Optical frequency comb generation method and device based on Brillouin scattering and electro-optical modulator

Abstract

The invention discloses an optical frequency comb generation method and device based on Brillouin scattering and an electro-optical modulator, and belongs to the field of photoelectric measurement. The method comprises the steps that a first laser and a second laser are used for generating pump light and seed light respectively, multi-wavelength pump light is generated through a cascade electro-optical modulator, the pump light and the seed light are emitted into a Sagnac loop, an optical frequency comb is output through the forward Brillouin scattering effect of an optical fiber and the electro-optical modulator, and the seed light and the pump light are output. The polarization controller is adjusted to optimize polarization state matching of the pump light and the seed light, so that the Brillouin scattering effect reaches the maximum value. The device is composed of a laser, an electro-optical modulator, a signal generator, an optical amplifier, an optical isolator, an optical coupler, a polarization controller and an optical fiber. The optical fiber forward Brillouin scattering effect and the electro-optical modulator are combined, the optical frequency comb giving consideration to the wide frequency spectrum and the narrow interval is generated, meanwhile, the comb tooth interval of the optical frequency comb can be accurately controlled by independently adjusting the frequency of the signal generator, and accurate measurement of signals or objects is achieved.

Description

Technical Field

[0001] The present invention relates to the field of photoelectric measurement, and in particular to a method and a device for generating an optical frequency comb based on Brillouin scattering and an electro-optical modulator. Background Art

[0002] As optical frequency comb technology develops towards wide spectrum and narrow spacing, it has shown unique advantages in the fields of high-precision spectral analysis, multi-channel optical communication, super-resolution imaging, etc. However, existing optical frequency comb systems still face the following technical challenges in achieving wide spectrum and narrow spacing output. (1) Traditional mode-locked lasers are limited by gain bandwidth and it is difficult to simultaneously achieve ultra-wide spectrum coverage and narrow comb line spacing. They need to rely on multi-level nonlinear frequency conversion to expand the spectrum, resulting in a surge in system complexity. (2) Ultra-dense comb lines (spacing less than 100 MHz) are prone to mode competition and phase noise accumulation. Existing phase locking technology is difficult to maintain comb line phase stability over a wide spectrum. (3) When expanding the spectrum in nonlinear optical fibers or crystals, effects such as four-wave mixing and self-phase modulation can lead to uneven comb line power and spectral distortion. Especially under narrow spacing conditions, crosstalk between adjacent comb lines is significantly aggravated. (4) Traditional dispersion compensation technology is difficult to simultaneously optimize group velocity dispersion and nonlinear effects under a wide spectrum, limiting the efficiency of spectrum expansion.

[0003] It can be seen that how to design a method and device for generating an optical frequency comb that takes into account both wide spectrum and narrow interval, while achieving the tunability and controllability of the optical frequency comb generation, is a core challenge that urgently needs to be solved in this field. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a method and device for generating an optical frequency comb based on Brillouin scattering and an electro-optical modulator, which generates a wide-spectrum, narrow-interval optical frequency comb by combining the forward Brillouin scattering effect of the optical fiber and the electro-optical modulator. By changing the frequency of the signal generator, the continuous and precise adjustment of the comb tooth interval of the optical frequency comb is achieved, thereby realizing accurate measurement of signals or objects.

[0005] A method for generating an optical frequency comb based on Brillouin scattering and an electro-optical modulator comprises the following steps: Step S1, using a first laser and a second laser to generate a pump light and a seed light respectively; Step S2, the first laser cascades the first electro-optic modulator and the second electro-optic modulator to modulate the pump light in step S1 into multi-wavelength pump light; Step S3, amplifying the multi-wavelength pump light in step S2 by using an optical fiber amplifier, so that the Brillouin scattering of the multi-wavelength pump light reaches the threshold value of the Brillouin scattering generated by the optical fiber, and ensuring the unidirectional transmission of the multi-wavelength pump light by using an optical isolator; Step S4: Process the seed light in step S1 with the second polarization controller, and inject the processed seed light and the multi-wavelength pump light that has passed through the optical isolator in step S3 into the Sagnac loop formed by the first optical coupler, the second optical coupler, the first polarization controller, and the optical fiber; Step S5: Output an optical frequency comb formed by splicing the multi-wavelength seed light and the multi-wavelength pump light at the second optical coupler through the forward Brillouin scattering effect of the optical fiber; Step S6: Adjust the first polarization controller and the second polarization controller to optimize the polarization state matching between the pump light and the seed light, so that the Brillouin scattering effect reaches the maximum value.

[0006] Furthermore, in step S1, the pump light excites the forward Brillouin scattering effect inside the optical fiber, and the seed light performs phase modulation through the excited forward Brillouin scattering effect to copy the comb teeth and frequency interval of the pump light.

[0007] Furthermore, in step S2, the driving signal of the first electro-optic modulator is a cosine signal with a frequency of f output by the first signal generator, and the magnitude of the frequency f is equal to the resonance frequency of the R 0,m acoustic mode of the forward Brillouin scattering. The first electro-optic modulator generates a positive integer N of comb teeth with the same power, and the driving signal of the second electro-optic modulator is a cosine signal with a frequency of N times f output by the second signal generator.

[0008] In addition, the present invention also provides an optical frequency comb generation device based on Brillouin scattering and electro-optic modulators. The optical frequency comb generation device based on Brillouin scattering and electro-optic modulators includes: a first laser, a second laser, a first electro-optic modulator, a second electro-optic modulator, a first signal generator, a second signal generator, an optical fiber amplifier, an optical isolator, a first optical coupler, a second optical coupler, a first polarization controller, a second polarization controller, and an optical fiber.

[0009] Furthermore, the first laser and the second laser adopt narrow linewidth semiconductor lasers.

[0010] Furthermore, the first optical coupler is a 1×2 optical coupler, and the second optical coupler is a 2×2 optical coupler.

[0011] Furthermore, the optical fiber adopts an optical fiber with a forward Brillouin scattering coefficient greater than 3 before hundreds of MHz.

[0012] Furthermore, the first electro-optic modulator and the second electro-optic modulator are cascaded to form a cascaded electro-optic modulator. The first electro-optic modulator is a Mach-Zehnder modulator, and the second electro-optic modulator is a dual-parallel Mach-Zehnder modulator.

[0013] Compared with the prior art, the present invention can achieve the following beneficial effects: (1)The present invention combines the forward Brillouin scattering effect of optical fiber with a cascaded electro-optic modulator. A signal generator is used to drive the modulator to generate multi-wavelength pump light. Through a Sagnac loop circuit, multi-wavelength seed light and pump light are spliced to generate an optical frequency comb with a coverage exceeding 10 GHz and a frequency interval equal to the Brillouin scattering resonance frequency, breaking through the gain bandwidth limitation of traditional mode-locked lasers.

[0014] (2)By independently adjusting the frequency of the signal generator, the present invention can accurately control the tooth interval of the optical frequency comb, solve the problems of non-adjustable comb line interval and phase noise accumulation in traditional technologies, realize continuously adjustable comb line interval and optimized phase stability, and this solution is easy to implement, low-cost, and low-power consumption.

[0015] (3)The present invention adopts a highly nonlinear optical fiber and a Sagnac loop structure, and uses the linear phase modulation characteristic of Brillouin scattering to avoid the uneven comb line power and spectral distortion caused by non-linear effects such as four-wave mixing. Compared with traditional non-linear extended spectrum schemes, the spectral flatness is improved, and the consistency of comb line power is significantly improved. Description of the Drawings

[0016] Figure 1 Schematic diagram of the optical frequency comb generation device based on Brillouin scattering and electro-optic modulator of the present invention; Figure 2 Spectrum diagram of the multi-wavelength pump light source after passing through the electro-optic modulator and the dual-parallel Mach-Zehnder modulator; Figure 3 Spectrum diagram of the optical frequency comb after splicing the multi-wavelength seed light source and the multi-wavelength pump light source. Detailed Embodiments

[0017] The following further describes the detailed embodiments of the present invention with reference to the drawings. The technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0018] An optical frequency comb generation method based on Brillouin scattering and electro-optic modulator includes the following steps: Step S1, using a first laser and a second laser to generate pump light and seed light respectively; The central wavelength of the pump light is 1550.290 nm, the line width is 5 kHz, and the power is 16 dBm; The central wavelength of the seed light is 1550.309 nm, the line width is 5 kHz, and the power is 10 dBm; Step S2: The first laser cascades with the first electro-optic modulator and the second electro-optic modulator to modulate the pump light in Step S1 into multi-wavelength pump light; The first electro-optic modulator generates three power-equalized combs, which is connected to a first signal generator with a frequency of 129.5 MHz, and this frequency is the same as the resonance frequency of the R 0,3 acoustic mode; The second electro-optic modulator is connected to a radio frequency signal source with a frequency of 388.5 MHz, that is, the second signal generator. The spectrum diagram of the modulated multi-wavelength pump light source is as Figure 2 shown.

[0019] Step S3: Amplify the multi-wavelength pump light in Step S2 through an optical fiber amplifier so that the Brillouin scattering of the multi-wavelength pump light reaches the threshold for the optical fiber to generate Brillouin scattering, and ensure the unidirectional transmission of the multi-wavelength pump light through an optical isolator; Step S4: Process the seed light in Step S1 through a second polarization controller, and inject the processed seed light and the multi-wavelength pump light that has passed through the optical isolator in Step S3 into a Sagnac loop formed by a first optical coupler, a second optical coupler, a first polarization controller, and an optical fiber; Step S5: Output an optical frequency comb formed by splicing multi-wavelength seed light and multi-wavelength pump light at the second optical coupler through the forward Brillouin scattering effect of the optical fiber; The splicing between the multi-wavelength seed light and the multi-wavelength pump light needs to reasonably consider the frequency difference and combs between the two lasers. The wavelengths of the lasers used here are all reasonable values after multiple adjustments; Step S6: Adjust the first polarization controller and the second polarization controller to optimize the polarization state matching between the pump light and the seed light, so that the Brillouin scattering effect reaches the maximum value.

[0020] Further, in Step S1, the pump light excites the forward Brillouin scattering effect inside the optical fiber. The interaction between this forward Brillouin scattering and the seed light can achieve energy and phase transfer through the stimulated scattering process, assign the spectral characteristics of the pump light to the seed light, and the seed light performs phase modulation through the already excited forward Brillouin scattering effect to replicate the combs and frequency intervals of the pump light.

[0021] Further, in Step S2, the drive signal of the first electro-optic modulator is a cosine signal with a frequency of f output by the first signal generator, and the magnitude of the frequency f is equal to the resonance frequency of the R 0,m acoustic mode of the forward Brillouin scattering. The number of combs with the same power generated by the first electro-optic modulator is a positive integer N, and the drive signal of the second electro-optic modulator is a cosine signal with a frequency of N times f output by the second signal generator.

[0022] In addition, the present invention also provides an optical frequency comb generating device based on Brillouin scattering and an electro-optic modulator, as Figure 1 shown. The optical frequency comb generating device based on Brillouin scattering and an electro-optic modulator includes: a first laser, a second laser, a first electro-optic modulator, a second electro-optic modulator, a first signal generator, a second signal generator, an optical fiber amplifier, an optical isolator, a first optical coupler, a second optical coupler, a first polarization controller, a second polarization controller, and an optical fiber.

[0023] Furthermore, the first laser and the second laser adopt narrow linewidth semiconductor lasers.

[0024] Furthermore, the first optical coupler is a 1×2 optical coupler, and the second optical coupler is a 2×2 optical coupler.

[0025] Furthermore, the optical fiber adopts an optical fiber with a forward Brillouin scattering coefficient greater than 3 before hundreds of MHz.

[0026] Furthermore, the first electro-optic modulator and the second electro-optic modulator are cascaded to form a cascaded electro-optic modulator. The first electro-optic modulator is a Mach-Zehnder modulator, and the second electro-optic modulator is a dual-parallel Mach-Zehnder modulator.

[0027] Furthermore, a suitable electro-optic modulator is added to the cascaded electro-optic modulator to align the power near the central wavelength and increase its flatness.

[0028] Furthermore, the frequency interval of the pump light is the resonance frequency of the highest peak of the forward stimulated Brillouin scattering of the optical fiber.

[0029] The optical fiber in the embodiment of the present invention adopts a HNLF single-mode optical fiber with a length of 100 km, and the overall loss of the optical fiber is about 2 dB. This device generates an optical frequency comb with a coverage range exceeding 6 GHz and a frequency interval of 129.5 MHz through the combination of a laser, an electro-optic modulator, and an optical fiber. The result is as Figure 3 . As the frequency interval expands, the frequency coverage range will continue to expand. Currently, 6 GHz is sufficient to cover the needs of most manufacturers and measurements.

[0030] The above is only the preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions within the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those of ordinary skill in the art, several improvements and refinements made without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A method for generating an optical frequency comb based on Brillouin scattering and an electro-optic modulator, characterized in that It includes the following steps: Step S1: Use a first laser and a second laser to generate pump light and seed light respectively; Step S2: The first laser cascades a first electro-optic modulator and a second electro-optic modulator to modulate the pump light in Step S1 into multi-wavelength pump light; Step S3: Amplify the multi-wavelength pump light in Step S2 through an optical fiber amplifier to make the Brillouin scattering of the multi-wavelength pump light reach the threshold for the optical fiber to generate Brillouin scattering, and ensure the unidirectional transmission of the multi-wavelength pump light through an optical isolator; Step S4: Process the seed light in Step S1 through a second polarization controller, and inject the processed seed light and the multi-wavelength pump light passing through the optical isolator in Step S3 into a Sagnac loop circuit composed of a first optical coupler, a second optical coupler, a first polarization controller, and an optical fiber; Step S5: Output an optical frequency comb spliced by multi-wavelength seed light and multi-wavelength pump light at the second optical coupler through the forward Brillouin scattering effect of the optical fiber; Step S6: Adjust the first polarization controller and the second polarization controller to optimize the polarization state matching between the pump light and the seed light, so that the Brillouin scattering effect reaches the maximum value.

2. The method for generating an optical frequency comb based on Brillouin scattering and an electro-optic modulator according to claim 1, wherein In the said Step S1, the pump light excites the forward Brillouin scattering effect inside the optical fiber, and the seed light performs phase modulation through the excited forward Brillouin scattering effect to replicate the comb teeth and frequency intervals of the pump light.

3. The optical frequency comb generation method based on Brillouin scattering and an electro-optic modulator according to claim 1, characterized in that, In the step S2, the driving signal of the first electro-optic modulator is a cosine signal with a frequency of f output by the first signal generator, and the magnitude of the frequency f is equal to the resonance frequency R of the forward Brillouin scattering acoustic mode. The first electro-optic modulator generates a comb with the same power and the number of teeth is a positive integer N. The driving signal of the second electro-optic modulator is a cosine signal with a frequency of N times f output by the second signal generator. 0,m The number of teeth of the comb generated by the first electro-optic modulator is a positive integer N, and the driving signal of the second electro-optic modulator is a cosine signal with a frequency of N times f output by the second signal generator.

4. An optical frequency comb generation device based on Brillouin scattering and an electro-optic modulator, characterized in that The optical frequency comb generating device based on Brillouin scattering and electro-optic modulator is applied to the optical frequency comb generating method based on Brillouin scattering and electro-optic modulator as described in any one of Claims 1-3. The optical frequency comb generating device based on Brillouin scattering and electro-optic modulator includes: a first laser, a second laser, a first electro-optic modulator, a second electro-optic modulator, a first signal generator, a second signal generator, an optical fiber amplifier, an optical isolator, a first optical coupler, a second optical coupler, a first polarization controller, a second polarization controller, and an optical fiber.

5. The optical frequency comb generation device based on Brillouin scattering and an electro-optic modulator according to claim 4, wherein The first laser and the second laser adopt narrow linewidth semiconductor lasers.

6. The optical frequency comb generation device based on Brillouin scattering and an electro-optic modulator according to claim 4, characterized in that, The first optical coupler is a 1×2 optical coupler, and the second optical coupler is a 2×2 optical coupler.

7. The optical frequency comb generation device based on Brillouin scattering and an electro-optic modulator according to claim 4, wherein The optical fiber adopts an optical fiber with a forward Brillouin scattering coefficient greater than 3 before hundreds of MHz.

8. The optical frequency comb generation device based on Brillouin scattering and an electro-optic modulator according to claim 4, characterized in that, The first electro-optic modulator and the second electro-optic modulator are cascaded to form a cascaded electro-optic modulator. The first electro-optic modulator is a Mach-Zehnder modulator, and the second electro-optic modulator is a dual-parallel Mach-Zehnder modulator.

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