CN115469496A - Quantum entanglement source for on-chip bi-periodic polarized lithium niobate - Google Patents
Quantum entanglement source for on-chip bi-periodic polarized lithium niobate Download PDFInfo
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- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 title claims abstract description 38
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- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/35—Non-linear optics
- G02F1/365—Non-linear optics in an optical waveguide structure
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/35—Non-linear optics
- G02F1/353—Frequency conversion, i.e. wherein a light beam is generated with frequency components different from those of the incident light beams
- G02F1/3544—Particular phase matching techniques
- G02F1/3548—Quasi phase matching [QPM], e.g. using a periodic domain inverted structure
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Abstract
The application is applicable to the technical field of quantum, and relates to a quantum entanglement source of on-chip bi-periodic polarized lithium niobate. The quantum entanglement source comprises a waveguide device formed by a PPLN waveguide and an on-chip beam splitter, and an entanglement device formed by an optical fiber fixer, first mode micro-nano optical fibers, second mode micro-nano optical fibers and an optical fiber polarization combiner, wherein the input end of the on-chip beam splitter is connected with a pump light source, photons are injected into the PPLN waveguide by the on-chip beam splitter to form two SPDC optical paths, the modes at the tail ends of the two micro-nano optical fibers have a 90-degree difference, the two micro-nano optical fibers are fixed by the optical fiber fixer, the lengths of the two micro-nano optical fibers are the same, the input ends of the two micro-nano optical fibers are respectively butted with the output ends of the two PPLN waveguides, the output ends of the two micro-nano optical fibers are respectively connected with the two input ends of the optical fiber polarization combiner, the optical fiber polarization combiner is used for forming interference and outputting after the two optical waveguides are combined, compared with the traditional free space entanglement form, the optical fibers are easy to achieve entanglement, and the occupied space of the whole optical path can be reduced.
Description
Technical Field
The application is suitable for the technical field of quantum optics and quantum information, and particularly relates to a quantum entanglement source of on-chip bi-periodic polarized lithium niobate.
Background
The communication safety is the guarantee of national information economy safety and people's social life. Quantum communication is based on quantum mechanics, is a unconditionally safe communication mode of information licenses in principle, has absolute safety which is not possessed by the traditional communication mode, and has huge application prospects in the safety fields of national information safety, military safety, financial safety and the like. Channel transmission attenuation in quantum communication is the square of a single link, and some restrictions exist on the aspect of improvement of the final code rate, and the improvement of the brightness of an entanglement source is one of the most direct means for improving the final code rate.
The traditional entanglement source utilizes Spontaneous Parametric Down-Conversion (SPDC) of periodically polarized second-order nonlinear crystals to generate quantum entanglement, but has the defects of low yield, large volume, large temperature control difficulty caused by large volume of a temperature control circuit and complex design, low integration and the like; compared with bulk quantum optics, quantum integrated optics has the characteristics of small volume, high stability, strong controllability, reconfigurability and the like. Lithium niobate is one of the most important nonlinear optical materials, and is widely used for preparation of quantum light sources and high-speed regulation and control of quantum states. With the introduction of micromachining technology, lithium Niobate has become an important platform of quantum integrated optics, a monolithic integrated entangled light source capable of realizing multiple degrees of freedom coding can be realized, and a Periodically Poled Lithium Niobate (PPLN) waveguide is the best choice for solving the entanglement source problem in the field of quantum information.
The existing quantum entanglement source needs to use lenses and the like to form a light path, the formed device is large in size and inconvenient to use, the effect of quantum entanglement by using the lenses is poor, the parameter requirement and the device sealing requirement on the lenses are high, and the quantum entanglement source is not easy to realize. Therefore, how to reduce the difficulty in implementing an entanglement source with a small volume and a good quantum entanglement effect is a problem to be solved urgently.
Disclosure of Invention
In view of this, the embodiments of the present application provide a quantum entanglement source of on-chip bi-periodic polarized lithium niobate, so as to solve the problem of how to reduce the difficulty in implementing an entanglement source with a small volume and a good quantum entanglement effect.
The application provides a quantum entanglement source of on-chip bi-periodic polarized lithium niobate, wherein the quantum entanglement source comprises a pumping light source, a waveguide device and an entanglement device;
the waveguide device comprises a PPLN waveguide and an on-chip beam splitter, wherein the input end of the on-chip beam splitter is connected with the pump light source, the on-chip beam splitter divides the pump light source into two paths of light which enter the PPLN waveguide, and two paths of SPDC optical paths are formed in the PPLN waveguide;
the entanglement device comprises an optical fiber fixer, a first mode micro-nano optical fiber, a second mode micro-nano optical fiber and an optical fiber polarization beam combiner, the mode difference of the tail ends of the first mode micro-nano optical fiber and the second mode micro-nano optical fiber is 90 degrees, and the first mode micro-nano optical fiber and the second mode micro-nano optical fiber are fixed by the optical fiber fixer, so that the lengths of the two paths of optical fibers are the same;
the output end of the first mode micro-nano optical fiber is in butt joint with one SPDC optical path output from the PPLN waveguide, the input end of the second mode micro-nano optical fiber is in butt joint with the other SPDC optical path output from the PPLN waveguide, the output end of the first mode micro-nano optical fiber and the output end of the second mode micro-nano optical fiber are respectively connected with two input ends of the optical fiber polarization beam combiner, and the optical fiber polarization beam combiner is used for forming interference and outputting after the two SPDC optical paths are combined.
In an embodiment, the optical fiber holder is an optical fiber array, the optical fiber array includes N parallel optical fiber fixing grooves with the same length, all the optical fiber fixing grooves are arranged at equal intervals, the interval of two paths of SPDC optical paths in the PPLN waveguide is an integral multiple of the interval distance between two adjacent optical fiber fixing grooves, the optical fiber fixing grooves are used for fixing the first mode micro-nano optical fiber and the second mode micro-nano optical fiber, and N is an integer greater than 1.
In an embodiment, the first mode micro-nano fiber and the second mode micro-nano fiber are both polarization maintaining fibers.
In an embodiment, the optical fiber holder is a Xiong Maoyan-shaped fixing structure, the fixing structure enables the first mode micro-nano optical fiber and the second mode micro-nano optical fiber to be adjacently arranged in parallel, and the interval between the cross section center of the first mode micro-nano optical fiber and the cross section center of the second mode micro-nano optical fiber is the same as the interval between the two SPDC optical paths in the PPLN waveguide.
In one embodiment, the on-chip beam splitter is a Y-beam splitter.
In one embodiment, the quantum entanglement source further comprises a substrate sheet and a temperature control device, the waveguide device, the entanglement device and the temperature control device are all fixedly arranged on the substrate sheet, and the temperature control device is used for controlling the temperature of the waveguide device and the entanglement device on the substrate sheet.
In an embodiment, the temperature control device is a TEC temperature control driver, the waveguide module and the compensation device are disposed on one surface of the substrate sheet, and the TEC temperature control driver is disposed on the other surface of the substrate sheet.
In an embodiment, the quantum entanglement source further comprises an output optical fiber, and the output end of the fiber polarization beam combiner is connected with the output optical fiber.
In one embodiment, the PPLN waveguide is a lithium niobate ridge waveguide, a titanium diffused waveguide, or a proton exchange waveguide.
In one embodiment, the PPLN waveguide is a Z-cut lithium niobate thin film having a film thickness of 5 μm to 600 μm, and is obtained by periodically poling the PPLN waveguide using a poling period of 2.55 μm to 18.9 μm at a duty ratio of 50%.
Compared with the prior art, the quantum entanglement source of the on-chip bi-periodic polarized lithium niobate has the beneficial effects that: the quantum entanglement source comprises a pumping light source, a waveguide device and an entanglement device, wherein the waveguide device comprises a PPLN waveguide and an on-chip beam splitter, the input end of the on-chip beam splitter is connected with the pumping light source, the on-chip beam splitter divides the pumping light source into two paths of light to enter the PPLN waveguide, two paths of SPDC light paths are formed in the PPLN waveguide, the entanglement device comprises an optical fiber fixer, a first mode micro-nano optical fiber, a second mode micro-nano optical fiber and an optical fiber polarization beam combiner, the mode difference between the tail ends of the first mode micro-nano optical fiber and the second mode micro-nano optical fiber is 90 degrees, the first mode micro-nano optical fiber and the second mode micro-nano optical fiber are fixed by the optical fiber fixer, the lengths of the two paths of optical fibers are the same, the output end of the first mode micro-nano optical fiber is in butt joint with one path of SPDC light path output from the PPLN waveguide, the input end of the second mode micro-nano optical fiber is in butt joint with the other SPDC optical path output from the PPLN waveguide, the output end of the first mode micro-nano optical fiber and the output end of the second mode micro-nano optical fiber are respectively connected with two input ends of an optical fiber polarization beam combiner, the optical fiber polarization beam combiner is used for forming interference and outputting after two optical waveguides are combined, two SPDC optical paths are formed on the PPLN waveguide, one SPDC optical path is converted through an optical fiber output mode, coupling output is finally formed, a quantum entanglement source is obtained, compared with a traditional free space entanglement mode, the optical fiber is adopted to easily achieve entanglement, and the occupied space of the whole optical path can be reduced, so that the volume of the entanglement source can be reduced.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise.
Fig. 1 is a schematic structural diagram of an on-chip bi-periodically poled lithium niobate quantum entanglement source provided in an embodiment of the present application;
FIG. 2 is a schematic diagram of a quantum entanglement source after a PPLN waveguide employing a Z-cut lithium niobate thin film as provided in one embodiment of the present application;
FIG. 3 is a graph of the yield of a quantum entanglement source at different temperatures according to one embodiment of the present disclosure;
FIG. 4 is a schematic structural diagram of an optical fiber holder of a quantum entanglement source according to the second embodiment of the present application;
FIG. 5 is a schematic structural diagram of an optical fiber holder of a quantum entanglement source according to a third embodiment of the present application;
FIG. 6 is a schematic structural diagram of an on-chip bi-periodically poled lithium niobate quantum entanglement source provided in the fourth application example;
in the figure, 1 is a pump light source, 2 is a waveguide device, 3 is an entanglement device, 4 is a substrate sheet, 5 is a temperature control device, 201 is a PPLN waveguide, 202 is an on-chip beam splitter, 2011 is a first SPDC optical path, 2012 is a second SPDC optical path, 301 is an optical fiber fixer, 302 is a first mode micro-nano optical fiber, 303 is a second mode micro-nano optical fiber, 304 is an optical fiber polarization beam combiner, 3011 is an optical fiber array, and 3012 is a fixing structure in the shape of Xiong Maoyan.
Detailed Description
In the following description, for purposes of explanation and not limitation, specific details are set forth, such as particular system structures, techniques, etc. in order to provide a thorough understanding of the embodiments of the present application. It will be apparent, however, to one skilled in the art that the present application may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present application with unnecessary detail.
It will be understood that the terms "comprises" and/or "comprising," when used in this specification and the appended claims, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It should also be understood that the term "and/or" as used in this specification and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.
As used in this specification and the appended claims, the term "if" may be interpreted contextually as "when", "upon" or "in response to" determining "or" in response to detecting ". Similarly, the phrase "if it is determined" or "if a [ described condition or event ] is detected" may be interpreted contextually to mean "upon determining" or "in response to determining" or "upon detecting [ described condition or event ]" or "in response to detecting [ described condition or event ]".
Furthermore, in the description of the present application and the appended claims, the terms "first," "second," "third," and the like are used for distinguishing between descriptions and not necessarily for describing or implying relative importance.
Reference throughout this specification to "one embodiment" or "some embodiments," or the like, means that a particular feature, structure, or characteristic described in connection with the embodiment is included in one or more embodiments of the present application. Thus, appearances of the phrases "in one embodiment," "in some embodiments," "in other embodiments," or the like, in various places throughout this specification are not necessarily all referring to the same embodiment, but rather "one or more but not all embodiments" unless specifically stated otherwise. The terms "comprising," "including," "having," and variations thereof mean "including, but not limited to," unless expressly specified otherwise.
It should be understood that, the sequence numbers of the steps in the following embodiments do not mean the execution sequence, and the execution sequence of each process should be determined by the function and the inherent logic of the process, and should not constitute any limitation to the implementation process of the embodiments of the present application.
In order to explain the technical means of the present application, the following description will be given by way of specific examples.
Example one
Referring to fig. 1, a schematic structural diagram of a quantum entanglement source of on-chip bi-periodic polarized lithium niobate provided in an embodiment of the present application is shown, where the quantum entanglement source includes a pump light source 1, a waveguide device 2, and an entanglement device 3, the waveguide device includes a PPLN waveguide 201 and an on-chip beam splitter 202, an input end of the on-chip beam splitter 202 is connected to the pump light source 1, and the entanglement device 3 includes an optical fiber holder 301, a first-mode micro-nano optical fiber 302, a second-mode micro-nano optical fiber 303, and an optical fiber polarization beam combiner 304.
Two output ends of the on-chip beam splitter 202 respectively inject photons into the PPLN waveguide 2, and two SPDC optical paths, i.e., a first SPDC optical path 2011 and a second SPDC optical path 2012 in fig. 1, are formed in the PPLN waveguide 2. The mode phase difference between the first mode micro-nano optical fiber 302 and the second mode micro-nano optical fiber 303 is 90 degrees, the first mode micro-nano optical fiber 302 and the second mode micro-nano optical fiber 303 are fixed by using the optical fiber fixer 301, and therefore the lengths of the first mode micro-nano optical fiber 302 and the second mode micro-nano optical fiber 303 are the same. For example, the on-chip beam splitter is a Y-type beam splitter.
The output end of the first mode micro-nano optical fiber 302 is in butt joint with one SPDC optical path output from the PPLN waveguide 201, namely a first SPDC optical path 2012, the input end of the second mode micro-nano optical fiber 303 is in butt joint with the other SPDC optical path output from the PPLN waveguide 201, namely a second SPDC optical path 2011, the output end of the first mode micro-nano optical fiber 302 and the output end of the second mode micro-nano optical fiber 303 are respectively connected with two input ends of the optical fiber polarization beam combiner 304, and the optical fiber polarization beam combiner 304 is used for forming interference and outputting after the two SPDC optical paths are combined.
The two SPDC optical paths respectively generate long | V by the light sent by the pump light source 1 through the SPDC process> s |V> i Photon, then, two paths | V> s |V> i Photons respectively enter the first mode micro-nano optical fiber 302 and the second mode micro-nano optical fiber 303, and | V is aligned in the first mode micro-nano optical fiber 302 or the second mode micro-nano optical fiber 303> s |V> i After the mode conversion of the photons, obtaining | H> s |H> i Photon, | V> s |V> i Photon sum | H> s |H> i Photons enter the fiber polarization beam combiner 304, so that two paths of light beams are converged together, the pair of photons form interference, different maximum entangled states can be constructed, one of the following 2 maximum entangled states is constructed in the polarization dimension, and the entanglement formula is as follows:
in the present application, the PPLN waveguide 201 may be in the micron or even the nanometer scale, and thus the difficulty of periodic polarization and fiber coupling entanglement corresponding to the PPLN waveguide 201 is exponentially increased compared to the conventional scheme. In order to realize the above-described PPLN waveguide 201, it can be realized by using a Z-cut lithium niobate thin film, which is a quantum entanglement source behind the PPLN waveguide 201 using the Z-cut lithium niobate thin film as shown in fig. 2. In the manufacturing process of the Z-cut lithium niobate film, a type-0 mode is adopted for spontaneous parameter down-conversion, and the method specifically comprises the following steps:
1. and calculating a quasi-phase matching period required by parametric down-conversion, and constructing a polarized electrode model through COMSOL numerical simulation software.
The method comprises the steps of establishing a polarized electrode model through COMSOL numerical simulation software in the polarization of a lithium niobate film, simulating and researching polarized electric field distribution corresponding to different electrode configurations, researching influence mechanisms of the polarized electrode configuration, polarization voltage, polarization time and polarization period on nucleation and transverse widening of an inversion domain through experiments, selecting the optimal polarized electrode configuration, establishing a corresponding relation between an external polarized electric field and polarization time and internal domain structure motion, accurately controlling the transverse widening of the inversion domain, and reducing the combination of adjacent inversion domains.
2. And preparing a periodically polarized electrode on the Z-cut lithium niobate thin film by using UV mask exposure according to the quasi-phase matching period.
The processing process can comprise the steps of spin coating, exposure (UV ultraviolet exposure and EBL), development, fixation, electrode plating, high-voltage polarization (polarization is carried out by adopting a polarization period) and the like, the exposure process adopts a double ultraviolet exposure technology to increase the exposure limit, and then the PVD is accurately controlled to carry out the manufacture of the accurate metal electrode. Of course, the single exposure technique may be adopted regardless of the processing accuracy, and the present application does not limit this.
3. And determining and selecting the optimal polarized electrode configuration based on the change curves of the inversion crystal domain nucleation and the transverse broadening along with the polarized electrode configuration, the polarization voltage and the polarization time.
4. Based on the optimal polarized electrode configuration, the Z-cut lithium niobate thin film of the prepared periodic polarized electrode is subjected to spontaneous parametric down-conversion by an external electric field method to obtain the PPLN waveguide with uniform polarization and inversion domain duty ratio, and the PPLN waveguide meets the requirement of first-order quasi-phase matching.
After periodic polarization, the reversed domain structure is tested and represented, polarization is required to be uniform, the reversed domain duty ratio is uniform, and the requirement of first-order quasi-phase matching is met.
The conventional periodic polarization second-order nonlinear crystal spontaneous parameter down-conversion adopts a type-II mode, the piezoelectric constant d33 is small (namely, the conversion capability is low, the performance of an entanglement source is low), and the period is large (namely, the magnitude is 10 mu m). The PPLN waveguide spontaneous parameter down-conversion in the application adopts a type-0 mode, the piezoelectric constant d33 is large (namely, the type-II mode is several times, and the entanglement source performance is increased by several times), the period is small (namely, the magnitude is within 10 grades, and particularly, the period is 2.55 mu m under 405 nm), so the preparation difficulty is high.
The method includes the steps that polarization electric field distribution corresponding to different electrode configurations is simulated and researched, a quasi-phase matching period required by SPDC is calculated, and a polarization electrode model is built through COMSOL numerical simulation software; and a periodically poled electrode was fabricated on the Z-cut PPLN waveguide by standard semiconductor precision processing techniques (UV mask exposure); through experiments, influence mechanisms of the configuration of the polarization electrode, the polarization voltage and the polarization time on nucleation and transverse broadening of the inversion domain are researched, the optimal configuration of the polarization electrode is selected, the corresponding relation between an external polarization electric field and the polarization time and the movement of an internal domain structure is established, the transverse broadening of the inversion domain is accurately controlled, and the combination of adjacent inversion domains is reduced; carrying out periodic polarization and SPDC process on the Z-cut PPLN waveguide by an external electric field method; the reverse domain structure is tested and characterized, the polarization is required to be uniform, and the duty ratio of the reverse domain is uniform, so that the requirement of first-order phase matching is met.
In one embodiment, a Z-cut lithium niobate thin film is used for the PPLN waveguide 201, the thickness of the thin film is 5 to 600 μm, and the PPLN waveguide is obtained by periodic polarization using a polarization period of 2.55 to 18.9 μm and a duty ratio of 50%.
The main index of the quantum entanglement source is entanglement visibility, and by using the Z-cut lithium niobate thin film, the contrast of a quantum entanglement source system is up to 103, which is more than 2 times of that of a traditional PPKDP crystal (50.
As shown in fig. 3, which is a graph of the yield of the quantum entanglement source at different temperatures, wherein the abscissa is temperature, the unit is c, the ordinate is yield, and the unit is G/mW), the yield of the quantum entanglement source in the present application can reach 6G pairs/mW (at 44 ℃), which is improved by more than 100 times compared with the conventional PPKDP crystal (yield is 30M pairs/mW/s), and the quantum entanglement source in the present application can efficiently provide quantum entanglement photon pairs at different temperatures.
Example two
Referring to fig. 4, for a schematic structural diagram of an optical fiber holder of a quantum entanglement source provided in the second embodiment of the present application, the optical fiber holder 301 is an optical fiber array 3011, the optical fiber array 3011 includes N parallel optical fiber fixing slots with the same length, all the optical fiber fixing slots are arranged at equal intervals, the interval of two SPDC optical paths in the PPLN waveguide is an integral multiple of the interval distance between two adjacent optical fiber fixing slots, the optical fiber fixing slots are used for fixing the first mode micro-nano optical fiber 302 and the second mode micro-nano optical fiber 303, N is an integer greater than 1.
Specifically, the first mode micro-nano fiber 302 and the second mode micro-nano fiber 303 are both polarization maintaining fibers.
At this time, according to the quasi-phase matching equation, a planning period is determined, and the lithium niobate thin film is periodically polarized, for example, the input light is 405nm continuous laser, the parametric light is 810nm, the polarization period is calculated to be 2.55 μm, and the duty ratio is 50%.
The periodic polarization is carried out through whirl coating, exposure, development, fixation, electrode plating and voltage polarization, the polarization period is 2.55 mu m, and the duty ratio is 50%.
The periodically polarized lithium niobate is made into a periodically polarized thin film lithium niobate waveguide (namely a PPLN waveguide) by a micro-nano processing technology.
Electron beam evaporation of SiO from PPLN waveguide 201 2 As a protective layer, cutting and polishing are then performed.
The front end coupling optical fiber of the PPLN waveguide 201 is used for connecting the on-chip beam splitter 202, the rear end is output to the optical fiber polarization beam combiner 304 entanglement device for interference through the optical fiber array 3011 coupling optical fiber, and the quantum entanglement light source can be obtained by combining with other settable equipment and then packaging.
The traditional periodically-polarized crystal and a free space optical device (namely mm magnitude) are directly adhered together and fixed, but the light-binding capacity is low, and the performance of an entanglement source is low (the brightness is in inverse relation to the beam waist of a light beam); in the application, the distance between the two SPDC optical paths is in the level of 100 microns, and the two SPDC optical paths need to be coupled with an entanglement device at the same time, so that the difficulty is high. Simulating electric field distribution corresponding to output light spot modes of the two SPDC optical paths through a numerical simulation software of a logical FDTD, calculating the coupling efficiency of the two SPDC optical paths, and exploring the highest parameter of the coupling efficiency; two SPDC optical paths are accurately controlled through a real-time monitoring system, so that an output light spot mode of the SPDC optical paths is accurately controlled to be matched with a light spot mode of an entanglement device and fixed by ultraviolet glue, and high-efficiency coupling of the waveguide is realized.
EXAMPLE III
Referring to fig. 5, for a schematic structural diagram of an optical fiber holder of a quantum entanglement source provided in the third embodiment of the present application, the optical fiber holder 301 is a fixing structure 3012 shaped like a cat eye, and the fixing structure 3012 shaped like Xiong Maoyan is used to adjacently and parallelly set the first mode micro-nano optical fiber 302 and the second mode micro-nano optical fiber 303, and a distance between a center of a cross section of the first mode micro-nano optical fiber 301 and a center of a cross section of the second mode micro-nano optical fiber 303 is the same as a distance between two SPDC optical paths in the PPLN waveguide 201. The spacing between the cross-sectional centers of the two fibers is illustrated in fig. 5 as 0.125 μm, the corresponding anchor structure 3012 may have a diameter of 1.8 μm, the two fibers may take the shape of Xiong Maoyan within the cladding, and the modes of the ends of the two fibers differ by 90 °.
Specifically, the first mode micro-nano fiber 302 and the second mode micro-nano fiber 303 are both polarization maintaining fibers.
At this time, according to the quasi-phase matching equation, a planning period is determined, the lithium niobate thin film is periodically polarized, for example, the input light is 780nm continuous laser, the parameter light is 1560nm, the polarization period is calculated to be 18.9 μm, and the duty ratio is 50%.
Wherein, the periodic polarization is carried out by whirl coating, exposure, development, fixation, electrode plating and voltage polarization, the polarization period is 2.55 μm, and the duty ratio is 50%.
The periodically polarized lithium niobate is made into a periodically polarized thin film lithium niobate waveguide (namely a PPLN waveguide) by a micro-nano processing technology.
Electron beam evaporation of SiO from PPLN waveguide 201 2 As a protective layer, cutting and polishing are then performed.
Coupling optical fibers at the front end of the PPLN waveguide 201 are used for connecting the on-chip beam splitter 202, and the optical fibers are assembled at the rear end through a Xiong Maoyan-shaped fixing structure 3012 and output to the optical fiber polarization beam combiner 304 entanglement device for interference, and then the quantum entanglement light source can be obtained by combining with other settable equipment and then packaging.
In one embodiment, the quantum entanglement source further comprises an output optical fiber, and the output end of the optical fiber polarization beam combiner is connected with the output optical fiber.
Example four
Referring to fig. 6, in order to apply for the structural schematic diagram of the quantum entanglement source of the on-chip bi-period polarized lithium niobate provided in the fourth embodiment, on the basis of the first embodiment, the quantum entanglement source further includes a substrate sheet 4 and a temperature control device 5, the waveguide device 2, the entanglement device 3, and the temperature control device 5 are all fixed on the substrate sheet, and the temperature control device 5 is used for performing temperature control on the waveguide device 2 and the entanglement device 3 on the substrate sheet 4.
Wherein, temperature control device 5 can realize whole accuse temperature, reduces the accuse temperature degree of difficulty, has integrateed little temperature control circuit, and the system volume reduces greatly, and is specific, and temperature control device is TEC accuse temperature driver, and waveguide module and compensation arrangement set up the one side at the base plate piece, and TEC accuse temperature driver sets up the another side at the base plate piece. In addition, the plane formed by the two SPDC optical paths of the PPLN waveguide 201 in the waveguide device 2 may be vertically arranged or parallel arranged by the substrate sheet 4.
In one embodiment, PPLN waveguide 201 is a ridge waveguide of lithium niobate material, a titanium diffused waveguide, or a proton exchange waveguide. This embodiment describes the fabrication of a basic PPLN waveguide by taking a ridge waveguide as an example.
Based on the optical waveguide theory, a PPLN ridge waveguide structure model is constructed by using COMSOL numerical simulation and Lumerical simulation, and the influence of waveguide structure parameters such as waveguide width, ridge height, side wall inclination angle and the like on the effective refractive index of different wavelength light spot modes in the waveguide is simulated and researched, so that ridge waveguide structure parameters are guided to be designed.
The design of this application makes the lithium niobate waveguide quantum entanglement source of bicycle polarization, and the space light path of the relative optical platform of volume reduces greatly, and last optical fiber input pump light, optical fiber output entanglement source, greatly increased integrate. By adopting a photon pair generation system of a type-0 bi-period polarization thin film lithium niobate waveguide, the conversion efficiency is high and the brightness is high; in addition, the system for generating the photon pair of the bi-period polarization thin film lithium niobate waveguide on the type-0 SPDC chip can realize integral temperature control, reduce the difficulty of temperature control, integrate a small temperature control circuit and greatly reduce the system volume.
The above embodiments are only used to illustrate the technical solutions of the present application, and not to limit the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications and substitutions do not substantially depart from the spirit and scope of the embodiments of the present application and are intended to be included within the scope of the present application.
Claims (10)
1. A quantum entanglement source of on-chip bi-periodic polarized lithium niobate is characterized in that the quantum entanglement source comprises a pump light source, a waveguide device and an entanglement device;
the waveguide device comprises a PPLN waveguide and an on-chip beam splitter, wherein the input end of the on-chip beam splitter is connected with the pump light source, the on-chip beam splitter divides the pump light source into two paths of light which enter the PPLN waveguide, and two paths of SPDC optical paths are formed in the PPLN waveguide;
the entanglement device comprises an optical fiber fixer, a first mode micro-nano optical fiber, a second mode micro-nano optical fiber and an optical fiber polarization beam combiner, the mode difference between the tail ends of the first mode micro-nano optical fiber and the second mode micro-nano optical fiber is 90 degrees, and the first mode micro-nano optical fiber and the second mode micro-nano optical fiber are fixed by the optical fiber fixer, so that the lengths of the two optical fibers are the same;
the output end of the first mode micro-nano optical fiber is in butt joint with one SPDC optical path output from the PPLN waveguide, the input end of the second mode micro-nano optical fiber is in butt joint with the other SPDC optical path output from the PPLN waveguide, the output end of the first mode micro-nano optical fiber and the output end of the second mode micro-nano optical fiber are respectively connected with two input ends of the optical fiber polarization beam combiner, and the optical fiber polarization beam combiner is used for forming interference and outputting after the two SPDC optical paths are combined.
2. The quantum entanglement source of claim 1, wherein the optical fiber holder is an optical fiber array, the optical fiber array comprises N parallel optical fiber fixing grooves with the same length, all the optical fiber fixing grooves are arranged at equal intervals, the interval of two SPDC optical paths in the PPLN waveguide is an integral multiple of the interval distance between two adjacent optical fiber fixing grooves, the optical fiber fixing grooves are used for fixing the first-mode micro-nano optical fiber and the second-mode micro-nano optical fiber, and N is an integer greater than 1.
3. The quantum entanglement source of claim 2, wherein the first mode micro-nanofiber and the second mode micro-nanofiber are both polarization maintaining fibers.
4. The quantum entanglement source of claim 1, wherein the optical fiber holder is a Xiong Maoyan-shaped fixing structure, the fixing structure is used for arranging the first mode micro-nano optical fiber and the second mode micro-nano optical fiber adjacently and parallelly, and the interval between the center of the cross section of the first mode micro-nano optical fiber and the center of the cross section of the second mode micro-nano optical fiber is the same as the interval between the two SPDC optical paths in the PPLN waveguide.
5. The quantum entanglement source of claim 1, wherein the on-chip beam splitter is a Y-splitter polarization maintaining fiber.
6. The quantum entanglement source of claim 5, further comprising a substrate sheet on which the waveguide device, the entanglement device, and the temperature control device are secured, and a temperature control device for temperature control of the waveguide device and the entanglement device on the substrate sheet.
7. The quantum entanglement source of claim 6, wherein the temperature control device is a TEC temperature-controlled driver, the waveguide module and the compensation device are disposed on one side of the substrate sheet, and the TEC temperature-controlled driver is disposed on the other side of the substrate sheet.
8. The quantum entanglement source of claim 1, further comprising an output fiber, wherein an output end of the fiber polarization combiner is connected to the output fiber.
9. The quantum entanglement source of claim 1, wherein the PPLN waveguide is a ridge waveguide of lithium niobate material, a titanium diffusion waveguide, or a proton exchange waveguide.
10. The quantum entanglement source of any one of claims 1 to 9, wherein the PPLN waveguide is a Z-cut lithium niobate thin film having a thickness of 5 μm to 600 μm, and is periodically poled using a poling period of 2.55 μm to 18.9 μm and a duty cycle of 50%.
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| CN116609985A (en) * | 2023-07-20 | 2023-08-18 | 中国船舶集团有限公司第七〇七研究所 | Compact entangled light source based on turn-back type periodic polarized crystal |
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| CN116609985A (en) * | 2023-07-20 | 2023-08-18 | 中国船舶集团有限公司第七〇七研究所 | Compact entangled light source based on turn-back type periodic polarized crystal |
| CN116609985B (en) * | 2023-07-20 | 2023-09-15 | 中国船舶集团有限公司第七〇七研究所 | Compact entangled light source based on turn-back type periodic polarized crystal |
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