A photonic ultra-wideband terahertz frequency hopping source based on four-wave mixing

Abstract

This invention relates to the field of terahertz signal generation technology, specifically a photonic ultra-wideband terahertz frequency-hopping source based on four-wave mixing. It utilizes the third-order nonlinear effect of a nonlinear medium to induce four-wave mixing in the combined beam of the pump light and seed light, thereby generating an Nth-order idler light and doubling the frequency-hopping bandwidth of the pump light. A first optical filter filters out the required idler light from the Nth-order idler light, amplifies it, and combines it with a reference laser. A photodetector performs square law detection on the idler light and the reference laser in the combined beam provided by a second optical coupler, downconverting its frequency from the optical frequency to the terahertz band based on the heterodyne beat frequency principle, thus obtaining a wideband terahertz frequency-hopping signal. Compared with existing technologies and traditional electronic frequency-hopping sources, this invention has significant advantages in frequency-hopping bandwidth, high operating frequency, and flexible controllability, enabling its application in next-generation terahertz communication and radar systems, enhancing their anti-interference and anti-interception capabilities.

Description

Technical Field

[0001] This invention relates to the field of terahertz signal generation technology, and in particular to a photonic ultrawideband terahertz frequency hopping source based on four-wave mixing, which can be applied to next-generation (5G, 6G) mobile communications, radar detection and other fields. Background Technology

[0002] With the development of science and technology, there is an urgent need for ultra-high-speed transmission of large-capacity data. In recent years, terahertz communication, with its advantages of high data rate and large bandwidth, has shown broad application prospects in short-range ultra-high-speed wireless communication, and can meet the ultra-high requirements of various emerging applications (such as VR, AR, satellite communication, etc.). Furthermore, with the increasing complexity of wireless communication environments, ensuring stable and efficient communication is also a key focus in the field of communication. Frequency hopping sources, which are frequency sources whose frequencies can hop within a certain range, have been widely used in communication and radar fields, enabling communication or radar systems to have better anti-interference and anti-interception capabilities. Therefore, realizing an ultra-wideband multi-frequency hopping source operating in the terahertz band can further improve the anti-interference and anti-interception capabilities of terahertz communication and radar systems.

[0003] Modern electronic frequency hopping source technology often employs hybrid frequency synthesis methods to meet demands. However, during frequency doubling, a phase noise degradation of up to 20lgN is inevitable. Meanwhile, traditional RF devices, limited by bandwidth and power consumption—"electronic bottlenecks"—are no longer sufficient to meet the demands of current terahertz communication. Photonic frequency hopping sources, born from the concept of optoelectronic convergence, leverage the unique advantages of photonics, such as ultra-high frequency and high speed, to easily achieve ultra-wideband and fast frequency hopping. Currently, photonic frequency hopping source implementation schemes mainly employ two types: frequency synthesis and frequency switching. Frequency-synthesized photonic frequency-hopping sources utilize optoelectronic frequency synthesizers with high-speed frequency switching capabilities to generate frequency-hopping signals. For example, the paper "Frequency-hopping microwave waveform generation based on a frequency-tunable optoelectronic oscillator, Optical Fiber Communication. 2014, 1-3" reports an optoelectronic oscillator using a polarization-maintaining phase-shifted fiber Bragg grating. This oscillator successfully achieved frequency hopping between 17.1 GHz and 15.75 GHz and between 9.58 GHz and 8.65 GHz, with a frequency hopping switching speed of approximately 100 ns. However, mode contention issues inherent in optoelectronic oscillators hinder the generation of multi-stage frequency-hopping signals. For example, the paper "Flexible frequency-hopping microwave generation by dynamic control of optically injected semiconductor laser, IEEE Photonics Journal. 2016, 8, 1-9" reports a method that utilizes the nonlinear dynamic characteristics of the single-cycle oscillation of a semiconductor laser to achieve a frequency-hopping signal that jumps between 10.5 GHz and 21.0 GHz, with a frequency-hopping bandwidth of 10.5 GHz. Although a frequency-hopping switching speed of 10 ns can be achieved, the maximum frequency-hopping range achievable using this method is only tens of GHz due to the limited tunability of semiconductor lasers. Frequency-switching photonic frequency-hopping sources, on the other hand, use an optoelectronic frequency selector to select frequencies from a pre-generated frequency set and output a frequency-hopping signal.The paper "High-Speed ​​and Wideband Frequency-Hopping Microwave Signal Generation via Switching the Bias Point of an Optical Modulator," IEEE Photonics Journal, 2018, Vol. 10, No. 1, reports a switching method utilizing electro-optic modulation to achieve a frequency hopping rate of 1 ns between 12 GHz and 24 GHz signals. This method mostly involves modulating multiple microwave signals of different frequencies onto light, then using a tunable microwave photonic filter to select and switch frequencies, thereby generating a frequency-hopping output. The frequency components are essentially derived from electronic methods, making it difficult to achieve frequency-hopping output in the millimeter-wave high-frequency band and terahertz band, and the frequency hopping bandwidth and number of frequency points are very limited. Overall, current photonic frequency-hopping sources can achieve ultra-fast frequency hopping switching speeds and easily achieve frequency hopping bandwidths much larger than electronic methods, but they still have the following three limitations and shortcomings:

[0004] First, the operating frequency range is mostly in the microwave band below 25 GHz, and frequency hopping source technology in the terahertz band above 100 GHz has not yet been reported.

[0005] Second, the frequency hopping bandwidth is relatively small, and the large bandwidth advantage of photonics technology has not been fully utilized;

[0006] Third, most of them focus on increasing the frequency hopping rate between two frequency points while ignoring other indicators, and the number of frequency points is significantly less than that of electronic frequency hopping sources. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing photonic frequency hopping sources by providing a photonic ultra-wideband terahertz frequency hopping source based on four-wave mixing. By selecting idler optical products of the four-wave mixing effect, the frequency hopping bandwidth of the output signal is doubled compared to the pump optical signal.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A photonic ultrawideband terahertz frequency hopping source based on four-wave mixing includes a first optical coupler, a nonlinear dielectric unit, a first optical filter, a first optical amplifier, a second optical coupler, and a photodetector.

[0010] The input of the first optical coupler is connected to the pump light and the seed light respectively, and the output is connected to the input of the nonlinear dielectric unit; it is used to combine the received pump light and the seed light.

[0011] The nonlinear medium unit can generate a third-order nonlinear effect, and its output is connected to the input of the first optical filter. By utilizing the third-order nonlinear effect of the nonlinear medium, the combined light undergoes a four-wave mixing effect to generate an Nth-order idler light, where N is an integer greater than or equal to 1.

[0012] The output of the first optical filter is connected to the first input of the second optical coupler via the first optical amplifier; it is used to filter out the idler light required for the application from the received Nth-order idler light and provide it to the first optical amplifier for amplification;

[0013] The second input of the second optical coupler is connected to the reference laser, and the output is connected to the photodetector; the reference light and the amplified idler light are combined.

[0014] The photodetector performs square law detection on the idler light and the reference laser in the combined light provided by the second optical coupler, and based on the heterodyne beat frequency principle, it downconverts the frequency from the optical frequency to the terahertz band to generate a broadband terahertz frequency hopping signal.

[0015] Furthermore, the pump light is a narrowband frequency-hopping optical signal, and the seed light is a single-frequency laser output signal.

[0016] Furthermore, the narrowband frequency-hopping optical signal can be generated by any method, such as electro-optic modulation, laser tuning, etc., with a starting frequency of f. p The frequency hopping bandwidth is ΔF p The frequency range is f p to f p +ΔF p The frequency interval between the seed light and the pump frequency-hopping light is determined by requirements, with the seed light frequency being f. s .

[0017] Furthermore, a second optical amplifier is provided between the first optical coupler and the nonlinear dielectric unit. The input of the second optical amplifier is connected to the first optical coupler, and the output is connected to the nonlinear dielectric unit.

[0018] Furthermore, the nonlinear medium unit is a highly nonlinear optical fiber, a semiconductor optical amplifier, or a semiconductor laser.

[0019] Furthermore, the photodetector is a photodiode of the PIN structure, single-row carrier structure, or similar type; its operating bandwidth should be greater than the frequency difference between the idler light and the reference light.

[0020] Furthermore, the operating frequency of the seed light or reference laser can be adjusted as needed.

[0021] This invention provides a photonic ultrawideband terahertz frequency hopping source based on four-wave mixing. It utilizes the third-order nonlinear effect of a nonlinear medium. When the optical power of the pump light and seed light is between 10mW and 100mW, the combined beam of the pump light and seed light undergoes a four-wave mixing effect, generating an Nth-order idler light, thus doubling the frequency hopping bandwidth of the pump light. A first optical filter filters out the required idler light from the Nth-order idler light, amplifies it, and combines it with a reference laser. A photodetector performs square law detection on the idler light and the reference laser in the combined beam provided by a second optical coupler. Based on the heterodyne beat frequency principle, its frequency is down-converted from the optical frequency to the terahertz band, thereby obtaining a broadband terahertz frequency hopping signal.

[0022] By adopting the above technical solution, the present invention has the following beneficial effects:

[0023] 1. This invention utilizes the third-order nonlinear effect of a nonlinear medium to induce a four-wave mixing effect in the combined beam of the pump light and seed light, thereby multiplying the frequency hopping bandwidth of the pump light signal. Based on this principle, this invention only requires an easily implementable narrowband frequency hopping pump light signal to achieve an ultra-wideband optically generated terahertz frequency hopping signal of tens of GHz. It offers a large frequency hopping bandwidth and fully utilizes the abundant spectral resources of the terahertz band, enhancing the anti-interference capability of the terahertz frequency hopping system.

[0024] 2. The operating frequency of the seed light or reference light of the present invention can be adjusted according to the requirements. By adjusting the operating frequency of the seed light or reference light, the operating frequency band of the photogenerated terahertz frequency hopping signal can be changed, giving it advantages such as higher operating frequency and better tuning performance. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the ultra-wideband photonic frequency hopping source structure in the terahertz band proposed in this invention.

[0026] Figure 2 This is a schematic diagram of the four-wave mixing principle proposed in this invention;

[0027] Figure 3 This is a schematic diagram of the photonic ultrawideband terahertz frequency hopping source system in Example 1;

[0028] Figure 4 This is a schematic diagram of the photonic ultra-wideband terahertz frequency hopping source system in Example 2. Detailed Implementation

[0029] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and embodiments. It should be particularly noted that in the following description, detailed descriptions of known functions and designs that might obscure the main content of the present invention will be omitted.

[0030] like Figure 1 As shown, this invention provides a photonic ultrawideband terahertz frequency-hopping source based on four-wave mixing, comprising a first optical coupler, a nonlinear dielectric unit, a first optical filter, a first optical amplifier, a second optical coupler, and a photodetector. The inputs of the first optical coupler are seeded optical signals and narrowband frequency-hopping optical signals, respectively. The output is sequentially connected to the first input of the second optical coupler via the nonlinear dielectric unit, the first optical filter, and the first optical amplifier. The second input of the second optical coupler is connected to a reference laser, and the output of the second optical coupler is connected to the photodetector.

[0031] Its principle is as follows Figure 2 As shown, when a narrowband frequency-hopping optical signal is used as pump light and combined with a single-frequency seed light, four-wave mixing occurs in the nonlinear dielectric unit, producing an Nth-order idler light. The frequency-hopping bandwidth of the narrowband frequency-hopping optical signal is ΔF. p The frequency range is f p to f p +ΔF p The single-frequency seed light frequency is f. s The lowest frequency of the Nth-order idler light selected by the filter should be (N+1)·f p -f s The highest frequency is (N+1)·(f p +ΔF p )-f s Its bandwidth should be [(N+1)·(f p +ΔF p )-f s ]-((N+1)·f p -f s )=(N+1)·ΔF p The narrowband frequency-hopping optical signal is amplified by N+1 times. The Nth-order idler light is combined with the reference light by an optical coupler and then enters a photodetector for square-law detection. The signal is then synthesized into a terahertz frequency-hopping signal via heterodyne beat frequency. Based on this principle, this invention can achieve an ultra-wideband optically generated terahertz frequency-hopping signal of tens of GHz using only an easily implementable narrowband frequency-hopping pump light signal. It has a large frequency-hopping bandwidth and can fully utilize the rich spectral resources of the terahertz band, improving the anti-interference capability of the terahertz frequency-hopping system. Based on the above, two specific embodiments are described below. In these two embodiments, the narrowband frequency-hopping optical signal of the pump light is generated using an electro-optic modulation method. The component that generates the narrowband frequency-hopping optical signal will be named the narrowband frequency-hopping optical signal generation unit.

[0032] Example 1

[0033] This embodiment provides a photonic ultrawideband terahertz frequency hopping source based on four-wave mixing, with an operating frequency range of 0.110-0.128THz, a channel spacing of 0.6GHz, 30 channels, and a total frequency hopping bandwidth of 18GHz.

[0034] like Figure 3 As shown, the narrowband frequency-hopping optical signal generation unit consists of a laser, an arbitrary waveform generator, a microwave power amplifier, an electro-optic modulator, and a second optical filter. The laser is connected to the first input of the electro-optic modulator via a first optical fiber, providing the initial optical signal. The arbitrary waveform generator is connected to the second input of the electro-optic modulator via the microwave power amplifier, providing an amplified narrowband microwave frequency-hopping signal. The output of the electro-optic modulator is connected to the second optical filter, which operates at the quadrature point by applying a bias voltage. It modulates the initial optical signal based on the received amplified narrowband microwave frequency-hopping signal, generating a narrowband frequency-hopping optical signal. The second optical filter filters out the desired narrowband frequency-hopping optical signal as pump light, which is provided to the first optical coupler. The input of the first optical coupler also receives seed light from another single-frequency laser, and its output is connected to the input of the nonlinear dielectric unit; the first optical coupler is used to combine the seed light and the pump light. The combined beam output from the first optical coupler is amplified by the second optical amplifier and then input into a highly nonlinear fiber. Utilizing the third-order nonlinear effect of the fiber, a four-wave mixing effect is generated, producing an Nth-order idler beam which is provided to the first optical filter to filter out the required idler beam. The filtered idler beam is amplified by the first optical amplifier and then combined with the reference laser output from the reference laser via the second optical coupler. This combined beam then enters a photodetector for square-law detection, generating a terahertz frequency-hopping signal based on the heterodyne beat frequency principle.

[0035] In this embodiment, both the first and second optical amplifiers are erbium-doped fiber amplifiers, the nonlinear dielectric unit is a highly nonlinear fiber, and both the first and second optical filters are optical bandpass filters. The wavelength of the single-frequency laser used for seed light generation is 193.397 THz, and the wavelength of the laser used for narrowband frequency-hopping optical signal generation is 193.413 THz. The electro-optic modulator is biased with a DC bias of 0.5 times the half-wave voltage to operate at the quadrature point. An arbitrary waveform generator generates a microwave frequency-hopping signal with a frequency range of 5 GHz to 14 GHz, a frequency interval of 0.3 GHz, and 30 frequency hopping points to drive the electro-optic modulator. The driving voltage after amplification is set to 3 times the half-wave voltage of the electro-optic modulator. A narrowband frequency-hopping optical signal with a frequency range of 193.418 THz to 193.427 THz is generated. After four-wave mixing and amplification, the first-order idler light has a frequency range of 193.439 THz to 193.457 THz, and the reference laser wavelength is 193.329 THz. The heterodyne beat frequency of the two generates a terahertz frequency hopping signal with a frequency range of 0.110 THz to 0.128 THz.

[0036] Example 2

[0037] This embodiment provides a photonic ultrawideband terahertz frequency hopping source based on four-wave mixing, with an operating frequency range of 0.30-0.32THz, a channel spacing of 1GHz, 20 channels, and a total frequency hopping bandwidth of 20GHz.

[0038] like Figure 4 As shown, the narrowband frequency hopping optical signal generation unit consists of a laser, an arbitrary waveform generator, a microwave power amplifier, an electro-optic modulator, and a second optical filter.

[0039] The laser is connected to the first input of the electro-optic modulator via a first optical fiber, providing the initial optical signal to the modulator. An arbitrary waveform generator is connected to the second input of the electro-optic modulator via a microwave power amplifier, providing an amplified narrowband microwave frequency-hopping signal. The output of the electro-optic modulator is connected to the input of a second optical filter via a second optical fiber. By applying a bias voltage, it operates at the quadrature point, modulating the initial optical signal according to the received amplified narrowband microwave frequency-hopping signal to generate a narrowband frequency-hopping optical signal. The second optical filter filters out the desired narrowband frequency-hopping optical signal as pump light. The output of the second optical filter is connected to a second optical amplifier, providing the pump light to the amplifier for optical power amplification. In this embodiment, the nonlinear dielectric unit is a semiconductor laser, and both the first and second optical filters are optical bandpass filters. The first coupler is replaced by an optical circulator, used to inject the pump light into the semiconductor laser. Port 1 of the optical circulator is connected to the second optical amplifier, receiving the amplified pump light; port 2 of the optical circulator is connected to the semiconductor laser; and port 3 of the optical circulator is the output, connected to the second optical filter. A semiconductor laser provides seed light. By changing the injection current of the semiconductor laser, it is made to operate in a state of four-wave mixing, thereby generating an Nth-order idler light. This idler light is then provided to a first optical filter to filter out the idler light required for the application. The filtered idler light is amplified by a first optical amplifier and then combined with a reference laser output from a reference laser via a second optical coupler. Finally, it enters a photodetector for square law detection, generating a terahertz frequency hopping signal based on the heterodyne beat frequency principle.

[0040] In this embodiment, the free resonant wavelength of the semiconductor laser used as the seed light is 193.393 THz, and the wavelength of the laser used to generate the narrowband frequency-hopping optical signal is 193.413 THz. The electro-optic modulator is biased with a DC bias of 0.5 times the half-wave voltage to operate at the quadrature point. An arbitrary waveform generator generates a microwave frequency-hopping signal with a frequency range of 5 GHz to 15 GHz, a frequency interval of 0.5 GHz, and 20 hopping points to drive the electro-optic modulator. The amplified driving voltage is set to three times the half-wave voltage of the electro-optic modulator. This generates a narrowband frequency-hopping optical signal with a frequency range of 193.418 THz to 193.428 THz. After four-wave mixing and amplification, the first-order idler light has a frequency range of 193.443 THz to 193.463 THz. The reference laser wavelength is 193.143 THz, and their heterodyne beat frequency generates a terahertz frequency-hopping signal with a frequency range of 0.30 THz to 0.32 THz.

[0041] In summary, the photonic ultra-wideband terahertz frequency hopping source based on four-wave mixing provided in this embodiment can be used to generate ultra-wideband terahertz frequency hopping signals with a frequency hopping bandwidth of tens of GHz. Compared with traditional electronic frequency hopping sources, this invention has a significant advantage in frequency hopping bandwidth, high operating frequency, and flexible controllability, and can be applied to next-generation terahertz communication and radar systems to improve their anti-interference and anti-interception capabilities.

[0042] 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 any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention should be considered as equivalent substitutions and are included within the protection scope of the present invention.

Claims

1. A photonic ultrawideband terahertz frequency hopping source based on four-wave mixing, comprising a first optical coupler, a nonlinear dielectric unit, a first optical filter, a first optical amplifier, a second optical coupler, and a photodetector, characterized in that: The input of the first optical coupler is connected to the pump light and the seed light respectively, and the output is connected to the input of the nonlinear medium unit; it is used to combine the received pump light and seed light; wherein, the pump light is a narrowband frequency hopping light signal, and the seed light is a single-frequency laser output signal; after the narrowband frequency hopping light signal is used as the pump light and combined with a single-frequency seed light, a four-wave mixing phenomenon occurs in the nonlinear medium unit; The nonlinear medium unit can generate a third-order nonlinear effect, and its output is connected to the input of the first optical filter. By utilizing the third-order nonlinear effect of the nonlinear medium, the combined light undergoes a four-wave mixing effect to generate an Nth-order idler light, where N is an integer greater than or equal to 1. The output of the first optical filter is connected to the first input of the second optical coupler via the first optical amplifier; it is used to filter out the idler light required for the application from the received Nth-order idler light and provide it to the first optical amplifier for amplification; The second input of the second optical coupler is connected to the reference laser, and the output is connected to the photodetector; the reference light and the amplified idler light are combined. The photodetector performs square law detection on the idler light and the reference laser in the combined light provided by the second optical coupler, and based on the heterodyne beat frequency principle, it downconverts the frequency from the optical frequency to the terahertz band to generate a broadband terahertz frequency hopping signal.

2. The photonic ultrawideband terahertz frequency hopping source based on four-wave mixing according to claim 1, characterized in that: The narrowband frequency-hopping optical signal is a frequency-hopping optical signal generated by electro-optic modulation or laser tuning, and its starting frequency is The frequency hopping bandwidth is The frequency range is to The frequency interval between the seed light and the pump frequency-hopping light is determined by requirements, and the seed light frequency is... .

3. The photonic ultrawideband terahertz frequency hopping source based on four-wave mixing according to claim 1, characterized in that: A second optical amplifier is provided between the first optical coupler and the nonlinear dielectric unit. The input of the second optical amplifier is connected to the first optical coupler, and the output is connected to the nonlinear dielectric unit.

4. The photonic ultrawideband terahertz frequency hopping source based on four-wave mixing according to claim 1, characterized in that: The nonlinear medium unit is a highly nonlinear optical fiber, a semiconductor optical amplifier, or a semiconductor laser.

5. A photonic ultrawideband terahertz frequency hopping source based on four-wave mixing according to any one of claims 1 to 4, characterized in that: The photodetector is a photodiode of the PIN structure, single-row carrier structure, or other similar types. Its operating bandwidth should be greater than the frequency difference between the idler light and the reference light.

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