Metal grating laser based on two different grating constants and with phase interval of lambda / 2

Abstract

The invention relates to the technical field of lasers, in particular to a metal grating laser based on two different grating constants and with a phase interval of lambda / 2. The optical waveguide is arranged in the center of the top of the gain chip; the metal BRAGG reflecting gratings are arranged at the top of the optical waveguide, the metal BRAGG reflecting gratings comprise the first metal BRAGG reflecting grating and the second metal BRAGG reflecting grating, and the grating constants of the first metal BRAGG reflecting grating and the second metal BRAGG reflecting grating are similar but different. The two metal gratings with similar grating constants and phase difference lambda / 2 are adopted to replace a traditional interlayer semiconductor grating, the inner cavity structure is optimized, the grating reflection efficiency is effectively improved, secondary epitaxy is omitted, the process is simplified, the cost is reduced, the SMSR performance of laser light beams is remarkably improved, the line width is compressed, and the light beam quality is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lasers, in particular to a metal grating laser based on two different grating constants and a phase interval of λ / 2. Background Art

[0002] Traditional DFB lasers face many challenges in practical applications. In terms of manufacturing process, the process is complex and requires high-cost secondary epitaxial operation. At the same time, a deeply buried sandwich structure semiconductor grating must be prepared. Secondary epitaxy not only increases the process steps and increases the difficulty of production, but also places extremely high demands on the production environment and equipment, thereby significantly increasing production costs. The preparation of deeply buried sandwich structure semiconductor gratings requires precise thickness, composition and interface quality of each layer of material. Any slight deviation will affect the grating performance, resulting in a low product yield.

[0003] In terms of performance, traditional DFB lasers have insufficient grating reflectivity and limited reflection filtering efficiency. In fields with stringent requirements on light source performance, such as quantum key distribution, which requires a precise light source at the single-photon level, and coherent optical communication, which requires a light source with high stability and narrow linewidth, traditional DFB lasers are difficult to meet these application requirements. Due to limited performance, additional equipment and technology are often required to compensate in order to meet the usage standards, which not only increases costs but also limits its application in a wider range of fields.

[0004] In addition, the inner cavity structure of traditional DFB lasers also has certain limitations. The beam quality of the inner cavity structure is affected. For example, its M2 factor is usually large, and the coupling efficiency in the photonic integrated system is low, which hinders the efficient transmission and integrated application of optical signals. Summary of the Invention

[0005] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a metal grating laser based on two different grating constants and a phase interval of λ / 2.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: based on two metal grating lasers with different grating constants and a phase interval of λ / 2, including: Gain chip; An optical waveguide is arranged centered on top of the gain chip; The metal BRAGG reflection grating is arranged on the top of the optical waveguide, and the metal BRAGG reflection grating includes a metal BRAGG reflection grating 1 and a metal BRAGG reflection grating 2. The grating constants of the metal BRAGG reflection grating 1 and the metal BRAGG reflection grating 2 are similar but different, and a phase difference is set between the metal BRAGG reflection grating 1 and the metal BRAGG reflection grating 2.

[0007] Preferably, the grating period of the metal BRAGG reflection grating 1 is 224.5±0.3 nm, and the grating period of the metal BRAGG reflection grating 2 is 225.5±0.3 nm.

[0008] Preferably, the length of the phase difference is λ / 2.

[0009] Preferably, the gain chip adopts an InP / InGaAsP quantum well structure.

[0010] Preferably, the lasing wavelength range of the gain chip is 1530-1610 nm.

[0011] Preferably, one side of the gain chip is set as a reflector end face, and the reflector end face is coated with a λ / 2 high reflective film, the λ / 2 high reflective film adopts a SiO2 / TiO2 multilayer structure, and the reflectivity of the λ / 2 high reflective film is greater than 99.9%.

[0012] Preferably, the side of the gain chip away from the reflector end face is an anti-reflection end face, and the anti-reflection end face is coated with a λ / 4 anti-reflection film. The λ / 4 anti-reflection film adopts a SiO2 / TiO2 multilayer structure, and the reflectivity of the λ / 4 anti-reflection film is less than 0.03%.

[0013] Preferably, the thickness of the metal BRAGG reflection grating is 200±5 nm, and the duty cycle of the metal BRAGG reflection grating is 50±1%.

[0014] Preferably, the metal BRAGG reflection grating adopts a Cr / Au multilayer structure, and the thicknesses of the Cr / Au layers are 50 nm and 150 nm respectively.

[0015] Preferably, the optical waveguide has a ridge structure with a ridge width of 3-5 μm and a ridge height of 2-4 μm.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention replaces the traditional sandwich semiconductor grating with two metal gratings with similar grating constants and a phase difference of λ / 2, optimizing the inner cavity structure. This design effectively improves the grating reflection efficiency, eliminates the need for secondary epitaxy, simplifies the process, reduces costs, significantly enhances the side mode suppression ratio (SMSR) performance of the laser beam, compresses the linewidth, improves the beam quality, and enhances the coupling efficiency in the photonic integrated system. The present invention focuses on optimizing the inner cavity structure of the DFB laser. Traditional inner cavity structures have problems with beam quality and coupling efficiency. The present invention improves the light field distribution in the inner cavity by adopting a top metal grating and a unique dual-grating design. The high reflectivity and precise grating structure of the top metal grating make the reflection and propagation of light in the cavity more orderly, reducing light scattering and loss, thereby improving beam quality and reducing the M2 factor. At the same time, the optimized inner cavity structure has a better match with the external optical system, improving the coupling efficiency in the photonic integrated system, and is more conducive to the transmission and integrated application of optical signals. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 This is a schematic diagram of the main structure of the present invention; Figure 2 It is a schematic diagram of the top view of the structure of the present invention; Figure 3 It is a side structural schematic diagram of the present invention.

[0017] In the figure: 1. Gain chip; 2. Optical waveguide; 3. Metal BRAGG reflection grating; 301. Metal BRAGG reflection grating 1; 302. Metal BRAGG reflection grating 2; 4. Phase difference; 5. λ / 2 high reflection film; 6. λ / 4 anti-reflection film. DETAILED DESCRIPTION The following description is intended to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments described below are merely examples, and those skilled in the art may conceive of other obvious variations.

[0018] like Figure 1-Figure 3 As shown, the present application provides a metal grating laser based on two different grating constants and a phase interval of λ / 2, including: a gain chip 1; an optical waveguide 2, arranged in the center of the top of the gain chip 1; a metal BRAGG reflection grating 3, arranged on the top of the optical waveguide 2, and the metal BRAGG reflection grating 3 includes a metal BRAGG reflection grating 1 301 and a metal BRAGG reflection grating 2 302, the grating constants of the metal BRAGG reflection grating 1 301 and the metal BRAGG reflection grating 2 302 are similar but different, and a phase difference 4 is set between the metal BRAGG reflection grating 1 301 and the metal BRAGG reflection grating 2 302.

[0019] Specifically, such as Figure 1 As shown, the grating period of the metal BRAGG reflection grating 301 is 224.5±0.3 nm, and the grating period of the metal BRAGG reflection grating 302 is 225.5±0.3 nm; the length of the phase difference 4 is λ / 2.

[0020] The parameters of the metal Bragg gratings were meticulously designed. The grating periods of the two metal gratings were set to Λ1 = 224.5 ± 0.3 nm and Λ2 = 225.5 ± 0.3 nm, respectively. This similar yet distinct grating period design, combined with a λ / 2 phase difference between the two gratings, was key to achieving high performance.

[0021] Specifically, such as Figure 1 As shown, the gain chip 1 adopts an InP / InGaAsP quantum well structure; the lasing wavelength range of the gain chip 1 is 1530-1610nm.

[0022] The InP / InGaAsP quantum well structure is selected as the basic architecture of the gain chip. This structure has good laser emission characteristics in the wavelength range of 1530-1610nm and can meet the needs of various application scenarios. At 25°C, its threshold current is less than 28mA, which means that laser emission can be achieved with lower energy consumption. The slope efficiency reaches 0.85W / A, indicating that under a certain current drive, electrical energy can be efficiently converted into light energy.

[0023] Specifically, such as Figure 1 As shown, one side of the gain chip 1 is set as a reflector end face, and the reflector end face is coated with a λ / 2 high-reflection film 5. The λ / 2 high-reflection film 5 adopts a SiO2 / TiO2 multilayer structure, and the reflectivity of the λ / 2 high-reflection film 5 is greater than 99.9%; the side of the gain chip 1 away from the reflector end face is an anti-reflection end face, and the anti-reflection end face is coated with a λ / 4 anti-reflection film 6. The λ / 4 anti-reflection film 6 adopts a SiO2 / TiO2 multilayer structure, and the reflectivity of the λ / 4 anti-reflection film 6 is less than 0.03%.

[0024] The λ / 2 high-reflection film 5 can effectively reduce the loss of light at the reflective end face and enhance the feedback of light in the cavity. The λ / 4 anti-reflection film 6 can maximize the output efficiency of the laser. Specifically, such as Figure 1 As shown, the thickness of the metal BRAGG reflection grating 3 is 200±5nm, and the duty cycle of the metal BRAGG reflection grating 3 is 50±1%; the metal BRAGG reflection grating 3 adopts a Cr / Au multilayer structure, and the thicknesses of the Cr / Au layers are 50nm and 150nm respectively.

[0025] The duty cycle is 50±1%, which ensures the uniformity and stability of the grating structure. The Cr layer can enhance the adhesion between the metal and the substrate, and the Au layer has good conductivity and optical reflection properties.

[0026] Specifically, such as Figure 1 As shown, the optical waveguide 2 is a ridge structure with a ridge width of 3-5 μm and a ridge height of 2-4 μm.

[0027] Theoretical basis: According to coupled-mode theory, for a conventional uniform grating DFB laser, the coupling coefficient is κ, and the light field distribution can be expressed by A(z), and satisfies the following coupled-mode equation: , where β is the propagation constant. In this equation, Describes the phase change of the light field during propagation. It reflects the coupling effect of the grating on the light field, and loss\terms represents the loss of light during the propagation process.

[0028] For the two metal grating DFB lasers with similar grating constants and a phase difference of λ / 2 in the present invention, the presence of phase shift profoundly affects the light field distribution. Assuming that the phase shift position is at z = 0, the light field distribution before and after the phase shift can be represented by A1(z) and A2(z), respectively, and the boundary conditions are satisfied: , which means that the light field produces a π / 2 phase jump at the phase shift. This phase jump will cause the redistribution of the light field, change the propagation characteristics of light in the laser cavity, and thus affect the mode selection characteristics of the laser. During the laser generation process, different modes of light will compete with each other, and this phase jump enables the main mode to more effectively suppress the side mode, thereby improving the side mode suppression ratio (SMSR) performance.

[0029] The difference in grating constants and the setting of phase difference λ / 2 change the light field distribution, causing subtle changes in the effective refractive index of light during propagation. According to the Bragg condition of the grating, for traditional uniform grating DFB lasers, its Bragg wavelength is satisfy: ,in Where λ is the effective refractive index and Λ is the grating period. In this invention, the actual Bragg wavelength slightly changes due to the altered light field distribution. This also affects the gains of the main and side modes, increasing the main mode gain while suppressing the side mode gain, further enhancing the SMSR. Furthermore, this structural change compresses the laser linewidth, improving laser purity and stability.

[0030] Practical case: In the actual preparation process, the electron beam lithography (EBG) technology is first used to draw a precise grating pattern on the gain chip of the InP / InGaAsP quantum well structure. The high precision of electron beam lithography ensures the accuracy of the grating pattern and provides a good foundation for the subsequent etching process. Then, the inductively coupled plasma (ICP) etching technology is used to etch the drawn pattern into a grating structure with a certain depth, and the grating depth is precisely controlled at 120±5nm. Then, the Cr / Au layer is deposited by magnetron sputtering to form a metal Bragg grating with a thickness of 200±5nm (Cr / Au=50nm / 150nm). During the deposition process, the process parameters are strictly controlled and the white light interferometer is used to detect to ensure that the surface flatness is less than 0.08nmRMS, thereby obtaining high-quality The metal grating surface with a certain amount of grating is precisely etched. At the same time, precise lithography and etching processes are used to achieve precise control of the two grating constants and accurate setting of the phase difference λ / 2 between the two gratings. After the preparation of the laser is completed, the linewidth and SMSR of the laser are measured by self-heterodyne interferometry, and its beam quality and coupling efficiency in the photonic integrated system are tested. The results show that compared with the traditional DFB laser, the SMSR of the DFB laser with two metal gratings with similar grating constants and a phase difference of λ / 2 has been significantly improved, and the measured SMSR value has reached more than 50dB; the measured value of the 3dB linewidth is 30Hz, which is much better than the 125kHz of the traditional DFB laser; the M2 factor is less than 1.2, and the coupling efficiency reaches more than 90%, which fully verifies the excellent improvement effect of this structure on laser performance.

[0031] Self-heterodyne interferometry was used for linewidth measurement, and the local oscillator linewidth was less than 500 Hz. Under this measurement method, the measured 3dB linewidth was only 30 Hz, while the 3dB linewidth of a traditional DFB laser is typically 125 kHz. The mode purity was further verified by a Lorenzian fitting broadening factor of 1.1, indicating that the laser mode output by the laser of the present invention is more single and pure, and has significant advantages in applications requiring high-resolution spectroscopy.

[0032] The laser was tested in a wide temperature range of -40°C to 85°C. After compensation by the temperature compensation circuit, the wavelength drift was less than 0.03pm / °C, its temperature tuning coefficient was 0.07pm / °C, its current tuning coefficient was 0.04pm / mA, and the tuning range was 1530-1545nm. This means that under different ambient temperature and driving current conditions, the laser can maintain stable wavelength output, providing reliable protection for applications such as optical communications that have extremely high requirements for wavelength stability.

[0033] After actual testing, the SMSR value of the laser of the present invention reached over 50dB, while the traditional DFB laser is generally around 30-35dB. This significant improvement shows that the laser of the present invention can more effectively suppress side modes, improve the output quality of the main mode, reduce signal interference during signal transmission, and improve communication quality.

[0034] The M2 factor was tested using a specialized beam quality analyzer, and the results showed that the M2 factor of the laser of the present invention was less than 1.2, which is a significant improvement compared to traditional intracavity DFB lasers. In the coupling efficiency test of the photonic integrated system, the coupling efficiency reached more than 90%, effectively improving the transmission efficiency of the optical signal.

[0035] The present invention: Abandoning the traditional sandwich-type semiconductor grating and adopting a top metal grating greatly simplifies the manufacturing process and reduces production costs. In particular, the metal grating is divided into two parts with similar but different grating constants, and the two gratings are phase-separated by λ / 2. This design can effectively improve the side mode suppression ratio (SMSR) of the laser beam, compress the laser linewidth, and provide a guarantee for the stable operation of the laser in high-performance application scenarios.

[0036] The present invention focuses on optimizing the inner cavity structure of the DFB laser. Traditional inner cavity structures have problems with beam quality and coupling efficiency. The present invention improves the light field distribution in the inner cavity by adopting a top metal grating and a unique dual-grating design. The high reflectivity and precise grating structure of the top metal grating make the reflection and propagation of light in the cavity more orderly, reducing light scattering and loss, thereby improving beam quality and reducing the M2 factor. At the same time, the optimized inner cavity structure has a better match with the external optical system, improving the coupling efficiency in the photonic integrated system, and is more conducive to the transmission and integrated application of optical signals.

[0037] The application of top metal grating brings about performance optimization in many aspects. The good optical reflection properties of metal materials greatly improve the reflection efficiency compared with traditional semiconductor gratings, which enhances the optical feedback capability of the laser, effectively narrows the laser linewidth, and makes the laser output purer. At the same time, the introduction of metal grating reduces the threshold current of the laser, improves energy utilization efficiency, and reduces power consumption.

[0038] Compared with traditional DFB lasers, the present invention has significant cost and efficiency advantages. Traditional DFB lasers require high-cost secondary epitaxy and the preparation of deeply buried sandwich-structured semiconductor gratings, which not only leads to complex manufacturing processes, but also long production cycles and high costs. The present invention uses a top metal grating to replace the traditional sandwich-type semiconductor grating, eliminating the need for secondary epitaxy and greatly simplifying the process flow. The simplified process reduces the steps in the manufacturing process and the dependence on high-precision equipment, reducing manufacturing costs while improving production efficiency and product yield. In addition, the reflection and filtering efficiency of the metal grating is about 30% higher than that of the semiconductor grating, which significantly improves the performance of the laser and can better meet the needs of fields with high requirements for light source performance, such as quantum communication, coherent optical communication, and photonic integrated chips, and has broader application prospects.

[0039] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions only describe the principles of the present invention. Various changes and improvements are possible without departing from the spirit and scope of the present invention, and such changes and improvements fall within the scope of the invention as claimed.

Claims

1. Based on two metal grating lasers with different grating constants and a phase interval of λ / 2, characterized by ,include: Gain chip (1); An optical waveguide (2) is arranged in the center of the top of the gain chip (1); A metal BRAGG reflection grating (3) is arranged on the top of the optical waveguide (2), and the metal BRAGG reflection grating (3) includes a metal BRAGG reflection grating 1 (301) and a metal BRAGG reflection grating 2 (302), the grating constants of the metal BRAGG reflection grating 1 (301) and the metal BRAGG reflection grating 2 (302) are similar but different, and a phase difference (4) is set between the metal BRAGG reflection grating 1 (301) and the metal BRAGG reflection grating 2 (302).

2. The metal grating laser based on two different grating constants and a phase interval of λ / 2 according to claim 1, characterized in that: The grating period of the metal BRAGG reflection grating 1 (301) is 224.5±0.3 nm, and the grating period of the metal BRAGG reflection grating 2 (302) is 225.5±0.3 nm.

3. The metal grating laser based on two different grating constants and a phase interval of λ / 2 according to claim 1, characterized in that: The length of the phase difference (4) is λ / 2.

4. The metal grating laser based on two different grating constants and a phase interval of λ / 2 according to claim 1, characterized in that: The gain chip (1) adopts an InP / InGaAsP quantum well structure.

5. The metal grating laser based on two different grating constants and a phase interval of λ / 2 according to claim 4, characterized in that: The lasing wavelength range of the gain chip (1) is 1530-1610 nm.

6. The metal grating laser based on two different grating constants and a phase interval of λ / 2 according to claim 5, characterized in that: One side of the gain chip (1) is set as a reflector end face, and the reflector end face is plated with a λ / 2 high reflective film (5), the λ / 2 high reflective film (5) adopts a SiO2 / TiO2 multilayer structure, and the reflectivity of the λ / 2 high reflective film (5) is greater than 99.9%.

7. The metal grating laser based on two different grating constants and a phase interval of λ / 2 according to claim 6, characterized in that: The side of the gain chip (1) away from the end face of the reflector is an anti-reflection end face, and the anti-reflection end face is plated with a λ / 4 anti-reflection film (6), the λ / 4 anti-reflection film (6) adopts a SiO2 / TiO2 multilayer structure, and the reflectivity of the λ / 4 anti-reflection film (6) is less than 0.03%.

8. The metal grating laser based on two different grating constants and a phase interval of λ / 2 according to claim 1, characterized in that: The thickness of the metal BRAGG reflection grating (3) is 200±5 nm, and the duty cycle of the metal BRAGG reflection grating (3) is 50±1%.

9. The metal grating laser based on two different grating constants and a phase interval of λ / 2 according to claim 8, characterized in that: The metal BRAGG reflection grating (3) adopts a Cr / Au multilayer structure, and the thicknesses of the Cr / Au layers are 50 nm and 150 nm respectively.

10. The metal grating laser based on two different grating constants and a phase interval of λ / 2 according to claim 1, characterized in that: The optical waveguide (2) is a ridge-shaped structure with a ridge width of 3-5 μm and a ridge height of 2-4 μm.

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