High performance intracavity laser based on micro-gain grating region double-side ar plus angle

Abstract

The application relates to the technical field of semiconductor lasers, in particular to a high-performance intracavity laser based on a micro-gain grating region double-side AR plus an inclined angle, which comprises a high-performance intracavity laser based on a micro-gain grating region double-side AR plus an inclined angle, including a substrate layer and a back ridge waveguide; the back ridge waveguide is arranged on the upper end face of the substrate layer; the back ridge waveguide comprises a composite structure grating section located on the left side and a gain region waveguide section located on the right side; an i-layer semiconductor Bragg grating is etched in the composite structure grating section, and i is a natural number; a metal grating electrode is covered on the top of the composite structure grating section; a quantum well layer is arranged in the gain region waveguide section; a gain region electrode is covered on the top of the gain region waveguide section; and an inclined end face is arranged at the left end of the gain region waveguide section. The application overcomes the inherent defects of traditional DBR, DFB and traditional external cavity lasers from the aspects of structure and mechanism.

Description

Technical Field

[0001] This invention relates to the field of semiconductor laser technology, specifically to a high-performance intracavity laser based on a double-sided AR with an angled micro-gain grating region. Background Technology

[0002] 1550nm semiconductor lasers are the core light source for the optoelectronic industry. Traditional distributed Bragg reflection (DBR) lasers, distributed feedback (DFB) lasers, and external cavity lasers (including grating external cavities and micro-ring external cavities) all have significant technical bottlenecks, making it difficult to simultaneously meet the industrial application requirements of high power, ultra-narrow linewidth, high integration, and low loss. The specific shortcomings are as follows:

[0003] 1. Inherent defects of traditional DBR lasers: The cleavage surface of traditional DBR lasers has a high reflectivity of about 30%. This cleavage surface and the DBR grating easily form a resonant cavity. The longitudinal mode wavelength needs to be strictly resonantly matched with the reflected wavelength of the DBR grating. Therefore, the device must add a phase tuning region and matching electrodes to adjust the optical path. This not only significantly increases the cost and difficulty of precise control, but also makes it extremely difficult to coordinate dual-zone control due to the different temperature sensitivity coefficients of the resonant cavity and the DBR grating under temperature drift. At the same time, the existence of the phase tuning region increases the absorption loss of light in the waveguide material, which is not conducive to building high-power output lasers. The high reflectivity of the end face cleavage surface can also easily cause multimode oscillation and linewidth expansion, which seriously affects spectral purity.

[0004] 2. The core shortcomings of traditional DFB lasers: The grating region of traditional DFB lasers overlaps with the high-gain quantum well region, which easily forms a strong standing wave field in the cavity. Under high-power operating conditions, the spatial hole burning effect is very likely to occur, which directly limits the upper limit of the laser power. Moreover, the process of etching the grating can easily cause physical damage to the adjacent quantum well layer, destroy the integrity of the gain medium, and affect the gain performance, reliability and lifespan of the laser. It is difficult to achieve both spectral linewidth and power output.

[0005] 3. Key issues of traditional grating external cavity lasers: The gain chip and external grating of traditional grating external cavity lasers are separate structures. The difference in refractive index of different materials and the end face reflection at the component connection interface will produce serious optical energy loss and multiple reflection noise. At the same time, mechanical vibration and ambient temperature drift can easily lead to collimation deviation of the external cavity optical path, causing wavelength instability and coupling loss. Furthermore, the introduction of external optical components will increase reflection noise and alignment complexity, significantly reduce system robustness, and limit the integration density of the device.

[0006] 4. Inherent drawbacks of micro-ring external cavity lasers: Although micro-ring external cavity lasers possess a certain degree of integration, they still suffer from insurmountable technical defects. First, mode hopping is an unavoidable technical issue, especially in applications requiring continuous linear wavelength adjustment. The resonant characteristics of the micro-ring are highly sensitive to environmental changes and adjustment operations, further amplifying the mode hopping problem and severely affecting the stability of the single longitudinal mode of the laser output. Second, the optical output power of micro-ring feedback lasers is inherently extremely low. If power is increased by integrating with an optical amplification module, the manufacturing cost of the device will increase significantly, while also significantly increasing the complexity of structural design and circuit control, completely negating its integrated technical advantages. Third, micro-rings are sensitive to ambient temperature, making precise control difficult. Furthermore, their resonant structure design requires high consistency in manufacturing processes, resulting in complex structures, poor consistency, and high costs, further limiting their industrial-scale application. Summary of the Invention

[0007] To address the problems mentioned in the background section, the present invention provides the following technical solution:

[0008] A high-performance intracavity laser based on a micro-gain grating region with bilateral AR and beveled angle, including a substrate layer and a back ridge waveguide;

[0009] The back ridge waveguide is disposed on the upper end face of the substrate layer, and the back ridge waveguide includes a composite structure grating segment on the left and a gain region waveguide segment on the right.

[0010] The composite structure grating segment has i layers of semiconductor Bragg gratings etched inside, where i is a natural number. A first λ / 4 phase shift is provided at the left 1 / 3 of the grating of the semiconductor Bragg grating. The top of the composite structure grating segment is covered with a metal grating electrode. A second λ / 4 phase shift is provided at the left 1 / 3 of the grating of the metal grating electrode, where λ = 1550 nm.

[0011] A quantum well layer is disposed inside the gain region waveguide section, a gain region electrode is covered on the top of the gain region waveguide section, and an angled end face is disposed on the left end of the gain region waveguide section.

[0012] Both the beveled end face and the right end face of the composite structure grating segment are coated with an AR film.

[0013] As a preferred embodiment of the above technical solution, i=3.

[0014] As a preferred embodiment of the above technical solution, the reflectivity R of the AR film is less than 1 x 10⁻⁶. -4 .

[0015] As a preferred embodiment of the above technical solution, the angle φ of the beveled end face is controlled between 6° and 26°.

[0016] As a preferred embodiment of the above technical solution, the angle φ of the beveled end face is controlled between 8° and 15°.

[0017] As a preferred embodiment of the above technical solution, the composite structure grating segment is etched with three layers of semiconductor Bragg gratings.

[0018] As a preferred embodiment of the above technical solution, the gain region waveguide segment is a tapered optical waveguide with a left ridge width W1 greater than a right ridge width W2.

[0019] This invention provides a high-performance intracavity laser based on a double-sided AR with a beveled end face in a micro-gain grating region. This invention is an on-chip integrated intracavity laser that overcomes the inherent defects of traditional DBR, DFB, and traditional external cavity lasers in terms of structure and mechanism through an integrated design of "double-sided AR film + beveled end face," "composite grating feedback," "separate grating-gain region," and "micro-gain compensation." At the same time, it has significant technical and application advantages compared to micro-ring external cavity lasers. Specific beneficial effects are as follows:

[0020] 1. Complete elimination of the phase region, simplified structure and reduced control costs: Through the design of double-sided AR films and beveled end faces, the longitudinal mode interference caused by the 30% high reflectivity of traditional cleaved surfaces is completely eliminated. There is no need to meet the resonance matching requirement between the longitudinal mode wavelength and the grating reflection wavelength, thus completely eliminating the "phase adjustment region" and its associated electrodes required by traditional lasers. This simplifies the device from a three-segment structure to a single-chip two-segment integrated structure. This not only reduces the chip's process complexity and mass production costs but also eliminates the additional light absorption loss caused by the phase region, improving the laser's photoelectric conversion efficiency. Furthermore, the control method is simple, requiring no dual-region coordinated tuning. Compared to the complex structure and difficult control of micro-ring external cavity lasers, this offers significant advantages.

[0021] 2. Avoiding spatial hole burning effect and achieving stable high-power output: The innovative design achieves complete separation between the grating region and the gain quantum well region, with no grating structure in the gain region. This eliminates the spatial hole burning effect caused by high-gain cavity standing waves, breaking through the power limit of traditional DFB lasers. At the same time, the passive phase adjustment region is removed, increasing the proportion of the effective gain region. Combined with the micro-gain compensation mechanism of the grating section (net loss approaches zero) and the design of the beveled end face to reduce the optical power density at the end face, a stable high-power output of 200mW-300mW at room temperature is achieved. Moreover, there is no mode hopping or parasitic oscillation across the entire power range. Compared with micro-ring external cavity lasers, which do not require the integration of an optical amplification module to achieve high-power output, this design completely solves the problem of extremely low optical power.

[0022] 3. Eliminating heterogeneous interface losses and noise, improving system robustness and integration: This invention features a monolithic fully integrated structure, with the grating and optical gain region integrated on the same substrate and in the same long waveguide structure. There are no external optical components or interfaces between the gain chip and external gratings / microrings, completely eliminating the light energy loss and multiple reflection noise caused by the difference in refractive index of different materials and end-face reflection in external cavity lasers. At the same time, it avoids wavelength instability and collimation coupling losses caused by mechanical vibration and temperature drift, and also eliminates reflection noise and alignment complexity introduced by external optical components. This significantly improves the system robustness, environmental adaptability, and integration density of the device, making it suitable for miniaturized and modular optoelectronic applications. Compared with microring external cavity lasers, which are temperature sensitive and have poor stability, this invention has stronger environmental adaptability.

[0023] 4. Ultra-narrow linewidth and high single-mode stability, no mode hopping and support for continuous linear wavelength adjustment: Utilizing a composite grating structure of "internal grating in the spine waveguide + top metal grating electrode," a dual-reflection combined filtering feedback mechanism is formed, greatly enhancing the grating's feedback efficiency and filtering selectivity, and significantly improving the Q value of the internal cavity resonator. Simultaneously, there is no longitudinal mode interference; the grating reflection wavelength becomes the sole determinant of the laser's operating wavelength, achieving an ultra-narrow linewidth output of 1kHz-5kHz, a side-mode rejection ratio >50dB, and excellent single-mode stability. Furthermore, continuous linear wavelength adjustment can be achieved through micro-current fine-tuning of the grating segment, without mode hopping during adjustment. This completely solves the core problem of unavoidable mode hopping in micro-ring external cavity lasers, making it particularly suitable for applications requiring continuous linear wavelength adjustment, while also addressing the issues of temperature sensitivity and difficulty in control.

[0024] 5. No need for integrated optical amplification module, significantly reducing cost and structural complexity: This invention achieves high power output of 200mW-300mW directly through micro-gain compensation and optimized gain region design. Unlike micro-ring external cavity lasers, it does not require integration with optical amplification modules to increase power, fundamentally avoiding the cost surge and increased structural and control complexity caused by integrated amplification. At the same time, this invention has a simple structure, mature technology, and excellent consistency, solving the problems of poor consistency and high cost of micro-ring external cavity lasers. It balances high performance and low cost, and has significant advantages for engineering mass production.

[0025] 6. Strong resistance to temperature drift and excellent environmental adaptability: Since it does not require real-time adjustment of the phase region current to match the longitudinal mode and grating wavelength (no longitudinal mode interference), and the grating segment can achieve fine dynamic compensation of wavelength through micro-current injection, the laser of this invention is not sensitive to temperature changes. It solves the control problem caused by the difference in temperature coefficients between the resonant cavity and the grating in traditional DBR lasers. It also solves the inherent defect of temperature sensitivity of micro-ring external cavity lasers. It can still maintain stable wavelength and linewidth performance over a wide temperature range and has excellent environmental adaptability.

[0026] 7. No damage to the gain medium, improved device reliability and lifespan: The absence of grating etching in the gain region avoids the physical damage to the adjacent quantum well layer caused by grating etching in traditional DFB lasers, ensuring the integrity of the gain medium and optical gain efficiency. This significantly improves the laser's operational reliability and lifespan, and reduces the device's failure rate. Compared to micro-ring external cavity lasers, which have a more complex structure and a higher failure rate, this device offers higher reliability.

[0027] 8. Flexible process adaptability, balancing high-end performance and mass production cost: This invention provides a variety of implementation and alternative solutions for grating structures, from the high-end solution of "three-layer internal grating + metal grating electrode" to the basic solution of "single-layer top surface metal grating". It can be flexibly adapted to the performance requirements and cost budget of different application scenarios, taking into account the ultra-narrow linewidth requirements of high-end precision optical applications as well as the cost control requirements of civilian and industrial applications, and has great potential for engineering mass production; at the same time, the process is mature and has good consistency, solving the problem of poor consistency and difficulty in large-scale mass production of micro-ring external cavity lasers. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the front cross-sectional structure of the present invention;

[0029] Figure 2 for Figure 1 Top view.

[0030] In the diagram: 1. Substrate layer; 2. Ridge waveguide;

[0031] 21. Composite structure grating segment; 211. Semiconductor Bragg grating; 2111. First λ / 4 phase shift; 212. Metal grating electrode; 2121. Second λ / 4 phase shift;

[0032] 22. Waveguide section in the gain region; 221. Quantum well layer; 222. Electrode in the gain region; 223. Angled end face;

[0033] 3. AR film. Detailed Implementation

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0035] Example 1

[0036] A high-performance intracavity laser based on a double-sided AR with a beveled angle in a micro-gain grating region, comprising a substrate layer 1 and a back ridge waveguide 2;

[0037] The back ridge waveguide 2 is disposed on the upper end face of the substrate layer 1. The back ridge waveguide 2 includes a composite structure grating segment 21 located on the left and a gain region waveguide segment 22 located on the right.

[0038] The composite structure grating segment 21 has i layers of semiconductor Bragg grating 211 etched inside, where i is a natural number. A first λ / 4 phase shift 2111 is provided at the left 1 / 3 of the grating of the semiconductor Bragg grating 211. The top of the composite structure grating segment 21 is covered with a metal grating electrode 212. A second λ / 4 phase shift 2121 is provided at the left 1 / 3 of the grating of the metal grating electrode 212, where λ = 1550 nm.

[0039] The gain region waveguide section 22 is provided with a quantum well layer 221 inside, and the top of the gain region waveguide section 22 is covered with a gain region electrode 222. The left end of the gain region waveguide section 22 is provided with a beveled end face 223. The angle φ of the beveled end face 223 is controlled between 6° and 26°, preferably between 8° and 15°.

[0040] The gain region waveguide segment 22 is a tapered optical waveguide with a left ridge width W1 greater than a right ridge width W2;

[0041] Both the beveled end face 223 and the right end face of the composite structure grating segment 21 are coated with an AR film 3; the reflectivity R of the AR film 3 is less than 1 x 10⁻⁶. -4 .

[0042] Preferably, the composite structure grating segment 21 has three layers of semiconductor Bragg gratings 211 etched inside.

[0043] The laser of the present invention is a monolithic integrated internal cavity structure with no external optical components. All functional segments are integrated on the same substrate layer 1, with no interface reflection loss and noise. It has a simple structure, convenient control and excellent consistency. Compared with micro-ring external cavity lasers, it effectively solves the problems of temperature sensitivity, difficult control and complex structure.

[0044] like Figure 1 As shown, the back ridge waveguide 2 of the present invention is divided into two main functional segments: the composite structure grating segment 21 on the right and the gain region waveguide segment 22 on the left. It is a dual-segment independent electrode structure with no phase adjustment region and no heterogeneous interface in the optical transmission path.

[0045] (I) Fabrication of composite structure grating segment 21

[0046] During the fabrication of the composite structure grating segment 21, a spine waveguide structure is first formed during the material epitaxial growth stage. This segment has no quantum well layer in its epitaxial layer and is only a semiconductor waveguide material.

[0047] Subsequently, periodic semiconductor Bragg gratings 211 are etched inside the spine waveguide using holographic exposure or electron beam lithography to form an internal grating, enabling precise wavelength mode selection. Next, a metal grating electrode 212 is fabricated on the top surface of the waveguide in the same region. This metal grating electrode 212 not only serves as an electrode to achieve precise injection of microcurrent, but its periodic metal structure itself also has strong light reflection characteristics.

[0048] The internal semiconductor Bragg grating 211 and the top metal grating electrode 212 form a composite feedback mechanism of dual reflection. Its reflectivity and filtering selectivity are much higher than those of a single-structure grating, which significantly improves the Q value of the internal cavity resonator, thereby achieving an extremely narrow spectral linewidth. At the same time, this structure supports continuous linear adjustment of wavelength and has no mode hopping phenomenon, which solves the core defects of micro-ring external cavity lasers, such as mode hopping that is difficult to avoid, temperature sensitivity, and difficulty in control.

[0049] Preferably, a composite structure of three semiconductor Bragg gratings 211 and one metal grating electrode 212 is adopted. This design maximizes the grating reflection feedback efficiency and filtering selectivity, achieving optimal narrow linewidth and single-mode stability, making it suitable for high-end precision optical applications. Although the metal grating electrode 212 does not have the periodic reflection enhancement effect of the grating, its overall feedback performance is still excellent due to the presence of three semiconductor Bragg gratings 211 inside, meeting the needs of most applications such as coherent optical communication and conventional lidar.

[0050] As the simplest implementation, the grating region can also operate using a composite structure of a zero-layer semiconductor Bragg grating 211 and a single-layer metal grating electrode 212. Although the linewidth performance of this solution is slightly inferior to the composite solution mentioned above, it has the simplest structure, the lowest manufacturing cost, and is suitable for cost-sensitive fiber optic sensing applications with moderate linewidth requirements.

[0051] Although the above solutions differ in performance and process, they all eliminate longitudinal mode interference caused by end-face reflection, remove the phase adjustment region, and realize the separation of the grating and gain region, fundamentally distinguishing them from traditional DBR, DFB, and external cavity (including micro-ring) lasers.

[0052] (II) Fabrication of waveguide segment 22 in the gain region

[0053] During the fabrication of waveguide section 22 in the gain region, the complete InP-based quantum well layer 221 is preserved to provide efficient optical gain. The epitaxial material and structure of the quantum well layer 221 adopt the GRIN-SCH technology scheme, and no grating etching is performed in this region to avoid light energy loss caused by grating scattering. At the same time, the physical damage to the quantum well layer 221 caused by the etching process is completely avoided, ensuring the integrity of the gain medium and the reliability of the device.

[0054] The gain region waveguide segment 22 and the composite structure grating segment 21 are an integrated spine waveguide 2 structure with no connecting interface. Light transmission between the two segments is free from interface loss and reflection noise. Moreover, this segment serves as the main gain region. In conjunction with the micro-gain compensation grating segment, it achieves a high power output of 200mW-300mW without the need for an additional integrated optical amplification module. This fundamentally controls the device cost and structural complexity. Compared with micro-ring external cavity lasers, it has significant advantages in power, cost, and structure, while also solving the problem of poor consistency.

[0055] (III) Integrated end-face processing

[0056] After the device is fabricated, AR film 3 coating is applied to both cleaved end faces of the chip to ensure the reflectivity of the end faces and completely eliminate the 30% high reflectivity of the traditional cleaved surface, thus avoiding longitudinal mode interference from the source.

[0057] Subsequently, using precision scribing or etching techniques, the left end face of the waveguide section 22 in the gain region is processed into an angled end face 223. The angle φ of the angled end face 223 is controlled between 6° and 26°, preferably between 8° and 15°. This end face is coated with an AR film 3, which serves as the main optical output surface of the laser. This angled design prevents the light emitted from the gain region from returning along the original waveguide path after reflection at the end face, thereby completely cutting off the FP resonant cavity formed by the two end faces. This ensures that the resonant feedback of the laser is completely dominated by the composite structure grating, and the grating reflection wavelength becomes the only determining factor of the laser's operating wavelength, while ensuring low-loss output of the main optical output surface.

[0058] (iv) Working principle of the device

[0059] The laser of this invention features dual-segment independent current injection control. During operation, the driving current is independently injected into the composite structure grating segment 21 and the gain region waveguide segment 22, respectively. The control method is simple and convenient, requiring no complex coordinated tuning. Compared with the difficulty of precise control of micro-ring external cavity lasers, this invention has significant advantages.

[0060] 1. Composite structure grating segment 21: A micro-current of 5-20mA is injected to make it work in a micro-gain state, which precisely cancels the light energy loss caused by band tail absorption and free carrier absorption in the grating region, making the net loss of the grating segment close to zero and ensuring low-loss transmission of optical signals in the cavity; at the same time, the refractive index of the grating region can be changed by fine-tuning the injected current, so as to achieve fine compensation and continuous linear adjustment of the output wavelength, to cope with temperature drift and manufacturing errors, and there is no mode jumping phenomenon during the adjustment process. Its stability is far superior to that of micro-ring external cavity lasers, effectively solving the problems of temperature sensitivity and frequent mode jumping.

[0061] 2. Waveguide section 22 in the gain region: Injecting a large current to achieve population inversion of the semiconductor material, serving as the sole gain source of the laser, generating optical gain and emitting optical signals outward.

[0062] Light is generated in the gain region and propagates towards the composite grating section. When passing through the composite grating region, only specific wavelengths of light that meet the Bragg reflection conditions are efficiently reflected back to the waveguide to form an internal cavity resonance, while other wavelengths are filtered out by the grating. Due to the absence of longitudinal mode interference caused by end-face reflection, the longitudinal mode of the laser is completely locked at the center of the reflection peak of the composite grating, without the need for an additional phase adjustment region for wavelength matching.

[0063] The resonant optical signal is transmitted multiple times within the cavity and continuously gains gain. Finally, it is stably output from the angled end face 223 of the waveguide section 22 in the gain region. This end face is the main optical output surface of the laser, realizing high-power, ultra-narrow linewidth laser output. It also eliminates spatial hole burning effect, interface loss, and reflection noise, and eliminates the need for an additional optical amplification module. This significantly reduces cost and structural complexity, while also providing good consistency and solving many inherent drawbacks of micro-ring external cavity lasers.

[0064] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-performance intracavity laser based on a double-sided AR with an angled bevel in a micro-gain grating region, characterized in that, include: A high-performance intracavity laser based on a micro-gain grating region with bilateral AR and bevel angles, comprising a substrate layer (1) and a back ridge waveguide (2). The back ridge waveguide (2) is disposed on the upper surface of the substrate layer (1). The back ridge waveguide (2) includes a composite structure grating segment (21) on the left and a gain region waveguide segment (22) on the right. The composite structure grating segment (21) has i layers of semiconductor Bragg grating (211) etched inside, where i is a natural number. A first λ / 4 phase shift (2111) is provided at the left 1 / 3 grating position of the semiconductor Bragg grating (211). The top of the composite structure grating segment (21) is covered with a metal grating electrode (212). A second λ / 4 phase shift (2121) is provided at the left 1 / 3 grating position of the metal grating electrode (212), where λ = 1550 nm. The gain region waveguide segment (22) is provided with a quantum well layer (221), the top of the gain region waveguide segment (22) is covered with a gain region electrode (222), and the left end of the gain region waveguide segment (22) is provided with a beveled end face (223). The right end face of the beveled end face (223) and the right end face of the composite structure grating segment (21) are both coated with an AR film (3).

2. The high-performance intracavity laser based on a micro-gain grating region with bilateral AR and bevel angle as described in claim 1, characterized in that: i=3。 3. The high-performance intracavity laser based on a micro-gain grating region with bilateral AR and bevel angle as described in claim 1, characterized in that: The reflectivity R of the AR film (3) is less than 1 x 10⁻⁶. -4 .

4. The high-performance intracavity laser based on a micro-gain grating region with bilateral AR and bevel angle as described in claim 1, characterized in that: The angle φ of the beveled end face (223) is controlled between 6° and 26°.

5. The high-performance intracavity laser based on a micro-gain grating region with bilateral AR and bevel angle as described in claim 4, characterized in that: The angle φ of the beveled end face (223) is controlled between 8° and 15°.

6. The high-performance intracavity laser based on a micro-gain grating region with bilateral AR and bevel angle as described in claim 1, characterized in that: The composite structure grating segment (21) has three layers of semiconductor Bragg gratings (211) etched inside.

7. The high-performance intracavity laser based on a double-sided AR with an angled bevel in a micro-gain grating region according to any one of claims 1-6, characterized in that: The gain region waveguide segment (22) is a tapered optical waveguide with a left ridge width W1 greater than a right ridge width W2.

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