A relative intensity noise suppression device for optical frequency combs

Abstract

A relative intensity noise suppression device for an optical frequency comb includes a temperature control device, a mode-locked laser, a beam splitter, an optical isolator, and an adjustable bandpass filter. The mode-locked laser is placed on the temperature control device, and the input end of the optical isolator is optically connected to the fiber output end of the mode-locked laser through the first output port of the beam splitter. The input end of the adjustable bandpass filter is optically connected to the output end of the optical isolator. This invention does not require changes to the basic structure of existing optical frequency comb systems; it achieves significant suppression of relative intensity noise through simple beam splitting and filtering processes, making it simple to operate and easy to implement.

Description

Technical Field

[0001] This utility model relates to the field of optical equipment technology, and in particular to a relative intensity noise suppression device for optical frequency combs. Background Technology

[0002] An optical frequency comb is an ultra-precise optical scale that appears in the frequency domain as a series of discrete, equally spaced, and phase-coherent segments. Its revolutionary significance lies in establishing a connection between optical frequencies (~10⁻⁶). 15 Hz) and microwave frequencies (~10 9 It serves as a bridge between (Hz) and provides core tools for fields such as precision spectroscopy, optical atomic clocks, absolute distance measurement, and high-speed optical communication.

[0003] Currently, the most mainstream and efficient technology for generating optical frequency combs is the mode-locked laser (MLL). A mode-locked laser, through active or passive methods, keeps the phases of all longitudinal modes within the laser cavity synchronized (locked), thereby generating a series of periodic ultrashort pulses in the time domain. According to the Fourier transform principle, the equally spaced pulse sequence in the time domain corresponds precisely to a series of equally spaced coherent spectral lines in the frequency domain, i.e., the optical frequency comb.

[0004] However, whether used as a basic research tool or applied in industrial settings, the performance of optical frequency combs is ultimately limited by their noise characteristics. Relative Intensity Noise (RIN) is a crucial parameter, used to quantify the random fluctuations in laser output power, defined as the normalized intensity of the power noise within a specified bandwidth. For optical frequency combs generated by mode-locked lasers, excessively high RIN directly translates into jitter in the comb tooth amplitude, introducing errors in numerous applications: in precision spectroscopy, it reduces the measurement signal-to-noise ratio of the absorbed signal; in optical communication, it worsens the bit error rate when used as a multi-wavelength light source; and in microwave photonics, it affects the signal-to-noise ratio of the microwave signal generated after photoelectric conversion. The root causes of RIN include spontaneous emission from the laser gain medium, fluctuations in the pump source, nonlinear effects within the cavity, and environmental vibrations. Therefore, analyzing and suppressing the relative intensity noise of mode-locked lasers is a key focus for improving the performance of optical frequency comb systems and propelling them from the laboratory to wider applications. Utility Model Content

[0005] This invention provides a relative intensity noise suppression device for optical frequency combs to solve the technical problems mentioned in the background art.

[0006] To achieve the above objectives, the technical solution of this utility model is implemented as follows: This utility model provides a relative intensity noise suppression device for optical frequency combs, including a temperature control device, a mode-locked laser, a beam splitter, an optical isolator, and an adjustable bandpass filter; The mode-locked laser is placed on a temperature control device. The input end of the beam splitter is optically connected to the fiber output end of the mode-locked laser, and the first output port of the beam splitter is optically connected to the input end of the optical isolator. The input end of the adjustable bandpass filter is optically connected to the output end of the optical isolator.

[0007] Furthermore, the relative intensity noise suppression device of the optical frequency comb also includes a time-delay fiber or a doped fiber, the input end of which is optically connected to the second output port of the beam splitter.

[0008] Furthermore, the length of the delay fiber is 1 to 5 km.

[0009] Furthermore, the optical frequency comb relative intensity noise suppression device also includes a praseodymium-doped fiber amplifier and a relative intensity noise testing system; The input of the praseodymium-doped fiber amplifier is optically connected to the output of the tunable bandpass filter, and the input of the relative intensity noise testing system is optically connected to the output of the praseodymium-doped fiber amplifier.

[0010] Furthermore, the optical frequency comb relative intensity noise suppression device also includes a control unit, which includes a current controller and a bias voltage controller, both of which are electrically connected to the mode-locked laser.

[0011] The beneficial effects of this utility model are: 1. This utility model discloses a relative intensity noise suppression device for optical frequency combs. Without changing the basic structure of the existing optical frequency comb system, it can achieve significant suppression of relative intensity noise simply by using a beam splitter and an adjustable bandpass filter. It is easy to operate and implement. 2. This utility model adopts a combination of an adjustable bandpass filter and a praseodymium-doped fiber amplifier to ensure the stability of the output power of the mode-locked laser, and can effectively obtain a single longitudinal mode and realize power amplification; 3. This utility model uses a beam splitter to divide the output light of the mode-locked laser into two different paths, and generates random distributed feedback after Rayleigh backscattering effect in the delay fiber, which effectively reduces the relative intensity noise of the mode-locked laser and improves the spectral purity and stability of the mode-locked laser. Attached Figure Description Figure 1 This is a schematic diagram of the structure of this utility model; Figure 2 The relative intensity noise result in step three of this utility model specific embodiment; Figure 3This is the relative intensity noise result for step four in a specific embodiment of this utility model.

[0012] Explanation of reference numerals in the attached figures: 1. Temperature control device; 2. Mode-locked laser; 3. Beam splitter; 4. Delay fiber; 5. Optical isolator; 6. Adjustable bandpass filter; 7. Praseodymium-doped fiber amplifier; 8. Relative intensity noise testing system. Detailed Implementation

[0013] To facilitate understanding of this utility model, a more complete description will be given below with reference to the accompanying drawings. The drawings illustrate preferred embodiments of this utility model. However, this utility model can be implemented in many other different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this utility model.

[0014] It should also be noted that in the embodiments of this application, the same reference numerals are used to represent the same component or part. For the same part in the embodiments of this application, the reference numerals may only be used to mark one part or component as an example. It should be understood that the reference numerals are also applicable to other identical parts or components.

[0015] Reference Figure 1 This application provides an optical frequency comb relative intensity noise suppression device, including a temperature control device 1 (Thermoelectric Cooler, TEC), a mode-locked laser 2, a beam splitter 3, an optical isolator 5 (optoelectronic isolator, ISO), and an adjustable bandpass filter 6 (Optical Band Pass Filter, OBPF). The mode-locked laser 2 is placed on the temperature control device 1, which is used to control the operating temperature of the mode-locked laser 2 within a set temperature range. The input end of the beam splitter 3 is optically connected to the fiber output end of the mode-locked laser 2, and the first output port of the beam splitter 3 is optically connected to the input end of the optical isolator 5. The input end of the tunable bandpass filter 6 is optically connected to the output end of the optical isolator 5. To achieve single longitudinal mode output, the center wavelength of the bandpass filter 6 is precisely tuned to resonate with the target longitudinal mode in the optical frequency comb, thereby isolating it from the dense longitudinal mode group and achieving selective passage of signals in a specific frequency band.

[0016] This invention does not require any changes to the basic structure of the existing optical frequency comb system. It can achieve significant suppression of relative intensity noise simply by using beam splitter 3 and adjustable bandpass filter 6. It is easy to operate and implement.

[0017] In some embodiments, the beam splitter 3 may be a variety of beam splitters 3 with different splitting ratios, such as 50:50 or 10:90 beam splitters 3.

[0018] In some embodiments, the optical frequency comb relative intensity noise suppression device further includes a time-delay fiber 4, the input end of which is optically connected to the second output port of the beam splitter 3.

[0019] This invention achieves relative intensity noise suppression of the mode-locked laser 2 by adding a delay fiber 4 to the optical frequency comb relative intensity noise testing device and utilizing the Rayleigh backscattering effect generated in the delay fiber 4. Specifically, since Rayleigh scattering in the Rayleigh backscattering effect occurs randomly, and the position and intensity of the scattering point are also random, Rayleigh scattering in the longer delay fiber 4 can form a random distributed feedback. This feedback plays a decisive role in the mode selection, phase noise conversion, and carrier number fluctuation suppression of the mode-locked laser 2, and can effectively reduce the relative intensity noise of the mode-locked laser 2.

[0020] This invention uses a beam splitter 3 to divide the output light of the mode-locked laser 2 into two different paths, and generates a random distributed feedback after Rayleigh backscattering effect in the delay fiber 4. This effectively reduces the relative intensity noise of the mode-locked laser 2 and improves the spectral purity and stability of the mode-locked laser 2.

[0021] In some embodiments, the length of the delay fiber 4 is 1 to 5 km, such as 1 km, 2 km, 5 km, etc.

[0022] In some embodiments, the delay fiber 4 in the relative intensity noise suppression device of the optical frequency comb can also be replaced with a doped fiber, and the input end of the doped fiber is optically connected to the second output port of the beam splitter 3.

[0023] In some embodiments, the optical frequency comb relative intensity noise suppression device further includes a praseodymium-doped fiber amplifier 7 (PDFA) and a relative intensity noise testing system 8; The input of the praseodymium-doped fiber amplifier 7 is optically connected to the output of the adjustable bandpass filter 6, and the input of the relative intensity noise test system 8 is optically connected to the output of the praseodymium-doped fiber amplifier 7.

[0024] This invention employs a combination of an adjustable bandpass filter 6 and a praseodymium-doped fiber amplifier 7 to ensure the stability of the output power of the mode-locked laser 2, effectively obtaining a single longitudinal mode and achieving power amplification. The praseodymium-doped fiber amplifier 7 is used to amplify the power of the single longitudinal mode output from the adjustable bandpass filter 6 to a specified optical power. The relative intensity noise testing system 8 is used for testing relative intensity noise.

[0025] In some embodiments, the optical frequency comb relative intensity noise suppression device further includes a control unit, which includes a current controller and a bias voltage controller, both of which are electrically connected to the mode-locked laser 2.

[0026] The working process of this utility model is as follows: Step 1: Temperature control device 1 controls the operating temperature of mode-locked laser 2 to approximately 25°C; Step 2: Turn on the control unit and adjust the current value of the current controller and the voltage value of the bias voltage controller to adjust the current and voltage of the mode-locked laser 2 to the set working range so that the mode-locked laser 2 is at the mode-locked working point; Step 3: The output light from mode-locked laser 2 is split into two separate paths (e.g., paths A and B) using beam splitter 3. The fiber output port of mode-locked laser 2 is connected to the input port of beam splitter 3. The second output port of beam splitter 3 is not connected. The first output port of beam splitter 3 is optically connected to the input of optical isolator 5. The insertion loss of optical isolator 5 is 3 dB. The output of optical isolator 5 is connected to the input of tunable bandpass filter 6. The wavelength range of tunable bandpass filter 6 covers 1260 nm to 1360 nm, and the bandwidth is 160 GHz. A single longitudinal mode is obtained through tunable bandpass filter 6. The output of tunable bandpass filter 6 is optically connected to the input of praseodymium-doped fiber amplifier 7. The gain of praseodymium-doped fiber amplifier 7 can reach 20 dB, and the maximum output power is 16 dBm. The obtained single longitudinal mode is amplified to a suitable optical power by a praseodymium-doped fiber amplifier 7 and then transmitted to a relative intensity noise testing system 8. The relative intensity noise result of the single longitudinal mode is obtained through testing by the relative intensity noise testing system 8. This result is used as the reference curve for subsequent verification of suppressing the relative intensity noise of the mode-locked laser 2. The results are as follows: Figure 2 As shown; Step 4: Connect the second output port of beam splitter 3 from step 3 to the input of delay fiber 4. The output of delay fiber 4 does not need to be connected. Connect the first output port of beam splitter 3 to the input of optical isolator 5. Connect the output of optical isolator 5 to the input of adjustable bandpass filter 6. Connect the output of adjustable bandpass filter 6 to the input of praseodymium-doped fiber amplifier 7. Amplify the obtained single longitudinal mode to a suitable optical power using praseodymium-doped fiber amplifier 7, and then send it to relative intensity noise testing system 8. The relative intensity noise result of the single longitudinal mode is obtained through testing by relative intensity noise testing system 8. The result is as follows: Figure 3 As shown. Comparing this result with the baseline curve obtained in step three, it is found that the optical frequency comb relative intensity noise suppression device can suppress the relative intensity noise of mode-locked laser 2 in the low frequency band.

[0027] The above description is merely a specific embodiment of this utility model, but the protection scope of this utility model is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this utility model should be included within the protection scope of this utility model. Furthermore, the technical solutions of the various embodiments of this utility model can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the protection scope claimed by this utility model. Therefore, the protection scope of this utility model should be determined by the protection scope of the claims.

Claims

1. An optical frequency comb relative intensity noise suppression device, characterized by, Includes a temperature control device (1), a mode-locked laser (2), a beam splitter (3), an optical isolator (5), and an adjustable bandpass filter (6); The mode-locked laser (2) is placed on the temperature control device (1). The input end of the beam splitter (3) is optically connected to the optical fiber output end of the mode-locked laser (2). The first output port of the beam splitter (3) is optically connected to the input end of the optical isolator (5). The input end of the adjustable bandpass filter (6) is optically connected to the output end of the optical isolator (5).

2. The optical frequency comb relative intensity noise suppression device of claim 1, wherein, It also includes a time-delay fiber (4), the input end of which is optically connected to the second output port of the beam splitter (3).

3. The optical frequency comb relative intensity noise suppression device of claim 2, wherein, The length of the delay fiber (4) is 1~5km.

4. The optical frequency comb relative intensity noise suppression device of claim 1, wherein, It also includes a doped fiber, the input end of which is optically connected to the second output port of the beam splitter (3).

5. The optical frequency comb relative intensity noise suppression device of claim 1, wherein, It also includes a praseodymium-doped fiber amplifier (7) and a relative intensity noise testing system (8); The input end of the praseodymium-doped fiber amplifier (7) is optically connected to the output end of the adjustable bandpass filter (6), and the input end of the relative intensity noise test system (8) is optically connected to the output end of the praseodymium-doped fiber amplifier (7).

6. The optical frequency comb relative intensity noise suppression device of claim 1, wherein, It also includes a control unit, which includes a current controller and a bias voltage controller, both of which are electrically connected to the mode-locked laser (2).

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