A mid-infrared laser based on three-device on-chip integration and its fabrication method

Abstract

A mid-infrared laser based on on-chip integration of three devices and its fabrication method is disclosed, involving the intersection of semiconductor laser technology and optical communication technology. This invention alleviates the problem of the existing quantum cascaded laser (QCL) technology being unable to simultaneously achieve high modulation rate and high power. The mid-infrared laser includes a QCL unit, an EAM unit, and an SOA unit sequentially disposed on a substrate; the substrate comprises semi-insulating InP; the QCL unit, EAM unit, and SOA unit share the same ridge waveguide structure and are grown through epitaxial docking. The method described in this invention is applicable to mid-infrared band space communication scenarios with high requirements for laser modulation rate, output power, and single-mode stability.

Description

Technical Field

[0001] This invention relates to the intersection of semiconductor laser technology and optical communication technology, specifically to the field of quantum cascade lasers. Background Technology

[0002] As space laser communication technology develops towards higher speeds, longer distances, and higher reliability, the mid-infrared band (typically referring to the 8-14μm wavelength range) has become one of the key technologies in the field of space communication due to its outstanding advantages such as high atmospheric transmittance, strong anti-interference capabilities, and low background noise. Among them, quantum cascade lasers (QCLs) serve as the core light source in the mid-infrared band, and their performance directly determines the communication rate, transmission distance, and stability of the mid-infrared laser communication system.

[0003] Currently, quantum cascaded lasers (QCLs) face the core challenge of simultaneously achieving high modulation rates and high power:

[0004] First, to meet the needs of high-speed space communication and increase the modulation rate (such as 10 GHz and above), the volume of the active region of the quantum cascade laser (QCL) needs to be reduced to reduce parasitic capacitance and improve modulation response speed, but this will lead to a significant reduction in laser output power.

[0005] For example, in 2016, ETH Zurich used semi-insulating InP as the insulating layer and employed a coplanar waveguide structure to reduce parasitic capacitance. Their QCL achieved a lasing wavelength of 4.5µm, a -3dB bandwidth of 6.6GHz, and an output power of only 12mW. In 2023, a team from Changchun University of Technology and the Institute of Semiconductors, Chinese Academy of Sciences, collaborated to develop a high-speed microcavity QCL. By reducing the microcavity size, they lowered parasitic capacitance, achieving a -3dB bandwidth of 11GHz and an output power of 0.1mW (283K).

[0006] Second, to meet the high power requirements, the output power needs to be increased by increasing the active region or adopting a multimode structure, but this will lead to severe mode competition, destroy the single-mode output characteristics, and the increase in parasitic parameters will make it difficult to break through 10GHz in modulation rate, which cannot meet the requirements of high-speed laser communication.

[0007] For example, in 2016, the Institute of Semiconductors of the Chinese Academy of Sciences used a step-by-step etching process and thickened SiO2 as an insulating layer to reduce the parasitic capacitance of the device. The device achieved a wavelength of 4.7µm, a room temperature power of 100mW, and a -3dB cutoff bandwidth of only 1.7GHz.

[0008] In summary, existing quantum cascaded laser (QCL) technology suffers from the problem of not being able to simultaneously achieve high modulation rate and high power. Summary of the Invention

[0009] This invention alleviates the problem of the inability to simultaneously achieve high modulation rate and high power in existing quantum cascaded laser (QCL) technology. This invention provides the following solution:

[0010] Option 1: A mid-infrared laser, comprising a QCL unit, an EAM unit, and an SOA unit sequentially disposed on a substrate;

[0011] The substrate comprises semi-insulating InP;

[0012] The QCL unit, EAM unit, and SOA unit share the same ridge waveguide structure and are grown through epitaxial docking.

[0013] Furthermore, in one embodiment of the present invention, the QCL unit adopts a distributed feedback DFB structure and a strain compensation structure; the active region of the QCL unit adopts 35 levels of strain and corresponding In... 1-x Ga x As quantum well and In 1-y Al y As a barrier material system, where x < 0.47 and y > 0.48.

[0014] Furthermore, in one embodiment of the present invention, the band structure of the active region of the QCL unit is used to transition electrons from a bound state to a continuous state.

[0015] Furthermore, in one embodiment of the present invention, the transition dipole matrix element Z of the active region of the QCL unit... 43 It is 1.1nm.

[0016] Furthermore, in one embodiment of the present invention, the active region includes a distributed feedback DFB structure comprising a sampled distributed Bragg reflection region and a distributed feedback gain region;

[0017] The distributed feedback gain region of the QCL unit has an equivalent λ / 4 phase shift.

[0018] Furthermore, in one embodiment of the present invention, in the active region of the QCL unit, level 5 is a parasitic level; the energy difference E between level 5 and level 4 is... 54 The energy level difference E between energy level 5 and ground state energy level i is 70 meV. 5i It is 84 meV.

[0019] Furthermore, in one embodiment of the present invention, the material system of the EAM unit is InGaAs / InAlAs; the structure is a quantum well; and the optical structure is waveguide type.

[0020] Option 2: A method for fabricating a mid-infrared laser, the method comprising:

[0021] Semi-insulating InP was used as the substrate;

[0022] The QCL unit, EAM unit, and SOA unit are integrated sequentially using a serial architecture.

[0023] The QCL unit, EAM unit, and SOA unit share the same ridge waveguide structure and are grown through epitaxial docking to complete the fabrication of a mid-infrared high-speed, high-power laser.

[0024] The present invention discloses a mid-infrared laser based on on-chip integration of three devices and its fabrication method. This is achieved by integrating a quantum cascade laser (QCL) unit, a mid-infrared modulator (EAM) unit, and a laser amplifier (SOA) unit, effectively alleviating the problem of the inability to simultaneously achieve high modulation rate and high power in existing quantum cascade laser (QCL) technology. Specific beneficial effects include:

[0025] 1. The mid-infrared laser described in this invention achieves a balance between high power and high speed. This invention designs a quantum cascade laser (QCL) unit, a mid-infrared modulator (EAM) unit, and a laser amplifier (SOA) unit. Using semi-insulating InP as a substrate, the QCL, EAM, and SOA units are sequentially integrated in a series architecture, sharing the same ridge waveguide structure. Integrated fabrication is achieved through epitaxial mating growth. This invention employs a "functional component design - on-chip collaborative integration" approach, achieving high-speed modulation through an electro-absorption modulator. Simultaneously, the QCL unit maximizes power output from the EAM unit under unsaturated conditions, and the SOA unit further amplifies the power. This effectively avoids the coupling losses and synchronization problems of discrete devices, achieving an organic integration of laser generation, high-speed modulation, and power amplification, thus achieving a balance between high power and high speed.

[0026] 2. The mid-infrared modulator EAM unit described in this invention can be integrated with quantum cascade laser (QCL) units and laser amplifier (SOA) units. Currently, mid-infrared modulators mainly include the following three technical systems: The first type is the Si / Ge electric refractive index modulation system based on the plasmonic dispersion effect, with a wavelength coverage range of 2-4 μm and a transmission rate of 80 Gbit / s; the second type is the lithium niobate modulator based on the Pockels effect, whose bandwidth currently exceeds 20 GHz and is applicable to a wavelength range of 2-3 μm; in addition, there are some new modulators based on two-dimensional materials such as graphene and black phosphorus, whose -3 dB bandwidth is on the order of kHz. Since the wavelengths of the above modulators cannot cover the mid-infrared band (8~14 µm), the current modulators are not suitable for mid-infrared lasers. To solve the above technical problems, this invention develops a mid-infrared modulator EAM unit based on a GaAs / InP quantum well system suitable for the mid-infrared band, realizing high-speed modulation of mid-infrared lasers.

[0027] The method described in this invention is applicable to mid-infrared space communication scenarios with high requirements for laser modulation rate, output power and single-mode stability, and can be widely used in fields such as space-to-ground communication, deep space exploration communication, and atmospheric environment monitoring communication. Attached Figure Description

[0028] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0029] Figure 1 This is a schematic diagram of the mid-infrared laser structure described in Embodiment 1;

[0030] Figure 2 This is the equivalent circuit diagram described in Implementation Method 1. Detailed Implementation

[0031] Various embodiments of the present invention will now be clearly and completely described with reference to the accompanying drawings. The embodiments described with reference to the drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0032] In embodiment one, the mid-infrared laser described in this embodiment includes a QCL unit, an EAM unit, and an SOA unit sequentially disposed on a substrate;

[0033] The substrate comprises semi-insulating InP;

[0034] The QCL unit, EAM unit, and SOA unit share the same ridge waveguide structure and are grown through epitaxial docking.

[0035] In this embodiment, the SOA unit adopts the same epitaxial wafer structure as the QCL unit.

[0036] In this embodiment, the preferred development process of the mid-infrared laser is as follows:

[0037] Step S1: Develop a highly stable QCL unit; the quantum band structure design of the SOA unit is designed in conjunction with the SOA unit.

[0038] Step S2: Develop a high modulation rate EAM unit;

[0039] Step S3: Based on the completed development of the high-stability QCL unit and the high-modulation-rate EAM unit, conduct laser research on the QCL-EAM integrated high-rate EML unit, verify the modulation performance of the EAM unit, and provide theoretical and technical guidance for the subsequent integration of QCL unit, EAM unit and SOA unit.

[0040] Step S4: Integrate the EM and SOA units to obtain a mid-infrared laser.

[0041] This implementation preferably uses commercial ADS software to perform equivalent circuit modeling for the three-device integrated structure: firstly, QCL, EAM, and SOA are modeled independently one by one; when constructing the equivalent circuit model of the integrated device, the above discrete equivalent circuit models are integrated into a unified whole through the coordinated connection of optical network and electrical network, such as... Figure 2 The diagram shown is the equivalent circuit diagram. To simplify the model complexity, components that contribute little to the high-frequency response are ignored. Then, circuit simulation is performed using ADS software, and the experimental test data is fitted and analyzed with the equivalent circuit simulation results to finally determine the specific parameter values ​​of each component in the equivalent circuit model. Furthermore, this embodiment preferably optimizes the device's performance by adding bypass capacitors and adjusting the end-face reflectivity.

[0042] The mid-infrared laser described in this embodiment achieves high-speed modulation through an electro-absorption modulator by adopting the concept of "functional component design - on-chip collaborative integration". At the same time, it enables the QCL unit to output as much power as possible when the EAM unit is unsaturated, and further amplifies the power with an SOA unit. This effectively avoids the coupling loss and synchronization problems of discrete devices, and achieves the organic integration of laser generation, high-speed modulation and power amplification, thereby achieving both high power and high speed.

[0043] This implementation provides one example, such as Figure 1 The diagram shown is a schematic diagram of the mid-infrared laser structure described in this embodiment.

[0044] Implementation Method Two: This implementation method further defines the mid-infrared laser described in Implementation Method One. In this implementation method, the QCL unit adopts a distributed feedback DFB structure and a strain compensation structure; the active region of the QCL unit adopts 35 levels of strain and corresponding In... 1-x Ga x As quantum well and In 1-y Al y As a barrier material system, where x < 0.47 and y > 0.48.

[0045] The band structure of the active region of the QCL unit is used to transition electrons from a bound state to a continuous state.

[0046] The transition dipole matrix element Z of the active region of the QCL unit 43 It is 1.1nm.

[0047] In this embodiment, the band structure of the active region of the QCL unit, used to transition electrons from bound states to continuous states, is achievable by those skilled in the art using existing technologies. For example, the active region is composed of multiple repeating quantum well-barrier periodic structures. By precisely designing the materials and geometric dimensions of each quantum well and barrier, electrons in the quantum energy levels of the active region are positioned such that low-energy states are in bound states, while high-energy states are in continuous states. When a suitable bias voltage is applied across the device, electrons can transition from bound states to continuous states. This transition process provides the crucial population inversion condition for stimulated emission of mid-infrared lasers, thereby ensuring the high-efficiency luminescence performance of the quantum cascade laser in the mid-infrared band.

[0048] In this embodiment, it is preferable to increase the energy gap between the upper energy state that generates laser transition and the quantum well aperture by increasing the conduction band level, thereby improving the output performance of the device.

[0049] In this embodiment, the In 1-x Ga x As quantum well and In 1-y Al y The preferred As barrier material system is In 0.53 Ga 0.47 As quantum well and In 0.52 Al 0.48 As barrier material system.

[0050] In this embodiment, the strain compensation structure suppresses carrier leakage by introducing strain into the potential well and the potential barrier, thereby achieving high output performance.

[0051] In this embodiment, it is preferable to introduce a Bragg distribution feedback grating in the laser waveguide layer, and rely on the frequency selection characteristics of the grating to achieve single longitudinal mode output.

[0052] In this embodiment, it is preferable to optimize the quantum well period and the grating period to ensure that the output laser wavelength covers the 8-14μm mid-infrared atmospheric window.

[0053] This embodiment further defines the mid-infrared laser and provides an example of a QCL unit scheme. This method employs a distributed feedback (DFB) structure to improve the stability of the mid-infrared single-mode laser, with the active region being In. 0.53 Ga 0.47 As quantum well and In 0.52 Al 0.48 As a barrier material system, the stability of the QCL unit is further improved.

[0054] Implementation Method 3: This implementation method further defines the mid-infrared laser described in Implementation Method 2. In this implementation method, the distributed feedback DFB structure in the active region includes a sampling distributed Bragg reflection region and a distributed feedback gain region.

[0055] The distributed feedback gain region of the QCL unit has an equivalent λ / 4 phase shift.

[0056] In this embodiment, it is preferable to use FDTD solutions software to design an equivalent phase-shift distributed feedback quantum cascade laser with an integrated distributed Bragg reflector. The equivalent λ / 4 phase-shift sampling grating structure and the sampling distributed Bragg reflector (SG-DBR) are integrated together to obtain the sampling distributed Bragg reflection region and the distributed feedback gain region.

[0057] This embodiment further defines the active region and provides an example of a distributed feedback DFB structure. This method integrates the sampling distributed Bragg reflection region and the distributed feedback gain region to obtain a distributed feedback DFB structure, which improves the single-mode stability of the device and more accurately controls the emission wavelength.

[0058] Implementation Method Four: This implementation method further defines the mid-infrared laser described in Implementation Method Two. In this implementation method, in the active region of the QCL unit, level 5 is a parasitic level; the energy difference E between level 5 and level 4 is... 54 The energy level difference E between energy level 5 and ground state energy level i is 70 meV. 5i It is 84 meV.

[0059] This embodiment further defines the active region of the QCL unit and provides an example of the energy level scheme. In this embodiment, the larger energy level difference can effectively suppress the thermal excitation of electrons from the lasing energy level 4 and the direct injection of electrons from the ground state energy level i into the parasitic energy level 5, thereby avoiding the rapid degradation of device performance during high current injection or continuous operation at room temperature, and improving stability from the structural design perspective.

[0060] Implementation Method 5: This implementation method further defines the mid-infrared laser described in Implementation Method 1. In this implementation method, the material system of the EAM unit is InGaAs / InAlAs; the structure is a quantum well structure; and the optical structure is a waveguide structure.

[0061] In this embodiment, the waveguide-type EAM unit band and structure are preferably designed based on the quantum well structure to restrict the Stark effect, which can realize the rapid modulation of laser.

[0062] In this embodiment, electromagnetic simulation software such as COMSOL and FDTD is preferably used to jointly design the integrated device of QCL and EAM units, study the optical field coupling efficiency of QCL and EAM units with different ridge waveguide widths, and obtain the waveguide parameters of the device with the highest coupling efficiency. Experimentally, EML unit fabrication process is carried out based on the epitaxial chip of QCL unit, and the EML unit size parameters are determined by using the designed structural parameters as the standard.

[0063] This embodiment further defines the mid-infrared laser and provides an example of the EAM unit scheme. The bandgap of a traditional InP-based InGaAs / InAlAs quantum well is 0.74 eV, much larger than 88.6–155 meV (8–14 µm in the mid-infrared range). Under bias, it can only absorb and modulate infrared light up to ~1.6 µm. To achieve mid-infrared modulation, an asymmetric multi-quantum structure is designed to reduce optical interface reflection, and a waveguide-type EAM with the same material system as the QCL (Quantum Laser Classifier) ​​suitable for integration is developed.

Claims

1. A mid-infrared laser, characterized by, The QCL unit, the EAM unit and the SOA unit are sequentially arranged on a substrate; The substrate comprises semi-insulating InP; The QCL unit, the EAM unit and the SOA unit share the same ridge waveguide structure and are grown by epitaxial butt joint; The QCL unit adopts a distributed feedback (DFB) structure and a strain compensation structure; an active region of the QCL unit adopts 35 levels of strain and corresponding In 1-x Ga x As quantum well and In 1-y Al y As barrier material system, wherein y is greater than or equal to 0.

48. The active region comprises a sampled distributed Bragg reflection region and a distributed feedback gain region; The distributed feedback gain region of the QCL unit is provided with an equivalent λ / 4 phase shift; The material system of the EAM unit is InGaAs / InAlAs; the structure is quantum well; and the optical structure is waveguide type; The In 1-x Ga x As quantum well is an In 0.53 Ga 0.47 As quantum well; The quantum well period and the grating period are optimized to ensure that the output laser wavelength covers the 8-14 μm mid-infrared atmospheric window.

2. The mid-infrared laser of claim 1, wherein, The energy band structure of the active region of the QCL unit is used to transition electrons from a bound state to a continuous state.

3. The mid-infrared laser of claim 1, wherein, Transition dipole matrix element Z of the active region of the QCL unit 43 is 1.1 nm.

4. The mid-infrared laser of claim 1, wherein, In the active region of the QCL unit, the energy level 5 is a parasitic energy level; the energy level difference E 54 between the energy level 5 and the energy level 4 is 70 meV; the energy level difference E 5i between the energy level 5 and the ground state energy level i is 84 meV.

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