Tunable external cavity semiconductor laser based on pentagonal prism rotation

Abstract

A tunable external cavity semiconductor laser based on a rotating pentagonal prism, wherein the laser diode, collimating lens, interference filter, and pentagonal prism are sequentially located on the same axis, and the interference filter includes a rotatable structure; the pentagonal prism can rotate around the center of its incident surface. Advantages: The laser output wavelength can be adjusted by regulating the angles of the interference filter and the pentagonal prism.

Description

Technical Field

[0001] This invention relates to a tunable external cavity semiconductor laser based on the rotation of a pentagonal prism. Background Technology

[0002] Narrow-linewidth external cavity semiconductor lasers are characterized by their compact structure, low phase noise, tunability, and direct modulation capability. As the research and development of narrow-linewidth semiconductor lasers matures and their performance improves, their applications have broadened. Currently, they have become a core fundamental light source in many fields, not only for basic research such as laser cooling and high-resolution spectroscopy, but also for applications in optical communication and lidar detection.

[0003] External cavity semiconductor lasers are based on existing semiconductor lasers by introducing an external cavity structure, thereby improving laser performance and frequency selectivity. The external cavity structure refers to constructing a resonant cavity outside the laser diode (LD) using optical feedback elements such as mirrors or gratings.

[0004] The basic model of an external cavity semiconductor laser is shown in the figure. The resonant cavity of the semiconductor laser itself is the internal cavity, r1, r2, and r3 represent the reflectivity of the cavity surface, l represents the length of the LD (internal cavity length), and d represents the distance from the right side of the chip to the external cavity mirror (external cavity length). Based on this model, other more complex external cavity structures can be constructed.

[0005] Common external cavity semiconductor laser structures include Littrow, Littman-Metcal, and cat's-eye structures. Wavelength selection is achieved using reflective gratings, Bragg gratings, microresonators, and interference filters. Figure 3 As shown, this is a Littrow structure external cavity semiconductor laser. The light from the laser diode (LD) is collimated by a collimating lens and then output to a diffraction grating. The first-order diffracted light generated by the grating returns along its original path, oscillating with the outer surface of the laser tube to form external cavity feedback. The zero-order diffracted light serves as the output light. By adjusting the angle of the diffraction grating relative to the incident light, the output wavelength of the laser is changed. The Littman-Metcal structure adds a mirror to the Littrow structure. The first-order diffracted light is reflected by the mirror and undergoes a second diffraction, forming a resonant cavity. The output wavelength is changed by adjusting the angle of the mirror. Both structures have their advantages and disadvantages. The Littrow structure external cavity semiconductor laser is simple in structure, small in size, and low in cost, but adjusting the wavelength of the diffraction grating changes the direction of the output light, which is inconvenient for practical applications. The Littman structure laser has a fixed output light direction and undergoes two diffractions, resulting in a relatively narrow linewidth, but also lower output power. There are also... Figure 5 As shown, this is a common external cavity semiconductor laser structure that uses an interference filter as the frequency selection element.

[0006] In 2020, Zhang Linbo et al. from the Key Laboratory of Time and Frequency Reference of the Chinese Academy of Sciences studied an external cavity semiconductor laser with an interference filter that uses a partial mirror attached to a piezoelectric ceramic to provide optical feedback. This fixing method and feedback method are susceptible to mechanical vibration and temperature changes, which affect the stability of the laser output wavelength.

[0007] In 2019, Wang Yan et al. fabricated a wide-range tunable external cavity diode laser (ECDL) with ultra-high side-mode suppression ratio (SMSR). The results showed that in the Littrow configuration, the performance of the external cavity laser can be improved by increasing the trench density of the grating. When a 65 l / mm grating with a first-order diffraction efficiency of 91% is used in the external cavity laser system, the maximum SMSR can reach 209 dB and the tunable range is 209.9 nm.

[0008] In 2023, Sheng Liwen et al. designed a narrow-linewidth external cavity tunable semiconductor laser based on the Littman structure using a mechanically etched blazed grating as the external cavity feedback element. They achieved a wide tuning range of 1480-1580nm and laser output with a linewidth of less than 98.27kHz without mode jumps.

[0009] Although lasers based on Littrow, Littman-Metcal, and cat's-eye structures have seen significant performance improvements in recent years, many problems remain. For example, in Littrow lasers, adjusting the wavelength causes the output light to rotate with the diffraction grating, causing considerable inconvenience. Littman-Metcal lasers, due to double diffraction, suffer from significantly reduced output power, and their complex structure and high cost further complicate matters. Additionally, cat's-eye lasers, using an interferometer as the frequency selection element, consist of a collimating lens and a mirror. Besides adjusting the wavelength via the interferometer, a piezoelectric ceramic element is typically added in front of the mirror for fine-tuning. During adjustment, the deformation of the piezoelectric ceramic alters the distance between it and the collimating lens, causing laser divergence and affecting feedback, leading to power variations. And the interferometer laser based on the external cavity mirror of the pyramidal array mentioned in patent CN 114899704A, when using the pyramidal array for feedback, the optical path cannot return completely along the original path, but there is a translation distance, which makes it impossible to achieve a good feedback state. Summary of the Invention

[0010] The purpose of this invention is to solve the problems of laser divergence and feedback degradation caused by changes in the output light angle and wavelength in the prior art, which lead to inconvenience in use, complex structure and poor stability. The invention proposes a tunable external cavity semiconductor laser based on the rotation of a pentagonal prism.

[0011] To achieve the above objectives, the present invention adopts the following technical solution: a tunable external cavity semiconductor laser based on the rotation of a pentagonal prism, comprising a laser diode, a collimating lens, an interference filter, and a pentagonal prism, wherein the laser diode, collimating lens, interference filter, and pentagonal prism are sequentially located on the same axis, and the interference filter includes a rotatable structure; the pentagonal prism can rotate around the center of the incident surface, and the laser beam from the laser diode is collimated by the collimating lens, filtered by the interference filter, and then emitted through the pentagonal prism.

[0012] Furthermore, the pentagonal prism has one interior angle of 90° and the other four interior angles of 112.5°, with two of its five faces being total reflection surfaces.

[0013] Furthermore, the collimating lens is an aspherical lens located at the light output path of the laser diode, used to collimate the laser diode.

[0014] Furthermore, the laser diode is temperature-controlled by a semiconductor cooler located at the bottom of the laser diode, allowing it to operate at a stable and suitable temperature.

[0015] Furthermore, the coating wavelength of the pentagonal prism and some reflective mirrors is consistent with the center wavelength of the laser diode output, and the reflectivity is 10%-60%.

[0016] Furthermore, the interference filter is a bandpass filter.

[0017] Furthermore, one end of the piezoelectric ceramic is in close contact with the exit surface of the pentagonal prism; the piezoelectric ceramic is ring-shaped, and the laser passes through the middle.

[0018] Furthermore, the exit surface of the pentagonal prism is also equipped with some reflectors.

[0019] Furthermore, the other end of the piezoelectric ceramic is bonded to part of the reflector.

[0020] Furthermore, some of the reflectors are bonded to the piezoelectric ceramics using epoxy resin adhesive.

[0021] The beneficial effects of this invention are as follows: The pentaangular prism ensures that regardless of the incident angle of the incident light relative to the prism, the outgoing light is deflected by 90° relative to the incident light, and the resulting image exhibits neither rotation nor specular reflection. Therefore, using a pentaangular prism as the feedback element in a semiconductor laser not only guarantees that the angle of light emission remains unchanged, but also allows for adjustment of the laser output wavelength by changing the incident angle of the laser relative to the pentaangular prism. Since only the laser optical path is changed, the optical path always returns along the original path when the wavelength changes, thus not affecting the quality of laser feedback or the laser divergence angle, and eliminating the need for secondary collimation. Therefore, using a single optical element like a pentaangular prism can achieve both feedback and wavelength adjustment functions, while consistently maintaining optimal feedback. The laser structure used as a feedback element is simple, has low component cost, and high stability, enabling the realization of a highly stable narrow-linewidth external cavity semiconductor laser. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of Example 1.

[0023] Figure 2 This is a structural schematic diagram of Embodiment 2 of this application.

[0024] Figure 3 This is a basic model diagram of an external cavity semiconductor laser in the background technology.

[0025] Figure 4 This is a schematic diagram of the existing Littrow structure. Figure 1 .

[0026] Figure 5 This is a schematic diagram of the existing Littman structure. Figure 2 .

[0027] Figure 6 This is a schematic diagram of an existing cat-eye laser structure. Detailed Implementation

[0028] The following will refer to the appendices in the embodiments of the present invention. Figure 1-6 The technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0029] Example 1 combined with appendix Figure 1A tunable external cavity semiconductor laser based on pentagonal prism rotation includes a laser diode 1, a collimating lens 2, an interference filter 3, and a pentagonal prism 4. The laser diode, collimating lens, interference filter, and pentagonal prism are located sequentially on the same axis. The interference filter includes a rotating structure with an adjustable angle along the center point of the interference filter. The pentagonal prism can be rotated with an adjustable angle based on the center of the incident surface of the pentagonal prism. The laser light from the laser diode is collimated by the collimating lens, filtered by the interference filter, and then emitted through the pentagonal prism.

[0030] This is a tunable external cavity semiconductor laser based on a rotating pentagonal prism. One interior angle of the pentagonal prism is 90°, and the other four interior angles are all 112.5°. Two of its five faces are total internal reflection surfaces. The angle between the incident and exit faces of the pentagonal prism is 90°. The outer adjacent faces of the incident and exit faces of the pentagonal prism are total internal reflection surfaces.

[0031] A tunable external cavity semiconductor laser based on pentagonal prism rotation uses an aspherical collimating lens located at the laser diode's output optical path to collimate the laser diode.

[0032] A tunable external cavity semiconductor laser based on a rotating pentagonal prism has a laser diode whose temperature is controlled by a thermoelectric cooler located at the bottom of the laser diode, allowing the laser diode to operate at a stable and suitable temperature.

[0033] A tunable external cavity semiconductor laser based on a rotating pentagonal prism, wherein the pentagonal prism and some of the mirrors are coated with wavelengths that are consistent with the center wavelength of the laser diode output, and the reflectivity is 10%-60%.

[0034] A tunable external cavity semiconductor laser based on pentagonal prism rotation, wherein the interference filter is a bandpass filter.

[0035] A tunable external cavity semiconductor laser based on a rotating pentagonal prism, wherein a portion of the pentagonal prism's exit surface is also provided with a reflector.

[0036] In a tunable external cavity semiconductor laser based on a rotating pentagonal prism, the light output from laser diode 1 is first collimated by collimating lens 2, and then partially reflected by pentagonal prism 4 onto partial reflector 5, forming a feedback laser. The resulting laser is a broadband laser with a peak wavelength equal to the center wavelength of the laser tube.

[0037] An interference filter 3 is installed between the laser diode 1 and the pentagonal prism 4. The desired wavelength is obtained by rotating the angle of the interference filter 3 and adjusting the laser current.

[0038] The pentagonal prism rotates around the center of its incident surface. The wavelength can be adjusted by rotating the pentagonal prism. The rotatable angle is θ, and the laser can be completely transmitted through the incident surface, the reflecting surface, and the exit surface.

[0039] The exit surface of the pentagonal prism is partially coated with a reflective film or partially reinforced with reflective mirrors. Part of the laser light returns along its original path to form a resonant cavity, while the light transmitted through the reflective mirrors becomes the output light. The wavelength is adjusted by changing the angle of the interference filter and the incident angle of the laser light relative to the pentagonal prism.

[0040] Example 2 combined with appendix Figure 2 A tunable external cavity semiconductor laser based on the rotation of a pentagonal prism includes a laser diode 1, a collimating lens 2, an interference filter 3, and a pentagonal prism 4. The laser diode, collimating lens, interference filter, and pentagonal prism are located on the same axis in sequence. The interference filter is a rotatable structure. The pentagonal prism can rotate around the center of the incident surface.

[0041] This is a tunable external cavity semiconductor laser based on a rotating pentagonal prism. One of the pentagonal prism's interior angles is 90°, and the other four interior angles are all 112.5°. Two of the five faces are total reflection surfaces.

[0042] A tunable external cavity semiconductor laser based on pentagonal prism rotation uses an aspherical collimating lens located at the laser diode's output optical path to collimate the laser diode.

[0043] A tunable external cavity semiconductor laser based on a rotating pentagonal prism has a laser diode whose temperature is controlled by a thermoelectric cooler located at the bottom of the laser diode, allowing the laser diode to operate at a stable and suitable temperature.

[0044] A tunable external cavity semiconductor laser based on a rotating pentagonal prism, wherein the pentagonal prism and some of the mirrors are coated with wavelengths that are consistent with the center wavelength of the laser diode output, and the reflectivity is 10%-60%.

[0045] A tunable external cavity semiconductor laser based on pentagonal prism rotation, wherein the interference filter is a bandpass filter.

[0046] A tunable external cavity semiconductor laser based on a rotating pentagonal prism has one end of a piezoelectric ceramic tightly attached to the exit surface of the pentagonal prism; the piezoelectric ceramic is ring-shaped, and the laser passes through the middle.

[0047] A tunable external cavity semiconductor laser based on a rotating pentagonal prism, wherein a portion of the pentagonal prism's exit surface is also provided with a reflector.

[0048] A tunable external cavity semiconductor laser based on the rotation of a pentagonal prism, with part of the reflector bonded to the other end of a piezoelectric ceramic.

[0049] A tunable external cavity semiconductor laser based on the rotation of a pentagonal prism is used to bond part of the reflector to the piezoelectric ceramic using epoxy resin adhesive.

[0050] The exit surface of the pentagonal prism is partially coated with a reflective film or partially reinforced with reflective mirrors. Part of the laser light returns along its original path to form a resonant cavity, while the light transmitted through the reflective mirrors becomes the output light. The wavelength is adjusted by changing the angle of the interference filter and the incident angle of the laser light relative to the pentagonal prism.

[0051] A tunable external cavity semiconductor laser based on pentagonal prism rotation is used to bond part of the reflector 5 to the piezoelectric ceramic 6 with epoxy resin, thereby enhancing the structural stability of the laser.

[0052] The laser output from laser diode 1 is collimated by collimating lens 2, then passes through pentagonal prism 4 and piezoelectric ceramic 6 to illuminate partial reflector 5, forming feedback. The wavelength can be coarsely adjusted by rotating the angle of the pentagonal prism, and the cavity length of the resonant cavity can be changed by changing the voltage of piezoelectric ceramic 6. Fine adjustment of the voltage of piezoelectric ceramic 6 is used to finely adjust the laser output wavelength.

[0053] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A tunable external cavity semiconductor laser based on pentagonal prism rotation, comprising a laser diode, a collimating lens, an interference filter, and a pentagonal prism, characterized in that: The laser diode, collimating lens, interference filter, and pentaangular prism are arranged sequentially on the same axis. The interference filter includes a rotatable structure. The pentaangular prism rotates around the center of its incident surface. The laser beam from the laser diode is collimated by the collimating lens, filtered by the interference filter, and then emitted through the pentaangular prism. One of the interior angles of the pentaangular prism is 90°, and the other four interior angles are all 112.5°. Two of the five faces of the pentaangular prism are total internal reflection surfaces. The angle between the incident and exit surfaces of the pentaangular prism is 90°. The adjacent outer faces of the incident and exit surfaces of the pentaangular prism are total internal reflection surfaces. Partial reflectors are also provided at the exit surface of the pentaangular prism.

2. The tunable external cavity semiconductor laser based on pentagonal prism rotation according to claim 1, characterized in that: The collimating lens is an aspherical lens located at the light output path of the laser diode and is used to collimate the laser diode.

3. The tunable external cavity semiconductor laser based on pentagonal prism rotation according to claim 1, characterized in that: The laser diode is temperature-controlled by a thermoelectric cooler located at the bottom of the laser diode, which allows the laser diode to operate at a stable and suitable temperature.

4. The tunable external cavity semiconductor laser based on pentagonal prism rotation according to claim 1, characterized in that: The pentagonal prism and some reflective mirrors are coated with wavelengths that match the center wavelength of the laser diode output, with a reflectivity of 10%-60%.

5. The tunable external cavity semiconductor laser based on pentagonal prism rotation according to claim 1, characterized in that: The interference filter is a bandpass filter.

6. The tunable external cavity semiconductor laser based on pentagonal prism rotation according to claim 1, characterized in that: One end of the piezoelectric ceramic is in close contact with the exit surface of the pentagonal prism; the piezoelectric ceramic is ring-shaped, and the laser passes through the middle.

7. The tunable external cavity semiconductor laser based on pentagonal prism rotation according to claim 6, characterized in that: Part of the reflector is bonded to the other end of the piezoelectric ceramic.

8. The tunable external cavity semiconductor laser based on pentagonal prism rotation according to claim 7, characterized in that: Part of the reflector is bonded to the piezoelectric ceramic using epoxy resin adhesive.

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