A Wide-Tuned Single-Passband Microwave Photonic Filter and Its Construction Method

Abstract

This invention discloses a wide-tunable single-passband microwave photonic filter and its construction method. The filter includes a light source device for generating a supercontinuum light source, comprising a generator, an RF power amplifier, a DFB laser, a first erbium-doped fiber amplifier, a first variable optical attenuator, and a highly nonlinear fiber connected in sequence. An optical filter for selecting a certain width of supercontinuum light source is connected between the light source device and a MZI structure for spectral segmentation of the supercontinuum light source. The MZI structure is connected to a photodetector via a single-mode fiber and a second erbium-doped fiber amplifier. The photodetector is connected to the MZI structure via a vector network analyzer. This application features a simple structure, low cost, and the constructed complex coefficient filter eliminates the fundamental frequency response.

Description

Technical Field

[0001] This invention relates to the field of microwave optics technology, specifically to a wide-tunable single-passband microwave photonic filter and its construction method. Background Technology

[0002] In the field of microwave signal processing, single-passband radio frequency filters are typically used to extract useful signals from noise or interference signals, thereby reducing the difficulty and cost of subsequent signal processing. However, with the continuous upgrading of communication technology, current spectrum resources are becoming increasingly scarce, and guard bands are constantly narrowing. In order for receivers to receive microwave signals of different frequency bands, various frequency band microwave filters need to be equipped at the front end of the signal receiver, which greatly increases the cost of the receiver, especially high-frequency microwave filters, which are very expensive. Therefore, the development of a wide-tunable single-passband microwave filter has always been a long-cherished dream. However, electronic devices are constrained by electronic bottlenecks, making it difficult to achieve wide tuning. Microwave photonic filters, on the other hand, combine the advantages of high speed and broadband of photonic technology with the flexibility and controllability of microwave technology, and are considered an effective way to address the above challenges.

[0003] Microwave photonic filters are photonic systems that can replace traditional electrical filters for filtering radio frequency signals. Compared to traditional electrical filters, microwave photonic filters have advantages such as high frequency, wide bandwidth, reconfigurability, and wide tuning range.

[0004] Microwave photonic filters based on discrete digital filter technology and employing time-delay line structures have seen rapid development due to their stable performance and insensitivity to environmental changes. However, their multi-passband spectral response limits their application in complex electromagnetic environments. For example, single-channel wide-tunable filters are urgently needed in satellite communication ground station systems and in future integrated communication-radar channel application systems with great potential. Therefore, achieving single-passband frequency response has always been a key research focus.

[0005] In prior art, Mora J et al. first implemented a single-passband microwave photonic filter with a tuning range of 5 GHz–17 GHz using a spectrum-cut amplified spontaneous emission (ASE) source. Due to the limitation that all tap coefficients are positive, this filter exhibits a baseband response and is not a true single-passband filter. The baseband response is negligible due to the large number of taps, as the fundamental frequency response width is inversely proportional to the number of taps; the more taps, the narrower the fundamental frequency response width. Furthermore, the ASE source introduces a significant amount of spontaneous emission noise into the system, resulting in high system bottom noise in the single-passband microwave photonic filter.

[0006] In prior art, Khan et al. constructed a single-passband microwave photonic filter based on an optical frequency comb. While the optical frequency comb overcomes the noise introduced by the ASE light source, the optical frequency comb generation system is complex, requiring cascaded multiple intensity and phase modulators and precise control of the modulation coefficients, bias voltages, and phase shifts of the RF modulation signal for each modulator, resulting in high system cost and operational complexity. Furthermore, this system also exhibits a fundamental frequency response.

[0007] Therefore, developing a single-passband microwave photonic filter that is easy to operate and has a low cost is an urgent problem to be solved in this field. Summary of the Invention

[0008] The purpose of this invention is to provide a wide-tunable single-passband microwave photonic filter and its construction method, so as to solve the problems of complex filter structure, high cost and fundamental frequency response in the prior art.

[0009] To achieve the above objectives, the present invention is implemented using the following technical solution:

[0010] In a first aspect, the present invention discloses a wide-tunable single-passband microwave photonic filter, comprising:

[0011] A light source device for generating a supercontinuum light source, the light source device comprising a generator, a radio frequency power amplifier, a DFB laser, a first erbium-doped fiber amplifier, a first variable optical attenuator, and a highly nonlinear fiber connected in sequence;

[0012] An optical filter for selecting a supercontinuum light source of a certain width is connected between the light source device and the MZI structure for spectral cutting of the supercontinuum light source.

[0013] The MZI structure is connected to a photodetector via a single-mode fiber and a second erbium-doped fiber amplifier. The photodetector is connected to the MZI structure via a vector network analyzer.

[0014] Furthermore, the MZI structure includes an upper and lower structure connected between the optical filter and the single-mode fiber via a 50:50 fiber coupler.

[0015] Furthermore, the uplink structure includes a first polarization controller, a second variable optical attenuator, and an adjustable fiber delay line, which are sequentially disposed between the optical filter and the single-mode fiber.

[0016] Furthermore, the downlink structure includes a second polarization controller and a phase modulator sequentially disposed between the optical filter and the single-mode fiber.

[0017] Furthermore, the vector network analyzer is connected between the phase modulator and the photodetector.

[0018] Furthermore, the light source device also includes a power meter, which is connected to the first variable optical attenuator via a 99:1 fiber coupler.

[0019] Furthermore, the highly nonlinear optical fiber is a 1KM highly nonlinear optical fiber.

[0020] Furthermore, the single-mode fiber is a 50KM single-mode fiber.

[0021] Secondly, this invention also discloses a method for constructing a wide-tunable single-passband microwave photonic filter, comprising:

[0022] Generates supercontinuum light sources;

[0023] A portion of a C-band supercontinuum light source is extracted, and a wide-tunable single-passband microwave photonic filter is constructed based on the C-band supercontinuum light source.

[0024] By changing the length of the tunable fiber delay line in the MZI structure, the tuning range of the single-passband microwave photonic filter was tested.

[0025] Furthermore, the supercontinuum light source includes:

[0026] The power amplifier amplifies the radio frequency signal output from the generator.

[0027] The output center wavelength of the DFB laser is fixed at 1550 nm. The DFB output optical pulse is amplified by an optical fiber amplifier and then sent into a highly nonlinear optical fiber.

[0028] By controlling the first variable optical attenuator, the optical power of the input highly nonlinear optical fiber is gradually increased, thereby generating a supercontinuum light source.

[0029] According to the above technical solution, the embodiments of the present invention have at least the following effects: The wide-tuned single-passband microwave photonic filter designed in this application can generate a broadband light source with correlation between the ASE light source and the optical frequency comb light source by designing a generator, RF power amplifier, DFB laser, fiber amplifier, first variable optical attenuator and highly nonlinear fiber connected in sequence. By selecting a supercontinuum light source of a certain width and performing spectrum cutting through MZI structure, the structure is simple and the cost is low. The complex coefficient filter formed eliminates the fundamental frequency response. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the filter structure of the present invention;

[0031] Figure 2 These are supercontinuum spectra at different power levels according to the present invention;

[0032] Figure 3This is a schematic diagram of the light source and frequency response of the filter constructed based on supercontinuum spectroscopy according to the present invention;

[0033] Figure 4 This is a schematic diagram of the filter tuning simulation and actual measurement of the present invention. Detailed Implementation

[0034] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0035] Example 1

[0036] To avoid using ASE light sources (high noise) and optical frequency combs (high cost and complex operation) and to eliminate the fundamental frequency response, and to construct a truly meaningful single-passband microwave photonic filter, this invention constructs a wide-tunable single-passband microwave photonic filter in the range of 1GHz-30GHz based on a spectrum-cutting supercontinuum light source.

[0037] This invention discloses a wide-tunable single-passband microwave photonic filter, comprising a light source device for generating a supercontinuum light source, the light source device including a generator, an RF power amplifier 1, a DFB laser 2, a first erbium-doped fiber amplifier 3, a first variable optical attenuator 4, and a highly nonlinear fiber 6 connected in sequence; an optical filter 16 for selecting a supercontinuum light source of a certain width, the optical filter 16 being connected between the light source device and an MZI structure for spectral cutting of the supercontinuum light source; the MZI structure being connected to a photodetector 15 via a single-mode fiber 12 and a second erbium-doped fiber amplifier 13, the photodetector 15 being connected to the MZI structure via a vector network analyzer 14.

[0038] The wide-tunable single-passband microwave photonic filter designed in this application can generate a broadband light source with correlation between ASE light sources and optical frequency comb light sources by sequentially connecting a generator, RF power amplifier 1, DFB laser 2, first erbium-doped fiber amplifier 3, first variable optical attenuator 4, and highly nonlinear fiber 6. By selecting a supercontinuum light source of a certain width and performing spectrum cutting through an MZI structure, the filter has a simple structure, low cost, and the complex coefficient filter thus eliminates the fundamental frequency response.

[0039] The system structure adopted by this invention to solve its technical problem is as follows: Figure 1 As shown. The entire system consists of a supercontinuum light source, an optical filter, an MZI structure, a 50 km single-mode fiber 12, two erbium-doped fiber amplifiers (first erbium-doped fiber amplifier 3 and second erbium-doped fiber amplifier 13), a photodetector 15, and a vector network analyzer 14.

[0040] In this invention, the supercontinuum light source consists of a single-frequency radio frequency signal RF, a radio frequency power amplifier 1, a DFB laser 2, a first erbium-doped fiber amplifier 3, a first variable optical attenuator 4, a 99:1 fiber coupler, a 1 km high nonlinear fiber 6, and a power meter 5. Its function is to provide a broadband light source with a correlation between that of an ASE light source and an optical frequency comb light source.

[0041] Specifically, such as Figure 1 As shown, the pulse sequence generator is connected to the radio frequency power amplifier, and outputs the generated radio frequency signal RF to the radio frequency power amplifier. The output of the radio frequency power amplifier 1 is connected to the DFB laser 2. The output of the DFB laser 2 is connected to the first erbium-doped fiber amplifier 3. The output of the first erbium-doped fiber amplifier 3 is connected to the first variable optical attenuator 4. The first variable optical attenuator 4 is connected to the power meter 5 and the 1 km high nonlinear fiber 6 through a 99:1 fiber coupler.

[0042] The optical filter 16 is used to select a supercontinuum light source of a certain width. The MZI structure consists of two 50:50 fiber couplers combined into upper and lower paths. The upper path includes a first polarization controller 7, a second variable optical attenuator 8, and an adjustable fiber delay line 9. The lower path includes a second polarization controller 10 and a phase modulator 11. The second variable optical attenuator is used to adjust the power of the upper and lower optical signals in the MZI structure, making the power of the two optical signals equal, thereby maximizing the amplitude response of the constructed single-passband microwave photonic filter. The adjustable fiber delay line is used to change the free spectral range of the MZI structure. Changing the adjustable fiber delay line allows for the tuning of the single-passband microwave photonic filter.

[0043] A phase modulator is used to provide a phase shift to the downstream optical signal in the MZI, thereby forming a complex coefficient filter to eliminate the fundamental frequency response. The function of the MZI structure is to perform spectral cutting on the supercontinuum light source to generate multiple taps. Note that the MZI tapping is performed in a coherent system, meaning the time delay between the upstream and downstream paths is less than the coherence time of the light source. A 50 km single-mode fiber is used to dispersively delay the multiple taps of the MZI output, ensuring that the time delay between taps is greater than the coherence time of the light source, i.e., the taps are incoherent.

[0044] Example 2

[0045] This invention also provides a method for constructing a wide-tunable single-passband microwave photonic filter, which involves three steps: Step 1: Generating a supercontinuum light source; Step 2: Constructing a single-passband microwave photonic filter based on the supercontinuum light source; Step 3: Testing the tuning range of the single-passband microwave photonic filter.

[0046] Step 1: Generate a supercontinuum light source.

[0047] The DFB output center wavelength was fixed at 1550 nm. The radio frequency (RF) signal was output from a pulse sequence generator with a repetition rate of 2.5 GHz. The pulse sequence was amplified by a 2.5 GHz single-frequency power amplifier and then directly modulated the DFB. The DFB output optical pulse was amplified by EDFA1 (saturated output power 25.6 dBm) and then fed into a 1 km long highly nonlinear optical fiber. VOA1 was controlled to gradually increase the optical power input to the highly nonlinear fiber from 0 dBm to 20 dBm in 2 dB steps, with a maximum tested optical power of 21.4 dBm. The output spectrum of the highly nonlinear fiber is shown below. Figure 2 As shown.

[0048] Depend on Figure 2 It can be seen that when the optical power is less than 12 dBm, the spectrum does not broaden significantly; when the injected power is greater than 16 dBm, the spectrum broadens significantly (nonlinear effects such as self-phase modulation of highly nonlinear optical fibers are excited), and the spectral coverage ranges from 1500 nm to 1600 nm, producing a supercontinuum light source.

[0049] Second: Construct a single-passband microwave photonic filter based on a supercontinuum light source.

[0050] A portion of the C-band supercontinuum light source (center wavelength 1553.9 nm, 10 dB bandwidth 4.4 nm) was selected using a wavelength selective switch, such as... Figure 3 As shown in (a), a single-passband microwave photonic filter is constructed based on the truncated supercontinuum light source, and its frequency response is as follows. Figure 3 As shown in (b).

[0051] Third: Test the tuning range of the single-passband microwave photonic filter.

[0052] By changing the length of the adjustable delay line in the MZI structure, the tuning range of the microwave photonic filter was experimentally measured as follows: Figure 4 As shown in (b).

[0053] For example Figure 4 The simulation results shown in (a) and as follows Figure 4 (b) shows the experimental results, indicating good agreement between the simulation and experimental results. The single-passband microwave photonic filter constructed based on the supercontinuum light source can achieve a tuning range of 1 GHz to 30 GHz, with a 3dB bandwidth of 230 MHz. Due to the loss of the RF link, the peak amplitude of its frequency response curve gradually decreases as the filter's center frequency is tuned towards higher frequencies.

[0054] As is known from common technical knowledge, this invention can be implemented through other embodiments that do not depart from its spirit or essential characteristics. Therefore, the disclosed embodiments described above are merely illustrative in all respects and are not the only ones. All modifications within the scope of this invention or its equivalents are included in this invention.

Claims

1. A wide-tuning single-passband microwave photonic filter, characterized in that, include: A light source device for generating a supercontinuum light source, the light source device comprising a generator, a radio frequency power amplifier, a DFB laser, a first erbium-doped fiber amplifier, a first variable optical attenuator, and a highly nonlinear fiber connected in sequence; An optical filter for selecting a supercontinuum light source of a certain width is connected between the light source device and the MZI structure for spectral cutting of the supercontinuum light source. The MZI structure is connected to a photodetector via a single-mode fiber and a second erbium-doped fiber amplifier. The photodetector is connected to the MZI structure via a vector network analyzer. The MZI structure includes an upper and lower structure connected between the optical filter and the single-mode fiber via a 50:50 fiber coupler. The uplink structure includes a first polarization controller, a second variable optical attenuator, and an adjustable fiber delay line, which are sequentially disposed between the optical filter and the single-mode fiber. The downlink structure includes a second polarization controller and a phase modulator sequentially disposed between the optical filter and the single-mode fiber. The vector network analyzer is connected between the phase modulator and the photodetector; The light source device also includes a power meter, which is connected to the first variable optical attenuator via a 99:1 fiber coupler.

2. The wide-tuning single-passband microwave photonic filter of claim 1, wherein, The highly nonlinear optical fiber is a 1KM highly nonlinear optical fiber.

3. The wide-tuning single-passband microwave photonic filter of claim 1 or 2, wherein, The single-mode fiber is a 50KM single-mode fiber, wherein the single-mode fiber is used to make the inter-tap delay greater than the coherence time of the light source.

4. A method of constructing a wide-tunable single-passband microwave photonic filter, characterized in that, include: Generates supercontinuum light sources; A portion of a C-band supercontinuum light source is extracted, and a wide-tunable single-passband microwave photonic filter is constructed based on the C-band supercontinuum light source. By changing the length of the tunable fiber delay line in the MZI structure, the tuning range of the single-passband microwave photonic filter was tested. The wide-tuned single-passband microwave photonic filter is the wide-tuned single-passband microwave photonic filter according to any one of claims 1-3.

5. The method of constructing a wide-tunable single-passband microwave photonic filter according to claim 4, wherein, The supercontinuum light source includes: The power amplifier amplifies the radio frequency signal output from the generator. The output center wavelength of the DFB laser is fixed at 1550 nm. The DFB output optical pulse is amplified by an optical fiber amplifier and then sent into a highly nonlinear optical fiber. By controlling the first variable optical attenuator, the optical power of the input highly nonlinear optical fiber is gradually increased, thereby generating a supercontinuum light source.

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