Integrated photonics mode splitter and converter

Abstract

To provide systems for an integrated photonics mode splitter and a converter.SOLUTION: In certain embodiments, a system includes a substrate having a first index of refraction. Additionally, the system includes a waveguide layer on the substrate, in which the waveguide has a second index of refraction different from the first index of refraction. Also, the waveguide layer includes one or more mode splitters that receive at least one of a first photon in a first mode and a second photon in a second mode through an input port and provide one of the first photon through a first output port and the second photon through a second output port. The waveguide layer also includes a mode converter coupled to the second output of a mode splitter, in which the mode converter receives the second photon through a port and outputs the second photon in the first mode through the port.SELECTED DRAWING: Figure 6

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 incorporated herein by reference.

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 distribute international time. Often, satellites are equipped with hardware to facilitate clock synchronization on separate satellites. Synchronization hardware with reduced size and weight and high - precision timing alignment enables the synchronization of atomic clocks on smaller satellites.

Summary of the Invention

[0003] Systems and embodiments for an integrated optical mode splitter and converter are provided herein. In certain embodiments, the system includes a substrate having a first refractive index. Further, the system includes a waveguide layer on the substrate, the waveguide having a second refractive index different from the first refractive index. Also, the waveguide layer includes one or more mode splitters that receive at least one of a first photon in a first mode and a second photon in a second mode via an input port and supply at least one of the first photon via a first output port and the second photon via a second output port. The waveguide layer also includes a mode converter coupled to a second output of one of the one or more mode splitters, the mode converter receiving a second photon via a port and outputting a second photon in the first mode via a port.

Brief Description of the Drawings

[0004] It should be understood that the drawings illustrate only exemplary embodiments and should not be regarded as limiting the scope. Exemplary embodiments will be described with further particularity and detail using the accompanying drawings.

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[0014] In accordance with a general approach, the various features described are not drawn to scale but are drawn to emphasize specific features relevant to 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 in which are shown by way of illustration specific exemplary embodiments. It should be understood, however, that other embodiments may be utilized and logical, mechanical, and electrical changes may be made.

[0016] Systems and methods for an integrated source and detector of entangled photons are provided herein. 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 can be accurately and reliably synchronized. When deployed throughout a swarm of LEO / MEO satellites, the embodiments described herein can improve signals intelligence modalities based on a coherent combination of distributed radio or optical apertures, including real-time computational interferometry to increase sensitivity to weak signals and active beams to form radar / imaging to improve secrecy by reducing both signal leakage and time-on-target.

[0017] Furthermore, in the clock synchronization scheme described herein, a chip-scale ultra-high optical beam source and interferometer for time-energy entanglement two photons can be used in a state where the size, weight, and power are reduced, the photon pair generation rate is high, and the beam pair background ratio of entangled photon pairs is high. Also, for promoting the reduction of size, weight, and power and improving the deployment ability on a small satellite platform, the devices described herein may be integrated into a chip. In particular, both the photon source and the interference detector may be integrated into a chip.

[0018] In certain embodiments, entangled photons can be generated by spontaneous parametric down-conversion of pump photons, also known as degenerate difference frequency generation. Generally, the above method of photon generation can generate entangled photons having polarizations orthogonal to each other. Generally, free space optical elements are used to separate the entangled photons, convert them to the same polarization state, and use them in the clock synchronization scheme. The embodiments described herein provide a chip-scale optical 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, the chip-scale optical integrated circuit can generate and interfere time-entangled photons. The chip-scale optical integrated circuit realizes optical functions for generating and interfering photons on a hybrid optical waveguide platform that combines the non-linear characteristics of periodically poled potassium titanyl phosphate (ppKTP) waveguides or waveguides made of materials similar to ppKTP, and the low transmission loss performance, high confinement performance, and filtering performance of silicon nitride waveguides or other waveguides made of materials similar to silicon nitride. This can be achieved. The chip-scale approach using a combination of waveguides made of different materials enables improvements over previous types of light sources based on fiber optics and free space optics.

[0020] In some embodiments, materials having non-linear characteristics and both low transmission loss performance, high confinement performance, and filtering performance are used to implement similar optical functions for generating and interfering photons within an optical waveguide platform 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 loss, enhanced mode overlap, efficient filtering of photons, improved contrast of interferometers, and improved mechanical robustness, while reducing size, weight, and power compared to fiber-based or free-space-based systems. Further, the embodiments described herein enable more precise time synchronization while allowing use in smaller satellite platforms such as microsats when used in a system.

[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 capable of generating pump photons 101. System 100 is capable of splitting the pump photons into two daughter photons 103 (referred to herein as photons 103-A and 103-B). For example, the pump photons 101 can be generated by a laser light source that generates laser light having a wavelength of 405 nm or other desired wavelength.

[0023] In certain embodiments, pump photon 101 is split into daughter photons 103 that are guided through an optical structure for recombination. For example, pump photon 101 is split by optical structure 105 into daughter photons 103-a and 103-b. Each of the daughter photons 103 may have a wavelength that is twice the wavelength of the pump photon 101 (i.e., if the pump photon 101 could have a wavelength of 405 nm, each of the daughter photons 103 could have a wavelength of 810 nm). Further, system 100 can include guiding optics 107 that direct daughter photons 103 to beam splitter 110, where the daughter photons 103 are combined, resulting in the quantum superposition of daughter photons 103-c and 103-d impinging on 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 a HOM interferometer.

[0024] In some embodiments, when detector 109 receives the associated daughter photon 103, detector 109 may supply a signal to electronic correlator 111, and electronic correlator 111 combines the electrical signals of the two detectors 109 for performing HOM interference. Electronic correlator 111 quantitatively determines the degree of temporal correlation of the signals generated by detector 109. For example, electronic correlator 111 can show that when the daughter photons 103 overlap substantially completely in time, the coincidence rate of the signals supplied by photodetector 109 may decrease towards zero. This decrease towards zero coincidence rate is known as the HOM dip shown in trace graph 113. This dip occurs when the two daughter photons 103 are substantially identical in all characteristics. The light between light source region 105 and beam splitter 110 Including and in particular with respect to the equality of the flight times of the photons 103, when the photons 103 become distinguishable, the HOM dip disappears. 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 light source region 105 and the beam splitter 110 is substantially exactly equal.

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

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

[0027] In some embodiments, the chip-scale device 200 is a chip-scale integrated optical 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 non-linear properties of a ppKTP waveguide (or other waveguides made from materials with similar properties) with the high confinement and filtering performance of a silicon nitride waveguide. This combination enables miniaturization, efficiency, and robustness while increasing the available optical beam of photon pairs 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 that has both non-linear properties and low transmission loss performance, high confinement performance, and filtering performance such as lithium niobate.

[0029] In certain embodiments, the chip-scale device can generate pump photons 205 from the pump photons 205 within the light source path 201, and can generate daughter photons 206a and 206b within the photon generation waveguide by dSPDC. Each of the photon pairs 206a and 206b may occupy different waveguide modes, either an electrical transverse wave (TE) or a magnetic transverse wave (TM). The vertical coupler (VC) region can adiabatically draw the daughter photons 206a and 206b from the photon generation waveguide into the photon conditioning waveguide patterned on top of the photon generation waveguide. Further, the TM photons and the TE photons can be separated by two diffraction waveguide mode splitters (MSs). Then, the TE photons pass through a bandpass filter (BPF) to exclude background photons, pass through a second MS, and then may leave the chip 200 as output photons 211. On the other hand, for the original TM photons, they may be converted to the TE mode by a diffraction mode converter (MC) that can also reverse the propagation direction of the photons. This photon (now TE polarized) passes through its own bandpass filter and may leave the chip 200 as output photon 209. The various functions performed on the chip may be performed by the photon conditioning waveguide (made of silicon nitride or other similar materials in some embodiments), and the waveguide structure including the photon generation waveguide is patterned in a film deposited on top of the substrate.

[0030] In a further embodiment, in the interferometer path 203, the photon pairs 209 and 211 may be reflected or sent back from a remote satellite or other remote system and recombined in the optical component waveguides on the chip-scale device 200 to complete the HOM interferometer 215. (In some embodiments, the photons may also have a polarization rotated by 90 degrees by a conventional waveplate). The photon pairs 209 and 211 may re-enter the same waveguide that was previously emitted, but now being rotationally polarized, may couple to the orthogonal waveguide mode (i.e., TM). Each photon can then interact 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 may be directed towards a photon detector 212 such as a single photon avalanche photodetector (SP-APD) that can detect the photons 209 and 211. The detection signal output of the photon detector 212 is directed towards an electronic correlator 215 that can determine the degree of coincidence of the arrival times of the signals, thereby completing the HOM interferometer 216.

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

[0032] In a specific embodiment shown in FIG. 3A, photons in the TE mode of the photonic vertical coupling waveguide 302 pass through the photonic adjustment waveguide network 304 and pass through the mode splitter 303 without diffraction. Then, the photons pass through a band-pass filter 305 that filters fluorescence and stray pump light coupled from the photon generation waveguide 301. Thereafter, the photons pass through the mode splitter 307 without diffraction and are emitted through the output port 321.

[0033] In a specific embodiment shown in FIG. 3B, photons in the TM mode of the photonic vertical coupling waveguide 302 pass through the photonic adjustment waveguide network 304 and are diffracted by the mode splitter 303. When the photons are further diffracted by the mode splitter 309, the photons enter the mode converter 311. The mode converter 311 diffracts the photons again but converts the photons from the TM mode to the TE mode. Now that the photons are in the TE mode, the photons are not diffracted by the mode splitter 309. Then, the photons pass through a band-pass filter 313 that filters fluorescence and stray pump light coupled from the photon generation waveguide. Thereafter, the photons pass through the mode splitter 315 without diffraction and are emitted through the output port 319.

[0034] In an additional embodiment illustrated in FIG. 3C, two daughter photons emitted from the photonic adjustment waveguide network 304 are in the TM mode in waveguides 319 and 321 in the photonic adjustment network It may be sent back from another optical device so as to be recombined with 304. The two received photons in the TM mode can each propagate in a waveguide to mode splitters 315 and 307. Both mode splitters 315 and 307 diffract the received photons. Then, the photons are interfered with each other via a 50 / 50 coupler 317 before being output at ports 323 and 325 for detection by subsequent photon detectors. In the above embodiment, the TM mode from the photon vertical coupling waveguide 302 is converted to the TE mode by the photon adjustment waveguide network 304 for transmission from the chip-scale device, while the light received back into the subsequent interference detection device is in the TM mode. However, in another embodiment, the TE mode from the photon vertical coupling waveguide is converted to the TM mode by the photon adjustment waveguide network 304 for transmission from the chip-scale device, while the light received back into the subsequent interference detection device 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, a photon adjustment waveguide network (similar to the photon adjustment waveguide network 304 in FIGS. 3A - 3C) with 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 of the vertical coupler 427, the mode splitters 403, 409, 407, and 415, the mode converter 411, and the bandpass filters will be 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, hardly perturbs the shape of the weakly confined mode in the photon generation waveguide 501. As discussed herein, the photon vertical coupling waveguide 503 gradually expands over the entire overlapping portion of the stacked waveguides. For example, the photon vertical coupling waveguide 503 may expand from 100 nm to 200 nm over a distance of approximately 500 microns. By the gradual expansion of the photon vertical coupling waveguide 503, the photons are adiabatically drawn into a much more tightly confined waveguide mode from the photon generation waveguide 501. Further, by the movement in a state of essentially zero-mode cross-coupling, the polarization mode of the propagating photons is maintained (i.e., TE→TE and TM→TM).

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

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

[0039] In certain embodiments, as shown in the isometric view 600, the mode splitter may include a single input port 603. The mode splitter can receive, as inputs 601, two photons propagating in different orthogonal modes in a waveguide via the input port. 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 to the output port 607 as the output photon 609. For example, the mode splitter can directly pass the TE-mode photon received at the input port 603 to the output port 607. Further, since the mode splitter may diffract one of the propagating photons, one of the propagating photons is coupled to the reverse-direction waveguide and passed to the output port 613 as the 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 for splitting two orthogonally polarized photons into different paths, the mode splitter may include a chirped diffraction grating assisted reverse mode coupler. As shown, FIG. 610 shows the waveguide structure and graph 620 shows the calculated result of its spectral response. As shown, the coupling portion consists of two waveguides 621 and 625 spaced closely apart. Further, the waveguide 621 can be patterned using the modulation sidewall 623, and thus, an in-waveguide diffraction grating having a large overlap essential for the TM-TM transition from one waveguide to the other can be formed. The effect of the modulation is to couple the TM mode from the forward direction in the waveguide 625 to the reverse direction in the waveguide 621, while the TE mode remains in the waveguide 625 and passes through the mode splitter in the forward direction. Further, the frequency of the modulation sidewall 623 may vary along the length direction of the mode splitter to enable a desired frequency response for the mode splitter.

[0041] FIG. 7 is a diagram showing a particular embodiment of a mode converter as seen in chip scale device 200. In particular, FIG. 7 shows an isometric view 700 of a 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 may receive photons as input 701 propagating in a particular mode within a waveguide. For example, the photons received through port 703 may be propagating in a TM mode. The mode converter can convert the mode from one mode to an orthogonal mode within conversion portion 705, where the mode converter converts the photons to an orthogonal propagation mode and outputs them as an output through port 703. For example, if the photons received at port 703 are in a TM mode, the photons output through port 703 may be in a TE mode.

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

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

[0045] In a particular embodiment, as shown in the isometric view 800, the bandpass filter may include a single port 803. The bandpass filter can receive, as input 801, photons propagating in a specific mode in the waveguide via port 803. For example, the photons received via the input port 803 may be propagating in the TE mode. The bandpass filter can filter out photons having unwanted wavelengths within the filtering portion 805 and supply the filtered photons as output 809 via the output port 807.

[0046] In some embodiments, as shown in the detailed isometric view 810 of the filtering portion 805 of the bandpass filter, a waveguide bandpass filter is implemented to exclude any background fluorescence photons and any residual pump photons that can propagate within the waveguide. As shown, the filter is made of two high reflectivity waveguide gratings 811 and 813 manifested by chirping within the modulation period along the length of the waveguide, in other words, the modulation of the waveguide grating varies symmetrically along the length direction along the length of the sidewall of the filter. Light just outside the passband is diffracted and recedes from the waveguide, while light at the pump wavelength is completely scattered from the waveguide. In some embodiments, the spectral positions of the waveguide gratings 811 and 813 can vary along the length direction of the filtering portion 805 of the passband.

[0047] As described above, FIG. 9 is a method 900 of testing a chip-scale device for generating and interfering correlated photon pairs. Method 900 proceeds to 901 where one photon pair is generated in a photon generation waveguide. Further, method 900 proceeds to 903 where the photon pair is coupled to a photon vertical coupling waveguide. Moreover, method 900 proceeds to 905 where one of the photons of the photon pair is converted within 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 supplied to one or more external devices. Further, method 900 proceeds to 909 where the photons are received from one or more external devices. Moreover, method 900 proceeds to 911 where an interference method is performed on the received photons. Exemplary embodiments

[0048] Example 1 includes an input port 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, a first output port, a second output port, and a first waveguide coupled to the input port and the first output port, the first waveguide receiving the first photon and the second photon via the input port and supplying the first photon to the first output port, and a second waveguide coupled to the second output port, the wall of the second waveguide proximate to the first waveguide having a modulated sidewall, the second photon being coupled to the second waveguide and output via the second output port, the first waveguide and the second waveguide being on a substrate of a first material and within a waveguide layer of a second material, the first material and the second material having different refractive indices.

[0049] Example 2 includes the device described in Example 1 where the first material is periodically poled potassium titanyl phosphate.

[0050] Example 3 includes the device described in any of Examples 1 - 2 where the first photon and the second photon are generated within a substrate layer.

[0051] Example 4 includes the device described in any of Examples 1 to 3, where the second material is silicon nitride.

[0052] Example 5 includes the device described in any of Examples 1 to 4, where the first photon and the second photon are entangled photons.

[0053] Example 6 includes the device described in any of Examples 1 to 5, where the first mode is the TE mode and the second mode is the TM mode.

[0054] Example 7 includes a system comprising a substrate layer having a first refractive index and a waveguide layer formed on the substrate layer and having a second refractive index different from the first refractive index. The waveguide layer includes one or more waveguides formed therein, at least one of which has a modulation sidewall, and one or more ports for receiving one or more input photons and supplying one or more output photons. One of the output modes of the one or more output photons and one of the one or more ports associated with the output photons comprises one or more ports based on the input mode of the one or more input photons.

[0055] Example 8 includes the system described in Example 7, where one or more waveguides and one or more ports form a mode splitter. The mode splitter includes a first waveguide among the one or more waveguides coupled to a first output port among the one or more ports, which receives a first photon and a second photon via the input port and supplies the first photon to the first output port, and a second waveguide among the one or more waveguides coupled to a second output port among the one or more ports, to which the second photon is coupled and output via the second output port.

[0056] Example 9 includes the system described in Example 8, where the wall of the second waveguide adjacent to the first waveguide has a modulation sidewall.

[0057] Example 10 includes the system described in any of Examples 7 to 9, where one or more waveguides and one or more ports form a mode converter, and the mode converter includes one of the one or more ports configured to receive photons propagating in a first mode, and a waveguide coupled to a port that outputs photons propagating in an orthogonal mode with respect to the first mode through the port.

[0058] Example 11 includes the system described in Example 10, where the waveguide includes a first periodically modulated sidewall and a second periodically modulated sidewall, and the modulation of the first periodically modulated sidewall and the second periodically modulated sidewall is out of phase with each other such that the width of the cross-section of the mode conversion waveguide is constant along the length direction of the mode conversion waveguide.

[0059] Example 12 includes a device including a substrate having a first refractive index and a waveguide layer on the substrate, the waveguide layer having a second refractive index different from the first refractive index, the waveguide layer including a port configured to receive photons propagating in a first mode, and a waveguide coupled to the port, the waveguide having a first periodically modulated sidewall and a second periodically modulated sidewall, where the modulation of the first periodically modulated sidewall and the second periodically modulated sidewall is out of phase with each other such that the width of the cross-section of the mode conversion waveguide is constant along the length direction of the mode conversion waveguide, and photons propagating in an orthogonal mode with respect to the first mode are output through the port by the first periodically modulated sidewall and the second periodically modulated sidewall.

[0060] Example 13 includes the device described in Example 12, where the first material is periodically poled potassium titanyl phosphate.

[0061] Example 14 includes the device described in any of Examples 12 to 13, where the second material is silicon nitride.

[0062] Example 15 includes the device described in any of Examples 12 to 14, where the first mode is the TE mode.

[0063] Example 16 includes a system comprising a substrate having a first refractive index and a waveguide layer on the substrate, where the waveguide layer has a second refractive index different from the first refractive index, and the waveguide layer receives at least one of the first photons of the first mode and the second photons of the second mode via an input port and supplies at least one of the first photons via a first output port and the second photons via a second output port, one or more mode splitters, and a mode converter coupled to a second output of one of the one or more mode splitters, the mode converter receiving the second photons via a port and outputting the second photons in the first mode via a port.

[0064] Example 17 includes the system described in Example 16, where one of the one or more mode splitters comprises a first waveguide coupled to the input port and the first output port and a second waveguide coupled to the second output port, and the second photons are coupled from the first waveguide to the second waveguide and output via the second output port.

[0065] Example 18 includes the system described in Example 17, where the wall of the second waveguide adjacent to the first waveguide is a modulation sidewall.

[0066] Example 19 includes the system described in any of Examples 16 to 18, where one of the one or more mode converters comprises a waveguide coupled to a port that outputs photons propagating in the first mode via the port.

[0067] Example 20 includes the system described in Example 19, where the waveguide includes a first modulation sidewall and a second modulation sidewall, and the first modulation sidewall is out of phase with the second modulation sidewall.

[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. A device, comprising: an input port configured to receive first photons propagating in a first mode and second photons propagating in a second mode orthogonal to the first mode; A first output port; A second output port; and a first waveguide coupled to the input port and the first output port, the first waveguide receiving the first photons and the second photons via the input port and providing the first photons to the first output port; and a second waveguide coupled to the second output port, a wall of the second waveguide proximate to the first waveguide having a modulated sidewall, and the second photons are coupled into the second waveguide and output via the second output port, the first waveguide and the second waveguide being on a substrate (501) of a first material and in a waveguide layer (503) of a second material, the first material and the second material having different refractive indices.

2. The device of claim 1 , wherein the first mode is a TE mode and the second mode is a TM mode.

3. 1. A system comprising: a substrate (501) having a first refractive index; a waveguide layer (503) on the substrate (501), the waveguide layer (503) having a second refractive index different from the first refractive index, the waveguide layer (503) comprising: one or more mode splitters that receive at least one of first photons in a first mode and second photons in a second mode via an input port (603) and provide at least one of the first photons via a first output port (607) and the second photons via a second output port (613); a mode converter coupled to the second output of one of the one or more mode splitters to receive the second photons via a port (703) and output the second photons in the first mode via the port (703).

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