A low phase noise frequency multiplication source

Abstract

The application discloses a kind of low phase noise frequency multiplication source, the frequency multiplication source includes laser, first fiber coupler, MZM, second fiber coupler, optical fiber, detector, power divider, first filter, second filter, microwave source and frequency feedback control part;Wherein, the laser is connected with the first input port of the first fiber coupler, the output port of the first fiber coupler is connected with the MZM, the MZM is connected with the input port of the second fiber coupler, the second fiber coupler has two output ports, wherein, first output port is connected with the detector, second output port is connected with the optical fiber, the optical fiber is connected with the second input port of the first fiber coupler, the detector is connected with the power divider, the first output port of the power divider is connected with the first filter, and the input port of the first filter is connected with the frequency mixer.

Description

Technical Field

[0001] This invention relates to the field of microwave technology, and in particular to a low phase noise frequency harmonic source. Background Technology

[0002] In applications such as radar and radio astronomy, there are requirements for the phase noise and short-term frequency stability of microwaves and millimeter waves. Current technologies typically employ microwave oscillators or synthesize low-noise microwave signals, then use frequency doubling to obtain low-phase-noise microwave or millimeter-wave signals. However, traditional microwave oscillators struggle to achieve high Q values ​​at high resonant frequencies, and traditional methods of synthesizing microwave signals suffer from limitations due to electronic bottlenecks in electronic devices. Therefore, microwave signals generated using traditional methods have poor phase noise performance, and microwave or millimeter-wave signals obtained using frequency doubling schemes also fail to achieve high levels of phase noise. Summary of the Invention

[0003] This invention provides the following technical solution:

[0004] This specification provides a low phase noise frequency doubling source, including a laser, a first fiber coupler, a micro-Zoom (MZM), a second fiber coupler, an optical fiber, a detector, a power divider, a first filter, a second filter, a microwave source, and a frequency feedback control section. The laser is connected to the first input port of the first fiber coupler, the output port of the first fiber coupler is connected to the MZM, the MZM is connected to the input port of the second fiber coupler, and the second fiber coupler has two output ports: the first output port is connected to the detector, and the second output port is connected to the optical fiber. The optical fiber is connected to the second input port of the first fiber coupler, and the detector is connected to the power divider. The power divider is connected to the first filter, the first filter is connected to the input port of the mixer, and the second output port of the power divider is connected to the second filter for frequency multiplication signal output. The microwave source is connected to the input port of the frequency multiplier, the output port of the frequency multiplier is connected to the input port of the mixer, the output port of the mixer is connected to the input port of the phase-locked loop, the output port of the phase-locked loop is connected to the voltage-controlled input terminal of the voltage-controlled phase shifter, the second output port of the microwave source is connected to the RF input terminal of the voltage-controlled phase shifter, and the output port of the voltage-controlled phase shifter is connected to the RF input port of the MZM. Attached Figure Description

[0005] Figure 1 This is a schematic diagram of a low phase noise frequency harmonic source in an embodiment of the present invention;

[0006] Figure 2This is a schematic diagram illustrating a specific implementation of the low phase noise frequency harmonic source in this invention.

[0007] Reference numerals in the attached figures: 1: Laser; 2: First fiber optic coupler; 3: MZM; 4: Second fiber optic coupler; 5: Detector; 6: Power divider; 7: First filter; 8: Microwave source and frequency feedback control section; 9: Fiber optic cable; 10: Second filter.

[0008] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description, claims, and drawings. Detailed Implementation

[0009] To make the objectives, technical solutions, and advantages of this specification clearer, the technical solutions of this specification will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this specification, and not all of them. Based on the embodiments in this specification, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this specification.

[0010] As described herein, the term “comprising” and its various variations can be understood as open-ended terms that mean “including but not limited to”, and the term “one embodiment” can be understood as “at least one embodiment”.

[0011] Example 1

[0012] This application proposes a low phase noise frequency doubling source, which uses a Mach-Zehnder modulator (MZM) to modulate a microwave signal onto a laser signal, biases the MZM at the minimum transmission point, and uses an optical fiber link to form a loop. The optical signal is transmitted multiple times in the loop, thereby achieving multi-level frequency doubling. The frequency of the frequency doubling output signal can be tunable by adjusting the frequency of the microwave signal.

[0013] A low phase noise frequency doubling source includes: a laser, a first fiber coupler, an MZM (microwave oscillator), a second fiber coupler, an optical fiber, a detector, a power divider, a first filter, a second filter, a microwave source, and a frequency feedback control section. The laser is connected to the first input port of the first fiber optic coupler, the output port of the first fiber optic coupler is connected to the MZM, the MZM is connected to the input port of the second fiber optic coupler, the second fiber optic coupler has two output ports, the first output port is connected to the detector, the second output port is connected to the optical fiber, the optical fiber is connected to the second input port of the first fiber optic coupler, the detector is connected to the power divider, the first output port of the power divider is connected to the first filter, the first filter is connected to the input port of the mixer, the second output port of the power divider is connected to the second filter for frequency multiplication signal output, the first output port of the microwave source is connected to the input port of the frequency multiplier, the output port of the frequency multiplier is connected to the input port of the mixer, the output port of the mixer is connected to the input port of the phase-locked loop, the output port of the phase-locked loop is connected to the voltage-controlled input terminal of the voltage-controlled phase shifter, the second output port of the microwave source is connected to the RF input terminal of the voltage-controlled phase shifter, and the output port of the voltage-controlled phase shifter is connected to the RF input port of the MZM.

[0014] Using MZM to achieve a frequency of f m When a microwave signal is modulated onto a laser signal, and the MZM is biased at its minimum transmission point, the output of the MZM is a spectrum that suppresses the carrier, generating only the spectrum spaced f from the optical carrier. m The two first-order optical sidebands are connected in a loop via an optical fiber link. Part of the optical signal is beat-frequencyd by the detector, while the other part is injected back into the MZM, generating a signal spaced 2f from the optical carrier. m The two optical sidebands can be generated at a frequency of 4f by the detector beat frequency. m The microwave and millimeter-wave signals, after part of the optical signal passes through a detector and a filter, have an output frequency of 4f. m One portion of the optical signal is used for feedback control of the modulation signal phase, while the other portion continues to propagate in the loop at a frequency of (2n+2)f. m The signal is output after filtering, where n is the number of times it passes through the MZM, and n≥2.

[0015] The feedback control method includes, but is not limited to, using a voltage-controlled phase shifter, and can also directly control the output frequency of the microwave source.

[0016] An optical amplifier can be added to the optical path.

[0017] Example 2

[0018] The specific implementation of the low phase noise frequency harmonic source is as follows: Figure 2 As shown, it includes: laser 1, first fiber coupler 2, MZM 3, second fiber coupler 4, detector 5, power divider 6, first filter 7, mixer 8, phase-locked loop 9, microwave source 10, voltage-controlled phase shifter 11, frequency multiplier 12, optical fiber 13, and second filter 14.

[0019] In this embodiment, the microwave source and frequency feedback control section consists of a mixer 8, a phase-locked loop 9, a microwave source 10, a voltage-controlled phase shifter 11, and a frequency multiplier 12. The connection method is as follows: the first filter 7 is connected to the input port of the mixer 8; the first output port of the microwave source 10 is connected to the input port of the frequency multiplier 12; the output port of the frequency multiplier 12 is connected to the input port of the mixer 8; the output port of the mixer 8 is connected to the input port of the phase-locked loop 9; the output port of the phase-locked loop 9 is connected to the voltage-controlled input terminal of the voltage-controlled phase shifter 11; the second output port of the microwave source 10 is connected to the RF input terminal of the voltage-controlled phase shifter 11; and the output port of the voltage-controlled phase shifter 11 is connected to the RF input port of the MZM3.

[0020] In this embodiment, the output wavelength of laser 1 is preferably 1550nm.

[0021] In this embodiment, the splitting ratio of the first fiber coupler 2 is 50:50, and the splitting ratio of the second fiber coupler 4 is 20:80. 20% of the optical signal is injected into the detector, and 80% of the light is injected into the first fiber coupler 2 after passing through the optical fiber.

[0022] In this embodiment, the output frequency of the microwave source 10 is preferably 2GHz. After passing through a voltage-controlled phase shifter, it is modulated onto the laser signal via an MZM3. The MZM is biased at the minimum transmission point, generating only two first-order optical sidebands spaced 2GHz apart from the optical carrier. The modulated optical signal is injected into the MZM again after passing through an optical fiber. After another modulation, part of the optical signal enters the detector, outputting a microwave signal. The signal with a frequency of 8GHz is extracted by the first filter 7 and used for microwave signal feedback control to improve the phase noise of the final output frequency-doubled signal.

[0023] In this embodiment, the frequency multiplier 12 is a 4-fold frequency multiplier, which multiplies the 2GHz output from the microwave source to 8GHz and mixes it with the 8GHz signal output by the first filter 7. The difference frequency signal is fed back through a phase-locked loop to control the voltage-controlled phase shifter, thereby optimizing the phase noise index of the final output frequency multiplied signal.

[0024] Considering factors such as transmission loss, the preferred length of fiber 13 is 5km, and it is a single-mode fiber.

[0025] The output frequency coverage of the photodetector 5 includes the center frequencies of the first filter 7 and the second filter 14. In this embodiment, the detection bandwidth of the photodetector 5 is selected to be 50 GHz.

[0026] The center frequency of the second filter 14 can be selected as (2n+2)×2GHz, where n is the number of times the signal passes through the MZM, and n≥2. In this embodiment, the center frequency of the second filter 14 is selected as 16GHz, i.e., n is 3. By changing the second filter 14, different output frequencies can be achieved. By adjusting the output frequency of the microwave source 10, the final output 16GHz signal frequency can be adjusted around the center frequency. Testing showed that the phase noise of the output 16GHz signal is -151dBc / Hz@10kHz.

[0027] In summary, in this embodiment of the invention, the low phase noise frequency doubling source utilizes optoelectronic methods to achieve frequency expansion. Taking advantage of the low loss of optical fibers and combining electro-optic modulation techniques, the generated microwave and millimeter-wave signals have advantages such as a wider tunable range and phase stability. By optimizing the phase noise of the frequency doubling output signal through frequency feedback control, and by adjusting the output frequency of the frequency source, the frequency of the frequency doubling output signal can be tunable.

[0028] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0029] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A low phase noise frequency multiplication source, characterized by, The frequency doubling source comprises a laser, a first fiber coupler, a MZM, a second fiber coupler, a fiber, a detector, a power divider, a first filter, a second filter, a microwave source and a frequency feedback control part; the microwave source and the frequency feedback control part are composed of a mixer, a phase-locked loop, a microwave source, a voltage-controlled phase shifter and a frequency doubler; wherein the laser is connected with a first input port of the first fiber coupler, an output port of the first fiber coupler is connected with an input port of the MZM, an output port of the MZM is connected with an input port of the second fiber coupler, the second fiber coupler has two output ports, wherein a first output port is connected with the detector, a second output port is connected with an input port of the fiber, an output port of the fiber is connected with a second input port of the first fiber coupler, an output port of the detector is connected with an input port of the power divider, a first output port of the power divider is connected with an input port of the first filter, an output port of the first filter is connected with a first input port of the mixer, a second output port of the power divider is connected with an input port of the second filter for frequency doubling signal output, a first output port of the microwave source is connected with an input port of the frequency doubler, an output port of the frequency doubler is connected with a second input port of the mixer, an output port of the mixer is connected with an input port of the phase-locked loop, an output port of the phase-locked loop is connected with a voltage-controlled input terminal of the voltage-controlled phase shifter, a second output port of the microwave source is connected with a radio frequency input terminal of the voltage-controlled phase shifter, and an output port of the voltage-controlled phase shifter is connected with a radio frequency input port of the MZM.

2. The frequency multiplication source of claim 1, wherein, The microwave signal with frequency f m is modulated to the laser signal by using the MZM, and the MZM is biased at the minimum transmission point, so that the output of the MZM is the optical spectrum with suppressed carrier, and only two first-order optical sidebands with a spacing of f m from the optical carrier are generated, a loop is formed by using the optical fiber link, a part of the optical signal is frequency-mixed by the detector, and another part of the optical signal is injected into the MZM again, so that two optical sidebands with a spacing of 2 f m from the optical carrier are generated, the two optical sidebands are frequency-mixed by the detector to generate a microwave millimeter wave signal with a frequency of 4 f m , and a part of the optical signal is filtered by the filter, and the output signal with a frequency of 4 f m is used for feedback control of the phase of the modulation signal, and another part of the optical signal continues to transmit in the loop, and the output signal with a frequency of (2 n+ 2) f m is output after being filtered, wherein n is the number of times of passing through the MZM, and n is greater than or equal to 2.

3. The frequency doubling source according to claim 1, wherein the frequency doubler is a 4 frequency doubler, the 2GHz output by the microwave source is doubled to 8GHz, the 8GHz signal output by the first filter is mixed, the difference frequency signal is fed back to control the voltage-controlled phase shifter through the phase-locked loop, and the phase noise index of the final output frequency doubling signal is optimized.

4. The frequency doubling source according to claim 1, wherein the output frequency coverage range of the detector includes the center frequencies of the first filter and the second filter, and the detector detection bandwidth is 50GHz.

5. The frequency doubling source according to claim 1, wherein ​ ​ The center frequency of the second filter is selected (2 n+ 2) × 2GHz, wherein n is the number of times of passing through the MZM, n≥2; the output 16GHz signal phase noise index is -151dBc / Hz@10kHz.

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