A steady-state tunable dual-wavelength generation method based on laser phase locking

Abstract

This invention discloses a steady-state tunable dual-wavelength generation method based on laser phase-locked loop (PLL), belonging to the field of microwave photonics technology. It includes carrier-suppressed optical double-sideband modulation, a laser PLL, and optical wavelength control. Carrier-suppressed optical double-sideband modulation: the reference signal generated by the reference laser directly drives the modulator, which operates at the carrier suppression point, modulating the RF source onto the two sidebands of the reference signal, providing two reference wavelengths for dual-wavelength generation. Costa laser PLL: based on Costa PLL technology, frequency capture and phase locking of the signal light to the reference light are achieved. Optical wavelength control: digital frequency discrimination is used to track the frequency and phase difference between the signal light and the reference light, controlling the signal light wavelength to remain consistent with the reference light wavelength. This invention solves the frequency drift problem caused by using two independent light sources, and by combining optical frequency doubling, achieves steady-state tunable dual-wavelength generation, thereby supporting the generation of high-quality millimeter-wave signals.

Description

Technical Field

[0001] This invention belongs to the field of microwave photonics technology, and more specifically, relates to a steady-state tunable dual-wavelength generation method based on laser phase-locked loop. Background Technology

[0002] For millimeter-wave signal generation systems, the common approach is to use all-electronic methods to generate the signal. A carrier wave generated by a millimeter-wave source is mixed with data to produce a modulated millimeter-wave signal, which is then transmitted by an antenna. Compared to traditional circuit-based signal generation methods, the main idea behind generating millimeter waves using microwave photonics technology is to use two optical wavelengths with a certain frequency interval for optical heterodyne detection to generate the millimeter-wave signal. This method effectively overcomes the bandwidth bottleneck of electronic devices, significantly simplifies the system structure, and has the advantages of simple structure and low cost. Dual-wavelength generation in photonics-assisted millimeter-wave generation technology is crucial and directly affects the quality of the generated millimeter-wave signal.

[0003] Dual-wavelength generation techniques can generally be divided into two categories: optical frequency doubling, including carrier suppression methods and optical frequency comb + wavelength selective switching methods; and direct generation of dual wavelengths using two independent light sources. Optical frequency doubling, due to the use of the same seed light source, results in coherent dual wavelengths, which can lead to coherent destructive and phase dilation phenomena during heterodyne analysis, affecting the power stability of the beat frequency signal. Directly using two independent light sources, on the other hand, results in poor frequency and phase stability of the heterodyne signal due to frequency and phase drift issues inherent in the light sources themselves. Summary of the Invention

[0004] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention proposes a steady-state tunable dual-wavelength generation method based on laser phase-locked loop (PLL). By employing PLL technology, it solves problems such as frequency drift caused by using two independent light sources. Combined with optical frequency doubling, it achieves steady-state tunable dual-wavelength generation, thereby supporting the generation of high-quality millimeter-wave signals.

[0005] To achieve the above objectives, the present invention provides a steady-state tunable dual-wavelength generation method based on laser phase-locked loop, comprising:

[0006] A reference signal with frequency f0 is obtained by frequency modulation by changing the current and temperature of the reference laser;

[0007] RF source f m Carrier-suppressed double-sideband modulation is performed by modulation, and the radio frequency source f m Modulated onto the two sidebands of the reference signal f0, generating the upper sideband f0+f m and the lower band f0-f m Then, it is split into two reference wavelengths by an optical fiber coupler;

[0008] A Costa optical phase-locked loop is used to lock the signal light of Laser1 to the upper sideband and the signal light of Laser2 to the lower sideband, thereby achieving wavelength and phase locking between the two laser beams, Laser1 and Laser2. The frequency difference between the wavelengths of Laser1 and Laser2 is equal to the RF source frequency f. m Twice that of Laser1 and Laser2 wavelengths, the frequency interval between Laser1 and Laser2 is adjusted by regulating the frequency of the radio frequency source.

[0009] In some optional implementations, the use of a Costa optical phase-locked loop to lock the signal light of Laser1 to the upper sideband and the signal light of Laser2 to the lower sideband, thereby achieving wavelength and phase locking of the two lasers Laser1 and Laser2, includes:

[0010] The signal beams from Laser1 and Laser2, along with the local oscillator lasers from the reference lasers, are input together into a 90° optical mixer to output four beams: in-phase beams at 0° and 180°, and orthogonal beams at 90° and 270°.

[0011] The in-phase branch beam and the quadrature branch beam are converted by the balanced detectors of their respective loops to obtain the in-phase branch electrical signal V. I and orthogonal branch electrical signal V Q for;

[0012] The in-phase branch electrical signal V I Orthogonal branch electrical signal V Q After multiplying to cancel the modulation signal, the phase error signal V is obtained. D ;

[0013] Phase error signal V D After being amplified by the loop filter, the signal is fed back to the frequency control terminals of Laser1 and Laser2, which control the local oscillator laser output frequency to pull the input signal laser, gradually reducing the phase error and finally achieving a locked state.

[0014] In some alternative implementations, by Determine the in-phase branch electrical signal V I ,Depend on Determine the orthogonal branch electrical signal V Q P Sig φ represents the signal optical power. Sig P represents the angular frequency of the signal light. Ref φ represents the reference optical power. Ref R represents the reference optical angular frequency. L Let r represent the load impedance, r represent the photoresponsivity, and θ represent the load impedance. e This indicates the phase angle of light.

[0015] In some alternative implementations, by Determine the phase error signal V D .

[0016] In some alternative implementations, the in-phase branch electrical signal V I Orthogonal branch electrical signal V Q After multiplying to cancel the modulation signal, the phase error signal V is obtained. D Subsequently, the method further includes:

[0017] Phase error signal V D The signal is processed by a frequency divider. After frequency division, the signal is counted by a counter. The counting result is input to the controller, which calculates the frequency difference value. The frequency difference value output by the controller is converted by a D / A converter, amplified, and filtered to obtain the target frequency difference value.

[0018] In some alternative implementations, by The frequency difference value is obtained, where Δf is the desired frequency difference value, m is the frequency division coefficient, and f o Δt represents the signal frequency after frequency division, N is the count value, and Δt is the technical time set by the controller.

[0019] In some alternative implementations, the phase error signal V D After being amplified by the loop filter, the signal is fed back to the frequency control terminals of Laser1 and Laser2, including:

[0020] The target frequency difference value is amplified by the loop filter and fed back to the frequency control terminals of Laser1 and Laser2, and the control signal laser output quickly reaches the lock state.

[0021] In some alternative implementations, the fiber coupler is a 50:50 fiber coupler.

[0022] In some alternative implementations, a narrow-linewidth tunable laser, Laser-REF, is used as a reference laser.

[0023] In some alternative implementations, the modulator includes a phase modulator or an intensity modulator.

[0024] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0025] This invention utilizes laser phase-locked loop (PLL) technology to achieve steady-state tunable dual-wavelength generation, supporting the generation of high-quality laser or millimeter-wave signals and high-sensitivity coherent detection. This invention solves the problems of frequency drift and signal coherence inherent in traditional dual-wavelength generation techniques, and can be applied to ultra-wideband microwave photonic wireless communication systems. The principle of this invention is simple, the solution is straightforward and efficient, and it has strong application value. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a steady-state tunable dual-wavelength generation method based on laser phase-locked loop provided in an embodiment of the present invention, wherein Laser represents a tunable laser and OC represents an optical coupler;

[0027] Figure 2 This is a schematic diagram of a Costa optical phase-locked loop structure provided in an embodiment of the present invention;

[0028] Figure 3 This is a schematic diagram of a frequency acquisition module based on digital frequency discrimination provided in an embodiment of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0030] The principle of the steady-state tunable dual-wavelength generation method based on laser phase-locked loop is as follows: Figure 1 As shown. A narrow-linewidth tunable laser, Laser-REF, serves as the reference laser, and GHz-level frequency modulation can be achieved by changing its current and temperature; then the radio frequency source f... m The upper and lower sidebands f0+f are generated by carrier suppression double-sideband modulation through intensity modulation. m and f0-f m The laser beams are then split into two beams via a 50:50 fiber coupler. A Costa optical phase-locked loop is used to lock Laser1 and Laser2 onto the upper and lower sidebands respectively, thus achieving wavelength and phase locking between the two laser beams. The frequency difference between the two wavelengths is equal to the RF source frequency f. m Twice that of the frequency range, the frequency interval between the two wavelengths can be adjusted by regulating the frequency of the radio frequency source.

[0031] The principle of the Costa optical phase-locked loop proposed in this invention is as follows: Figure 2As shown. Taking Laser1 as an example, the calculation method of Laser2 is the same as that of Laser1. First, the signal laser Laser1 and the reference laser are input together into the 90° optical mixer through the output local oscillator laser, and then four beams are output, namely 0° and 180° (in-phase branch) beams and 90° and 270° (orthogonal branch) beams.

[0032] For the Kostas phase-locked loop signal light E Sig Heben Zhenguang E Ref This can be expressed as:

[0033]

[0034]

[0035] Among them, P Sig φ Sig P Ref φ Ref These represent the signal optical power, signal optical angular frequency, reference optical power, and reference optical angular frequency, respectively.

[0036] After 90° mixing, the four output beams are as follows:

[0037]

[0038]

[0039]

[0040]

[0041] The in-phase branch beam and the quadrature branch beam are converted by the balanced detectors of their respective loops to obtain the in-phase branch electrical signal V. I and orthogonal branch electrical signal V Q for:

[0042]

[0043]

[0044] Among them, R L , r, θ e These represent load impedance, photoelectric responsivity, and optical phase angle, respectively.

[0045] Then convert the in-phase branch electrical signal V I Orthogonal branch electrical signal V Q After multiplying to cancel the modulation signal, the phase error signal V is obtained. D for:

[0046]

[0047] The phase error signal V D It contains the frequency and phase error information of the two laser beams, and the phase error signal V D After being amplified by the loop filter, the signal is fed back to the frequency control terminal of the laser, controlling the local oscillator laser output frequency to pull the input signal laser frequency, gradually reducing the phase error and eventually achieving a locked state. However, in an optical phase-locked loop system, relying solely on the phase-locked loop to capture the frequency difference is a slow and iterative process. When the initial frequency difference is large, the frequency acquisition time can be very long or even impossible. Therefore, this invention uses a digital frequency discrimination method to assist in frequency acquisition.

[0048] Figure 3 This is a schematic diagram of the frequency acquisition structure based on digital frequency discrimination proposed in this invention. The phase error signal V output by the Costa phase-locked loop is shown. D The signal is processed by a frequency divider. After frequency division, the signal is counted by a counter, and the counting result is input to the controller. The frequency difference value can then be obtained through calculation. The principle is as follows:

[0049]

[0050] Δf is the desired frequency difference, m is the frequency division coefficient, and f o Here, N is the signal frequency after frequency division, N is the count value, and Δt is the technical time set by the controller. It can be seen that digital frequency discrimination can convert large frequency differences into smaller frequency differences for tracking, greatly improving the efficiency of frequency acquisition. Afterwards, the target frequency difference value of the digital signal output by the controller is fed back to the frequency control terminal of the laser after D / A conversion, amplification, and filtering, and the control signal laser output quickly reaches the locked state.

[0051] This invention proposes a steady-state tunable dual-wavelength generation technique based on laser phase-locked loop (PLL). Utilizing PLL technology, steady-state tunable dual-wavelength generation can be achieved, supporting the generation of high-quality millimeter-wave signals. This invention solves the problems of frequency drift and signal coherence inherent in traditional dual-wavelength generation techniques and can be applied to ultra-wideband millimeter-wave wireless communication systems. The principle of this invention is simple, the solution is straightforward and efficient, and it has strong application value.

[0052] The above implementation scheme is only a typical application of the present invention. Using lasers with different principles, using phase modulators or intensity modulators, etc., are all specific implementations of the present invention.

[0053] It should be noted that, depending on the implementation needs, the various steps / components described in this application can be broken down into more steps / components, or two or more steps / components or parts of the operation of steps / components can be combined into new steps / components to achieve the purpose of this invention.

[0054] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A steady-state tunable dual-wavelength generation method based on laser phase-locked loop, characterized in that, include: A reference signal with frequency f0 is obtained by frequency modulation by changing the current and temperature of the reference laser; RF source f m Carrier-suppressed double-sideband modulation is performed by modulation, and the radio frequency source f m Modulated onto the two sidebands of the reference signal f0, generating the upper sideband f0+f m and the lower band f0-f m Then, it is split into two reference wavelengths by an optical fiber coupler; A Costa optical phase-locked loop is used to lock the signal light of Laser1 to the upper sideband and the signal light of Laser2 to the lower sideband, thereby achieving wavelength and phase locking between the two laser beams, Laser1 and Laser2. The frequency difference between the wavelengths of Laser1 and Laser2 is equal to the RF source frequency f. m Twice that of Laser1 and Laser2 wavelengths, the frequency interval between the lasers is adjusted by regulating the frequency of the radio frequency source; The method of using a Costa optical phase-locked loop to lock the signal light of Laser1 to the upper sideband and the signal light of Laser2 to the lower sideband, thereby achieving wavelength and phase locking of the two lasers Laser1 and Laser2, includes: The signal beams from Laser1 and Laser2, along with the local oscillator lasers from the reference lasers, are input together into a 90° optical mixer to output four beams: in-phase beams at 0° and 180°, and orthogonal beams at 90° and 270°. The in-phase branch beam and the quadrature branch beam are converted by the balanced detectors of their respective loops to obtain the in-phase branch electrical signal V. I and orthogonal branch electrical signal V Q ; The in-phase branch electrical signal V I Orthogonal branch electrical signal V Q After multiplying to cancel the modulation signal, the phase error signal V is obtained. D ; Phase error signal V D After being amplified by the loop filter, the signal is fed back to the frequency control terminals of Laser1 and Laser2, which control the local oscillator laser output frequency to pull the input signal laser, gradually reducing the phase error and finally achieving a locked state. Depend on Determine the in-phase branch electrical signal V I ,Depend on Determine the orthogonal branch electrical signal V Q , Indicates signal optical power. Indicates the angular frequency of the signal light. Indicates the reference optical power. Indicates the reference optical angular frequency. Indicates the load impedance. Indicates photoelectric responsivity, Indicates the phase angle of light; Depend on Determine the phase error signal V D .

2. The method according to claim 1, characterized in that, The in-phase branch electrical signal V I Orthogonal branch electrical signal V Q After multiplying to cancel the modulation signal, the phase error signal V is obtained. D Subsequently, the method further includes: Phase error signal V D The signal is processed by a frequency divider. After frequency division, the signal is counted by a counter. The counting result is input to the controller, which calculates the frequency difference value. The frequency difference value output by the controller is converted by a D / A converter, amplified, and filtered to obtain the target frequency difference value.

3. The method according to claim 2, characterized in that, Depend on The frequency difference value is obtained, where, The desired frequency difference value, For frequency division coefficients, The signal frequency after frequency division. For count values, The technical time set for the controller.

4. The method according to claim 3, characterized in that, The phase error signal V D After being amplified by the loop filter, the signal is fed back to the frequency control terminals of Laser1 and Laser2, including: The target frequency difference value is amplified by the loop filter and fed back to the frequency control terminals of Laser1 and Laser2, and the control signal laser output quickly reaches the lock state.

5. The method according to claim 1, characterized in that, The fiber optic coupler is a 50:50 fiber optic coupler.

6. The method according to claim 1, characterized in that, The narrow-linewidth tunable laser Laser-REF was used as the reference laser.

7. The method according to claim 5 or 6, characterized in that, The modulation uses a phase modulator or an intensity modulator.

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