High-frequency-band millimeter wave low-phase-noise source structure based on optical injection gain-switched optical frequency comb and generation method

Abstract

The application discloses a high-frequency-band millimeter wave low-phase-noise source structure based on an optical injection gain switch optical frequency comb and a generation method, and is applied to the technical field of high-frequency millimeter wave signal generation. In the prior art, the millimeter wave is generated by an optical injection gain switch. However, the optical comb teeth have a large frequency interval, the power is low, frequency beating is difficult to be performed, and specific numerical analysis on the phase noise performance of the beat signal is seldom performed. The structure of the application comprises optical frequency comb generated by an optical injection gain switch. A certain comb tooth of the optical frequency comb is filtered out by an optical band-pass filter and is used for injection locking a semiconductor laser. The comb tooth obtained by filtering is locked and amplified based on the optical injection locking technology of the semiconductor laser. The output light of the first and second semiconductor lasers is beat in the injection locking state, and a millimeter wave signal with good phase noise performance, a large tuning range and a phase noise performance which does not deteriorate with the increase of the order of the optical frequency comb is generated.

Description

Technical Field

[0001] This invention belongs to the field of high-frequency millimeter-wave signal generation technology, and specifically relates to a low phase noise source structure. Background Technology

[0002] To address the limitations of traditional microwave communication technology in terms of the operating bandwidth of electronic devices, which restricts their development to higher frequencies, and to meet the demands for rapidly increasing communication speeds, it is essential to improve the performance of signal sources in terms of operating frequency, tuning range, and phase noise. In the high-frequency millimeter-wave band, a larger bandwidth allows for faster data transmission rates. Furthermore, millimeter waves offer advantages such as narrow beamwidth and good directivity, improving transmission efficiency, which is crucial for applications requiring real-time data transmission. Therefore, realizing a low-phase-noise millimeter-wave source operating at high frequencies can fully utilize spectrum resources and improve communication quality. The main methods for achieving high-frequency millimeter-wave low-phase-noise sources include electronic and photonic methods. However, the development of electronic methods is limited by the physical limits of electronic device speed and device size. Photonic approaches not only solve these problems but also provide a readily achievable high-performance millimeter-wave source with wide bandwidth, large tuning range, and low phase noise.

[0003] One of the main methods for realizing high-frequency millimeter-wave low-phase-noise sources through photonics is heterodyne beat frequency generation using optical frequency combs. A common method for generating optical frequency combs is external modulation of the optical signal. Millimeter-wave source realization methods based on externally modulated optical frequency combs mainly involve using different types of modulators to generate the optical frequency comb, with electro-optic modulators (such as Mach-Zehnder modulators, MZM) being the most representative type. For example, the method described in the paper "Schneider GJ, Murakowski JA, Schuetz CA, et al. Radiofrequency signal-generation system with over seven octaves of continuous tuning[J]. Nature Photonics, 2013" generates millimeter-wave signals up to 110 GHz using an electro-optic modulator optical frequency comb. However, the insufficient number of comb teeth results in a small high-frequency signal tuning range and a phenomenon where phase noise deteriorates with increasing optical frequency comb order. For example, the literature "Hasanuzzaman G KM, Kanno A, Dat PT, et al. Self-oscillating optical frequency comb: Application to low phase noise millimeter wave generation and radio-over-fiber link [J]. Journal of Lightwave Technology, 2018" reports a method for generating millimeter-wave signals using a dual-drive MZM in an optoelectronic oscillator circuit. This method replaces the electro-optic modulator in the optoelectronic oscillator with a dual-drive MZM modulator and requires a more complex feedback loop to control the dual-drive MZM modulator. This feedback loop not only increases the complexity of the system but also requires a large 2-kilometer-long optical fiber. Although it can achieve millimeter-wave signals up to 260 GHz and excellent phase noise performance, its structure is very complex and difficult to integrate. In summary, while current methods using external modulation to generate optical frequency combs and then generating millimeter-wave signals can achieve very high operating frequencies and good phase noise, they still have the following two limitations and shortcomings:

[0004] First, the use of electro-optic modulators causes phase noise to deteriorate with increasing modulation order and has a limited frequency coverage, thus failing to fully leverage the advantages of photonics technology's wide tuning range.

[0005] Second, it is difficult to integrate. In order to achieve a wide spectral range and low phase noise performance, it is usually necessary to cascade other modulators or use complex feedback loops.

[0006] Currently, the method of generating millimeter waves through optical injection gain switching has problems such as large frequency intervals, low power of optical combs, difficulty in beat frequency, and a lack of specific numerical analysis of the phase noise performance of its beat frequency signal. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing methods for generating millimeter-wave signals using externally modulated optical frequency combs and optically injected gain-switched optical frequency combs, and to provide a high-frequency millimeter-wave low-phase-noise source structure based on an optically injected gain-switched optical frequency comb. This invention also provides a method for generating millimeter-wave signals that can operate at high frequencies in the millimeter-wave band, have good phase noise performance, a large tuning range, and whose phase noise performance is roughly consistent across different frequencies.

[0008] To achieve the above objectives, one of the technical solutions adopted by the present invention is: a high-frequency millimeter-wave low phase noise source structure based on optical injection gain-switching optical frequency comb, comprising: a main laser, a first optical coupler, a signal generator, a directly modulated laser, an adjustable optical attenuator, a first optical circulator, a first optical bandpass filter, a second optical circulator, a first semiconductor laser, a second optical bandpass filter, a third optical circulator, a second semiconductor laser, a second optical coupler, and a photodetector;

[0009] The output of the main laser is connected to the input of the adjustable optical attenuator. The output of the adjustable optical attenuator is connected to the first port of the first optical circulator. The second port of the first optical circulator is connected to the directly modulated laser. The signal generator is connected to the directly modulated laser. The output signal of the directly modulated laser is input to the first optical coupler through the third port of the first optical circulator. After passing through the first optical coupler, it is output as two signals, upper and lower.

[0010] The uplink signal enters the first optical bandpass filter, which filters out a comb tooth with a frequency close to that of the first semiconductor laser. The output of the first optical bandpass filter is connected to the first port of the second optical circulator. The comb tooth is injected into the first semiconductor laser through the second port of the second optical circulator. The first semiconductor laser locks with the comb tooth and outputs an optical signal with the same frequency as the comb tooth. The output light of the first semiconductor laser is injected into the second optical coupler through the third port of the second optical circulator.

[0011] The downstream signal is filtered out by the second optical bandpass filter to select a comb tooth with a frequency close to that of the second semiconductor laser. The second optical bandpass filter is connected to the first port of the third optical circulator. The comb tooth is injected into the second semiconductor laser through the second port of the third optical circulator. The second semiconductor laser is injection locked to the comb tooth and outputs an optical signal with the same frequency as the comb tooth. The output light of the second semiconductor laser is output to the second optical coupler through the third port of the third optical circulator. After being combined with the output light signal of the third port of the second optical circulator, it enters the photodetector for square law detection and generates a high-frequency millimeter-wave signal through heterodyne beat frequency.

[0012] To achieve the above objectives, the second technical solution adopted by the present invention is: a method for generating a high-frequency millimeter-wave low phase noise source based on an optical frequency comb with optical injection gain switching, comprising: an optical frequency comb generated by optical injection gain switching; filtering out a certain tooth of the optical frequency comb through an optical bandpass filter and using it for two injection-locked semiconductor lasers; locking and amplifying the filtered tooth using optical injection-locking technology based on semiconductor lasers; and performing beat frequency analysis on the output light of the first and second semiconductor lasers in the injection-locked state to generate a millimeter-wave signal with good phase noise performance, a large tuning range, and phase noise performance that does not deteriorate with the increase of the optical frequency comb order.

[0013] The beneficial effects of this invention are as follows: This invention provides a method for generating high-frequency millimeter-wave low-phase-noise signals based on an optically injected gain-switched optical frequency comb. It utilizes the optical injection effect in two distinct stages. In the first stage, the output light from the master laser is input into a directly modulated laser to generate an optical frequency comb with a wide spectral coverage and a sufficient number of comb teeth. In the second stage, the optical frequency comb signal output from the directly modulated laser is filtered and two comb teeth are injected into two semiconductor lasers, causing each of the two semiconductor lasers to output optical signals with the same frequency as the injected comb teeth. Subsequently, a photodetector detects the square factor of the output light from the two semiconductor lasers, and the heterodyne beat frequency generates a high-frequency millimeter-wave signal.

[0014] The present invention has the following advantages:

[0015] 1. The present invention utilizes the combination of optical frequency comb of optical injection gain switch and heterodyne beat frequency generation, which has the characteristics of high operating frequency and large tuning bandwidth, and can realize high-frequency millimeter wave low phase noise source.

[0016] 2. The high-frequency millimeter wave generation method based on optical injection gain switching frequency comb proposed in this invention has the advantages of integration potential and phase noise performance that does not deteriorate with the increase of optical frequency comb order, which is difficult to achieve with the optical frequency comb generated by electro-optic modulation method. Attached Figure Description

[0017] Figure 1This is a schematic diagram of the high-frequency millimeter-wave low phase noise source structure based on optical injection gain switching optical frequency comb proposed in this invention.

[0018] Figure 2 This is a schematic diagram illustrating the principle of the optical injection gain-switching optical frequency comb generation and optical injection-locked semiconductor laser proposed in this invention.

[0019] Figure 3 This is a schematic diagram of the high-frequency millimeter-wave low phase noise source system based on optical injection gain switching optical frequency comb, as shown in Example 1.

[0020] Figure 4 The results are shown in the phase noise curves at 10GHz, 30GHz, and 100GHz generated in Example 1.

[0021] Figure 5 This is a schematic diagram of the high-frequency millimeter-wave low phase noise source system based on optical injection gain switching optical frequency comb, as shown in Example 2. Detailed Implementation

[0022] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and two 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.

[0023] like Figure 1 As shown, this invention provides a high-frequency millimeter-wave low-phase-noise source based on an optically injected gain-switched optical frequency comb. Its structure includes: a main laser, a first optical coupler, a signal generator, a directly modulated laser, an adjustable optical attenuator, a first optical circulator, a first optical bandpass filter, a second optical circulator, a first semiconductor laser, a second optical bandpass filter, a third optical circulator, a second semiconductor laser, a second optical coupler, and a photodetector. The principle of the optically injected gain-switched optical frequency comb generating and the optically injected locked semiconductor laser is as follows: Figure 2As shown. Specifically, the main laser output is connected to an adjustable optical attenuator and then to port 1 of the first optical circulator. Port 2 of the first optical circulator is connected to a directly modulated laser. A signal generator is connected to the directly modulated laser. The output signal of the directly modulated laser is input to the first optical coupler via port 3 of the first optical circulator. After passing through the first optical coupler, it outputs two signals, an upper and a lower path. The upper path signal is connected to a first optical bandpass filter. The first optical bandpass filter filters out a comb tooth with a frequency close to that of the first semiconductor laser. The first optical bandpass filter inputs to port 1 of the second optical circulator. This comb tooth is injected into the first semiconductor laser via port 2 of the second optical circulator. The first semiconductor laser achieves injection lock with this comb tooth and outputs a signal corresponding to the comb tooth. A light signal with the same frequency is generated. The output light of the first semiconductor laser is injected into the second optical coupler through the second optical circulator port 3. The downstream signal is filtered out by the second optical bandpass filter to select a comb tooth with a frequency close to that of the second semiconductor laser. The second optical bandpass filter is connected to the third optical circulator port 1. This comb tooth is injected into the second semiconductor laser through the third optical circulator port 2. The second semiconductor laser is injection locked with the comb tooth and outputs a light signal with the same frequency as the comb tooth. The output light of the second semiconductor laser is output to the second optical coupler through the third optical circulator port 3. After being combined with the light signal output from the second optical circulator port 3, the light enters the photodetector for square law detection and generates a high-frequency millimeter-wave signal through heterodyne beat frequency.

[0024] The directly modulated laser has no built-in isolator with the first and second semiconductor lasers, which can realize the injection of external light; the first and second semiconductor lasers have frequency tuning function, and the operating frequency tuning range is greater than the spectral coverage range of the optical frequency comb to achieve locking of different comb teeth with the optical frequency comb.

[0025] The photodetector is a photodiode of the PIN structure or single-row carrier structure. The optical signals output by the first and second semiconductor lasers in the optical injection locked state are combined by an optical coupler and input to the PIN structure or single-row carrier structure photodiode. Its operating bandwidth should be greater than the frequency difference between the output light of the semiconductor laser and the reference light. Then, the heterodyne beat frequency is performed in the photodiode to generate a millimeter wave signal.

[0026] By adjusting the relevant optical injection parameters of the optical injection gain switch, the optical frequency comb is locked to follow the performance of the master laser, thereby improving the phase noise performance of the millimeter-wave source.

[0027] Those skilled in the art will know that there is a locking range around the free operating frequency of a semiconductor laser. This range is related to the power of the injected light, and the frequency of the injected light can be locked when it is within this range.

[0028] Those skilled in the art will know that the aforementioned optical injection locking technology for locking and amplifying a certain comb tooth involves injecting the comb tooth into a semiconductor laser without a built-in isolator, adjusting the power ratio and frequency detuning of the comb tooth and the semiconductor laser to put the semiconductor laser in an optical injection locked state, and then the semiconductor laser outputs an optical signal with the same frequency and higher power as the comb tooth, thereby achieving power amplification of optical comb teeth with large frequency intervals and lower power.

[0029] The high-frequency millimeter-wave low phase noise source of the present invention has good phase noise performance. Specifically, the performance of the first and second semiconductor lasers will follow the performance of the injected optical frequency comb, and the optical frequency comb will follow the performance of the main laser, thereby resulting in low phase noise of the final millimeter-wave signal.

[0030] Example 1

[0031] This embodiment provides a high-frequency millimeter-wave source solution based on an optically injected gain-switched optical frequency comb, with a maximum operating frequency of 100 GHz. For example... Figure 3 The system structure of Embodiment 1 is shown. The main laser is connected to a tunable optical attenuator. The attenuated optical signal is injected into a directly modulated laser connected to port 2 via port 1 of the first optical circulator. The output of the directly modulated laser is output via port 3 of the first optical circulator. The microwave signal output from the microwave source drives the directly modulated laser to generate a spectrum with distinct comb teeth. The optical frequency comb generated by the directly modulated laser is input into the first optical coupler and split into upper and lower paths. The upper path signal passes through the first optical bandpass filter, which is connected to port 1 of the second optical circulator. A certain comb tooth is filtered out and injected into the first semiconductor laser connected to port 2 via port 1 of the second optical circulator. The output light of the first semiconductor laser is output via port 3 of the second optical circulator. The lower path signal passes through the second optical bandpass filter and filters out a certain comb tooth. This comb tooth passes through port 1 of the third optical circulator and is injected into the second semiconductor laser connected to port 2. The output light of the second semiconductor laser is input into the second optical coupler via port 3 of the third optical circulator. The output light from the first and second semiconductor lasers is combined by the second optical coupler and input into the photodetector, where it is converted into a high-frequency millimeter-wave signal via heterodyne beat frequency.

[0032] In this embodiment, the coupling ratio of the two optical couplers is 50:50.

[0033] In this embodiment, the wavelength of the directly modulated laser is 1549.13 nm, the frequency tuning range of the first and second semiconductor lasers is 1548-1550 nm, and the injection wavelength of the main laser is 1549.1260 nm. A microwave source generates a microwave signal with a frequency of 10 GHz and a power of 20 dBm to drive the directly modulated laser. By adjusting the operating bandwidth of the filter, the power of each comb tooth is adjusted to -34 dBm, ensuring that the ratio of the power to the output power of the semiconductor laser remains a fixed value, satisfying the injection power ratio requirement for injection locking. Frequency tuning is achieved by controlling the operating temperature of the semiconductor laser, adjusting its output signal frequency to a value close to the corresponding comb tooth frequency to achieve optical injection locking for different comb teeth. After locking, the output wavelength of the first semiconductor laser is 1548.78 nm, and the output wavelength of the second semiconductor laser is 1549.58 nm, with both output signal powers remaining constant. With a frequency tuning interval of 10 GHz, by filtering out two comb teeth with a 100 GHz interval, injecting them, and then beat-frequency, signals with a maximum frequency range of 100 GHz can be generated. Furthermore, by changing the modulation frequency, a wide range of continuous tuning can be achieved, i.e., generating optical combs with different comb tooth spacings. By selecting comb teeth with different frequency intervals, millimeter-wave signals of different frequencies can be generated. For example, setting the modulation frequency to 9.5 GHz can generate signals up to 95 GHz, with a frequency tuning interval of 9.5 GHz. Figure 4 As shown, in Example 1, the phase noise curves of signals of different frequencies are roughly the same and are all below -100dBc / Hz at a frequency offset of 10kHz.

[0034] The large tuning range millimeter-wave signal mentioned in this embodiment refers to the optical injection lock between different comb teeth obtained after filtering the optical frequency comb and the semiconductor laser, that is, the beat frequency of the signals output by the first and second semiconductor lasers can be selected to generate millimeter-wave signals of different frequencies.

[0035] The fact that the phase noise performance of different frequencies is roughly the same in this embodiment means that the phase noise of different frequency signals generated by the beat frequency will not deteriorate as the order of the optical frequency comb increases.

[0036] Example 2

[0037] This embodiment provides a high-frequency millimeter-wave low phase noise source solution based on an optically injected gain-switched optical frequency comb, with a maximum operating frequency of 105 GHz. For example... Figure 5 The diagram shown is a schematic of the system structure of Embodiment 2. The working principle of this embodiment is the same as that of Embodiment 1, the difference being the change in the driving frequency of the microwave source. By changing the frequency of the radio frequency driving signal, this millimeter-wave source scheme can generate high-frequency millimeter-wave signals of different frequencies and a wide range of continuous tuning.

[0038] In this embodiment, the wavelength of the directly modulated laser is 1549.23 nm, the frequency tuning range of the first and second semiconductor lasers is 1548-1550 nm, and the injection wavelength of the main laser is 1549.1360 nm. A microwave source generates a microwave signal with a frequency of 10.5 GHz and a power of 20 dBm to drive the directly modulated laser. The power of the comb teeth obtained from both upper and lower filtering paths is adjusted to the same -31 dBm, so that the ratio of its power to the output power of the first and second semiconductor lasers meets the injection power ratio requirement for injection locking. The first and second semiconductor lasers are temperature-tuned to match the frequency of the injected comb teeth. After locking, the output wavelength of the first semiconductor laser is 1548.57 nm, and the output wavelength of the second semiconductor laser is 1549.41 nm. The generated signal frequency can reach up to 105 GHz, with a frequency tuning interval of 10.5 GHz.

[0039] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the scope of the claims of the invention.

Claims

1. A high-frequency millimeter-wave low phase noise source structure based on an optically injected gain-switched optical frequency comb, characterized in that, include: The system comprises: a main laser, a first optical coupler, a signal generator, a directly modulated laser, a tunable optical attenuator, a first optical circulator, a first optical bandpass filter, a second optical circulator, a first semiconductor laser, a second optical bandpass filter, a third optical circulator, a second semiconductor laser, a second optical coupler, and a photodetector. The output of the main laser is connected to the input of the adjustable optical attenuator. The output of the adjustable optical attenuator is connected to the first port of the first optical circulator. The second port of the first optical circulator is connected to the directly modulated laser. The signal generator is connected to the directly modulated laser. The output signal of the directly modulated laser is input to the first optical coupler through the third port of the first optical circulator. After passing through the first optical coupler, it is output as two signals, upper and lower. The uplink signal enters the first optical bandpass filter, which filters out a comb tooth with a frequency close to that of the first semiconductor laser. The output of the first optical bandpass filter is connected to the first port of the second optical circulator. The comb tooth is injected into the first semiconductor laser through the second port of the second optical circulator. The first semiconductor laser locks with the comb tooth and outputs an optical signal with the same frequency as the comb tooth. The output light of the first semiconductor laser is injected into the second optical coupler through the third port of the second optical circulator. The downstream signal is filtered out by the second optical bandpass filter to select a comb tooth with a frequency close to that of the second semiconductor laser. The second optical bandpass filter is connected to the first port of the third optical circulator. The comb tooth is injected into the second semiconductor laser through the second port of the third optical circulator. The second semiconductor laser is injection locked to the comb tooth and outputs an optical signal with the same frequency as the comb tooth. The output light of the second semiconductor laser is output to the second optical coupler through the third port of the third optical circulator. After being combined with the output light signal of the third port of the second optical circulator, it enters the photodetector for square law detection and generates a high-frequency millimeter-wave signal through heterodyne beat frequency.

2. The high-frequency millimeter-wave low phase noise source structure based on an optically injected gain-switched optical frequency comb according to claim 1, characterized in that, The first and second semiconductor lasers adjust their respective frequencies by temperature, and the locking range also changes with the frequency, thus achieving optical injection locking of different comb teeth.

3. The high-frequency millimeter-wave low phase noise source structure based on an optically injected gain-switched optical frequency comb according to claim 2, characterized in that, By adjusting the operating bandwidth of the first and second filters, the comb power obtained from filtering the upper and lower signals is made the same.

4. The high-frequency millimeter-wave low phase noise source structure based on an optically injected gain-switched optical frequency comb according to claim 3, characterized in that, By changing the driving frequency of the signal generator, high-frequency millimeter-wave signals of different frequencies can be generated.

5. A high-frequency millimeter-wave low phase noise source structure based on an optically injected gain-switched optical frequency comb according to claim 4, characterized in that, The coupling ratio of the first optical coupler and the second optical coupler is 50:

50.

6. A method for generating a high-frequency millimeter-wave low phase noise source based on an optically injected gain-switched optical frequency comb, characterized in that, include: Optical injection gain switching generates an optical frequency comb; Two teeth of the optical frequency comb are filtered out by an optical bandpass filter and used in two injection-locked semiconductor lasers. Optical injection locking technology based on semiconductor lasers is used to lock and amplify the filtered comb teeth; In the injection-locked state, the output light from two semiconductor lasers beats, generating a high-frequency millimeter-wave signal.

7. The method for generating a high-frequency millimeter-wave low phase noise source based on an optically injected gain-switched optical frequency comb according to claim 6, characterized in that, By controlling the spacing between the two comb teeth obtained through filtering, millimeter-wave signals of different frequencies can be generated.

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