Improvements in and related to photonics

Abstract

Optical switching using an optical resonator in which a propagating light mode (4) having a given light frequency can be selectively coupled and uncoupled by electro-optically modulating the resonance characteristics (e.g., resonant light frequency) of the optical resonator (12) in response to a signal generated by a single-photon detector (20). Detection of a photon (27B) controls how (and when) the propagating light mode couples to or uncouples from the optical resonator. This allows the light path of the propagating light mode to be switched in response to (i.e., conditional upon) the detection of a single photon.

Description

[Technical Field]

[0001] The present invention relates to optical switches and / or optical signal routers, and more particularly (but not limited to) single-photon triggered optical switches and / or optical signal routers. [Background technology]

[0002] Integrated photonics, as a platform for quantum technology, offers many advantages, including the potential to integrate thousands of components onto a single chip, ease of integration with conventional photonics techniques, and the relatively inexpensive, fast, and robust nature of information transmission methods in the form of single photons or other quantum states of light. However, the main drawback of photonics lies in the challenge of engineering any coupling between optical signals. This is because optical signals do not interact in the same way as, for example, two electrons interacting by Coulomb force. This makes constructing all-optical logic gates between optical signals a challenge.

[0003] One engineering approach to achieve effective interaction between optical signals is to electrically detect all or part of one signal, convert it into an electronic signal, and then amplify this electronic signal to drive or modulate the target optical signal. However, this approach has the drawback of latency associated with the detection, amplification, and light-to-electron conversion processes. Total latency is contributed to by numerous factors, including the response time of the single-photon detector, the bandwidth of the amplifier that converts the voltage signal generated by the detector for use in driving the optical modulator, the bandwidth of the modulator itself, and the delay due to the electronic connections between each element.

[0004] This latency typically requires the target signal to pass through a delay line that is on the order of meters in length. Such delay lines can occupy a significant amount of valuable physical space on an integrated chip. Furthermore, propagation losses occur. This is particularly detrimental to single-photons in quantum information applications because the information encoded in the quantum state of a single photon cannot be amplified or copied. As a result of these factors, there is currently no effective way to achieve switching or controllable coupling involving single-photons or other optical quantum states. This is a major challenge in optical quantum technology, where high-speed switching is required for applications such as stochastic source multiplexing, providing the feedforward necessary for quantum teleportation, quantum gates, and ultimately conditional operations for optical quantum information processing.

[0005] This invention was devised in consideration of the above-mentioned factors. [Overview of the project]

[0006] With the above challenges in mind, the inventors recognized that current quantum optical technologies lack the fundamental ability for high-speed switching conditioned on single-photon detection. The key to solving this lies in eliminating the need for large-scale and / or off-chip amplification of the electrical signal generated from the single-photon detector, because amplification typically causes the greatest latency penalty. To eliminate the amplification step and modulate the target signal directly from the voltage pulse generated by the single-photon detector, the inventors recognized that advantages could be gained by using a highly sensitive structure, such as a resonator that responds to relatively weak signals. Preferably, using a non-standard material platform such as a lithium niobate thin film with a high electro-optic coefficient (or carrier injection in CMOS materials) is effective in this regard. The inventors recognized that by detecting a photon and operating an optical switch or rerouting in response to that detection, the target optical signal can be rerouted or switched without the need for off-chip amplifiers and the associated long delay lines and losses.

[0007] Generally, the present invention provides a method for rerouting or switching a target optical signal, subject to the detection of one or more photons, in a manner that does not require large-scale and / or off-chip amplification. This innovation can preferably be implemented by modulating the resonance of a resonator using a small (tens to hundreds of mV) voltage output obtained, for example, from a known and available single-photon detector. For example, a resonator typically couples multiple optical modes (e.g., waveguide modes). The optical signal propagating in one of the waveguide modes can be distributed among the modes (e.g., waveguide modes) through the resonator in a manner that depends on the resonance of the resonator and the coupling between the resonator and the optical modes (e.g., optical waveguide modes). This results in the initial optical signal being distributed in different ways in response to the detection of a single photon.

[0008] This provides a high-speed single-photon converter capable of performing optical transformations conditional on the detection of a single photon, eliminating the need for long delay lines and real-time feedforward logic requiring long electronic connections. The high-speed single-photon converter generates a laser pulse output (e.g., a strong laser pulse) when a single photon is detected, and this laser pulse is used to directly drive an optical transformation (e.g., using a nonlinear optical element). This performs an optical transformation to the target mode of light (e.g., a waveguide mode), resulting in a single-photon conditional optical operation.

[0009] In its most common form, the present invention performs optical switching using an optical resonator on which a propagating optical mode having a given optical signal frequency can be coupled and uncoupled by electro-optically modulating the resonant characteristics (e.g., resonant optical frequency) of the optical resonator in response to a signal generated by a single-photon detector (SPD). By detecting the photon, the manner (or timing) in which the propagating optical mode couples and / or uncouples from the optical resonator can be controlled. Thus, in response to the detection of a single photon (i.e., conditional on its detection), the travel path of the propagating optical mode of light can be switched. The single photon can be generated by any desired optical or photon process occurring in part of an optical circuit or photon circuit on which the optical switch is part or optically coupled. Examples of optical or photon circuits include photon information processing circuits, photon quantum computer circuits, photon communication circuits and components, and the like.

[0010] The quantum states of the propagating optical modes, conditionally routed by optical switching, can then undergo further optical processing (e.g., quantum optical processing) as needed. Here, "quantum optical processing" refers to processing of an optical signal by treating the optical signal as having quantum states that can be manipulated according to a quantum process that realizes a desired quantum state. "Quantum optical processing" may include applying quantum operators (e.g., "displacement operators," "phase shift operators," etc.) to the optical signal. "Quantum optical processing" may require defining the optical signal as a quantum state or a set of quantum states (e.g., representing photons or streams of photons rather than classical electromagnetic waves).

[0011] For example, "quantum optics processing" may include quantum entanglement. The quantum states of propagating light modes can become quantum entangled by mixing modes at appropriately selected multiports. The simplest example is the superposition of two propagating modes by an optical beam splitter. Therefore, combining a beam splitter and a measuring device on a specific output channel may be a method for designing the quantum states of the propagating light field. For example, "quantum optics processing" may include generating a "squeezed" state from an optical signal. For example, "quantum optics processing" may include generating a phase-shifted quantum state from an optical signal. For example, "quantum optics processing" may include generating a "displaced" quantum state from an optical signal (e.g., displacing the state to a desired magnitude in phase space).

[0012] Optical resonators may include ring resonators, racetrack resonators, disk resonators, bowtie resonators, photonic crystal ring resonators, photonic crystal cavity resonators (two-dimensional or one-dimensional cavities), and semiconductor micropillar cavity resonators. Ring resonator structures and racetrack resonator structures have proven particularly beneficial because they can combine a high quality factor (Q), relatively easy integration into optical circuits, and improved modulation efficiency.

[0013] The present invention enables optical switching by conditionally routing an optical signal of a given optical signal frequency from an optical signal source, according to the following conditions. (Path 1: When the resonator resonates with light from the light source) This condition can be met when no photons are detected by the single-photon detector, resulting in a strong coupling of the optical input to the system into the resonator, and having the effect of low or negligible optical output through the system's designated optical output path. (Path 2: When the resonator is not resonating with the light from the light source) This condition can be met when a photon is detected by a single-photon detector, resulting in a weak or negligible coupling of the optical input to the system to a non-resonant resonator, which has the effect of increasing the optical output through the designated optical output path of the system.

[0014] In this sense, the absence of a single-photon detection event by a single-photon detector allows the optical resonator to accommodate the input optical signal (i.e., the resonator becomes at least part of the path), whereas the occurrence of a single-photon detection event makes the optical resonator unable to accommodate the input optical signal (i.e., the resonator is not part of the path). Alternatively, the rerouter may be configured in the opposite way: if no single photon is detected, the input optical signal does not strongly couple with the resonator, the optical resonator becomes unable to accommodate the input optical signal (i.e., the resonator is not part of the path), and the input optical signal can escape from a particular waveguide. On the other hand, if a single photon is detected, the input optical signal enters a resonant state, and the optical resonator becomes able to accommodate the input optical signal (i.e., the resonator becomes at least part of the path). The optical signal may not escape, or in some cases may escape through a different waveguide. Therefore, as an alternative, the present invention can achieve optical switching by conditionally routing an optical signal of a given optical signal frequency from an optical signal source according to the following conditions. (Path 1: When the resonator resonates with light from the light source) This condition can be met when a photon is detected by a single-photon detector, resulting in a strong coupling of the optical input to the system into the resonator, and the optical output through the system's designated optical output path becomes low or negligible. (Path 2: When the resonator is not resonating with the light from the light source) This condition can be met when no photons are detected by the single-photon detector, resulting in a weak or negligible coupling of the optical input to the system to a non-resonant resonator, which has the effect of increasing the optical output through the system's designated optical output path.

[0015] In a first embodiment, the present invention can provide an optical switch that receives an optical signal of a predetermined optical signal frequency from an optical signal source and outputs the optical signal, the optical switch comprising an optical router configured to route an optical signal in response to the detection of a single photon, the optical router comprising an optical resonator configured to resonate at a resonant optical frequency within a resonant bandwidth determined by the refractive index of an optical resonator, an input optical waveguide portion optically coupled to the optical resonator and receiving an optical input signal input from an optical signal source as input to the optical router, and an output optical waveguide portion optically coupled to the input optical waveguide portion and the optical resonator and configured to receive an optical signal for output from the optical router, the optical switch further comprising a single-photon detection unit configured to output an electrical detection signal in response to the detection of a single photon, and an optical modulator connected to the single-photon detector and configured to output an electrical modulation signal in response to the electrical detection signal, the optical modulator configured to modulate the refractive index of the optical resonator using the electrical modulation signal and modulate the resonant bandwidth to one of the following: (a) Change from a resonant bandwidth that includes the optical signal frequency to a resonant bandwidth that does not include the optical signal frequency; or (b) Change from a resonant bandwidth that does not include the optical signal frequency to a resonant bandwidth that includes the optical signal frequency.

[0016] The resonant bandwidth of an optical resonator can be determined by factors at the time of manufacture (such as physical dimensions and other characteristics), but it should be understood that it is also determined by the refractive index of the optical resonator after manufacture. The refractive index of the optical resonator can be controlled and adjusted after the resonator is manufactured, and this will be discussed later.

[0017] In this specification, the term "resonant bandwidth" refers to the precise resonant frequency ω res Furthermore, it is interpreted to refer to a continuous frequency range that includes adjacent frequencies that differ by less than half the value of the resonant linewidth (e.g., FWHM) of the spectral resonant profile of the optical resonator. For example, the term "...resonant bandwidth..." can be interpreted to refer to a continuous range of frequencies ω that satisfy the following conditions:

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[0018] The term "...modulating the resonant bandwidth..." is interpreted as including a change, shift, or transition of the spectral position or location (e.g., the position of its center) of the resonant bandwidth. res Considering the surrounding area, the resonant frequency ω res The resonant frequency may be located at or near the center of the bandwidth. Therefore, a change, shift, or transition in the spectral position or position of the resonant bandwidth corresponds to a change, shift, or transition in the spectral position or position of the resonant frequency within it. Thus, a change (modulation) in the frequency position of the resonant bandwidth may include a change / shift (modulation) in the resonant frequency.

[0019] It has also been pointed out that modulation of the refractive index of an optical resonator can cause a change in the magnitude of the resonant linewidth (e.g., FWHM) of the optical resonator's spectral resonant profile. Therefore, depending on the modulation of the refractive index of the optical resonator, a change in the size of the resonant bandwidth (due to a change in the linewidth of the spectral resonant profile) may occur alone, or in combination with a change in the spectral position (and resonant frequency) of the resonant bandwidth. Either one or both of these effects may contribute to the final result of whether or not the resonant bandwidth includes a particular optical signal frequency.

[0020] In the above configuration (a), by changing the resonant bandwidth to exclude the optical signal frequency, it becomes possible to transmit the optical input signal as a non-resonant optical output signal to the output optical waveguide section for output from the optical switch.

[0021] In the above configuration (b), by changing the resonant bandwidth to include the optical signal frequency, the following becomes possible: (b1) Enable the transmission of the optical input signal to the output optical waveguide section as a resonant optical output signal output from the optical switch, or (b2) Suppress (for example, prevent) the transmission of the optical input signal to the output optical waveguide section as an optical output signal output from the optical switch.

[0022] The two alternatives (b1 and b2) in configuration (b) are determined by how the output optical waveguide is optically coupled to the input optical waveguide. For example, in configuration (b1), if the output optical waveguide and the input optical waveguide are two physically separated waveguides, the optical coupling is indirect, via an optical resonator as an intermediate. For example, in configuration (b2), if the output optical waveguide and the input optical waveguide are two separated parts of a single continuous waveguide, the optical coupling is direct.

[0023] Therefore, the optical input signal transmitted to the output optical waveguide is either transmitted directly from the input optical waveguide without resonating within the optical resonator, or transmitted indirectly from the input optical waveguide through the optical resonator, and is resonantly "loaded" into the optical resonator from the input optical waveguide beforehand.

[0024] Thus, in the stationary state where the single-photon detector does not generate an electrical detection signal, the optical switch is configured to implement a signal path setting (e.g., Route 1) that includes a resonator in the path or as part of the path of the propagation light mode of the input optical signal, provided that the signal path substantially excludes or ignores other available designated optical output paths from the path of the propagation light mode. On the other hand, in the active state where the single-photon detector generates an electrical detection signal, the optical switch is configured to implement a signal path setting (e.g., Route 2) that substantially excludes or ignores a resonator in the path or as part of the path of the moving light mode of the input optical signal, provided that the signal path includes other available designated optical output paths as part of the path of the moving light mode.

[0025] In other words, in the stationary state, the propagating optical modes substantially resonate with the resonator and enter the resonator. After entering the resonator, the resonant propagating optical modes either remain within the resonator (e.g., are confined there) or propagate through the resonator to a subsequent path away from it. This path may be via an optical waveguide optically coupled (e.g., critically coupled) to the optical resonator. In either case, as a result of implementing this signal path configuration (path 1), the output of the optical signal in other available designated optical output paths of the system is low or negligible. In the active state, the optical resonator no longer participates in the path or path of the moving optical modes of the input optical signal, and thus the path or path of the input optical signal can include other available designated optical output paths of the system.

[0026] The refractive index can be changed only in a limited portion of the optical resonator's length / circumference, or preferably along the entire length / circumference of the optical resonator. Changing the refractive index along a limited region of the optical resonator's length / circumference may cause more backscattering of light, resulting in a lower resonant shift (i.e., lower efficiency) for the same electrical signal.

[0027] For example, an optical modulator can operate to locally change the refractive index of the optical resonator material in a local portion (i.e., not the entire) of the optical path defined by the optical resonator. Alternatively, an optical modulator can operate to globally change the refractive index of the optical resonator material in substantially the entire optical path (i.e., the entire) of the optical path defined by the optical resonator. An optical modulator can operate to implement refractive index changes induced by effects including, but not limited to, thermal light, electric light, carrier injection, piezoelectricity, birefringence, microelectromechanical, strain-induced, or acoustic light.

[0028] The input optical waveguide and / or output optical waveguide are attenuated optically coupled to the optical resonator (e.g., physically and materially separated from the optical resonator, but close enough for the attenuated electromagnetic field or quantum mode / state to couple across the separation). Alternatively, the input optical waveguide and / or output optical waveguide are physically and optically coupled to the optical resonator (e.g., physically in contact with the optical resonator, integrally formed with the optical resonator, or optically joined). The input optical waveguide and / or output optical waveguide are optically coupled to the optical resonator via an adjustable directional coupler or a Mach-Zehnder interferometer. This coupling can be adjusted before use to change the “stationary state” of the coupling to the optical resonator (a state in which no photons are detected). This allows for fine-tuning to optimize the critical coupling to the optical resonator in the state in which no photons are detected.

[0029] The input optical waveguide section and the output optical waveguide section can each be a portion of a single continuous optical waveguide, optically coupled to the optical resonator in the optical coupling region of the optical resonator. Here, the input optical waveguide section extends to the optical coupling region, and the output optical waveguide section extends from the optical coupling region. For example, the optical resonator may include a loop-shaped waveguide such as a ring optical resonator (e.g., a microring optical resonator), a racetrack resonator, or a disk resonator, which is physically separated from the continuous optical waveguide by a gap (which may be filled with material or substance as needed) and configured to be attenuatedly optically coupled to the continuous optical waveguide. Alternatively, the continuous optical waveguide may constitute an optical resonator, which may be formed integrally with the continuous optical waveguide as an optical waveguide structure including an optical resonator cavity (e.g., a photonic crystal cavity resonator (2D or 1D cavity) or a semiconductor micropillar cavity resonator). Optical resonators may include loop optical resonators (e.g., ring optical resonators, optical racetrack resonators, photonic crystal ring optical resonators, disk optical resonators), bowtie optical resonators, photonic crystal cavity optical resonators (2D or 1D cavities), or semiconductor micropillar cavity optical resonators.

[0030] Loop-type optical resonator structures (e.g., particularly ring, racetrack, or photonic crystal ring optical resonators, and disk optical resonators) have proven particularly beneficial because they combine a high quality factor (Q), relatively easy integration into optical circuits, and improved modulation efficiency. Preferably, the optical resonator has a Q factor of 1,000,000 or greater. This allows for very large relative changes (e.g., % changes) in the optical coupling strength between the optical resonator and the output optical waveguide with relatively small modulation of the resonator's resonant frequency. This relative change is reflected as a corresponding relative change in the optical output signal intensity from the switch. These Q factors may be less than 1,000,000 when using SPADs capable of outputting higher voltages, thereby achieving large frequency shifts. Therefore, there are scenarios where setting the Q factor to less than 1,000,000 is advantageous, such as when rerouting optical signals with a wide spectral width.

[0031] The optical resonator is preferably a single-mode optical waveguide, but may also be a multi-mode optical waveguide.

[0032] The continuous optical waveguide is preferably critically coupled to an optical resonator. By critically coupling the continuous optical waveguide to the optical resonator, it becomes possible to accumulate enough phase at the output of the continuous optical waveguide to produce destructive interference in order to filter out light that travels forward beyond the resonator of the waveguide as light enters and exits the waveguide. As a result, the optical output in the direction of waveguide propagation beyond the resonator is severely suppressed, negligible, or virtually nonexistent.

[0033] The optical switch may include yet another output optical waveguide, in which case the continuous optical waveguide and the yet another output optical waveguide are independent optical waveguides, optically coupled in different optical coupling regions of the optical resonator.

[0034] Furthermore, the output optical waveguide is preferably critically coupled to an optical resonator. Therefore, by critically coupling the further output optical waveguide to the optical resonator, it becomes possible to accumulate the phase necessary to cause destructive interference in the region in the direction of propagation of the resonator, while simultaneously accumulating the phase necessary to cause constructive interference in the region in the direction of propagation of the further output optical waveguide, before the light in the resonator couples to the further output optical waveguide. This suppresses the light in the direction of propagation of the optical resonator while strengthening and promoting the light in the direction of propagation of the output optical waveguide beyond the resonator. As a result, the optical output to the further output optical waveguide is strengthened and its path is set to propagate along the output optical waveguide beyond the resonator.

[0035] The optical modulator is preferably configured to modulate the refractive index of the optical resonator with an electrical modulation signal at a predetermined modulation time interval, starting from the time a single photon is detected by the single-photon detection unit. This modulates the resonant bandwidth at the predetermined modulation time interval.

[0036] The preset modulation time interval T is preferably the decay time of the optical resonator.

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[0037] Similarly, this mitigation can be implemented by a controlled relationship between a pre-set modulation time interval T and the coupling ratio of the resonator. For example, the output optical waveguide is optically coupled to the optical resonator according to a coupling ratio Γ1, which is set to be less than the reciprocal of the pre-set modulation time interval (i.e., Γ1 < 1 / T). This ensures that, during use, the optical input light resonating in the optical resonator becomes non-resonant during the pre-set modulation time interval T and is transferred from the optical resonator to the output optical waveguide at a coupling ratio Γ1 during that interval. The optical coupling ratio Γ1 may correspond to the coupling ratio when an electrically detected signal is output from the single-photon detector unit and the refractive index of the optical resonator is modulated. Modulation of the refractive index of the resonator may have the side effect of modulating the coupling ratio between the optical resonator and the input / output optical waveguide. This effect is expected to be small compared to the frequency shift between the resonator and the input optical signal.

[0038] The output optical waveguide is optically coupled to the optical resonator according to the coupling ratio Γ1, and the single-photon detection unit is configured to output an electrical detection signal in the form of a voltage pulse, and the voltage value of the electrical detection signal is set to a preset voltage attenuation ratio Γ greater than the coupling ratio. d Accordingly, it is set to decrease from the peak value of the voltage pulse. Here, τ dΓ is the decay time of the voltage pulse. In this way, the duration of the electrical detection signal pulse can be adjusted to occur faster than the coupling time (i.e., the reciprocal of the coupling ratio) for coupling light from the optical resonator to the output optical waveguide. That is, the coupling of light to the optical resonator is delayed or suppressed on the time scale of the voltage signal, but light already present in the optical resonator may continue to leak out due to the coupling. By imposing the above constraint on the duration of the electrical detection signal pulse, the amount of leaked light can be reduced to an appropriate level. Furthermore, the voltage decay rate Γ d It has been found that by appropriately shortening the coefficient, oscillations in the optical output signal intensity can be suppressed. The optical coupling coefficient Γ1 may correspond to the coupling ratio when an electrical detection signal is output from the single-photon detector unit and the refractive index of the optical resonator is modulated.

[0039] Alternatively, in another embodiment, the optical resonator can be pre-filled with resonant optical signal light that is prepared to be emitted from the optical resonator to the output optical waveguide or further down the output optical waveguide as a non-resonant optical output signal output from the optical switch in response to a single-photon detection event by a single-photon detector. For example, the output optical waveguide and the optical resonator are optically coupled according to a coupling ratio Γ1, which is greater than the reciprocal of a preset modulation time interval (i.e., Γ1 > 1 / T). The optical coupling ratio Γ1 corresponds to the coupling ratio when an electrical detection signal is output from the single-photon detector unit and the refractive index of the optical resonator is modulated. During use, the optical input signal resonating in the optical resonator becomes non-resonant at a preset modulation time interval T, is transferred by the optical resonator to the output optical waveguide at a coupling ratio Γ1, and becomes a non-resonant optical output signal output from the optical switch. In other words, the response time of an optical resonator is set to be shorter than a predetermined modulation time interval in order to ensure "sufficient time" to release the resonant light stored inside it in order to respond to modulation in its resonant band.

[0040] The output optical waveguide section can be optically coupled to an optical resonator according to the coupling ratio Γ1. The optical resonator has an optical loss rate

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[0041] When the input optical waveguide section and the output optical waveguide section constitute part of a single continuous optical waveguide, the continuous optical waveguide is optically coupled to an optical resonator according to a coupling ratio Γ1, and the optical resonator has an optical loss ratio (e.g., total loss ratio) substantially equal to twice the coupling ratio Γ1.

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[0042] The optical switch may further include an optical signal source configured to output an optical signal having a predetermined optical signal frequency. The optical signal source is configured to output an optical signal in the form of either an optical pulse consisting of multiple photons or an optical pulse consisting of one or fewer photons.

[0043] Ideally, the output optical waveguide is optically coupled to the optical resonator according to the coupling ratio Γ1, and the optical signal source is configured to output the optical signal in the form of an optical pulse with a pulse duration σ, where σ is greater than the reciprocal of the coupling ratio.

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[0044] Furthermore, it is preferable that the output optical waveguide section is optically coupled to the optical resonator according to the coupling ratio Γ2. Here, Γ2 is substantially equal to the coupling ratio Γ3 in which the input optical waveguide section is optically coupled to the optical resonator. This makes it possible for the input optical waveguide section and the output optical waveguide section to be collectively critically coupled to the optical resonator. Preferably, the optical resonator has an optical loss ratio

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[0045] This can significantly improve the routing efficiency of the input optical signal. Specifically, critical coupling allows the resonant propagation mode of the input optical signal to be substantially completely coupled to the output optical waveguide via the optical resonator.

[0046] When an output optical waveguide section and another output optical waveguide section form a continuous waveguide, preferably, the continuous waveguide is optically critically coupled to the optical resonator. Critical coupling is provided at least when no electrical detection signal is output from the single-photon detection unit and no modulation of the refractive index of the optical resonator occurs.

[0047] The optical signal source can be configured to output an optical signal in the form of an optical pulse. Preferably, the spectral width of the optical signal is smaller than the resonant bandwidth of the resonator. As a result, when no electrical detection signal is output from the single-photon detector unit, the spectral components of the propagation mode of the optical input signal are substantially contained within the resonant bandwidth of the optical resonator, and when an electrical detection signal is output from the single-photon detector unit, they are completely excluded from the resonant bandwidth of the optical resonator.

[0048] The optical signal source can be configured to output an optical signal having a continuous optical output. The optical signal can be substantially monochromatic.

[0049] In a second embodiment, the present invention provides an optical switch assembly including an optical switch according to any aspect of the present invention, further including an output monitoring unit that generates a detection signal depending on the presence or absence of an optical output signal from the optical switch. Preferably, the output monitoring unit is configured to determine the presence or absence of an optical output signal depending on whether the detected optical output power exceeds the optical output power detected by the output monitoring unit in the absence of an electrical detection signal from a single-photon detection unit.

[0050] In a third embodiment, the present invention can provide an optical switch assembly that further includes an optical switch according to any aspect of the present invention, and an output monitoring unit that generates a detection signal depending on the presence or absence of an optical output signal from the optical switch. The optical signal source is configured to output an optical signal in the form of an optical pulse having a pulse duration. The output monitoring unit is configured to determine the presence or absence of an optical output signal within a monitoring time interval Δt. This time interval Δt is set so as not to exceed the pulse duration, Δt ≤ σ. This time interval has been confirmed to be an effective and reliable interval for encompassing the peaks of the optical output signal associated with the optical pulse and capturing peaks resulting from the electrodetection signal output from the single-photon detector unit. The monitoring time interval corresponds to the binning time interval. In some cases, the "no detection" and "detection" cases may result in a single or double peak in the output optical signal. In this case, if the binning time interval is shorter than the separation distance between these peaks, whether there is a signal in a particular bin may depend on the detection event.

[0051] In a fourth aspect, the present invention can provide an optical switching assembly including an optical switch disclosed according to any aspect of the present invention. In this optical switching assembly, the optical resonator has an optical loss rate (e.g., total loss rate)

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[0052] An optical switching assembly may include a laser unit configured to generate a continuous-wave (CW) laser light output or a pulsed laser light output that is fed into an input optical waveguide. For example, the laser unit may have an optical output port optically coupled to the input optical waveguide (e.g., an input port at its end, or at any suitable location along the waveguide via an optical coupler) and configured to propagate to an optical resonator. In this way, the laser light output from the laser unit either directly supplies the optical input signal transmitted from the input optical waveguide to the output optical waveguide without resonance in the optical resonator, or indirectly supplies it from the input optical waveguide through the optical resonator. In the latter case, the laser light output is first resonantly "loaded" from the input optical waveguide to the optical resonator, and then transmitted from the input optical waveguide to the output optical waveguide through the optical resonator.

[0053] The laser unit can generate a laser pulse output (e.g., a strong laser pulse) or a CW laser output when a single photon is detected, and use that laser pulse or CW laser output to directly drive optical conversions (e.g., using nonlinear optical elements). For example, the output monitoring unit may include the following configurations: Furthermore, another optical signal input port for receiving another optical input signal; An optical converter unit configured to be optically coupled to yet another optical signal input port and to apply a pre-configured optical conversion to yet another optical input signal in response to the generation of a detection signal, thereby generating a converted optical signal; An optical signal output port for outputting the converted optical signal as an optical output signal.

[0054] In a fifth embodiment, the present invention can provide an optical switching assembly having the following configuration. The optical switching assembly includes an optical switch that receives an optical signal of a predetermined optical signal frequency from an optical signal source and outputs the optical signal. The optical switch includes an optical router configured to route optical signals in response to the detection of a single photon, The optical router is, An optical resonator configured to resonate at a resonant optical frequency within a resonant bandwidth determined by the refractive index of the optical resonator, An input optical waveguide section is optically coupled to an optical resonator and configured to receive an optical input signal from an optical signal source as an input to an optical router, It includes an output optical waveguide section that is optically coupled to an input optical waveguide section and optically coupled to an optical resonator, and is operable to receive an optical signal as an output from an optical router, Here, the optical switch further includes the following components: A single-photon detection unit configured to output an electrical detection signal in response to the detection of a single photon; and, An optical modulator connected to a single-photon detector and configured to output an electrically modulated signal in response to an electrically detected signal, wherein the optical modulator is configured to modulate the refractive index of an optical resonator using the electrically modulated signal, thereby changing the resonant bandwidth from a resonant bandwidth that excludes the frequency of the optical signal to a resonant bandwidth that includes the frequency of the optical signal, thereby suppressing the transmission of the optical input signal to the output optical waveguide as an optical output signal output from an optical switch; An output monitoring unit that generates a detection signal depending on the presence or absence of an optical output signal from an optical switch; The output monitoring unit further, Furthermore, there is yet another optical signal input port that receives yet another optical input signal, Furthermore, an optical converter unit is optically coupled to another optical signal input port, applies a preset optical conversion to yet another optical input signal, conditional on the generation of a detection signal, and generates a converted optical signal. It includes an optical signal output port that outputs the converted optical signal as an optical output signal.

[0055] In any aspect of the present invention, a given optical transformation preferably includes one or more of the following: Conversion to a single-mode optical compression state; Conversion to two modes of optical compression; Transformation into a light phase-shifted quantum state; Transformation into a displaced quantum state.

[0056] In a sixth aspect, the present invention can provide an integrated optical circuit including an optical switch or optical switching assembly disclosed according to any aspect of the present invention. The present invention can provide an optical processing network or circuit that constitutes part of a broader optical circuit or system. In some aspects, the present invention can constitute (or be contained within) an integrated optical chip. The optical circuit and / or chip can be formed from materials including, but are not limited to, silicon (Si), silicon nitride (SiN), silica (SiO2), gallium arsenide (GaAs), indium phosphide (InP), polymers, lithium niobate (LiNbO), or aluminum nitride (AlN).

[0057] In a seventh embodiment, the present invention can provide an optical switching method for switching an optical signal of a predetermined optical signal frequency from an optical signal source by routing an optical signal in response to the detection of a single photon. This method includes the following steps. A step of providing an optical resonator, wherein the optical resonator is configured to resonate at a resonant optical frequency within a resonant bandwidth determined by the refractive index of the optical resonator; A step of providing an input optical waveguide section that is optically coupled to an optical resonator and capable of receiving an optical input signal from an optical signal source as an input to an optical router; A step of providing an output optical waveguide that is optically coupled to an input optical waveguide and optically coupled to an optical resonator, and capable of receiving an optical signal as an output from an optical router; Here, the optical switching method further includes the following steps: A single-photon detection unit is provided and configured to output an electrical detection signal in response to the detection of a single photon; and The step of providing an optical modulator connected to a single-photon detector and configured to output an electrically modulated signal in response to an electrically detected signal; and, The optical modulator modulates the refractive index of the optical resonator using an electrically modulated signal, thereby modulating the resonant bandwidth to one of the following: (a) Change from a resonant bandwidth that includes the optical signal frequency to a resonant bandwidth that does not include the optical signal frequency; or (b) Change from a resonant bandwidth that does not include the optical signal frequency to a resonant bandwidth that includes the optical signal frequency.

[0058] In configuration (a) of the above method, the configuration in which the resonant bandwidth is modified so as not to include the optical signal frequency enables the optical input signal to be transmitted as a non-resonant optical output signal to the output optical waveguide and output from the optical switch. In configuration (b) of the above method, the configuration in which the resonant bandwidth is modified to include the optical signal frequency enables one of the following results / methods: (b1) Enable the transmission of the optical input signal to the output optical waveguide section as a resonant optical output signal output from the optical switch, or (b) Suppress (for example, prevent) the transmission of the optical input signal to the output optical waveguide section as an optical output signal output from the optical switch.

[0059] The method may include the step of providing an optical converter unit for receiving yet another optical input signal and using it to apply a pre-configured optical conversion to yet another optical input signal.

[0060] This method may include providing an output monitoring unit that generates a detection signal depending on the presence or absence of an optical output signal from an optical switch. This method may also include using an output converter unit to further apply a pre-set optical conversion to the optical input signal, conditional on the generation of a detection signal, to generate a converted optical signal. This method may also include outputting the converted optical signal as an optical output signal.

[0061] In an eighth embodiment, the present invention provides an optical switching method for switching an optical signal of a predetermined optical signal frequency from an optical signal source in response to the detection of a single photon, the method comprising the following steps: A step of providing an optical resonator, wherein the optical resonator is configured to resonate at a resonant optical frequency within a resonant bandwidth determined by the refractive index of the optical resonator; A step of providing an input optical waveguide section that is optically coupled to an optical resonator and capable of receiving an optical input signal from an optical signal source as an input to an optical router; A step of providing an output optical waveguide that is optically coupled to an input optical waveguide and optically coupled to an optical resonator, and capable of receiving an optical signal for output from an optical router; Here, the optical switching method further includes the following: A single-photon detection unit is provided, which is configured to output an electrical detection signal in response to the detection of a single photon; and The step of providing an optical modulator connected to a single-photon detector and configured to output an electrically modulated signal in response to an electrically detected signal; and, The optical modulator modulates the refractive index of the optical resonator using an electrically modulated signal, changing the resonant bandwidth from a resonant bandwidth that does not include the optical signal frequency to a resonant bandwidth that includes the optical signal frequency, thereby suppressing (for example, preventing) the transmission of the optical input signal to the output optical waveguide as an optical output signal output from the optical switch; Here, the optical switching method further includes the following steps: A step of generating a detection signal depending on the presence or absence of an optical output signal from an optical switch; A step of providing a converter unit and further receiving an optical input signal with the converter unit; In the converter unit, conditional on the generation of the detection signal, a pre-set optical conversion is applied to the optical input signal to generate the converted optical signal; and, A step to output the converted optical signal.

[0062] The predetermined optical transformation preferably includes one or more of the following: transformation to a single-mode optical compression state; transformation to a two-mode optical compression state; transformation to an optical phase-shift quantum state; transformation to a phase-shift quantum state.

[0063] The present invention includes combinations of the described aspects and preferred features, unless such combinations are clearly impossible or explicitly avoided. [Brief explanation of the drawing]

[0064] Examples and experiments illustrating the principle of the present invention will be described with reference to the following drawings. [Figure 1] Figure 1 shows a ring optical resonator apparatus. [Figure 2] Figure 2 shows a ring light resonator apparatus. [Figure 3A] Figure 3A shows an optical switching / routing device according to the first embodiment of the present invention in a first switching / routing state. [Figure 3B] Figure 3B shows the optical switching / routing device shown in Figure 3A in a second switching / routing state. [Figure 3C] Figure 3C shows a schematic diagram of the optical transmission spectrum of the optical switching / routing device in the optical transformation device shown in Figures 3A and 3B according to the first embodiment. [Figure 4A] Figure 4A shows an optical switching / routing device according to a second embodiment of the present invention in a first switching / routing state. [Figure 4B] Figure 4B shows the optical switching / routing device shown in Figure 4A in a second switching / routing state. [Figure 4C] Figure 4C shows a schematic diagram of the optical transmission spectrum of the optical switching / routing device within the optical conversion device shown in Figures 4A and 4B according to the first embodiment. [Figure 4D]Figure 4D shows an optical switching / routing device according to a third embodiment of the present invention in a first switching / routing state. [Figure 4E] Figure 4E shows the optical switching / routing device shown in Figure 4D in a second switching / routing state. [Figure 4F] Figure 4F shows an optical switching / routing device according to a fourth embodiment of the present invention in a first switching / routing state. [Figure 4G] Figure 4G shows the optical switching / routing device shown in Figure 4F in the second switching / routing state. [Figure 5] Figure 5 shows a schematic diagram of the parameters of the optical switching / routing device according to the first embodiment of the present invention. [Figure 6] Figure 6 shows a schematic diagram of the parameters of the optical switching / routing device according to the second embodiment of the present invention. [Figure 7] Figure 7 shows the optical power output spectra of an optical switching / routing device according to one embodiment of the present invention in graph form. [Figure 8A] Figures 8A to 8C show the optical power spectrum of a laser pulse (Figure 8A) and the corresponding optical power spectra of the optical output for an optical switching / routing device according to one embodiment of the present invention. [Figure 8B] Figures 8A to 8C show the optical power spectrum of a laser pulse (Figure 8A) and the corresponding optical power spectra of the optical output for an optical switching / routing device according to one embodiment of the present invention. [Figure 8C] Figures 8A to 8C show the optical power spectrum of a laser pulse (Figure 8A) and the corresponding optical power spectra of the optical output for an optical switching / routing device according to one embodiment of the present invention. [Figure 9A] Figures 9A to 9C show the optical power-time profile of the laser pulse (Figure 9A) and the corresponding optical power-time profiles of the optical output for an optical switching / routing device according to one embodiment of the present invention. [Figure 9B]Figures 9A to 9C show the optical power-time profile of the laser pulse (Figure 9A) and the corresponding optical power-time profiles of the optical output for an optical switching / routing device according to one embodiment of the present invention. [Figure 9C] Figures 9A to 9C show the optical power-time profile of the laser pulse (Figure 9A) and the corresponding optical power-time profiles of the optical output for an optical switching / routing device according to one embodiment of the present invention. [Figure 10A] Figures 10A to 10E show the optical power-time profile of a laser pulse (Figure 10A) and the corresponding optical power-time profiles of the optical output for an optical switching / routing device according to one embodiment of the present invention. [Figure 10B] Figures 10A to 10E show the optical power-time profile of a laser pulse (Figure 10A) and the corresponding optical power-time profiles of the optical output for an optical switching / routing device according to one embodiment of the present invention. [Figure 10C] Figures 10A to 10E show the optical power-time profile of a laser pulse (Figure 10A) and the corresponding optical power-time profiles of the optical output for an optical switching / routing device according to one embodiment of the present invention. [Figure 10D] Figures 10A to 10E show the optical power-time profile of a laser pulse (Figure 10A) and the corresponding optical power-time profiles of the optical output for an optical switching / routing device according to one embodiment of the present invention. [Figure 10E] Figures 10A to 10E show the optical power-time profile of a laser pulse (Figure 10A) and the corresponding optical power-time profiles of the optical output for an optical switching / routing device according to one embodiment of the present invention. [Figure 11A] Figures 11A and 11B show the time profiles of the electrical signals generated by the single-photon detector, respectively. [Figure 11B] Figures 11A and 11B show the time profiles of the electrical signals generated by the single-photon detector, respectively. [Figure 12A] Figures 12A to 12E show the optical power-time profile of the laser pulse (Figure 12A) and the corresponding optical power-time profiles of the optical output for an optical switching / routing device according to one embodiment of the present invention. [Figure 12B] Figures 12A to 12E show the optical power-time profile of the laser pulse (Figure 12A) and the corresponding optical power-time profiles of the optical output for an optical switching / routing device according to one embodiment of the present invention. [Figure 12C] Figures 12A to 12E show the optical power-time profile of the laser pulse (Figure 12A) and the corresponding optical power-time profiles of the optical output for an optical switching / routing device according to one embodiment of the present invention. [Figure 12D] Figures 12A to 12E show the optical power-time profile of the laser pulse (Figure 12A) and the corresponding optical power-time profiles of the optical output for an optical switching / routing device according to one embodiment of the present invention. [Figure 12E] Figures 12A to 12E show the optical power-time profile of the laser pulse (Figure 12A) and the corresponding optical power-time profiles of the optical output for an optical switching / routing device according to one embodiment of the present invention. [Figure 13A] Figures 13A and 13B show the optical power-time profiles of the optical output for an optical switching / routing device according to one embodiment of the present invention. [Figure 13B] Figures 13A and 13B show the optical power-time profiles of the optical output for an optical switching / routing device according to one embodiment of the present invention. [Figure 14A] Figures 14A to 14C show the optical power-time profiles of the optical output for an optical switching / routing device according to one embodiment of the present invention. [Figure 14B] Figures 14A to 14C show the optical power-time profiles of the optical output for an optical switching / routing device according to one embodiment of the present invention. [Figure 14C]Figures 14A to 14C show the optical power-time profiles of the optical output for an optical switching / routing device according to one embodiment of the present invention. [Figure 15] Figure 15 shows a schematic diagram of the optical conversion device. [Figure 16A] Figures 16A to 16D show schematic diagrams of different embodiments of the optical conversion device shown in Figure 15. [Figure 16B] Figures 16A to 16D show schematic diagrams of different embodiments of the optical conversion device shown in Figure 15. [Figure 16C] Figures 16A to 16D show schematic diagrams of different embodiments of the optical conversion device shown in Figure 15. [Figure 16D] Figures 16A to 16D show schematic diagrams of different embodiments of the optical conversion device shown in Figure 15. [Figure 17A] Figures 17A to 17C show schematic diagrams of different embodiments of the optical resonator according to the embodiments of the present invention. [Figure 17B] Figures 17A to 17C show schematic diagrams of different embodiments of the optical resonator according to the embodiments of the present invention. [Figure 17C] Figures 17A to 17C show schematic diagrams of different embodiments of the optical resonator according to the embodiments of the present invention. [Figure 18A] Figures 18A to 18E show schematic diagrams of different embodiments of the optical waveguide according to embodiments of the present invention. [Figure 18B] Figures 18A to 18E show schematic diagrams of different embodiments of the optical waveguide according to embodiments of the present invention. [Figure 18C] Figures 18A to 18E show schematic diagrams of different embodiments of the optical waveguide according to embodiments of the present invention. [Figure 18D] Figures 18A to 18E show schematic diagrams of different embodiments of the optical waveguide according to embodiments of the present invention. [Figure 18E] Figures 18A to 18E show schematic diagrams of different embodiments of the optical waveguide according to embodiments of the present invention. [Modes for carrying out the invention]

[0065] Aspects and embodiments of the present invention will be described with reference to the accompanying drawings. Further aspects and embodiments will also become apparent to those skilled in the art. All documents referenced in this manuscript are incorporated by reference.

[0066] The following example describes a photonic transducer in which a voltage output from a single-photon detector generates an optical signal at a specified optical output port. The optical output signal can be a continuous wave (CW), a coherent pulse, or a single photon. This forms the basis of an "optical transistor" in which a pulsed optical input is switched (or not switched) by the detection (or non-detection) of a single photon. A conditional single-photon gate or switch can be provided so that if a single photon is detected, an operation on a second photon (e.g., a quantum optical operation defined on the application of quantum operators to the quantum state of light) is triggered.

[0067] We consider three types of optical inputs: continuous wave (CW), pulsed light, and single photons (e.g., Gaussian wave packets). These optical inputs are coupled into a waveguide, then coupled into an optical resonator (e.g., an optical ring resonator), and then decoupled out of the resonator to be coupled into the same or a different optical waveguide.

[0068] The following disclosure presents a detailed quantum mechanical model encompassing both optical loss and optical inverse scattering effects. The time-dependent voltage output of a single-photon detector is used to modulate (i.e., shift) the resonant frequency of an optical resonator, thereby altering the manner in which light couples to and decouples from the optical resonator. The inventors have found that if a sufficiently large voltage output is obtained from the single-photon detector, it is possible to cause a sufficient shift in the resonant frequency of the optical resonator, thereby stopping the coupling of input light, which was initially in a resonant state, to the optical resonator. The rate at which coupling (in-coupling) is stopped has been found to be determined by the time scale of the time-dependent voltage output of the single-photon detector. This is in contrast to out-coupling of light, which occurs on the time scale of the optical resonator (i.e., the reciprocal of the total loss rate of the resonator, and related to the resonator's Q factor). However, it was discovered that if the input light is not initially in resonance with the optical resonator, and the resonant frequency of the optical resonator subsequently shifts to bring the input light into resonance, the light couples to the optical resonator on the time scale of the ring, rather than on the time scale of the time-dependent voltage output of the single-photon detector. It has been found that using an optical resonator with a high Q factor results in lower losses from the resonator, and as a result, the time scale on which the light couples to the optical resonator is extended, significantly improving performance. As a result, the inventors discovered that much higher sensitivity and controllability can be achieved by first restricting the input light to a resonant state with the optical resonator, and then modulating the resonant frequency of the optical resonator to a time scale much shorter than the time scale of the time-dependent voltage output of the single-photon detector. The transition from resonant to non-resonant state is easy to implement. Simulations have shown that this method is more efficient. However, according to the present invention, it is also possible to implement the reverse process, namely, a process in which the optical resonator is initially in a non-resonant state with the input light, and then modulated to a resonant state.

[0069] The inventors are investigating the use of input light in the form of a continuous wave (CW). They have found that good performance can be obtained when using CW input light, provided that two optical waveguides are coupled to an optical resonator. The first output optical wave tube, contained within two optical wave tubes, may be positioned such that when there is no detection event from the single-photon detector, the optical output of the first output optical wave tube becomes as close to zero as possible, and at the same time, the light in the optical resonator decouples and couples to a further (second) output optical waveguide. Thus, when a single photon is detected, the input CW light ceases coupling to the optical resonator, thereby enabling an optical output from the first waveguide that is easily distinguishable from the optical output when no photon is detected by the single-photon detector. In this way, an optical signal is generated that was previously effective (i.e., almost or substantially) absent. This is a good property for an optical transducer.

[0070] The inventors also investigated the use of pulsed input light. This is equivalent to single-photon input, in terms of the proportion of the input signal coupled, provided that the bandwidth of the photon matches the bandwidth of the corresponding pulsed input light. The inventors discovered the conditions under which as much light as possible can be switched when a single photon is detected by a single-photon detector. Good performance is obtained when a single optical output waveguide is coupled to an optical resonator. This has been found to be effective in causing the system to emit as much light as possible (i.e., the optical output waveguide) when the optical resonator is in a non-resonant state with the pulsed input light.

[0071] The time-binning procedure for the output has also proven advantageous. As mentioned above, detection / non-detection can produce multiple peaks or a single peak in the output optical signal. Time binning to separate a single peak can produce a detection-dependent signal.

[0072] To switch as much light as possible, it has been found advantageous that the timescale of the optical pulse / photon be on the same order as the decay time of the optical resonator. This is advantageous because, otherwise, a long voltage signal decay time may be required in the detection signal generated by the single-photon detector. A long decay time is an undesirable use of time, as it makes it difficult to design a long detector response time and also difficult to align the timescales of each of the various other components. Furthermore, it has been found that without this careful tuning of the timescale, there will be insufficient light coupling from the input optical signal to the optical resonator, resulting in insufficient difference in output whether or not a single-photon detector is present. Through the inventors' research and modeling, it has been found that careful tuning of the system parameters allows for a regime in the output optical signal that includes a significant and reliable identifiable pulse / peak output when no photon is detected by the single-photon detector. When the single-photon detector detects a photon, the output optical signal may also include a significant and reliable different pulse / peak output. This allows the system to provide the functionality of an optical transducer or transistor, and / or a conditional gate.

[0073] The following disclosures aim to model the characteristics of a ring optical resonator coupled to one or two optical waveguides and a single-photon detector (SPD), such as a single-photon avalanche diode (SPAD) or a superconducting nanowire single-photon detector (SNSPD), configured to generate a voltage after the detection of a single photon, and to illuminate a preferred configuration for carrying out the invention. This voltage signal is used to modulate the resonant frequency of the ring optical resonator over time. The optical signal input to this system is either conventionally continuous wave (CW) or pulsed (e.g., a single-photon wave packet). This model includes effects such as optical power, wavefunction, and phase between the input optical signal and the output optical signal from the system, as well as the effect of optical backscattering within the system.

[0074] This model is presented for classical (CW and Gaussian) coherent states (both with and without backscattering effects) and includes the time dependence (both with and without backscattering effects) resulting from the voltage signal input to a single-photon detector. This model is also presented for any quantum state under the above conditions.

[0075] [Ring resonator: Classical description] An optical ring resonator typically consists of a structure in which a straight optical waveguide 3 is coupled to a circular optical waveguide 2, as shown in ring resonator 1 in Figure 1, or a structure in which two separate straight optical waveguides (3, 9) are optically coupled to the same circular optical waveguide 2, and therefore optically coupled to each other through the circular optical waveguide, as shown in ring resonator 11 in Figure 2.

[0076] In the first case (see Figure 1), the input light 4 (e.g., a continuous beam or pulse) that enters the ring resonator through the waveguide input port of the linear optical waveguide section is coupled (i.e., transferred) to the circular optical waveguide section, depending on the strength of the optical coupling at the coupling point (or short coupling region) 7 in the linear optical waveguide section that is close to (or in contact with) the circular optical waveguide section. Due to the presence of this optical coupling, a certain percentage of the light 5 is transferred from the portion of the input light 4 in the linear optical waveguide section to the circular optical waveguide section. The amount thus transferred depends on the strength of the optical coupling provided by the coupling point or short coupling region, and the wavelength of the light receiving the coupling in question.

[0077] On the other hand, the proportion of light 6 that completely passes through the straight optical waveguide section (from waveguide input to waveguide output) is sensitive to the proportion of light coupled to the circular optical waveguide section, and therefore the proportion of light that is not transmitted to the waveguide output of the straight optical waveguide section. The proportion of light 6 that completely passes through relative to the amount of input light 4 is defined as the transmittance T of the optical ring resonator and is given by the following equation:

number

number

number

number

Equation

Equation

[0078] As a result, the value of the optical frequency (i.e., the resonance frequency) that minimizes the transmittance is given by the following equation:

Equation

Equation

[0079] Referring to FIG. 2, in this arrangement, the transmittance of the light 6 passing through the two straight waveguide sections (3, 9) to the lower waveguide output port is given by the following equation:

Equation

number

[0080] The conditions for the minimum transmittance through the lower waveguide 3 and the maximum transmittance through the upper waveguide 9 are again expressed by the following equation:

number

number

number

[0081] T Lower Res The equation that defines r L -ar U If = 0, then T Lower Res This means that = 0. In this case, the transmittance T through the upper straight waveguide 6 is... Upper Res It takes the following form:

number

[0082] As a result, the relative change in the resonance wavelength (frequency) is equal to the relative change in the effective refractive index. Therefore, an important parameter regarding the ability to change the resonance wavelength (frequency) of an optical ring resonator is the dependence of the refractive index experienced by the light of the propagation mode in the resonator. This is a measure of the sensitivity of the system when intentionally modulating the refractive index n (Δn) as a means of modulating the resonance wavelength (Δλ res ) of the system or as a means of modulating the resonance frequency (Δω res ) of the system.

[0083] Figures 3A and 3B show an optical switch according to an embodiment of the present invention employing the optical ring resonator shown in Figure 1, respectively. The optical switch is a single-photon triggered optical signal switch and includes a ring resonator that functions as an optical router configured to route an optical signal 4 (continuous wave signal or optical pulse) output by a laser unit 140 to an input optical waveguide 14 optically coupled to the optical output port of the laser unit 140, and to propagate it forward along the input optical waveguide 14 toward the ring resonator 22. Routeping is performed by the action of the ring resonator described herein, subject to the detection of a single photon (27A / 27B). The optical router includes an optical ring resonator 22 configured to resonate at a resonant optical frequency within a resonant bandwidth determined by the refractive index n of the optical resonator. The input optical waveguide portion 14 is optically coupled to the optical ring resonator 22 by the input optical waveguide portion being physically close to the ring resonator 22 in the coupling region 7. The input optical waveguide section 14 is configured to receive an optical input signal 4 from an optical signal source (not shown) as input to the optical router. The optical switch includes an output optical waveguide section 18, which is an extension of the input optical waveguide section 14 and is therefore also optically coupled to an optical resonator. The output optical waveguide section 18 is configured to receive an optical signal 4 from the optical signal source via the input optical waveguide section 14 and output it from the optical router.

[0084] The optical switch further comprises a single-photon detector unit 20 configured to output an electrical detection signal in response to the detection of a single photon. The optical input port of the single-photon detector is coupled to the optical output end of a feed waveguide 21 for transmitting photons to the single-photon detector. The optical input end of the feed waveguide 21 is optically coupled to a single-photon source (not shown) from which a single photon is received and directed to the optical input port of the single-photon detector for detection. This single-photon source may be any suitable light source readily understood and available to those skilled in the art. The single-photon detector unit 20 is electrically coupled to an electro-optical modulator 26 configured to receive an electrical detection signal and output an electrical modulation signal in response to the electrical detection signal. An optional electrical contact portion 24 electrically connects the single-photon detector 20 and the electro-optical modulator 26. This electrical contact portion 24 provides signal processing or amplification of the electrical detection signal generated by the single-photon detector unit 20 and may include signal filtering elements or capacitive elements. For example, it is used to generate a larger output voltage pulse by passing a signal through a cascade array of nanowire detectors to amplify the output pulse from a single detector. Alternatively, or in addition, the electrical contact portion 24 may include an impedance-matching taper and / or a compact low-power signal amplifier.

[0085] The electro-optic modulator 26 is configured to modulate the refractive index n of the material forming the waveguide defining the optical ring resonator 22 by an electrical modulation signal in response to the detection of a single photon by the single-photon detector unit. The effect of the electrical modulation signal is on the spectral position ω at the center of the resonant bandwidth of the optical ring resonator. res0 Modulate (Δω resThis modulates the optical signal frequency, changing the resonant bandwidth from one that includes the optical signal frequency (Figure 3A) to one that does not include the optical signal frequency (Figure 3B). The effect of the spectral position modulation is to enable the optical input signal 4, which is transferred from the input optical waveguide section 14 to the output optical waveguide section 18 (Figure 3B), to be output from the optical switch as a non-resonant optical output signal without resonating within the optical resonator 22.

[0086] As shown in Figure 3A, if there are no photons 27A in the supply waveguide 21 to the single-photon detector 20, no photons are detected, and as a result, no electrical detection signal is generated. This means that the electro-optic modulator is not driven to modulate (Δn) the refractive index of the waveguide material forming the ring resonator (i.e., the modulator is in the "OFF" state). As a result, the resonant frequency (or resonant wavelength) is modulated Δω res (Δλ res This does not happen. This is because the resonant bandwidth of the ring resonator is configured to include the frequency (wavelength) of the input signal 4 input to the input waveguide portion 14, and because the ring resonator is critically coupled to the input waveguide portion 14, the input signal 4 is resonantly coupled to the ring resonator and not routed to the output waveguide 18. Critical coupling of a ring with a single waveguide input means high loss or low coupling ratio. In the case of a pulse input, the input signal is routed to the output waveguide, but with additional phase and time delays.

[0087] On the other hand, as shown in Figure 3B, when one or more photons 27B are detected through the supply waveguide 21, the single-photon detector 20 generates a photon detection electrical signal, which drives the electro-optic modulator 26 (i.e., switches the modulator "ON"), changing the resonant frequency (wavelength) and the bandwidth of the resonant profile of the ring resonator 22 to a resonant frequency (wavelength) position where the bandwidth of the resonant profile does not include the frequency (wavelength) of the input signal 4 in the input waveguide portion 14. As a result, the input signal 4 is not coupled to the ring resonator and is instead routed to the output waveguide portion 18.

[0088] Thus, the detection of a single photon by the single-photon detector 20 changes the function of the optical router 12 from a router that does not route the input optical signal 4 to the output waveguide section to a router that routes the input optical signal 4 to the output waveguide section as the output signal 10. In this way, single-photon detection affects how the impinging optical signal is redistributed between the ring resonator 22 and the output waveguide section 18.

[0089] Figures 4A and 4B show, respectively, an optical switch according to another embodiment of the present invention, employing the optical ring resonator shown in Figure 2. The optical switch has the structure of the optical switch described above with reference to Figures 3A and 3B, but further includes an additional output optical waveguide in the form of an upper output optical waveguide 12 (corresponding to the upper straight waveguide 9 in Figure 2), which is optically coupled to the optical resonator 22 at a distance in the optical coupling region 8 of the optical resonator.

[0090] As shown in Figure 4A, if there are no photons 27A in the supply waveguide 21 to the single-photon detector 20, no photons will be detected, and consequently, no electrical detection signal will be generated. This means that the refractive index of the waveguide material forming the ring resonator will not be driven to modulate (Δn) (i.e., the modulator is in the "OFF" state). As a result, the resonant frequency (or resonant wavelength) will be modulated Δω res (Δλ res This does not happen. This is because the resonant bandwidth of the ring resonator is configured to include the frequency (wavelength) of the input signal 4 input to the input waveguide portion 14, and because the ring resonator is critically coupled to the input waveguide portion 14, the input signal 4 is resonantly coupled to the ring resonator and routed to the waveguide output A of the upper waveguide 12. The input signal 4 is not routed as the optical output signal 10A to the waveguide output B of the lower waveguide portion 18.

[0091] On the one hand, as shown in FIG. 4B, when one or more photons 27B are detected via the supply waveguide 21, the single photon detector 20 generates a photon detection electrical signal, and this signal drives the electro-optic modulator 26 (i.e., switches the modulator to “ON”), changing the resonance frequency (wavelength) of the ring resonator 22 and the bandwidth of the resonance profile to a bandwidth that does not include the frequency (wavelength) of the input signal 4 input to the input waveguide portion 14. As a result, the input signal 4 is not coupled to the ring resonator 22 as the optical output signal 10B, but instead is routed to the waveguide output B of the lower waveguide portion 18.

[0092] Thus, the detection of a single photon by the single photon detector 20 changes the function of the optical router 12 from a router that routes the input optical signal 4 to the optical waveguide ica and outputs it from the optical waveguide output A to a router that routes the input optical signal 4 to the lower optical waveguide portion 18 and outputs it as the output signal 10B from the optical waveguide output B. Thus, single photon detection affects how the incident optical signal is redistributed between the upper optical waveguide portion 12 and the lower optical waveguide portion of 18.

[0093] [Quality factor (Q)] An optical resonator temporarily confines light three-dimensionally in its entirety, dramatically enhancing the electric field strength within the resonator compared to a light beam that freely propagates in a continuous medium.

[0094] The decay lifetime τ of the optical mode within the optical resonator may be regarded as follows as the rate of change of the energy ε(t) of the optical mode stored within the resonator: [Equation] This means that the stored energy ε(t) changes with time as follows: [Equation] This means that the quality factor Q is related to the ratio of the stored energy to its rate of change: [Equation]

[0095] Therefore, if L is the loss for each round trip "passage" of an optical mode through the resonator (for example, the passage of a photon), and l is the path length of each "passage," then the fractional loss per unit time is given by cL / nl, where n is the refractive index of the resonator material and c is the speed of light in a vacuum. Thus, it can be written as follows: τ = nl / cL

[0096] For example, the average number of photons N in a steady state in a low-loss ring optical resonator that is coherently driven in a resonant state is given as follows:

number

[0097] The quality factors related to optical resonators are the resonant frequency ω at which the resonator resonates. res And the resonance linewidth (e.g., FWHM) of the spectral resonance profile of the optical resonator.

number

number

[0098] Therefore, a spectral resonance profile with a narrow full width at half maximum (FWHM) is characteristic of an optical resonator with a large quality factor Q. This is because the resonance frequency ω of such a resonator is...res It only means that the spectral position of res shifts slightly, and the light that was initially resonant in the resonator becomes completely non-resonant (i.e., significantly deviated from resonance). Therefore, more generally, light of frequency ω can be considered to be within the “… resonance bandwidth …” of a resonator with quality factor Q in the sense of the terms used herein when the following conditions are satisfied:

Number

[0099] Therefore,

Number

Number

[0100] This means that the “… resonance bandwidth …” includes not only the exact resonance frequency ω res but also nearby adjacent frequencies that differ from the exact resonance frequency by less than half of the resonance linewidth (e.g., FWHM) of the spectral resonance profile of the optical resonator. As the value of the quality factor Q of the resonator increases, it can be seen that the “… resonance bandwidth …” becomes increasingly narrower centered around the exact resonance frequency position.

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[0103] The following discussion assumes a ring optical resonator formed using waveguides, but please note that the following analysis and conclusions are not limited to optical resonators of a specific structure and configuration. In fact, as stated above, the following analysis and conclusions are readily applicable to optical resonators of other structures and configurations.

[0104] The benefits of using optical resonators with a high quality factor may have to be weighed against the impact of manufacturing defects that cause optical loss from the resonator due to light scattering. While manufacturing defects exist in devices with low quality factors as well, their impact is amplified in resonators with high quality factors Q because photons reside in the resonator for longer periods. In other words, enhanced light confinement also enhances the interaction with scattering-causing defects. These effects are particularly important in quantum technology applications where it may be necessary to operate with a small number of photons.

[0105] For example, a photon in an optical resonator may escape from the resonator via a dedicated output channel, and this dedicated output channel can be used for a specific purpose, with a coupling ratio Γ from the resonator to the channel. Alternatively, scattering from the resonator may result in unwanted loss / escape with a loss ratio M. The probability P that a photon escapes into the dedicated output channel can be expressed as follows:

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[0106] Figure 5 shows a schematic diagram of a ring resonator model used to quantum mechanically describe the process occurring in the optical switch described above, with reference to Figures 3A and 3B.

[0107] Figure 6 shows a schematic diagram of a ring resonator model used to quantum mechanically describe the process occurring in the optical switch described above, with reference to Figures 4A and 4B.

[0108] Each ring resonator model has a resonant frequency ω0 and loss

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[0109] Below, we construct a calculation using the Heisenberg picture to describe the optical output of a system in response to its initial input state. The following analysis is performed in terms of linear dynamics, characterizing the related traveling optical modes involved in the related phenomena of the system. These modes include narrowband resonant modes of the optical resonator and continuous modes of the channel field from which light is injected and extracted. Furthermore, modes arising from scattering losses are also represented. By introducing appropriate coupling between these modes, we impart appropriate spectral, spatial, and temporal characteristics to the optical dynamics in the system. The methods, analyses, and conclusions presented in this book can be used to describe arbitrary structures supporting a set of optical modes weakly coupled to the input / output channel in a spatial region smaller than the wavelength of light. This is applicable to a wide range of resonator structures.

[0110] (Effective Hamiltonian) The following method generates the equations of motion using the known general formula of the Hamiltonian, which has been used in contexts where Maxwell's equations are used in the context of periodic media (e.g., notional three-dimensional photon crystals).

[0111] Sipe et al. [Reference [1]: Sipe et al., "Effective field theory for the nonlinear optical properties of photonic crystals": PHYSICAL REVIEW E 69, 016604 (2004)] showed that the displacement field D(r,t) corresponding to the electromagnetic field can be expressed as follows:

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[0112] The mode index α consists of the crystal wave vector k and the crystal band mode m within the Brillouin zone. According to Sipe et al., the steady-state form of the displacement field is the mode amplitude a α (t) a mk (t) can be written as follows:

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[0113] When the field mode is far from the Brillouin bandgap, or within the bandgap but close to the band edge, the amplitude f m It has been found that one of the (r,t) modes outperforms the others. This outperforming amplitude is known as the "principal component," and the Schrödinger equation can be used for the "principal component." In this regard, the "effective field" g(r,t) can be formulated for the modes as follows:

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[0114] The displacement field D(r,t) can be expressed using this effective field as follows:

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[0115] This discussion has been made for media that exhibit periodicity in all three spatial dimensions. Of course, this discussion can also be applied to media that exhibit periodicity in two or only one spatial dimension. Examples of media with periodicity in only two spatial dimensions include loop-shaped optical resonator structures (e.g., ring optical resonators, racetrack optical resonators, disk optical resonators, etc.). Examples of media with periodicity in only one spatial dimension include dielectric multilayer structures, distributed Bragg reflectors, and fiber Bragg lattice structures. More generally, an optical resonator can be considered to exhibit periodicity in the sense that the modes of light propagating within it repeatedly pass through, propagate along, or propagate within the structure of the resonator periodically (e.g., reciprocating reflection in a linear resonator, or a periodic loop in a loop-shaped resonator structure). Such structures are considered herein.

[0116] (Channel mode) The optical channel outside the resonator is assumed to encompass a continuum of modes localized in the transverse yz-plane and freely propagating in the longitudinal x-direction. The quantized electric displacement field operator D(r) can be expressed as follows:

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[0117] operator

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[0118] Photon field operator ψ J (x) is used to express the Hamiltonian Hch that describes light propagating within an isolated channel as follows:

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[0119] (Resonance mode) If we temporarily ignore the optical coupling with channels and scattering modes, we can assume that the resonator supports a discrete set of resonant modes J. The frequencies of these modes are ω J Therefore, the electric displacement field operator within the resonator can be expressed as follows:

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[0120] For each of the ring resonator's resonant modes J, a discrete annihilation operator b J A quantized harmonic oscillator described by is used. This operator is the one shown above in the equation for D(r). The Hamiltonian for these modes, neglecting the contribution of the zero-point energy, can be expressed as follows:

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[0121] (Resonator-channel coupling) The energy transfer between the resonator and the channel structure is described below. The coupling term in the Hamiltonian that defines the coupling between the ring operator and the channel field is derived. This coupling is defined to occur at a single point located at z = 0 within the channel. This is an accurate approximation under the condition that the spatial extent of the coupling region is small in practical applications. The coupling Hamiltonian has the following form: [Number] Here, γ J is the channel-ring coupling constant. In this model, like in a real system, the possibility that the coupling strength between different resonances is different is allowed.

[0122] (Scattering loss) As described above, the influence of defects in a high-Q optical resonator is amplified compared to the same influence present in the optical channel outside the resonator. For example, the roughness of the sidewalls of the resonator and other manufacturing defects cause photon loss from the resonator due to scattering. Generally, the scattering loss from the resonator in a given resonance can be described by including the term H SC in the Hamiltonian. This term describes a continuum of scattering modes having the annihilation operator D J (κ) and also describes the coupling between these scattering modes and the optical modes of the resonator: [Number] Here, ω J (κ) represents the frequency of the scattering mode, and [Number] represents these couplings to the modes of the resonator. Further, the field operator φ J (x) is introduced and defined as follows: [Number]

[0123] The coupling constant within the resonance range of the resonator in question

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[0124] The term ω J (κ) is expanded in the vicinity of the reference wave vector k<​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Note that this is the same form as the Hamiltonian that describes the hypothetical additional channel coupled to the resonator. Scattering losses are considered in the model described in more detail below.

[0126] In the above disclosure, the exponent J is the reference wave vector k J Note that this is explicitly applied to refer to different frequency ranges of interest corresponding to the quantity k. J This corresponds to the resonance of the optical resonator into which the channels are coupled. For the sake of simplification, in the following discussion we limit the discussion to one frequency range of interest corresponding to one reference wave vector k, and assume one resonance of the optical resonator into which the channels are coupled.

[0127] First, we ignore the inverse scattering effect of photons. This is because it corresponds to a linear model with a single ("pump") input (e.g., a single-frequency continuous-wave (CW) input or a Gaussian pulsed profile optical pulse). Single-mode operator b P =b(in the ring),ψ P,n =ψ n Let's begin. When a ring resonator is coupled to a single waveguide, the number of waveguides n is 1 (one). When a ring resonator is coupled to two independent waveguides, the number of waveguides n takes two values ​​(n=1,2), where n=1 represents the lower (input, conditional output) waveguide and n=2 represents the upper (conditional output) waveguide. Field φ P =φ represents a hypothetical mode propagating through the "phantom waveguide" and is used to model the optical loss from the system. The Hamiltonian considering linear effects (nonlinear effects are not included) is given as follows:

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[0128] The Hamiltonian described above, the subsequent analysis, and the conclusions herein are understood to be applicable to a wider range of optical resonator structures, not limited to (or not intended to be limited to) the ring optical resonator structure disclosed in the drawings. The ring optical resonator structure was chosen as an example of the application of the present invention because it was thought to help the reader better understand the present invention.

[0129] (Probability density and probability current density) At this point, the Hamiltonian term H waveguides ,H ring,L The (physical or conceptual) channels described by each are the field operators ψ n (x), φ(x), group velocity v n , has a coupling constant γ associated with the resonator. n It is useful to note that they are coupled by μ. Each of these Hamiltonian terms contains a component in the form of a probability density, as follows:

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[0130] These probability current density terms correspond to the product of the associated group velocity of the mode and the expected value of its momentum. Here, the expected value of the momentum of the field ψ is given using the momentum operator and the probability current density j as follows:

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[0131] (Model details) The following discussion and analysis assume a ring optical resonator structure optically coupled to two independent optical waveguides (n=1 and n~2). Naturally, when considering coupling with only a single optical waveguide, this is simply modeled as γ2=0. For example, refer to Figures 5 and 6 and consider the following conditions:

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[0132] As a simple way to consider dispersion effects within waveguides, rings, and materials, we can first take the waveguide operators immediately before and after the connection point to the ring (i.e., x=0) and divide them into "input" (when x<0) and "output" (when x>0) operators for the first (lower) waveguide and the "phantom waveguide" as follows:

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[0133] The single-point coupling model of loss corresponds to a state where there is some loss at each point of a ring optical resonator. Two main approaches have been proposed for this analysis: the first considers a continuous-wave optical input (CW) in a steady state, and the second considers a pulsed optical input, which is analyzed in frequency space, for example, using a Fourier transform.

[0134] [Continuous wave state] Under CW conditions (regime), the input is a single-frequency input with a certain frequency shift from the ring frequency, given as follows:

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[0135] Similar to phantom channels, a single input can be defined as follows to produce exactly the same result as multiple inputs: γα = Σ n γ n α n In this case, the inputs have the same frequency. Under CW conditions, this is therefore given as the (ring) solution:

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[0136] These equations show the extra "-" sign that appears in the phase of the ring output, which is a direct result of coupling to and from the ring.

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[0137] In particular, in critical coupling with zero detuning (Δ=0) and zero additional loss (μ=0),

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[0138] [Pulse conditions] The pulse solution is obtained by performing a Fourier transform on the operators as follows:

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[0139] Referring to Figure 8A, the spectral profile of the normalized pulsed power optical input 4 to the input (lower) waveguide 14 is shown. Here, the optical frequency ω is expressed in units of the spectral width (standard deviation, σHz) of the optical input pulse relative to the resonant frequency ω0 of the ring resonator (i.e., (ω0-ω) / σ). The inventors found that three different regimes arise depending on whether the spectral width of the optical pulse is (1) significantly smaller, (2) approximately equal, or (3) significantly larger compared to the linewidth of the resonant spectral profile of the ring resonator. The spectral width of the wave packet used here is relative to the spectral width of the input / output power because the optical power is obtained by squaring the wave packet function.

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[0140] Figures 8B and 8C show plots of output intensity calculated as a function of normalized relative frequency (i.e., (ω0-ω) / σ) for broadband input pulses in the lower output optical waveguide 18 (Figure 8B) and upper output optical waveguide 12 (Figure 8C). Lines labeled "critical" correspond to parameters where critical coupling occurs and no photon detection event occurs. The coupling ratio from the lower (input) optical waveguide to the resonant ring is shown as Γ in the graph. ↓ This is shown as follows: This ratio represents the line width of the ring resonator's resonant spectral profile in each curve of each graph.

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[0141] Figure 9A shows the time profile of the normalized pulsed power optical input 4 to the input (lower) waveguide 14. The unit of time is the decay time of the ring resonator.

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[0142] In Figures 8A, 8B, 9A, and 9B, we can see that the "critical coupling" very effectively transmits the power 10A from the input optical pulse (Figures 8A and 9A) to the upper output waveguide 12 (see Figure 6), resulting in almost no output power 10B being output in the lower optical waveguide 18.

[0143] [Consideration of backscattering] Backscattering can be considered by modeling it as an additional ring resonator as a backpropagation mode. The amount (i.e., rate) of backscattering gives the amount (i.e., rate) of coupling between these modes. Incoherent scattering can be modeled using a "phantom channel" as described above. This introduces a total of three couplings: Backscattering within the ring = ring-ring coupling Backscattering within a waveguide = waveguide-waveguide coupling • Waveguide-ring back coupling (∝μ,γ) These are modeled using parameters (ring-ring coupling), g (waveguide-waveguide coupling), and ε (ratio of ring-waveguide coupling), where εγ and εμ are the ring-waveguide couplings. Backscattering within the ring is introduced by including additional ring modes. Waveguide backscattering and backcoupling can be introduced by doubling the number of waveguides, γ N+n =εγ n and μ M+n =εμ n This results in a total of four waveguide modes, two of which are phantom waveguide modes and two are ring modes. These modes are H without backscattering. L =H L1 +H L2This can be considered as follows: Here, the group velocities are u2=-u1 and v3=-v4=-v1, and b2 propagates counterclockwise within the ring. Backscattering can be modeled using an additional coupled Hamiltonian as follows:

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[0144] The equation of motion for the channel operator in the lower (input) waveguide 14 is given as follows:

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[0145] When solving the wave equation, the velocity becomes negative in a channel where the wave propagates in the opposite direction, but Θ(x)-Θ(x+vt) is x - It is non-zero only in this case. This means that all ψ n<An additional "-" sign is introduced to make the equations equivalent. This solution is greatly simplified if either g(x)=0 (i.e., no inverse scattering from waveguide-waveguide) or g(x)=gδ(x) (i.e., inverse scattering exists only in interaction with the ring). Alternatively, the complete solution can also be obtained perturbatively. g(x)=0 is defined as Vernon and Sipe [References [2]: Z. Vernon and J. Sipe, "Spontaneous four-wave mixing in lossy microring resonators": Physical Review A, vol.91, no.5, p.053802, 2015. (arXiv:1502.05900v2[quant-ph] May 5, 2015); References [3]: Z. Vernon and J. Sipe, "Strongly driven nonlinear quantum optics in microring resonators": Physical Review A, vol.92, no.3, p.033840, This is reduced to (2015.(arXiv:1508.03741v1[quant-ph] August 15, 2015)), while g(x)=gδ(x) is attributed to McCutcheon [Reference [4]: ​​W. McCutcheon, "Gaussian nonlinear optics in coupled cavity systems: Back-scattering in micro-ring resonators" arXiv preprint arXiv:2010.09038,2020]. Since the latter reduces to the former when g=0, we will consider the latter case as follows:

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[0146] This results in the following:

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[0147] The equations of motion for the ring operator can be expressed in matrix form as follows:

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[0148] This allows us to derive the following relationship:

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[0149] [Time-dependent (without backscattering)] Returning to the equations of motion, for a time-independent Hamiltonian, we have the following:

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[0150] however, ω(t) = ω0 + ω1f(t) If the Hamiltonian's binding terms are changed to the following form:

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[0151] The Hamiltonian can also be written as follows: H = H0 + λH1 We want to convert this Hamiltonian into an effective Hamiltonian as follows: H' = H0' + λH1' + ... To do this, you can use unitary transformations that can be expressed as, for example, Dyson series or Magnus series: U = U0 + λU1 + ... To do this, we adopt the following definition:

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[0152] However, instead of taking the perturbation term as follows: λH1=ω1f(t) (Using double perturbation theory) we define it as follows: ΛH Λ1 +λH λ1 =ΛH coupling,rw +λω1f(t) This is γ n This is valid because ≪ω0,μ≪ω0 and ω1≪ω0. This means that H0 is H λ1 It commutes with H0+H Λ1 This means that a complete (non-perturbative) solution is known for . Therefore, we aim for a solution of the following form: H'=H0'+ΛH Λ1 ´+λH λ1 ´+λΛH Λ1λ1 ´ Note that when λ=0 or Λ=0, H'=H. The terms in the Magnus expansion are as follows:

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[0153] The integrand of the last term is given by the following equation:

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[0154] formula:

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[0155] One special case of this is when ω is time-dependent, for example, when the resonant frequency of a ring optical resonator is modulated / driven by an electrical signal (e.g., voltage) output from a superconducting nanowire single-photon detector (SNSPD) in single-photon detection. This electrical signal can be expressed as a voltage as follows:

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[0156] Figure 11A shows the temporal shape of the electrical signal output when a conducted nanowire single-photon detector (SNSPD) detects a single photon. Figure 11B shows the temporal shape according to the analytical approximation formula above. In this case, the equation of motion is expressed as follows:

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[0157] However, when integrating the experimentally corrected voltage output (for example, by substituting u = e -t ), a hypergeometric function that may impose an unnecessary computational load during integration is obtained. Therefore, for simplicity, the following analytical expression is used:

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[0158] Since the input of the wave function into the waveguide is a Gaussian function, this process can also be considered by using the Fourier transform instead. That is, use the following:

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[0159] However, the frequency of the input wavefunction may differ from the resonant frequency of the optical ring resonator. Therefore, we provide the following analysis, which is not based on a rotated basis, where the (unperturbed) resonant frequency of the ring is denoted as ω0 and the frequency of the input wavefunction (assuming no dispersion) as ω. In this case, the input is given by one of the following:

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[0160] Examples are shown in Figures 13A, 13B and 14A, 14B, 14C. For a pulsed optical input as shown in Figure 10A, the output at the time before photon detection is given by the following equation:

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[0161] Examples of these optical outputs are shown in Figures 10B, 10C, 10D, and 10E. Figure 10A shows the time profile of the normalized pulsed power optical input 4 to the input (lower) optical waveguide 14. The unit of time is the decay time of the ring resonator.

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[0162] Lines marked "critical" correspond to the parameters that cause critical coupling. The coupling ratio from the lower (input) optical waveguide to the resonator ring is shown as Γ on the graph. This ratio is the linewidth of the ring resonator's resonant spectral profile in each curve of each graph.

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[0163] In Figures 10D and 10E, we can see that the photon detection event under "critical coupling" conditions very effectively transfers power 10B from the input optical pulse to the lower output waveguide 18 (see Figure 6), resulting in almost no output power 10A output in the upper optical waveguide 12.

[0164] In the case of a pulsed optical input as shown in Figure 12A, the output after the detection of a single photon is shown in Figures 12B, 12C, and 12D. These will be discussed in detail below.

[0165] Alternatively, the SPD voltage output modulation f(t) can be approximated by a top-hat function as follows: f1(t) = Θ(t-t0) - Θ(t-t0-τ) d ´) Here, τ d ' is a numerical approximation of τ d This is related to the frequency shift of the ring, which is necessary for the light that was originally coupled to clearly separate from the ring.

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[0166] This is the point at which the detuning effect is most pronounced. This may be useful for approximating the system output when (numerical) integration using a more precise formula for SPD voltage output modulation is undesirable. For the parameters typically used in the examples disclosed here,

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[0167] This allows us to approximate the output without relying on numerical integration in both the time and frequency domains. Using this approximation, we obtain: Before the SPD detection event, as shown above:

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[0168] [Time dependence due to backscattering] Starting with the following equation:

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[0169] Since this is commutative, the solution is a Green's function solution and is given as follows:

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[0170] The correlation function of mode n at time (t1, t2) is given as follows:

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[0171] The correlation coefficients for pulsed optical input, shown in Figures 12A, 12B, 12C, and 12D, and the correlation functions for continuous wave (CW) optical input, shown in Figures 13A and 13B, are as follows: G N(t1,t2) = ψ >,N (t1)〉〈ψ >,N (t2) Referring to Figures 12A, 12B, 12C, 12D, and 12E, Figure 12A shows the time intensity profile of the pulsed optical input 4 at the input end of the lower waveguide 14 of the system shown in Figures 5 and 3A, or Figures 6 and 4A. The time is the decay time of the optical ring resonator.

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[0172] Figures 12B and 12C correspond to the system response schematically shown in Figures 6 and 4A. Figure 12B shows the simultaneous optical output power at the optical output 10B in the lower optical waveguide 18 in response to the pulsed optical input 4 at the input end of the lower waveguide 14 of the system schematically shown in Figures 6 and 4A. The time is the decay time of the optical ring resonator to match Figure 12A.

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[0173] Figure 12D corresponds to the system response schematically shown in Figures 5 and 3A. This figure shows the optical output power at the optical output 10 in the lower optical waveguide 18 in response to a pulsed optical input 4 at the input end of the lower waveguide 14 of the system in Figures 5 and 3A.

[0174] Figure 12E corresponds to the system response schematically shown in Figures 5 and 3A. This figure shows the backscattered light output power at the optical output 10C in the lower optical waveguide 14 in response to the pulsed optical input 4 at the input end of the lower waveguide 14 of the system in Figures 5 and 3A. Note that the intensity scale (vertical axis) of this graph is about one-tenth (1 / 10) of the corresponding intensity scale of the graph in Figure 12D, indicating a low backscattering level.

[0175] Figures 12B, 12C, 12D, and 12E show the optical output power under two different conditions: (1) when a single-photon detection event (SPD voltage output) occurs at time t=τ / 10 in the graphs of Figures 12B and 12C and at time t=-τ in the graph of Figure 12D; and (2) when no single-photon detection event occurs. These results correspond to the "critical coupling" of the waveguide and ring resonator, which is the coupling condition.

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[0176] From these results, we can conclude that when the modulation (frequency shift) of the ring resonator's resonant frequency is sufficiently large, single-photon detection by the SPD causes non-resonant input light to cease coupling to the ring at a time interval corresponding to the duration of the frequency shift modulation. This non-resonant light may then interact with light already present in the ring, which is in a non-resonant state and is departing from the ring at the ring's decay rate. In other words, the coupling of light to the ring may be delayed by the time scale of the SPD's electrical signal (e.g., voltage), but pre-resonant light already present in the ring continues to detach. Figures 12D and 12E correspond to the output optical signal caused by pulsed input light to the ring resonator when the ring resonator is coupled to only a single waveguide, as shown in Figures 5 and 3A, and appear to show a favorable configuration in which the output pulse intensity is relatively high and relatively narrow / sharp (at least with respect to the initial rise and fall of the output pulse). As a result, the configurations illustrated in Figures 3A and 5 may be more likely to generate output pulses that are easily distinguishable with and without a single-photon detection event. It provides a "cleaner" signal and couples all the light (except for losses) back into a single waveguide. This can be advantageous when used as a single-photon gate.

[0177] Figure 13A is a graph showing the optical output power at the optical output 10B in the lower waveguide 18 in response to the CW optical input 4 at the input end of the lower waveguide 14 when a single-photon detection event occurs at time t=0. Figure 13B is a graph showing the optical output power at the optical output 10A in the upper waveguide 12 in response to the CW optical input 4 at the input end of the lower waveguide 14 when a single-photon detection event occurs at time t=0. The results corresponding to the "critical coupling" of the waveguide and ring resonator are shown in the graph, and the coupling conditions

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[0178] Figures 14A, 14B, and 14C graph the optical output power at the optical output 10B in the lower waveguide 18 in response to the CW optical input 4 at the input end of the lower waveguide 14 when a single-photon detection event occurs at time t=0, respectively. Time represents the decay time of the optical ring resonator.

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[0179] Figure 14A shows the relatively long decay time of the SPD electrical pulse's time pulse shape, resulting in oscillations with multiple peaks in the output optical power. Note that these are actual oscillations of the output optical power and not merely oscillations of the optical phase.

[0180] Figure 14B shows that when the decay time of the SPD electrical pulse's time pulse shape is relatively short (compared to Figure 14A), the oscillations in output optical power observed in Figure 14A may be eliminated. However, as a trade-off, relatively lower optical output power is generated over shorter periods (note the vertical scale of the graph; the output power is reduced to about one-fifth).

[0181] Figure 14C shows how increasing the amplitude ω1 of the ring's resonant frequency shift (for example,

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[0182] The critical coupling of the waveguide and the resonator ring has a remarkable advantage: the optical output power at the optical output 10B in the lower waveguide 18 increases sharply from a substantially negligible value in response to the occurrence of a single-photon detection event and the increase in the SPD electrical pulse, and then rapidly decays back to a substantially negligible value immediately after the SPD electrical pulse decays. The width (Δt) of the optical output pulse 10B in the lower waveguide 18. widthThe width of the optical output pulse (Δt) can be defined as the full width at half maximum (FWHM), as shown in Figures 12B, 12D, and 13A. In this embodiment, the width of the optical output pulse (Δt) width ) is approximately equal to the decay time of the optical ring resonator:

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[0183] For example, a photodetector (not shown) may be provided as part of the optical components downstream of the output terminal of the lower waveguide 18 that responds to the detection of an optical switching signal or pulse, to issue a control signal to a component of the optical circuit, etc. The photodetector can be configured to consider that the detection of the optical switching signal or pulse has occurred once if the detection event occurs at any one of a series of detection time slots (e.g., detection time bins). The time of occurrence of such a detection event may be determined as the time associated with the detection time slot in which the detection event occurred (e.g., the temporal start, middle, or end of the detection time slot). Preferably, the duration of each time slot is greater than or equal to the width of the optical switching signal or pulse (e.g., FWHM) (e.g., greater than or equal to the decay time τ of the optical resonator). This means that the majority of the optical switching signal or pulse may reside within a single detection time slot, preventing the undesirable situation in which multiple “detection” events are triggered by the same optical switching signal or pulse spanning multiple detection time slots. Preferably, the duration of each time slot is no more than twice (×2) or three times (×3) the width of the optical switching signal or pulse (e.g., FWHM) (e.g., more than twice (×2) or three times (×3) the decay time τ of the optical resonator). This increases the likelihood of encompassing substantially the entirety of a single optical switching signal or pulse within a single detection time slot, while limiting the duration of the detection time slot to be similar to the duration of the optical switching signal or pulse.

[0184] Alternatively, or in addition, a photodetector (not shown) provided as part of an optical component located downstream of the output terminal of the lower waveguide 18 may issue a control signal to a component of the photon circuit, etc., in response to the detection of an optical switching signal or pulse, if the detected optical output power rises to a value greater than the output power when no photons are detected by the single-photon detector. The photodetector may include a signal threshold detector configured to compare the detected optical output power with a preset optical power threshold and issue a detection signal if the detected optical output power exceeds the preset optical power threshold. The clear and distinguishable nature of the switching signal or pulse under critical coupling conditions shown in Figures 12B, 12D, 13A, and 14A, 14B, and 14C has a special advantage in making this thresholding process efficient.

[0185] In particular, the inventors discovered that light already present in a ring resonator in a resonant state separates from the ring when it is de-resonant. It is desirable that the separation time frame be set later than the voltage modulation time frame so that the optical input pulse can pass through the ring (without coupling to the ring) before a large amount of non-resonant residual light (in the ring) is released from the ring and contributes to the optical output of the device.

[0186] By using a single waveguide coupled to an optical ring resonator, the effect of leakage from the ring resonator on the optical output can be reduced. Using a single optical waveguide increases the optical output, and the backscattered light output is relatively small compared to the optical output (e.g., about 10%).

[0187] By making the SPD voltage decay time relatively short, oscillations in the optical output power at the waveguide output can be suppressed to some extent. The SPD voltage decay time is the effective decay time τ d If (as defined above) is less than (or approximately equal to) the decay time τ of the resonator, it can be considered relatively short. The coupling ratio of light from the input waveguide to the ring resonator does not significantly affect the amplitude of the oscillation of the optical power of the output signal, at least for long SPD voltage decay times.

[0188] These results suggest that implementing a downstream detection scheme for detecting pulsed optical output generated by a switch / router responding to a pulsed optical input would enable a favorable implementation of the optical switch / router. A detection scheme suitable for such an optical output would involve detecting the output optical pulse (generated using the pulsed optical input) in one of a series of detection time bins (where each time bin has a duration of one or several times the pulse width (temporal) of the optical input pulse), and / or implementing a thresholding / device that counts the output optical pulse only if the detected optical output power is greater than the peak optical output power generated and detected by the optical switch / router when no photons are detected by the SPD.

[0189] As a further explanation of the "time binning / thresholding" method described above, consider, for example, a series of time bins that may (or may not) be approximately the same as (or equal to) the decay time of the resonator. For each of these time bins, a threshold power output is defined, and an output above this threshold is considered "1," while an output below the threshold is considered "0" (it is also possible to set multiple thresholds and multiple values). If no single photon is detected, the result is a specific binary (or other form) output sequence obtained by applying the thresholding rule above to a specific power distribution. If a single photon is detected, the output power distribution is significantly different (i.e., there are multiple peaks in at least one of the cases where the photon was detected / not detected, some overlap is expected, but at least one peak is at a different time position), so applying the threshold rule (or a similar rule) above will result in a different output binary sequence.

[0190] Figure 15 shows a schematic diagram of an optical conversion device 99 that performs single-photon conditional optical conversion. Figures 16A, 16B, 16C, and 16D show different implementation examples of the device in Figure 15.

[0191] The optical conversion device 99 is configured to detect a single photon 27B propagating into the device along a first waveguide 21 ("waveguide A") that is optically communicable with the single photon detector of the single photon transducer (switch / router) unit 100. In response to the detection of the single photon, the single photon transducer (switch / router) unit 100 outputs a laser pulse 131 to propagate along a second waveguide 130 ("waveguide B"). Optionally, the laser pulse 131 is input to a laser pulse shaping unit 132 via waveguide 131 ("waveguide B"), which shapes the time profile and / or spectral profile of the input laser pulse 131 into a desired new profile and outputs the shaped laser pulse 133 to the output optical waveguide of a pulse shaper 138. A laser pulse 131 (or optionally a shaped laser pulse 132) is input to an optical transformer 136, which includes a first optical input port optically coupled to the output optical waveguide 130 ("waveguide output B") of a single-photon transducer (switch / router) unit 100 (or, optionally, the output waveguide 138 of the pulse shaper, if used). The laser pulse 131 (or shaped 132) is then input to an optical transducer, where it is used to drive a nonlinear optical process, which performs a conversion on the optical signal input to the optical transducer 136 in a third optical waveguide (waveguide C) of the device. The third optical waveguide (waveguide C) is optically coupled to a second optical input port configured to receive the optical signal for the optical conversion.

[0192] Figures 3A, 3B, and 5, or Figures 4A, 4B, and 6, show schematic layouts of two embodiments of the optical switch / router, each of which has been described in detail above. It is understood that either of these two embodiments may be used as the single-photon transducer (switch / router) unit 100 of the optical converter 99. The embodiments of the optical switch / router shown in Figures 3A to 3C, Figures 4A to 4C, and Figures 5 and 6 are referred to below as separate examples of the single-photon transducer (switch / router) unit 100.

[0193] The structures shown in Figures 3A and 3B, or Figures 4A and 4B, can be implemented as an integrated photon chip including a single-photon transducer (switch / router) unit 100, the various different components of which include:

[0194] - A group of waveguides (12, 14, 16, 18) used to transmit optical signals (4, 10, 10A, 10B). These waveguides can be realized from any material transparent to the wavelength of the optical signal, such as silicon, silicon nitride, aluminum nitride, or thin-film lithium niobate. Generally, waveguides can transmit bidirectional (i.e., leftward or rightward) modes, continuous wave signals or pulsed signals, and high-intensity (i.e., laser light) or low-intensity (i.e., single-photon) signals. Waveguides may be partially outside the chip or may be incident from an optical fiber outside the chip.

[0195] - A high-quality ring resonator 22 coupled to a group of waveguides (12, 14, 16, 18), which may be made from a different material or manufacturing process than the group of waveguides (12, 14, 16, 18). The ring resonator 22 may be constructed by looping a waveguide structure in any of the above materials, or it may be another resonator structure as described above (e.g., disk resonator, linear resonator, photon crystal structure, etc.). In general, the resonator structure may be any of a variety of shapes (not necessarily circular). Preferably, it supports optical modes propagating in both clockwise and counterclockwise directions. Coupling of the resonator to the group of waveguides (12, 14, 16, 18) can be achieved and controlled by physically / spatially bringing the structures into close proximity. The resonant bandwidth of the resonator can be controlled as desired by adjusting the coupling to the group of waveguides (12, 14, 16, 18) or by adjusting the coupling to the surrounding loss modes.

[0196] - A chip-integrated single-photon detector 20 is positioned at the end of the first waveguide 21 and optically coupled to it. This single-photon detector may be implemented using either a superconducting nanowire detector or a single-photon avalanche photodiode. The detector is configured to absorb photons propagating through the first waveguide 21 in the direction toward the single-photon detector and generates an electrical signal in response to the reception of a single photon. The single-photon detector may be optimized to produce an optimal output voltage, for example, by arranging multiple superconducting nanowires in parallel or by increasing the load resistance of the detector drive circuit.

[0197] - An optional electrical contact 24 is configured to electrically connect the single-photon detector 20 to the electro-optical modulator unit 26. This electrical contact 24 preferably functions to perform on-chip processing and / or amplification for use in driving the electrical signal generated by the single-photon detector to the electro-optical modulator unit 26. Processing may include filtering of the voltage signal, and the electrical contact may include a suitable capacitive element suitable for filtering and / or signal amplification. This may be used to generate larger output voltage pulses by cascading multiple nanowire single-photon detectors to amplify the output pulse from a single detector, using an impedance matching taper, or using a compact low-power on-chip amplifier.

[0198] - The high-speed electro-optic modulator 26 is configured to modulate the refractive index of the ring resonator, thereby producing a change corresponding to the resonant frequency of the ring resonator 22. The electro-optic modulator may be configured to implement a process such as the DC Kerr effect or Pockels effect in the ring resonator material, or to inject carriers into the ring resonator material, in order to achieve the desired refractive index modulation. Methods and techniques readily available to those skilled in the art may be employed for this purpose. The modulator can be optimized using a combination of designed electrodes and high impedance to achieve a strong effect on the ring resonator (resonant frequency shift per voltage input).

[0199] With the various elements described above in place, the overall operation of the device proceeds as follows:

[0200] First, considering the case schematically shown in Figure 3A, the single-photon detector 20 does not generate an electrical signal, and the electro-optic modulator 26 has a default effect of being in a "resting" state with respect to the ring resonator. As a result, the ring resonator has a default frequency value (f) given by the total coupling intensity to all external optical modes. res) has a resonant frequency, which is determined by the manufacturing process used to create the optical switch / router. Figure 3C (upper graph) shows a schematic diagram of the transmission spectrum 140 of the ring resonator of the input and output optical waveguide structure (14, 18) through the ring resonator in the state shown in Figure 3A. That is, the frequency (ω) of the optical signal 4 in the input optical waveguide 14 signal ) corresponds to the resonant frequency of the ring resonator (or is at least contained within the resonant bandwidth 142) (i.e., ω res =ω signal As a result, the optical signal 4 in the input optical waveguide 14 is strongly resonantly coupled to the ring resonator 22 and is not substantially transmitted to the output optical waveguide portion 18.

[0201] Thus, the optical signals within the optical modes of the optical waveguide impinge into the ring resonator, and depending on their frequency distribution and the strength of the coupling between the optical modes of the waveguide and the resonator, they either couple into the resonator or disengage from it. In "critical coupling," the signal propagating to the right in the waveguide section 14 during resonance with the ring resonator does not exit the resonator 12. Similarly, in the case of a broadband signal propagating to the right in waveguide 14, the frequency components closest to the ring's resonance enter the resonator, while components outside the resonance do not enter the resonator and instead propagate to the right via waveguide 18 to the "waveguide output," thus escaping from the device.

[0202] As shown in Figure 3B, when a photon propagating to the right within the waveguide 21 is present, the single-photon detector absorbs this photon, thereby generating an output voltage signal. This signal drives the electro-optic modulator 26, which changes the resonant frequency of the ring resonator 22. As a result of the modulation, the resonant frequency of the ring resonator changes from the default frequency value (ω res ) from the shifted resonant frequency (ω res →ω res The frequency is shifted to +Δω, and the shifted resonant frequency is shifted by a frequency shift 144(Δω) determined by the modulator 26. Figure 3C (lower graph) shows a schematic diagram of the transmission spectrum 146 of the ring resonator 22 in the state shown in Figure 3B. That is, the frequency (ω) of the optical signal 4 in the input optical waveguide 14.signal The ) is excluded from the resonant bandwidth 148 of the ring resonator. This means that the optical signal 4 in the input optical waveguide 14 is no longer resonantly coupled to the ring resonator 22 and is transmitted to the output optical waveguide section 18. This controls how the incident optical signal in the input waveguide 14 is redistributed to the ring resonator to suppress the corresponding output signal, or to the output waveguide 18 to provide the corresponding output signal, thereby achieving single-photon triggered rerouting of the optical signal.

[0203] Next, considering the case schematically shown in Figure 4A, the single-photon detector 20 does not generate an electrical signal, and the electro-optic modulator 26 exhibits a default "rest" effect on the ring resonator. Again, the ring resonator has a default frequency value (ω) given by the total coupling strength to all external optical modes. res ) has a resonant frequency, which is determined by the manufacturing process used to create the optical switch / router. Figure 3C (upper graph) also applies to this configuration and shows a schematic diagram of the transmission spectrum 140 of the input and output waveguide structure (14, 18) through the ring resonator in the state shown in Figure 4A.

[0204] Optical signals within optical modes in an optical waveguide enter the ring resonator and, depending on their frequency distribution and the coupling strength between the optical modes in the waveguide and the resonator, either couple to or disengage from the resonator. This process corresponds to the redistribution of the entering optical signals to the exiting modes within the same optical waveguide. For example, if the coupling strength between the mode propagating to the right in waveguides 14 and 18 and the counterclockwise mode in the ring resonator is equal to the coupling strength between the mode propagating to the left in waveguides 12 and 16 and the counterclockwise mode in the ring resonator, the system can be said to be in a "critically coupled" state. In the "critically coupled" state, the signal propagating to the right in waveguide 14, which resonates with the ring resonator, propagates to the left only through waveguide 12 to "waveguide output A" and disengages from the resonator. Similarly, in the case of a broadband signal propagating to the right in waveguide 14, the frequency component closest to the ring's resonance propagates to the left via waveguide 12 and escapes, while the component outside the resonance propagates to the right via waveguide 18 to "waveguide output B" and escapes. The waveguide section (waveguide 3) does not receive the optical signal from the direct output of the optical resonator 22, but it may receive the backscattered component of the ring's optical output 10, and the optical output 10 is coupled to waveguide 12, which is heading towards "waveguide output A".

[0205] As shown in Figure 4B, when a photon propagating to the right within waveguide 21 is present, the single-photon detector absorbs this photon, thereby generating an output voltage signal. This signal drives the electro-optic modulator 26, which changes the resonant frequency of the ring resonator 22. As a result, the optical signals incident on waveguides (12, 14, 16, 18) are redistributed to the corresponding output signals, realizing a change in the optical signal path triggered by a single photon. For example, in "critical coupling," the frequency component of the broadband optical signal propagating to the right within waveguide 14 that previously resonated with the ring resonator and escaped via waveguide 12 as "waveguide output A" now propagates to the right via waveguide 18 and escapes as "waveguide output B." Figure 3C (lower graph) shows a schematic diagram of the transmission spectrum 146 of the ring resonator 22 in the state shown in Figure 4B.

[0206] Alternative embodiments are schematically shown in Figures 4D, 4E, 4F, and 4G. These embodiments correspond to a configuration where the single-photon detector 20 does not detect a photon, the modulator 26 is in the "OFF" state, and therefore does not output an electrical signal. Thus, the electro-optic modulator 26 exhibits a "rest" (or "OFF") default effect with respect to the ring resonator, and the resonator's resonant frequency is set to the default frequency value (ω res ) is the result. Figure 4C (upper graph) shows a schematic diagram of the transmission spectrum 147 of the input and output waveguide structures (14, 18) coupled to the ring resonator in the state shown in Figure 4D. In other words, the frequency (ω) of the optical signal 4 in the input optical waveguide portion 14 is signal ) is the resonant bandwidth of the ring resonator, 149 (i.e., ω res =ω signal It is excluded from +Δω). This means that the optical signal 4 in the input optical waveguide 14 is not resonantly coupled to the ring resonator 22 and is not transmitted to the output optical waveguide section 18.

[0207] Figure 4E shows the optical switching / routing device of Figure 4D in the second switching / routing state when the single-photon detector 20 detects a photon. The modulator 26 is in the "ON" state and therefore generates an electrically modulated signal. Thus, the electro-optic modulator 26 exerts an "active" (or "ON") effect on the ring resonator, and the resonator's resonant frequency is shifted from the default frequency value to the shifted resonant frequency by a frequency shift of 145 (-Δω) determined by the modulator 26 (ω res →ω res -Δω=ω signal +Δω-Δω=ω signa ), and as a result the ring resonator enters a state of resonance with the input optical signal 4. Figure 4C (lower graph) shows a schematic diagram of the transmission spectrum 144 of the input and output waveguide structures (14, 18) coupled to the ring resonator in the state shown in Figure 4E. That is, the frequency (ω) of the optical signal 4 in the input optical waveguide section 14 signal ) is included in the resonant bandwidth 143 of the ring resonator (i.e., ω res =ω signalThis means that the optical signal 4 in the input optical waveguide 14 is resonantly coupled to the ring resonator 22 and is not transmitted to the output optical waveguide portion 18.

[0208] The optical switching / pathing configuration according to one configuration of the present invention shown in Figures 4F and 4G is similar to the configuration shown in Figure 4D, except that a second output waveguide 12 is added. When the modulator is "OFF", the input optical signal 4 that does not resonantly couple to the ring resonator 22 is not passed for output at waveguide output A (see Figure 4F), but instead is passed along output waveguide 18 for output at waveguide output B. On the other hand, when the modulator is "ON", the input optical signal 4 that resonantly couples to the ring resonator 22 is passed to output waveguide 12 for output at waveguide output A (see Figure 4G), and is not passed along output waveguide 18 for output at waveguide output B.

[0209] [Single-photon transducer] The single-photon transducer (switch / router) unit 100 of the optical converter 99 may be implemented as follows: A ring resonator and waveguide can be constructed / fabricated with the component arrangement shown in Figures 4A and 4B so that the system is in a "critically coupled" state. Next, an optical pulse corresponding to a broadband optical signal or single photon propagating to the right is injected into the optical waveguide 14 ("waveguide input") such that its frequency spectral width is small compared to the spectral frequency width of the resonator 22. The single-photon detector 20, the electrical contact 24 (optional) 24, and the electro-optical modulator 26 are configured such that the duration of the effect (modulation) that the modulator has on the ring resonator is sufficiently long compared to the temporal duration of the optical signal in waveguide 14. When these conditions are met, and there are no photons in waveguide 21 and no single-photon detection event occurs, the optical signal in waveguide 14 propagates to the left through optical waveguide 12 toward waveguide output A and escapes from the device. When a single photon propagates to the right within the optical waveguide 21, a single-photon detection event occurs, and then the modulation of the resonant band position of the ring resonator 22 coincides with the optical signal in the waveguide 14 entering the resonator, the optical signal propagates to the right through the optical waveguide 18 towards the waveguide output B and escapes from the device.

[0210] The optical conversion device 99 provides a means for conditioning a laser pulse (e.g., a strong pulse) based on the detection of a single photon, as described above. As a result, a method for generating single-photon conditional optical conversion becomes possible. An example of the arrangement of the optical conversion device 99 is schematically shown in Figures 15 and 16A to 16D.

[0211] This example includes:

[0212] - Optical waveguides (110, 130, 133, and 134) used to transmit optical signals. As described above, these waveguides could be realized in a number of integrated photon platforms, e.g., silicon, silicon nitride, aluminum nitride, or thin-film lithium niobate. Waveguides generally support multiple spectral modes, transverse modes, and polarization modes, and the optical field can be a continuous wave or a pulsed wave. The quantum states of light confined in these waveguides are considered in a completely generalized sense, i.e., they can be either Gaussian (e.g., compressed light) or non-Gaussian (e.g., single photon). Furthermore, these quantum states may be quantum entangled and / or correlated with quantum states of other physical systems not explicitly described or illustrated.

[0213] - A single-photon transducer (switch / router) unit 100 is configured such that the optical input terminal at the end of waveguide 21 is optically coupled to the optical output terminal of waveguide 110 ("Optical Waveguide A") of optical converter 99. Thus, the single-photon detector 20 can receive and detect a single photon 27B input to waveguide 110 ("Waveguide A"). Upon detecting such a single photon, the single-photon transducer (switch / router) unit 100 responds by generating a strong laser pulse 131 in the output optical waveguide 18 of the unit 100 for output at its "Waveguide Output B" and for supply to waveguide 130 ("Waveguide B") of optical converter 99, which is optically coupled for this purpose. Photons in the waveguide 110 (waveguide A) of the optical conversion device 99 may be detected using a single-photon detector device 20 having one of several configurations, which may be selected from a superconducting nanowire single-photon detector; or a single-photon avalanche diode. In this example, the conversion is performed by such a device.

[0214] - The pulse shaper (132) modifies the optical signal 131 supplied through waveguide 130 ("waveguide B"). Such modification could be achieved by linear passive elements such as optical filters or active elements such as electro-optical modulators or acoustic-optical modulators, as would be obvious to those skilled in the art.

[0215] - The optical converter unit 136 (for example, a multimode optical converter such as a nonlinear optical element) uses the laser pulse (131 or 133) received from the single-photon transducer unit 100 (or pulse shaper 132) to perform optical conversion on the optical mode of the laser pulse received in waveguide B and the optical mode of the optical signal 135 simultaneously received through the second input waveguide 134 ("waveguide C"), thereby generating the optically converted optical output result 137.

[0216] Depending on the configuration and settings of the optical converter unit 136, the transformations performed on the optical signal received through the second input waveguide 134 ("waveguide C") include, but are not limited to, phase displacement, compression, or rotation in phase space. These can be realized by combinations of available integrated optical components such as optical resonators, waveguides, and modulators, as illustrated below with reference to Figures 16A to 16D.

[0217] [Compression operation] In this configuration, the optical transducer unit 136 is configured to perform single-mode optical compression (e.g., photon pair generation) in the second input waveguide 134 ("waveguide C"). This can be achieved, for example, in a periodically polarized, inverted thin-film lithium niobate waveguide where quasi-phase matching is optimized for type 0 pair generation, i.e., both photon production pairs are generated in the same polarization and spatial modes as the excitation light, are frequency-degenerate, and are compressed to a single-mode output state. In another embodiment, the laser pulse 133 may be configured to excite a helical or ring resonator in a highly nonlinear tertiary material such as silicon, silicon nitride, or gallium arsenide, and generate compression by self-phase modulation. By adjusting the phase-energy matching conditions, the nonlinear waveguide can generate frequency-non-degenerate photon pairs, resulting in a two-mode compression conversion in two of the modes of the second input waveguide 134 ("waveguide C").

[0218] [Passive operation: Phase shift] In this configuration, the optical transducer unit 136 is configured to include a passive phase-shift optical element for implementing a phase shift in the quantum state of light received in the second input waveguide 134 ("waveguide C"). The passive phase-shift optical element may be an electric optical waveguide modulator acting on the second input waveguide 134 ("waveguide C") within the optical transducer unit 136. Therefore, the optical waveguide 130 ("waveguide B"), the pulse shaping unit 132, and the first optical input waveguide 138 of the optical transducer 136 can be replaced in the apparatus 99 with an electrical transmission line (Figure 16C) arranged to transmit an electrical pulse signal from the single-photon transducer unit 100 to the optical transducer unit 136. This electrical pulse signal is used to drive the electric optical waveguide modulator.

[0219] [Passive action: Displacement] Alternatively, the pulse shaping unit 132 may be configured to generate a bright, coherent state output pulse 133 that is mode-matched with the mode of the second input waveguide 134 ("waveguide C"). A passive phase-shifting optical element may perform optical mixing on a high-transmittance beam splitter to realize the optical displacement of the quantum state of the target optical mode.

[0220] The examples in Figures 16A(1) and 16B(2) can be realized, for example, by a spontaneous parametric down conversion (SPDC) process or a four-wave mixing (FWM) process, which are carried out using resonators / helves / waveguides, etc., respectively. (2) Process and χ (3) This is done by a process, and the corresponding Hamiltonian is as follows:

number

[0221] The example in Figure 16C(3) shows, for example, using the electrical output of an SPD to directly adjust the refractive index of a given section of material (as disclosed in the remainder of this specification), causing a phase shift in the input state |ψ> to the next output state: e iφ │ψ> This can be achieved by providing [something].

[0222] The example in Figure 16D(4) shows the following displacement operator applied to the input state │ψ>:

number

[0223] Figures 17A to 17C show schematic diagrams of different embodiments of the optical resonator according to the present invention. In the embodiments shown in Figures 3A, 3B, and 5, a linear waveguide coupled to a loop-shaped optical resonator structure (for example, a circular ring structure in these examples) is employed. However, in other embodiments, the linear waveguide may be coupled to the linear resonator structure. While not exhaustive, examples are schematically shown in Figures 17A to 17C.

[0224] For example, Figure 17A shows a linear optical resonator structure 150A formed within the material (or at least a portion thereof) of the core of an optical waveguide. Two fiber Bragg photon structures 152 (e.g., distributed Bragg reflectors) with a resonator optical cavity 153 formed between them are formed within the waveguide core and separated by a linear separation along the waveguide axis, defining a linear lattice-free region extending along the waveguide core between the two separated fiber Bragg lattice structures. Light 162 input to the linear optical resonator structure 150A is coupled to the resonator optical cavity 153 via one of the two separated Bragg lattice structures 152 and, depending on the parameters of the resonator, may resonate 164 within the resonator optical cavity 153 or pass through the cavity 153 and be output as output light 162. The electro-optic modulator 26 (having the same function as item 26 in Figures 3A and 3B) is positioned to apply an electrical signal generated by the single-photon detector (item 20 in Figure 3A) to modulate the refractive index of the core material of the optical waveguide that defines the optical resonator 153, thereby shifting the frequency at which the resonant spectral profile of the linear optical resonator structure 150A is centered or positioned, as described above. The linear optical resonator structure 150A may be formed within the input optical waveguides (14, 18) of the optical switch / router described above with reference to Figures 3A and 3B, omitting the optical ring resonator 22.

[0225] Figure 17A shows an alternative linear optical resonator structure 150B formed within a dielectric multilayer film that defines an optical waveguide (or at least a portion thereof). Two distributed Bragg reflectors 156, between which a resonator optical cavity 154 is formed, are formed by the dielectric multilayer film and separated by a linear partition along the axis of the multilayer film, defining a linear lattice-free region extending along the axis of the multilayer film between the two separated distributed Bragg reflectors 156. Light 162 input to the linear optical resonator structure 150B is coupled to the resonator optical cavity 154 via one of the two separated distributed Bragg reflectors 156 and, depending on the parameters of the resonator, may resonate 164 within the resonator optical cavity 154 or pass through the cavity 154 and be output as output light 162. The electro-optic modulator 26 (having the same function as item 26 in Figures 3A and 3B) is positioned to apply an electrical signal generated by the single-photon detector (item 20 in Figure 3A) to modulate the refractive index of the dielectric multilayer core material that defines the resonant optical cavity 154, thereby shifting the frequency at which the resonant spectral profile of the linear optical resonator structure 150B is centered or positioned, as described above. The linear optical resonator structure 150B may be formed within the input optical waveguides (14, 18) of the optical switch / router described above with reference to Figures 3A and 3B, omitting the optical ring resonator 22.

[0226] Figure 17C shows an alternative linear optical resonator structure 150C formed by a photonic crystal defect structure within the dielectric material of an optical waveguide (or at least a portion thereof). The photonic crystal is formed as a periodic linear arrangement of cylinders of a first dielectric material (e.g., solid material, air layer, or void) embedded in the surrounding material of the waveguide, where the surrounding material of the waveguide is a second dielectric material different from the first dielectric material. The defect in the periodicity of the periodic linear arrangement of cylinders is provided by the absence of one or more cylinders that should be present according to the periodicity of the arrangement. This defect, i.e., the absence of one or more cylinders from the periodic arrangement, is defined by defining an optical resonator optical cavity 160 in the linear space between two separated subsections of the linear arrangement of cylinders 158 separated by a linear partition along the axis of the waveguide, thereby defining a linear cylinder-free region extending along the axis of the photonic crystal between the two separated subsections of the linear arrangement of cylinders 158. The light 162 input to the linear optical resonator structure 150C is coupled to the resonator optical cavity 160 via one of two separate subsections of the linear array of cylinders 158, and depending on the parameters of the resonator, may resonate 164 within the resonator optical cavity 160 or pass through the cavity 160 and be output as output light 162. An electro-optical modulator 26 (having the same function as item 26 in Figures 3A and 3B) is positioned to apply an electrical signal generated by a single-photon detector (item 20 in Figure 3A) to modulate the refractive index of the dielectric material of the waveguide defining the optical cavity 160, thereby shifting the frequency at which the resonant spectral profile of the linear optical resonator structure 150C is centered or positioned, as described above. The linear optical resonator structure 150C may be formed within the input optical waveguide (14, 18) of the optical switch / router described with reference to Figures 3A and 3B, omitting the optical ring resonator 22.

[0227] The detailed analysis described above uses a loop-shaped optical resonator structure (e.g., a ring) as an example, but please note that this analysis can be generalized to other optical resonator structures such as linear optical waveguides.

[0228] Figures 18A to 18E each show an example of a waveguide structure suitable for forming an optical waveguide and resonator structure according to the present invention.

[0229] Figure 18A shows an embedded channel waveguide in which a waveguide core 171 of a high refractive index (n1) is embedded in a surrounding medium 170 of a low refractive index (n2) with a width “w” and a depth “d”. The waveguide core can have any cross-sectional shape, but is usually rectangular.

[0230] Figure 18B shows a strip stacked waveguide 172 formed by stacking a dielectric strip 175 with an intermediate refractive index n3 < n1 or a metal strip that facilitates optical confinement in the width “w” direction on a planar waveguide (already providing optical confinement in the depth “d” direction) having a low refractive index (n1) layer 174 under a high refractive index (n2) slab 173. The waveguide core of the strip type waveguide is a high refractive index (n1) region under the stacked strip 175, the thickness is determined by the thickness “d” of the high refractive index (n1) region, and the width “w” is defined by the width of the stacked strip 175.

[0231] Figure 18C shows a ridge type waveguide having a structure similar to the strip type waveguide. The ridge type waveguide has a strip or ridge 177 with a width “w”, a depth “d”, and a high refractive index (n1) disposed on a planar structure 176 of a low refractive index (n2), which functions as a waveguide core. Since the ridge type waveguide is surrounded by air (or a coating material) with a low refractive index in three directions, it has a strong optical confinement effect.

[0232] Figure 18D shows a rib type waveguide having a structure similar to the strip type or ridge type waveguide. The rib type waveguide has a strip 181 having a width “w” and a height “h” with the same high refractive index (n1) as the underlying high refractive index planar layer 180 and is different in that it constitutes a part of the core of the waveguide. The total thickness of the planar layer 180 and the strip (height “h”) is represented by “d”. The planar layer is disposed on a planar structure 179 of a low refractive index (n2).

[0233] The four types of waveguides shown in Figures 18A to 18D are usually called rectangular waveguides, having a thickness "d" (or height "h") in the x-direction and a width "w" in the y-direction, but their shape is not usually exactly rectangular.

[0234] Figure 18E shows a diffuse waveguide created by forming a high refractive index region 183 with depth "d" and width "w" within a substrate 182 by dopant diffusion. As an example, there is a LiNbO3 waveguide in which a high refractive index (n1) core is formed by diffusing Ti within a low refractive index (n2) substrate material. Due to the diffusion process, the core boundary within the substrate is not clearly defined. The diffuse waveguide also has a thickness "d" defined by the diffusion depth of the dopant in the x-direction and a width "w" defined by the distribution of the dopant in the y-direction.

[0235] Any of the above waveguide structures can be used in the present invention. Preferred waveguide structures are rib waveguides, ridge waveguides, and strip-type laminated waveguides. Suitable dimensions are that the depth or thickness of the waveguide core is in the range of d = about 200 nm to about d = 800 nm, and the width of the waveguide core is in the range of w = about 300 to about w = 2000 nm. The preferred wavelength of the optical signal 4 guided by the optical waveguide of the present invention may be in the range of about 700 nm to about 1600 nm. The bending radius of a loop-shaped resonator structure, such as the ring resonator 22, can be in the range of about 10 μm to about 200 μm.

[0236] The features disclosed in the above description, or in the following claims, or in the accompanying drawings, are appropriately expressed in their particular form, or as means for performing the disclosed function, or as methods or processes for obtaining the disclosed results, and can be used, alone or in any combination of such features, to realize various forms of the present invention.

[0237] Although the present invention has been described in conjunction with the embodiments described above, many equivalent modifications and variations will become apparent to those skilled in the art in this disclosure. Therefore, the embodiments of the present invention disclosed above are illustrative and not limiting. Various modifications can be made to the described examples without departing from the spirit and scope of the invention.

[0238] To avoid any ambiguity, the theoretical explanations provided herein are intended to aid the reader's understanding. The inventors do not intend to be bound by any of these theoretical explanations.

[0239] The section headings used herein are for structural purposes only and should not be construed as limiting the subject matter described herein.

[0240] Throughout this specification (including the following claims), unless the context requires otherwise, the words “comprise” and “include,” as well as variations such as “comprises,” “comprising,” and “including,” mean to include the integer or step or group of integers or group of steps described, and not to exclude other integers or steps or group of integers or group of steps.

[0241] In this specification and the appended claims, the singular forms “a,” “an,” and “the” are to be interpreted as including the plural unless the context clearly intends otherwise. Ranges may be expressed as “about” a particular value and / or “about” another particular value. Where such ranges are expressed, another embodiment includes a range from a particular value and / or another particular value. Similarly, where a value is expressed as an approximation using the preceding term “about,” the particular value is understood to constitute another embodiment. The term “about” with respect to numbers is arbitrary and means, for example, ±10%. [Prior art documents] [Non-patent literature]

[0242] [References] To further explain and disclose the present invention and the related state of the art, several references are cited above. All of these references are listed below. The entirety of these references is incorporated herein.

[0243] [Non-Patent Document 1] [1] Sipe et al. "Effective field theory for the nonlinear optical properties of photonic crystals": PHYSICAL REVIEW E 69, 016604 (2004) [Non-Patent Document 2] [2] Z. Vernon and JESipe, "Spontaneous four-wave mixing in lossy microring resonators": Physical Review A, vol.91, no.5, p.053802, 2015. (arXiv:1502.05900v2[quant-ph] May 5, 2015) [Non-Patent Document 3] [3] Z. Vernon and J. Sipe, "Strongly driven nonlinear quantum optics in microring resonators," Physical Review A, vol.92, no.3, p.033840, 2015. (arXiv:1508.03741v1[quant-ph] August 15, 2015) [Non-Patent Document 4] [4] W. McCutcheon, "Gaussian nonlinear optics in coupled cavity systems: Back-scattering in micro-ring resonators," arXiv preprint arXiv:2010.09038,2020.

Claims

1. An optical switch that receives an optical signal of a given optical signal frequency from an optical signal source and outputs the optical signal, The optical router is configured to route the optical signal on the condition of detecting a single photon, The aforementioned optical router is An optical resonator configured to resonate at a resonant optical frequency within a resonant bandwidth, wherein the resonant bandwidth is determined by the refractive index of the optical resonator, An input optical waveguide portion, which is optically coupled to the optical resonator and is operable to receive the optical input signal from the optical signal source as an input to the optical router, The input optical waveguide portion and the output optical waveguide portion, which is optically coupled to the optical resonator and is operable to receive the optical signal for output from the optical router, The aforementioned optical switch further, A single-photon detector unit configured to output an electrical detection signal in response to the detection of a single photon, Includes an optical modulator connected to the single-photon detector and configured to output an electrically modulated signal in response to the electrically detected signal, The optical modulator modulates the refractive index of the optical resonator using the electrical modulation signal, and the resonant bandwidth, (a) The resonant bandwidth is changed from one that includes the optical signal frequency to one that does not include the optical signal frequency, thereby causing the optical input signal to be transmitted to the output optical waveguide portion as a non-resonant optical output signal output from the optical switch, or (b) Change the resonant bandwidth from one that does not include the optical signal frequency to one that includes the optical signal frequency, thereby causing the optical input signal to be transmitted to the output optical waveguide portion as a resonant optical output signal output from the optical switch, An optical switch configured to modulate in one of the following ways.

2. The input optical waveguide portion and the output optical waveguide portion are each a portion of a single continuous optical waveguide that is optically coupled to the optical resonator in the optical coupling region of the optical resonator. The optical switch according to claim 1, wherein the input optical waveguide portion extends to the optical coupling region, and the output optical waveguide portion extends from the optical coupling region.

3. The optical switch according to claim 2, wherein the continuous optical waveguide is critically coupled to the optical resonator.

4. Equipped with an additional output optical waveguide, The optical switch according to claim 2 or 3, wherein the continuous optical waveguide and the further output optical waveguide are separate optical waveguides that are separately optically coupled to the optical resonator in each of the separate optical coupling regions of the optical resonator.

5. The optical switch according to claim 4, wherein the further output optical waveguide is critically coupled to the optical resonator.

6. The optical switch according to claim 4, wherein the further output optical waveguide portion is optically coupled to the optical resonator with a coupling ratio substantially equal to the coupling ratio to which the output optical waveguide portion is optically coupled to the optical resonator.

7. The optical modulator is configured to modulate the refractive index of the optical resonator with the electrical modulation signal at a preset modulation time interval T, thereby modulating the resonant bandwidth at the preset modulation time interval. The optical switch according to any one of claims 1 to 6, wherein the modulation time interval T starts from the detection of a single photon by the single-photon detector unit.

8. The output optical waveguide portion has a coupling ratio of Γ １ It is optically coupled to the optical resonator, The coupling rate Γ １ is smaller than the reciprocal of the modulation time interval (Γ １ <1 / T), During use, the optical input signal resonating within the optical resonator is During the aforementioned pre-set modulation time interval T, a non-resonant state occurs. The non-resonant optical output signal output from the optical switch is coupled to the optical resonator with a coupling ratio of Γ １ The optical switch according to claim 7, wherein the signal is transferred to the output optical waveguide portion.

9. The output optical waveguide portion has a coupling ratio of Γ １ It is optically coupled to the optical resonator accordingly, The single-photon detector unit is configured to output the electrical detection signal in the form of a voltage pulse, and the voltage value of the electrical detection signal is a preset voltage attenuation rate Γ ｄ The voltage pulse peak value decreases accordingly. The voltage attenuation rate Γ ｄ is Γ that is larger than the coupling rate ｄ > Γ １ , the optical switch according to any one of claims 1 to 8.

10. The optical resonator has an optical loss rate [Number 227] It has, The optical modulator modulates the resonant bandwidth by modulating the refractive index of the optical resonator, and the resonant frequency shift ω １ It is configured to change its frequency position by The aforementioned resonant frequency shift ω １ The optical loss rate [Number 228] An optical switch according to any one of claims 1 to 9, having a value exceeding [a certain value].

11. The output optical waveguide portion is optically coupled to the optical resonator according to the coupling ratio Γ1. The optical resonator has an optical loss rate having a coupling ratio Γ1 greater than 1. [Number 229] It has, [Number 230] The optical switch according to any one of claims 1 to 10.

12. The optical switch according to any one of claims 1 to 11, wherein the optical resonator includes a ring optical resonator.

13. The optical switch according to any one of claims 1 to 12, wherein the optical resonator has a Q factor of 1,000,000 or more.

14. In the aforementioned optical signal source, The output optical waveguide portion is optically coupled to the optical resonator according to the coupling ratio. The optical switch according to any one of claims 1 to 13, wherein the optical signal source is configured to output an optical signal in the form of an optical pulse having a pulse duration width exceeding the reciprocal of the coupling ratio.

15. The optical switch according to any one of claims 1 to 14, comprising an optical signal source configured to output an optical signal having a given optical signal frequency.

16. The optical switch according to claim 15, wherein the optical signal source is configured to output an optical signal in the form of a continuous optical output.

17. The optical switch according to claim 15, wherein the optical signal source is configured to output an optical signal in the form of an optical pulse consisting of multiple photons or no more than one photon.

18. The optical switch includes the one described in any one of claims 1 to 17, An optical switching assembly further includes an output monitoring unit that generates a detection signal in response to the presence of an optical output signal from the optical switch.

19. The output monitoring unit is configured to determine the presence or absence of the optical output signal depending on whether the detected optical output power exceeds a preset detection power threshold. The optical switching assembly according to claim 18, wherein the preset detection power threshold exceeds the optical output power detected by the output monitoring unit when there is no electrical detection signal from the single-photon detection unit.

20. The optical signal source is configured to output an optical signal in the form of an optical pulse having a pulse time width σ, The output monitoring unit is configured to determine the presence of the optical output signal within a monitoring time interval Δt. The duration of the monitoring time interval does not exceed the pulse time width, Δt ≤ σ, and the optical switching assembly according to any one of the preceding claims when subject to claims 17 and 18.

21. The optical resonator has a light loss rate [Number 231] It has, The optical switching assembly further includes an output monitoring unit that generates a detection signal in response to the presence of an optical output signal from the optical switch, The output monitoring unit is configured to determine the presence of the optical output signal within a monitoring time interval Δt. The duration of the aforementioned monitoring time interval is the reciprocal of the optical loss rate. [Number 232] Do not exceed, [Number 233] The optical switching assembly according to claim 18 or 19, or claim 20 as a reference to claim 18.

22. The output monitoring unit is, Further additional optical signal input ports for receiving further optical input signals, An optical converter unit is optically coupled to the aforementioned further optical signal input port and configured to apply a preset optical conversion to the further optical input signal, conditional on the generation of a detection signal, thereby generating a converted optical signal. An optical switching assembly according to any one of claims 18 to 21, comprising: an optical signal output port that outputs the converted optical signal as an optical output signal.

23. The optical switch receives an optical signal of a given optical signal frequency from an optical signal source and outputs the optical signal, The aforementioned optical switch is The optical router is configured to route the optical signal on the condition of detecting a single photon, The aforementioned optical router is An optical resonator configured to resonate at a resonant optical frequency within a resonant bandwidth, wherein the resonant bandwidth is determined by the refractive index of the optical resonator, An input optical waveguide portion, which is optically coupled to the optical resonator and is operable to receive the optical input signal from the optical signal source as an input to the optical router, The input optical waveguide portion and the output optical waveguide portion, which is optically coupled to the optical resonator and is operable to receive the optical signal for output from the optical router, The aforementioned optical switch further, A single-photon detector unit configured to output an electrical detection signal in response to the detection of a single photon, An optical modulator connected to the single-photon detector and configured to output an electrically modulated signal in response to the electrically detected signal, wherein the optical modulator is configured to modulate the refractive index of the optical resonator using the electrically modulated signal, and to change the resonant bandwidth from a resonant bandwidth that does not include the optical signal frequency to a resonant bandwidth that includes the optical signal frequency, thereby suppressing the transmission of the optical input signal to the output optical waveguide portion as an optical output signal output from the optical switch, The system includes an output monitoring unit that generates a detection signal in response to the presence of the optical output signal output from the optical switch, The output monitoring unit further, Further optical signal input ports for receiving further optical input signals, An optical converter unit is optically coupled to the aforementioned further optical signal input port and configured to apply a preset optical conversion to the further optical input signal, conditional on the generation of a detection signal, thereby generating a converted optical signal. An optical switching assembly comprising an optical signal output port for outputting the converted optical signal as an optical output signal.

24. The aforementioned pre-configured optical conversion is Conversion to a single-mode optically compressed state, Conversion to a two-mode optically compressed state, Transformation to an optically phase-shifted quantum state, The optical switching assembly according to claim 22 or 23, comprising one or more of the following: conversion to a displaced quantum state.

25. An integrated optical circuit comprising an optical switch according to any one of claims 1 to 17, or an optical switching assembly according to claims 18 to 24.

26. This optical switching method involves switching an optical signal of a given optical signal frequency from an optical signal source by routing the optical signal, conditional on the detection of a single photon. The process of providing an optical resonator configured to resonate at a resonant optical frequency within a resonant bandwidth, wherein the resonant bandwidth is determined by the refractive index of the optical resonator, The process of providing an input optical waveguide portion that is optically coupled to the optical resonator and is operable to receive the optical input signal from the optical signal source as an input to the optical router, The process includes providing an output optical waveguide portion that is optically coupled to the input optical waveguide portion and the optical resonator and is operable to receive the optical signal for output from the optical router, The optical switching method further, A step of providing a single-photon detector unit configured to output an electrical detection signal in response to the detection of a single photon, The step of providing an optical modulator connected to the single-photon detector and configured to output an electrically modulated signal in response to the electrically detected signal, The optical modulator modulates the refractive index of the optical resonator using the electrical modulation signal, and the resonant bandwidth is, (a) The resonant bandwidth is changed from one that includes the optical signal frequency to one that does not include the optical signal frequency, thereby causing the optical input signal to be transmitted to the output optical waveguide portion as a non-resonant optical output signal output from the optical switch, or (b) Change the resonant bandwidth from one that does not include the optical signal frequency to one that includes the optical signal frequency, thereby causing the optical input signal to be transmitted to the output optical waveguide portion as a resonant optical output signal output from the optical switch, A method of optical switching, comprising the step of modulating to one of the following.

27. This optical switching method involves switching an optical signal of a given optical signal frequency from an optical signal source by routing the optical signal, conditional on the detection of a single photon. The objective is to provide an optical resonator configured to resonate at a resonant optical frequency within a resonant bandwidth, wherein the resonant bandwidth is determined by the refractive index of the optical resonator. To provide an input optical waveguide portion that is optically coupled to the optical resonator and is operable to receive the optical input signal from the optical signal source as an input to the optical router, The invention includes providing an output optical waveguide portion that is optically coupled to the input optical waveguide portion and the optical resonator and is operable to receive the optical signal for output from the optical router, The optical switching method further, To provide a single-photon detector unit configured to output an electrical detection signal in response to the detection of a single photon, To provide an optical modulator connected to the single-photon detector and configured to output an electrically modulated signal in response to the electrically detected signal, The optical modulator modulates the refractive index of the optical resonator using the electrical modulation signal, changing the resonant bandwidth from a resonant bandwidth that does not include the optical signal frequency to a resonant bandwidth that includes the optical signal frequency, thereby suppressing (for example, preventing) the transmission of the optical input signal to the output optical waveguide portion as an optical output signal output from the optical switch. The optical switching method further, A step of generating a detection signal in response to the presence of the optical output signal from the optical switch, A step of providing a conversion unit and receiving further optical input signals with the conversion unit, The conversion unit performs the steps of applying a pre-set optical conversion to the further optical input signal, conditional on the generation of the detection signal, to generate a converted optical signal. An optical switching method comprising the step of outputting the converted optical signal.

28. The optical switching method according to claim 26 or 27, wherein the pre-configured optical conversion includes one or more of the following: conversion to a single-mode optical compression state, conversion to a two-mode optical compression state, conversion to an optical phase-shift quantum state, and conversion to a displacement quantum state.

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