Device and method for accurately fitting pumping threshold value of double-resonance optical parametric cavity

Abstract

The invention provides a device and a method for accurately fitting a pumping threshold value of a double-resonance optical parametric cavity, and belongs to the technical field of quantum optics. The device comprises a double-resonance optical parameter cavity, a signal generator, an acousto-optic modulation frequency shift system, a high-precision temperature controller and a balanced zero beat detection system. By means of the PDH locking technology, stable locking of the cavity length of the double-resonance optical parametric cavity and the compression angle of the compression state optical field can be achieved. Based on the stable locking state, a signal generator is used for scanning the relative phase of background detection light and compressed light, and meanwhile the dynamic change characteristic of the threshold value along with the pumping power is obtained through a high-precision temperature controller and a balanced zero beat detection system. Compared with an existing test evaluation system, the problem of limitation of a traditional model in fitting of loss and phase jitter of the dual-resonance compression source system is effectively solved, and quantifiable technical support is provided for scientific evaluation and optimization design of the performance of the dual-resonance compression source.

Description

Technical Field

[0001] The present application relates to the field of quantum optics technology, and in particular to a device and method for accurately fitting the pumping threshold of a double-resonance optical parametric cavity. Background Art

[0002] Continuously variable squeezed-state light fields, as core quantum resources in nonclassical optics, demonstrate significant application value in cutting-edge fields such as quantum precision measurement, quantum communication, and quantum computing. In experiments, double-resonant optical parametric oscillators, due to their low threshold and easy locking properties, have become a common approach for achieving stable output of squeezed-state light fields. By fitting and analyzing the loss and phase jitter parameters in the compression system, the primary noise source causing the compression level to drop can be precisely located, allowing targeted improvement strategies to be developed accordingly. However, the temperature sensitivity of the double-resonant cavity and the dynamic variation of the threshold limit traditional parameter evaluation schemes. Using the compression noise variance formula with a fixed threshold in the ideal model to fit the relationship between compression / anticompression and pump power, it is difficult to accurately extract the total system loss and phase jitter. This directly impacts the scientific evaluation and optimized design of the double-resonant compression source performance. Therefore, a device or method is urgently needed to address this issue. Summary of the Invention

[0003] Affected by the dynamic changes in the threshold of a dual-resonant optical parametric cavity, existing models are unable to scientifically evaluate the loss and phase jitter of a dual-resonant compression source system. To address this technical problem, this application proposes a device and method for accurately fitting the pump threshold of a dual-resonant optical parametric cavity. By constructing an intra-cavity temperature model and establishing a quantitative correlation between the threshold and the incident pump power, accurate evaluation of the loss and phase jitter of the dual-resonant compression source system is achieved.

[0004] The technical solution adopted in this application is: a device for accurately fitting the pumping threshold of a double-resonance optical parametric cavity, comprising a single-frequency solid-state laser, a double-resonance optical parametric cavity, and a balanced zero-beat detection system; the laser beam output by the single-frequency solid-state laser is split into two beams by a first beam splitter, one of which is injected into the double-resonance optical parametric cavity after passing through an acousto-optic modulation frequency shifting system, and the reflected field output by the double-resonance optical parametric cavity enters a first photodetector, which feeds the obtained signal back to a first phase shifter through a first photoelectric feedback control system;

[0005] The other beam is split into two beams again after passing through the second beam splitter. One of the beamlets is directly injected into the second harmonic cavity after passing through the first phase shifter. The laser output from the second harmonic cavity is injected into the double-resonance optical parametric cavity through the isolator and the dichroic mirror. The reflected field of the double-resonance optical parametric cavity enters the second photodetector through the dichroic mirror and the isolator again. The second photodetector feeds the signal back to the double-resonance optical parametric cavity through the second photoelectric feedback control system.

[0006] The other beamlet passes through the optical mode cleaner and the second phase shifter in sequence;

[0007] The squeezed-state light field output by the double-resonant optical parametric cavity and the local probe light after passing through the second phase shifter are injected into the balanced zero-beat detection system. The balanced zero-beat detection system cooperates with the third photoelectric feedback control system to lock the relative phase of the squeezed-state light field and the local probe light field.

[0008] The double-resonance optical parametric cavity is also connected to a high-precision temperature controller, which is used to control the temperature inside the double-resonance optical parametric cavity.

[0009] Furthermore, the double-resonance optical parametric cavity adopts a semi-monolithic cavity structure, which is composed of an output coupling mirror and a plano-convex nonlinear crystal. The convex surface of the crystal and the output coupling mirror form a resonant cavity, and a temperature control structure is provided in the resonant cavity.

[0010] Furthermore, the output coupling mirror is coated with a dual-wavelength dielectric film, the plane surface of the plano-convex nonlinear crystal is coated with a dual-wavelength anti-reflection film, and the convex surface is coated with a dual-wavelength high-reflection film.

[0011] Furthermore, the temperature control structure is composed of a thermistor, a Peltier and a copper furnace.

[0012] Furthermore, the laser output by the acousto-optic modulation frequency shifting system passes through the second high-reflection mirror, the third beam splitter and the third high-reflection mirror in sequence, and is then injected into the double-resonance optical parametric cavity; the reflected field output by the double-resonance optical parametric cavity enters the first photodetector through the third high-reflection mirror and the third beam splitter.

[0013] Furthermore, another sub-beam of laser light outputted from the second beam splitter passes through the first high-reflection mirror and enters the optical mode cleaner.

[0014] Furthermore, the balanced zero-beat detection system consists of a beam splitter and a balanced zero-beat detector. The compressed state light field output by the double-resonant optical parametric cavity and the local detection light passing through the second phase shifter are coupled into the balanced zero-beat detector on the beam splitter.

[0015] Furthermore, the acousto-optic modulation frequency shifting system adopts a two-stage acousto-optic modulator. According to the center modulation frequency and bandwidth of the acousto-optic modulator, a signal source of a specific frequency is set to drive the acousto-optic modulator, and the generated upper sideband light field is injected into the double-resonance optical parametric cavity as the frequency shift auxiliary light field.

[0016] Furthermore, a signal generator is connected to the second phase shifter, and a spectrum analyzer is connected to the balanced zero-beat detection system. The compression angle and cavity length of the compressed state light field are locked through the first photoelectric feedback control system and the second photoelectric feedback control system. The signal generator is used to output a sawtooth wave signal of a specific frequency to act on the second phase shifter, and the scanning signal of the compressed state light field is displayed on the spectrum analyzer.

[0017] A method for accurately fitting the pumping threshold of a double-resonant optical parametric cavity, using the device, includes the following steps:

[0018] Step 1: A single-frequency solid-state laser outputs a laser beam, which is then split into a first laser beam and a second laser beam after passing through a first beam splitter. The first laser beam enters an acousto-optic frequency modulation (AOFM) system, while the second laser beam is injected into a second harmonic cavity through a first phase shifter to generate a pump light field. The pump light field passes through an isolator and a dichroic mirror and then enters a double-resonance optical parametric cavity, thereby generating a compressed state light field.

[0019] Step 2: The first laser beam is injected into the double-resonance optical parametric cavity through the second high-reflection mirror, the third beam splitter, and the third high-reflection mirror.

[0020] Step 3: Extract the pump light field reflected by the dual-resonance optical parametric cavity through the isolator. The reflected pump light field passes through the dichroic mirror and the isolator again and enters the second photodetector. The second photodetector feeds back the cavity locking signal to the dual-resonance optical parametric cavity through the second photoelectric feedback control system to achieve stable control of the cavity length.

[0021] Step 4: The frequency-shifted auxiliary light field reflected by the double-resonance optical parametric cavity is extracted through a third beam splitter. The reflected frequency-shifted auxiliary light field passes through the third beam splitter again and enters the first photodetector. The first photodetector feeds back the phase information of the squeezed state light field and the pump light field to the first phase shifter through a first photoelectric feedback control system to achieve stable locking of the compression angle.

[0022] Step 5: The second laser beam is further split into a third laser beam after passing through the second beam splitter. The third laser beam is used as the local detection light field. The third laser beam is efficiently coupled with the squeezed state light field output by the double-resonant optical parametric cavity and the frequency-shifted auxiliary light field in the balanced zero-beat detection system through the first high-reflection mirror, the optical mode cleaner, and the second phase shifter.

[0023] Step 6: Scan the second phase shifter in the third laser path using a signal generator, and record the compression information of the scanning detection angle using a spectrum analyzer;

[0024] Step 7: Change the pump light power incident on the double-resonance optical parametric cavity according to the set step size. Lock the cavity length and compression angle through steps 3 and 4 again. Use a high-precision temperature controller to finely adjust the temperature of the double-resonance optical parametric cavity until the compression / anti-compression recorded by the spectrum analyzer reaches the maximum value. At this temperature, both the double resonance condition and the quasi-phase matching condition are met (the optimal double resonance point).

[0025] Step 8: Record the temperature values ​​corresponding to the optimal double resonance point under different pump powers, and fit the empirical formula of the cavity temperature and the incident pump light power;

[0026] In step 9, based on the relationship between the threshold and temperature, and the relationship between temperature and pump light power, the dynamic variation characteristics of the threshold with pump light power are obtained, and the characteristics are substituted into the calculation formula of the compression noise variance to improve the existing theoretical model of loss and phase jitter fitting.

[0027] The beneficial effects of the present application compared to the prior art are as follows: the present application relates to a technical solution comprising a dual-resonance optical parametric cavity, a signal generator, an acousto-optic modulation frequency shifting system, a high-precision temperature controller, and a balanced zero-beat detection system. With the help of PDH locking technology, the stable locking of the cavity length of the dual-resonance optical parametric cavity and the compression angle of the compressed state light field can be achieved. Based on this stable locking state, the relative phase of the local detection light and the compressed light is scanned by a signal generator, and the dynamic change characteristics of the threshold with the pump power are obtained by a high-precision temperature controller and a balanced zero-beat detection system. Compared with the existing test and evaluation system, the present application effectively solves the limitations of the traditional model in fitting the loss and phase jitter of the dual-resonance compression source system, and provides quantifiable technical support for the scientific evaluation and optimal design of the dual-resonance compression source system. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present application will be further described below with reference to the accompanying drawings:

[0029] Figure 1 A schematic diagram of the device structure provided in an embodiment of the present application;

[0030] Figure 2 This is a record of the phase of the scanned compressed light detection;

[0031] Figure 3 The fitting diagram of the temperature in the double-resonance optical parametric cavity and the incident pump power is shown in Fig. ;

[0032] Figure 4 The dynamic change diagram of the threshold of the double-resonance optical parametric cavity ;

[0033] Figure 5 Comparison of fitting curves of loss and phase jitter of double resonance compression system;

[0034] In the figure: 1-single-frequency solid-state laser, 2-double-resonance optical parametric cavity, 3-high-precision temperature controller, 4-signal generator, 5-second phase shifter, 6-balanced zero-beat detection system, 7-spectrum analyzer, 8-first photodetector, 9-first photoelectric feedback control system, 10-first phase shifter, 11-second harmonic cavity, 12-isolator, 13-dichroic mirror, 14-second photodetector, 15-second photoelectric feedback control system, 16-acousto-optic modulation frequency shifting system, 17-optical mode cleaner, 18-third photoelectric feedback control system, 19-first beam splitter, 20-second beam splitter, 21-third beam splitter, 22-first high-reflection mirror, 23-second high-reflection mirror, 24-third high-reflection mirror. DETAILED DESCRIPTION

[0035] like Figures 1 to 5 As shown, the present application provides a device for accurately fitting the pumping threshold of a double-resonance optical parametric cavity, comprising a single-frequency solid-state laser 1, a double-resonance optical parametric cavity 2, a high-precision temperature controller 3, a signal generator 4, a second phase shifter 5, a balanced zero-beat detection system 6, a spectrum analyzer 7, a first photodetector 8, a first photoelectric feedback control system 9, a first phase shifter 10, a second harmonic cavity 11, an isolator 12, a dichroic mirror 13, a second photodetector 14, a second photoelectric feedback control system 15, an acousto-optic modulation frequency shifting system 16, and an optical mode cleaner. The optical fiber transmission device 17, the third photoelectric feedback control system 18, the first beam splitter 19, the second beam splitter 20, the third beam splitter 21, the first high-reflection mirror 22, the second high-reflection mirror 23 and the third high-reflection mirror 24; it can be divided into the following parts: initial laser beam splitting, the path and control of the first light beam, the secondary beam splitting of the second light beam, the path and control of the first sub-beam, the path and control of the second sub-beam; including the manipulation of the cavity length of the double-resonance optical parametric cavity, the stable locking of the compression angle of the compressed state light field, and the detection of the dynamic change characteristics of the threshold with the pump power.

[0036] Initial laser beam splitting: The single-frequency solid-state laser 1 is used to output a laser beam with a wavelength of 1064 nm, which is split into two beams after passing through the first beam splitter 19.

[0037] Path and Control of the First Light Beam: A first laser beam with a wavelength of 1064 nm enters the AOM frequency shifting system 16, then passes sequentially through the second high-reflection mirror 23, the third beam splitter 21, and the third high-reflection mirror 24 before being injected into the double-resonant optical parametric cavity 2. The reflected field output by the double-resonant optical parametric cavity 2 passes through the third high-reflection mirror 24 and the third beam splitter 21 and enters the first photodetector 8. The first photodetector 8 feeds the acquired signal back to the first phase shifter 10 via the first photoelectric feedback control system 9. The first phase shifter 10 and the first photodetector 8 work in conjunction with the AOM frequency shifting system 16 and the first photoelectric feedback control system 9 to lock the compression angle of the squeezed-state light field.

[0038] Secondary beam splitting of the second light beam: After the second light beam passes through the second beam splitter 20, the 1064 nm laser beam is split into two beams again;

[0039] Path and control of the first sub-beam: A 1064 nm laser beam is directly injected into the second harmonic cavity 11 after passing through the first phase shifter 10. The second harmonic cavity 11 outputs a 532 nm laser beam. This 532 nm laser beam is injected into the double-resonance optical parametric cavity 2 through the isolator 12 and the dichroic mirror 13. The reflected field of the double-resonance optical parametric cavity 2 passes through the dichroic mirror 13 and the isolator 12 again and enters the second photodetector 14. The second photodetector 14 feeds the signal back to the double-resonance optical parametric cavity 2 through the second photoelectric feedback control system 15, thus achieving cavity length locking of the double-resonance optical parametric cavity.

[0040] Path and control of the second sub-beam: Another 1064 nm laser beam passes through the first high-reflection mirror 22, and then sequentially passes through the optical mode cleaner 17 and the second phase shifter 5. The signal generator 4 is used to perform slow scanning on the second phase shifter 5.

[0041] The light field output by the dual-resonance optical parametric cavity 2 is injected into the balanced zero-beat detection system 6 together with the light field passing through the second phase shifter 5. The balanced zero-beat detection system 6 cooperates with the third photoelectric feedback control system 18 to lock the relative phase of the squeezed-state light field and the local detection light field.

[0042] The double-resonance optical parametric cavity 2 is also connected to a high-precision temperature controller 3 for controlling the temperature inside the double-resonance optical parametric cavity 2 ; the spectrum analyzer 7 is connected to the balanced zero-beat detection system 6 .

[0043] The double-resonant optical parametric cavity 2 utilizes a semi-monolithic cavity structure, consisting of an output coupling mirror and a plano-convex nonlinear crystal. The output coupling mirror has a radius of curvature of 25 mm and is coated with a 532 nm / 1064 nm dual-wavelength dielectric coating, resulting in a reflectivity of 97.5% for 532 nm laser light and 85% for 1064 nm laser light. The nonlinear crystal is made of PPKTP nonlinear material, with a convex surface having a radius of curvature of 12 mm. The flat surface is coated with a 532 nm / 1064 nm dual-wavelength antireflection coating (residual reflectivity <0.2%), while the convex surface is coated with a dual-wavelength high-reflectivity coating (reflectivity >99% at both 532 nm and 1064 nm). The convex surface of the crystal and the output coupling mirror form a resonant cavity with a length of 31 mm, corresponding to a linewidth of 98.8 MHz, a free spectral range of 3.8 GHz, and a finesse of 38.6. A piezoelectric ceramic is fixed to the outer surface of the output coupling mirror. The cavity also features a temperature control structure, comprised of a thermistor, a TEC (Technical Engineering Design) (TEC), and a copper furnace. This structure is used to fine-tune the optimal dual resonance point for varying pump powers. The crystal is placed within the copper furnace, while the TEC is encased within it. The thermistor, installed within a hole in the furnace, monitors the crystal's temperature. TEC, short for Thermo Electric Cooling (TEC), is a popular term for semiconductor coolers, also known as thermoelectric coolers. It utilizes the Peltier effect of thermoelectric materials for solid-state cooling.

[0044] The coating parameters of the output coupling mirror in the dual-resonant optical parametric cavity 2 are specifically configured to allow simultaneous resonance of 532 nm and 1064 nm wavelengths within the cavity. This structure exploits the nonlinear effects of the resonant 532 nm light field to achieve efficient parametric gain for the 1064 nm light field, thereby lowering the theoretical threshold of the dual-resonant optical parametric cavity 2.

[0045] The acousto-optic frequency shifting system 16 uses a two-stage acousto-optic modulator with a central modulation frequency of 100 MHz and a bandwidth of 30 MHz. The acousto-optic modulator is driven by signal sources with frequencies of -90 MHz and +110 MHz, respectively, to generate a +20 MHz upper sideband light field, which is injected into the double-resonance optical parametric cavity 2 as a frequency-shifting auxiliary light field.

[0046] The balanced zero-beat detection system 6 consists of a 50 / 50 beam splitter and a balanced zero-beat detector. The compressed light output by the dual-resonance optical parametric cavity 2 and the local detection light passing through the second phase shifter 5 are coupled into the balanced zero-beat detector on the 50 / 50 beam splitter. The signal is collected by a high-quantum-efficiency diode, and the noise level of the compressed state light field is detected in combination with a spectrum analyzer 7.

[0047] Signal generator 4 is a digital signal generator with a minimum frequency resolution of 1 µHz. The compression angle and cavity length of the squeezed-state light field are locked via the first and second optoelectronic feedback control systems 9 and 15. A 500 mHz sawtooth wave signal output by signal generator 4 acts on the second phase shifter 5, and the scanned signal of the squeezed-state light field can be observed on the spectrum analyzer 7.

[0048] Change the pump power of the incident double-resonance optical parametric cavity 2 and the temperature of the high-precision temperature controller 3 at the same time, so that the compressed state light field scanning signal measured by the spectrum analyzer 7 reaches the maximum, and record the different temperature points corresponding to this experiment.

[0049] This application also proposes a method for accurately fitting the pumping threshold of a double-resonant optical parametric cavity, using the above-mentioned device, including the following steps:

[0050] In step 1, a single-frequency solid-state laser 1 outputs a 1064 nm laser beam, which is then split into beam 1 and beam 2 after passing through a first beam splitter 19. Beam 1 enters an acousto-optic frequency modulation (AOFM) system 16, while beam 2 passes through a first phase shifter 10 and is injected into a second harmonic generator 11, generating a 532 nm pump field through nonlinear interaction. The pump field passes through an isolator 12 to suppress the backscattered light field, and then passes through a dichroic mirror 13 and is directly injected into a double-resonant optical parametric cavity 2, generating a squeezed state field.

[0051] In step 2, the light beam 1 passes through the acousto-optic modulation frequency shifting system 16 to generate a +20 MHz frequency-shifted auxiliary light field, and then is injected into the double-resonance optical parametric cavity 2 through the second high-reflection mirror 23, the third beam splitter 21 and the third high-reflection mirror 24 to participate in the nonlinear process.

[0052] In step 3, the isolator 12 consists of two polarization beam-splitting prisms and an optically active crystal. The reflective end of the first polarization beam-splitting prism can extract the pump light field reflected by the dual-resonance optical parametric cavity 2. The reflected pump light field passes through the dichroic mirror 13 and the isolator 12 again and enters the second photodetector 14. The second photodetector 14 feeds the extracted signal back to the piezoelectric ceramic of the dual-resonance optical parametric cavity 2 through the second photoelectric feedback control system 15, achieving stable control of the cavity length.

[0053] In step 4, the frequency-shifted auxiliary light field reflected by the double-resonance optical parametric cavity 2 is extracted through the third beam splitter 21, injected into the first photodetector 8, and fed back to the first phase shifter 10 through the first photoelectric feedback control system 9. The first phase shifter 10 acts on the fundamental frequency light field in front of the second harmonic cavity 11, which can change the phase of the pump light field generated by the second harmonic cavity 11, thereby achieving locking of the compression angle.

[0054] In step 5, light beam 2 generates light beam 3 through the third beam splitter 20. Light beam 3 serves as local detection light, passes through the optical mode cleaner 17 and the second phase shifter 5, and is efficiently coupled with the compressed state light field and the frequency-shifted auxiliary light field output by the double-resonance optical parametric cavity 2, and is injected into the balanced zero-beat detection system 6.

[0055] In step 6, signal generator 4 sweeps the second phase shifter 5 in the optical path of beam 3. This second phase shifter 5 acts on the local probe light, changing the detection angle of the squeezed-state light field. By connecting a spectrum analyzer 7 to the balanced zero-beat detection system 6, the noise distribution of the squeezed-state under the sweeping condition can be measured.

[0056] In step 7, gradually increase the pump power incident on the double-resonant optical parametric cavity 2 from P1 mW to P2 mW, with a step size of x mW. Each time the pump power is changed, steps 3 and 4 must be repeated to re-lock the cavity length of the double-resonant optical parametric cavity 2 with the compression angle of the compressed state light field. Then, step 6 is repeated. At the same time, the temperature of the double-resonant optical parametric cavity 2 must be finely adjusted using the high-precision temperature controller 3 (the initial optimal double-resonance temperature is around 33°C) to maximize the compressed state light field noise distribution recorded on the spectrum analyzer 7. At this point, the temperature point corresponding to the high-precision temperature controller 3 satisfies the double-resonance condition and quasi-phase matching condition of the double-resonant optical parametric cavity 2.

[0057] Step 8: Record the temperature values ​​corresponding to different pump powers, and accurately fit the empirical formula between the cavity temperature of the double-resonance optical parametric cavity 2 and the incident pump light power through experimental parameters. :

[0058] ;

[0059] Where, is the incident pump light power, which is the independent variable of the formula, and is the experimental fitting parameter, which depends on the experimental measured value.

[0060] Step 9: Based on the relationship between the threshold of the double-resonance optical parametric cavity 2 and the cavity temperature Finally, the relationship between the threshold of the double-resonance optical parametric cavity 2 and the incident pump light power is obtained. .

[0061] The details are as follows: It can be written as:

[0062] ;

[0063] Where, is the relationship between the threshold and temperature, is the pump light transmittance of the output coupling mirror, is the intracavity loss of the pump light, is the fundamental frequency light transmittance of the output coupling mirror, is the intracavity loss of fundamental frequency light, is the coupling coefficient.

[0064] The coupling coefficient E is expanded as:

[0065] ;

[0066] Where, is the vacuum permeability, is the effective nonlinear coefficient, = is the angular frequency of the fundamental light, is the crystal length, is the focusing factor, is the speed of light, is the refractive index of the pump light (at room temperature), is the angular frequency of the pump light, is the phase mismatch.

[0067] The phase mismatch Related to temperature, its expression can be written as:

[0068] ;

[0069] Where: is the refractive index of the pump light (varies with temperature), is the wavelength of the pump light, = is the refractive index of the fundamental frequency light (varies with temperature), = is the wavelength of the fundamental frequency light, is the crystal polarization period.

[0070] According to the relationship between refractive index and temperature, the phase mismatch The refractive index It can be written as:

[0071] ; Its actual value is related to the crystal material and the incident light band.

[0072] The expanded form at this time With the above formula By combining the above, we can get the trend of the threshold changing with the incident pump light power by calculation and fitting. .

[0073] The traditional compression noise variance fitting model can be written as:

[0074] ;

[0075] Where, is the threshold power of the double-resonant optical parametric cavity 2, through Replace the fixed threshold in the compression noise variance formula , the dynamic change characteristics of the threshold can be introduced. is the incident pump power, is the Fourier frequency, is the cavity decay rate.

[0076] After combining multiple Substituting the above traditional compression noise variance fitting model, we can obtain the compression noise variance fitting model with dynamically changing thresholds.

[0077] The signal of the balanced zero-beat detection system 6 is fed back to the second phase shifter 5 through the third photoelectric feedback control system 18 to lock the detection angle of the compressed state light field. The spectrum analyzer 7 is used to test and record different pump powers. The corresponding compression and anti-compression , by substituting it into the compression noise variance fitting model with dynamically changing thresholds, the system loss can be accurately analyzed. and phase jitter .

[0078] The following are the test and fitting results provided in this embodiment.

[0079] Test 1

[0080] After the cavity length and compression angle of the double-resonance optical parametric cavity 2 are locked, the compression light detection angle is scanned at a frequency of 500 MHz by the signal generator 4, and the spectrum analyzer 7 records the graph as shown in FIG. Figure 2 shown. Figure 2 The following is the compression noise variance test result at 1 MHz corresponding to the incident pump light power of 7 mW and the high-precision temperature controller at 33.062 ℃. Figure 2 It can be seen from the figure that the noise component of the squeezed state light field increases or decreases with scanning the detection angle. The noise component below the shot noise baseline corresponds to compression, while the noise component above the shot noise baseline corresponds to anti-compression. Changing the incident pump light power and the temperature of the high-precision temperature controller 3 will cause changes in both compression and anti-compression.

[0081] Test 2

[0082] The incident pump light power is gradually increased from 1 mW to 10 mW with a step size of 1 mW. The detection angle is scanned by the signal generator 4, and the temperature of the high-precision temperature controller 3 is changed so that the compression noise curve recorded by the spectrum analyzer 7 is the largest at this time. The corresponding cavity temperature under different pump powers is recorded. The relationship between the cavity temperature and the incident pump power of the double-resonant optical parametric cavity 2 is obtained by linear fitting. ,like Figure 3 As shown. Figure 3 It can be seen from FIG1 that as the incident pump light power changes, the temperature of the optimal double resonance point that satisfies the double resonance optical parametric cavity 2 also changes.

[0083] Fit 1

[0084] Will and Combined, the threshold dynamic change curve of the double-resonance optical parametric cavity 2 is obtained by fitting ,like Figure 4 As shown. Figure 4 It can be seen from the figure that with the increase of the incident pump light power, the actual threshold of the corresponding double-resonant optical parametric cavity 2 becomes smaller and smaller.

[0085] Test 3

[0086] The incident pump light power is gradually increased from 1 mW to 10 mW with a step size of 1 mW. The cavity length locking of the double-resonant optical parametric cavity 2 and the phase locking of the squeezed state light field are achieved by the first photoelectric feedback control system 15, the second photoelectric feedback control system 9 and the third photoelectric feedback control system 18. The compression and anti-compression degrees of different pump powers are tested and recorded by the spectrum analyzer 7. The compression and anti-compression curves of the system are fitted by fixed thresholds and dynamic thresholds, as shown in Figure 1. Figure 5 As shown. Figure 5 It can be seen that if the threshold is fixed, the compression and anti-compression degrees are poorly fitted; but when a dynamic threshold is introduced, the compression and anti-compression degrees are perfectly fitted at different pump powers, successfully achieving a scientific evaluation of the loss and phase jitter of the dual-resonance compression source system.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A device for accurately fitting the pumping threshold of a double-resonant optical parametric cavity, characterized by: The invention comprises a single-frequency solid-state laser (1), a double-resonance optical parametric cavity (2) and a balanced zero-beat detection system (6); the laser beam output by the single-frequency solid-state laser (1) is split into two beams by a first beam splitter (19), one of which is injected into the double-resonance optical parametric cavity (2) after passing through an acousto-optic modulation frequency shifting system (16); the reflected field output by the double-resonance optical parametric cavity (2) enters a first photoelectric detector (8), and the first photoelectric detector (8) feeds back the obtained signal to a first phase shifter (10) through a first photoelectric feedback control system (9); The other beam is split into two beams again after passing through the second beam splitter (20), one of which is directly injected into the second harmonic cavity (11) after passing through the first phase shifter (10), and the laser output from the second harmonic cavity (11) is injected into the double-resonance optical parametric cavity (2) through the isolator (12) and the dichroic mirror (13), and the reflection field of the double-resonance optical parametric cavity (2) enters the second photodetector (14) again through the dichroic mirror (13) and the isolator (12), and the second photodetector (14) feeds back the signal to the double-resonance optical parametric cavity (2) through the second photoelectric feedback control system (15); The other sub-beam passes through the optical mode cleaner (17) and the second phase shifter (5) in sequence; The compressed state light field output by the double-resonance optical parametric cavity (2) and the local detection light passing through the second phase shifter (5) are injected into the balanced zero-beat detection system (6). The balanced zero-beat detection system (6) cooperates with the third photoelectric feedback control system (18) to lock the relative phase of the compressed state light field and the local detection light field. The double-resonance optical parametric cavity (2) is also connected to a high-precision temperature controller (3), and the high-precision temperature controller (3) is used to control the cavity temperature of the double-resonance optical parametric cavity (2).

2. The device for accurately fitting the pumping threshold of a double-resonant optical parametric cavity according to claim 1, characterized in that: The double-resonance optical parametric cavity (2) adopts a semi-monolithic cavity structure, which is composed of an output coupling mirror and a plano-convex nonlinear crystal. The convex surface of the crystal and the output coupling mirror form a resonant cavity, and a temperature control structure is provided in the resonant cavity.

3. The device for accurately fitting the pumping threshold of a double-resonant optical parametric cavity according to claim 2, characterized in that: The output coupling mirror is coated with a dual-wavelength dielectric film, the plane surface of the plano-convex nonlinear crystal is coated with a dual-wavelength anti-reflection film, and the convex surface is coated with a dual-wavelength high-reflection film.

4. The device for accurately fitting the pumping threshold of a double-resonant optical parametric cavity according to claim 2, characterized in that: The temperature control structure consists of a thermistor, a Peltier and a copper furnace.

5. The device for accurately fitting the pumping threshold of a double-resonant optical parametric cavity according to claim 1, characterized in that: The laser output by the acousto-optic modulation frequency shift system (16) passes through the second high-reflection mirror (23), the third beam splitter (21) and the third high-reflection mirror (24) in sequence, and is then injected into the double-resonance optical parametric cavity (2); the reflected field output by the double-resonance optical parametric cavity (2) enters the first photodetector (8) through the third high-reflection mirror (24) and the third beam splitter (21).

6. The device for accurately fitting the pumping threshold of a double-resonant optical parametric cavity according to claim 1, characterized in that: Another sub-beam of laser light outputted from the second beam splitter (23) enters the optical mode cleaner (17) after passing through the first high-reflection mirror (22).

7. The device for accurately fitting the pumping threshold of a double-resonant optical parametric cavity according to claim 1, characterized in that: The balanced zero-beat detection system (6) consists of a 50 / 50 beam splitter and a balanced zero-beat detector. The compressed state light field output by the double-resonance optical parametric cavity (2) and the local detection light passing through the second phase shifter (5) are coupled into the balanced zero-beat detector on the 50 / 50 beam splitter.

8. The device for accurately fitting the pumping threshold of a double-resonant optical parametric cavity according to claim 1, characterized in that: The acousto-optic modulation frequency shifting system (16) adopts a two-stage acousto-optic modulator. According to the central modulation frequency and bandwidth of the acousto-optic modulator, a signal source of a specific frequency is set to drive the acousto-optic modulator, and the generated upper sideband light field is injected into the double-resonance optical parametric cavity (2) as a frequency shift auxiliary light field.

9. The device for accurately fitting the pumping threshold of a double-resonant optical parametric cavity according to any one of claims 1 to 8, characterized in that: The second phase shifter (5) is connected to a signal generator (4), and the balanced zero-beat detection system (6) is connected to a spectrum analyzer (7). The compression angle and cavity length of the compressed state light field are locked through the first photoelectric feedback control system (9) and the second photoelectric feedback control system (15). The signal generator (4) is used to output a sawtooth wave signal of a specific frequency to act on the second phase shifter (5), and the scanning signal of the compressed state light field is displayed on the spectrum analyzer (7).

10. A method for accurately fitting the pumping threshold of a double-resonant optical parametric cavity, using the apparatus according to any one of claims 1 to 9, characterized in that: The following steps are involved: Step 1: A single-frequency solid-state laser (1) outputs a laser beam, which is then divided into a first laser beam and a second laser beam after passing through a first beam splitter (19). The first laser beam enters an acousto-optic modulation frequency shifting system (16), and the second laser beam is injected into a second harmonic cavity (11) through a first phase shifter (10) to generate a pump light field. The pump light field passes through an isolator (12) and a dichroic mirror (13) and then enters a double-resonance optical parametric cavity (2), thereby generating a compressed state light field. Step 2, the first laser beam passes through the acousto-optic modulation frequency shifting system (16) to generate a frequency-shifted auxiliary light field, and then is directly injected into the double-resonance optical parametric cavity (2) through the second high-reflection mirror (23), the third beam splitter (21) and the third high-reflection mirror (24); Step 3, extracting the pump light field reflected by the dual-resonance optical parametric cavity (2) through the isolator (12), and the reflected pump light field again passes through the dichroic mirror (13) and the isolator (12) to enter the second photodetector (14), and the second photodetector (14) feeds back the cavity locking signal to the dual-resonance optical parametric cavity (2) through the second photoelectric feedback control system (15), thereby realizing stable control of the cavity length; Step 4, extracting the frequency-shifted auxiliary light field reflected by the double-resonance optical parametric cavity (2) through the third beam splitter (21), and the reflected frequency-shifted auxiliary light field again passes through the third beam splitter (21) and enters the first photodetector (8), and the first photodetector (8) feeds back the phase information of the compressed state light field and the pump light field to the first phase shifter (10) through the first photoelectric feedback control system (9), thereby achieving stable locking of the compression angle; Step 5, the second laser beam is further split into a third laser beam after passing through the second beam splitter (20), and the third laser beam is used as a local detection light field, and is efficiently coupled with the compressed state light field output by the double-resonance optical parametric cavity (2) and the frequency-shifted auxiliary light field in the balanced zero-beat detection system (6) through the first high-reflection mirror (22), the optical mode cleaner (17) and the second phase shifter (5); Step 6, scanning the second phase shifter (5) in the third laser path through the signal generator (4), and recording the compression information of the scanning detection angle through the spectrum analyzer (7); Step 7, changing the pump light power incident on the double-resonance optical parametric cavity (2) according to the set step size, again achieving the locking of the cavity length and the compression angle through steps 3 and 4, and using a high-precision temperature controller (3) to finely adjust the temperature of the double-resonance optical parametric cavity (2) so that the compression / anti-compression recorded by the spectrum analyzer (7) reaches a maximum value, and the temperature point at this time satisfies both the double resonance condition and the quasi-phase matching condition; Step 8: Record the temperature values ​​corresponding to the optimal double resonance point at different pump powers and fit the empirical formula of the cavity temperature and the incident pump light power; In step 9, based on the relationship between the threshold and temperature, and the relationship between temperature and pump light power, the dynamic variation characteristics of the threshold with pump light power are obtained, and the characteristics are substituted into the calculation formula of the compression noise variance to improve the existing theoretical model of loss and phase jitter fitting.

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