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

Abstract

The invention 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 mode of generating millimeter waves through an optical injection gain switch has the problems that optical comb teeth with large frequency intervals are low in power, frequency beating is difficult to carry out, and specific numerical analysis on phase noise performance of beat frequency signals is rarely carried out. The structure comprises an optical frequency comb generated by an optical injection gain switch; a certain comb tooth of the optical frequency comb is filtered out through an optical band-pass filter and is used for being injected into a locked semiconductor laser; locking and amplifying the comb teeth obtained by filtering based on a light injection locking technology of a semiconductor laser; in the injection locking state, the output light of the first semiconductor laser and the second semiconductor laser is subjected to beat frequency, and millimeter wave signals which have good phase noise performance and a large tuning range are generated, and the phase noise performance does not deteriorate along with the increase of the order of the optical frequency comb.

Description

Technical Field

[0001] The invention belongs to the technical field of high-frequency millimeter wave signal generation, and in particular relates to a low phase noise source structure. Background Art

[0002] In the face of the problem that the working bandwidth of electronic devices in traditional microwave communication technology is difficult to develop to higher frequency bands, and at the same time, in order to adapt to the demand for rapid increase in communication rate, it is necessary to improve the performance of the signal source in terms of working frequency, tuning range and phase noise. In the high-frequency millimeter wave band, a faster data transmission rate can be achieved through a larger bandwidth. In addition, millimeter waves also have the advantages of narrow beam and good directivity, which can improve the efficiency of transmission, which is very important for applications with real-time data transmission requirements. Therefore, realizing a millimeter wave low phase noise source working in a high frequency band can make full use of spectrum resources and improve the quality of communication. The main methods for realizing a high-frequency millimeter wave low phase noise source are electronic methods and photonic methods, and the physical upper limit of the electronic device rate and the device size of the electronic method limit its development. The photonics-based solution can not only solve these problems, but also is a technical means to easily achieve high-performance millimeter wave sources such as wide bandwidth, large tuning range, and low phase noise.

[0003] At present, one of the main methods to realize high-frequency millimeter-wave low phase noise sources through photonics is through heterodyne beat frequency of optical frequency comb. One of the more common methods to generate optical frequency comb is to externally modulate the optical signal. The method of realizing millimeter-wave source based on external modulation optical frequency comb is mainly to generate optical frequency comb by using different types of modulators, among which the most representative type is electro-optical modulator (such as Mach-Zehnder Modulator, MZM). For example, the method described in the literature "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 through the optical frequency comb of electro-optical modulator, but the number of teeth of the optical frequency comb generated is not enough, resulting in a small signal tuning range in the high frequency band and the phenomenon that the phase noise deteriorates with the increase of the order of the optical frequency comb. Another example is the method reported in 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”, which uses a dual-drive MZM to generate millimeter wave signals in an optoelectronic oscillator loop. 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 the use of a 2-kilometer-long optical fiber with a large footprint. Although it can achieve a maximum of 260GHz millimeter wave signals and excellent phase noise performance, its structure is very complex and difficult to integrate. In general, the current method of using external modulation to generate optical frequency combs and then generate millimeter wave signals can achieve a very high operating frequency band and good phase noise, but it still has the following two limitations and shortcomings:

[0004] First, the method of using electro-optic modulators will cause the phase noise to deteriorate as the modulation order increases and the frequency coverage is limited, which has not yet fully utilized the advantages of the large tuning range of photonics technology;

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

[0006] However, the current method of generating millimeter waves through optical injection gain switching has problems such as the large frequency interval of the optical comb teeth, low power, difficulty in beat frequency, and few specific numerical analyses of the beat frequency signal phase noise performance. Summary of the invention

[0007] The purpose of the present invention is to provide a high-frequency millimeter-wave low phase noise source structure based on an optical injection gain switching optical frequency comb to address the shortcomings of the existing methods of generating millimeter-wave signals by externally modulating an optical frequency comb and an optical injection gain switching optical frequency comb, and to provide a millimeter-wave signal generation method that can achieve an operating frequency in the high frequency band of the millimeter wave and has good phase noise performance, a large tuning range, and roughly consistent phase noise performance at different frequencies.

[0008] To achieve the above-mentioned purpose, 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 end of the adjustable optical attenuator, the output end 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, wherein 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, and is output as upper and lower signals after passing through the first optical coupler;

[0010] The added signal enters the first optical bandpass filter, the first optical bandpass filter filters out a comb tooth with a frequency close to the frequency of the first semiconductor laser, the output end 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 is injection-locked with the comb tooth and outputs an optical signal with the same frequency as the comb tooth, and 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 downlink signal is filtered out through the second optical bandpass filter to obtain a comb tooth with a frequency close to the frequency 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 with 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, and after being combined with the output light signal of the third port of the second optical circulator, it enters the photodetector for square rate detection and generates a high-frequency millimeter wave signal through heterodyne beat frequency.

[0012] To achieve the above-mentioned purpose, 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 injection gain switch optical frequency comb, comprising: an optical frequency comb generated by an optical injection gain switch; filtering out a certain comb tooth of the optical frequency comb through an optical bandpass filter and using it for two injection-locked semiconductor lasers; locking and amplifying the comb teeth obtained by filtering based on the optical injection locking technology of the semiconductor laser; beating 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 order of the optical frequency comb.

[0013] Beneficial effects of the invention: The invention provides a method for generating a high-frequency millimeter-wave low phase noise signal based on an optical injection gain switch optical frequency comb, which utilizes the optical injection effect in two different stages. In the first stage, the output light of the main laser is input into the directly modulated laser to generate an optical frequency comb with a large spectral coverage and a sufficient number of comb teeth. In the second stage, the optical frequency comb signal output by the directly modulated laser is injected into two semiconductor lasers after passing through different filters, so that the two semiconductor lasers respectively output optical signals with the same frequency as the injected comb teeth. Subsequently, the square rate of the output light of the two semiconductor lasers is detected by a photodetector, 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 a combination of an optical frequency comb of an optical injection gain switch and heterodyne beat frequency generation, which has the characteristics of high operating frequency and large tuning bandwidth, and can realize a millimeter-wave low phase noise source in the high frequency band.

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

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

[0018] Figure 2 It is a schematic diagram of the principle of optical injection gain switching optical frequency comb generation and optical injection locking semiconductor laser proposed in the present invention;

[0019] Figure 3 This is a schematic diagram of the composition of a high-band millimeter-wave low phase noise source system based on optical injection gain switching optical frequency comb according to Example 1;

[0020] Figure 4 The phase noise curve results of 10 GHz, 30 GHz and 100 GHz generated in Example 1;

[0021] Figure 5 This is a schematic diagram of the composition of the high-band millimeter-wave low phase noise source system based on the optical injection gain switching optical frequency comb of Example 2. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and two embodiments. It should be noted that in the following description, when the detailed description of known functions and designs may dilute the main content of the present invention, these descriptions will be omitted here.

[0023] like Figure 1 As shown, the present invention provides a high-frequency millimeter-wave low phase noise source based on optical injection gain switching optical frequency comb, and its composition 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 optical injection gain switching optical frequency comb generation and the optical injection locking semiconductor laser principle are as shown in FIG. Figure 2As shown. The specific process is that the main laser outputs to the adjustable optical attenuator and is connected to the first optical circulator port 1, the first optical circulator port 2 is connected to the direct modulation laser, wherein the signal generator is connected to the direct modulation laser, the direct modulation laser output signal is input to the first optical coupler through the first optical circulator port 3, and is output as an upper and lower signal after passing through the first optical coupler. The upper signal is connected to the first optical bandpass filter, the first optical bandpass filter filters out a comb tooth with a frequency close to the frequency of the first semiconductor laser, the first optical bandpass filter is input to the second optical circulator port 1, the comb tooth is injected into the first semiconductor laser through the second optical circulator port 2, the first semiconductor laser is injection-locked with the comb tooth and outputs the comb tooth. The optical signal with the same frequency, the output light of the first semiconductor laser is injected into the second optical coupler through the second optical circulator port 3, the downlink signal is filtered out by the second optical bandpass filter to obtain a comb tooth with a frequency close to the frequency of the second semiconductor laser, the second optical bandpass filter is connected to the third optical circulator port 1, the 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 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 optical circulator port 3, and after being combined with the output light signal of the second optical circulator port 3, enters the photodetector for square rate detection and generates a high-frequency millimeter wave signal through heterodyne beat frequency.

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

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

[0026] By adjusting the relevant light injection parameters of the light 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 should know that there is a locking range around the free-running frequency of the semiconductor laser, and this range is related to the power of the injected light. When the frequency of the injected light is within this range, the light can be locked.

[0028] Those skilled in the art should know that the locked amplification of a certain comb tooth based on the optical injection locking technology is to inject the comb tooth into a semiconductor laser without a built-in isolator, and adjust the power ratio and frequency detuning amount between the comb tooth and the semiconductor laser to put the semiconductor laser in an optical injection locked state. The semiconductor laser then outputs an optical signal with a consistent frequency and high power for the comb tooth, thereby achieving power amplification of optical comb teeth with a large frequency interval and low 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 teeth, and the optical frequency comb teeth will follow the performance of the main laser, so that the phase noise of the millimeter wave signal finally generated is low.

[0030] Example 1

[0031] This embodiment provides a high-frequency millimeter-wave source solution based on optical injection gain switching optical frequency comb, with a maximum operating frequency of 100 GHz. Figure 3 The system structure of the present embodiment 1 is shown. The main laser is connected to the adjustable optical attenuator, and the attenuated optical signal is injected into the directly modulated laser connected to the port 2 through the first optical circulator port 1, and the directly modulated laser output is output through the first optical circulator port 3, wherein the microwave signal output by the microwave source drives the directly modulated laser to generate a spectrum with obvious comb teeth. The optical frequency comb generated by the directly modulated laser is input into the first optical coupler, and is divided into upper and lower paths through the first optical coupler. The upper path signal passes through the first optical bandpass filter, and the first optical bandpass filter is connected to the second optical circulator port 1, and a certain comb tooth filtered out is injected into the first semiconductor laser connected to the port 2 through the second optical circulator port 1, and the output light of the first semiconductor laser is output through the second optical circulator port 3, and the lower path signal passes through the second optical bandpass filter and filters out a certain comb tooth, and the comb tooth is injected into the second semiconductor laser connected to the port 2 after passing through the third optical circulator port 1, and the output light of the second semiconductor laser is input into the second optical coupler through the third optical circulator port 3. The output lights of the first and second semiconductor lasers are combined by the second optical coupler and input into the photoelectric detector, and a high-frequency millimeter wave signal is generated through heterodyne beat frequency.

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

[0033] The wavelength of the directly modulated laser in this embodiment is 1549.13nm, the frequency tunable range of the first and second semiconductor lasers is 1548-1550nm, and the injection wavelength of the main laser is 1549.1260nm. The microwave source generates a microwave signal with a frequency of 10GHz and a power of 20dBm to drive the directly modulated laser. By adjusting the working bandwidth of the filter, the power of each comb tooth is adjusted to -34dBm, so that the ratio with the output power of the semiconductor laser is always a fixed value and meets the injection power ratio required by injection locking. Among them, the operating temperature of the semiconductor laser is adjusted for frequency tuning, and the frequency value of its output signal is adjusted to a value close to the corresponding comb tooth frequency value to perform optical injection locking on different comb teeth. After locking, the output wavelength of the first semiconductor laser is 1548.78nm, and the output wavelength of the second semiconductor laser is 1549.58nm after locking, and the output signal power of both is constant. The frequency tuning interval is 10GHz. By filtering out two comb teeth with an interval of 100GHz, injecting and then beating the frequency, a signal with a frequency range of up to 100GHz can be generated. Secondly, by changing the modulation frequency, large-scale continuous tuning can be achieved, that is, generating optical combs with different comb tooth spacings, selecting comb teeth with different frequency intervals to generate millimeter wave signals of different frequencies, for example, if the modulation frequency is 9.5GHz, a signal of up to 95GHz can be generated, and the frequency tuning interval is 9.5GHz. Figure 4 As shown, in Example 1, the phase noise curves of signals of different frequencies are substantially consistent and are all lower than -100dBc / Hz at a frequency offset of 10kHz.

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

[0035] The substantially consistent performance of phase noises at different frequencies described in this embodiment means that the phase noises of signals at different frequencies 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-band millimeter-wave low phase noise source solution based on optical injection gain switching optical frequency comb, and its maximum operating frequency is 105 GHz. Figure 5 The system structure diagram of Example 2 is shown. The working principle of this embodiment is consistent with that of Example 1, except that the driving frequency of the microwave source is changed. By changing the frequency of the RF driving signal, the millimeter wave source solution can generate high-frequency millimeter wave signals of different frequencies and continuous tuning over a wide range.

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

[0039] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the scope of protection of the present invention is not limited to such specific statements and embodiments. For those skilled in the art, the present invention may have various changes and variations. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A high-band millimeter-wave low phase noise source structure based on optical injection gain switching optical frequency comb, characterized in that: include: A master 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 output of the main laser is connected to the input end of the adjustable optical attenuator, the output end 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, wherein 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, and is output as upper and lower signals after passing through the first optical coupler; The added signal enters the first optical bandpass filter, the first optical bandpass filter filters out a comb tooth with a frequency close to the frequency of the first semiconductor laser, the output end 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 is injection-locked with the comb tooth and outputs an optical signal with the same frequency as the comb tooth, and 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 downlink signal is filtered out through the second optical bandpass filter to obtain a comb tooth with a frequency close to the frequency 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 with 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, and after being combined with the output light signal of the third port of the second optical circulator, it enters the photodetector for square rate detection and generates a high-frequency millimeter wave signal through heterodyne beat frequency.

2. According to claim 1, a high-band millimeter-wave low phase noise source structure based on optical injection gain switching optical frequency comb is characterized in that: The first semiconductor laser and the second semiconductor laser adjust their respective frequencies through temperature and the locking range will also change with the frequency change, thereby achieving light injection locking of different comb teeth.

3. According to claim 2, a high-band millimeter-wave low phase noise source structure based on optical injection gain switching optical frequency comb is characterized in that: By adjusting the working bandwidth of the first filter and the second filter, the comb teeth powers obtained by filtering the upper and lower signals are made the same.

4. According to claim 3, a high-band millimeter-wave low phase noise source structure based on optical injection gain switching optical frequency comb is characterized in that: By changing the driving frequency of the signal generator, high-frequency millimeter-wave signals of different frequencies are generated.

5. According to claim 4, a high-band millimeter-wave low phase noise source structure based on optical injection gain switching optical frequency comb is characterized in that: The coupling ratio of the first optical coupler to the second optical coupler is 50:

50.

6. A method for generating a high-band millimeter-wave low phase noise source based on an optical injection gain switching optical frequency comb, characterized in that: include: Optical injection gain switching generates optical frequency combs; Two comb teeth of the optical frequency comb are filtered out by an optical bandpass filter and used for two injection-locked semiconductor lasers; The optical injection locking technology based on semiconductor laser is used to lock and amplify the comb teeth obtained by filtering. In the injection-locked state, the output lights of the two semiconductor lasers beat each other to generate high-frequency millimeter-wave signals.

7. The method for generating a high-frequency millimeter-wave low phase noise source based on an optical injection gain switching optical frequency comb according to claim 6, characterized in that: By controlling the interval between the two comb teeth obtained by filtering, millimeter wave signals of different frequencies are generated.

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