Integral photon source and detector of entangled photon

Abstract

To provide a system and a method for an integral photon source and a detector of an entangled photon.SOLUTION: A system includes a first waveguide layer including a photon generation waveguide configured so as to provide two photons propagated in an orthogonal mode of a single waveguide. The system also includes a second waveguide layer including a photon adjustment waveguide network. The second waveguide layer is formed on the first waveguide layer. The second waveguide layer has a different refractive index. Further, the system includes a photon vertical coupling waveguide for coupling the photons into the photon adjustment waveguide network. The photon adjustment waveguide network converts the photons such that they are propagated in two different waveguides in the same mode. The photon adjustment waveguide network provides an external device with photos as output, and the photon adjustment waveguide network receives the photons from the external device and provides an interferometer with the photons.SELECTED DRAWING: Figure 3C

Description

Technical Field

[0001] (Cross - reference to Related Applications) This application claims the benefit of U.S. Provisional Application No. 62 / 924,058, filed Oct. 21, 2019, entitled "INTEGRATED PHOTONICS SOURCE AND DETECTOR OF ENTANGLED PHOTONS", which is hereby incorporated by reference in its entirety.

Background Art

[0002] Networks of synchronized atomic clocks are frequently used to distribute accurate time over distances. For example, global navigation satellite systems (GNSS) such as the Global Positioning System (GPS), GLONASS, BeiDou, and Galileo are composed of satellites with synchronized atomic clocks and provide international time distribution. Often, satellites are equipped with hardware to facilitate the synchronization of clocks on separate satellites. Synchronization hardware that enables small, lightweight, and highly accurate timing adjustments makes it possible to synchronize the atomic clocks of small satellites.

Summary of the Invention

[0003] A system and method for an integrated photon source and a detector for entangled photons are provided. In certain embodiments, the system includes a first waveguide layer including a photon generation waveguide configured to provide two photons propagating in two orthogonal modes of a single waveguide. The system also includes a second waveguide layer including a photon conditioning network including waveguides, the second waveguide layer being formed on the first waveguide layer and having different refractive indices. Further, the system includes a photon vertical coupling waveguide that couples the two photons into the photon conditioning waveguide network, the photon conditioning waveguide network including the photon vertical coupling waveguide that converts the two photons to propagate in two different waveguides in the same mode, the photon conditioning waveguide network providing the two photons as an output to an external device, the photon conditioning waveguide network receiving the two photons from the external device and providing the two photons to an interferometer. BRIEF DESCRIPTION OF THE DRAWINGS

[0004] It is to be understood that the drawings depict only some embodiments and are not to be considered limiting, and exemplary embodiments will be described with additional specificity and detail using the accompanying drawings.

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[0014] According to convention, the various features described are not drawn to exact scale but are drawn to emphasize specific features relevant to the exemplary embodiments.

DETAILED DESCRIPTION OF THE INVENTION

[0015] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and which are shown by way of specific exemplary embodiments. However, it should be understood that other embodiments may be utilized and logical, mechanical, and electrical changes may be made.

[0016] Systems and methods are provided herein for entangled photon-based integrated photon sources and detectors. In certain embodiments, hardware is described herein that uses quantum interference of time-entangled photons to enable methods for accurate and reliable synchronization of optical atomic clocks. For example, optical atomic clocks on orbiting satellites may be accurately and reliably synchronized. Distributed radio or optical aperture coherent combinations, including real-time computational interferometry to improve sensitivity to weak signals, improved modalities of signal intelligence based on, and increased covertness due to reducing both signal spillover and time-on-target, may be enabled by the embodiments described herein, which are deployed across a constellation of LEO / MEO satellites.

[0017] Furthermore, the clock synchronization methods described herein may use chip-scale ultra-high flux sources and interferometers for time-energy entangled two photons that reduce size, weight, and power, achieve a high pair generation rate, and achieve a high flux-to-background ratio for entangled photon pairs. Also, for improved size, weight, and power reduction and deployment in small satellite platforms, the devices described herein may be integrated on-chip. Specifically, both the photon source and the interference detector may be integrated on-chip.

[0018] In certain embodiments, entangled photons may be generated by spontaneous parametric down-conversion of pump photons, also known as degenerate difference frequency generation. Typically, the methods for the above photon generation may result in entangled photons having polarizations orthogonal to each other. Typically, free-space optical communication is used to separate and convert entangled photons to the same polarization state for use within the clock synchronization method. Embodiments described herein provide a chip-scale photonic integrated circuit having on-chip waveguide photonics for separating entangled photons and converting the separated photons to the same polarization state.

[0019] In some embodiments, a chip-scale photonic integrated circuit may generate and interfere with time-entangled photons. The chip-scale photonic integrated circuit may utilize the nonlinear properties of periodically poled potassium titanyl phosphate (ppKTP) waveguides or waveguides made from materials similar to ppKTP, such as nitrogen. Combined with the low transmission loss, high confinement, and filtering capabilities of silicon nitride waveguides or other waveguides made from similar materials, optical functionality for generating and interfering photons may be realized on a hybrid optical waveguide platform. A chip-scale approach using a combination of waveguides made from different materials allows for improvements over previous types of light sources based on fiber and free space optical communications.

[0020] In some embodiments, materials with both nonlinear properties and low transmission loss, high confinement, and filtering capabilities can be used to implement similar optical functions for photon generation and interference in optical waveguide platforms based on a single material system such as lithium niobate.

[0021] In certain embodiments, the optical functions for generating and receiving entangled photons are implemented on a single integrated platform, resulting in reduced optical losses, enhanced mode overlap, efficient filtering of photons, increased interferometric contrast, and improved mechanical robustness while reducing size, weight, and power compared to fiber or free-space based systems. Additionally, the embodiments described herein enable more precise time synchronization when used in systems while enabling use on small satellite platforms such as microsats.

[0022] FIG. 1 is a diagram showing a system 100 for a Hong-Ou-Mandel (HOM) interferometer. As used herein, a chip-scale integrated circuit may be used within the HOM interferometer. As used herein, the HOM interferometer is a device that can generate pump photons 101. The system 100 may split the pump photons into two daughter photons 103 (referred to herein separately as photon 103-A and photon 103-B). For example, the pump photons 101 may be generated by a laser source that generates a laser having a wavelength of 405 nm or a laser having another desired wavelength.

[0023] In certain embodiments, the pump photons 101 are split into daughter photons 103 that are directed through an optical structure for recombination. For example, the pump photons 101 are split into daughter photons 103-a and 103-b by the optical structure 105. Each of the daughter photons 103 may have a wavelength that is twice the wavelength of the pump photons 101 (i.e., if the pump photons 101 may have a wavelength of 405 nm, the daughter photons 103 may each have a wavelength of 810 nm). Further, the system 100 may include guiding optics 107 that direct the daughter photons 103 to a beam splitter 110 where the daughter photons 103 are combined, such that quantum superpositions 103-c and 103-d of the daughter photons impinge on a detector 109 for reception. For example, detector 109-a may receive and detect daughter photon 103-a, detector 109-b may receive and detect daughter photon 103-b, or detector 109-a may receive and detect daughter photon 103-b, detector 109-b may receive and detect daughter photon 103-a, or detector 109-a may receive and detect both daughter photons 103-a and 103-b, or detector 109-b may receive and detect both daughter photons 103-a and 103-b in the manner of the HOM interferometer method.

[0024] In some embodiments, when detector 109 receives the associated daughter photon 103, detector 109 may provide a signal to electronic correlator device 111, and electronic correlator device 111 combines the electrical signals of the two detectors 109 for the performance of HOM interferometry. The electronic correlator device 111 quantitatively determines the degree of temporal correlation of the signals generated by the detectors 109. For example, the electronic correlator 111 may indicate that when the daughter photons 103 overlap substantially completely in time, the coincidence rate of the signals provided by the photodetectors 109 may decrease towards zero. This decrease of the coincidence detection rate towards zero is known as the HOM dip shown in the trace graph 113. This dip occurs when the two daughter photons 10 3 are substantially identical in all characteristics. The HOM dip disappears when the photons 103 become particularly distinguishable, including when their flight times between the source region 105 and the beam splitter 110 are equal. In this way, the system 100 is sensitive to the fact that the quality of the flight times of the daughter photons 103 between the source region 105 and the beam splitter 110 is substantially exactly equal.

[0025] FIG. 2 shows different optical paths 201 and 203 on the chip-scale device 200, both of which are capable of generating photons, splitting the photons into daughter photons, providing the daughter photons as outputs (e.g., into free space or an optical fiber), receiving the daughter photons that may have been reflected from a remote mirror or optical system, and providing the received photons to an interferometer for performing HOM interferometry. As shown, FIG. 2 shows a source path 201 and an interferometer path 203. In the source path 201, the incident pump photons are split into daughter photons that can be directed to different remote platforms. In the interferometer path 203, the daughter photons reflected by the remote platform are received and interfered in a method of HOM interferometry.

[0026] In certain embodiments, the chip-scale device 200 utilizes the nonlinear optical effect of degenerate spontaneous parametric down conversion (dSPDC) in which a pump photon 205 splits into two "twin" daughter photons 209 and 211 that are "born" at approximately the same instant (e.g., within less than 100 femtoseconds of each other). This simultaneity is implemented by quantum mechanics and can be utilized to synchronize separated atomic clocks. To synchronize separated atomic clocks (i.e., when different atomic clocks are located on different satellites), the synchronization is achieved by projecting daughter photons 209 and 211 from the chip-scale device 200, reflecting a portion of the photons 209 and 211 from each satellite, and providing them to recombine within a Hong-Ou-Mandel (HOM) interferometer 215, and a pure quantum mechanical interference "dip" in the coincidence rate is observed only when the paths are substantially exactly equal as described above with respect to FIG. 1. The arrival times of some of the entangled photons from each satellite can be compared to a classical channel, enabling the controller to synchronize the clocks with high precision (i.e., potentially with femtosecond accuracy).

[0027] In some embodiments, the chip-scale device 200 is a chip-scale photonic integrated circuit that generates and interferes time-entangled photons. The chip-scale device 200 may include optical functions and components on a hybrid optical waveguide platform that combines the nonlinear properties of a ppKTP waveguide (or other waveguides made from materials with similar properties) with the high confinement and filtering capabilities of a silicon nitride waveguide. This combination enables miniaturization, efficiency, and robustness while increasing the usable flux of the twin photons 209 and 211.

[0028] In some embodiments, the chip-scale device 200 may include optical functions and components on a single optical waveguide material platform having both nonlinear properties and low transmission losses, high confinement, and filtering capabilities such as lithium niobate.

[0029] In certain embodiments, the chip-scale device may generate pump photons 205, and from the pump photons 205 in the source path 201, daughter photons 206a and 206b in the photon generation waveguide may be generated by dSPDC. Each of the twin photons 206a and 206b may occupy a different waveguide mode, either transverse electric (TE) or transverse magnetic (TM). The vertical coupler (VC) region may adiabatically draw in the daughter photons 206a and 206b from the photon generation waveguide and adiabatically draw them into a photon conditioning waveguide patterned on top of the photon generation waveguide. Further, the TM photons and the TE photons may be separated by two diffraction waveguide mode splitters (MS ). Next, the TE photons may pass through a bandpass filter (BPF) to reject background photons, pass through a second MS, and then, together with the emitted photons 211 leave the chip 200. On the other hand, the original TM photons may be converted to the TE mode by a diffraction mode converter (MC) that may reverse the propagation direction of the photons. This (here TE polarized) photon may pass through its own bandpass filter and leave the chip 200 as the emitted photon 209. The various functions implemented on the chip may be implemented by the photon conditioning waveguide (made of silicon nitride or other similar materials in some embodiments), and the waveguide structure is patterned in a film deposited on top of the substrate including the photon generation waveguide.

[0030] In an additional embodiment, in the interferometer path 203, the twin photons 209 and 211 are reflected or sent back from a remote satellite or other remote system, recombined, and become a photonic component waveguide on the chip-scale device 200, and can complete the HOM interferometer 215. (In some implementations, the photons can also have their polarization rotated by 90° by a conventional waveplate). The twin photons 209 and 211 can enter the same waveguide again as previously emitted due to their then-rotated polarization, but they can combine to form an orthogonal waveguide mode (i.e., TM). Next, each photon can interfere with a diffraction mode splitter (MS) that can reverse the propagation direction in the waveguide and send the photons 209 and 211 to a 50 / 50 waveguide coupler. The output port of the interferometer can be directed to a photodetector 212 such as a single-photon avalanche photodetector (SP-APD) where the photons 209 and 211 can be detected. The photodetector 212 The detected signal output of is directed to an electronic correlator 215 that can determine the degree of coincidence of the arrival times of the signals, and thus the HOM interferometer 216 can be completed.

[0031] Figures 3A - 3C show the propagation of two photons generated by a photon generation waveguide that becomes a photon vertical coupling waveguide and passes through a photon adjustment waveguide network. As described above, the photon generation waveguide generates two photons with orthogonal waveguide modes, one propagating in the TM mode and the other in the TE mode. Depending on the mode of the photons, the photons propagate along different paths through the waveguide network that provides two photons propagating in the TE mode outside the chip and receives two photons returning to the chip propagating in the TM mode. Figure 3A shows the path of the photon originally in the TE mode of the photon vertical coupling waveguide 302. Figure 3B shows the path of the photon originally in the TM mode of the photon vertical coupling waveguide 302. Figure 3C shows the path of the photon passing through the photon adjustment waveguide network 304 of the photons received from an external device.

[0032] In a particular embodiment shown in FIG. 3A, photons in the TE mode of the photonic vertical coupling waveguide 302 that transition to the photonic adjustment waveguide network 304 pass through the mode splitter 303 without diffraction. Next, the photons pass through the bandpass filter 305, where not only fluorescence but also stray pump light coupled from the photon generation waveguide 301 is filtered out. Next, the photons pass through the mode splitter 307 without diffraction and are emitted through the output port 321.

[0033] In a particular embodiment shown in FIG. 3B, photons in the TM mode of the photonic vertical coupling waveguide 302 that transition to the photonic adjustment waveguide network 304 are diffracted by the mode splitter 303. When the photons enter the mode converter 311, they are further diffracted by the mode splitter 309. The mode converter 311 diffracts the photons again but converts the photons from the TM mode to the TE mode. At this time, since the photons are in the TE mode, the photons are not diffracted by the mode splitter 309. Next, the photons pass through the bandpass filter 313, where not only fluorescence but also stray pump light coupled from the photon generation waveguide is filtered out. Next, the photons pass through the mode 315 without diffraction and are emitted through the output port 319.

[0034] In an additional embodiment shown in FIG. 3C, two daughter photons emitted from the photon conditioning waveguide network 304 can be sent back from another optical device such that they recombine in waveguides 319 and 321 and become within the photon conditioning network 304 in the TM mode. The two received photons in the TM mode can propagate through the waveguides, each towards mode splitters 315 and 307. Both splitters 315 and 307 diffract the received photons. The photons then output at ports 323 and 325 and interfere with each other via a 50 / 50 coupler 317 before being subsequently detected by photon detectors. In the embodiment described above, the TM mode from the photon vertical coupling waveguide 302 is converted by the photon conditioning waveguide network 304 to the TE mode for transmission from the chip-scale device, but the light received back into this device for subsequent interference detection is in the TM mode. However, in another embodiment, the TE mode from the photon vertical coupling waveguide is converted by the photon conditioning waveguide network 304 to the TM mode for transmission from the chip-scale device, but the light received back into this device for subsequent interference detection is in the TE mode.

[0035] FIG. 4 shows various photonics components within a chip-scale device 400. For example, the chip-scale device 400 includes a photon generation waveguide 401, a photon vertical coupling waveguide 427, and a photon conditioning waveguide network (similar to the photon conditioning waveguide network 304 of FIGS. 3A - 3C), and the photon conditioning waveguide network comprises mode splitters 403, 409, 407, and 415, a mode converter 411, bandpass filters 413 and 405, input / output waveguides 419, 421, 423, and 425, and a 50 / 50 coupler 417. Possible embodiments for the vertical coupler 427, mode splitters 403, 409, 407, and 415, mode converter 411, and bandpass filters are described in more detail below.

[0036] FIG. 5 is a side view showing the operation of the vertical coupler. In order to efficiently couple photons from the photon generation waveguide 501 into the photon vertical coupling waveguide 503, a stacked waveguide is formed. Further, the photon vertical coupling waveguide 503, which is relatively thin compared to the width of the photon generation waveguide 501, has little perturbation in the shape of the weak confinement mode in the photon generation waveguide 501. As described herein, the photon vertical coupling waveguide 503 gradually widens across the entire overlapping portion of the stacked waveguides. For example, the photon vertical coupling waveguide 503 can widen its width from 100 nm to 200 nm over a distance of about 500 microns. The gradually widening width of the photon vertical coupling waveguide 503 adiabatically draws photons from the photon generation waveguide 501 into a much more tightly confined waveguide mode. Further, this transition preserves the polarization mode of the propagating photons with substantially zero-mode crossing coupling (i.e., TE→TE and TM→TM).

[0037] In a further embodiment, there may be a large difference between the refractive indices of the materials used to generate the photon generation waveguide and the materials used to generate the photon vertical coupling waveguide. For example, if KTP is used for the photon generation waveguide, the photon vertical coupling waveguide can be fabricated using a silicon-rich nitride film.

[0038] FIG. 6 is a diagram showing a particular side view of a mode splitter as seen in the chip-scale device 200. Specifically, FIG. 6 shows an isometric view 600 of the mode splitter, a detailed isometric view 610 of a portion of the mode splitter, and a frequency response graph 620 of the coupling of different modes within the mode splitter.

[0039] In a particular embodiment, as shown in the isometric view 600, the mode splitter can include a single input port 603. Through the input port, the mode splitter is within the waveguide Two photons propagating in different orthogonal modes can be received as input 601. For example, one photon may propagate in the TE mode and another photon may propagate in the TM mode. The mode splitter can pass one of the photons received at the input port 603 as the output photon 609 to the output port 607. For example, the mode splitter can directly pass the TE mode photon received at the input port 603 to the output port 607. Further, the mode splitter can diffract one of the propagating photons such that one of the propagating photons is coupled and becomes a backward waveguide and is passed to the output port 613 as output 611. For example, the TM mode can be diffracted by the coupling portion 605 of the mode splitter and passed to the output port 613.

[0040] In some embodiments, as shown in the detailed isometric view 610 of the coupling portion 605 of the mode splitter, the mode splitter may include a chirped grating assisted backward mode coupler to split two orthogonally polarized photons into different paths. As shown, FIG. 610 depicts the waveguide structure and graph 620 shows the result of the calculation of its spectral response. As shown, the coupling portion consists of two closely spaced waveguides 621 and 625. Waveguide 621 is further patterned with a modulating sidewall 623 and thus can create an in-waveguide diffraction grating with a large overlap integral during the TM transition from one waveguide to the other. The effect of the modulation is to couple the TM mode from the forward direction in waveguide 625 to the backward direction in waveguide 621, while the TE mode passes through the mode splitter in the forward direction and remains in waveguide 625. Further, the frequency of the modulating sidewall 623 can vary along the length of the mode splitter to enable the desired frequency response for the mode splitter.

[0041] FIG. 7 is a diagram showing a specific aspect of the mode converter as seen in the chip scale device 200. Specifically, FIG. 7 shows an isometric view 700 of the mode splitter, a detailed isometric view 710 of the conversion portion of the mode splitter, and a frequency response graph 720 of the mode conversion within the mode converter.

[0042] In certain embodiments, as shown in isometric view 700, the mode converter may include a single port 703. Through port 703, the mode converter can receive, as input 701, photons propagating in a specific mode within a waveguide. For example, the photons received through port 703 may propagate in the TM mode. The mode converter may convert the mode from one mode to an orthogonal mode within conversion section 705, and the mode converter converts the photons to an orthogonal propagation mode so as to be output as an output through port 703. For example, if the photons received at port 703 are in the TM mode, the photons output through port 703 may be in the TE mode.

[0043] In some embodiments, as shown in the detailed isometric view 710 of conversion section 705 of the mode converter, in order to make all waveguide paths as similar as possible for two photons, a chip-scale device can use a single waveguide grating structure designed with asymmetric modulation sidewalls 709 and 711 to repel the in-waveguide polarization of TM photons. For example, the modulation of the sidewalls may have different phases such that the cross-section of the waveguide is constant along the length of the modulation. This asymmetric modulation creates a cross-coupling between the forward TM mode and the backward TE mode. As shown in graph 720, within the stop band of the grating, only mode conversion occurs. To control the stop band of the grating, the length of conversion section 705 can vary with the modulation frequencies of modulation sidewalls 709 and 711. For example, the frequency of the modulation sidewalls may decrease or increase along the length of the conversion section of the mode converter.

[0044] FIG. 8 is a diagram showing a particular aspect of a bandpass filter as seen in chip-scale device 200. Specifically, FIG. 8 shows an isometric view 800 of the bandpass filter, a detailed isometric view 810 of the filtering section of the bandpass filter, and a frequency response graph 820 of the filtering of photons by the bandpass filter. of photons by the bandpass filter.

[0045] In certain embodiments, as shown in the isometric view 800, the bandpass filter may include a single port 803. Through port 803, the bandpass filter can receive photons propagating in a specific mode within the waveguide as input 801. For example, the photons received through input port 803 can propagate in the TE mode. The bandpass filter can filter photons having unwanted wavelengths in filter processing unit 805 and provide the filtered photons as output 809 through output port 807.

[0046] In some embodiments, as shown in the detailed isometric view 810 of the filter processing unit 805 of the bandpass filter, a waveguide bandpass filter is implemented to reject any background fluorescence photons that may propagate within the waveguide and to reject any residual pump photons. As shown, the filter is fabricated with two high-reflectivity waveguide gratings 811 and 813 represented by a chirp of the modulation period along the length of the waveguide, in other words, the symmetric modulation of the waveguide grating has a longitudinal variation along the length of the sidewall of the filter. Light just outside the passband is diffracted and returns to the waveguide, while light at the pump wavelength is completely scattered outside the waveguide. In some embodiments, the spectral positions of waveguide gratings 811 and 813 can vary along the length of the filter processing unit 805 of the passband.

[0047] FIG. 9 is a method 900 of generating and interfering with correlated photon pairs as described above using a chip-scale device. Method 900 proceeds to 901 to generate a photon pair within a photon generation waveguide. Further, method 900 proceeds to 903 where the photon pair is combined into a photon vertical coupling waveguide. Further, method 900 proceeds to 905 where one of the photons in the photon pair is converted in a photon conditioning waveguide network such that the photons propagate in the same mode in two different waveguides. In certain embodiments, method 900 proceeds to 907 where the photons are provided to one or more external devices. Further, method 900 proceeds to 909 where the photons are received from one or more external devices. Further, method 900 proceeds to 911 where an interferometric measurement is performed on the received photons. Exemplary embodiments

[0048] Example 1 is a system comprising a photon generation waveguide configured to provide two photons propagating in two orthogonal modes of a single waveguide, and a photon vertical coupling waveguide that couples the two photons into a photon conditioning waveguide network, the photon conditioning waveguide network converting the two photons so that they propagate in two different waveguides in the same mode, the photon conditioning waveguide network providing the two photons as an output, and the photon conditioning waveguide network receiving the two photons as an input and providing the two photons to an interferometer.

[0049] Example 2 includes the system of Example 1, wherein the photon vertical coupling waveguide comprises a first waveguide having two photons provided by a photon generation waveguide therein, and a second waveguide having a second coupling portion proximate to a first coupling portion of the first waveguide, the width of the second waveguide varying along the length of the second coupling portion such that the first photon and the second photon adiabatically transition into separate orthogonal modes of the second waveguide.

[0050] Example 3 includes the system of Example 2, wherein the two photons are coupled at different locations within the second coupling portion based on the respective modes of the two photons to form the second waveguide.

[0051] Example 4 includes the system according to Example 2 or 3, in which, when two photons propagate in the first waveguide, the orthogonal modes of the two photons are maintained by the adiabatic transfer of the two photons to the second waveguide.

[0052] Example 5 includes the system according to any one of Examples 1 to 4, in which the photon adjustment waveguide network includes a plurality of mode splitters, a mode converter, a plurality of bandpass filters, a plurality of transmission ports through which two photons are provided as outputs and received as inputs, and a plurality of interferometer ports.

[0053] Example 6 includes the system according to Example 5, in which a certain mode splitter among the plurality of mode splitters is configured to receive a first photon propagating in a first mode and a second photon propagating in a second mode orthogonal to the first mode, and includes a splitter input port, a first output port, a second output port, a first waveguide coupled to the splitter input port and the first output port, which receives the first photon and the second photon and provides the first photon to the first output port, and a second waveguide coupled to the second output port, in which a wall of the second waveguide adjacent to the first waveguide has a modulated side wall, the second photon is coupled, becomes the second waveguide, and is output through the second output port.

[0054] Example 7 includes the system according to Example 5 or 6, in which the mode converter includes a port configured to receive a photon propagating in a first mode and a waveguide coupled to the port, the waveguide having a first periodically modulated side wall and a second periodically modulated side wall, and a spatial phase of modulation of the first periodically modulated side wall is distorted with respect to a spatial phase of the second periodically modulated side wall, and the first periodically modulated side wall and the second periodically modulated side wall output the photon through port propagation in a mode orthogonal to the first mode.

[0055] Example 8 includes the system according to any one of Examples 5 to 7, in which a certain bandpass filter among a plurality of bandpass filters includes an input port configured to receive photons, an output port, and a first waveguide coupled to the input port and the output port, the first waveguide includes a first sidewall formed as a first waveguide grating and a second sidewall facing the first sidewall and formed as a second waveguide grating, and there is a variation in the longitudinal direction along the lengths of the first sidewall and the second sidewall in the symmetric modulation between the first waveguide grating and the second waveguide grating.

[0056] Example 9 includes the system according to any one of Examples 1 to 8, in which a photon-adjusting waveguide network is formed in a second waveguide layer formed across a first waveguide layer, the first waveguide layer serves as a substrate for the photon-adjusting waveguide network, and the refractive indices of the first waveguide layer and the second waveguide layer are different.

[0057] Example 10 includes a method that includes generating a pair of photons in a photon generation waveguide, combining the pair of photons to form a photon vertical coupling waveguide in which the photon polarization modes are clearly coupled, converting one of the photons in the pair of photons so that both photons propagate in the same mode in different waveguides, providing the photons to one or more external devices, receiving the photons from the one or more external devices, and performing an interferometric measurement on the received photons.

[0058] Example 11 includes the method according to Example 10, in which the width of the vertical coupling waveguide varies along the length of the coupling portion between the vertical coupling waveguide and photon generation so as to adiabatically transfer a pair of photons to different orthogonal modes of the vertical coupling waveguide.

[0059] Example 12 includes the method according to Example 11, in which a pair of photons adiabatically transfers to the vertical coupling waveguide at different locations of the coupling portion based on the respective modes of the photons in the pair of photons.

[0060] Example 13 includes the method according to any one of Examples 10 to 12, which involves splitting a pair of photons such that one of the photons is converted, the first photon in the pair of photons propagates through the first waveguide, and the second photon in the pair of photons propagates through the second waveguide, and converting the first mode of the first photon to be the same as the second mode of the second photon.

[0061] Example 14 includes the method according to Example 13, which involves splitting a pair of photons, receiving the first photon and the second photon at an input port, coupling the second photon to a second output port where the second output port is coupled to the input port, and coupling the first photon to a first output port where the first output port is connected to a coupled waveguide and the coupled waveguide has a modulation sidewall.

[0062] Example 15 includes the method according to Example 13 or 14, which involves converting the first mode of the first photon, receiving the first photon at a certain port, and propagating the first photon through a mode conversion waveguide coupled to the port, where the mode conversion waveguide has a first periodic modulation sidewall and a second periodic modulation sidewall, and the modulation between the first periodic modulation sidewall and the second periodic modulation sidewall has phases different from each other such that the width of the cross-section of the mode conversion waveguide is constant along the length of the mode conversion waveguide where the photon is output through port propagation in a mode orthogonal to the first mode.

[0063] Example 16 includes the method according to any one of Examples 10 to 15, which involves providing photons to one or more external devices, passing the first photon through a first bandpass filter, passing the second photon through a second bandpass filter, passing the first photon and the second photon through a related mode splitter, and transmitting the first photon through a first output port and the second photon through a second output port to one or more external devices.

[0064] Example 17 includes receiving photons from one or more external devices by receiving a first photon through a first output port and a second photon through a second output port, where the reception modes of the received first photon and the received second photon are orthogonal to the transmission modes of the transmitted first photon and the transmitted second photon, and outputting the received first photon and the received second photon through respective interferometer ports, and includes the method described in Example 16.

[0065] Example 18 includes the method described in any of Examples 1 to 17, where a photon generation waveguide is formed in a first waveguide layer, a photon vertical coupling waveguide is formed in a second waveguide layer, and the first waveguide layer and the second waveguide layer have different refractive indices.

[0066] Example 19 includes a first waveguide layer including a photon generation waveguide configured to provide two photons propagating in two orthogonal modes of a single waveguide, and a second waveguide layer including a photon adjustment waveguide network formed on the first waveguide layer and having a refractive index different from that of the first waveguide layer, a photon vertical coupling waveguide for coupling the two photons into the photon adjustment waveguide network, where the photon adjustment waveguide network converts the two photons to propagate in two different waveguides in the same mode, the photon adjustment waveguide network provides the two photons as an output to an external device, the photon adjustment waveguide network receives two photons from the external device, and provides the two photons to an interferometer.

[0067] Example 20 includes a photon adjustment waveguide network including a plurality of mode splitters, a mode converter, a plurality of bandpass filters, and a plurality of transmission ports through which two photons are provided as an output and received as an input, and a plurality of interferometer ports, and includes the system described in Example 19. Example 18 includes the method described in any of Examples 1 to 17, where a photon generation waveguide is formed in a first waveguide layer, a photon vertical coupling waveguide is formed in a second waveguide layer, and the first waveguide layer and the second waveguide layer have different refractive indices.

[0068] Although specific embodiments are illustrated and described in this specification, it will be understood by those skilled in the art that any configuration that can be expected to achieve the same purpose may be used instead of the specific embodiments shown. Therefore, it is clearly intended that the present invention be limited only by the claims and their equivalents.

Claims

1. 1. A system comprising: a photon generating waveguide (301) configured to provide two photons propagating in two orthogonal modes in a single waveguide; a photon vertical coupling waveguide (302) that couples the two photons into a photon conditioning waveguide network, the photon conditioning waveguide network converting the two photons to propagate in two different waveguides with the same mode; the photon conditioning waveguide network providing the two photons as an output; The system, wherein the photon conditioning waveguide network receives the two photons as an input and provides the two photons to an interferometer (215).

2. the photon modulating waveguide network comprising: A plurality of mode splitters; A mode converter; A plurality of band pass filters; a plurality of transmit ports through which the two photons are provided as outputs and received as inputs; The system of claim 1 comprising: a plurality of interferometer ports.

3. 1. A method comprising: generating photon pairs in a photon generating waveguide (301); coupling the photon pairs into a photon vertical coupling waveguide, where the photon polarization modes are distinctly coupled; converting one of the photons of the photon pair such that both photons propagate in the same mode in different waveguides; providing the photons to one or more external devices; receiving the photons from the one or more external devices; and performing an interferometric measurement on the received photons.

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