A wide-tuned single-passband microwave photonic filter

Abstract

This invention discloses a wide-tunable single-passband microwave photonic filter, comprising a tunable laser source and an optical fiber coupler; the tunable laser source is connected to a polarization modulator via a polarization controller PC1, the polarization modulator is connected to a polarization beamsplitter via a polarization controller PC2, one path of the polarization beamsplitter is connected to the optical fiber coupler via a polarization controller PC3, and the other path is connected to a semiconductor laser via a polarization controller PC4, the semiconductor laser is connected to the optical fiber coupler, the optical fiber coupler is connected to a photodetector, and the photodetector is connected to the polarization modulator via a vector network analyzer.

Description

Technical Field

[0001] This invention relates to a wide-tunable single-passband microwave photonic filter, belonging to the field of microwave photonics technology. Background Technology

[0002] Filtering is the first step in signal processing. Extracting useful signals from noise or interference signals using a single-passband filter can effectively reduce the difficulty and cost of subsequent signal processing. Currently, with increasingly scarce spectrum resources, narrowing guard bands at receivers, and increasingly harsh receiving environments, high-performance filters are urgently needed to ensure normal system operation. However, traditional electrical filters are limited by electronic bottlenecks, with significant limitations in tuning range and bandwidth variation. Against this backdrop, microwave photonic filters have emerged.

[0003] Microwave photonic filters are specially designed photonic systems capable of filtering microwave signals. Compared to traditional electrical filters that process microwave signals in the electrical domain, microwave photonic filters process microwave signals in the optical domain. They offer advantages such as high operating frequency, large bandwidth, and resistance to electromagnetic interference, making them an important research direction for the future of signal processing.

[0004] Currently, mainstream single-passband photonic filters are implemented based on Phase Modulation to Intensity Modulation Conversion (PM-IM) technology. This involves mapping a single-passband optical filter in the optical domain to a microwave photonic filter in the electrical domain via a spectral mapping mechanism. The resulting microwave photonic filter has the same frequency response shape as the optical filter. Commonly used optical filters include Stimulated Brillouin Scattering (SBS). i Semiconductor Optical Amplifier (SOA) ii Fabry-Perot Laser (FP) III and Distributed Feedback Laser (DFB) iv Compared to other optical filters, single-passband microwave photonic filters based on semiconductor lasers (DFBs) have advantages such as compact structure, large tuning range, and potential integrability.

[0005] In the prior art v, Zhang Tingting et al. constructed a single-passband microwave photonic filter based on phase-modulated optical signal injection into a semiconductor laser, achieving a tuning range of 12.8 GHz to 40.1 GHz. However, due to the limitation of the nonlinear effect inside the cavity of the optically injected semiconductor laser, the tuning range could not be extended to 0, which limited its application in the field of communication.

[0006] In prior art VI, Zhu Huatao et al. constructed a single-passband microwave photonic filter based on single-sideband optical signal injection into a semiconductor laser, achieving a tuning range of 10 GHz to 39 GHz. However, due to the non-ideal roll-off factor of the programmable optical filter used in the scheme, the tuning range of the single-passband microwave photonic filter could not be extended to 0. In addition, the programmable optical filter used in the system is expensive and difficult to widely adopt.

[0007] Therefore, in order to meet the increasing demand for microwave signal processing technology in fields such as information and communication, developing a wide-tunable single-passband microwave photonic filter with a tuning range starting from 0 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 that eliminates the influence of intracavity nonlinearity of the optically injected laser on the tuning range of the optically injected single-passband microwave photonic filter and avoids the use of high-cost programmable optical filters, achieving a tuning range of 0 to 40 GHz.

[0009] A wide-tunable single-passband microwave photonic filter includes a tunable laser source and an optical fiber coupler;

[0010] The tunable laser source is connected to a polarization modulator via a polarization controller PC1. The polarization modulator is connected to a polarization beamsplitter via a polarization controller PC2. One path of the polarization beamsplitter is connected to an optical fiber coupler via a polarization controller PC3, and the other path is connected to a semiconductor laser via a polarization controller PC4. The semiconductor laser is connected to an optical fiber coupler, and the optical fiber coupler is connected to a photodetector. The photodetector is connected to the polarization modulator via a vector network analyzer.

[0011] Furthermore, the polarization modulator, polarization controller PC2, and polarization beam splitter constitute a double-sideband module with carrier suppression.

[0012] Furthermore, the tunable laser light source is used as a master laser, and the semiconductor laser is used as a slave laser.

[0013] Furthermore, the polarization controller PC1 is used to adjust the polarization state of the optical carrier output by the tunable laser source and the main axis of the polarization modulator to 45°.

[0014] Furthermore, the optical carrier is modulated by the radio frequency signal output by the vector network analyzer through a polarization modulator to generate a polarization-modulated optical signal.

[0015] Furthermore, the polarization-modulated optical signal enters the polarization beam splitter and is split into one path including an optical carrier and another path including ±1st order optical sidebands by the polarization controller PC2.

[0016] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: the present invention eliminates the influence of intracavity nonlinearity of optically injected laser on the tuning range of optically injected single-passband microwave photonic filters and avoids the use of high-cost programmable optical filters, achieving a tuning range of 0 to 40 GHz. Attached Figure Description

[0017] Figure 1 This is a structural diagram of the wide-tuned single-passband microwave photonic filter system of the present invention;

[0018] Figure 2 This is a schematic diagram of the working principle of the wide-tunable single-passband microwave photonic filter of the present invention;

[0019] Figure 3 This is the present invention. Figure 1 (a) Polarization-modulated optical signal output by PolM; (b) and (c) represent the optical signal output by PBS;

[0020] Figure 4 The frequency response curve (a) and passband width variation curve (b) of the single-channel microwave photonic filter of the present invention during tuning are shown. Detailed Implementation

[0021] 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.

[0022] like Figure 1 As shown, a wide-tunable single-passband microwave photonic filter is disclosed, comprising a tunable laser source, a polarization modulator, a polarization beam splitter, an optical circulator, a semiconductor laser, an optical fiber coupler, four polarization controllers (PC1, PC2, PC3, PC4), a photodetector, and a vector network analyzer.

[0023] The tunable laser source is connected to a polarization modulator via a polarization controller PC1. The polarization modulator is connected to a polarization beamsplitter via a polarization controller PC2. One path of the polarization beamsplitter is connected to an optical fiber coupler via a polarization controller PC3, and the other path is connected to a semiconductor laser via a polarization controller PC4. The semiconductor laser is connected to an optical fiber coupler, and the optical fiber coupler is connected to a photodetector. The photodetector is connected to the polarization modulator via a vector network analyzer.

[0024] The tunable laser source is used as the master laser, the semiconductor laser is used as the slave laser, and the polarization modulator, polarization controller PC2 and polarization beam splitter constitute a carrier-suppressed double-sideband module.

[0025] like Figure 2 As shown, the working principle of this technical solution is as follows:

[0026] The optical carrier output from the main laser (TLS) is adjusted by polarization controller PC1. ω c The polarization state of the optical carrier is such that its polarization state is at a 45° angle to the principal axis of the polarization modulator (PolM). When the optical carrier passes through the polarization modulator (PolM), it is modulated by the radio frequency signal output by the vector network analyzer (VNA), generating a polarization-modulated optical signal. Figure 2 As shown at point B), it contains a polarized optical carrier with mutually perpendicular polarization states (indicated by the blue arrow at point B) and ±1st-order optical sidebands (indicated by the two red rectangles at point B). The polarization-modulated optical signal enters the polarization beam splitter (PBS) through the polarization controller PC2. Adjusting the polarization controller PC2 causes the polarization-modulated light to be split into two paths by the polarization beam splitter PBS, one of which contains only the optical carrier (…). Figure 2 As shown at point C), the other path contains only ±1st order optical sidebands ( Figure 2 (As shown at point D). An optical signal containing only ±1st-order optical sidebands is injected into a secondary laser (DFB) after passing through a polarization controller PC4. The polarization controller PC4 is adjusted so that the polarization state of the ±1st-order optical sideband signal is the same as that of the secondary laser. Utilizing the frequency-selective amplification characteristics of the secondary semiconductor laser (DFB), optical sidebands falling within the DFB's gain spectrum range are selected and amplified, while optical sidebands not falling within the gain spectrum range remain unaffected. Figure 2 (As shown at point E). The magnified optical sideband and optical carrier pass through a coupler ( Figure 2 (As shown at point F) is then detected by a photodetector. After photoelectric conversion, the photodetector outputs a microwave signal (…). Figure 2 The signal (as shown at point G) is fed into the VNA to complete the spectral mapping from the optical filter (DFB gain spectrum) to the microwave filter. The frequency response shape of the microwave filter is the same as that of the DFB gain spectrum, and the center frequency of the microwave filter is equal to the difference between the center wavelengths of the optical carrier and the DFB gain spectrum. Since the DFB gain spectrum exhibits a single-passband characteristic, the microwave filter also exhibits a single-passband characteristic. Tuning of the microwave filter can be achieved by changing the center wavelength of either the optical carrier or the DFB gain spectrum (this can be done by changing the operating current or operating temperature of the DFB).

[0027] This embodiment further verifies the effect of the filter:

[0028] like Figure 1 The experimental system is shown below. Experimental equipment includes: a tunable laser source TLS (Agilent 8198A), a polarization modulator PolM (Versawave PL-40G-5-1550-V-FCP-FCO), a vector network analyzer VNA (Anritsu MS4647A), and a photodetector PD (FINISARu2t XPDV2120RA, 50GHz, 0.65A / W). The experiment consists of three steps:

[0029] Step 1: Verify the features of PolM

[0030] Adjust polarization controller PC1 so that the polarization state of the optical carrier is 45° to the principal axis of the polarization modulator. A single-frequency microwave signal (2dBm power, 5GHz frequency) output from the RF signal generator (GT-201Sweep Oscillator) is loaded onto the polarization modulator PolM. Adjust polarization controller PC2 so that the polarization-modulated light output from the polarization modulator PolM is split into two paths by the polarization beam splitter PBS. The spectra of the optical signals before and after the polarization beam splitter PBS are as follows: Figure 3 As shown.

[0031] Figure 3 (a) is the spectrum of the polarization modulator output optical signal, i.e., the polarization modulated optical signal, which contains an optical carrier and ±1st order optical sidebands. Figure 3 (b) is the spectrum at point C of the PBS output, which contains only the optical carrier. Figure 3 (c) is the spectrum of point D, another output of the polarization beam splitter PBS, which contains only ±1st order sidebands. Figure 3 It was demonstrated that the polarization state of the optical carrier and the ±1st order optical sideband contained in the polarization modulated optical signal output by the polarization modulator PolM is perpendicular to each other.

[0032] Step 2: Measure the tuning range of the single-passband microwave photonic filter;

[0033] The tuning of the microwave photonic filter can be achieved by changing the center wavelength of either the master or slave laser. This invention fixes the TLS output wavelength and only gradually increases the slave laser's operating temperature from 22.6℃ to 25.8℃ (the slave laser's output wavelength gradually increases), in 0.2℃ steps. The experimentally measured tuning range of the microwave photonic filter is as follows: Figure 4 As shown.

[0034] Depend on Figure 4(a) It can be seen that as the laser operating temperature gradually increases from 22.6℃ to 25.8℃, the microwave photonic filter can be gradually tuned from 0GHz to 40GHz while maintaining a single passband frequency response. However, as the filter center frequency increases, the peak response of the filter gradually decreases due to the increased loss of the RF transmission line. Figure 3 (b) It can be seen that the 3dB passband bandwidth of the microwave photonic filter decreases with the increase of the passband center frequency. This is because the injection-locked range of the semiconductor laser DFB, i.e., the gain spectrum range, is inversely proportional to the square root of the injection ratio. When the passband center frequency of the microwave photonic filter increases, the RF signal power loaded on the polarization modulator PolM decreases due to the increased transmission loss of the RF line, i.e., the modulation coefficient of the polarization modulator PolM decreases. This leads to a decrease in the ±1st order optical sideband power injected into the semiconductor laser DFB, a decrease in the injection-locked range of the semiconductor laser DFB, i.e., a decrease in the gain spectrum, and thus a decrease in the 3dB bandwidth of the microwave photonic filter.

[0035] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A wide-tunable single-passband microwave photonic filter, characterized in that, This includes tunable laser sources and fiber couplers; The tunable laser source is connected to a polarization modulator via a polarization controller PC1. The polarization modulator is connected to a polarization beamsplitter via a polarization controller PC2. One path of the polarization beamsplitter is connected to an optical fiber coupler via a polarization controller PC3, and the other path is connected to a semiconductor laser via a polarization controller PC4. The semiconductor laser is connected to an optical fiber coupler, and the optical fiber coupler is connected to a photodetector. The photodetector is connected to the polarization modulator via a vector network analyzer. The polarization state of the optical carrier output by the main laser is adjusted by the polarization controller PC1 so that its polarization state is 45° with the principal axis of the polarization modulator. When the optical carrier passes through the polarization modulator, it is modulated by the radio frequency signal output by the vector network analyzer to generate a polarization modulated optical signal, which contains optical carriers with mutually perpendicular polarization states and ±1st order optical sidebands. The polarization modulated optical signal enters the polarization beam splitter through the polarization controller PC2. The polarization controller PC2 is adjusted so that the polarization modulated light is split into two paths by the polarization beam splitter PBS. One path contains only the optical carrier, and the other path contains only ±1st order optical sidebands. An optical signal containing only ±1st-order optical sidebands is injected into the slave laser after passing through polarization controller PC4. The polarization controller PC4 is adjusted so that the polarization state of the ±1st-order optical sideband signal is the same as that of the slave laser. Utilizing the frequency-selective amplification characteristic of the slave semiconductor laser, optical sidebands falling within the DFB gain spectrum range of the semiconductor laser are selected and amplified, while optical sidebands not falling within the gain spectrum range remain unaffected. The amplified optical sidebands and the optical carrier are then detected by a photodetector after passing through a coupler. After photoelectric conversion, the microwave signal output by the photodetector is sent to the VNA, completing the spectral mapping from the optical filter to the microwave filter. The frequency response shape of the microwave filter is the same as that of the DFB gain spectrum of the semiconductor laser, and the center frequency of the microwave filter is equal to the difference between the center wavelength of the optical carrier and the center wavelength of the DFB gain spectrum of the semiconductor laser.

2. The wide-tuned single-passband microwave photonic filter according to claim 1, characterized in that, The polarization modulator, polarization controller PC2, and polarization beam splitter constitute a double-sideband module with carrier suppression.

3. The wide-tuned single-passband microwave photonic filter according to claim 1, characterized in that, The tunable laser source is used as the master laser, and the semiconductor laser is used as the slave laser.

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