Ultra-stable microwave signal generating device

Abstract

The invention discloses a signal generating device which comprises a laser, an optical modulator, a Fabry-Perot ultra-stable cavity, a controlled signal generator, a radio frequency source and a photoelectric detector. The laser modulated by the light modulator is input into the Fabry-Perot ultra-stable cavity; the photoelectric detector detects transmission light of the Fabry-Perot ultra-stable cavity and converts an optical signal into a detection signal; the detection signal is divided into two paths, the first path of detection signal and a first target locking signal generate a first control signal, so that the laser is locked on a first target locking frequency; and the second path of detection signal and the second target locking signal generate a second control signal, so that the first frequency of the first signal generated by the controlled signal generator is locked on the second target locking frequency. The signal generating device does not need to use a femtosecond optical frequency comb and only uses the laser and the ultra-stable cavity, so that the cost, the system complexity and the system size can be remarkably reduced.

Description

Technical Field

[0001] The present application relates to the technical fields of laser mode locking, laser modulation, microwaves, etc., and in particular to an ultra-stable microwave signal generating device. Background Art

[0002] Ultra-stable microwave signal sources have important applications in precision measurement, navigation, wireless communications and other fields. Currently, devices that generate ultra-stable microwave signals are generally based on optical frequency combs and ultra-stable cavities. Ultra-stable laser sources are used as the reference frequency of photogenerated microwaves. The stability of the laser frequency is transferred to the radio frequency band through a femtosecond optical frequency comb to obtain ultra-stable microwave signals. The core components of this method are ultra-stable cavities and optical frequency combs. At present, commercial femtosecond optical frequency combs are expensive, bulky, and have complex system links, which limits the large-scale application of ultra-stable microwave signal generation devices.

[0003] With respect to the technical problems existing in the above-mentioned prior art, such as high cost, complex optical system and large size of the ultra-stable microwave signal generating device, no effective solution has been proposed so far. Summary of the invention

[0004] The present disclosure provides an ultra-stable microwave signal generating device to at least solve the technical problems existing in the prior art that the ultra-stable microwave signal generating device has a high cost, a complex optical system, and a large volume.

[0005] According to one aspect of the present application, a signal generating device is provided, characterized in that it includes: a laser, an optical modulator, a Fabry-Perot ultrastable cavity, a controlled signal generator, a radio frequency source and a photodetector; the controlled signal generator generates a first signal with a first frequency, the radio frequency source generates a radio frequency signal with a radio frequency frequency, the first frequency and the radio frequency are each an integer multiple of the free spectrum range of the Fabry-Perot ultrastable cavity; a first modulation signal is generated by the first signal and the radio frequency signal, the first modulation signal is input to the optical modulator, the optical modulator modulates the laser light emitted by the laser, and the laser light output by the optical modulator is input to the Fabry-Perot ultrastable cavity; the photodetector detects the reflected light of the Fabry-Perot ultrastable cavity, and converts the reflected light of the Fabry-Perot ultrastable cavity into a signal. The optical signal is converted into a detection signal, and the detection signal is divided into two paths; a first target locking signal is determined, the first target locking signal has a first target locking frequency, a first control signal is generated by the first detection signal and the first target locking signal, and the first control signal is input to the laser, so that the laser frequency output by the laser is locked on the first target locking frequency; a second target locking signal is generated by the first signal and the radio frequency signal, the second target locking signal has a second target locking frequency, a second control signal is generated by the second detection signal and the second target locking signal, and the second control signal is input to the controlled signal generator, and the controlled signal generator locks the first frequency of the first signal on the second target locking frequency according to the second control signal.

[0006] Optionally, the first modulated signal is a composite signal, the composite signal includes the first frequency and the radio frequency frequency, the first signal and the radio frequency signal are combined via a combiner to generate the composite signal, and the composite signal is input to the optical modulator.

[0007] Optionally, the first target locking signal is the RF signal, and the first target locking frequency is the RF frequency; the first target locking signal is input into a first mixer, the first detection signal is input into the first mixer, the output end of the first mixer is connected to a first low-pass filter, the output end of the first low-pass filter is connected to a first PID controller, the output end of the first PID controller is connected to the laser, and the first control signal is generated by the first PID controller.

[0008] Optionally, the controlled signal generator and the RF source are connected to a second mixer, an output end of the second mixer is connected to a second low-pass filter, the second low-pass filter outputs the second target locking signal, and the second target locking frequency is the absolute value of the difference between the first frequency and the RF frequency.

[0009] Optionally, the second target locking signal is input to a third mixer, the second detection signal is input to the third mixer, the output of the third mixer is connected to a third low-pass filter, the output of the third low-pass filter is connected to a second PID controller, the output of the second PID controller is connected to the controlled signal generator, and the second control signal is generated by the second PID controller.

[0010] Optionally, the optical modulator is an electro-optical modulator.

[0011] Optionally, the controlled signal generator is a voltage-controlled oscillator.

[0012] Optionally, the Fabry-Perot ultrastable cavity material is glass or single crystal silicon.

[0013] Optionally, the thermal noise limit stability of the Fabry-Perot ultrastable cavity length is at least 10 -14 Magnitude.

[0014] Optionally, the first signal is a microwave signal, and the second target locking frequency is in the microwave frequency band.

[0015] The ultra-stable microwave signal generating device disclosed in the present invention does not require a femtosecond optical frequency comb as a transmission medium from optical frequency to microwave frequency, and therefore can significantly reduce system cost and complexity; further, the ultra-stable microwave signal generating device disclosed in the present invention only uses a laser and an ultra-stable cavity, thereby reducing the system volume.

[0016] Based on the detailed description of the specific embodiments of the present application in combination with the accompanying drawings below, those skilled in the art will become more aware of the above and other objects, advantages and features of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Hereinafter, some specific embodiments of the present application will be described in detail in an exemplary and non-limiting manner with reference to the accompanying drawings. The same reference numerals in the accompanying drawings indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the accompanying drawings:

[0018] Figure 1 This is an optical path diagram of an ultra-stable microwave signal generating device according to an embodiment of the present application.

[0019] The symbols included in the above drawings are explained as follows:

[0020] 1-laser; 2-electro-optic modulator; 3-ULE cavity; 4-photodetector; 5-voltage-controlled oscillator; 6-RF source; 7-combiner; 8-second mixer; 9-first mixer; 10-first low-pass filter; 11-first PID controller; 12-second low-pass filter; 13-third mixer; 14-third low-pass filter; 15-second PID controller; 16-polarization beam splitter; 17-quarter wave plate. DETAILED DESCRIPTION

[0021] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present disclosure may be combined with each other. The present disclosure will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0022] In order to enable those skilled in the art to better understand the scheme of the present disclosure, the technical scheme in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, not all of the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in the field without creative work should fall within the scope of protection of the present disclosure.

[0023] It should be noted that the terms "first", "second", etc. in the specification and claims of the present disclosure and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchanged where appropriate, so as to describe the embodiments of the present disclosure described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0024] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0025] Figure 1It is an optical path diagram of an ultra-stable microwave signal generating device according to an embodiment of the present application, which generally may include a laser 1, an electro-optic modulator (EOM) 2, a ULE cavity 3, a photodetector 4, a radio frequency source 6, a voltage-controlled oscillator (VCO) 5, a combiner 7, a first PID controller 11, a second PID controller 15, a first mixer 9, a second mixer 8, a third mixer 13, a first low-pass filter 10, a second low-pass filter 12, a third low-pass filter 14, a polarization beam splitter 16, and a quarter-wave plate 17. The ULE cavity is a Fabry-Perot cavity with an ultra-stable cavity length made of ultra-low thermal expansion coefficient glass, and the radio frequency source 6 generates a radio frequency of f 2 The RF signal RF, the voltage-controlled oscillator (VCO) generates a frequency of f 1 The first signal and the RF signal are fed back to be stabilized. The first signal and the RF signal are combined by the combiner 7 to generate a composite signal, which contains a frequency f 1 and f 2 The two frequencies and the synthesized signal are input to the electro-optic modulator (EOM) 2 to phase modulate the laser output by the laser 1. The laser light field after dual-frequency modulation can be expressed as:

[0026]

[0027] in is the laser light field before modulation, E 0 is the light field amplitude, f 0 is the initial frequency, β 1 , β 2 are the amplitudes of the modulation signals, and J is the Bessel function. From the above formula, we can see that the laser light field after dual-frequency modulation will produce a frequency interval nf with the initial frequency. 1 +mf 2 The sideband components of the EOM2 modulated laser are input to the ULE cavity 3 through the polarization beam splitter 16 and the quarter wave plate 17. The device disclosed in the present invention requires the frequency f of the first signal to be 1 It is preset to be near a certain integer multiple of the ULE cavity free spectral range (FSR) (e.g. ±0.5Δν), that is, Where K is an integer, Δν is the free optical spectrum of the ULE cavity, Δν = c / 2L, where c is the speed of light in a vacuum, and L is the cavity length of the ULE cavity. The Δν value is generally in the order of 1 GHz, and may vary slightly depending on the cavity length of the ULE cavity. K is usually taken below 10, so that K·Δν is between 1 GHz and 10 GHz, which is a microwave frequency band. The reflected light of the ULE cavity 3 passes through the quarter-wave plate 17 and then is reflected by the polarization beam splitter 16 to the photodetector 4, and the photodetector 4 converts the light signal reflected by the ULE cavity 3 into a detection signal. The output of the photodetector 4 is divided into two paths, and the first detection signal is input to the first mixer 9, mixed with the radio frequency signal RF output from the radio frequency source 6, and then filtered by the first low-pass filter 10 to obtain an error signal, and the error signal is input to the first PID controller 11. The control signal obtained by the gain adjustment of the first PID controller 11 is input to the laser 1, so that the output frequency of the laser 1 is locked on N·Δν, where N is an integer. N is usually a large integer, typically around 10. 5 The frequency of the radio frequency signal RF output by the radio frequency source 6 is f2, the frequency component f2 in the first detection signal of the photodetector 4 and the radio frequency signal are mixed in the mixer 9, and the mixed signal is a DC signal or a signal with a frequency of 2*f2, so that the DC component of the mixed signal is taken out as the error signal after passing through the low-pass filter 10.

[0028] The RF signal RF output by the RF source 6 and the first signal are mixed by the second mixer 8 and then passed through the second low-pass filter 12 to obtain a second signal. The second signal and the second detection signal output by the photodetector 4 are input to the third mixer 13 for mixing, and then passed through the third low-pass filter 14 to obtain an error signal. The error signal is input to the second PID controller 15, and the control signal is obtained by gain adjustment of the second PID controller 15 and input to the voltage-controlled oscillator 5. Under the control signal, the frequency f of the first signal generated by the voltage-controlled oscillator 5 is 1 is locked on K·Δν.

[0029] The frequency stability of the first signal output by the voltage-controlled oscillator 5 depends on the stability of the free spectrum of the ULE cavity. Since Δν = c / 2L, the frequency stability of the first signal depends on the stability of the cavity length of the ULE cavity. For an ultrastable cavity, the thermal noise limit stability of its cavity length can generally be less than 10 -14 Therefore, in principle, the stability of the first signal output by the VCO can be less than 10 -14 By replacing the material of the ultra-stable cavity with single-crystal silicon and placing it in an ultra-low temperature environment (~124K), the thermal noise limit stability of the length of the ultra-stable cavity can reach 10 -17At this time, the stability of the first signal output by the VCO will reach 10 -17 Therefore, the frequency of the first signal output by the voltage-controlled oscillator 5 is sufficiently stable and can be used as an ultra-stable microwave signal source.

[0030] The above embodiments use VCO as the first signal generating device. Of course, other types of electronic oscillation circuits whose oscillation frequency is controlled by input parameters may also be used as the first signal generating device. These specific choices of the first signal generating device do not limit the present disclosure.

[0031] Unless otherwise specifically stated, the relative arrangement of the parts and steps described in these embodiments, numerical expressions and numerical values ​​do not limit the scope of the present disclosure. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. The technology, methods and equipment known to ordinary technicians in the relevant field may not be discussed in detail, but in appropriate cases, the technology, methods and equipment should be regarded as a part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0032] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0033] In the description of the present disclosure, it is necessary to understand that the orientation or positional relationship indicated by directional words such as "front, back, up, down, left, right", "lateral, vertical, perpendicular, horizontal" and "top, bottom" are usually based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present disclosure and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the scope of protection of the present disclosure; the directional words "inside and outside" refer to the inside and outside relative to the outline of each component itself.

[0034] The above is only a preferred specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A signal generating device, It is characterized in that include: A laser (1), an optical modulator (2), a Fabry-Perot ultrastable cavity (3), a controlled signal generator (5), a radio frequency source (6) and a photodetector (4); the controlled signal generator (5) generates a first signal having a first frequency, the radio frequency source (6) generates a radio frequency signal having a radio frequency frequency, and the first frequency is preset near an integer multiple of the free spectrum range of the Fabry-Perot ultrastable cavity (3); The first signal is used to generate a first modulation signal together with the radio frequency signal, the first modulation signal is input to the optical modulator (2), the optical modulator (2) modulates the laser light output by the laser (1), and the laser light emitted by the optical modulator (2) is input to the Fabry-Perot ultrastable cavity (3); the photodetector (4) detects the reflected light of the Fabry-Perot ultrastable cavity (3) and converts the optical signal into a detection signal, and the detection signal is divided into two paths; The first detection signal is used to generate a first control signal together with the radio frequency signal, and the first control signal is input to the laser (1), so that the laser frequency output by the laser (1) is locked at a first target locking frequency; The first signal is used to generate a second signal together with the radio frequency signal, the second detection signal is used to generate a second control signal together with the second signal, and the second control signal is input to the controlled signal generator (5), so that the first frequency of the first signal output by the controlled signal generator (5) is locked to an integer multiple of the free spectrum range of the Fabry-Perot ultrastable cavity (3).

2. The signal generating device according to claim 1, Features: The first modulation signal is a composite signal, the composite signal includes the first frequency and the radio frequency, and the composite signal is input to the optical modulator (2).

3. The signal generating device according to claim 2, Features: The first frequency is preset to be around K·Δν, wherein K is an integer, Δν is the free spectrum range of the Fabry-Perot ultrastable cavity (3), and the value of K·Δν is in the microwave frequency band; the second control signal is input to the controlled signal generator (5), so that the first frequency of the first signal output by the controlled signal generator (5) is locked to K·Δν.

4. The signal generating device according to claim 3, Features: The first target locking frequency is N·Δν, where N is an integer, and the N value is not equal to the K value.

5. The signal generating device according to claim 4, Features: The N value is much larger than the K value.

6. The signal generating device according to claim 4, Features: The radio frequency signal is input to a first mixer (9), the first detection signal is input to the first mixer (9), the output end of the first mixer (9) is connected to a first low-pass filter (10), the output end of the first low-pass filter (10) is connected to a first PID controller (11), the output end of the first PID controller (11) is connected to the laser (1), and the first PID controller (11) generates the first control signal.

7. The signal generating device according to claim 4, Features: The first signal is input to a second mixer (8), the radio frequency signal is input to the second mixer (8), an output end of the second mixer (8) is connected to a second low-pass filter (12), and the second low-pass filter (12) outputs the second signal.

8. The signal generating device according to claim 7, Features: The second signal is input to a third mixer (13), the second detection signal is input to the third mixer (13), the output end of the third mixer (13) is connected to a third low-pass filter (14), the output end of the third low-pass filter (14) is connected to a second PID controller (15), the output end of the second PID controller (15) is connected to the controlled signal generator (5), and the second PID controller (15) generates the second control signal.

9. The signal generating device according to any one of claims 1 to 8, Features: The optical modulator (2) is an electro-optical modulator; the controlled signal generator (5) is a voltage-controlled oscillator.

10. The signal generating device according to any one of claims 1 to 8, Features: The thermal noise limit stability of the cavity length of the Fabry-Perot ultrastable cavity (3) is at least 10 -14 Magnitude.

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