Broadband low-noise microwave photonic link

Abstract

The application relates to a broadband low-noise microwave photon link, comprising a low-noise light source, a modulator connected with the low-noise light source and a photoelectric detector connected with the modulator, the low-noise light source is used for generating a laser signal, and the laser signal is sequentially subjected to optical amplification and narrow-band photon filtering, so that a high-power low-noise laser signal is output as an optical carrier of an electro-optic intensity modulator. In the application, the RIN noise of the laser source is suppressed by adopting the combination of optical amplification and optical filtering, the high-power low-noise laser signal is output, the noise coefficient of the microwave photon link can be reduced, and the application can be used in application fields such as radars, electronic warfare, communication, navigation and monitoring.

Description

Technical Field

[0001] This invention belongs to the field of microwave photonics technology and relates to a broadband low-noise microwave photonic link. Background Technology

[0002] Microwave photonics technology is a new technology formed by the deep integration of photonics and microwave technologies. It possesses the flexibility and ubiquity of microwave technology, as well as the broadband and low transmission loss advantages of photonics. Therefore, microwave photonics technology has been widely studied both domestically and internationally. Microwave photonics technology has many advantages, including wide operating frequency band, large instantaneous bandwidth, long transmission distance, strong parallel processing capability, light weight, high-density integration capability, and resistance to electromagnetic interference. Therefore, microwave photonics technology has great application potential in dual-use fields such as radar, communication, electronic warfare, and measurement and control.

[0003] While microwave photonics technology offers numerous advantages, the core components—lasers, modulators, and photodetectors—are all active devices. These active devices introduce additional noise during the electro-optical-photoelectric conversion of microwave signals, which is further amplified by optical amplifiers, thus worsening noise performance. High noise levels reduce key performance indicators such as system sensitivity, dynamic range, and detection accuracy. Therefore, noise suppression is crucial for achieving high-performance microwave photonics systems. Literature reports solutions such as low-biased modulators or balanced detectors to reduce the noise figure; however, low-biased modulators significantly sacrifice bandwidth, and balanced detectors not only increase system complexity but also limit the range of detectors, thereby restricting the application of microwave photonics technology. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is to provide a broadband low-noise microwave photonic link.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A broadband low-noise microwave photonic link includes a low-noise light source, a modulator connected to the low-noise light source, and a photodetector connected to the modulator. The low-noise light source is used to generate a laser signal and sequentially perform optical amplification and narrowband photonic filtering on the laser signal to output a high-power, low-noise laser signal as the optical carrier of the electro-optic intensity modulator.

[0007] Furthermore, the low-noise light source includes

[0008] Laser assembly, used to output laser signals;

[0009] An optical amplifier is used to amplify the power of the laser signal output from a laser component, resulting in a high-power laser signal.

[0010] An optical filter, specifically a narrowband photonic filter, is used for signal gating and noise suppression of the high-power laser signal output from the optical amplification unit, resulting in a high-power, low-noise laser signal.

[0011] The wavelength locking unit is used to adjust the wavelength of the laser output by the laser component according to the power change of the laser signal output after filtering by the narrowband photonic filter, thereby locking the wavelength of the laser signal output by the laser component.

[0012] Furthermore, the laser assembly includes a high-power, low-noise DFB laser, an automatic temperature control circuit for the laser, and an automatic power control circuit for the laser.

[0013] Furthermore, the method for controlling the wavelength of the laser signal output by the wavelength-locking unit to lock the laser assembly includes the following steps:

[0014] S101, High-power low-noise DFB laser power-on startup;

[0015] S102. Increase the cooling current of the semiconductor cooler in the automatic temperature control circuit of the laser;

[0016] S103. Detect the power change of the laser signal output after filtering by the narrowband photonic filter. If the power of the laser signal increases, return to step S102; otherwise, proceed to step S104.

[0017] S104. Reduce the cooling current of the semiconductor cooler in the automatic temperature control circuit of the laser;

[0018] S105. Detect the power change of the laser signal output after filtering by the narrowband photonic filter. If the power of the laser signal increases, return to step S104; otherwise, return to step S102.

[0019] Furthermore, the optical amplifier is a high-power erbium-doped fiber amplifier.

[0020] Furthermore, the modulator includes an electro-optic intensity modulator and a bias control circuit; the photodetector is a broadband high-speed photodetector.

[0021] Furthermore, the passband shape of the narrowband photonic filter is a Gaussian filter shape.

[0022] Furthermore, the narrowband photonic filter includes a Mach-Zehnder interferometer and a microring resonator. The Mach-Zehnder interferometer has a first interferometer arm and a second interferometer arm. The microring resonator is optically coupled to the first interferometer arm of the Mach-Zehnder interferometer. The second interferometer arm of the Mach-Zehnder interferometer is connected to a wavelength locking unit and a modulator, respectively.

[0023] Furthermore, the narrowband photonic filter is made of silicon nitride waveguide.

[0024] Furthermore, the transfer function of the narrowband photonic filter is:

[0025]

[0026]

[0027]

[0028] Where T1(λ) represents the transmission function of the first interferometer arm of the narrowband photonic filter; T2(λ) represents the transmission function of the second interferometer arm of the narrowband photonic filter; E0(t) represents the expression for the optical signal input to the narrowband photonic filter; E1(t) represents the expression for the optical signal output from the first interferometer arm of the narrowband photonic filter; E2(t) represents the expression for the optical signal output from the second interferometer arm of the narrowband photonic filter; κ represents the optical field coupling coefficient between the microring resonator and the first interferometer arm; α represents the optical waveguide loss of the narrowband photonic filter; β represents the propagation constant of the optical waveguide; L represents the perimeter of the microring resonator; λ represents the wavelength of light; N eff This represents the effective refractive index of the optical waveguide in a narrowband photonic filter.

[0029] In this invention, using optical amplification to increase the optical power of the laser source can significantly improve the transmission efficiency of the microwave optical link, by an order of magnitude compared to conventional levels. Employing optical filtering in the pre-stage of electro-optic modulation to suppress RI N noise from the laser source not only offers the advantage of high noise suppression, improving the noise figure by more than an order of magnitude, but also overcomes the sub-octave band operation limitation of traditional low-bias noise reduction schemes, enabling large-bandwidth operation across octave bands. Therefore, the broadband low-noise microwave photonic link of this embodiment can play an important role in applications such as radar, electronic warfare, communication, navigation, and monitoring. Attached Figure Description

[0030] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0031] Figure 1 This is a functional block diagram of one embodiment of the broadband low-noise microwave photonic link of the present invention.

[0032] Figure 2 This is a schematic diagram of a narrowband photonic filter structure.

[0033] Figure 3 A flowchart for locking the wavelength of the laser signal output by the laser component.

[0034] Figure 4 This is a schematic diagram simulating the relationship between the RF transmission efficiency of an optical link and the photocurrent under orthogonal bias conditions.

[0035] Figure 5 This is a schematic diagram of the spectral process by which optical amplification and filtering improves the relative intensity noise of a light source.

[0036] Figure 6 A comparison of the relationship between link noise figure and photocurrent under different RIN noise conditions.

[0037] Figure 7 The amplitude-frequency response curve of the narrowband photonic filter obtained from simulation is shown.

[0038] Figure 8 The graph shows a comparison of the response curves of T2(λ) under different optical field coupling coefficients κ.

[0039] Figure 9 The simulation results show the comparison of the noise figure of the microwave photonic link after suppressing RIN noise.

[0040] Laser assembly-1; Optical amplifier-2; Optical filter-3; Wavelength locking unit-4; Electro-optic intensity modulator-5; Bias control circuit-6; Photodetector-7; First interferometer-31a; Second interferometer-31b; Micro-ring resonator-32. Detailed Implementation

[0041] The following specific examples illustrate the implementation of the present invention. The illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0042] Please see Figure 1 , Figure 1 This is a structural block diagram of one embodiment of the broadband low-noise microwave photonic link of the present invention. The broadband low-noise microwave photonic link of this embodiment includes a low-noise light source, a modulator connected to the low-noise light source, and a photodetector 7 connected to the modulator. The low-noise light source is used to generate a laser signal, and the laser signal is sequentially optically amplified and narrowband photonic filtered to output a high-power, low-noise laser signal as the optical carrier of the electro-optic intensity modulator 5. The modulator includes an electro-optic intensity modulator 5 and a bias control circuit 6; the electro-optic intensity modulator 5 is a lithium niobate electro-optic intensity modulator (EOM), and the photodetector 7 is a broadband high-speed photodetector.

[0043] Please continue reading. Figure 1The low-noise light source may include a laser assembly 1, an optical amplifier 2, an optical filter 3, and a wavelength locking unit 4. The laser is used to output a laser signal; in this embodiment, the laser assembly 1 includes a high-power low-noise DFB laser (hereinafter referred to as a DFB laser), an automatic temperature control (ATC) circuit, and an automatic power control (APC) circuit; the above structure is a conventional structure of the laser assembly 1 and will not be described in detail here. The optical amplifier 2 is used to amplify the laser signal output by the DFB laser, outputting a high-power laser signal. In this embodiment, the optical amplifier 2 is a high-power erbium-doped fiber amplifier (EDFA). To suppress noise in low-frequency signals, the bandwidth of the optical filter 3 needs to be sufficiently narrow to suppress noise in the near-carrier end and the frequency region far from the carrier. The narrow filter bandwidth requires real-time adjustment of the laser wavelength to ensure passband locking. Typically, the passband shape of the optical filter 3 is a Gaussian filter shape. The wavelength locking unit 4 can control the operating temperature of the DFB laser in real time by detecting the power change of the output optical signal of the optical filter 3, thereby adjusting the wavelength of the output optical signal of the DFB laser to achieve the final wavelength locking purpose.

[0044] Optical filter 3 is used to suppress RIN noise (relative intensity noise) in the DFB laser. This requires optical filter 3 to have a narrow passband width, high out-of-band rejection, and low passband insertion loss, while also ensuring that the parasitic passband is far away or sufficiently low. Therefore, in this embodiment, the optical filter 3 is a narrowband photonic filter. The narrowband photonic filter is used for signal gating and noise suppression of the high-power laser signal output from the optical amplification unit, outputting a high-power, low-noise laser signal. The passband shape of the narrowband photonic filter (OF) is a Gaussian filter shape, and the narrowband photonic filter can be a grating filter, thin-film filter, etc.

[0045] Please see Figure 2 In this embodiment, the narrowband photonic filter includes a Mach-Zehnder interferometer (MZI) and a microring resonator 32. The Mach-Zehnder interferometer has a first interferometer arm 31a and a second interferometer arm 31b. The microring resonator 32 is optically coupled to the first interferometer arm 31a of the Mach-Zehnder interferometer. The second interferometer arm 31b of the Mach-Zehnder interferometer is connected to the wavelength locking unit 4 and the electro-optic intensity modulator 5, respectively.

[0046] Please see Figure 3The wavelength locking unit 4 is used to adjust the wavelength of the laser output from the laser component 1 according to the power change of the laser signal output after filtering by the narrowband photonic filter, thereby locking the wavelength of the laser signal output by the laser component 1. To achieve locking between the laser output frequency and the center frequency of the narrowband photonic filter, the wavelength locking unit 4 in this embodiment employs the maximum power approximation method. By detecting the output power of the narrowband photonic filter, it adjusts the TEC cooling current of the laser component 1, thereby changing the die temperature of the DFB laser in real time, and thus adjusting the wavelength of the DFB laser output light signal in real time to achieve locking with the center wavelength of the filter passband. The control method for locking the wavelength of the laser signal output by the wavelength locking unit 4 includes the following steps:

[0047] S101, Laser assembly 1 is powered on and started.

[0048] The S102 and ATC circuits increase the cooling current of the semiconductor cooler (TEC). At this time, the die temperature of the DFB laser decreases, and the frequency of the laser signal output by the DFB laser increases, i.e., the wavelength decreases.

[0049] S103, Wavelength locking unit 4 detects the power change of the laser signal output after filtering by the narrowband photonic filter. If the power of the laser signal increases, it indicates that the wavelength of the laser signal output by the DFB laser has decreased and is closer to the center wavelength of the narrowband photonic filter passband. The process then returns to step S102 to further increase the cooling current of the TEC, causing the wavelength of the laser signal output by the DFB laser to continue decreasing. Otherwise, it indicates that the wavelength of the laser signal output by the DFB laser has decreased and deviated from the center wavelength of the narrowband photonic filter passband. The process then executes step S104 to decrease the cooling current of the TEC.

[0050] The S104 and ATC circuits reduce the cooling current of the TEC. At this time, the die temperature of the DFB laser increases, and the frequency of the laser signal output by the DFB laser decreases, that is, the wavelength increases.

[0051] S105. Wavelength locking unit 4 detects the power change of the laser signal output after filtering by the narrowband photonic filter. If the power of the laser signal increases, it indicates that the wavelength of the laser signal output by the DFB laser has increased and is closer to the center wavelength of the narrowband photonic filter passband. The process then returns to step S104 to further reduce the cooling current of the TEC, causing the wavelength of the laser signal output by the DFB laser to continue increasing. Otherwise, it indicates that the wavelength of the laser signal output by the DFB laser has increased and deviated from the center wavelength of the narrowband photonic filter passband. The process then returns to step S102 to increase the cooling current of the TEC.

[0052] In this embodiment, the optical signal output by the DFB laser (frequency f)c First, the signal is amplified by a high-power erbium-doped fiber amplifier. After amplification, it is fed into a narrowband photonic filter for signal gating and noise suppression. Then, it is used as an optical carrier and fed into an electro-optic intensity modulator 5. The radio frequency signal (frequency f) RF In the electro-optic intensity modulator 5, the light is modulated onto the optical carrier via the electro-optic effect. After transmission through the optical link, it is finally sent to the photodetector 7, where the optical signal is converted into an electrical microwave signal. This link enables low-noise transmission of broadband microwave signals. In this embodiment, the optical amplifier 2 amplifies the power of the laser output signal. This reduces the degradation of the light source noise floor and ensures that after the laser source noise is suppressed by the optical filter 3, there is still sufficient optical power to enter the electro-optic intensity modulator 5, thus obtaining a high-performance link under shot noise constraints. For the spectral processing procedure, please refer to [link to spectral processing details]. Figure 4 As shown.

[0053] The principle of this embodiment will be explained in detail below. The optical field expression of the output optical carrier signal of the DFB laser is set as follows:

[0054]

[0055] In the formula P LD f represents the optical power of the output optical signal of the DFB laser. c This represents the frequency of the output optical signal of the DFB laser. Under the influence of noise, the output optical field E of the DFB laser... opt (t) can be expressed as:

[0056]

[0057] In the formula, n RIN (t) represents the RIN noise of the DFB laser.

[0058] After the optical signal is amplified by a high-power erbium-doped fiber amplifier, the output optical field E EDFA (t) can be expressed as:

[0059]

[0060] In the formula, g EDFA Indicates the gain of a high-power erbium-doped fiber amplifier; n sp (t) represents the spontaneous emission noise of a high-power erbium-doped fiber amplifier.

[0061] The amplified signal is fed into a narrowband photonic filter for signal gating and noise suppression. The output signal E after optical filtering is... OF (t) can be expressed as:

[0062]

[0063] In the formula, h(t) represents the response function of optical filter 3.

[0064] The optical signal, after noise suppression by a narrowband photonic filter, is used as an optical carrier and fed into the electro-optic intensity modulator 5 to modulate the radio frequency signal V. RF (t). Radio frequency signal V RF (t) can be expressed by the formula:

[0065] V RF (t)=V RF cos(2πf RF t)

[0066] In the formula, f RF This indicates the frequency of the radio frequency signal.

[0067] After radio frequency signal V RF (t) Modulated output optical field E MZM (t) can be expressed as:

[0068]

[0069] In the formula, L MZM V represents the optical insertion loss of the electro-optic intensity modulator 5; RF Indicates radio frequency signal V RF Voltage at (t); V B V represents the DC bias voltage of the electro-optic intensity modulator 5; πRF V represents the radio frequency half-wave voltage of the electro-optic intensity modulator 5. πDC This represents the DC half-wave voltage of the electro-optic intensity modulator 5.

[0070] The modulated signal is sent to photodetector 7, and the output signal I after photodetection is... pd (t) can be represented as:

[0071]

[0072] In the formula, E represents the responsivity of photodetector 7. MZM * (t) represents E MZM The complex conjugate of (t).

[0073] Based on the above formula, the electro-optical conversion efficiency G of the radio frequency signal can be further calculated. RF It can be represented as:

[0074]

[0075] In the formula, L OF Z represents the insertion loss of a narrowband photonic filter.2 =Z in ×Z out Z in Z represents the input impedance of the optical link; out The output impedance of the optical link can be directly taken as Z = Z0. in =Z out .

[0076] Let the DC photocurrent I of photodetector 7 dc =P LD L MZM G EDFA L OF / 2, for a conventional electro-optic intensity modulator 5, the RF half-wave voltage is V πRF =5V, RF impedance Z=50Ω. Please refer to [link / reference]. Figure 5 This is a schematic diagram illustrating the simulation of the relationship between the RF transmission efficiency of an optical link and the photocurrent under orthogonal bias conditions; where, Figure 5 (a) is a schematic diagram of the spectrum of the output optical signal of the DFB laser. Figure 5 (b) is a schematic diagram of the spectrum of the output optical signal after amplification by optical amplifier 2. Figure 5 (c) is a schematic diagram of the spectrum of the output optical signal after filtering by optical filter 3.

[0077] For this microwave optical transmission link, the noise figure is a crucial parameter characterizing its noise properties. To analyze the noise figure, it is first necessary to analyze the noise sources and transmission characteristics. The main noise sources in the microwave optical transmission link include shot noise from the photodetector 7, input and output thermal noise, RIN noise introduced by the DFB laser, and spontaneous emission noise introduced by the erbium-doped fiber amplifier. Since the microwave optical transmission link has high optical power, laser RIN noise will dominate under high power conditions. Therefore, this scheme focuses on suppressing laser RIN noise to reduce the link noise figure.

[0078] The noise figure NF of a microwave optical transmission link can be expressed as:

[0079]

[0080]

[0081] Among them, SNR in The input signal-to-noise ratio (SNR) of the radio frequency signal for the electro-optic intensity modulator 5. out N represents the radio frequency output signal-to-noise ratio of photodetector 7. out To reduce the output noise floor of photodetector 7; κ Bdenoted by Boltzmann constant; T is the noise temperature of the optical link; B is the noise bandwidth of the optical link; RIN(f) represents the noise distribution of the laser after amplification by optical amplifier 2 and filtering by optical filter 3; q represents the charge constant.

[0082] Please see Figure 6 The figure shows a comparison of the link noise figure with photocurrent under different RIN noise conditions. As can be seen from the figure, when the RIN noise introduced by the light source in the link is sufficiently suppressed (for example, RIN noise is considered sufficiently suppressed if it is 10 dB or more lower than shot noise), under shot noise-limited conditions, the link transmission efficiency and better noise characteristics can be obtained by increasing the light source power.

[0083] In this embodiment, a Mach-Zehnder interferometer and a micro-ring resonator 32 are used to construct an optical filter 3. The frequency response of the optical filter 3 can be expressed by the following formula:

[0084]

[0085] In the formula, E0(t) is the expression for the optical signal input to the narrowband photonic filter; E1(t) is the expression for the optical signal output from the first interferometer arm 31a of the narrowband photonic filter; E2(t) is the expression for the optical signal output from the second interferometer arm 31b of the narrowband photonic filter; T0 is the transfer function of the micro-ring, which can be expressed as:

[0086]

[0087]

[0088]

[0089] κ represents the optical field coupling coefficient between the micro-ring resonator 32 and the first interferometer arm 31a; α represents the optical waveguide loss of the narrowband photonic filter; β represents the propagation constant of the optical waveguide; L represents the perimeter of the micro-ring resonator 32; λ represents the wavelength of light; N eff The effective refractive index of the optical waveguide of the narrowband photonic filter is represented by FSR, which represents the free spectrum range of the narrowband photonic filter and is used to characterize the frequency spacing between two adjacent passbands of the narrowband photonic filter.

[0090] The transfer function of the entire optical filter 3 can be written as:

[0091]

[0092]

[0093] In the formula, T1(λ) represents the transfer function of the first interferometer arm 31a of the narrowband photonic filter; T2(λ) represents the transfer function of the second interferometer arm 31b of the narrowband photonic filter.

[0094] Silicon nitride waveguides have great potential for high-performance photonic filtering due to their extremely low waveguide loss and small bending radius. Typical losses of silicon nitride waveguides are less than 0.1 dB / cm, coupling losses are approximately 1 dB / endface, and the effective refractive index N0 is [missing information]. eff Approximately 1.5. In this embodiment, the narrowband photonic filter is made of silicon nitride waveguide; please refer to [link / reference]. Figure 7 Here is the amplitude-frequency response curve of the simulated narrowband photonic filter, where... Figure 7 (a) is the amplitude-frequency response curve of T1(λ). Figure 7 (b) shows the amplitude-frequency response curve of T2(λ). From Figure 7 As can be seen, the optical filter 3 has a periodic amplitude-frequency response characteristic, and the amplitude-frequency response of T1(λ) is a periodic notch response, while the amplitude-frequency response of T2(λ) is a periodic bandpass response. Therefore, in this embodiment, the second interferometer arm 31b of the Mach-Zehnder interferometer is connected to the wavelength locking unit 4 and the electro-optic intensity modulator 5, thereby using the amplitude-frequency response of T2(λ) (i.e., the second interferometer arm 31b) to align the optical carrier generated by the DFB laser with the passband center frequency of the narrowband photonic filter to suppress the RIN noise of the DFB laser.

[0095] Please see Figure 8 This is a comparison of the response curves of T2(λ) under different optical field coupling coefficients κ. Figure 8 Comparative analysis shows that the smaller the optical field coupling coefficient κ, the narrower the bandwidth of the 3-passband of the optical filter, the better the selectivity, and the stronger the ability to suppress RIN noise in the low-frequency band of the DFB laser.

[0096] Because the filter response is periodic, the frequency spacing between passbands needs to be increased to avoid the influence of parasitic passbands. For example, to ensure that the microwave photonic link operates at 40 GHz, the filter passband frequency spacing can be set to 50 GHz or higher (with an effective frequency range of approximately 80% based on a noise suppression level of 30 dB), and the optical field coupling coefficient κ = 0.1. The noise-suppressed optical signal is sent as an optical carrier to the electro-optic intensity modulator 5 to modulate the radio frequency signal; finally, the modulated optical carrier radio frequency signal is transmitted through the optical fiber link to the photodetector 7 for photoelectric conversion to recover the radio frequency signal.

[0097] Figure 9 The figure shows the simulation results of the noise figure comparison for microwave photonic links. Figure 9(a) Simulation results without RIN noise suppression (the RIN noise of the DFB laser is set to a typical value of approximately -160 dBc / Hz); Figure 9 (b) shows the simulation results of the noise figure after suppressing RIN noise using optical filter 3. Figure 9 It is evident that the noise figure of the microwave photonic link is significantly improved after light source noise suppression. Moreover, the higher the photocurrent and the higher the link optical power, the greater the improvement in noise figure. Simulations show that the noise figure can be improved by more than an order of magnitude. Therefore, after using optical filter 3 to suppress the relative intensity noise of the light source, even under high optical power levels, the link noise still mainly depends on shot noise. In this way, an ultra-low noise and ultra-high efficiency microwave optical transmission link can be obtained.

[0098] This embodiment addresses the problem of severe noise degradation in microwave photonic links caused by the insufficient performance of active photonic devices such as lasers and modulators. It proposes a low-noise combined light source using a conventional DFB laser, an optical amplifier 2, and a narrowband photonic filter to achieve broadband low-noise capability in the microwave photonic link, while simultaneously achieving high-efficiency, high dynamic range transmission. In this embodiment, the optical amplifier 2 is used to increase the output optical power of the laser component 1, and the optical filter 3 is used to suppress far-end noise. This results in a high-power, low-noise, high-quality light source. This light source is then injected as an optical carrier into the electro-optic intensity modulator 5 to modulate microwave and millimeter-wave signals. This method significantly reduces link noise while ensuring broadband transmission capability of the microwave photonic link. This link has broad application potential in high-resolution radar imaging, broadband radio frequency telemetry, and broadband electronic countermeasures systems.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A broadband low-noise microwave photonic link, characterized in that: The device includes a low-noise light source, a modulator connected to the low-noise light source, and a photodetector connected to the modulator. The low-noise light source is used to generate a laser signal and sequentially perform optical amplification and narrowband photon filtering on the laser signal to output a high-power, low-noise laser signal as the optical carrier of the electro-optic intensity modulator. The low-noise light source includes A laser assembly for outputting laser signals; the laser assembly includes a high-power, low-noise DFB laser, an automatic temperature control circuit for the laser, and an automatic power control circuit for the laser. An optical amplifier is used to amplify the power of the laser signal output from a laser component, resulting in a high-power laser signal. An optical filter, which is a narrowband photonic filter, is used to perform signal gating and noise suppression on the high-power laser signal output by the optical amplification unit, and output a high-power, low-noise laser signal. as well as The wavelength locking unit is used to adjust the wavelength of the laser output by the laser component according to the power change of the laser signal output after filtering by the narrowband photonic filter, thereby locking the wavelength of the laser signal output by the laser component. The method for controlling the wavelength of the laser signal output by the laser assembly using a wavelength-locking unit includes the following steps: S101, High-power low-noise DFB laser power-on startup; S102. Increase the cooling current of the semiconductor cooler in the automatic temperature control circuit of the laser; S103. Detect the power change of the laser signal output after filtering by the narrowband photonic filter. If the power of the laser signal increases, return to step S102. Otherwise, proceed to step S104; S104. Reduce the cooling current of the semiconductor cooler in the automatic temperature control circuit of the laser; S105. Detect the power change of the laser signal output after filtering by the narrowband photonic filter. If the power of the laser signal increases, return to step S104; otherwise, return to step S102.

2. The broadband low-noise microwave photonic link according to claim 1, characterized in that: The optical amplifier is a high-power erbium-doped fiber amplifier.

3. The broadband low-noise microwave photonic link according to claim 1, characterized in that: The modulator includes an electro-optic intensity modulator and a bias control circuit; the photodetector is a broadband high-speed photodetector.

4. The broadband low-noise microwave photonic link according to any one of claims 1 to 3, characterized in that: The passband shape of the narrowband photonic filter is a Gaussian filter shape.

5. The broadband low-noise microwave photonic link according to any one of claims 1 to 3, characterized in that: The narrowband photonic filter includes a Mach-Zehnder interferometer and a microring resonator. The Mach-Zehnder interferometer has a first interferometer arm and a second interferometer arm. The microring resonator is optically coupled to the first interferometer arm of the Mach-Zehnder interferometer. The second interferometer arm of the Mach-Zehnder interferometer is connected to a wavelength locking unit and a modulator, respectively.

6. The broadband low-noise microwave photonic link according to claim 5, characterized in that: The narrowband photonic filter is made of silicon nitride waveguide.

7. The broadband low-noise microwave photonic link according to claim 5, characterized in that: The transfer function of the narrowband photonic filter is in, T 1( λ ) represents the transfer function of the first interferometer arm of the narrowband photonic filter; T 2( λ ) represents the transfer function of the second interferometer arm of the narrowband photonic filter; E 0( t This represents the expression for the optical signal input to the narrowband photonic filter; E 1( t This represents the expression for the optical signal output from the first interferometer arm of the narrowband photonic filter; E 2( t This represents the expression for the optical signal output from the second interferometer arm of the narrowband photonic filter; κ This represents the optical field coupling coefficient between the microring resonator and the first interferometer arm; α This represents the optical waveguide loss of a narrowband photonic filter; β Represents the propagation constant of an optical waveguide; L This represents the perimeter of the microring resonator; λ Indicates the wavelength of light; N eff This represents the effective refractive index of the optical waveguide in a narrowband photonic filter.

Images