Ultra-wideband gain spectrum epitaxial material structure of tunable laser and application of ultra-wideband gain spectrum epitaxial material structure

Abstract

The invention provides an ultra-wide-band gain spectrum epitaxial material structure of a tunable laser and application of the ultra-wide-band gain spectrum epitaxial material structure. The epitaxial material structure comprises a substrate, a lower cladding, a waveguide layer, an upper limiting layer, an upper cladding and a contact layer which are sequentially arranged from bottom to top, the waveguide layer comprises an intrinsic waveguide layer and a bismuth compound quantum dot layer embedded in the intrinsic waveguide layer, and the gain bandwidth is widened through the energy band anti-cross effect instead of suppressing radiation recombination. The epitaxial material structure grows in a molecular beam epitaxy or metal organic vapor phase epitaxy mode, and the crystal quality is optimized in combination with a rapid thermal annealing process. By regulating and controlling the number of layers of the quantum dots and the bismuth component, the ultra-wideband gain spectrum coverage from near ultraviolet to near infrared bands is realized, the gain spectrum is wide, the gain peak value of the material is relatively high, and meanwhile, the material has a low linewidth enhancement factor and high temperature stability. The epitaxial material structure can be monolithically integrated in a DFB laser array and a semiconductor optical amplifier, and a core gain medium is provided for a high-performance tunable semiconductor laser.

Description

Technical Field

[0001] This invention relates to the field of information photonics, specifically to an ultrawideband gain spectrum epitaxial material structure for tunable lasers and its applications. Background Technology

[0002] With the rapid development of fields such as optical communication, quantum information processing, and precision spectroscopy, the performance requirements for tunable semiconductor lasers are increasing, especially in terms of tuning range, spectral purity, and output power. Traditional tunable lasers based on quantum well structures are limited by their finite gain bandwidth and high linewidth enhancement factor, making it difficult to simultaneously achieve narrow linewidth and continuous tuning over a wide spectral range. This severely restricts their further development in high-end applications such as multi-wavelength systems, high-capacity optical communication, and atomic and molecular spectroscopy. Furthermore, traditional epitaxial material structures also have significant shortcomings in high-temperature stability and nonlinear loss suppression, limiting breakthroughs in laser integration and high efficiency.

[0003] Meanwhile, advancements in photonic integration technology have placed higher demands on the compactness, tunability, and stability of tunable laser sources. Photonic platforms based on advanced substrates such as lithium niobate on insulators provide a solid foundation for the integration of high-performance modulators, resonant cavities, and other functional units; however, their efficient coupling with semiconductor gain media still relies on epitaxial materials with ultra-wideband gain characteristics. Therefore, developing an epitaxial material structure compatible with existing photonic platforms and possessing ultra-wideband gain spectra, high stability, and easy tunability has become a core issue driving the development of next-generation integrated tunable lasers. Summary of the Invention

[0004] The purpose of this invention is to provide an ultra-wideband gain spectrum epitaxial material structure for tunable lasers and its application, in order to solve the problem that traditional epitaxial material structures cannot simultaneously achieve narrow linewidth and continuous tuning over a wide spectral range.

[0005] This invention is implemented as follows: An ultrawideband gain spectrum epitaxial material structure for a tunable laser includes, from bottom to top, a substrate, a lower cladding layer, a waveguide layer, an upper confinement layer, an upper cladding layer, and a contact layer; the waveguide layer includes an intrinsic waveguide layer and a bismuth compound quantum dot layer embedded within the intrinsic waveguide layer.

[0006] Preferably, the bismuth compound quantum dot layer material is GaAsBi.

[0007] Preferably, the atomic percentage of Bi in the bismuthide quantum dot layer is 10.5-50%.

[0008] Preferably, the number of bismuthide quantum dot layers is 2 to 5, and adjacent bismuthide quantum dot layers are separated by intrinsic waveguide layers.

[0009] Preferably, the thickness of the intrinsic waveguide layer between adjacent bismuthide quantum dot layers is 30~50 nm.

[0010] Preferably, the thickness of each bismuthide quantum dot layer is 2 to 3 single-atom thickness.

[0011] Preferably, the intrinsic waveguide layer is made of InGaAsP or InAlGaAs; the substrate material is InP or GaAs, and the substrate orientation is (001) crystal orientation; the lower cladding layer is n-type doped InP or AlGaAs, the upper cladding layer is p-type doped InP or AlGaAs, and the upper confinement layer is p-type doped InAlAs.

[0012] Preferably, the materials on the substrate are grown by molecular beam epitaxy or metal-organic vapor phase epitaxy, and then subjected to rapid thermal annealing to optimize crystal quality.

[0013] The ultra-wideband gain spectrum epitaxial material structure of the tunable laser provided by this invention is used to manufacture tunable lasers, which can be applied to fields such as optical communication, quantum technology, or precision measurement.

[0014] The method for fabricating a tunable laser using the ultrawideband gain spectrum epitaxial material structure of the aforementioned tunable laser includes the following steps: (1) A distributed feedback grating or a ring resonator is formed on the epitaxial material structure of the ultrawideband gain spectrum of the tunable laser; (2) The integrated micro heater and current injection electrode can achieve mode-skipping continuous tuning through thermal tuning and carrier injection. The tuning range is large and the linewidth is below kilohertz.

[0015] This invention aims to propose a solution for the ultra-wideband gain spectrum epitaxial material structure of tunable lasers. This solution fully utilizes the discrete energy state characteristics of quantum dot materials and the band reversal effect of bismuth compounds. By leveraging the low-dimensional confinement effect of quantum dots, the linewidth enhancement factor can be effectively reduced, achieving excellent narrow linewidth characteristics. Simultaneously, the band reversal effect introduced by bismuth atoms in the bismuth compound significantly broadens the gain spectrum and suppresses nonradiative recombination losses. Furthermore, this waveguide structure embedded with bismuth compound quantum dot layers exhibits good temperature stability and carrier injection efficiency, providing a material basis for achieving continuous tuning and high power output over a wide spectral range.

[0016] The frequency tuning mechanism of the epitaxial material structure is based on the synergistic effect of carrier injection and thermo-optical effects. By fabricating a distributed feedback grating or micro-ring resonator on the epitaxial material structure, and combining it with a microheater and current injection electrodes, continuous wavelength tuning based on the material's gain spectrum characteristics can be achieved. This material design scheme provides a core material platform for the development of high-performance tunable semiconductor lasers and has significant application value in fields such as optical communication, quantum technology, and precision measurement.

[0017] The present invention has the following beneficial effects: 1. The ultra-wideband gain spectrum epitaxial material structure of the tunable laser provided by this invention proposes a new scheme for quantum dot bismuth compound gain and a new mechanism for band synergistic control, fundamentally breaking through the technical contradiction between broadband tuning and narrow linewidth performance of traditional gain materials, and realizing the synergistic optimization of key performances such as ultra-wideband gain, high spectral purity and excellent temperature stability.

[0018] 2. The epitaxial material structure of the present invention, through the band engineering co-design of quantum dot bismuth compounds, fully leverages the discrete state characteristics of quantum dots and the band modulation advantages of bismuth compounds, achieving a wide range of gain spectrum expansion and a significant improvement in carrier recombination efficiency, effectively solving the problems of limited gain bandwidth and temperature sensitivity of traditional epitaxial materials.

[0019] 3. This epitaxial material structure has good material compatibility and process adaptability, and can be seamlessly integrated with existing semiconductor process platforms, providing a reliable material basis for the development of high-performance tunable lasers and promoting the application and development of integrated photonics technology in fields such as optical communication and quantum information. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the ultrawideband gain spectrum epitaxial material structure of a tunable laser provided in an embodiment of the present invention.

[0021] Figure 2 An optical micrograph of a tunable laser integrated chip provided in an embodiment of the present invention.

[0022] Figure 3 The image shows the wavelength diagram of the tunable light source based on the epitaxial material structure of the ultrawideband gain spectrum epitaxial laser provided in the embodiments of the present invention. Detailed Implementation

[0023] like Figure 1As shown, the ultra-wideband gain spectrum epitaxial material structure of the tunable laser provided by this invention includes a substrate as the bottom layer, on which a lower cladding layer and a waveguide layer are sequentially grown. The waveguide layer contains a bismuth compound quantum dot layer, specifically GaAsBi. An upper confinement layer, an upper cladding layer, and a contact layer are sequentially grown on the waveguide layer. The substrate provides the basis for crystal growth and determines the epitaxial orientation; the cladding layers (including the upper and lower cladding layers) achieve optical field confinement and carrier confinement. The waveguide layer is used for optical field confinement and low-loss propagation, and the bismuth compound quantum dot layer in the waveguide layer provides ultra-wideband optical gain and efficient radiative recombination. Each epitaxial layer achieves atomic-level precision interface control through epitaxial technology, ensuring an optimal balance between carrier injection efficiency and optical transmission performance. Through bandgap engineering optimization matching, a wide-spectrum gain coverage from short wavelengths to long wavelengths is achieved.

[0024] The substrate can be InP or GaAs material, oriented in the (001) crystal direction. The lower cladding is n-type doped InP or AlGaAs, with a thickness on the micrometer scale, used to confine the optical field and transport electrons. The waveguide layer includes an intrinsic waveguide layer and 2-5 layers of bismuthide quantum dot layers embedded via the Stranski-Krastanov (SK) self-assembly mode. Adjacent bismuthide quantum dot layers are separated by intrinsic waveguide layers to optimize carrier confinement. The thickness of the intrinsic waveguide layer between adjacent bismuthide quantum dot layers is approximately 40 nm. The intrinsic waveguide layer can be InGaAsP or InAlGaAs material, used for optical field confinement and low-loss propagation. The bismuthide quantum dot layers are embedded in the intrinsic waveguide layer, and the thickness of each bismuthide quantum dot layer is typically 2-3 single-atom layers. Bismuth compound quantum dot layers, such as GaAsBi, are sized by precisely controlling the deposition amount, growth temperature (400–450°C), and growth rate of GaAsBi material, thereby utilizing the quantum confinement effect to initially define the emission wavelength range. The Bi content in the GaAsBi quantum dot layer is precisely controlled at an atomic percentage of 10.5–50%. The introduction of a high Bi content not only significantly reduces the material's bandgap to the 1.5 μm communication band, but more importantly, it makes the spin-orbit splitting energy greater than the material's bandgap. This physically suppresses Auger recombination and valence band absorption—the two main efficiency loss pathways—laying the foundation for manufacturing high-temperature stable, low-threshold, and high-efficiency lasers.

[0025] The waveguide layer was grown using molecular beam epitaxy (MBE). Except for the waveguide layer, all other layers were grown using metal-organic vapor phase epitaxy (MOVPE).

[0026] The upper confinement layer on the waveguide layer is carbon-doped (approximately 5 × 10⁻⁶). 17 cm -3 The p-type InAlAs with a thickness of approximately 0.8 μm is used. The upper cladding layer on the upper confinement layer is carbon-doped (approximately 1 × 10⁻⁶). 18cm -3 The structure consists of p-type InP or AlGaAs with a thickness of approximately 1.8 μm. The top layer of the structure is carbon-doped (approximately 1 × 10⁻⁶). 19 cm -3 A p++ type InGaAs contact layer with a thickness of approximately 150 nm is used to form a low-resistivity ohmic contact.

[0027] This invention utilizes advanced epitaxial growth technology to precisely control the thickness and composition of each layer during material growth. The quantum dot layer is formed using a self-assembly growth mode, exhibiting excellent dimensional uniformity, and is grown at an optimized temperature to promote the effective incorporation of bismuth. Post-growth heat treatment optimizes crystal quality, reducing interface defects and non-radiative recombination centers.

[0028] The core of this invention is the embedding of a bismuth compound quantum dot layer within the waveguide layer. By precisely adjusting the bismuth source beam pressure and maintaining a low-temperature growth environment during the MBE process, bandgap engineering is precisely controlled, effectively expanding the gain spectrum range and suppressing nonradiative recombination processes. Quantum dots, due to their atom-like discrete energy state characteristics, can achieve lower linewidth enhancement factors and wider gain spectra, significantly improving the linewidth performance and temperature stability of lasers. Meanwhile, bismuth compounds (such as GaAsBi), through their unique bandgap anti-crossing effect, can not only effectively suppress nonradiative loss mechanisms such as Auger recombination and valence band absorption, but also significantly extend the gain spectrum range to the near-infrared band.

[0029] Bismuthide quantum dot layers exhibit controlled emission wavelengths through size regulation. The control principle is that the emission wavelength of quantum dots is dominated by the quantum confinement effect, which is determined by their size. Smaller sizes result in stronger quantum confinement, larger band gaps, and shorter emission wavelengths; larger sizes result in smaller band gaps and longer emission wavelengths. GaAsBi quantum dots were grown on InP substrates using molecular beam epitaxy (MBE) in the Stranski-Krastanov growth mode. The size and density of the quantum dots were adjusted by precisely controlling growth parameters (such as substrate temperature, deposition rate, and V / III ratio). The number of quantum dot layers was precisely designed, and adjusting the number of layers (e.g., 2–5 layers) optimized the optical confinement factor and linewidth enhancement factor, thus indirectly affecting the emission characteristics. Experimental results showed that the linewidth enhancement factor of the 5-layer quantum dot structure decreased from 2.5 to 0.6 compared to the 2-layer structure, leading to a significant reduction in linewidth. Finally, a post-processing technique was employed: rapid thermal annealing at 750°C after growth to reduce defects and stabilize the quantum dot size, ensuring wavelength consistency.

[0030] Bismuth compound quantum dot layers achieve precise modulation of bandgap engineering through bismuth composition control. The control principle is as follows: Bi doping into the GaAs lattice introduces valence band anti-crossing, leading to a decrease in bandgap (approximately 80 meV / % Bi) and an increase in spin-orbit splitting energy (ΔSO). When ΔSO > bandgap (Eg), Auger recombination and spacer band absorption can be suppressed, improving laser efficiency. This invention uses MBE to grow GaAsBi quantum dot layers. By optimizing the growth temperature, V / III ratio, and reactor gas flow distribution, Bi composition fluctuations on the wafer are reduced, decreasing the Bi composition from 2.2% at the wafer center to 1.8% at the edge. Finally, bandgap design is performed. Based on the 12-bandk·p theoretical model, the influence of Bi composition on the bandgap and ΔSO is pre-calculated to guide the setting of growth parameters, achieving the target wavelength and high-efficiency gain.

[0031] In terms of epitaxial growth technology selection, molecular beam epitaxy (MBE) is used to grow bismuth compound quantum dot layers, providing atomic-level thickness control and low defect density. Metal-organic vapor phase epitaxy (MOVPE) is used to grow cladding and contact layers, offering high throughput and good uniformity. Regarding thickness control, growth time and rate are controlled; the quantum dot layer thickness is precisely set by calibrating the growth rate and controlling the growth time. In MBE, shutter switching time is used to control the deposition rate; in-situ monitoring, using RHEED (for MBE) or laser interferometry (for MOVPE), ensures thickness uniformity by monitoring the layer thickness in real time. Temperature and pressure are optimized, as growth temperature (e.g., 400℃) and reactor pressure (50 mbar) significantly affect Bi component incorporation. Doping is controlled using Si (n-type) and C (p-type) doping sources, and carrier concentration is adjusted through flow control to optimize conductivity and optical properties.

[0032] This invention employs bandgap engineering techniques to ensure the continuity and stability of the gain spectrum. By precisely controlling the quantum dot size distribution and bismuth concentration, a seamless transition of the gain spectrum from shortwave to longwave bands is achieved, ensuring a smooth transition of gain characteristics. The gain spectrum morphology is optimized by adjusting the carrier injection concentration and distribution, and the gain characteristics are stabilized through a thermal management mechanism.

[0033] This invention achieves stable gain characteristics through a thermal management mechanism. It employs a temperature control method, integrating an Au / Ti micro-heater on the chip. By adjusting the heater current (e.g., 0-100 mA), the waveguide layer temperature is locally controlled, achieving wavelength tuning (e.g., 10 nm / laser) and mode stability. Through heat sink design, using high thermal conductivity materials (e.g., Cu heat sinks) and thermoelectric coolers (TECs), the chip temperature is maintained stable (e.g., ±0.1℃), reducing gain fluctuations caused by thermal drift. Driving conditions are optimized, employing pulsed driving (e.g., 500 ns, 20 kHz) to reduce self-heating effects, or using a battery source to minimize current noise, ensuring linewidth stability (<200 kHz). For thermal coupling management, by simulating heat distribution and optimizing device layout (e.g., DFB laser spacing) and packaging structure, thermal crosstalk is reduced. Through thermal management, linewidth temperature dependence can be minimized.

[0034] like Figure 2 As shown in the figure, four lasers are illustrated, each a DFB laser. The DFB lasers are connected to a semiconductor optical amplifier (SOA) via couplers. In this integrated device, the currents of the DFB lasers, couplers, and SOA are independently controlled to adjust the photon density and carrier distribution, resulting in a flatter or wider gain spectrum. Test results demonstrate its excellent gain characteristics, such as... Figure 3 As shown, gain spectral measurements reveal ultra-wideband gain characteristics covering a broad spectral range, with a flat gain distribution. Continuous tuning of the gain spectrum can be achieved by adjusting carrier injection conditions or operating temperature, thus supporting the laser's wavelength tuning capability.

[0035] The ultra-wideband gain spectrum epitaxial material structure for tunable lasers provided by this invention is particularly suitable for monolithic integration of distributed feedback lasers and semiconductor optical amplifiers. By fabricating gratings (such as distributed feedback gratings) or microring resonators on the epitaxial material structure, and combining thermal tuning and carrier injection tuning mechanisms, mode-hopping-free continuous tuning can be achieved. This structure supports the realization of high-performance tunable lasers, offering advantages such as a wide tuning range and high spectral purity.

[0036] The technical solution of this invention achieves ultra-wideband and highly stable gain spectrum characteristics, providing a reliable material basis for the application of tunable semiconductor lasers in fields such as optical communication, quantum technology and precision measurement.

[0037] The specific embodiments described above provide a more detailed explanation of the technical solution of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An ultrawideband gain spectrum epitaxial material structure for a tunable laser, characterized in that, It includes a substrate, a lower cladding layer, a waveguide layer, an upper confinement layer, an upper cladding layer, and a contact layer arranged sequentially from bottom to top; the waveguide layer includes an intrinsic waveguide layer and a bismuth compound quantum dot layer embedded in the intrinsic waveguide layer.

2. The ultra-wideband gain spectrum epitaxial material structure for a tunable laser according to claim 1, characterized in that, The bismuth compound quantum dot layer material is GaAsBi.

3. The ultra-wideband gain spectrum epitaxial material structure for a tunable laser according to claim 2, characterized in that, The atomic percentage of Bi in the bismuth compound quantum dot layer is 10.5-50%.

4. The ultra-wideband gain spectrum epitaxial material structure for a tunable laser according to claim 1, characterized in that, The number of bismuth compound quantum dot layers is 2 to 5, and adjacent bismuth compound quantum dot layers are separated by intrinsic waveguide layers.

5. The ultra-wideband gain spectrum epitaxial material structure for a tunable laser according to claim 4, characterized in that, The thickness of the intrinsic waveguide layer between adjacent bismuthate quantum dot layers is 30~50 nm.

6. The ultra-wideband gain spectrum epitaxial material structure for a tunable laser according to claim 4, characterized in that, Each bismuthide quantum dot layer is 2 to 3 atom thick.

7. The ultra-wideband gain spectrum epitaxial material structure for a tunable laser according to claim 1, characterized in that, The intrinsic waveguide layer is made of InGaAsP or InAlGaAs; the substrate is made of InP or GaAs and the substrate orientation is (001); the lower cladding is made of n-type doped InP or AlGaAs; the upper cladding is made of p-type doped InP or AlGaAs; and the upper confinement layer is made of p-type doped InAlAs.

8. The ultra-wideband gain spectrum epitaxial material structure for a tunable laser according to claim 1, characterized in that, The materials on the substrate are grown by molecular beam epitaxy or metal-organic vapor phase epitaxy, and then subjected to rapid thermal annealing to optimize crystal quality.

9. The ultrawideband gain spectrum epitaxial material structure of the tunable laser according to any one of claims 1 to 8 is used to manufacture tunable lasers and for applications in optical communication, quantum technology or precision measurement.

10. The application according to claim 9, characterized in that, A method for fabricating a tunable laser using the ultrawideband gain spectrum epitaxial material structure of the tunable laser includes the following steps: (1) A distributed feedback grating or a ring resonator is formed on the epitaxial material structure of the ultrawideband gain spectrum of the tunable laser; (2) The micro heater and current injection electrode are integrated, and mode-skipping continuous tuning can be achieved through thermal tuning and carrier injection.

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