CN110068978B - Non-classical optical field generator with self-compensated phase - Google Patents
Non-classical optical field generator with self-compensated phase Download PDFInfo
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Abstract
The invention belongs to the technical field of non-classical optics, and discloses a phase self-compensating non-classical optical field generator, which comprises a laser, a compressed optical field generator, a first phase shifter, a beam splitter, a central controller, a balanced homodyne detector and a spectrum analyzer; the compressed light field generator is used for generating a compressed light field detected by the balanced homodyne detector; the output signal of the balanced homodyne detector is connected with a spectrum analyzer, and the output end of the spectrum analyzer is connected with a central controller; the output end of the central controller is connected with the input end of the temperature controller, and is used for changing the crystal temperature through the temperature controller, finding out the double resonance temperature of the optical parametric cavity amplifier according to the output signal of the single detector under different crystal temperatures, and finding out the phase self-compensation temperature of the optical parametric amplifier according to the compression degree of the first compressed light field under different crystal temperatures. The invention improves the non-classical characteristic of the light field and can be applied to the field of non-classical light fields.
Description
Technical Field
The invention belongs to the technical field of non-classical optics, and particularly relates to a phase self-compensation non-classical optical field generator.
Background
The compressed state light field is a non-classical light field which compresses the quantum noise of a certain orthogonal component to be below the limit of classical shot noise, and is applied to improving the sensitivity of precise optical measurement and weak gravitational wave signal detection due to the characteristic of breaking through the limit of the quantum noise; in addition, two beams of single-mode compressed light or one beam of dual-mode compressed light can be used for generating an entangled-state light field, and further applied to research of quantum computation, quantum information and quantum communication. Therefore, the research on a continuously and stably operated high-compression non-classical light source has become a hot spot of scientific research nowadays. As early as 1985, the united states bell laboratory first experimentally observed a state of compression using four-wave mixing; subsequently, an Optical parametric amplification technique (OPA) was proposed and becomes an important technique for generating a compressed state.
A low threshold stable optical parametric cavity becomes a critical component for generating compression. The optical parametric cavity is divided into a single-resonance optical parametric cavity, a double-resonance optical parametric cavity and the like according to whether the injected light resonates in the cavity or not. The single resonant cavity only resonates the fundamental frequency seed light in the cavity, and the pumping light passes through the nonlinear crystal once or twice and then is output out of the cavity. The seed light and the pump light of the double-resonance optical parametric cavity resonate in the cavity, and compared with the single-resonance optical parametric cavity, the nonlinear interaction of the pump light and the crystal is enhanced because the pump light passes through the nonlinear crystal repeatedly back and forth, so that the pumping threshold value of the optical parametric cavity can be effectively reduced, and the energy consumption of the pump laser is saved; meanwhile, the pump light resonance can effectively reflect the pump light which is not matched with the mode, so that the pump light outside the volume of the fundamental mode is prevented from heating the crystal, and the heat effect of the crystal is effectively reduced; secondly, the optical parameter cavity can be directly locked by utilizing the resonance condition of the pump light, the signal-to-noise ratio of the extracted error signal is higher, and the cavity length locking stability is greatly improved. Therefore, the double-resonance optical parametric cavity can easily realize the high stability, miniaturization and easy maintenance design of a low-power laser system, and is more beneficial to the preparation and practical application of a high-compression-degree compressed-state optical field.
However, the dual-resonance optical parametric cavity needs to strictly satisfy the simultaneous resonance of the seed light and the pump light cavity under a specific phase matching temperature condition, and thus the relationship between the cavity length, the crystal length and the phase matching temperature bandwidth needs to be considered more accurately. In the experimental operation, due to the influence of the nonlinear crystal on the dispersion characteristic, when the condition that the seed light and the pump light resonate simultaneously in the cavity is met, the corresponding temperature is usually deviated from the optimal phase matching temperature. The theoretical analysis of compression generation shows that the crystal is in a phase mismatch state at the moment, so that the nonlinear interaction strength is reduced, and the phase offset of pump light is introduced, so that classical gain reduction and compression angle rotation are caused, and the generated orthogonal component compression degree is reduced. In order to avoid the situation, the dispersion effect of the pump light and the seed light is compensated by inserting a dispersion compensation plate into a wedge-shaped crystal or a cavity, and the optical path difference of the two beams of light is changed by transversely moving the crystal or adjusting the angle of the compensation plate, so that dispersion compensation is achieved, and the superposition of the double-resonance temperature point and the phase matching temperature point is realized. However, the former will increase the difficulty of adjusting the optical cavity, and the latter introduces cavity loss, which is not good for the preparation of high-compression and high-stability compressed optical field.
Disclosure of Invention
The invention overcomes the defects of the prior art, and solves the technical problems that: a phase self-compensating non-classical optical field generator is provided.
In order to solve the technical problems, the invention adopts the technical scheme that: a phase self-compensating non-classical optical field generator comprises a laser, a compressed optical field generator, a first phase shifter, a first beam splitter, a central controller, a balanced homodyne detector and a spectrum analyzer; the compressed optical field generator comprises a second phase shifter, an optical parametric amplifier, a PDH frequency stabilizer and a temperature controller, and is used for receiving fundamental frequency light and frequency doubling light emitted by the laser and generating a compressed optical field; the frequency doubling light emitted by the laser is phase-shifted by the second phase shifter and then is injected into the optical parametric amplifier together with the fundamental frequency light; the signal light emitted by the optical parametric amplifier is detected by a single detector and then output to the central controller; the signal light emitted from the optical parametric amplifier is further respectively incident on two incidence surfaces of a first beam splitter with the base frequency light emitted by the laser and subjected to phase shifting by a first phase shifter, and then is detected by a balanced homodyne detector, an alternating current output signal of the balanced homodyne detector is connected with a spectrum analyzer, and an output end of the spectrum analyzer is connected with the central controller and is used for analyzing and obtaining the compression degree of a first compressed light field according to a detection signal of the balanced homodyne detector; the output end of the PDH frequency stabilizer is connected with the piezoelectric ceramic on the cavity mirror of the optical parametric amplifier and used for locking the cavity length of the optical parametric amplifier to a resonance enhancement point; the temperature controller is used for adjusting the temperature of the crystal in the optical parametric amplifier, the output end of the central controller is connected with the input end of the temperature controller, the temperature controller is used for changing the temperature of the crystal, the double resonance temperature of the optical parametric amplifier is automatically searched according to the direct current output signal of the single detector at different crystal temperatures, and the phase self-compensation temperature of the optical parametric amplifier is automatically searched according to the compression degree of the first compressed light field at different crystal temperatures.
A double-resonance temperature measuring module is arranged in the central controller; the dual resonance temperature measurement module is configured to perform the following procedure: outputting a control signal to set the temperature setting value of the temperature controller at a certain initial temperature, and recording the peak-to-peak value of a gain curve obtained by the single detector after the temperature of the temperature controller is stable; then outputting a signal to change the temperature setting value of the temperature controller, forming a new gain curve after the temperature of the temperature controller is stable, recording the peak-to-peak value of the gain curve obtained by the detection of the single detector, comparing the peak-to-peak value with the previous peak-to-peak value, and selecting the larger value; and outputting the signal again to change the temperature setting value of the temperature controller, changing the circulation until the maximum peak value is found, and recording the temperature corresponding to the maximum peak value as the double-resonance temperature.
When the double-resonance temperature measurement module adjusts the temperature setting value of the temperature controller, the change amount of the temperature setting value of the temperature controller at each time is 0.01-0.1 ℃.
A phase self-compensation module is arranged in the central controller; the phase self-compensation module is used for executing the following procedures: outputting a control signal to set the control temperature of the temperature controller at the double resonance temperature, and recording the optical field compression value output by the spectrum analyzer; then outputting a control signal to change the temperature setting value of the temperature controller in a small amplitude manner, and recording the optical field compression value output by the spectrum analyzer at the corresponding temperature; and repeating the operation for multiple times, recording to obtain multiple groups of temperature setting values and the light field compression values at corresponding temperatures, performing curve fitting, and finding the temperature corresponding to the minimum compression on the curve as the phase self-compensation temperature.
When the phase self-compensation module adjusts the temperature setting value of the temperature controller, the change amount of the temperature setting value of the temperature controller at each time is 0.01-0.1 ℃.
The non-classical optical field generator with the self-compensated phase position further comprises a second compressed optical field generator and a second beam splitter, wherein the second compressed optical field generator comprises a third phase shifter, a second optical parametric amplifier, a second PDH frequency stabilizer and a second temperature controller, and the second compressed optical field generator is used for receiving fundamental frequency light and frequency doubling light emitted by the laser and generating a second compressed optical field; the frequency doubling light emitted by the laser is phase-shifted through a third phase shifter and then is injected into a second optical parametric amplifier together with the fundamental frequency light; the signal light emitted by the second optical parametric amplifier is detected by a single detector and then output to the central controller; the output end of the central controller is connected with the input end of the temperature controller of the second compressed optical field generator, and the central controller is used for changing the crystal temperature in the second optical parametric amplifier through the temperature controller, finding the double resonance temperature of the second optical parametric cavity amplifier according to the output signal of the single detector at different crystal temperatures, and finding the phase self-compensation temperature of the second optical parametric amplifier according to the compression degree of the second compressed optical field at different crystal temperatures.
The balanced homodyne detector is used for respectively detecting the compression degrees of the first compressed light field and the second compressed light field and is also used for detecting the entanglement degrees of the first compressed light field and the second compressed light field after being coupled by the beam splitter.
Compared with the prior art, the invention has the following beneficial effects: the invention provides a phase self-compensation non-classical optical field generator which has the characteristics of stable structure, convenient adjustment, no insertion loss and the like, and adopts a central control unit to automatically adjust a temperature controller to control the temperature of a nonlinear crystal, firstly, the temperature controller can be controlled to automatically find out the double resonance temperature of an optical parameter cavity, secondly, the temperature controller can be controlled to automatically find out the proper temperature to realize phase self-compensation, thereby obtaining larger compression degree, the device has simple integral structure and automatic adjustment function, the adjustment process is convenient, quick and efficient, and the problem of inaccurate measurement of the compression degree of a non-classical optical field can be well solved.
Drawings
Fig. 1 is a schematic structural diagram of a phase self-compensated non-classical optical field generator according to an embodiment of the present invention;
FIG. 2 is a schematic diagram illustrating the principle of phase self-compensation in the implementation of the present invention;
FIG. 3 is a schematic diagram of a working flow of a dual-resonance temperature measurement module according to an embodiment of the present invention;
FIG. 4 is a schematic diagram illustrating a working flow of the phase self-compensation module according to an embodiment of the present invention;
fig. 5 is a schematic diagram of an optical path of a phase self-compensated non-classical optical field generator according to an embodiment of the present invention;
FIG. 6 is a transmission peak curve of the output of the optical parametric amplifier according to one embodiment of the present invention;
FIG. 7 is a graph illustrating interference between the output signal light and the coherent light output from the optical parametric amplifier according to an embodiment of the present invention;
FIG. 8 is a gain curve diagram of an optical parametric amplifier according to an embodiment of the present invention;
FIG. 9 is a graph of the compression and decompression of the compressed light output of a phase self-compensated non-classical optical field generator as a function of temperature in accordance with one embodiment of the present invention;
fig. 10 is a schematic structural diagram of a phase self-compensated non-classical optical field generator according to a second embodiment of the present invention;
fig. 11 is a schematic diagram of an optical path of a phase self-compensated non-classical optical field generator according to a second embodiment of the present invention;
in the figure: 1 is a first dichroic mirror, 2 is a second dichroic mirror, 3 is a third beam splitter, 4 is a first matching lens group, 5 is a second piezoelectric ceramic, 6 is a fourth beam splitter, 7 is a first high reflection mirror, 8 is a second matching lens group, 9 is a first isolator, 10 is a first electro-optic modulator, 11 is a second PDH frequency stabilizer, 111 is a lock cavity detector, 112 is a modulation signal, 113 is a mixer, 114 is a proportional integral differentiator, 115 is a high voltage amplifier, 12 is a third dichroic mirror, 13 is a fourth dichroic mirror, 14-garbage stack, 15 is a fifth high reflection mirror, 16 is a second balanced homodyne detector, 17 is an automatic adjusting part of a phase self-compensating non-classical light field generator, 18 is a fifth dichroic mirror, 19 is a sixth high reflection mirror, 20 is a fifth beam splitter, 21 is a second high reflection mirror, 22 is a third high reflection mirror, 24 is a fourth high reflection mirror, 25 is a sixth beam splitter, 26 is a third piezoelectric ceramic, 27 is a fourth piezoelectric ceramic, 28 is a seventh beam splitter, 29 is a second optical parametric amplifier, 30 is a second signal light, 31 is a first optical parametric amplifier, a1 is a nonlinear crystal, a2 is a meniscus concave mirror, a3 is a first piezoelectric ceramic, 32 is a first beam splitter, 33 is a first balanced homodyne detector, 34 is a digital-to-analog converter, 35 is a central controller, 36 is an analog-to-digital converter, 37 is a temperature controller, 38 is a subtractor, 39 is a spectrum analyzer, 40 is a light barrier, 41 is a laser, 42 is a seed light, 43 is an doubled light, 44 is a noise reducer, 45 is a second phase shifter, 46 is a first PDH frequency stabilizer, 47 is a first signal light, 48 is a fundamental frequency light, 49 is a first phase shifter, 50 is a third phase shifter, 51 is a fourth phase shifter, 52 is a second beam splitter, 53 is a temperature controller, 54 is a third matching lens group, 55 is a second isolator and 56 is a second electro-optic modulator.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments; all other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1, an embodiment of the present invention provides a phase self-compensated non-classical optical field generator, which includes a laser 41, a compressed optical field generator, a first phase shifter 49, a first beam splitter 32, a central controller 35, a balanced homodyne detector 33, and a spectrum analyzer 39. The laser 41 is a laser capable of emitting laser beams of 1550nm and 775nm at the same time.
Specifically, as shown in fig. 1, the compressed optical field generator includes a second phase shifter 45, an optical parametric amplifier 31, a PDH frequency stabilizer 46 and a temperature controller 37, and is configured to receive fundamental light and doubled light emitted from a laser 41 and generate a compressed optical field; wherein, the frequency doubling light emitted by the laser 41 is phase-shifted by the second phase shifter 45 and then injected into the optical parametric amplifier 31 together with the fundamental frequency light; the signal light emitted from the optical parametric amplifier 31 is detected by a single detector and then output to the central controller 35; the signal light emitted from the optical parametric amplifier 31 and the fundamental frequency light 48 emitted by the laser 41 and phase-shifted by the first phase shifter 49 enter two incidence surfaces of the first beam splitter 32 respectively, and are detected by the balanced homodyne detector 33, an output signal of the balanced homodyne detector 33 is connected with the spectrum analyzer 39, and an output end of the spectrum analyzer 39 is connected with the central controller 35, and is used for analyzing a detection signal of the balanced homodyne detector 33 to obtain the compression degree of the first compressed light field; the output end of the PDH frequency stabilizer 46 is connected to the piezoelectric ceramic on the cavity mirror of the optical parametric amplifier 31, and is used for locking the cavity length of the optical parametric amplifier 31 to the resonance enhancement point. Wherein the single detector for detecting the signal light may be one of the balanced homodyne detectors 33. In addition, a noise reducer 44 is included in the optical path, which is disposed between the laser and the optical parametric amplifier 31, and is used for performing noise reduction processing on the light emitted by the laser 41.
Specifically, the temperature controller 37 is configured to adjust the crystal temperature in the optical parametric amplifier 31, and the output end of the central controller 35 is connected to the input end of the temperature controller 37, and is configured to change the crystal temperature through the temperature controller 37, find the dual-resonance temperature of the optical parametric amplifier 31 according to the output signal of the single detector at different crystal temperatures, and find the phase self-compensation temperature of the optical parametric amplifier 31 according to the compression degree of the first compressed optical field at different crystal temperatures.
Specifically, the present embodiment provides a phase self-compensated non-classical optical field generator further comprising an analog-to-digital converter 34 and a digital-to-analog converter 36. The signal sent by the single detector is output to the central controller after passing through the analog-to-digital converter 34, and the temperature setting signal output by the central controller is output to the temperature controller 37 after passing through the digital-to-analog converter 36.
The phase self-compensation principle of the invention is as follows: the dual-resonance optical parametric cavity needs to strictly satisfy the simultaneous resonance in the seed light and the pumping light cavity under the condition of specific phase matching temperature, so that the relationship among the cavity length, the crystal length and the phase matching temperature bandwidth needs to be considered more accurately. In the experimental operation, the temperature at which the seed light and the pump light resonate simultaneously in the cavity does not necessarily satisfy the phase matching temperature condition. For example: in the experiment, the temperature of the nonlinear crystal is changed by adjusting a temperature controller, so that the 1550nm and 775nm of light beams realize double resonance in an optical parametric cavity, the temperature at the moment is T1, and the compression degree at the moment is measured. Theoretically, to generate compressed light with high degree of compression, the temperature should satisfy both the dual resonance condition and the phase matching condition Δ k ═ 0, where Δ k is a phase mismatch factor representing the difference between the injected multiplied light and the fundamental light, the generated compressed light wave vector. By adjusting the temperature of the nonlinear crystal with the temperature controller to vary around the temperature T1, it was found that more compression occurred, at which point the temperature was no longer at the 1550nm and 775nm double resonance of the beam. This phenomenon indicates that the temperature at which dual resonance of the light beams 1550nm and 775nm is achieved does not satisfy the temperature condition for phase matching in the experiment. Let the temperature satisfying the phase matching condition be TpWhen the phases are not matched, namely delta k is not equal to 0, namely the difference value between the injected fundamental frequency light, the frequency doubling light and the generated compressed light wave vector is not zero, and the momentum conservation and energy conservation conditions are not met among the three photons. Let delta T1＝T1-TpCausing a phase change amount delta1＝vδT1Corresponding compression angle of theta1Resulting in a reduced degree of compression projected onto the orthogonal component. If the temperature of the nonlinear crystal is finely adjusted by the temperature controller, the temperature approaches the temperature T of phase matchingPSetting the adjusted temperature to be T2. At this point, the temperature change introduces new variations, one of which is the amount of detuning Δ introduced by the beams 1550nm and 775nm not resonating2＝vδT2τ, where δ T2＝T2-T1Corresponding compression angle of theta2(ii) a The other is due to the temperature T2Phase variation delta introduced by phase mismatch caused by not meeting phase matching condition3＝vδT3Wherein δ T3＝T2-TPCorresponding compression angle of theta3. If the temperature of the nonlinear crystal is adjusted by the temperature controller, the compression angle theta is adjusted2And theta3Compensating each other, i.e. theta2+θ3When the compression angle is 0, namely complete compensation is realized between the two compression angles, as shown in fig. 2, namely phase self-compensation is realized, a larger compression degree can be obtained, and the measurement value of the compression degree of the non-classical optical field is higher and more accurate.
Specifically, in this embodiment, a dual-resonance temperature measurement module is disposed in the central controller; as shown in fig. 3, the dual resonance temperature measurement module is configured to perform the following procedure: outputting a control signal to set the temperature setting value of the temperature controller at a certain initial temperature T0Then, the initial temperature may be a double resonance temperature estimated value obtained through other ways, and after the temperature of the temperature controller is stabilized, the peak-to-peak value a of the gain curve obtained by the detection of the single detector is recorded1(ii) a Then the output signal changes the temperature setting value of the temperature controller, a new gain curve is formed after the temperature of the temperature controller is stable, and the peak value a of the gain curve obtained by the detection of the single detector is recorded2And the last peak-to-peak value a1Comparing, and selecting a larger value from the values to be assigned to b; outputting the signal again to change the temperature setting value of the temperature controller, changing the circulation until the maximum peak value is found, and then taking the temperature corresponding to the maximum peak value as the double-resonance temperature T1And (7) recording. In FIG. 3, b represents the larger of the two peak-to-peak values, aiRepresenting the peak-to-peak value of the gain curve.
Specifically, in this embodiment, when the dual-resonance temperature measurement module adjusts the temperature setting value of the temperature controller, the change amount of the temperature setting value of the temperature controller is 0.01 to 0.1 ℃. In addition, the initial temperature set value T of the temperature controller01The laser wavelength and the crystal characteristic can be specifically set according to the crystal characteristic and the laser wavelength, for example, in this embodiment, the laser 41 is a laser capable of emitting 1550nm and 775nm laser simultaneously, the crystal is a PPKTP nonlinear crystal, and the initial temperature setting value T of the temperature controller042.6 ℃. Specifically, in the present embodiment, after the fundamental light (seed light) 42 and the frequency-doubled light 43 outputted from the laser 41 pass through the noise reducer 44, the frequency-doubled light 43 is phase-shifted by the phase shifter 45, injected into the optical parametric amplifier 31 together with the fundamental light (seed light) 42, and the cavity length is locked by the PDH frequency stabilization technique 46Until resonance enhancement, the output signal light 47, i.e. compressed light, is blocked by the light blocking sheet 40 to the fundamental frequency light 48, is detected by the balanced homodyne detector 33, the direct current signal of one of the detectors is connected to the 34 analog-to-digital converter AD, the gain curve is converted into data by the 34 analog-to-digital converter AD, the peak-to-peak value is input into the central controller 35, the central controller 35 records the data, then the data is transmitted to the 36 digital-to-analog converter DA, the 36 digital-to-analog converter DA is connected with the temperature controller 37, the central controller changes the crystal temperature by the temperature controller 37 to form a new gain curve, the central controller 35 records a new peak-to-peak value, compares the new peak-to-peak value with the previous peak-to-peak value to select a larger value, the temperature. Temperature T at this time1Namely the temperature for realizing double resonance of the two beams of light of the fundamental frequency light omega and the frequency doubling light 2 omega in the optical parametric cavity.
In addition, a phase self-compensation module is arranged in the central controller; as shown in fig. 4, the phase self-compensation module is configured to perform the following procedures: outputting a control signal to set the control temperature of the temperature controller at the double resonance temperature T1Next, recording the optical field compression value output by the spectrum analyzer; then outputting a control signal to change the temperature setting value of the temperature controller in a small amplitude manner, and recording the optical field compression value output by the spectrum analyzer at the corresponding temperature; repeating the operation for multiple times, recording to obtain multiple groups of temperature setting values and light field compression values at corresponding temperatures, performing curve fitting, and finding the temperature corresponding to the minimum compression on the curve as the phase self-compensation temperature TP. In FIG. 4, d represents the lesser of the two light-field compressibility values, ciRepresenting the light field compressibility value.
Specifically, in this embodiment, when the phase self-compensation module adjusts the temperature setting value of the temperature controller, the change amount of the temperature setting value of the temperature controller at each time is 0.01-0.1 ℃.
Specifically, in the present embodiment, after removing the light-blocking sheet 40, the signal light 47 interferes with the local light 48 phase-shifted by the phase shifter 49 at the first beam splitter 32, and is detected by the balanced homodyne detector 33, the ac signals of the two detectors 33 are input to the subtracter 38, the subtracter 38 is connected to the input terminal of the spectrum analyzer SA 39, and the frequency spectrum analyzer SA 39 is input to the subtracter 38The compression is measured by the spectrum analyzer SA, the output end of the spectrum analyzer SA is connected with a 34 analog-to-digital converter AD, the 34 analog-to-digital converter AD converts an image into data, the minimum value is input into a central controller 35, the central controller 35 records the data and then transmits the data to a 36 digital-to-analog converter DA, the temperature of the crystal is changed through a temperature controller 37, the central controller 35 records new data, the new data is compared with the previous data, the smaller value is selected, the process is circulated until the minimum value is found, and the corresponding temperature is the temperature T of phase self-compensation at the momentP. This achieves phase self-compensation.
Fig. 5 is a schematic diagram of an optical path of a phase self-compensated non-classical optical field generator provided in this embodiment. In the figure, a 1550nm single-frequency laser 41 is used for inner cavity frequency doubling, and a fundamental frequency light beam is divided into two beams in the inner cavity, wherein one beam enters a frequency doubling cavity to perform a parametric up-conversion process to generate a frequency doubling light beam, and a fundamental frequency light beam 48 and a frequency doubling light beam 43 are output, and the corresponding wavelength of the frequency doubling light beam 43 is 775nm and is used for pumping the optical parametric cavity 31. The output frequency-doubled light 43 and the fundamental frequency light (seed light) 42 reflected by the third beam splitter 3 are incident to the dual-resonance optical parametric cavity 31 from the input mirror of the dual-resonance optical parametric cavity 31, and operate below a threshold value to perform parametric down-conversion to generate a first output signal light 47, i.e., a compressed light 47. Scanning a first meniscus concave mirror a2 adhered with a first piezoelectric ceramic a3 to obtain a transmission peak curve in a free spectral region range, observing and recording the mode matching efficiency through a single detector, and as a result, as shown in fig. 6, adjusting a second matching lens group 8 (the focal lengths are respectively-50 mm and 100mm), focusing the focus through the lens group to fall at the waist spot of an optical parameter cavity 31, wherein the mode matching efficiency reaches more than 99.5%, then, adding the power of pumping light to the threshold value of the optical parameter cavity, and carefully adjusting the temperature of a nonlinear crystal a1 to realize double resonance. And the cavity length of the optical parametric cavity 31 is locked to the resonance point by a lock-in loop 46 in the frequency doubling optical loop. The reflected light of the optical parametric cavity 31 is reflected by the first isolator 9, output and sent into the lock cavity detector 111 to obtain an error signal, the cavity length of the optical parametric cavity 31 is locked to resonance enhancement by adopting the PDH frequency stabilizer 46, and a stronger first output signal light 47 is obtained by adjusting the temperature of the nonlinear crystal a 1. Finally, the first matching lens group 4 is adjusted toThe interference efficiency of the signal light output above the threshold and the coherent light on the first beam splitter 32 reaches above 99.5%, and as shown in fig. 7, the relative phase of the two beams of light is scanned by a light guide mirror adhered with the second piezoelectric ceramic 5 and observed and recorded by a detector. 17 is an automatic adjusting part (not shown in the figure) of the phase self-compensation non-classical optical field generator, the temperature T of the nonlinear crystal a1 is controlled by an automatic adjusting temperature controller, and the temperature T of the double resonance is found out first1FIG. 8 is a gain curve, and then phase self-compensation is performed to find the temperature T with the maximum compressionP. Experimental results as shown in fig. 9, where the back compression and compression are varied with temperature, with the temperature of the 1550nm and 775nm double resonance of the light beam being 0 c, and the vicinity of the phase matching temperature in the enlarged view, it can be found that the maximum degree of compression occurs when the temperature is about 0.08 c away from the resonance temperature point.
The first isolator 9 is used for isolating a reflected signal of the optical parametric cavity 31, protecting the laser, and preventing the reflected light from being fed back into the laser to damage the laser; sine wave signals generated by the signal source are loaded to the electro-optic phase modulator 10 and used for transmitting fundamental frequency galvanic signals to the locking loop, the fundamental frequency galvanic signals and local sine wave electrical signals loaded by the modulator are mixed in the locking loop to generate error signals, and the error signals are fed back to the cavity mirror with the optical resonant cavity adhered with the piezoelectric ceramics, so that the cavity length of the optical parameter is locked.
In the light path, the optical parameters of the double-resonance optical parametric cavity are as follows: the optical parametric cavity consists of two concave mirrors, two plane mirrors and a PPKTP crystal a 1. Wherein, one flat mirror is used as an input mirror, the inner surface is plated with film HR1550nm/775nm, and the outer end surface is plated with film AR1550nm/775 nm; the inner end surface of the other plane mirror is HR1550/775, and the outer end surface is not coated with a film; the curvature radius of the two concave mirrors is 100mm, wherein the inner surface of the meniscus concave mirror a2 is coated with a film T775 which is 2.5 percent/T1550 which is 15 percent, the outer end surface is coated with a film AR1550/775, the size of a light spot cannot be changed by the meniscus output mirror, and the auxiliary light path is adjusted; the inner end face of the other concave mirror is HR1550/775, and the outer end face is not coated with a film; the total cavity length of the optical parametric cavity a is 622.8mm, the distance between the two concave mirrors is 108mm, the corresponding eigenmode radius is 25 μm, the size of the PPKTP nonlinear crystal a1 is 1 x 2 x 10mm, and the PPKTP nonlinear crystal a1 is positioned in the middle of the two concave mirrors, namely the waist spot position of the cavity. The electro-optical phase modulator 10 applies a 120MHz sine wave signal.
As shown in fig. 10, a phase self-compensated non-classical optical field generator according to a second embodiment of the present invention is different from the first embodiment in that the phase self-compensated non-classical optical field generator of the present embodiment generates entangled light, and further includes a second compressed optical field generator and a second beam splitter 52, in addition to the laser 41, the compressed optical field generator, the first phase shifter 49, the first beam splitter 32, the central controller 35, the balanced homodyne detector 33, and the spectrum analyzer 39, the second compressed optical field generator includes a third phase shifter 50, a second optical parametric amplifier 29, a second PDH frequency stabilizer 11, and a second temperature controller 53, and the second compressed optical field generator is configured to receive fundamental frequency light and frequency doubling light emitted from the laser 41 and generate a second compressed optical field.
As shown in fig. 10, the frequency-doubled light emitted from the laser 41 is phase-shifted by the third phase shifter 50 and then injected into the second optical parametric amplifier 29 together with the fundamental light; the signal light emitted from the second optical parametric amplifier 29 is detected by a single detector and then output to the central controller 35; the output end of the central controller 35 is connected to the input end of the temperature controller 53 of the second compressed optical field generator, and is configured to change the crystal temperature in the second optical parametric amplifier 29 by the temperature controller, find the double resonance temperature of the second optical parametric amplifier 29 according to the output signal of the single detector at different crystal temperatures, and find the phase self-compensation temperature of the second optical parametric amplifier 29 according to the compression degree of the second compressed optical field at different crystal temperatures.
In addition, in this embodiment, the optical fiber driving circuit further includes a fourth phase shifter 51, and after the first compressed light generated by the first compressed optical field generator passes through the fourth phase shifter 51, the first compressed light and the second compressed light generated by the second compressed optical field generator are combined on the beam splitter 52, and then the combined light passes through the beam splitter 32 and is detected by the balanced homodyne detector 33.
In addition, in the present embodiment, an optical parametric amplifier is used, which is different from that in the first embodiment, specifically, as shown in fig. 11, the dual-resonance optical parametric cavity used in the apparatus of the present embodiment is a two-mirror cavity. In the optical path of the present embodiment, the optical parameters of the dual-resonance optical parametric cavity are as follows: the optical parametric cavity consists of a meniscus concave mirror a2 and a nonlinear crystal a 1. The nonlinear crystal a1 is a PPKTP crystal, the size is 1 x 2 x 10mm, the curvature radius of the front end face convex surface is 12mm, the coating film is HR1550nm/775nm, and the PPKTP crystal serves as an input mirror of the optical parametric cavity; the back end surface is a plane, and the coating film is AR 1550/775. The curvature radius of the meniscus concave mirror a2 is 25mm, the concave coating T775 is 2.5%, the T1550 is 15%, the rear end face coating AR1550/775, the meniscus design ensures that the laser can not change the size of the light spot when passing through, and the auxiliary light path is adjusted. The total cavity length of the optical parametric cavity is 31mm, the corresponding base mode waist spot radius is 49 mu m, and the base mode waist spot position is at the crystal center. The electro-optical phase modulator 10 applies a 120MHz sine wave signal.
The device of the first embodiment generates a compressed light field, and the present embodiment generates a two-mode entangled light field. In this embodiment, the fifth beam splitter 20 splits the frequency-doubled light 43 generated by the laser 41 into two beams, which pass through two identical frequency-doubled light portions respectively, and respectively enters the optical parametric cavity with the fundamental frequency light reflected by the third beam splitter 3 to generate two signal lights, wherein, after the first output signal light 47 sequentially passes through the fifth dichroic mirror 18, the second high reflection mirror 21 and the third high reflection mirror 22, the second output signal light 30 reflected by the third dichroic mirror 12 and the fifth high reflection mirror 15 interferes with the second beam splitter 52 to generate entangled light, is split into two beams by the second beam splitter 52, in addition, the fundamental frequency light 48 is reflected by the fourth high-reflection mirror 24, is divided into two beams by the sixth beam splitter 25, and after being reflected by the high-reflection mirrors with the third piezoelectric ceramics 26 and the fourth piezoelectric ceramics 27 respectively, interfering with the first two respectively entangled light beams on the seventh beam splitter 28 and detected by the balanced homodyne detector 16. And 17 is an automatic adjusting part (not shown in the figure) of the phase self-compensation non-classical optical field generator.
In addition, in this embodiment, the balanced homodyne detector 33 and the balanced homodyne detector 16 are configured to detect the degrees of compression of the first compressed light field and the second compressed light field, respectively, and also to detect the degrees of entanglement of the first compressed light field and the second compressed light field.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (7)
1. The non-classical optical field generator with self-compensated phase is characterized by comprising a laser (41), a first compressed optical field generator, a first phase shifter (49), a first beam splitter (32), a central controller (35), a balanced homodyne detector (33) and a spectrum analyzer (39);
the first compressed optical field generator comprises a second phase shifter (45), a first optical parametric amplifier (31), a first PDH frequency stabilizer (46) and a first temperature controller (37), and is used for receiving fundamental frequency light and frequency doubling light emitted by a laser (41) and generating a first compressed optical field; the frequency doubling light emitted by the laser (41) is phase-shifted by a second phase shifter (45) and then is injected into the first optical parametric amplifier (31) together with the fundamental frequency light; the signal light emitted by the first optical parametric amplifier (31) is detected by a first single detector and then output to the central controller (35); the signal light emitted from the first optical parametric amplifier (31) and the base frequency light emitted by the laser (41) and phase-shifted by the first phase shifter (49) are respectively incident on two incidence surfaces of the first beam splitter (32) and then are detected by the balanced homodyne detector (33), the output signal of the balanced homodyne detector (33) is connected with the spectrum analyzer (39), and the output end of the spectrum analyzer (39) is connected with the central controller (35) and is used for analyzing and obtaining the compression degree of the first compressed light field according to the detection signal of the balanced homodyne detector (33); the output end of the first PDH frequency stabilizer (46) is connected with the piezoelectric ceramic on the cavity mirror of the first optical parametric amplifier (31) and used for locking the cavity length of the first optical parametric amplifier (31) to a resonance enhancement point;
the first temperature controller (37) is used for adjusting the crystal temperature in the first optical parametric amplifier (31), the output end of the central controller (35) is connected with the input end of the first temperature controller (37) and used for changing the crystal temperature through the first temperature controller (37), finding the double-resonance temperature of the optical parametric amplifier (31) according to the output signal of the first single detector at different crystal temperatures and finding the phase self-compensation temperature of the first optical parametric amplifier (31) according to the compression degree of the first compressed optical field at different crystal temperatures.
2. A phase self-compensating, non-classical optical field generator according to claim 1, wherein a dual resonance temperature measurement module is provided within the central controller; the dual resonance temperature measurement module is configured to perform the following procedure:
outputting a control signal to set the temperature setting value of the temperature controller at a certain initial temperature, and recording the peak-to-peak value of a gain curve obtained by the detection of the first single detector after the temperature of the temperature controller is stable; then outputting a signal to change the temperature setting value of the temperature controller, forming a new gain curve after the temperature of the temperature controller is stable, recording the peak-to-peak value of the gain curve detected by the first single detector, comparing the peak-to-peak value with the previous peak-to-peak value, and selecting the larger value; and outputting the signal again to change the temperature setting value of the temperature controller, changing the circulation until the maximum peak value is found, and recording the temperature corresponding to the maximum peak value as the double-resonance temperature.
3. The phase self-compensated non-classical optical field generator according to claim 2, wherein the dual resonance temperature measurement module adjusts the temperature setting of the temperature controller by a change amount of 0.01-0.1 ℃ each time.
4. A phase self-compensating non-classical optical field generator according to claim 1, wherein a phase self-compensating module is provided within the central controller; the phase self-compensation module is used for executing the following procedures:
outputting a control signal to set the control temperature of the temperature controller at the double resonance temperature, and recording the optical field compression value output by the spectrum analyzer; then outputting a control signal to change the temperature setting value of the temperature controller in a small amplitude manner, and recording the optical field compression value output by the spectrum analyzer at the corresponding temperature; and repeating the operation for multiple times, recording to obtain multiple groups of temperature setting values and the light field compression values at corresponding temperatures, performing curve fitting, and finding the temperature corresponding to the minimum compression on the curve as the phase self-compensation temperature.
5. The phase self-compensated non-classical optical field generator according to claim 4, wherein the phase self-compensation module adjusts the temperature setting value of the temperature controller by a change amount of 0.01-0.1 ℃ each time.
6. A phase self-compensating non-classical optical field generator according to claim 1, further comprising a second compressed optical field generator and a second beam splitter (52), the second compressed optical field generator comprising a third phase shifter (50), a second optical parametric amplifier (29), a second PDH frequency stabilizer (11) and a second temperature controller (53), the second compressed optical field generator being configured to receive the fundamental light and the frequency doubled light from the laser (41) and generate a second compressed optical field;
the frequency doubling light emitted by the laser (41) is phase-shifted by a third phase shifter (50) and then is injected into a second optical parametric amplifier (29) together with the fundamental frequency light; the signal light emitted by the second optical parametric amplifier (29) is detected by a second single detector and then output to the central controller (35);
the output end of the central controller (35) is connected with the input end of a temperature controller (53) of the second compressed optical field generator, and the central controller is used for changing the crystal temperature in the second optical parametric amplifier (29) through the temperature controller (53), finding out the double resonance temperature of the second optical parametric amplifier (29) according to the output signal of the second single detector at different crystal temperatures, and finding out the phase self-compensation temperature of the second optical parametric amplifier (29) according to the compression degree of the second compressed optical field at different crystal temperatures.
7. A phase self-compensated non-classical optical field generator according to claim 6, wherein the balanced homodyne detector (33) is configured to detect the degree of compression of the first and second compressed optical fields, respectively, and is further configured to detect the degree of entanglement of the first and second compressed optical fields.
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