Dual-color marking photon source generation module and dual-compatible communication device including the module

Abstract

The present invention relates to the fields of laser technology, nonlinear optical physics technology, quantum optics and quantum communication technology, and in particular to a dual-color marking photon source generation module and a dual-compatible communication device including the module, wherein the dual-color marking photon source generation module includes an optical sheet component and a third quasi-phase matching crystal PPKTP3, which are sequentially arranged on an optical path and used to adjust the polarization state and focusing of input pulse light, and an input end of the optical sheet component inputs a third pump light of a set wavelength, and the third pump light is converted into a pair of signal photons and idler photons under the spontaneous output of the third quasi-phase matching crystal PPKTP3, and the wavelengths and bandwidths of the signal photons and the idler photons conform to the energy conservation and momentum conservation formulas and are converted into: ω p =ω s +ω i (1)Δk=k p ‑k s ‑k i +2π / Λ=0(2). The advantages of the invention are: the dual-color marking photon source generation module in the invention that meets formula (1) and formula (2) can simultaneously generate two pulse photon signals, and the wavelength can be compatible with both the underwater communication window and the optical fiber communication window.

Description

Technical Field

[0001] The invention relates to the fields of laser technology, nonlinear optical physics technology, quantum optics and quantum communication technology, and in particular to a dual-color marking photon source generating module and a dual-compatible communication device comprising the module. Background Art

[0002] At present, the channels used for communication mainly include optical fiber, free space and underwater channels. To increase the communication distance, the optical wavelength that needs to be encoded must be in the low-loss window of the channel. The low-loss window of the optical fiber channel is in the 1.5-micron band, while the low-loss window of the underwater communication channel is in the blue-green laser band (ranging from 450nm to 530nm).

[0003] In the field of quantum communication, labeled two-photon sources are important resources for studying quantum communication technology. Future quantum communication systems need to be compatible with different communication channels, so preparing photon sources in different types of communication channel window bands is an important basis for realizing hybrid quantum networks. Currently available two-color photon sources are mainly used to connect quantum memories and low-loss optical fiber communication windows. However, there are no reports on two-color photon sources that are compatible with both underwater communication windows and optical fiber communication windows. The development of such two-color photon pairs will facilitate the construction of future optical fiber and underwater hybrid quantum communication networks.

[0004] In view of this, it is necessary to study a high-quality two-color photon source that is compatible with both underwater and fiber optic channels. The development of this light source will help build a hybrid quantum network. On the other hand, this photon source can also play an advantage in the two-color ghost imaging system. Summary of the invention

[0005] In order to overcome the above-mentioned deficiencies in the prior art, the present invention provides a dual-color marking photon source generating module and a dual-compatible communication device including the module.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] The dual-color marking photon source generation module includes an optical sheet component and a third quasi-phase matching crystal PPKTP3, which are sequentially arranged on the optical path and used to adjust the polarization state and focusing of the input pulse light. The input end of the optical sheet component inputs a third pump light of a set wavelength. The third pump light is converted into a pair of signal photons and idler photons under the spontaneous output of the third quasi-phase matching crystal PPKTP3. The wavelength and bandwidth of the signal photon and the idler photon conform to the energy conservation and momentum conservation formulas, and are converted into:

[0008] ω p =ω s +ω i (1)

[0009] Δk=k p -k s -k i +2π / Λ=0 (2)

[0010] where k q =2πn q / λ q (q=p,s,i),k p , k s , k i are the wave vectors of the third pump light, signal photon and idler photon respectively, Λ is the polarization period of the third quasi-phase matching crystal PPKTP3, ω p ,ω s ,ω i are the vibration frequencies of the third pump light, signal photon and idler photon in the quasi-phase matching crystal, n p 、n s 、n i are the refractive indices of the third pump light, signal photon and idler photon in the quasi-phase matching crystal, λ p , s , i are the wavelengths of the third pump light, signal photon and idler photon respectively. The bandwidths of signal photon and idler photon can be obtained according to the vibration frequency.

[0011] Optimally, the third quasi-phase-matched crystal PPKTP3 is a quasi-phase-matched type II phase-matched crystal.

[0012] Optimally, both end faces of the third quasi-phase matching crystal PPKTP3 are coated with anti-reflection films of three wavelengths corresponding to the third pump light, signal photons and idler photons.

[0013] Preferably, the optical sheet assembly includes a deflection adjustment unit and a focusing unit arranged on the optical path.

[0014] Optimally, the module further comprises a temperature-controlled furnace, and the third quasi-phase-matched crystal PPKTP3 is arranged in the temperature-controlled furnace.

[0015] The dual-compatible communication device including the above-mentioned dual-color marking photon source generating module also includes a photon receiving module, which includes a second dual-color mirror DM2, a first communication component, and a second communication component. The second dual-color mirror DM2 emits signal photons and idler photons into the first optical branch and the second optical branch, and transmits them to the first communication component and the second communication component respectively; the first communication component includes a long-pass filter LPF and a second collimation component arranged on the first optical branch to filter out the third pump light; the second communication component includes a band-pass filter BPF and a third collimation component arranged on the second optical branch to filter out the third pump light.

[0016] Optimally, the photon receiving module also includes a coincidence counting unit, which includes a first single-photon detector SPD1, a second single-photon detector SP2, and a coincidence counter; the first single-photon detector SPD1 and the second single-photon detector SP2 are correspondingly arranged at the output ends of the first optical branch and the second optical branch, and the output ends of the first single-photon detector SPD1 and the second single-photon detector SP2 are respectively connected to the coincidence counter.

[0017] Optimized, the device also includes a frequency doubling module, which includes a first pump light source Laser, a transmission dimming unit, a first frequency doubling unit, a first dichroic mirror DM1, and a second frequency doubling unit arranged in sequence along the optical path, and the first frequency doubling unit and the second frequency doubling unit both include a focusing lens and a periodically polarized crystal.

[0018] Optimally, the periodically poled crystals in the first frequency doubling unit and the second frequency doubling unit are type I phase-matched periodically poled crystals.

[0019] Optimized, the first pump light source Laser outputs a 1560nm pump light, the first frequency doubling unit outputs a 780nm doubled frequency light, the second frequency doubling unit outputs a 390nm quadruple frequency light, the quadruple frequency light is used as the third pump light, and is sequentially transmitted through the first collimating transmission component and the optical sheet component to the third quasi-phase matching crystal PPKTP3, the first collimating transmission component includes a purple single-mode optical fiber SMF and a second collimating unit and a third collimating unit respectively arranged at both ends of the purple single-mode optical fiber SMF.

[0020] The advantages of the present invention are:

[0021] (1) The dual-color labeling photon source generation module in the present invention that complies with formula (1) and formula (2) can simultaneously generate two pulse photon signals, and the wavelength can be compatible with both the underwater communication window and the optical fiber communication window.

[0022] (2) The polarization adjustment unit in the present invention is used to adjust the polarization state of the pump light entering the third quasi-phase matching crystal PPKTP3, and the focusing unit is used to focus the pump light into the third quasi-phase matching crystal PPKTP3.

[0023] (3) The present invention is provided with a temperature-controlled furnace, and the polarization period of the third quasi-phase matching crystal PPKTP3 is adjusted by adjusting the temperature.

[0024] (4) The dual-compatible communication device in the present invention uses a dual-color labeled photon source generation module to specifically realize compatible underwater communication and optical fiber communication, wherein the first communication optical path formed by the first communication component is located in the low-loss blue-green laser window of underwater communication, and the second communication optical path formed by the second communication component is located in the low-loss optical fiber communication band window.

[0025] (5) The coincidence counting unit is used to characterize the quality of the light source generated by the dual-color marking photon source generating module.

[0026] (6) The first pump light source Laser is a fiber picosecond laser. The present invention adopts a frequency doubling module to obtain an ultraviolet laser for pump parameter down-conversion, i.e., the third pump light. Since the fiber pulse laser has the characteristics of small size and high power, the laser of the fiber picosecond laser with a wavelength of 1560nm can be directly converted to the third pump light with a wavelength of 390nm through the frequency doubling process in two type I quasi-phase matching crystals. The advantage of using ultrafast lasers is that they have high peak power and high single-pass nonlinear conversion efficiency, thereby avoiding the complex external cavity frequency doubling process, making the structure of the entire system simpler and more compact.

[0027] (7) In the present invention, the periodically polarized crystals in the first frequency doubling unit and the second frequency doubling unit and the third quasi-phase matching crystal PPKTP3 all use quasi-phase matching crystals. Compared with angle matching crystals, quasi-phase matching crystals have high nonlinear conversion efficiency and no spatial walk-off effect.

[0028] (8) Purple light single-mode fiber SMF has two functions. On the one hand, it can effectively filter out 1560nm pump light and 780nm double frequency light, avoiding complex composite filtering devices. On the other hand, single-mode fiber has a good mode filtering effect, which can ensure that the output light spot is close to the ideal Gaussian beam.

[0029] (9) The present invention proposes a high-brightness dual-color marking light source that is compatible with both underwater and optical fiber low-loss channels. It has dual-wavelength output and high brightness, and has great potential in constructing long-distance hybrid quantum communication networks and dual-color ghost imaging.

[0030] (10) The present invention is based on the parametric down-conversion process in the third quasi-phase matching crystal PPKTP3 to prepare a two-color labeled photon pair. Its pump light uses a high repetition rate, high-power fiber picosecond laser to generate a four-fold frequency pump laser in a type-one phase-matched periodic polarization crystal. The generated four-fold frequency pump laser is collected by a single-mode fiber SMF for ultraviolet light, so that the pump light and the doubled frequency laser can be efficiently filtered out. At the same time, the ultraviolet pump light can be spatially filtered, so that the parametric down-conversion crystal can be pumped efficiently to generate high-brightness two-color photon pairs. One photon of the two-color photon pair is in the blue-green laser band, which is used for the low-loss underwater optical window, and the other wavelength is located in the optical fiber communication window. The two-color photon pair will lay the foundation for the construction of a hybrid quantum communication network. At the same time, this type of high-brightness photon source can also be used for two-color ghost imaging experimental research, using the detection advantages of visible detectors and the transmission advantages of infrared light fields in spatial channels. Therefore, the two-color photon source is of great significance to hybrid quantum communication networks and two-color ghost imaging research. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic diagram of the optical path structure of a high-brightness dual-color marking light source compatible with both underwater and optical fiber low-loss channels provided by an embodiment of the present invention.

[0032] Figure 2 The figure is a relationship diagram of the single-channel count of the two-color photon pairs generated in the present invention and the pump power.

[0033] Figure 3 This is a relationship diagram of the ratio CAR of the coincidence count of photons to the dark coincidence and the pump power in the present invention.

[0034] Figure 4 A relationship diagram of the signal-to-noise ratio of the two-photon coincidence provided in an embodiment of the present invention versus the pump power. DETAILED DESCRIPTION

[0035] Example 1

[0036] like Figure 1As shown, the dual-color marking photon source generation module includes an optical sheet component and a third quasi-phase matching crystal PPKTP3, which are sequentially arranged on the optical path and used to adjust the polarization state and focus of the input pulse light. The input end of the optical sheet component inputs a third pump light of a set wavelength, and the optical sheet component includes a polarization adjustment unit and a focusing unit arranged on the optical path. The polarization adjustment unit includes a half-wave plate HWP2 and a quarter-wave plate QWP, which are sequentially arranged on the optical path, and the focusing unit is a third collimating lens L4. The half-wave plate HWP2 and the quarter-wave plate QWP are used to adjust the third pump light to a suitable polarization state, and the lens L4 is used to focus and transmit the third pump light with adjusted polarization into the third quasi-phase matching crystal PPKTP3. In this embodiment, the third quasi-phase matching crystal PPKTP3 is a quasi-phase matching type II phase matching crystal. In this embodiment, the wavelength of the third pump light is 390nm.

[0037] The third pump light is converted into a pair of signal photons and idler photons under the spontaneous output of the third quasi-phase matching crystal PPKTP3. The wavelengths and bandwidths of the signal photons and idler photons conform to the energy conservation and momentum conservation formulas and are converted into:

[0038] ω p =ω s +ω i (1)

[0039] Δk=k p -k s -k i +2π / Λ=0 (2)

[0040] where k q =2πn q / λ q (q=p,s,i),k p , k s , k i are the wave vectors of the third pump light, signal photon and idler photon respectively, Λ is the polarization period of the third quasi-phase matching crystal PPKTP3, ω p ,ω s ,ω i are the vibration frequencies of the third pump light, signal photon and idler photon in the quasi-phase matching crystal, n p 、n s 、n i are the refractive indices of the third pump light, signal photon and idler photon in the quasi-phase matching crystal, λ p , s , iare the wavelengths of the third pump light, signal photon and idler photon respectively. The bandwidths of signal photon and idler photon can be obtained according to the vibration frequency. If the wavelength of signal photon is one of 1560nm and 520nm, the wavelength of idler photon is the other of 1560nm and 520nm.

[0041] Both end faces of the third quasi-phase matching crystal PPKTP3 are coated with anti-reflection films of three wavelengths corresponding to the third pump light, signal photons and idler photons, that is, they are coated with anti-reflection films of three wavelengths of 390nm, 520nm and 1560nm.

[0042] The module also includes a temperature-controlled furnace, in which the third quasi-phase-matched crystal PPKTP3 is arranged. Thus, the polarization period of the third quasi-phase-matched crystal PPKTP3 in formula (2) is adjusted. In this embodiment, the temperature control range is 15 to 70 degrees Celsius, and the temperature control accuracy is 2mK.

[0043] Example 2

[0044] like Figure 1 As shown, the dual-compatible communication device including the dual-color marking photon source generating module described in Example 1 also includes a frequency doubling module arranged at the front end of the dual-color marking photon source generating module and a photon receiving module arranged at the rear end of the dual-color marking photon source generating module.

[0045] The frequency doubling module includes a first pump light source Laser, a transmission dimming unit, a first frequency doubling unit, a first dichroic mirror DM1, and a second frequency doubling unit arranged in sequence along the optical path. The first frequency doubling unit and the second frequency doubling unit both include a lens and a periodic polarization crystal for focusing. The periodic polarization crystals in the first frequency doubling unit and the second frequency doubling unit are type I phase-matched periodic polarization crystals. The advantage of type I matching is that the maximum nonlinear coefficient of the crystal can be utilized, and the conversion efficiency is high. The first pump light source Laser is a pulsed laser with a central wavelength of 1560nm, a pulse width of 1ps, a repetition rate of 80MHz, and an average power of 1W.

[0046] The transmission dimming unit includes a polarization-maintaining fiber PMF, a first fiber collimator FC1, a half-wave plate HWP1, and a polarization beam splitter PBS for transmitting the pump light with a wavelength of 1560nm output by the first pump light source Laser. The polarization-maintaining fiber PMF is used to maintain the output polarization state of the fiber laser. The output pump light is collimated by the first collimator FC1, and then passes through the half-wave plate HWP1 and the polarization beam splitter PBS in sequence to adjust the light intensity of the pump light with a wavelength of 1560nm.

[0047] The first frequency doubling unit includes a lens L1 and a first quasi-phase matching crystal PPKTP1. The pump light passing through the polarization beam splitter PBS is focused into the first quasi-phase matching crystal PPKTP1 through the 1560nm lens L1. The two end faces of the first quasi-phase matching crystal PPKTP1 along the optical path are coated with 1560nm and 780nm anti-reflection films. The first frequency doubling unit is used to output 780nm double frequency light.

[0048] The function of the first dichroic mirror DM1 is to reflect the pump light with a wavelength of 780 nm into the second frequency doubling unit.

[0049] The second frequency doubling unit includes a lens L2 and a second quasi-phase matching crystal PPKTP2. The 780nm pump light is focused into the second quasi-phase matching crystal PPKTP2 through the 780nm lens L2. Both the first quasi-phase matching crystal PPKTP1 and the second quasi-phase matching crystal PPKTP2 are equipped with a temperature control furnace with a temperature control range of 15 to 70 degrees Celsius and a temperature control accuracy of 2mK. The two end faces of the second quasi-phase matching crystal PPKTP2 along the optical path are coated with 390nm and 780nm anti-reflection films. The second frequency doubling unit outputs 390nm quadrupled light.

[0050] The quadrupled frequency light is transmitted to the third quasi-phase matching crystal PPKTP3 after passing through the first collimation transmission component and the optical sheet component in sequence. The first collimation transmission component includes a purple single-mode optical fiber SMF and a second collimation unit and a third collimation unit arranged on both sides of the purple single-mode optical fiber SMF. The second collimation unit includes a collimation lens L3 and a second optical fiber collimator FC2 arranged in sequence, and the third collimation unit is a third optical fiber collimator FC3.

[0051] After the quadrupled frequency 390nm laser is coupled into the single-mode fiber SMF through the second collimation unit, it is emitted through the third fiber collimator FC3, and the emitted laser polarization is adjusted to a suitable polarization state through the half-wave plate HWP2 and the quarter-wave plate QWP, and then focused into the parametric down-conversion crystal PPKTP3 through the lens L4 to generate a two-color photon pair. By using the single-mode fiber SMF of purple light to couple the quadrupled frequency light into the optical fiber, the pump light and the generated doubled frequency light can be effectively filtered out, avoiding complicated filtering optical paths, making the system more integrated, and at the same time, the spatial mode of the quadrupled frequency can be purified, which is helpful to generate a high-quality two-color labeled photon source.

[0052] The photon receiving module includes a second dichroic mirror DM2, a first communication component, and a second communication component. The second dichroic mirror DM2 emits signal photons and idler photons into the first optical branch and the second optical branch, and transmits them to the first communication component and the second communication component respectively; the first communication component includes a long-pass filter LPF and a second collimation component arranged on the first optical branch to filter out the third pump light, and the second collimation component includes a collimation lens L5 and a fourth optical fiber collimator FC4; the second communication component includes a bandpass filter BPF and a third collimation component arranged on the second optical branch to filter out the third pump light, and the third collimation component includes a collimation lens L6 and a fifth optical fiber collimator FC5.

[0053] Example 3

[0054] In order to characterize the quality of the light source generated by the dual-color labeling photon source generating module, in addition to the structure in Example 2, Figure 1 As shown, the photon receiving module also includes a coincidence counting unit. The coincidence counting unit includes a first single photon detector SPD1, a second single photon detector SP2, and a coincidence counter; the first single photon detector SPD1 and the second single photon detector SP2 are correspondingly arranged at the output ends of the first optical branch and the second optical branch, and the output ends of the first single photon detector SPD1 and the second single photon detector SP2 are respectively connected to the coincidence counter. Photons with wavelengths of 520nm and 1560nm are collected into single-mode optical fibers through the fourth optical fiber collimator FC4 and the fifth optical fiber collimator FC5 on the first optical branch and the second optical branch, respectively, and detected and coincidentally measured by the visible single photon detector SPD1 and the infrared single photon detector SPD2.

[0055] In the present invention, in order to characterize the quality of the generated two-color marking light source, the following parameters of the photon source need to be measured. First, the relationship between the generation rate of signal photons and idler photons with wavelengths and the pump power needs to be measured, such as Figure 2 , Figure 3 As shown, in this example, the single-channel photon count rate can reach 110kHz / mW, and the coincidence count rate can reach 13.1kHz / mW. Then it is necessary to characterize the relationship between the ratio of the coincidence count to the dark coincidence of the photons and the power, as shown in Figure 4 As shown, in this example, the ratio of the photon coincidence count to the dark coincidence count CAR can reach 161 when the pump is 0.86mW. For the marking light source, it is necessary to calculate the marking efficiency of the photon source. In this formula, N cc Indicates the count value that meets the set power, N s is the single-channel count of signal photons at a set power, N i The labeling efficiency can be achieved to a higher level by optimizing the collection parameters for single-pass counting of idler photons at a set power.

[0056] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A dual-compatible communication device for a dual-color label photon source generation module, characterized in that: It includes a two-color marking photon source generating module and a photon receiving module, the photon receiving module includes a second two-color mirror DM2, a first communication component, and a second communication component, the second two-color mirror DM2 emits signal photons and idler photons into the first optical branch and the second optical branch, and transmits them to the first communication component and the second communication component respectively; the first communication component includes a long-pass filter LPF and a second collimation component arranged on the first optical branch to filter out the third pump light; the second communication component includes a band-pass filter BPF and a third collimation component arranged on the second optical branch to filter out the third pump light; The dual-color marking photon source generation module includes an optical sheet component and a third quasi-phase matching crystal PPKTP3, which are sequentially arranged on the optical path and used to adjust the polarization state and focus of the input pulse light. The input end of the optical sheet component inputs a third pump light of a set wavelength. The third pump light is converted into a pair of signal photons and idler photons under the spontaneous output of the third quasi-phase matching crystal PPKTP3. The wavelength and bandwidth of the signal photon and the idler photon conform to the energy conservation and momentum conservation formulas, and are converted into: oh p =ω s +oh i (1) Δk=k p -k s -k i +2π / Λ=0 (2) where k q =2πn q / λ q (q=p,s,i),k p , k s , k i are the wave vectors of the third pump light, signal photon and idler photon respectively, Λ is the polarization period of the third quasi-phase matching crystal PPKTP3, ω p ,ω s ,ω i are the vibration frequencies of the third pump light, signal photon and idler photon in the quasi-phase matching crystal, n p 、n s 、n i are the refractive indices of the third pump light, signal photon and idler photon in the quasi-phase matching crystal, λ p , s , i are the wavelengths of the third pump light, signal photon and idler photon respectively. The bandwidths of signal photon and idler photon can be obtained according to the vibration frequency; The optical sheet assembly includes a deflection adjustment unit and a focusing unit arranged on the optical path; The dual-color marking photon source generation module further includes a temperature-controlled furnace, and the third quasi-phase matching crystal PPKTP3 is arranged in the temperature-controlled furnace.

2. The dual-compatible communication device of the dual-color marking photon source generation module according to claim 1, characterized in that: The third quasi-phase matching crystal PPKTP3 is a quasi-phase matching type II phase matching crystal.

3. The dual-compatible communication device of the dual-color marking photon source generation module according to claim 1, characterized in that: Both end faces of the third quasi-phase matching crystal PPKTP3 are plated with anti-reflection films of three wavelengths corresponding to the third pump light, signal photons and idler photons.

4. The dual-compatible communication device of the dual-color marking photon source generation module according to claim 1, characterized in that: The photon receiving module also includes a coincidence counting unit, which includes a first single-photon detector SPD1 and a second single-photon detector SP2, and a coincidence counter; the first single-photon detector SPD1 and the second single-photon detector SP2 are correspondingly arranged at the output ends of the first optical branch and the second optical branch, and the output ends of the first single-photon detector SPD1 and the second single-photon detector SP2 are respectively connected to the coincidence counter.

5. The dual-compatible communication device of the dual-color marking photon source generation module according to claim 1, characterized in that: The device also includes a frequency doubling module, which includes a first pump laser source, a transmission dimming unit, a first frequency doubling unit, a first dichroic mirror DM1, and a second frequency doubling unit, which are arranged in sequence along the optical path. The first frequency doubling unit and the second frequency doubling unit both include a focusing lens and a periodically polarized crystal.

6. The dual-compatible communication device of the dual-color marking photon source generation module according to claim 5, characterized in that: The periodically poled crystals in the first frequency doubling unit and the second frequency doubling unit are type I phase-matched periodically poled crystals.

7. The dual-compatible communication device of the dual-color marking photon source generation module according to claim 5, characterized in that: The first pump laser source outputs a 1560nm pump light, the first frequency doubling unit outputs a 780nm doubled frequency light, the second frequency doubling unit outputs a 390nm quadrupled frequency light, and the quadrupled frequency light is used as the third pump light and is sequentially transmitted through the first collimating transmission component and the optical sheet component and then transmitted to the third quasi-phase matching crystal PPKTP3. The first collimating transmission component includes a purple single-mode optical fiber SMF and a second collimating unit and a third collimating unit respectively arranged at both ends of the purple single-mode optical fiber SMF.

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