumped MEMS-VCSELs do not require electrical conductivity and utilize GaAs and Al. x O y As a bottom DBR, it can provide a larger high-reflectivity bandwidth, thereby increasing the tuning range of the device. However, in current optically pumped MEMS-VCSEL technologies, the design focus is concentrated on the mechanical properties of the MEMS structure, the laser tuning range, and beam quality. The design of the top DBR prioritizes achieving high reflectivity at the target lasing wavelength, while neglecting the transmittance of the pump light. Its optical design presents a single lasing-centric optimization paradigm. The design freedom is entirely focused on forming a high-reflectivity band in the lasing band, without considering the transmittance of the pump light as a design goal for structural optimization. This leads to higher reflection losses of the pump light upon incident, resulting in an increased laser threshold and decreased efficiency.

[0005] Currently, dielectric dielectric polymer (DBR) is mainly used as the top reflector of tunable VCSELs. It consists of alternating stacks of high-refractive-index and low-refractive-index dielectric films, with each film having an optical thickness one-quarter of the device's operating center wavelength. This design ensures phase consistency of the reflected light, satisfying interference enhancement and thus achieving high reflectivity. Currently, TiO2, Ta2O5, Nb2O5, and SiN are primarily used. x High-refractive-index dielectric materials are used as the high-refractive-index film layer in the DBR. These materials exhibit excellent transmittance and high refractive index characteristics in the near-infrared and visible light bands. Al₂O₃ and SiO₂ are used as the low-refractive-index film layer in the DBR. Due to the large refractive index difference between the dielectric films, a wider high-reflectance band can be provided, which is beneficial for improving the tuning range of the device. By increasing the logarithm of the DBR, the reflectivity can be increased to 99% or higher.

[0006] Existing technologies for designing the top reflector of tunable VCSELs suffer from a significant limitation: their optical design exhibits a singular, goal-oriented approach, with design freedom and optimization objectives focused solely on ensuring high reflectivity within the laser's operating wavelength range. By alternately stacking dielectric materials with large refractive index differences, each layer's optical thickness is designed to be one-quarter of the center wavelength, aiming to create a wide and highly reflective reflection band to support stable lasing and wide-wavelength tuning. However, this lasing-centric optimization paradigm, neglecting pump light transmittance, results in excessively high reflectivity of the top DBR in the pump light band, reducing the optical injection power in the active region and causing significant energy loss. This reduction in optical pump efficiency directly manifests as an increase in the laser threshold and a decrease in slope efficiency. Summary of the Invention

[0007] The main objective of this invention is to provide an optically pumped tunable vertical-cavity surface-emitting laser, a mirror, and their applications, to solve the technical problems of low pump efficiency and high energy loss in existing technologies caused by the failure of the top mirror to synergistically optimize the pump light transmittance and lasing light reflectance. The core of this invention lies in treating the pump light transmittance efficiency as an optimization objective of equal importance to the lasing light reflectance performance. Through a synergistically optimized mirror design method, using a specially designed dielectric film stack, it achieves synergistic optimization of high transmittance (>99%) in the pump light band (e.g., 850nm) and high reflectance (>99.5%) in the lasing light band (e.g., 1050nm). Furthermore, this invention reduces the penetration depth of the light field in the mirror by finely controlling the internal structure of the mirror, increasing the longitudinal mode spacing of the laser, thereby ensuring that the device can stably output single-mode laser light over a wide spectral range.

[0008] To achieve the aforementioned objectives, the technical solution adopted by this invention includes: A first aspect of the present invention provides a wavelength-selective reflector, comprising: a phase-matching region and an optimization region sequentially arranged along a vertical direction. The phase-matching region is formed by periodically alternating stacking of a first high-refractive-index material layer and a first low-refractive-index material layer in the vertical direction, wherein the optical thickness of the first high-refractive-index material layer and the first low-refractive-index material layer are both one-quarter of the lasing wavelength of the laser, and x≥1; The optimized region is formed by y second high refractive index material layers and z second low refractive index material layers, which are stacked alternately in the vertical direction. The optical thicknesses of the second high refractive index material layers and the second low refractive index material layers are not equal, and are both greater than or less than one-quarter of the lasing wavelength of the laser, y≥1, z≥1. The phase-matching region and the optimization region are configured such that the wavelength-selective reflector has a reflectivity of more than 99.5% for lasing light with a wavelength of 1000nm~1100nm and a transmittance of more than 99% for pump light with a wavelength of 845nm~855nm.

[0009] A second aspect of the present invention provides an optically pumped tunable vertical-cavity surface-emitting laser (VCSEL), comprising a tunable VCSEL unit, wherein the tunable VCSEL unit includes a bottom mirror, a top mirror, and an active region, wherein the active region is disposed vertically between the bottom mirror and the top mirror, and together they form a vertically oriented optical resonant cavity, wherein the top mirror of the optically pumped tunable VCSEL is the wavelength-selective mirror, and the phase-matching region of the wavelength-selective mirror is located at the bottom layer near the active region.

[0010] A third aspect of the present invention provides a method for synergistically optimizing the pump light transmittance and lasing light reflectance of a tunable vertical-cavity surface-emitting laser, comprising: using the wavelength-selective mirror as the top mirror of the tunable vertical-cavity surface-emitting laser, and making the longitudinal mode spacing of the tunable vertical-cavity surface-emitting laser greater than 100 nm.

[0011] Compared with the prior art, the advantages of the present invention include: The present invention provides an optically pumped tunable vertical cavity surface-emitting laser, which breaks away from the traditional DBR design that only serves the lasing wavelength by designing the top reflector to have a synergistically optimized optical response in the pump light band and the lasing light band.

[0012] The present invention provides an optically pumped tunable vertical cavity surface-emitting laser, which enables the top mirror to maintain extremely high reflectivity of lasing light (>99%) while achieving near-lossless transmission of pump light (>99%). This significantly reduces the threshold power of the optically pumped laser and improves the optical-to-optical conversion efficiency, providing a key technological foundation for realizing next-generation high-performance, low-threshold, and low-power optically pumped tunable lasers.

[0013] This invention provides an optically pumped tunable vertical-cavity surface-emitting laser. While achieving dual-band optical performance, it effectively reduces the penetration depth of the light field in the mirror and shortens the resonant cavity length by controlling the optical thickness of the film layer on the top mirror near the active region to one-quarter of the laser's operating center wavelength. This design increases the longitudinal mode spacing, making it almost identical to the longitudinal mode spacing of traditional DBR-type MEMS-VCSELs, thus enhancing the single-mode stability of the device throughout the entire tuning range. The larger longitudinal mode spacing ensures a wider tuning range for the device.

[0014] The optically pumped tunable vertical cavity surface-emitting laser provided by this invention breaks the single optimization paradigm centered on lasing light in traditional DBR. While ensuring a wide tuning range and free spectral range, it significantly improves the optical pumping efficiency, thereby realizing a high-efficiency wide-tunable single longitudinal mode output MEMS-VCSEL, laying the foundation for the next generation of high-performance tunable lasers. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of an optically pumped tunable vertical cavity surface-emitting laser (MEMS-VCSEL) provided in a typical embodiment of the present invention. Figure 2a This is a schematic diagram of a traditional DBR structure; Figure 2b This is a schematic diagram of the structure of a wavelength-selective reflector provided in a typical embodiment of the present invention; Figure 3 The reflection spectrum is that of a traditional DBR reflector and a wavelength-selective reflector provided in a typical embodiment of the present invention; Figure 4 It is the reflection spectrum of an optically pumped tunable vertical-cavity surface-emitting laser using an integrated microelectromechanical system with a traditional DBR mirror; Figure 5 This is the reflection spectrum of an optically pumped tunable vertical cavity surface-emitting laser (VCSEL) provided in a typical embodiment of the present invention. Detailed Implementation

[0016] In view of the shortcomings of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The following will further explain and illustrate this technical solution, its implementation process, and its principles.

[0017] This invention introduces a wavelength-selective mirror optimized for both pump and lasing light bands. This design uses the transmission efficiency of the pump light and the cavity surface reflection spectrum of the lasing light as structural design objectives. This invention enables pump photons to be incident on the active region with extremely low loss, significantly improving pump light utilization, directly resulting in a reduction in the laser threshold and an increase in slope efficiency. Furthermore, this invention optimizes the optical characteristics of the resonant cavity by precisely controlling the distribution of the mirror's film structure.

[0018] Specifically, by designing the optical thickness of several pairs of dielectric films near the active region to be one-quarter of the laser's operating wavelength, this specific design can effectively reduce the penetration depth of the light field in the mirror structure, shorten the effective optical length of the resonant cavity, and increase the longitudinal mode spacing of the laser, thereby ensuring that the device can stably output single-mode laser over a wide spectral range.

[0019] A first aspect of the present invention provides a wavelength-selective reflector, comprising: a phase-matching region and an optimization region sequentially arranged along a vertical direction. The phase-matching region is formed by periodically alternating stacking of a first high-refractive-index material layer and a first low-refractive-index material layer in the vertical direction, wherein the optical thickness of the first high-refractive-index material layer and the first low-refractive-index material layer are both one-quarter of the lasing wavelength of the laser, and x≥1; The optimized region is formed by y second high refractive index material layers and z second low refractive index material layers, which are stacked alternately in the vertical direction. The optical thicknesses of the second high refractive index material layers and the second low refractive index material layers are not equal, and are both greater than or less than one-quarter of the lasing wavelength of the laser, y≥1, z≥1. The phase-matching region and the optimization region are configured such that the wavelength-selective reflector has a reflectivity of more than 99.5% for lasing light with a wavelength of 1000nm~1100nm and a transmittance of more than 99% for pump light with a wavelength of 845nm~855nm.

[0020] Furthermore, the materials of the first high-refractive-index material layer, the first low-refractive-index material layer, the second high-refractive-index material layer, and the second low-refractive-index material layer include TiO2, Ta2O5, Nb2O5, and SiN. x At least one of HfO2, SiO2 and Al2O3.

[0021] Furthermore, the first high refractive index material layer and the second high refractive index material layer are made of the same material, and the first low refractive index material layer and the second low refractive index material layer are made of the same material.

[0022] In a typical implementation, the phase matching region includes three TiO2 / SiO2 periodic structures stacked sequentially in a vertical direction, wherein the thickness of the TiO2 layer in each of the three TiO2 / SiO2 periodic structures is 181 nm and the thickness of the SiO2 layer is 109 nm. The optimized region comprises eleven film layers stacked sequentially on the phase matching region along the vertical direction. These eleven film layers are, in order, a SiO2 layer with a thickness of 221 nm, a TiO2 layer with a thickness of 94 nm, a SiO2 layer with a thickness of 159 nm, a TiO2 layer with a thickness of 97 nm, a SiO2 layer with a thickness of 163 nm, a TiO2 layer with a thickness of 101 nm, a SiO2 layer with a thickness of 174 nm, a TiO2 layer with a thickness of 126 nm, a SiO2 layer with a thickness of 204 nm, a TiO2 layer with a thickness of 104 nm, and a SiO2 layer with a thickness of 316 nm.

[0023] A second aspect of the present invention provides an optically pumped tunable vertical-cavity surface-emitting laser (VCSEL), comprising a tunable VCSEL unit, wherein the tunable VCSEL unit includes a bottom mirror, a top mirror, and an active region, wherein the active region is disposed vertically between the bottom mirror and the top mirror, and together they form a vertically oriented optical resonant cavity, wherein the top mirror of the optically pumped tunable VCSEL is the wavelength-selective mirror, and the phase-matching region of the wavelength-selective mirror is located at the bottom layer near the active region.

[0024] In a more specific embodiment, the optically pumped tunable vertical-cavity surface-emitting laser further includes: A microelectromechanical system (MEMS) unit includes a bottom electrode, a top electrode, a sacrificial layer, and a cantilever structure layer. The sacrificial layer is stacked on the active region and has an air cavity within it. The cantilever structure layer is stacked on the sacrificial layer and at least covers the air cavity. The top electrode and the top reflective layer are disposed on the cantilever structure layer. The bottom electrode is disposed on the active region and located within the air cavity. An optical window is also disposed on the bottom electrode, and the optical window is located in the central region of the optically pumped MEMS tunable vertical-cavity surface-emitting laser. When a voltage is applied to the top electrode and the bottom electrode, the electrostatic attraction generated between the top electrode and the bottom electrode can cause the cantilever structure layer to bend, thereby causing the top reflector to move.

[0025] Furthermore, the bottom reflector is a distributed Bragg reflector.

[0026] Furthermore, the area of ​​the bottom reflector covered by the air cavity has an oxide etching hole extending in a vertical direction. The portion of the bottom reflector located around the oxide etching hole is oxidized by wet water vapor to form an oxide zone, which serves as the working area of ​​the bottom reflector.

[0027] Furthermore, the air chamber is formed in situ by removing a portion of the sacrificial layer.

[0028] In a typical implementation, the optically pumped tunable vertical-cavity surface-emitting laser further includes an antireflection coating, which is stacked on the active region, and the sacrificial layer and the bottom electrode are disposed on the antireflection coating.

[0029] Furthermore, the longitudinal mode spacing of the optically pumped tunable vertical cavity surface-emitting laser exceeds 100 nm.

[0030] A third aspect of the present invention provides a method for synergistically optimizing the pump light transmittance and lasing light reflectance of a tunable vertical-cavity surface-emitting laser, comprising: using the wavelength-selective mirror as the top mirror of the tunable vertical-cavity surface-emitting laser, and making the longitudinal mode spacing of the tunable vertical-cavity surface-emitting laser greater than 100 nm.

[0031] The following will further explain and illustrate the technical solution, its implementation process, and its principles in conjunction with the accompanying drawings and specific implementation examples. Those skilled in the art should understand that the examples described herein are merely illustrative and do not constitute a limitation on the scope of protection of this invention.

[0032] In a typical implementation case, please refer to Figure 1 A light-pumped tunable vertical-cavity surface-emitting laser with an emission wavelength in the 1050nm band (the light-pumped tunable vertical-cavity surface-emitting laser in this embodiment of the invention is a MEMS-VCSEL), comprising: a substrate 11, a bottom mirror 12, a quantum well active region 13, an antireflection coating 14, a bottom electrode 16, a sacrificial layer 17, a cantilever structure layer 18, a top electrode 19, and a top mirror; Among them, the substrate 11, the bottom mirror 12, the quantum well active region 13, the antireflection film 14, the sacrificial layer 17, and the cantilever structure layer 18 are stacked in sequence from bottom to top in the vertical direction. There is an air cavity in the sacrificial layer 17. The bottom electrode 16 is stacked on the antireflection film 14 and is located in the air cavity. The top electrode 19 and the top mirror are arranged on the cantilever structure layer 18. The bottom mirror 12, the quantum well active region 13 and the top mirror are configured as a tunable vertical cavity surface emitting laser structure / unit. The sacrificial layer 17, the cantilever structure layer 18, the bottom electrode 16 and the top electrode 19 are configured as a microelectromechanical structure / unit; When a voltage is applied between the top electrode 19 and the bottom electrode 16, the electrostatic attraction generated between the top electrode 19 and the bottom electrode 16 can cause the cantilever structure layer 18 to bend, thereby driving the top mirror to move.

[0033] Specifically, a light-pumped tunable vertical cavity surface emitting laser in an embodiment of the present invention is a laser based on semiconductor materials such as GaAs material system, InP material system, GaN-based material system, etc.

[0034] Typically, the substrate 11 can be a GaAs substrate with a thickness of 100 μm to 600 μm.

[0035] Typically, the bottom mirror 12 is a DBR mirror. Among them, the initial epitaxial structure 121 of the bottom mirror 12 is composed of Al x Ga 1-x As and GaAs are alternately stacked, with a total of 7 cycles, 0.96 < x < 1. The optical thickness of each layer of material is one-fourth of the center wavelength (1050 nm) of the laser. To increase the width of the high reflection band of the bottom mirror and reduce the penetration depth of the light field in the bottom mirror, during the preparation process, Al x Ga 1-x As in the initial epitaxial structure 121 is oxidized into Al m O n to form an oxidized region 122 where Al m O n and GaAs are alternately stacked. 7 cycles of Al m O n and GaAs can provide a high reflection band width exceeding 400 nm and a reflectivity exceeding 99%.

[0036] Typically, in the present invention, an oxidation etching hole 15 is formed by etching the initial epitaxial structure 121 located below the air cavity, so that the initial epitaxial structure 121 around the oxidation etching hole 15 is exposed to air, and then high-temperature wet water vapor is used to oxidize Al x Ga 1-xAs is oxidized laterally to Al m O n Moisture enters the oxide etching hole 15 under high temperature conditions and reacts with the Al surrounding the oxide etching hole 15. x Ga 1-x As reacts to form Al with a high refractive index difference. m O n / GaAs DBR. With increasing oxidation time, the lateral oxidation area increases, and the overlapping area of ​​the lateral oxidation between the two etched holes 15 forms a unified oxidation region, which is the working area of ​​the bottom DBR. The oxidation rate is related to Al... x Ga 1-x The Al component in As is related to the oxidation conditions.

[0037] Typically, the active region 13 of the quantum well uses InGaAs as the quantum well and GaAsP as the quantum barrier, with thicknesses of 6 nm to 15 nm for both. Specifically, the In composition of the InGaAs quantum well can be tuned to provide a larger gain in the 1050 nm wavelength band. Specifically, the gain spectrum can be broadened and the tuning range of the device increased by introducing a second confined quantum state by widening the thickness of the InGaAs quantum well. Specifically, the compressive strain of the quantum well can be compensated by tuning the P composition of the GaAsP quantum barrier, avoiding material defects caused by strain accumulation. Specifically, lattice-matched GaAs can be used as the cladding of the quantum well structure to control the resonant cavity length and align the quantum well with the antinodes of the standing wave of the optical field. Specifically, this embodiment of the invention uses a multi-quantum-well structure to improve gain, with GaAs separating the quantum well structures. Specifically, the overall optical thickness of the active region 13 of the quantum well is approximately two-thirds of the center wavelength of the laser to achieve the resonance condition.

[0038] Typically, the antireflective coating 14 can be made of SiN x A dielectric thin film formed from dielectric materials such as SiO2, SiON, and Al2O3, whose refractive indices are between those of GaAs and the air cavity, is used to promote coupling between the active region 13 of the quantum well and the air cavity, thereby increasing the tuning range of the device. The optical thickness of the antireflection film 14 is selected to be one-quarter of the center wavelength. For example, the present invention generally uses a SiO2 film as the antireflection film.

[0039] Typically, an optical window is provided on the bottom electrode 16 to provide an optical transmission path for pump light and lasing light, and the optical window is located in the central region of the device. Specifically, the electrode material of the bottom electrode 16 can be a metal with good adhesion, such as Ti or Cr. For example, the bottom electrode 16 can be a Ti electrode with a thickness of 200 nm.

[0040] Typically, the sacrificial layer 17 can be made of materials such as Si, Ge, SiGe alloys, and organic polymers. Specifically, the air cavity is formed by etching the sacrificial layer 17. For example, the air cavity can be fabricated by dry etching to form a suspended microbridge structure. For example, the sacrificial layer is a Ge sacrificial layer. Specifically, the thickness of the sacrificial layer determines the tuning range and initial lasing wavelength of the laser. In a typical case, the thickness of the sacrificial layer is approximately 1.8 μm, and the longitudinal mode spacing of the laser exceeds 100 nm, enabling single-mode tuning in the range of 1000 nm to 1100 nm.

[0041] Typically, the cantilever structure layer 18 supports the top reflector. A dielectric thin film with a high elastic modulus can be used to increase the resonant frequency of the cantilever, thereby increasing the sweep rate. A typical example uses SiN... x As a cantilever structure layer, the optical thickness of the cantilever structure layer is three-quarters of the center wavelength. The desired resonant frequency can be achieved by adjusting the film stress through changes in deposition conditions.

[0042] Typically, the top electrode 19 can be made of a metal with a high elastic modulus to improve the resonant frequency of the device; Al is a typical example. The thickness of the top electrode 19 is approximately 200 nm. Applying a voltage between the top electrode 19 and the bottom electrode 16 of the MEMS-VCSEL generates an electrostatic attraction between the electrodes, causing the cantilever structure layer 18 to bend and move the top reflector, thereby changing the cavity length of the laser resonant cavity and achieving wavelength tuning. Applying an AC voltage between the electrodes causes the cantilever to vibrate, and the cavity length changes rapidly to achieve rapid wavelength tuning; the tuning rate is proportional to the cantilever resonant frequency.

[0043] The wavelength-selective reflector (i.e., optimized reflector, hereinafter the same) used in the top reflector of this invention includes a phase-matching region 1101 and an optimization region 1102 arranged sequentially along the vertical direction. The phase-matching region is formed by periodically alternating stacking of x pairs of first high-refractive-index material layers and first low-refractive-index material layers along the vertical direction. The optical thickness of the first high-refractive-index material layer and the first low-refractive-index material layer are both one-quarter of the lasing wavelength of the laser, and x≥1. The optimization region is formed by y second high-refractive-index material layers and z second low-refractive-index material layers. The second high-refractive-index material layer and the second low-refractive-index material layer are stacked alternately in the vertical direction. The optical thicknesses of the second high-refractive-index material layer and the second low-refractive-index material layer are not equal, and both are greater than or less than one-quarter of the lasing wavelength of the laser, y≥1, z≥1. The phase-matching region and the optimization region are configured such that the wavelength-selective reflector has a reflectivity of more than 99.5% for lasing light with a wavelength of 1000nm~1100nm and a transmittance of more than 99% for pump light with a wavelength of 845nm~855nm.

[0044] Specifically, the phase matching region 1101 of the top reflector is used to reduce the penetration depth of the light field and increase the longitudinal mode spacing of the laser, while the optimization region 1102 is used to optimize the reflectivity of the laser operating wavelength and the transmittance of the pump light wavelength in the top reflector.

[0045] Typically, the top reflector can be made of TiO2, Ta2O5, Nb2O5, or SiN. x It is composed of materials such as HfO2, SiO2 and Al2O3.

[0046] The following explanation uses TiO2 and SiO2 dielectric materials as examples. In traditional DBR mirrors designed around a lasing beam, the optical thickness of each dielectric film is one-quarter of the center wavelength of the lasing beam. For example, as... Figure 2a As shown, a traditional DBR mirror is formed by alternating stacks of TiO2 and SiO2 in eight cycles, with the TiO2 thickness being 109 nm and the SiO2 thickness being 181 nm. Figure 2b As shown, in an embodiment of the present invention, the bottom of a top reflector uses three periods of TiO2 and SiO2 as a phase matching region. The optical thickness of each dielectric film in the phase matching region is designed to be one-quarter of the center wavelength to reduce the penetration depth of the light field in the reflector. The present invention achieves high transmission of pump light and high reflection of lasing light by optimizing the thickness of the dielectric film in the top region. Typically, the optimized region of the top reflector includes eleven film layers stacked sequentially in the phase matching region along the vertical direction. These eleven film layers are, in order, a SiO2 layer with a thickness of 221 nm, a TiO2 layer with a thickness of 94 nm, a SiO2 layer with a thickness of 159 nm, a TiO2 layer with a thickness of 97 nm, a SiO2 layer with a thickness of 163 nm, a TiO2 layer with a thickness of 101 nm, a SiO2 layer with a thickness of 174 nm, a TiO2 layer with a thickness of 126 nm, a SiO2 layer with a thickness of 204 nm, a TiO2 layer with a thickness of 104 nm, and a SiO2 layer with a thickness of 316 nm.

[0047] The reflection spectra of a conventional DBR mirror and the wavelength-selective mirror in this embodiment of the invention are as follows: Figure 3 As shown, both mirror structures have a reflectivity of over 99.5% in the 1000nm~1100nm range. This invention uses an 850nm laser as the pump light, and the wavelength-selective mirror has a transmittance of over 99% in the 845nm~855nm range, which allows the pump light to enter the active region with extremely low loss and be fully absorbed by the gain material.

[0048] The reflection spectrum of a MEMS-VCSEL using a conventional DBR mirror as the top mirror is as follows: Figure 4As shown, the reflection spectrum of a MEMS-VCSEL using a wavelength-selective mirror as the top mirror is as follows: Figure 5 As shown. The structures of the two lasers are identical except for the top reflector. The calculated reflection spectra of the two lasers are nearly identical, and the longitudinal mode spacing of both exceeds 100 nm.

[0049] The core of the optically pumped tunable vertical cavity surface-emitting laser provided in this embodiment of the invention lies in the use of a wavelength-selective reflector that is synergistically optimized for the pump light and lasing light bands, replacing the traditional top distributed Bragg reflector (DBR), thereby achieving near-lossless transmission of the pump light while ensuring efficient feedback of the lasing light.

[0050] Based on this, by designing the optical thickness of several pairs of dielectric films near the active region to be one-quarter of the laser's operating wavelength, the penetration depth of the light field in the mirror is reduced, thereby shortening the cavity length. This structural design yields two important results: First, according to the Fabry-Perot resonator theory, the longitudinal mode spacing is inversely proportional to the cavity length. The shortened optical cavity length directly leads to a significant increase in the longitudinal mode spacing, which provides the necessary physical conditions for achieving stable single-mode operation. Second, the increased longitudinal mode spacing effectively reduces mode competition between adjacent longitudinal modes, enabling the device to maintain stable single-mode characteristics throughout the tuning range and avoiding the adverse effects of mode hopping on laser performance.

[0051] The present invention provides an optically pumped tunable vertical cavity surface-emitting laser, which breaks away from the traditional DBR design that only serves the lasing wavelength by designing the top reflector to have a synergistically optimized optical response in the pump light band and the lasing light band.

[0052] The present invention provides an optically pumped tunable vertical cavity surface-emitting laser, which enables the top mirror to maintain extremely high reflectivity of lasing light (>99%) while achieving near-lossless transmission of pump light (>99%). This significantly reduces the threshold power of the optically pumped laser and improves the optical-to-optical conversion efficiency, providing a key technological foundation for realizing next-generation high-performance, low-threshold, and low-power optically pumped tunable lasers.

[0053] This invention provides an optically pumped tunable vertical-cavity surface-emitting laser. While achieving dual-band optical performance, it effectively reduces the penetration depth of the light field in the mirror and shortens the resonant cavity length by controlling the optical thickness of the film layer on the top mirror near the active region to one-quarter of the laser's operating center wavelength. This design increases the longitudinal mode spacing, making it almost identical to the longitudinal mode spacing of traditional DBR-type MEMS-VCSELs, thus enhancing the single-mode stability of the device throughout the entire tuning range. The larger longitudinal mode spacing ensures a wider tuning range for the device.

[0054] The optically pumped tunable vertical cavity surface-emitting laser provided by this invention breaks the single optimization paradigm centered on lasing light in traditional DBR. While ensuring a wide tuning range and free spectral range, it significantly improves the optical pumping efficiency, thereby realizing a high-efficiency wide-tunable single longitudinal mode output MEMS-VCSEL, laying the foundation for the next generation of high-performance tunable lasers.

[0055] It should be understood that the above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A wavelength-selective reflector, characterized in that, include: The phase matching region and optimization region are set sequentially along the vertical direction. The phase-matching region is formed by periodically alternating stacking of a first high-refractive-index material layer and a first low-refractive-index material layer in the vertical direction, wherein the optical thickness of the first high-refractive-index material layer and the first low-refractive-index material layer are both one-quarter of the lasing wavelength of the laser, and x≥1; The optimized region is formed by y second high refractive index material layers and z second low refractive index material layers, which are stacked alternately in the vertical direction. The optical thicknesses of the second high refractive index material layers and the second low refractive index material layers are not equal, and are both greater than or less than one-quarter of the lasing wavelength of the laser, y≥1, z≥1. The phase-matching region and the optimization region are configured such that the wavelength-selective reflector has a reflectivity of more than 99.5% for lasing light with a wavelength of 1000nm~1100nm and a transmittance of more than 99% for pump light with a wavelength of 845nm~855nm.

2. The wavelength-selective reflector according to claim 1, characterized in that: The materials of the first high-refractive-index material layer, the first low-refractive-index material layer, the second high-refractive-index material layer, and the second low-refractive-index material layer include TiO2, Ta2O5, Nb2O5, and SiN. x At least one of HfO2, SiO2 and Al2O3.

3. The wavelength-selective reflector according to claim 1 or 2, characterized in that: The first high refractive index material layer and the second high refractive index material layer are made of the same material, and the first low refractive index material layer and the second low refractive index material layer are made of the same material.

4. The wavelength-selective reflector according to claim 1 or 2, characterized in that: The phase matching region includes three TiO2 / SiO2 periodic structures stacked sequentially along the vertical direction, wherein the thickness of the TiO2 layer in each of the three TiO2 / SiO2 periodic structures is 181 nm and the thickness of the SiO2 layer is 109 nm. The optimized region comprises eleven film layers stacked sequentially on the phase matching region along the vertical direction. These eleven film layers are, in order, a SiO2 layer with a thickness of 221 nm, a TiO2 layer with a thickness of 94 nm, a SiO2 layer with a thickness of 159 nm, a TiO2 layer with a thickness of 97 nm, a SiO2 layer with a thickness of 163 nm, a TiO2 layer with a thickness of 101 nm, a SiO2 layer with a thickness of 174 nm, a TiO2 layer with a thickness of 126 nm, a SiO2 layer with a thickness of 204 nm, a TiO2 layer with a thickness of 104 nm, and a SiO2 layer with a thickness of 316 nm.

5. A tunable vertical-cavity surface-emitting laser (VCSEL) pumped by an optical pump, comprising a tunable VCSEL unit, wherein the tunable VCSEL unit includes a bottom mirror, a top mirror, and an active region, the active region being disposed vertically between the bottom mirror and the top mirror, and together forming a vertically oriented optical resonant cavity, characterized in that: The top mirror of the optically pumped tunable vertical cavity surface-emitting laser is the wavelength-selective mirror as described in any one of claims 1-4, and the phase-matching region of the wavelength-selective mirror is located in the bottom layer near the active region.

6. The optically pumped tunable vertical-cavity surface-emitting laser according to claim 5, characterized in that, Also includes: A microelectromechanical system (MEMS) unit includes a bottom electrode, a top electrode, a sacrificial layer, and a cantilever structure layer. The sacrificial layer is stacked on the active region and has an air cavity within it. The cantilever structure layer is stacked on the sacrificial layer and at least covers the air cavity. The top electrode and the top reflective layer are disposed on the cantilever structure layer. The bottom electrode is disposed on the active region and located within the air cavity. An optical window is also disposed on the bottom electrode, and the optical window is located in the central region of the optically pumped MEMS tunable vertical-cavity surface-emitting laser. When a voltage is applied to the top electrode and the bottom electrode, the electrostatic attraction generated between the top electrode and the bottom electrode can cause the cantilever structure layer to bend, thereby causing the top reflector to move.

7. The optically pumped tunable vertical-cavity surface-emitting laser according to claim 6, characterized in that: The bottom reflector is a distributed Bragg reflector; And / or, the area of ​​the bottom reflector covered by the air cavity has an oxide etching hole extending in a vertical direction, and the portion of the bottom reflector located around the oxide etching hole is oxidized by wet water vapor to form an oxide area, which serves as the working area of ​​the bottom reflector; Preferably, the air chamber is formed in situ by removing a portion of the sacrificial layer.

8. The optically pumped tunable vertical-cavity surface-emitting laser according to claim 6, characterized in that, Also includes: An antireflection membrane is stacked on the active region, and the sacrificial layer and the bottom electrode are disposed on the antireflection membrane.

9. The optically pumped microelectromechanical system tunable vertical-cavity surface-emitting laser according to claim 6, characterized in that: The longitudinal mode spacing of the optically pumped tunable vertical cavity surface-emitting laser exceeds 100 nm.

10. A method for synergistically optimizing the pump light transmittance and lasing light reflectance of a tunable vertical-cavity surface-emitting laser, characterized in that, include: The wavelength-selective reflector described in any one of claims 1-4 is used as the top reflector of the tunable vertical cavity surface-emitting laser, and the longitudinal mode spacing of the tunable vertical cavity surface-emitting laser is greater than 100 nm.

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