Integrated polarization encoder

Abstract

The invention provides an integrated polarization encoder, and relates to the technical field of quantum information, and the integrated polarization encoder comprises an optical integrated chip and a micro-optical device. The optical integrated chip comprises an optical switch, four on-chip waveguides and two two-dimensional gratings; each two-dimensional grating comprises two input ends; the four on-chip waveguides are respectively connected with the input ends of the two two-dimensional gratings; the optical switch controls an initial light beam to enter the corresponding input ends of the two two-dimensional gratings through one of the four on-chip waveguides according to control signals at four different moments, and four incident light beams at different moments are obtained respectively; the two two-dimensional gratings diffract four incident light beams at different moments respectively to obtain four quantum states at different moments respectively; the micro-optical device obtains two pairs of quantum states with a polarization included angle of 45 degrees and an orthogonal polarization state based on the quantum states at different moments, so as to meet the coding requirements of four quantum states of the quantum key distribution system.

Description

Technical Field

[0001] The present disclosure relates to the field of quantum information technology, and more particularly to an integrated polarization encoder. Background Art

[0002] Quantum secure communication can generate completely consistent unconditional security keys between the two communicating parties. This key encrypts information in a "one-time one-pass" manner to ensure the security of information transmission. The communication system based on quantum secure communication is mainly a quantum key distribution system, which includes a sender and a receiver. The sender mainly uses a sampling encoder to achieve quantum state encoding and transmission, while the receiver uses a decoder to decode and detect the quantum state.

[0003] Polarization encoding scheme is the mainstream scheme in quantum key distribution, which is used to prepare the target quantum state required by the quantum key distribution system. The on-chip polarization encoder in the silicon substrate in the related technology has the technical problem of poor power consistency caused by phase-related loss. In addition, when synthesizing polarization states, since pulse driving voltage is required for driving, factors such as amplitude jitter of high-speed pulse voltage and pulse time domain jitter will cause fluctuations in the polarization angle when preparing different quantum states, increase the error rate of the quantum key distribution system, and further affect the code rate of the quantum key distribution system. Summary of the invention

[0004] In view of this, the present disclosure provides an integrated polarization encoder capable of preparing a target quantum state based on an optical chip and discrete optical devices.

[0005] The present disclosure provides an integrated polarization encoder, comprising an optical integrated chip and a micro-optical device; the optical integrated chip comprises an optical switch, four on-chip waveguides and two two-dimensional gratings; each two-dimensional grating comprises two input ends; the four on-chip waveguides are respectively connected to the input ends of the two two-dimensional gratings; the optical switch is adapted to control an initial light beam to enter the corresponding input ends of the two two-dimensional gratings via one of the four on-chip waveguides according to control signals at four different moments, so as to obtain four incident light beams at different moments respectively; the two two-dimensional gratings are adapted to diffract the four incident light beams at different moments respectively, so as to obtain four quantum states at different moments respectively; wherein each of the two-dimensional gratings can obtain a pair of quantum states with orthogonal polarization states; the four quantum states at different moments include two pairs of quantum states with orthogonal polarization states; the micro-optical device is adapted to obtain two pairs of quantum states with orthogonal polarization states with a polarization angle of 45° based on the quantum states at different moments, so as to meet the encoding requirements of the four quantum states of a quantum key distribution system.

[0006] According to an embodiment of the present disclosure, the transmission distance of each on-chip waveguide transmitting the initial light beam to the corresponding input end is the same.

[0007] According to an embodiment of the present disclosure, when the output polarization angles of the above-mentioned two two-dimensional gratings are consistent, the above-mentioned integrated polarization encoder also includes two polarization-maintaining optical fibers; the above-mentioned two polarization-maintaining optical fibers are respectively connected to the top of the above-mentioned at least two two-dimensional gratings, and are suitable for coupling the above-mentioned four quantum states at different times to the above-mentioned micro-optical device.

[0008] According to an embodiment of the present disclosure, the above-mentioned micro-optical device includes a 45-degree rotating beam combiner; the above-mentioned 45-degree rotating beam combiner is suitable for adjusting the polarization angle of one pair of quantum states with orthogonal polarization states among the above-mentioned four quantum states at different times, so as to obtain the above-mentioned two pairs of quantum states with orthogonal polarization states with a polarization angle of 45°.

[0009] According to an embodiment of the present disclosure, when the output polarization angle of the above-mentioned two two-dimensional gratings is 45 degrees, the above-mentioned micro-optical device includes a beam-combining crystal; the above-mentioned two two-dimensional gratings are suitable for respectively diffracting the above-mentioned four incident light beams at different times to obtain the above-mentioned two pairs of quantum states with orthogonal polarization states with a polarization angle of 45°; the above-mentioned beam-combining crystal is arranged above the above-mentioned at least two two-dimensional gratings, and is suitable for directly outputting the above-mentioned two pairs of quantum states with orthogonal polarization states with a polarization angle of 45°.

[0010] According to an embodiment of the present disclosure, the optical switch comprises an on-chip 1×4 optical switch.

[0011] According to an embodiment of the present disclosure, the optical switch includes an interference type optical switch.

[0012] According to an embodiment of the present disclosure, the optical switch includes an electro-absorption optical switch.

[0013] According to an embodiment of the present disclosure, the optical integrated chip further includes a one-dimensional grating, and the one-dimensional grating is suitable for coupling an off-chip light source into the initial light beam.

[0014] According to an embodiment of the present disclosure, the optical integrated chip further includes an on-chip light source, and the on-chip light source is suitable for generating the initial light beam.

[0015] According to the embodiments of the present disclosure, a pair of quantum states with orthogonal polarization states can be obtained based on a two-dimensional grating, and two pairs of quantum states with orthogonal polarization states can be obtained by controlling the conduction of four on-chip waveguides through optical switches. Four quantum states can be output at different times through micro-optical devices. By combining optical integrated chips and micro-optical devices, a hybrid integrated miniaturized polarization encoder is realized, and quantum states with stable polarization angles can be output after packaging and curing. The integrated polarization encoder of the embodiment of the present disclosure does not adjust the phase of each optical path separately, thereby avoiding the technical problem of inconsistent power of each quantum state caused by phase-related loss; the integrated polarization encoder of the embodiment of the present disclosure does not need to combine multiple polarization states after phase adjustment, does not need driving pulse voltage, etc., avoids the fluctuation of polarization angle caused by factors such as amplitude jitter and pulse time domain jitter, reduces the operation error rate of the quantum key distribution system, and improves the coding rate of the quantum key distribution system. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings.

[0017] Figure 1 A polarization encoder chip on a silicon substrate in a related example is schematically shown.

[0018] Figure 2 The optical chip in the related example in which four quantum states are prepared by pre-biasing is schematically shown.

[0019] Figure 3 An on-chip polarization encoder in a related example is schematically shown.

[0020] Figure 4 A schematic diagram of an integrated polarization encoder according to an embodiment of the present disclosure is schematically shown.

[0021] Figure 5 A schematic diagram of an integrated polarization encoder based on an on-chip 1×4 optical switch according to an embodiment of the present disclosure is schematically shown.

[0022] Figure 6 A schematic diagram of an integrated polarization encoder based on an interferometric optical switch according to an embodiment of the present disclosure is schematically shown.

[0023] Figure 7 A schematic diagram of an integrated polarization encoder based on an electro-absorption optical switch according to an embodiment of the present disclosure is schematically shown.

[0024] Figure 8 A schematic diagram of an integrated polarization encoder based on a beam-combining crystal according to an embodiment of the present disclosure is schematically shown. DETAILED DESCRIPTION

[0025] In order to make the objectives, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0026] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0027] All terms used herein, including technical and scientific terms, have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification, and should not be interpreted in an idealized or overly rigid manner.

[0028] When using expressions such as "at least one of A, B, and C, etc.", it should generally be interpreted as the meaning of the expression generally understood by those skilled in the art. For example, "a system having at least one of A, B, and C" should include but not be limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc. When using expressions such as "at least one of A, B, or C, etc.", it should generally be interpreted as the meaning of the expression generally understood by those skilled in the art. For example, "a system having at least one of A, B, or C" should include but not be limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.

[0029] It should also be noted that the directional terms mentioned in the embodiments, such as "upper", "lower", "front", "back", "left", "right", etc., are only reference directions of the drawings and are not intended to limit the scope of protection of the present disclosure. Throughout the drawings, the same elements are represented by the same or similar reference numerals. Conventional structures or configurations will be omitted when they may cause confusion in the understanding of the present disclosure.

[0030] Polarization-encoded optical chips prepare quantum states through the principle of phase modulation. For example, quantum states are prepared by cascading the on-chip Mach-Zehnder interferometer of the previous stage and the on-chip polarization beam combiner of the next stage. The on-chip Mach-Zehnder interferometer quickly adjusts the relative phase difference between the upper arm and the lower arm based on the plasma dispersion effect to adjust the light intensity distribution between the upper arm and the lower arm of the on-chip polarization beam combiner. When transmitting only from the upper arm of the on-chip Mach-Zehnder interferometer, or transmitting only from the lower arm of the on-chip Mach-Zehnder interferometer, or balancing the power of the upper arm and the lower arm of the on-chip Mach-Zehnder interferometer, the relative phase difference between the upper arm and the lower arm of the on-chip polarization beam combiner is controlled to prepare four quantum states.

[0031] The preparation of quantum states on silicon-based chips is mainly achieved by phase modulating two reference lights to achieve the synthesis of different polarization states. Since silicon-based phase modulation is based on the carrier dispersion effect, different modulation voltages need to be loaded when modulating different phases, resulting in different carrier absorption, that is, phase-related losses. In other words, when modulating different phases to prepare various polarization states, there are differences in the power consistency of each polarization state.

[0032] Figure 1 A polarization encoder chip on a silicon substrate in a related example is schematically shown.

[0033] like Figure 1 As shown, in the related art, the polarization encoder chip on the silicon substrate also integrates functions such as intensity modulation and adjustable light attenuation. The polarization encoder consists of a balanced Mach-Zehnder interferometer and a polarization rotation coupler 19. The Mach-Zehnder interferometer includes a PIN diode 12, a heating tube 13, a PIN diode 14 and a heating tube 15. The Mach-Zehnder interferometer controls the amplitude ratio of the two input ends of the polarization rotation coupler 19. The polarization rotation coupler 19 converts the transverse electric mode (TE mode) of one of the input ends (such as the lower arm) into a transverse magnetic mode (TM mode), and after combining with the TE mode of the other input end (such as the upper arm), the output end outputs the final quantum state (0 degrees, 90 degrees, 45 degrees, -45 degrees). The polarization extinction ratio reaches 30dB, and the maximum power difference of each quantum state is 0.9dB.

[0034] Figure 2 The optical chip in the related example in which four quantum states are prepared by pre-biasing is schematically shown.

[0035] like Figure 2 As shown, in the related art, the intermediate state is prepared by pre-biasing through direct current thermo-optic modulation , four carrier depletion modulators are used to prepare four quantum states ( , , , ), simply shift the phase of each carrier depletion modulator . Therefore, the phase-dependent transmission loss of the four quantum states can be minimized. Two of the four carrier depletion modulators are inside the Mach-Zehnder interferometer, and the other two are outside the Mach-Zehnder interferometer. The two Mach-Zehnder interferometers inside include a first Mach-Zehnder interferometer and a second Mach-Zehnder interferometer. The first Mach-Zehnder interferometer is composed of element 21, element 22, element 23 and element 24; the second Mach-Zehnder interferometer is composed of element 25, element 26, element 27 and element 28. It turns out that the maximum dynamic modulation required is , using this combined modulation method, only modulate to , reducing the dynamic phase modulation voltage, thereby reducing the phase-related loss to a certain extent. However, this problem has not been fundamentally solved in theory, so there is still a difference in the power of the four prepared quantum states.

[0036] Figure 3 An on-chip polarization encoder in a related example is schematically shown.

[0037] like Figure 3 As shown, in the related art, the phase bias of the signal light and the high-speed response of the signal light switch are realized by utilizing the thermo-optical effect and plasma dispersion effect of silicon materials. Four quantum state signal lights are generated by the logical combination between the signal light switch 300 and the phase bias modulator 400, etc.: 45-degree linear polarization signal light, left-handed circular polarization signal light, 135-degree linear polarization signal light and right-handed circular polarization signal light, which just meet the modulation requirements of the quantum key distribution protocol.

[0038] like Figure 3 As shown in the figure, two paths are randomly selected from the light path after the beam splitter is split by a high-speed optical switch, one of which is the transverse electric field TE0 and the other is the transverse magnetic field TM0. According to the different paths chosen by the light path, different phase shifts are experienced, and different relative phase differences are generated when TE0 and TM0 are synthesized, thereby synthesizing different polarization states. This scheme improves the power consistency problem of the four polarization states to a certain extent. However, due to the polarization-related characteristics of the on-chip combiner and the need for at least two pulse voltages, the timing consistency and amplitude consistency of the two pulse voltages are difficult to fully guarantee. In practice, it is still difficult to achieve completely consistent power for different quantum states output.

[0039] In addition to the above-mentioned technical problem of poor power consistency caused by phase-correlated loss, the on-chip polarization encoder in the silicon substrate in the related technology requires a pulse driving voltage to drive the polarization state synthesis. Factors such as the amplitude jitter of the high-speed pulse voltage and the pulse time domain jitter will cause fluctuations in the polarization angle when preparing different quantum states, increase the error rate of the quantum key distribution system, and thus affect the coding rate of the quantum key distribution system.

[0040] The present disclosure provides an integrated polarization encoder, in order to solve at least one of the above technical problems.

[0041] Figure 4 A schematic diagram of an integrated polarization encoder according to an embodiment of the present disclosure is schematically shown.

[0042] like Figure 4 As shown, the integrated polarization encoder includes an optical integrated chip and a micro-optical device. The optical integrated chip includes an optical switch, four on-chip waveguides and two two-dimensional gratings; each two-dimensional grating includes two input ends; and the four on-chip waveguides are respectively connected to the input ends of the two two-dimensional gratings.

[0043] According to an embodiment of the present disclosure, the material of the optical integrated chip may be a silicon optical material or an indium phosphide (InP) material. The micro-optical device may be a combination of discrete optical devices or a customized device.

[0044] According to an embodiment of the present disclosure, the optical switch is adapted to control the initial light beam to enter the corresponding input end of the two two-dimensional gratings through one of the four on-chip waveguides according to the control signals at four different times, respectively, to obtain four incident light beams at different times. The two two-dimensional gratings are adapted to diffract the four incident light beams at different times, respectively, to obtain four quantum states at different times. The micro-optical device is adapted to obtain two pairs of quantum states with orthogonal polarization states with a polarization angle of 45° based on the quantum states at different times, respectively, to meet the encoding requirements of the four quantum states of the quantum key distribution system.

[0045] According to the embodiments of the present disclosure, each two-dimensional grating can obtain a pair of quantum states with orthogonal polarization states. The four quantum states at different times include two pairs of quantum states with orthogonal polarization states.

[0046] According to an embodiment of the present disclosure, at least four control signals are obtained respectively according to at least four random numbers of a quantum key distribution system. In the quantum key distribution system, a sender and a receiver transmit quantum bits through a quantum channel. The sender uses a quantum random number generator to select the polarization direction of the quantum state, and the receiver also randomly selects a measurement basis vector for measurement.

[0047] According to an embodiment of the present disclosure, a two-dimensional grating can input a light beam into a grating region for diffraction by designing the process parameters of the grating region to obtain a polarization state with a fixed polarization angle. Polarization states with different fixed polarization angles can be obtained by entering the grating region from different angles. In one example, two incident light beams are separately received by a two-dimensional grating with preset process parameters to enter the grating region at orthogonal angles, and a pair of quantum states with orthogonal polarization states are obtained.

[0048] According to the embodiments of the present disclosure, a pair of quantum states with orthogonal polarization states can be obtained based on a two-dimensional grating, and two pairs of quantum states with orthogonal polarization states can be obtained by controlling the conduction of four on-chip waveguides through optical switches. Four quantum states can be output at different times through micro-optical devices. By combining optical integrated chips and micro-optical devices, a hybrid integrated miniaturized polarization encoder is realized, and quantum states with stable polarization angles can be output after packaging and curing. The integrated polarization encoder of the embodiment of the present disclosure does not adjust the phase of each optical path separately, thereby avoiding the technical problem of inconsistent power of each quantum state caused by phase-related loss; the integrated polarization encoder of the embodiment of the present disclosure does not need to combine multiple polarization states after phase adjustment, does not need driving pulse voltage, etc., avoids the fluctuation of polarization angle caused by factors such as amplitude jitter and pulse time domain jitter, reduces the operation error rate of the quantum key distribution system, and improves the coding rate of the quantum key distribution system.

[0049] According to an embodiment of the present disclosure, the transmission distance of each on-chip waveguide transmitting the initial light beam to the corresponding input end is the same.

[0050] According to the embodiments of the present disclosure, by strictly designing the length of the on-chip waveguide, it is ensured that the transmission distance of each on-chip waveguide when transmitting the initial light beam is the same, so that the amplitudes of the four quantum states at different times can be kept consistent. By fine-tuning the polarization angle of the micro-optical device when coupling the output, after the process is solidified, in principle, the consistency of the amplitudes of the four quantum states at different times can remain unchanged for a long time.

[0051] According to an embodiment of the present disclosure, when the output polarization angles of the two two-dimensional gratings are consistent, the integrated polarization encoder further includes two polarization-maintaining fibers. The two polarization-maintaining fibers are respectively connected to the top of at least two two-dimensional gratings, and are suitable for coupling the four quantum states at different times to the micro-optical device.

[0052] In one example, the micro-optical device includes two input ends and one output end. The two input ends of the micro-optical device are respectively connected to two polarization-maintaining optical fibers, and the output end of the micro-optical device is connected to a single-mode optical fiber.

[0053] According to an embodiment of the present disclosure, the micro-optical device may be a 45-degree rotating beam combiner. The 45-degree rotating beam combiner is suitable for adjusting the polarization angle of one pair of quantum states with orthogonal polarization states among four quantum states at different times, so as to obtain two pairs of quantum states with orthogonal polarization states with a polarization angle of 45°.

[0054] According to an embodiment of the present disclosure, the 45-degree rotating beam combiner can be a 45-degree rotating beam combining crystal. The two pairs of quantum states with orthogonal polarization states with a polarization angle of 45 degrees outputted can be a quantum state with a polarization angle of 0 degrees, a quantum state with a polarization angle of 45 degrees, a quantum state with a polarization angle of 90 degrees, and a quantum state with a polarization angle of 135 degrees, so as to meet the requirements of the quantum key distribution protocol BB84.

[0055] According to an embodiment of the present disclosure, when the output polarization angle between two two-dimensional gratings is 45 degrees, the micro-optical device may be a beam-combining crystal.

[0056] According to an embodiment of the present disclosure, two two-dimensional gratings are suitable for diffracting four incident light beams at different times respectively, and obtaining two pairs of quantum states with orthogonal polarization states with a polarization angle of 45°; the beam-combining crystal is arranged above at least two two-dimensional gratings, and is suitable for directly outputting two pairs of quantum states with orthogonal polarization states with a polarization angle of 45°.

[0057] According to the embodiments of the present disclosure, by using a customized beam-combining crystal and designing the position angle between two two-dimensional gratings on the integrated chip, the relative angle requirements of the two pairs of quantum states with orthogonal polarization states are already met on the optical integrated chip before the two pairs of quantum states with orthogonal polarization states are combined. The customized beam-combining crystal is directly integrated on the optical integrated chip through hybrid integration on the chip, and there is no need for the rotation function like the off-chip beam-combining device, which simplifies the difficulty of coupling output.

[0058] According to an embodiment of the present disclosure, a beam combining crystal includes a plurality of combined reflectors, a spherical lens or a self-focusing lens, and a fiber coupler. The processing difficulty of the plurality of combined reflectors is relatively low, and the manufacturing cost is relatively low. The spherical lens or the self-focusing lens can constitute a passive device with a small volume and a compact structure, which is easy to integrate and install. The fiber coupler can realize efficient coupling of light beams and has good directivity. The passive device beam combining crystal can stably output a quantum state with a specific polarization angle.

[0059] According to the embodiments of the present disclosure, the polarization angle between the four quantum states can be guaranteed by the design and processing accuracy of the two-dimensional grating, as well as the intrinsic characteristics of passive devices such as a rotating beam combiner or a beam combining crystal, so that after the process is solidified, in principle, the polarization angle between the four quantum states can remain unchanged for a long time, thereby reducing the error rate of the quantum key distribution system and improving the working stability.

[0060] According to an embodiment of the present disclosure, the optical integrated chip further includes a one-dimensional grating, which is suitable for coupling an off-chip light source into an initial light beam.

[0061] According to an embodiment of the present disclosure, the optical integrated chip further includes an on-chip light source, which is suitable for generating an initial light beam.

[0062] According to an embodiment of the present disclosure, the optical switch may be an on-chip 1×4 optical switch.

[0063] According to an embodiment of the present disclosure, the on-chip 1×4 optical switch may be a 1×4 silicon-based high-speed optical switch having one input port and four output ports, capable of switching optical signals from a single input port to any output port at high speed and precision.

[0064] Figure 5 A schematic diagram of an integrated polarization encoder based on an on-chip 1×4 optical switch according to an embodiment of the present disclosure is schematically shown.

[0065] like Figure 5 As shown, in one example, the optical integrated chip includes a 1D grating coupler, a 1×4 high-speed optical switch, four on-chip waveguides and two 2D grating couplers. The 1×4 high-speed optical switch is an on-chip 1×4 high-speed optical switch. The off-chip laser light source is coupled into an initial light beam through the 1D grating coupler. The 1×4 high-speed optical switch randomly switches one of the on-chip waveguides ①, ②, ③ and ④ according to the encoding requirements of the quantum key distribution system, and inputs the initial light beam into the corresponding input end of the 2D grating coupler to achieve the encoding of different target quantum states. In one example, the on-chip waveguide ① and the on-chip waveguide ② are respectively connected to the two input ends of a 2D grating coupler, and the coupled output quantum states with orthogonal polarization states can be used as a basis vector of polarization encoding of the quantum key distribution protocol. The on-chip waveguide ③ and the on-chip waveguide ④ are respectively connected to the input ends of two orthogonal polarization directions of another 2D grating coupler, and the coupled output quantum state can be used as another basis vector of polarization encoding of the quantum key distribution protocol. The orthogonal characteristics of the two polarization states in each basis vector are determined and guaranteed by the structure of the designed 2D grating coupler and will not be affected by external factors such as the debugging voltage.

[0066] like Figure 5 As shown, in one example, the two 2D grating couplers can be designed with the same structure, and the position angles on the optical integrated chip are designed so that the transmission distances of the four on-chip waveguides are consistent, and the polarization directions of the above two basis vectors (i.e., two pairs of quantum states with orthogonal polarization states) are consistent. The output ports of the two 2D grating couplers are respectively coupled with polarization-maintaining pigtails, and the fast and slow axes of the polarization-maintaining pigtails are respectively consistent with the polarization directions of the two 2D grating couplers.

[0067] like Figure 5 As shown, in one example, the micro-optical device can be an off-chip 45-degree rotating beam combining crystal. After the polarization-maintaining pigtails that couple the output of the two basis vectors are polarized by the 45-degree rotating beam combining crystal, the four polarization quantum states of H, V, P, and N are finally output by the single-mode optical fiber. represents the H polarization quantum state, represents the V polarization quantum state, represents the P polarization quantum state, represents the N polarization quantum state.

[0068] According to an embodiment of the present disclosure, the optical switch may be an interference type optical switch.

[0069] According to an embodiment of the present disclosure, the interference optical switch may be a Mach-Zehnder interferometer structure. A Mach-Zehnder interferometer made based on the plasma dispersion effect of silicon material is used as a high-speed optical switch, and a half-wave voltage is loaded on the two arms of the Mach-Zehnder interferometer to control the Mach-Zehnder interferometer to output from the upper port or the lower port, thereby realizing the gating or disconnection of the waveguide on the chip.

[0070] Figure 6 A schematic diagram of an integrated polarization encoder based on an interferometric optical switch according to an embodiment of the present disclosure is schematically shown.

[0071] like Figure 6 As shown, in one example, the interference type optical switch can be an interferometer high-speed optical switch (PN), and the interferometer high-speed optical switch (PN) includes a Mach-Zehnder interferometer. The optical integrated chip includes a 1D grating coupler, an interferometer high-speed optical switch (PN), four on-chip waveguides and two 2D grating couplers. When the Mach-Zehnder interferometer in the on-chip waveguide is not loaded with voltage, light is output from the lower port and light is not output from the upper port, that is, the on-chip waveguide is in a disconnected state. According to the encoding requirements of the quantum key distribution system, voltage is randomly loaded on one of the four Mach-Zehnder interferometers, so that it outputs the incident light beam from the upper port and outputs the quantum state through the 2D grating coupler. As shown in FIG. Figure 6 As shown, in one example, two 2D grating couplers can be designed with the same structure, and the position angle on the optical integrated chip is designed so that the transmission distances of the four on-chip waveguides are consistent, and the polarization directions of the two pairs of quantum states with orthogonal polarization states are consistent. Figure 6 As shown, in one example, the micro-optical device can be an off-chip 45-degree rotating beam combining crystal. After the polarization-maintaining pigtails that couple and output two pairs of quantum states are polarized and combined through the 45-degree rotating beam combining crystal, the final four polarization quantum states of H, V, P, and N are output by the single-mode optical fiber. represents the H polarization quantum state, represents the V polarization quantum state, represents the P polarization quantum state, Represents an N - polarized quantum state.

[0072] According to an embodiment of the present disclosure, the optical switch can be an electro - absorption optical switch.

[0073] According to an embodiment of the present disclosure, the electro - absorption optical switch can adjust the absorption characteristics of the material by changing the applied electric field, thereby realizing the switching function of the optical signal.

[0074] Figure 7 Schematically shows a schematic diagram of an integrated polarization encoder based on an electro - absorption optical switch according to an embodiment of the present disclosure.

[0075] As Figure 7 shown, in one example, an optical integrated chip based on indium phosphide (InP) material includes an on - chip light source, an electro - absorption optical switch (EA), four on - chip waveguides, and two 2D grating couplers. When the electro - absorption optical switch (EA) in the on - chip waveguide is under a loaded voltage, it is in an absorption state, and the on - chip waveguide is in a closed state. According to the coding requirements of the quantum key distribution system, voltages are randomly loaded on three of the four electro - absorption optical switches (EA), so that the three on - chip waveguides are closed, and the electro - absorption optical switch (EA) of the on - chip waveguide to be output is not loaded with voltage, thereby realizing the output of this on - chip waveguide and outputting the quantum state through the 2D grating coupler. As Figure 7 shown, in one example, the two 2D grating couplers can have the same structural design, and the included angle of the positions designed on the optical integrated chip is such that the transmission distances of the four on - chip waveguides are the same, and also such that the polarization directions of two pairs of quantum states with orthogonal polarization states are the same. As Figure 7 shown, in one example, the micro - optical device can be an off - chip 45 - degree rotation beam - combining crystal. After the polarization - maintaining pigtails that couple and output two pairs of quantum states achieve polarization beam - combining through the 45 - degree rotation beam - combining crystal, the final four polarization quantum states of H, V, P, and N are output by a single - mode fiber, Represents an H - polarized quantum state, Represents a V - polarized quantum state, Represents a P - polarized quantum state, Represents an N - polarized quantum state.

[0076] Figure 8 Schematically shows a schematic diagram of an integrated polarization encoder based on a beam - combining crystal according to an embodiment of the present disclosure.

[0077] As Figure 8As shown in the figure, in one example, an optical integrated chip based on indium phosphide (InP) material includes an on-chip light source, an electro-absorption optical switch (EA), four on-chip waveguides, and two 2D grating couplers. The micro-optical device can be a customized beam combining crystal. By customizing discrete optical devices such as micro-optical beam combining crystals, the off-chip 45-degree rotating beam combining device is removed and hybrid integration is performed directly on the chip. Figure 8 As shown, in one example, when designing an on-chip waveguide on an optical integrated chip, the polarization direction of one of the 2D grating couplers is rotated 45 degrees relative to the other 2D grating coupler, so that before the two pairs of quantum states with orthogonal polarization states are combined, the relative angle between the two pairs of basis vectors on the optical integrated chip has met the requirement of 45 degrees.

[0078] like Figure 8 As shown, a customized beam-combining crystal (BS) is integrated on an optical integrated chip directly through hybrid integration.

[0079] In one example, a customized beam combining crystal (BS) may include several combined reflectors, C-lens (spherical lens) or G-lens (self-focusing lens), fiber couplers, etc. The combined reflector mainly changes the direction of the light path from perpendicular to the paper plane to parallel to the paper plane and performs beam combining output. The C-lens (spherical lens) or G-lens (self-focusing lens) can couple at least two pairs of target quantum states after beam combining into the optical fiber, and the final four polarization quantum states of H, V, P, and N are output by the single-mode optical fiber. represents the H polarization quantum state, represents the V polarization quantum state, represents the P polarization quantum state, represents the N polarization quantum state.

[0080] The method disclosed herein includes but is not limited to four signals and four quantum states.

[0081] Advantages of materials and processes of integrated optical chips: for example, silicon photonic materials have small device size, high integration, and compatibility with CMOS processes; for example, indium phosphide (InP) materials are easy to integrate light sources and have good high-speed modulation characteristics. The integrated polarization encoder of the disclosed embodiment is based on the advantages of materials and processes of integrated optics, combined with the advantages of micro-optical discrete optical devices, such as low loss, good polarization-related and wavelength-related characteristics, and combines integrated optical chips and micro-optical devices, or integrates them in a hybrid integration manner, to achieve a miniaturized polarization encoder. While achieving high-speed encoding, the polarization-related loss of the prepared quantum state can theoretically be completely eliminated, and the polarization angle can be kept stable for a long time, and is not affected by factors such as fluctuations in the driving pulse voltage.

[0082] The embodiments of the present disclosure are described above. However, these embodiments are only for illustrative purposes and are not intended to limit the scope of the present disclosure. Although the embodiments are described above, this does not mean that the measures in the various embodiments cannot be used in combination to advantage. Without departing from the scope of the present disclosure, those skilled in the art may make a variety of substitutions and modifications, which should all fall within the scope of the present disclosure.

Claims

1. An integrated polarization encoder, characterized in that: It comprises an optical integrated chip and a micro-optical device; the optical integrated chip comprises an optical switch, four on-chip waveguides and two two-dimensional gratings; each two-dimensional grating comprises two input ends; the four on-chip waveguides are respectively connected to the input ends of the two two-dimensional gratings; The optical switch is adapted to control the initial light beam to enter the corresponding input end of the two two-dimensional gratings through one of the four on-chip waveguides according to the control signals at four different times, so as to obtain four incident light beams at different times; The two two-dimensional gratings are suitable for diffracting the four incident light beams at different times respectively to obtain four quantum states at different times respectively; wherein each of the two-dimensional gratings can obtain a pair of quantum states with orthogonal polarization states; the four quantum states at different times include two pairs of quantum states with orthogonal polarization states; The micro-optical device is suitable for obtaining two pairs of quantum states with orthogonal polarization states with a polarization angle of 45° based on the quantum states at different times, so as to meet the encoding requirements of the four quantum states of the quantum key distribution system.

2. The integrated polarization encoder according to claim 1, characterized in that: The transmission distance of each on-chip waveguide in transmitting the initial light beam to the corresponding input end is the same.

3. The integrated polarization encoder according to claim 1, characterized in that: When the output polarization angles of the two two-dimensional gratings are consistent, the integrated polarization encoder further comprises two polarization-maintaining optical fibers; The two polarization-maintaining optical fibers are respectively connected to the top of the at least two two-dimensional gratings, and are suitable for coupling the four quantum states at different times to the micro-optical device.

4. The integrated polarization encoder according to claim 3, characterized in that: The micro-optical device includes a 45-degree rotating beam combiner; The 45-degree rotating beam combiner is suitable for adjusting the polarization angle of one pair of quantum states with orthogonal polarization states among the four quantum states at different times to obtain the two pairs of quantum states with orthogonal polarization states with a polarization angle of 45°.

5. The integrated polarization encoder according to claim 1, characterized in that: When the output polarization angle of the two two-dimensional gratings is 45 degrees, the micro-optical device includes a beam combining crystal; The two two-dimensional gratings are suitable for diffracting the four incident light beams at different times respectively to obtain the two pairs of quantum states with orthogonal polarization states with a polarization angle of 45°; The beam combining crystal is arranged above the at least two two-dimensional gratings and is suitable for directly outputting the two pairs of quantum states with orthogonal polarization states whose polarization angle is 45°.

6. The integrated polarization encoder according to any one of claims 1 to 5, characterized in that: The optical switch comprises an on-chip 1×4 optical switch.

7. The integrated polarization encoder according to any one of claims 1 to 5, characterized in that: The optical switch includes an interferometric optical switch.

8. The integrated polarization encoder according to any one of claims 1 to 5, characterized in that: The optical switch includes an electro-absorption type optical switch.

9. The integrated polarization encoder according to any one of claims 1 to 5, characterized in that: The optical integrated chip further comprises a one-dimensional grating, which is suitable for coupling an off-chip light source into the initial light beam.

10. The integrated polarization encoder according to any one of claims 1 to 5, characterized in that: The optical integrated chip further comprises an on-chip light source, which is suitable for generating the initial light beam.

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