High-power narrow-linewidth on-chip laser based on lithium niobate platform and preparation method of high-power narrow-linewidth on-chip laser

Abstract

The invention discloses a high-power narrow-linewidth on-chip laser based on a lithium niobate platform and a preparation method of the high-power narrow-linewidth on-chip laser, and the high-power narrow-linewidth on-chip laser is characterized in that an on-chip laser structure formed by mixing and integrating a wide waveguide Fabry-Perot semiconductor laser and a thin-film lithium niobate external cavity chip is adopted, so that high-power and narrow-linewidth output is realized; the wide waveguide Fabry-Perot semiconductor laser is used for providing multi-mode laser; the lithium niobate external cavity chip adopts a tapered waveguide suppression high-order transverse mode, and through combination of an up-down speech channel type echo wall mode microcavity and an SLR, the preparation method comprises the steps of preparation of a lithium niobate waveguide structure, preparation of the thin-film lithium niobate external cavity chip, preparation of an on-chip laser and the like. Compared with the prior art, the on-chip laser has the advantages of being simple and compact in structure, low in cost and high in stability, high-power, narrow-linewidth and continuous-wavelength-adjustable and stable laser output is achieved, and the problems that an existing on-chip laser is low in output and wide in linewidth are effectively solved.

Description

Technical Field

[0001] This invention relates to the field of micro-nano integrated photonic devices and their fabrication technology, and in particular to a high-power narrow-linewidth on-chip laser based on a lithium niobate platform and its fabrication method. Background Technology

[0002] In recent years, photonic integrated chips have gradually become an important development direction for next-generation chip technology, with enormous application potential in fields such as optical communication, optical storage, optical computing, and optical sensing. Since the concept of photonic integrated chips was first proposed by Bell Labs in 1969, it has developed rapidly in the 21st century. Photonic integrated chips use light as the information carrier, offering advantages such as high bandwidth, high speed, large capacity, and low power consumption. Simultaneously, they avoid the frequent photoelectric conversions found in fiber optic communication and do not require high precision in processing. Lithium niobate crystals, due to their high nonlinear optical coefficient and strong electro-optic effect, have become an ideal substrate material for photonic integration. In the field of photonic integrated chips, lithium niobate is also known as "optical silicon." On-chip lasers are one of the key components in integrated photonics. Compared to traditional lasers, on-chip lasers have higher integration density, lower threshold voltage, and narrower linewidth.

[0003] In summary, existing on-chip laser structures generally suffer from low output power, wide linewidth, low efficiency, and high cost. Therefore, the development of lasers with higher output power and conversion efficiency has become a key research focus. Overcoming the problems of low output power and wide linewidth in existing on-chip lasers is crucial. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a high-power, narrow-linewidth on-chip laser based on a lithium niobate platform and its fabrication method. This invention utilizes a wide-waveguide Fabry-Perot semiconductor laser to provide multimode laser output, while the lithium niobate external cavity chip employs a tapered waveguide to suppress higher-order transverse modes. Linearity is narrowed through self-injection locking, thus fabricating a high-power, narrow-linewidth laser with an on-chip laser structure, achieving both high power and narrow linewidth output. This invention, through the integrated design of a thin-film lithium niobate external cavity chip and a multimode Fabry-Perot semiconductor laser chip, simultaneously achieves a high-output, narrow-linewidth on-chip laser, effectively solving the problems of low output and wide linewidth in existing on-chip lasers. The on-chip laser fabricated by this method is characterized by low cost, simple fabrication process, and promising application prospects.

[0005] The specific technical solution for realizing the present invention is: a high-power narrow-linewidth on-chip laser based on a lithium niobate platform, characterized by an on-chip laser structure that integrates a wide-waveguide Fabry-Perot semiconductor laser with a thin-film lithium niobate external cavity chip to achieve high-power and narrow-linewidth output. The wide-waveguide Fabry-Perot semiconductor laser provides multimode laser; the lithium niobate external cavity chip uses a tapered waveguide to suppress higher-order transverse modes, through a combination of a whispering-gallery microcavity and an SLR.

[0006] The output wavelength of the on-chip laser is locked at around 1551.45 nm, the output power is 7.62 mW, and the linewidth is narrowed to 717 kHz.

[0007] The on-chip laser outputs a wavelength locked around 1551.45 nm, with an output power of up to 7.62 mW and a linewidth narrowed to 717 kHz. Furthermore, by adjusting the microelectrodes on the microring, a wavelength tuning range of approximately 74 pm was achieved at 1551.2 nm, with a voltage range of -60 V to 60 V.

[0008] A method for fabricating a high-power, narrow-linewidth on-chip laser based on a lithium niobate platform, characterized in that the fabrication of the on-chip laser specifically includes the following steps: Step 1: Prepare lithium niobate thin film material and perform chromium plating. The lithium niobate thin film material consists of three layers: the first layer is a lithium niobate thin film with a thickness of 100nm-5μm; the second layer is a silicon dioxide thin film with a thickness of 1μm-10μm; the third layer is a silicon substrate layer with a thickness of 100μm-1mm; and a chromium film layer with a thickness of 50nm-900nm is deposited on the surface of the lithium niobate thin film material.

[0009] Step 2: Femtosecond laser direct writing combined with chemical mechanical polishing The thin-film lithium niobate material with a chromium-plated surface is fixed on a three-dimensional computer-programmable displacement platform. A femtosecond laser is focused onto the chromium film layer on the surface of the thin-film material through a microscope objective. The displacement platform is driven by computer programming, and the femtosecond laser direct writing process is started simultaneously. The chromium film layer on the surface of the lithium niobate thin film material is removed, and the required planar mask pattern is directly written. The lithium niobate thin film material after femtosecond laser direct writing is placed in a mechanical polishing machine, and its surface is chemically and mechanically polished using a chemical polishing solution. The chromium film on the surface of the lithium niobate thin film material that was not removed by the femtosecond laser direct writing protects the lithium niobate thin film from chemical mechanical polishing etching. The thin-film lithium niobate material in other areas is polished and etched. Then, the surface chromium mask is removed using a chromium etchant, and finally the desired lithium niobate waveguide structure is obtained.

[0010] Step 3: End face polishing The lithium niobate waveguide structure obtained in step 2 was fixed onto a quartz glass fixture using paraffin wax, exposing the end face to be polished. The fixture was then fixed onto a polishing machine, and a cerium oxide suspension polishing solution was used. The polishing pressure was controlled at 0.1 MPa-1.2 MPa, the speed at 50 r / s-100 r / s, and the time at 10 min-100 min to ensure that the end face achieved nanoscale flatness and smoothness. The end face quality was inspected using an optical microscope, and the polished lithium niobate waveguide structure was then cleaned sequentially with ultrapure water and anhydrous ethanol to remove residual polishing solution and impurities from the surface, thus obtaining a thin-film lithium niobate external cavity chip.

[0011] Step 4: Hybrid integration of multimode Fabry-Perot semiconductor laser chip and thin-film lithium niobate external cavity chip A semiconductor laser chip and a thin-film lithium niobate external cavity chip are spliced ​​together using a six-axis coupling platform to produce an on-chip laser. During the splicing process, the two chips are ensured to have the same tilt angle and parallel end faces to ensure that the laser can be seamlessly spliced ​​with the optical chip.

[0012] Compared with the prior art, the present invention has the following beneficial technical effects and significant technical progress: 1) By combining a high-Q microring resonator with a Sagnac loop, high-power, narrow-linewidth and continuously tunable on-chip single-mode laser output is achieved simultaneously compared to previous lasers, with a wavelength tuning range of 74 pm.

[0013] 2) By using self-injection locking technology, a narrow linewidth and stable frequency output laser output can be achieved. Compared with other solutions, it has the advantages of simple structure, compactness, low cost and high stability. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the preparation process of the present invention; Figure 2 This is a three-dimensional structural schematic diagram of the thin-film lithium niobate external cavity chip prepared in Example 1. Detailed Implementation

[0015] The present invention will be further described below with reference to embodiments and accompanying drawings, but this should not be construed as limiting the scope of protection of the present invention.

[0016] Example 1 See Figure 1 The present invention relates to a method for fabricating a high-power, narrow-linewidth on-chip laser based on a lithium niobate platform, which specifically includes the following steps: Step 1: Prepare lithium niobate thin film material and perform chromium plating. See Figure 1a. Lithium niobate thin film material, consisting of three layers: the first layer is lithium niobate thin film 1, with a thickness of 500 nm; the second layer is silicon dioxide thin film layer 2, with a thickness of 2.8 μm; the third layer is silicon substrate layer 3, with a thickness of 500 μm. See Figure 1 b. A chromium film layer 4 with a thickness of 200 nm is deposited on the surface of the lithium niobate thin film material.

[0017] Step 2: Femtosecond laser direct writing combined with chemical mechanical polishing See Figure 1 c. A lithium niobate thin film with a chromium-plated surface is fixed on a three-dimensional computer-programmable displacement platform. A femtosecond laser 6 is focused onto the chromium film layer 4 on the surface of the thin film through a microscope objective 5. The displacement platform is driven by computer programming, and the femtosecond laser direct writing process is started simultaneously. The chromium film layer 4 on the surface of the lithium niobate thin film is removed, and the required planar mask pattern 7 is directly written. The lithium niobate thin film after femtosecond laser direct writing is placed in a mechanical polishing machine, and its surface is chemically mechanically polished using a chemical polishing solution. The chromium film on the surface of the lithium niobate thin film that was not removed by the femtosecond laser direct writing protects the lithium niobate thin film from being etched by chemical mechanical polishing. The lithium niobate thin film in other areas is polished and etched. Then, a chromium etching solution is used to remove the surface chromium mask, and finally the desired lithium niobate waveguide structure 8 is obtained.

[0018] Step 3: End face polishing See Figure 1 d. The lithium niobate waveguide structure obtained in step 2 is fixed onto a quartz glass fixture using paraffin wax, exposing the end face to be polished. The fixture is then fixed onto a polishing machine, and a cerium oxide suspension polishing slurry is used. The polishing pressure is controlled at 0.2 MPa, the speed at 50 r / s, and the time at 30 min to ensure that the end face achieves nanometer-level flatness and smoothness. The polished lithium niobate waveguide structure is then sequentially cleaned with ultrapure water and anhydrous ethanol to remove residual polishing slurry and impurities from the surface, thus obtaining a thin-film lithium niobate external cavity chip.

[0019] Step 4: Hybrid integration of multimode Fabry-Perot semiconductor laser chip and thin-film lithium niobate external cavity chip A semiconductor laser chip and a thin-film lithium niobate external cavity chip are spliced ​​together using a six-axis coupling platform to produce an on-chip laser. During the splicing process, the two chips are ensured to have the same tilt angle and parallel end faces to ensure that the laser can be seamlessly spliced ​​with the optical chip.

[0020] See Figure 2In this embodiment, the thin-film lithium niobate external cavity chip has a substrate 3 as the bottom layer, a silicon dioxide layer 2 as the second layer, and a thin-film lithium niobate 3 on top of the silicon dioxide layer 2, thus forming the desired lithium niobate waveguide structure 8. The specific structure of this chip is as follows: the waveguide is made of a lithium niobate thin film and is located at the bottom of the silicon dioxide layer 2. The silicon dioxide layer 2 is bonded to the lithium niobate substrate 3. The waveguide shape consists of a micro-ring waveguide, a tapered waveguide, and a sagnac. The tapered waveguide is 4 mm long, and the micro-rings are composed of quarter-circle Bezier curves connected by straight waveguides, with a total circumference of approximately 1.7 mm. The coupling region is formed by the parallel portion between the micro-rings and the straight waveguides, with a coupling length of 10 micrometers and a gap of 3.2 micrometers. The bending radius of the sagnac ring is 250 micrometers.

[0021] The preparation methods for Examples 2, 3, and 4 are the same as those for Example 1, and their specific parameters are detailed in Table 1 below: Table 1 Preparation parameters for each embodiment

[0022] The above embodiments demonstrate that the present invention, based on femtosecond laser processing combined with chemical mechanical polishing (CMP), can effectively fabricate a self-injection-locked lithium niobate external cavity. The microcavity coupling spacing and structural parameters of the waveguide are controlled by femtosecond laser direct writing. This invention allows for free selection of the structural parameters of the lithium niobate self-injection-locked external cavity chip, the thickness of the lithium niobate thin film, and the thickness of the silicon dioxide layer. This facilitates full utilization of the inherent properties of the lithium niobate thin film material, solves the problem of low output power in on-chip lasers, and broadens the application range.

[0023] The above description is merely a further explanation of the present invention and is not intended to limit this patent. All equivalent implementations of the present invention should be included within the scope of the claims of this patent. The protection scope of the present invention is not limited to the above embodiments. Variations and advantages that can be conceived by those skilled in the art without departing from the spirit and scope of the inventive concept are included in the present invention and are protected by the appended claims.

Claims

1. A high-power, narrow-linewidth on-chip laser based on a lithium niobate platform, characterized in that, An on-chip laser structure integrating a wide-waveguide Fabry-Perot semiconductor laser with a thin-film lithium niobate external cavity chip is adopted to achieve high power and narrow linewidth output. The wide-waveguide Fabry-Perot semiconductor laser provides multimode laser; the lithium niobate external cavity chip uses a tapered waveguide to suppress higher-order transverse modes, and combines a whispering-gallery microcavity with an SLR.

2. The high-power, narrow-linewidth on-chip laser based on a lithium niobate platform according to claim 1, characterized in that, The output wavelength of the on-chip laser is locked at around 1551.45 nm, the output power is 7.62 mW, and the linewidth is narrowed to 717 kHz.

3. The high-power, narrow-linewidth on-chip laser based on a lithium niobate platform according to claim 1 or claim 2, characterized in that, The on-chip laser achieves a wavelength tuning range of approximately 74 pm at 1551.2 nm by adjusting the microelectrodes on the microring, with a voltage range of -60 V to 60 V.

4. A method for fabricating a high-power, narrow-linewidth on-chip laser based on a lithium niobate platform as described in claim 1, characterized in that, The fabrication of the on-chip laser specifically includes the following steps: Step 1: Preparation of lithium niobate thin film material Step 1-1: A three-layer stacked thin film structure is adopted, with the upper layer being a lithium niobate film with a thickness of 100nm-5μm; the middle layer being a silicon dioxide film with a thickness of 1μm-10μm; and the bottom layer being a silicon substrate with a thickness of 100μm-1mm. Steps 1-2: A chromium film layer with a thickness of 50nm-900nm is deposited on the surface of the lithium niobate thin film to obtain a lithium niobate thin film material with a chromium-plated surface. Step 2: Fabrication of Lithium Niobate Waveguide Structure Step 2-1: Fix the lithium niobate thin film material with chromium-plated surface on a computer-programmed three-dimensional displacement platform. Focus a femtosecond laser onto the chromium film layer on the surface of the thin film material through a microscope objective. Drive the displacement platform to move using computer programming, and simultaneously start the femtosecond laser direct writing to remove the chromium film layer on the surface of the lithium niobate thin film material and directly write out the required planar mask pattern. Step 2-2: Place the lithium niobate thin film material after femtosecond laser direct writing in a mechanical polishing machine and use a chemical polishing solution to polish and etch its surface; Steps 2-3: Use chromium etching solution to remove the surface chromium mask to obtain the lithium niobate waveguide structure; Step 3: Fabrication of thin-film lithium niobate external cavity chip Step 3-1: Fix the prepared lithium niobate waveguide structure onto a quartz glass fixture using paraffin wax, exposing the end face to be polished. Fix the fixture onto a polishing machine and polish the end face using cerium oxide suspension polishing solution. The polishing pressure is 0.1 MPa-1.2 MPa, the speed is 50 r / s-100 r / s, and the time is 10 min-100 min. Step 3-2: Laser cut one end of the polished lithium niobate waveguide to create a boss with a width of 100μm-500μm and a length of 50μm-500μm; Step 3-3: Use ultrapure water and anhydrous ethanol to clean the lithium niobate waveguide structure that has undergone end-face polishing and laser cutting in sequence to remove residual polishing liquid and impurities on the surface, and obtain thin film lithium niobate external cavity chip; Step 4: Fabrication of on-chip laser Step 4-1: Using a six-axis coupling platform, a multimode Fabry-Perot semiconductor laser and a thin-film lithium niobate external cavity chip are spliced ​​together through the hybrid integration of a whispering-gallery mode microcavity with an SLR. The resulting on-chip laser is a high-power, narrow-linewidth, self-injection-locked laser. During the splicing, the semiconductor laser and the thin-film lithium niobate external cavity chip have the same tilt angle and their two end faces are parallel, ensuring a seamless splicing of the multimode Fabry-Perot semiconductor laser and the thin-film lithium niobate external cavity chip.

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