CN219936257U - Broadband entanglement source - Google Patents
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Abstract
The utility model discloses a broadband entanglement source, which comprises a laser source module, a polarization controller, an optical circulator, a polarization beam splitter, a two-photon generation module, a Faraday rotator and a wavelength division multiplexer, wherein all devices are connected by adopting polarization maintaining fibers, so that optical signals are transmitted among different optical devices through an all-fiber channel, optical alignment among the optical devices is easy to realize, and the system stability and the efficiency of photon pair generation of the entanglement source are improved. In addition, a silicon waveguide structure is adopted in the two-photon generation module as a nonlinear medium to generate photon pairs, the silicon waveguide structure consists of a silicon nanowire waveguide and two grating couplers, the silicon nanowire waveguide has a wider photon pair radiation spectrum, and the generated photon pairs also have a wider spectrum width, so that the quantum key distribution with high capacity density is realized.
Description
Technical Field
The utility model belongs to the technical field of quantum information, and particularly relates to a broadband entanglement source.
Background
The quantum entanglement source is a core component in the quantum key distribution technology, the good entanglement source is a key for realizing high-reliability and long-distance quantum communication, and the main problem of limiting the application of entangled quantum cryptography is the lack of high-brightness, high-quality and small-size photon entanglement sources in communication wave bands. Among photon entanglement sources, the most basic research relates to the development and application of two-photon entanglement sources, wherein the research and application of two-photon polarization single-degree-of-freedom entanglement sources are mature, and the two-photon polarization single-degree-of-freedom entanglement sources are the main entanglement sources of various quantum communication experiments at present. Although the development of the multi-degree-of-freedom and multi-photon entanglement source is closer to the actual application demand, the operation and debugging difficulties are larger as a whole.
The most common method of obtaining photon entanglement sources is by optical nonlinear coupling, two of which are commonly used: the first is based on a spontaneous parametric down-conversion (SPDC) process, using nonlinear media comprising: common block nonlinear crystals (such as KDP, BBO and the like) and periodic polarized crystals (such as PPLN and PPKTP), but the scheme has higher cost, and some entanglement source structures realized based on PPKTP crystals are disclosed in the prior art, however, the prior art is often built under experimental environment by utilizing space optics, the debugging difficulty is higher, the system stability and the optical efficiency are not high, and the system integration is not facilitated.
The second is based on the spontaneous four-wave mixing (SFWM) nonlinear effect, with nonlinear optics including: dispersion shifted optical fibers, microstructured optical fibers, birefringent optical fibers, and the like. The great advantage of the SFWM process in obtaining photon entanglement sources is high compatibility with fiber optic communication systems, but currently there are few fiber optic media with high nonlinear coefficients, and a pulse laser is generally required to be used as a pumping source. In the prior art, the bandwidth of a micro-ring cavity entangled light source based on spontaneous four-wave mixing is very narrow, and the pump wavelength needs to be precisely tuned to the formants of the micro-ring cavity and the temperature stability of the micro-ring cavity is kept to ensure that the formant wavelength is stable, so that the operation is complex and the practicability is limited.
Disclosure of Invention
In order to solve the problems, the utility model provides a broadband entanglement source, which adopts a silicon waveguide structure as a nonlinear medium to generate photon pairs and realizes the transmission of optical signals among different optical devices by using an all-fiber channel, so that the optical alignment among the optical devices is easy to realize, the system stability is good, and the efficiency of the entanglement source for generating photon pairs is improved. The specific scheme is as follows:
the utility model discloses a broadband entanglement source, which comprises a laser source module, a polarization controller, an optical circulator, a polarization beam splitter, a two-photon generation module, a Faraday rotator and a wavelength division multiplexer, wherein the polarization controller is arranged on the optical circulator;
the laser source module is connected with the polarization controller and used for generating, preprocessing and outputting pumping laser; the polarization controller generates linearly polarized light based on the pump laser; the optical circulator has a first port, a second port and a third port, the first port is connected with the polarization controller, the second port is connected with the polarization beam splitter, the third port is connected with the Faraday rotator, and the circulator is used for inputting linearly polarized light input by the first port to the polarization beam splitter through the second port and inputting photon pairs input by the second port to the Faraday rotator through the third port; the polarization beam splitter is used for dividing input linearly polarized light into orthogonal horizontally polarized light and vertical polarized light;
the two-photon generation module comprises a Sagnac ring, a silicon waveguide structure and an adjustable optical delay device, wherein the silicon waveguide structure and the adjustable optical delay device are arranged on the Sagnac ring, two ports of the Sagnac ring are respectively connected with two ports of the polarization beam splitter, horizontal polarized light and vertical polarized light are respectively transmitted in opposite directions along the Sagnac ring, the adjustable optical delay device is used for delaying the horizontal polarized light or the vertical polarized light to enable the horizontal polarized light and the vertical polarized light to simultaneously reach the silicon waveguide structure, and the silicon waveguide structure is used for simultaneously receiving the horizontal polarized light and the vertical polarized light which are transmitted in opposite directions and generating entangled photon pairs in a four-wave mixing process; the entangled photon pair is input to the Faraday rotator from a third port of the optical circulator through the polarization beam splitter and a second port of the optical circulator, and the Faraday rotator is connected with the wavelength division multiplexer and is used for rotationally rectifying the polarization direction of the entangled photon pair; the wavelength division multiplexer is used for separating and outputting the signal photons and idler photons in the entangled photon pair;
the polarization controller, the optical circulator, the polarization beam splitter, the two-photon generation module, the Faraday rotator and the wavelength division multiplexer are connected by adopting polarization maintaining optical fibers.
Further, the laser source module comprises a pumping light source, an adjustable attenuator and a first filter which are sequentially connected; the pump light source is used for generating pump laser, the adjustable attenuator attenuates the intensity of the pump laser, and the first filter filters the attenuated pump laser.
Further, the silicon waveguide structure is composed of a silicon nanowire waveguide and two grating couplers, wherein the two grating couplers are respectively connected with two ends of the silicon nanowire waveguide in a coupling mode, and an axial included angle between each grating coupler and a port of the silicon nanowire waveguide is 10 degrees.
Preferably, the adjustable attenuator is an adjustable optical fiber attenuator.
Preferably, the pump light source is a laser diode, a pulse laser or a continuous light laser.
Further, the broadband entanglement source further comprises a beam splitter and a photoelectric detector, wherein the input end of the beam splitter is connected with the output end of the polarization controller, the two output ends of the beam splitter are respectively connected with the photoelectric detector and the first port of the optical circulator, and the photoelectric detector is used for detecting the light intensity of linearly polarized light generated by the polarization controller.
Further, the broadband entanglement source further comprises a second filter, and the second filter is arranged on the transmission paths of the Faraday rotator and the wavelength division multiplexer and used for filtering out pump laser.
Preferably, the second filter is a fiber optic filter.
In general, the above technical solutions conceived by the present utility model, compared with the prior art, enable the following beneficial effects to be obtained:
the utility model provides a broadband entanglement source, which comprises a laser source module, a polarization controller, an optical circulator, a polarization beam splitter, a two-photon generation module, a Faraday rotator and a wavelength division multiplexer, wherein all devices are connected by adopting polarization maintaining fibers, so that optical signals are transmitted among different optical devices through an all-fiber channel, optical alignment among the optical devices is easy to realize, and the system stability and the efficiency of photon pair generation of the entanglement source are improved. In addition, a silicon waveguide structure is adopted in the two-photon generation module as a nonlinear medium to generate photon pairs, the silicon waveguide structure is composed of a silicon nanowire waveguide and two grating couplers, the silicon nanowire waveguide has a wider photon pair radiation spectrum, quantum key distribution with high capacity density is facilitated, the grating couplers are connected to two ends of the silicon nanowire waveguide, the coupling efficiency is improved, incident polarized light is converted into TE polarized modes after passing through the grating couplers and is coupled into the silicon nanowire waveguide, polarization mode conversion can not occur any more in a stable state in a subsequent transmission process, and the efficiency and performance of entanglement sources are improved.
Drawings
In order to more clearly illustrate this embodiment or the technical solutions of the prior art, the drawings that are required for the description of the embodiment or the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the present utility model, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a broadband entanglement source according to an embodiment of the present utility model;
FIG. 2 is a schematic diagram of a broadband entanglement source according to another embodiment of the present utility model;
FIG. 3 is a schematic diagram of a polarization maintaining fiber in accordance with the present utility model;
FIG. 4 is a schematic diagram of the principle of the present utility model in which linearly polarized light is transmitted through a polarization maintaining fiber on a polarization beam splitter;
FIG. 5 is a schematic diagram of a silicon waveguide structure in accordance with the present utility model;
FIG. 6 is a schematic diagram of a broadband entanglement source according to still another embodiment of the present utility model;
fig. 7 is a schematic diagram of a broadband entanglement source according to the present utility model based on the one provided in fig. 6.
Detailed Description
In order that the above-recited objects, features and advantages of the present utility model will become more readily apparent, a more particular description of embodiments of the utility model will be rendered by reference to the appended drawings and appended drawings. It will be apparent that the described embodiments are only some, but not all, embodiments of the utility model. All other embodiments, which can be made by those skilled in the art based on the embodiments of the utility model without making any inventive effort, are intended to be within the scope of the utility model.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present utility model, but the present utility model may be practiced in other ways other than those described herein, and persons skilled in the art will readily appreciate that the present utility model is not limited to the specific embodiments disclosed below.
In order to facilitate understanding and explanation of the technical solutions provided by the embodiments of the present utility model, the following description will first explain the background art of the present utility model.
The quantum entanglement source is a core component in the quantum key distribution technology, and the good entanglement source is a key for realizing high-reliability and long-distance quantum communication. The most common method of obtaining photon entanglement sources is by optical nonlinear coupling, two of which are commonly used: the first is based on a spontaneous parametric down-conversion (SPDC) process, using nonlinear media comprising: common bulk nonlinear crystals (such as KDP, BBO, etc.) and periodically poled crystals (such as PPLN, PPKTP). The second is based on the spontaneous four-wave mixing (SFWM) nonlinear effect, with nonlinear optics including: dispersion shifted optical fibers, microstructured optical fibers, birefringent optical fibers, and the like. The great advantage of the SFWM process in obtaining photon entanglement sources is high compatibility with fiber optic communication systems, but currently there are few fiber optic media with high nonlinear coefficients, and a pulse laser is generally required to be used as a pumping source. In the prior art, the bandwidth of a micro-ring cavity entangled light source based on spontaneous four-wave mixing is very narrow, and the pump wavelength needs to be precisely tuned to the formants of the micro-ring cavity and the temperature stability of the micro-ring cavity is kept to ensure that the formant wavelength is stable, so that the operation is complex and the practicability is limited.
In contrast, silicon waveguide structures have very broad photon-to-radiation spectra (up to several THz), a characteristic that is well suited for preparing multiplexed entanglement sources with channels of dense wavelength division multiplexing devices, thereby enabling high volume density quantum key distribution.
Based on this, the present utility model provides a broadband entanglement source, as shown in fig. 1, including a laser source module, a polarization controller, an optical circulator, a polarization beam splitter, a two-photon generation module, a faraday rotator, and a wavelength division multiplexer. The laser source module, the polarization controller, the optical circulator, the polarization beam splitter, the two-photon generation module, the Faraday rotator and the wavelength division multiplexer are connected by adopting polarization maintaining optical fibers, so that optical signals are transmitted among different optical devices through all-fiber channels, optical alignment among the optical devices is easy to realize, and the system stability and the efficiency of generating photon pairs by entanglement sources are improved.
The laser source module is connected with the polarization controller and used for generating, preprocessing and outputting pump laser. The polarization controller generates linearly polarized light based on the pump laser light.
Here, the pretreatment of the laser source module includes attenuation, filtering, and the like, specifically, in one embodiment of the present utility model, the light source module includes a pump light source, an adjustable attenuator, and a first filter, which are sequentially connected, as shown in fig. 2. The pump light source is used for generating pump laser, the adjustable attenuator attenuates the intensity of the pump laser, and the first filter filters the attenuated pump laser.
The pump light source can be a laser diode, a pulse laser or a continuous light laser. The adjustable attenuator is an adjustable optical fiber attenuator. The adjustable attenuator attenuates the energy of the pump laser to meet the occurrence condition of the subsequent four-wave mixing process, and the attenuated pump laser is input to the first filter for filtering to inhibit noise in the pump laser. Preferably, the first filter may be an optical fiber filter having a center wavelength of 1550.12 nm.
The optical circulator is provided with a first port, a second port and a third port, the first port is connected with the polarization controller, the second port is connected with the polarization beam splitter, the third port is connected with the Faraday rotator, and the circulator is used for inputting linearly polarized light input by the first port to the polarization beam splitter through the second port and inputting photon pairs input by the second port to the Faraday rotator through the third port.
The optical circulator is a polarization maintaining fiber circulator, is an irreversible unidirectional transmission three-port device, and can only transmit light along a specific port sequence. Linearly polarized light is input from the first port and output from the second port; entangled photon pairs are input from the second port and output from the third port.
The polarizing beam splitter is used to split the input linearly polarized light into orthogonal horizontally polarized light and vertically polarized light. The polarizing beam splitter includes an upper transmission port and a lower transmission port. From these two ports, horizontally polarized light and vertically polarized light are input to the two-photon generation module, respectively.
The polarization maintaining fiber has two main transmission axes, namely a fast axis and a slow axis of the fiber, as shown in fig. 3, wherein the fast axis has small refractive index, the light transmission speed is high, and the slow axis has large refractive index and the light transmission speed is low. The principle that linearly polarized light is transmitted on a polarization beam splitter through a polarization maintaining fiber is shown in fig. 4, the polarization beam splitter consists of an A prism and a B prism, an S surface of a contact surface of the A prism and the B prism is plated with a polarization splitting film, an included angle between the S surface and a plane is 45 degrees, the ports of the polarization beam splitter are connected with the polarization maintaining fiber, wherein a 1 port is an incident port, a 2 port and a 3 port are respectively corresponding to a lower transmission port and an upper transmission port of the polarization beam splitter, a slow axis of the polarization maintaining fiber connected with the 1 port is parallel to the S surface, the linearly polarized light is divided into orthogonal horizontal polarized light and vertical polarized light under the action of the polarization beam splitter, the horizontal polarized light enters a slow axis of the polarization maintaining fiber from one port 2 or 3, and the vertical polarized light enters the slow axis of the polarization maintaining fiber from the other port.
The two-photon generation module comprises a Sagnac ring, a silicon waveguide structure and an adjustable optical delay device, wherein the silicon waveguide structure and the adjustable optical delay device are arranged on the Sagnac ring, the two ports of the Sagnac ring are respectively connected with the two ports (an upper transmission port and a lower transmission port) of the polarization beam splitter, the horizontal polarized light and the vertical polarized light are respectively transmitted in opposite directions along the Sagnac ring, the adjustable optical delay device is used for delaying the horizontal polarized light or the vertical polarized light to enable the horizontal polarized light and the vertical polarized light to simultaneously reach the silicon waveguide structure, and the silicon waveguide structure is used for simultaneously receiving the horizontal polarized light and the vertical polarized light which are transmitted in opposite directions and generating entangled photon pairs in a four-wave mixing process; the entangled photon pair is input to a Faraday rotator from a third port of the optical circulator through a polarizing beam splitter and a second port of the optical circulator, and the Faraday rotator is connected with the wavelength division multiplexer and is used for rotationally rectifying the polarization direction of the entangled photon pair; the wavelength division multiplexer is used for separating and outputting the signal photons and idler photons in the entangled photon pair.
When the horizontal polarized light is transmitted clockwise, the horizontal polarized light is input to one port of the Sagnac ring from the upper transmission port of the polarization beam splitter, the vertical polarized light is transmitted anticlockwise, the vertical polarized light is input to the other port of the Sagnac ring from the lower transmission port of the polarization beam splitter, and the vertical polarized light is delayed by the adjustable optical delay device, so that the horizontal polarized light and the vertical polarized light arrive at the silicon waveguide structure simultaneously to generate entangled photon pairs in the four-wave mixing process. In contrast, when the horizontally polarized light is transmitted in the counterclockwise direction, the horizontally polarized light is input to one port of the sagnac loop from the transmission lower port of the polarization beam splitter and the horizontally polarized light is delayed by the adjustable optical delay, while the vertically polarized light is transmitted in the clockwise direction, and is input to the other port of the sagnac loop from the transmission upper port of the polarization beam splitter.
Specifically, the silicon waveguide structure is composed of a silicon nanowire waveguide and two grating couplers, the structure is as shown in fig. 5, the two grating couplers are respectively connected with two ends of the silicon nanowire waveguide in a coupling way, and the included angle between each grating coupler and a polarization maintaining optical fiber connected with the grating coupler is 10 degrees so as to improve the coupling efficiency.
The horizontal polarized light and the vertical polarized light reach the grating couplers at two ends of the silicon nanowire waveguide at the same time, and are respectively coupled into the silicon nanowire waveguide through the grating couplers. The grating coupler has strong selective action on TE polarized light, only TE polarized light can be directly coupled into the silicon waveguide wire, the TM polarized light is converted into TE polarized light under the action of the grating coupler, namely, the polarized light modes coupled to the silicon nanowire waveguide through the grating coupler are TE modes, the TE modes cannot be subjected to mode conversion in the transmission process, and entangled photon pairs are generated in the four-wave mixing process in the silicon nanowire waveguide, namely, signal photons and idler photons of the TE modes are generated.
In the two-photon generation module, the parametric photon state generated by the horizontally polarized light is denoted as |V S V i >The parametric photon state generated by the vertically polarized light is recorded as |H S H i >Where s represents a signal photon, i represents an idler photon, and the quantum state of entangled two photons at the output end of the two-photon generation module is expressed as:
based on the principle that linearly polarized light is transmitted on a polarization beam splitter through a polarization maintaining fiber, the entangled photon pair output from the two-photon generation module rotates 45 degrees relative to the slow axis of the polarization maintaining fiber connected with the port of the polarization beam splitter 1, so that the output entangled photon pair has components of a fast axis and a slow axis. The Faraday rotator corrects the polarization direction of the entangled photon pair input by the third port of the optical circulator by 45 degrees, and returns the polarization direction of the entangled photon pair to the slow axis to return to stable polarized light. In the subsequent process, the polarization direction and the quantum state of the entangled photon pair are not changed any more.
The silicon nanowire waveguide has a wider photon pair radiation spectrum, so that the generated photon pair also has a wider spectrum width, the quantum key distribution with high capacity density is realized, the grating couplers are connected to the two ends of the silicon nanowire waveguide, the coupling efficiency is improved, incident polarized light is converted into TE polarized modes after passing through the grating couplers and is coupled into the silicon nanowire waveguide, the polarized mode conversion can not occur any more in a stable state in the subsequent transmission process, and the efficiency and the performance of entanglement sources are improved.
In another embodiment of the present utility model, the broadband entanglement source further includes a beam splitter and a photo detector, the structure is shown in fig. 6, an input end of the beam splitter is connected with an output end of the polarization controller, two output ends of the beam splitter are respectively connected with the photo detector and a first port of the optical circulator, and the photo detector is used for detecting light intensity of linearly polarized light generated by the polarization controller and monitoring stability of the pump light source to output pump laser.
Based on fig. 6, another embodiment of the present utility model is provided, as shown in fig. 7, where the broadband entanglement source further includes a second filter, and the second filter is disposed on the transmission path of the faraday rotator and the wavelength division multiplexer, for filtering out the residual pump laser. Preferably, the second filter is a fiber optic filter.
It is noted that relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that an article or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such article or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in an article or apparatus that comprises such element.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present utility model. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the utility model. Thus, the present utility model is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (8)
1. The broadband entanglement source is characterized by comprising a laser source module, a polarization controller, an optical circulator, a polarization beam splitter, a two-photon generation module, a Faraday rotator and a wavelength division multiplexer;
the laser source module is connected with the polarization controller and used for generating, preprocessing and outputting pumping laser; the polarization controller generates linearly polarized light based on the pump laser; the optical circulator has a first port, a second port and a third port, the first port is connected with the polarization controller, the second port is connected with the polarization beam splitter, the third port is connected with the Faraday rotator, and the circulator is used for inputting linearly polarized light input by the first port to the polarization beam splitter through the second port and inputting photon pairs input by the second port to the Faraday rotator through the third port; the polarization beam splitter is used for dividing input linearly polarized light into orthogonal horizontally polarized light and vertical polarized light;
the two-photon generation module comprises a Sagnac ring, a silicon waveguide structure and an adjustable optical delay device, wherein the silicon waveguide structure and the adjustable optical delay device are arranged on the Sagnac ring, two ports of the Sagnac ring are respectively connected with two ports of the polarization beam splitter, horizontal polarized light and vertical polarized light are respectively transmitted in opposite directions along the Sagnac ring, the adjustable optical delay device is used for delaying the horizontal polarized light or the vertical polarized light to enable the horizontal polarized light and the vertical polarized light to simultaneously reach the silicon waveguide structure, and the silicon waveguide structure is used for simultaneously receiving the horizontal polarized light and the vertical polarized light which are transmitted in opposite directions and generating entangled photon pairs in a four-wave mixing process; the entangled photon pair is input to the Faraday rotator from a third port of the optical circulator through the polarization beam splitter and a second port of the optical circulator, and the Faraday rotator is connected with the wavelength division multiplexer and is used for rotationally rectifying the polarization direction of the entangled photon pair; the wavelength division multiplexer is used for separating and outputting the signal photons and idler photons in the entangled photon pair;
the polarization controller, the optical circulator, the polarization beam splitter, the two-photon generation module, the Faraday rotator and the wavelength division multiplexer are connected by adopting polarization maintaining optical fibers.
2. The broadband entanglement source according to claim 1, wherein said laser source module comprises a pump light source, a tunable attenuator and a first filter connected in sequence; the pump light source is used for generating pump laser, the adjustable attenuator attenuates the intensity of the pump laser, and the first filter filters the attenuated pump laser.
3. A broadband entanglement source according to claim 1, wherein said silicon waveguide structure is composed of a silicon nanowire waveguide and two grating couplers, said two grating couplers being respectively coupled to two ends of said silicon nanowire waveguide, said grating couplers having an angle of 10 ° with respect to a polarization maintaining fiber to which they are coupled.
4. A broadband entanglement source according to claim 2, wherein said adjustable attenuator is an adjustable optical fiber attenuator.
5. A broadband entanglement source according to claim 2, wherein said pump light source is a laser diode, a pulsed laser or a continuous light laser.
6. A broadband entanglement source according to any of claims 1-5, further comprising a beam splitter and a photo detector, wherein an input of said beam splitter is connected to an output of said polarization controller, and wherein two outputs of said beam splitter are connected to said photo detector and to a first port of said light circulator, respectively, said photo detector being adapted to detect the intensity of linearly polarized light generated by said polarization controller.
7. A broadband entanglement source according to any of claims 1-5, further comprising a second filter arranged in the transmission path of said faraday rotator and said wavelength division multiplexer for filtering out pump laser light.
8. The broadband entanglement source according to claim 7, wherein said second filter is a fiber optic filter.
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