High-power high-stability narrow-linewidth external cavity semiconductor laser and application thereof

Abstract

The invention relates to a high-power high-stability narrow-linewidth external cavity semiconductor laser and application thereof, and belongs to the technical field of lasers. The laser comprises a gain chip, a collimating lens, a polarization beam splitter, an F-P etalon A, an F-P etalon B, a narrow-band-pass filter, a focusing lens, a partial reflection RSOA, a collimating lens and an isolator which are sequentially arranged along a light path. According to the invention, the double F-P etalon is arranged in the external cavity laser, a vernier effect is formed through different free spectral ranges and central wavelength bandwidths of the double F-P etalon to screen spectrums and compress the bandwidths, and wavelength tuning and further bandwidth compression can be carried out through incident angle fine tuning of the double F-P etalon. Single-mode screening and linewidth compression are carried out through a narrow-band-pass filter, and finally single-mode narrow-linewidth output is obtained through cooperation with an external cavity laser.

Description

Technical Field

[0001] This invention relates to a high-power, high-stability, narrow-linewidth external cavity semiconductor laser and its applications, belonging to the field of laser technology. Background Technology

[0002] With the rapid development of optoelectronic technology, semiconductor lasers have wide applications in aerospace, materials processing, military, and medical fields. Narrow-linewidth semiconductor lasers, due to their narrow linewidth, low noise, high stability, high coherence, and good dynamic single-mode characteristics, have become core light source devices in long-distance space optical communication, high-sensitivity optical sensing, and energy detection, and have extremely wide applications in high-precision coherent lidar, precision fiber optic sensors, inter-satellite communication, and fiber optic coherent communication.

[0003] In the field of quantum precision measurement, systems requiring higher measurement accuracy place extremely high demands on laser stability, narrow linewidth, high power, and small-size integration. External cavity lasers are typically used to achieve the required narrow linewidth. However, in practical applications, external cavity lasers face challenges such as optimizing for even narrower linewidths, higher power requirements, higher laser performance stability, and designing low-cost, high-isolation, anti-reflection solutions that can meet miniaturized packaging requirements. These are areas that urgently need improvement, hence this invention. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a high-power, high-stability, narrow-linewidth external cavity semiconductor laser and its applications.

[0005] The technical solution of the present invention is as follows: A high-power, high-stability, narrow-linewidth external cavity semiconductor laser includes a gain chip, a collimating lens, a polarization beam splitter, a FP etalon A, an FP etalon B, a narrow-bandpass filter, a focusing lens, a partially reflective RSOA, a collimating lens, and an isolator, arranged sequentially along the optical path. The partially reflective RSOA, also known as a reflective SOA, differs from a conventional SOA optical amplifier. In a conventional SOA, light incident from the left is amplified by the SOA and output from the right; in a partially reflective RSOA, light incident from the left is amplified by the SOA, reflected at the right end face, and still output from the left.

[0006] By incorporating two FP etalons into the external cavity laser, a vernier effect is formed to screen the spectrum through their different free spectral ranges and center wavelength bandwidths, thereby expanding the FSR and increasing the mode spacing. This facilitates single-mode screening and bandwidth compression. Simultaneously, wavelength tuning and further bandwidth compression can be achieved by fine-tuning the incident angle of the two FP etalons. Then, single-mode screening and linewidth compression are performed through a narrow bandpass filter. Finally, in conjunction with the external cavity laser, a single-mode extremely narrow linewidth output is obtained.

[0007] According to a preferred embodiment of the present invention, the reflective surface on the right side of the partially reflective RSOA is coated with a partial reflective film (e.g., 40%), and this end face is used as the output surface of the external cavity laser. In this case, the rear cavity surface of the external cavity laser is the rear cavity surface of the gain chip, and the front cavity surface is the reflective surface of the partially reflective RSOA. The internal resonant light is amplified by the gain chip and the partially reflective RSOA, two active components, to obtain higher output power. Furthermore, the active light amplification of the partially reflective RSOA is performed inside the external cavity laser. Its internal mode filtering and spectral width compression system can effectively suppress noise and broaden the spectral width, ultimately satisfying both high power and narrow linewidth output.

[0008] According to a preferred embodiment of the present invention, the gain chip employs a gradually curved waveguide. In the gain chip, the waveguide is gradually curved from the rear cavity surface to the front cavity surface, and the front cavity surface is the light-emitting surface. The laser is refracted at the front end surface and emitted at an angle.

[0009] The gain chip design features a gradually curved waveguide, sacrificing some power to effectively reduce front cavity surface reflection, prevent internal resonance of the gain chip, and ensure a wide gain spectrum range; it is particularly designed to address insufficient transmittance of the front cavity surface antireflection film and front cavity surface feedback of the gain chip caused by SOA amplification.

[0010] According to a preferred embodiment of the present invention, the isolator includes an analyzer A, a magnetostrictive rotator and an analyzer B arranged sequentially along the optical path. The analyzers A and B have the same main polarization direction as the laser output light. After passing through the magnetostrictive rotator, the polarization direction is rotated by 45°, and then the light is emitted after passing through the analyzer B.

[0011] The application of the aforementioned high-power, high-stability, narrow-linewidth external cavity semiconductor laser follows these steps: (1) The gain chip is powered on and emits light. After the beam is shaped by the collimating lens, it becomes collimated. After passing through the polarization beam splitter, only the main polarized light is retained to resonate internally, reducing noise and improving stability. Then, it passes through FP etalon A and FP etalon B. By utilizing the vernier effect formed by them, a wider free spectrum range and a narrower bandwidth of the center wavelength are obtained. At the same time, the incident angle of the two FP etalons can be finely adjusted to achieve wavelength tuning and spectral width compression. After that, a narrow bandpass filter is used for single-mode selection and further compression of the linewidth. (2) The converging light enters the partially reflected RSOA, where the optical power is amplified. At the same time, it is reflected and resonated at the front cavity surface of the partially reflected RSOA and output. Finally, it passes through a collimating lens to shape a parallel beam. (3) The light beam exits after passing through the isolator.

[0012] According to a preferred embodiment of the present invention, in step (3), the beam passes through analyzer A, which has the same polarization direction as the laser beam, allowing the beam to pass normally. Then the beam passes through a magnetostrictive rotator, and after passing through the magnetostrictive rotator, the polarization direction is rotated by 45°. After passing through analyzer B, the reflected light is emitted. After passing through the magnetostrictive rotator, the polarization direction is rotated by 45° again, perpendicular to the polarization direction of analyzer A. The polarization component passing through is minimized, achieving maximum isolation of reflected light.

[0013] The beneficial effects of this invention are as follows: 1. This invention incorporates two FP etalons within an external cavity laser. Through their different free spectral ranges and center wavelength bandwidths, a vernier effect is formed to screen the spectrum, expand the FSR, increase the mode spacing, facilitate single-mode screening, and compress the bandwidth. Simultaneously, wavelength tuning and further bandwidth compression can be achieved by fine-tuning the incident angle of the two FP etalons. Then, single-mode screening and linewidth compression are performed through a narrow bandpass filter, ultimately resulting in a single-mode narrow linewidth output in conjunction with the external cavity laser.

[0014] 2. This invention utilizes the rear cavity surface of a partially reflected RSOA as the front cavity feedback mirror of an external cavity laser, enabling power amplification via SOA; it saves on some reflectors and beam shaping devices, reducing package size; at the same time, since the optical amplification of SOA is inside the external cavity laser, its gain spectrum is also tuned by the built-in polarization optimization and spectral optimization system, reducing the linewidth broadening effect caused by SOA and ensuring high-power, narrow-linewidth output.

[0015] 3. The present invention features a specially designed isolator to achieve maximum isolation of reflected light. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the present invention; The components are: 1. Gain chip; 2. Collimating lens A; 3. Polarizing beam splitter; 4. FP etalon A; 5. FP etalon B; 6. Narrow bandpass filter; 7. Focusing lens; 8. Partial reflection RSOA; 9. Collimating lens B; 10. Analyzer A; 11. Magnetostrictive rotator; 12. Analyzer B. Detailed Implementation

[0017] The present invention will be further described below with reference to the embodiments and accompanying drawings, but is not limited thereto.

[0018] Example 1: like Figure 1As shown, this embodiment provides a high-power, high-stability, narrow-linewidth external cavity semiconductor laser, including a gain chip 1, a collimating lens A2, a polarization beam splitter 3, a FP etalon A4, an FP etalon B5, a narrow-bandpass filter 6, a focusing lens 7, a partially reflective RSOA 8, a collimating lens B9, and an isolator arranged sequentially along the optical path. The partially reflective RSOA 8 is a reflective SOA, which differs from a conventional SOA optical amplifier. In a conventional SOA amplifier, light incident from the left is amplified by the SOA and output from the right; in a partially reflective RSOA amplifier, light incident from the left is amplified by the SOA, reflected at the right end face, and still output from the left.

[0019] The dual FP etalon design has the following functions: First: The FP spectrum of the external cavity laser is screened using a comb-shaped transmission spectrum with dual FP etalons. For example, when the longitudinal mode spacing of the FP spectrum of the external cavity laser is 30 GHz, in order to achieve the final single-mode output, the FP etalon A is first used, with an FSR of 1000 GHz and a -3 dB center bandwidth of 100 GHz. The purpose of the 1000 GHz FSR is to obtain a wide FSR spacing, which facilitates the subsequent single-mode screening by the narrow bandpass filter. However, at this time, the -3 dB center bandwidth is relatively wide, and there may be 3 to 5 FP longitudinal modes of the external cavity laser within 100 GHz. At this time, the spectral shape is a comb-shaped spectrum with each group spaced at 1000 GHz. Then, the FP etalon B is used, with an FSR of 1000 GHz and a center bandwidth of 1000 GHz. At 100GHz, with a -3dB bandwidth of 25GHz, a single longitudinal mode can be selected from the previously grouped 3-5 longitudinal modes. The resulting spectrum is a comb-like spectrum with 1000GHz intervals for a single longitudinal mode. Furthermore, the -3dB bandwidth of the FP etalon B center wavelength is narrower than the spectral width of the external cavity FP, achieving bandwidth compression. The reason a single FP etalon wasn't used to achieve a 1000GHz interval comb-like transmission spectrum for a single longitudinal mode is that it's difficult to achieve a narrow center wavelength bandwidth, high transmittance, and high mode isolation while maintaining high FSR. Finally, a narrow-bandpass filter with a -3dB bandwidth of 500GHz filters the comb spectrum to a single mode, as narrow-bandpass filters are difficult to use for bandwidth compression. Therefore, this embodiment uses two FP etalons and one narrow-bandpass filter to achieve single-mode selection within the external cavity laser, compressing the linewidth, ensuring narrow-linewidth single-mode intracavity resonance, and obtaining high gain, thus achieving an extremely narrow linewidth output from the external cavity laser.

[0020] Second, the vernier effect can be used to improve the FSR: that is, for the FP etalon B, if the FSR is selected to be 150GHz, similar to the misalignment amplification mechanism of a vernier caliper, under ideal conditions, two FP etalons can obtain a single-mode comb spectrum with an FSR of about 6000GHz. Considering the existence of mode spectral width, the FSR is less than 6000GHz, but much greater than 1000GHz. Therefore, by using this vernier effect, it is easier to achieve single longitudinal mode screening and reduce the difficulty and cost of narrowband pass filters.

[0021] Third, bandwidth compression: When the incident angle is changed by adjusting the FP etalon, the propagation path of light in the FP etalon changes due to refraction, and its constructive interference conditions change, thus changing the center wavelength of the transmitted spectrum. By changing the incident angle and finely adjusting the center projection wavelength of the two FP etalons (e.g., on the order of GHz), the center wavelength bandwidth can be further compressed by utilizing their comb-like spectral edges.

[0022] The right-side reflective surface of the partially reflective RSOA8 is coated with a partial reflective film (e.g., 40%), and this end face is used as the output surface of the external cavity laser. In this case, the rear cavity surface of the external cavity laser is the rear cavity surface of the gain chip, and the front cavity surface is the reflective surface of the partially reflective RSOA. The internal resonant light is amplified by both the gain chip and the partially reflective RSOA, resulting in higher output power. Furthermore, the active light amplification of the partially reflective RSOA occurs inside the external cavity laser. Its internal mode filtering and spectral width compression system effectively suppresses noise and broadens the spectral width, ultimately achieving both high power and narrow linewidth output.

[0023] Gain chip 1 uses a gradually curved waveguide. In the gain chip, the waveguide is gradually curved from the rear cavity surface to the front cavity surface. The front cavity surface is the light-emitting surface. The laser is refracted at the front surface and emitted at an angle.

[0024] Gain Chip 1 features a gradient curved waveguide design that sacrifices some power to effectively reduce front cavity surface reflection, prevent internal resonance within the gain chip, and ensure a wide gain spectrum range. It is specifically designed to address insufficient transmittance of the front cavity surface antireflection film and front cavity surface feedback of the gain chip caused by SOA amplification.

[0025] The isolator includes a polarizer A10, a magnetostrictive rotator 11, and a polarizer B12 arranged sequentially along the optical path. The polarizers A10 and B12 have the same polarization direction as the main polarization direction of the laser output. After passing through the magnetostrictive rotator 11, the polarization direction is rotated by 45°, and then the laser outputs after passing through the polarizer B12.

[0026] The application of the aforementioned high-power, high-stability, narrow-linewidth external cavity semiconductor laser follows these steps: (1) When the gain chip 1 is powered on, light is emitted. After the beam is shaped by the collimating lens A2, collimated light is obtained. After passing through the polarization beam splitter 3, only the main polarized light is retained in the internal resonance, which reduces noise and improves stability. Then, after passing through the FP etalon A4 and FP etalon B5, the vernier effect formed by them is used to obtain a wider free spectrum range and a narrower bandwidth of the center wavelength resonance spectrum. At the same time, the incident angle of the two FP etalons can be finely adjusted to achieve wavelength tuning and spectral width compression. Then, the narrow bandpass filter 6 is used for single-mode selection and further compression of linewidth. (2) The converging light enters the partially reflected RSOA8 for optical power amplification. At the same time, it is reflected and resonated at the front cavity surface of the partially reflected RSOA and output. Finally, it passes through the collimating lens B9 to shape a parallel beam. (3) The beam passes through the analyzer A10. The analyzer A10 has the same polarization direction as the main polarization direction of the laser beam, allowing the beam to pass normally. Then the beam passes through the magnetostrictive rotator 11. After passing through the magnetostrictive rotator 11, the polarization direction is rotated by 45°. Then it passes through the analyzer B12 and exits. The reflected light returns and passes through the magnetostrictive rotator 11. The polarization direction is rotated by 45° again and is perpendicular to the polarization direction of the analyzer A10. The polarization component is minimized, achieving maximum isolation of the reflected light.

Claims

1. A high-power, high-stability, narrow-linewidth external cavity semiconductor laser, characterized in that, It includes a gain chip, collimating lens, polarization beam splitter, FP etalon A, FP etalon B, narrow bandpass filter, focusing lens, partial reflector RSOA, collimating lens and isolator arranged sequentially along the optical path.

2. The high-power, high-stability, narrow-linewidth external cavity semiconductor laser as described in claim 1, characterized in that, The reflective surface on the right side of the partially reflective RSOA is coated with a partially reflective film, and this end face is used as the light output surface of the external cavity laser.

3. The high-power, high-stability, narrow-linewidth external cavity semiconductor laser as described in claim 2, characterized in that, The gain chip uses a gradually curved waveguide. In the gain chip, the waveguide is gradually curved from the rear cavity surface to the front cavity surface. The front cavity surface is the light-emitting surface. The laser is refracted at the front surface and emitted at an angle.

4. The high-power, high-stability, narrow-linewidth external cavity semiconductor laser as described in claim 3, characterized in that, The isolator includes an analyzer A, a magnetostrictive rotator, and an analyzer B arranged sequentially along the optical path. Analyzer A and analyzer B have the same main polarization direction as the laser output light. After passing through the magnetostrictive rotator, the polarization direction is rotated by 45°, and then the light is emitted after passing through analyzer B.

5. The application of the high-power, high-stability, narrow-linewidth external cavity semiconductor laser as described in claim 4, characterized in that, The steps are as follows: (1) The gain chip is powered on to produce light. After the beam is shaped by the collimating lens, it becomes collimated. After passing through the polarization beam splitter, only the main polarized light is retained to resonate internally. Then, it passes through FP etalon A and FP etalon B. By utilizing the vernier effect formed by them, a wider free spectrum range and a narrower bandwidth of the center wavelength are obtained. Then, a narrow bandpass filter is used for single-mode selection and further compression of the linewidth. (2) The converging light enters the partially reflected RSOA, where the optical power is amplified, and finally passes through the collimating lens to shape a parallel beam; (3) The light beam exits after passing through the isolator.

6. The application of the high-power, high-stability, narrow-linewidth external cavity semiconductor laser as described in claim 5, characterized in that, In step (3), the beam passes through analyzer A, which has the same main polarization direction as the laser beam, allowing the beam to pass normally. Then the beam passes through a magnetostrictive rotator, and after passing through the magnetostrictive rotator, the polarization direction is rotated by 45°. After passing through analyzer B, the beam is emitted. The reflected light returns and passes through the magnetostrictive rotator, and the polarization direction is rotated by 45° again, perpendicular to the polarization direction of analyzer A. The polarization component passing through is minimized, achieving maximum isolation of reflected light.

Images