Parallel parametric devices

Abstract

A parametric system (1) comprising two or more parametric devices (3,4,21,22), arranged in parallel to each other, the parametric system (1) comprising a first input arranged to receive an input signal, means (2, 20, 43, 83) to split the input signal into two or more signal branches, wherein each signal branch is provided to one of the parametric devices (3,4,21,22), means to supply at least one pump signal to each of the parametric devices alongside the input signal, such that each signal branch undergoes an n-wave mixing process at the corresponding parametric device (3,4,21,22), means (16, 20', 20", 27, 48, 70, 84) to combine the output of the parametric devices (3,4,21,22) into an output signal, wherein the output of each parametric device (3,4,21,22) includes signal components including: an amplified signal portion, one or more pump signal and an idler signal; and means to control the relative phase of the pump signals and / or signal branches at each parametric device (3,4,21,22) such that the output signal includes at least a first output signal component formed by the constructive interference of a signal component from each parametric device (3,4,21,22) and a second output signal component formed by the destructive interference of a signal component from each parametric device (3,4,21,22).

Description

[0001] Parallel parametric devices

[0002] The present application relates to a parametric system and a method of processing at least one signal. In particular, but not exclusively, the application is related to the use of two or more parametric devices arranged in parallel.

[0003] In quantum noise limited parametric amplifiers or any other parametric devices, the noise is reduced to near the quantum limit, meaning the sensitivity of the amplifier or other device approaches the fundamental limit of sensitivity imposed by the uncertainty principle.

[0004] There are many fields which would benefit enormously from building and operating quantumlimited parametric amplifiers and parametric frequency converters with enough gain, bandwidth, and power handling for multiplexed readout and versatility. Whether it is desired to detected axion dark matter or perform a superconducting qubit readout, the task remains that of detecting a weak microwave signal with small number of photons and reading the signal from a detector. In order to do so, such microwave signals need to be amplified so that it could be further processed with conventional electronics.

[0005] Desirables characteristics of quantum-limited parametric devices include the ability to isolate the amplifier components and the element to be read out from the noisy electrical environment.

[0006] Travelling-wave parametric amplifies (TWPAs) are one example of an amplifier that could potentially achieve noise levels approaching the quantum limit. There are a number of different types of travelling wave parametric amplifiers, including, inter alia, Josephson junction based travelling parametric amplifiers (J-TWPA), TWPAs composed of transmission lines made up of chains of coupled symmetric / asymmetric superconducting quantum interference devices (SQUIDs) or combinations of a variety of junctions, or kinetic inductance TWPAs (KI-TWPA) based on superconducting thin film of certain quality. There may be many more types of TWPAs, and the teachings disclosed herein would apply to any type of parametric amplifier or other parametric device.

[0007] In a TWPA or other types of parametric amplifiers, a weak input signal tone is propagated in a superconducting transmission line alongside a strong signal, known as the pump tone. A supercurrent passing along the transmission line alters the superconductor density of states of the transmission line and lowers the energy gap, with the inductance per unit length having a nonlinear dependence on the current. This nonlinear behaviour, which is not unlike the nonlinear Kerr effect in an optical material where the refractive index becomes intensity dependent, results in particular conditions (energy, momentum conservation and phase matching) in parametric signal gain and the mixing of tones at three, four or more different frequencies. Three-wave mixing occurs when a DC current or magnetic bias is added to the amplifier, and results in a signal photon of frequency JSstimulating the conversion of a single pump photon of frequency a>pinto a signal photon of frequency a>sand an idler photon of frequency a>i, the latter being an inherent, unavoidable by-product of this conversion, with conservation laws dictating the relationship

[0008] <i)p = a»s+ <Dj.

[0009] Four-wave mixing (4WM) requires two pump tones and a signal tone to generate an idler tone with frequencies related by

[0010] In the case of degenerate four wave mixing process where <DPI= a>P2, the above relation simplifies to a>i = 2 a>p— a>s.

[0011] Parametric amplification relies on a nonlinear process, such as a nonlinear reactance (inductance or capacitance) and as such the dissipation can be made arbitrarily small such that Johnson and other noise can be altogether eliminated, allowing the device to be effectively lossless and quantum-limited.

[0012] Different operational modes of the superconducting parametric amplifiers described above can be distinguished: degenerate four wave mixing, four wave mixing, and three-wave, and variants thereof.

[0013] "A wideband, low-noise superconducting amplifier with high dynamic range", Byeong Ho Eom et al, Nature Physics, b, 623 2012, discloses a TWPA formed from a superconducting wire. Loading elements are provided periodically along the wire to provide stopbands at predetermined frequencies in the dispersion relation of the wire, enabling phase matching between the input signal, idler signal, and the pump signal.

[0014] Phase-matching the pump and input signal is desirable because parametric gain is maximised when efficient energy conversion is achieved via phase-matching which compensates inter alia for unavoidable dispersion in the materials and waveguides. "Resonant Phase Matching of Josephson Junction Travelling Wave Parametric Amplifiers", Kevin O'Brien et al, Physical Review Letters, 113, 157001, 2014 discloses a TWPA formed from an array of Josephson junctions. A series of resonators are coupled to the Josephson junction embedded superconducting transmission line. The resonators again provide a stopband at a predetermined frequency in the dispersion relation of the array, giving phase matching between the input signal and the pump signal.

[0015] "Travelling-wave parametric amplifier based on a chain of coupled asymmetric squids", M. T. Bell and A. Samolov, Phys. Rev. Applied, 4:024014 2015 disclosed a Josephson junction based TWPA consisting of a chain of asymmetric Superconducting Quantum Interface Devices (SQUIDs), a flux-tuneable device wherein the pump power dependent phase modulation terms are a function of both the pump power and the flux bias point of the SQUID.

[0016] EP 3 424 143 Bl discloses a four-wave mixing transmission line for use in a TWPA. The transmission line includes dispersion control elements arranged along the transmission line provide means to control the dispersion relation of the transmission line and thus control the total phase difference between the various signals present, including pumps, input signals and idlers.

[0017] The TWPAs discussed above still suffer from several issues, including inter alia complex and often difficult to control pump injection, no means of pump cancellation, no means of signal and idler discrimination, gain ripples, zero-gain gap, and gain roll off.

[0018] A dual pump approach may help mitigate the zero gain gap problem and the gain roll off. However, the output spectrum is distorted when compared to the input spectrum due to mixing of the idler and signal to be amplified, except for situations where the signal and idler frequencies are the same. This is true for all types of parametric amplifiers, including the narrower bands JPAs, because in all cases the idler will be generated irrespective of the process (whether it is a three wave mixing or a four wave mixing process) to conserve momentum.

[0019] The mixing of the idler tone and signal to be amplified may be mitigated by using a bandpass filter to remove half of the spectrum both at the input, before the signal tone is fed to the parametric amplifier, and after the parametric amplifier output. However, this results in only half the bandwidth of the parametric amplifier being used.

[0020] In addition to the above, parametric amplifiers also may suffer from non-negligible reflections, as the gain profile is very sensitive to the impedance difference at different stages, in particular the input and output ports of the device. This is because it is an amplification device, hence a small difference would be amplified, hence causing unwanted gain ripple issue. Due to the difficulties in designing and manufacturing a TWPA where the input and outputs are exactly impedance-matched to the external circuit, care must often be taken to prevent any backwards propagating reflected signals from returning to the input port of the circuit and thus potentially interfering with any system being measured. Even if the parametric device is perfectly impedance matched, if the subsequent components are not, the signal, or especially noise, would be reflected towards the parametric devices, and potentially get amplified and fed back to the component before the parametric device. If used alongside qubits, such reflection signals may dephase said qubits or otherwise cause parametric oscillations in the amplifier. J-TWPAs have proved a useful substitute for the JPAs which were used in experiments such as the Axion Dark Matter experiment (ADMX). These JPAs suffered from being single port devices, which meant the signal had to enter and exit the device through the same port, making the use of circulators or isolators unavoidable. When used in astronomical detectors, such as the JTWPA used in the Axion Dark Matter experiment as reported in "Dark matter axion search using a Josephson Travelling wave parametric amplifier", Bartram et. a!., Rev Sci Instrum 1 April 2023; 94 (4): 044703, circulators need to be used alongside TWPAs to both shield the element to be read by the TWPA (i.e., the microwave cavity) from the electronics noise and to shield the electronics themselves from any residual stray fields required by the experiment. In such situations, use of circulator or isolators alongside TWPA may also be needed to prevent the reflected signal re-entering the TWPA from the output port. An isolator or circulator is therefore often used alongside TWPAs. However, isolator / circulators are often bulky, add unwanted noise and are bandwidth limited.

[0021] A parametric amplifier or frequency converter requires the injection of strong pump(s) to allow for wave mixing. However, the strong pump(s) would exit the device together with the detected signal and the generated idler. The pump is often many orders of magnitude stronger than the detected signal, hence will significantly affect the operation of any subsequent component(s). For example, such strong pumps may result in driving the subsequent amplifier chain into saturation, and hence causing the entire system unusable. Therefore, in practical use of parametric devices, the pump tone(s) needs to be eliminated after the device. This can be done in several ways, but all require a series of additional components and complicated operation methods. The pump(s) needs to be injected to the parametric devices with minimal effect to the incoming weak signal. The conventional method to combine the pump(s) and signal tone before the parametric device is using a coupler. For example, one way consists of using a lOdB coupler to co-inject the strong pump and weak signal. However, this implies that 10% of the weak signal is then lost to the terminated port, which is not ideal. The need for pump cancellation often also requires the input pump tone to be split before entering the parametric device, hence further complicating the operation of the device. In short, the TWPA cannot be operated as a modular device and requires many more components to be used.

[0022] Addressing issues such as pump injection, pump cancellation, isolation and circulation of back- propagating modes, as well as idler and signal discrimination requires complex circuitry having multiple components. These components may be bulky and / or heavy, and occupy valuable cryogenic space if the amplifier is held at low temperatures. This issue is only marginally mitigated by miniaturisation. These components would also be required to be mounted at different locations e.g., some components near the TWPA, some at different temperature stages, and some components metres away from the TWPA at room temperature, with cables and wires between them. This implies that the entire system needs to be modified so that the TWPA can be used. Therefore, the TWPA devices in use nowadays in such systems are not modular and plug-and-play.

[0023] In the following the words "signal" and "tone" may refer to both the input signal to be amplified and / or processed, the amplified signal, the pump signals, the generated idler signal, and any electronic signal in general.

[0024] According to a first aspect of the invention, there is provided a parametric system comprising two or more parametric devices arranged in parallel to each other, the parametric system comprising a first input arranged to receive an input signal. The parametric system may further comprise means to split the input signal into two or more signal branches, wherein each signal branch is provided to one of the parametric devices. The parametric system may further comprise means to supply at least one pump signal to each of the parametric devices alongside the input signal, such that each signal branch undergoes an n-wave mixing process at the corresponding parametric device. The parametric device system may further comprise means to combine the output of the parametric devices into an output signal, wherein the output of each parametric device includes signal components including: an amplified signal portion, one or more pump signal, and an idler signal. The system may further include means to control the relative phase of the pump signals and / or signal branches at each parametric device such that the output signal includes at least a first output signal component formed by the constructive interference of a signal component from each parametric device and a second output signal component formed by the destructive interference of a signal component from each parametric device.

[0025] The n-wave mixing process may involve three tones or more. The output of each parametric device may include additional signal components such as harmonics.

[0026] The parametric devices may be amplifiers and / or frequency converters and / or any other type of parametric device.

[0027] The parametric devices may be non-resonance parametric devices. These non-resonance parametric devices may be transmissive or reflective. Transmissive non-resonance parametric devices may function as amplifiers, resulting in travelling wave parametric amplifiers (TWPAs). The parametric devices may be resonance parametric devices. These resonance parametric devices may be transmissive or reflective.

[0028] Reflective -resonance parametric device may function as amplifiers, resulting in traditionally named JPAs.

[0029] The parametric device may be a TWPA or frequency converter.

[0030] The output signal may include a third output signal component which may arise from further splitting of the output of the parametric devices.

[0031] At the means to combine signals one or more additional signal components may undergo interference. This interference may be completely destructive, or completely constructive, or partially constructive or partially destructive.

[0032] The pump signals provided at the input of each of the parametric devices may stem from the splitting of a single pump signal with an external splitting means, and wherein the resulting two pump branches may be provided to the parametric device system between the means to split the signals and the parametric devices.

[0033] The pump signals provided at the input of each of the parametric devices may stem from the splitting of a single pump signal provided at an input of the means to split the input signal. The means to split the signals may comprise a power divider comprising a three port network.

[0034] The means to recombine the signal may comprise a three port network.

[0035] The three port network may be such that the output signals are substantially in phase with each other, irrespective of the phase of the input signals. Instead of a three port network, the parametric device may employ a diplexer, a circulator, or any suitable component.

[0036] The means to split the signals may be any suitable n port network, where n may be one, two, three or more. The means to recombine the signals may comprise any suitable n-port network, where n may be one, two, three or more.

[0037] The means to control the relative phase of the pump signals and / or signal branches may comprise means to apply a DC bias or magnetic field or other means across one or more of the parametric devices to alter the effective electrical length of the device. This means across one or more of the parametric devices may also be equivalent to adjusting the length of the signal branches.

[0038] The means to split the input signal into two or more signal branches and the means to control the relative phase of the pump signals and / or signal branches may be provided by a four port device. The means to combine the signals may comprise a four port device. Each output of the four port device may have a phase difference between signal components provided at the same input.

[0039] The four port device may be a symmetric coupler. The four port device may be an asymmetrical coupler.

[0040] The input signal may be provided at a first the input port of the four port device, and the pump signal may be provided at a second input of the four port device.

[0041] An additional pump signal may be provided at the first input of the four port device alongside the input signal.

[0042] The means to control the relative phase of the pump signals and / or signal branches at each parametric device may be arranged such that at a first output, at least some of the output signal components from different parametric devices destructively interfere and at least some of the output signal components from different parametric devices constructively interfere, and at a second output, at least some of the output signal components from different parametric devices destructively interfere and at least some of the output signal components from different parametric devices constructively interfere.

[0043] Any suitable configuration of the parametric devices in parallel may be used, including configurations where the parametric devices can be cascaded before or after another component in one or both branches of the parametric devise system.

[0044] Different output signal components may constructively interfere at each output of the four port device, and different components may destructively interfere at each output of the four port device.

[0045] At one or both outputs of the four port device, one or more additional signal components may undergo interference. This interference may be completely destructive, or completely constructive, or partially constructive or partially destructive.

[0046] The means to control the relative phase of the pump signals and / or signals may comprise a phase shifting means provided between the means to split the signals and the means combine signals on any branch to provide means for modifying the phase of the signal components in that branch.

[0047] The phase shifting means may be provided before or after the parametric device.

[0048] The ports of the four port device may be A, B, C and D, wherein A is a first input port, B is a first output port, C is a second input port and D is a second output port, wherein port B comprises a through signal from port A and a coupled signal from port C, and port D comprises a through signal from port C and a coupled signal from port A. A phase difference may be introduced between through signals and coupled signals at an output.

[0049] The input signal may be coupled to port A of the splitting coupler. The output signal may be collected from the port C of the combining four port coupler.

[0050] At least one output signal component of the parametric device system may be fed to another parametric device system to process another signal.

[0051] At least one output signal component of the parametric device system may be fed to another parametric device system in a cascading series of parametric device systems wherein each parametric device system receives at least one signal component from a preceding parametric device system. One or more signal component at an output of the means to combine signals may be redirected to an input port of the means to split signals.

[0052] The signals at the output of the means to combine signals may propagate through a means to mix signals and then may propagate to another mean to combine signals.

[0053] The means to mix signals may comprise frequency converters and / or modulators. The means to mix signals may comprise a signal demodulator.

[0054] The means to control the relative phase of the pump signals and / or signal branches at each parametric device may be separate to the means to split the input signal into two or more signal branches, the means to combine the output of the parametric devices into an output signal, and the parametric devices.

[0055] According to a second aspect of the invention there is provided a method of processing at least one signal using a parametric system comprising two or more parametric devices, arranged in parallel to each other, the method comprising splitting an input signal into two or more signal branches, and providing each signal branch to one of the parametric devices, supplying at least one pump signal to each of the parametric devices alongside the input signal; at each parametric device performing an n-wave mixing process (where n may be three or more); The method may further comprise combining the output of the parametric devices into an output signal. The output of each parametric device includes signal components may include: an amplified signal portion, one or more pump signal and an idler signal and other harmonics. The output may comprise further signals. The method may further comprise controlling the relative phase of the pump signals and / or signal branches at each parametric device such that the output signal includes at least a first output signal component formed by the constructive interference of a signal component from each parametric device and a second output signal component formed by the destructive interference of a signal components from each parametric device.

[0056] The parametric devices may be operated as amplifiers and / or frequency converters and / or any other type of parametric device.

[0057] The parametric devices may be non-resonance parametric devices. These non-resonance parametric devices may be transmissive or reflective. Transmissive non-resonance parametric devices may function as amplifiers, resulting in travelling wave parametric amplifiers (TWPAs). Reflective resonance parametric device may function as amplifiers, resulting in traditionally named JPAs. The parametric devices may be resonance or non resonance parametric devices. These resonance or non resonance parametric devices may be transmissive or reflective.

[0058] At least some of the signal components from different parametric devices may destructively interfere and at least some of the signal component from different parametric devices may constructively interfere.

[0059] One or more additional signal components may undergo complete or partial constructive or destructive interference.

[0060] The method may comprise splitting the input signal using a three port network and combining the signal components with a three port network. The method may comprise splitting and combining the signals using a four port device. The four-port device may be a directional coupler. The method may comprise using a combination of three port and four port device, and devices with more than four ports. The method may comprise any suitable n-port device to split and / or combine signals.

[0061] The method may comprise amplifying or frequency converting a signal and segregating the generated idler from the amplified signal, and / or separating the pump and the amplified signal, and collecting the separated amplified signal and / or idler and / or pump at different ports of the means used to combine signals.

[0062] The method may comprise amplifying or frequency converting the signal wherein the output signal includes an amplified signal, one or more pumps and an idler, which itself may be amplified or frequency converted.

[0063] The method may further comprise separating the pump and the amplified signal, or separating the amplified signal and the idler.

[0064] When four port couplers are used to split and combined the signals, the ports of the four port device may be A, B, C and D, wherein A is a first input port, B is a first output port, C is a second input port and D is a second output port, wherein port B comprises a through signal from port A and a coupled signal from port C, and port D comprises a through signal from port C and a coupled signal from port A, and wherein a phase difference is introduced between through signals and coupled signals.

[0065] The input signal may be coupled to port A of the splitting coupler and the output signal may be collected from the port C of the combining four port coupler. The method may comprise controlling the relative phase difference of the signals such that at the port A of the input coupler the reflected signal components are out of phase with each other and destructively interfere, and wherein the phases of the reflected signal components at the port D of the input coupler are such that they constructively interfere.

[0066] Controlling the relative phase of the pump signals and / or signal branches at each parametric device may be separate to splitting the input signal into two or more signal branches, combining the output of the parametric devices into an output signal, and the parametric devices.

[0067] According to a further aspect of the invention, there is provided a frequency converter comprising two or more parametric devices, arranged in parallel to each other, the frequency converter comprising: a first input arranged to receive an input signal to be converted; means to split the input signal into two or more signal branches, wherein each signal branch may be provided to one of the parametric devices; means to combine the output of the parametric devices into an output signal, wherein the output of each parametric device may include the input signal and one or more harmonics or sub-harmonics of the input signal; and means to control the relative phase of the input signal and harmonics or sub-harmonics at each parametric device such that the output signal may include at least a first output signal component formed by the constructive interference of a signal component from each parametric device and a second output signal component formed by the destructive interference of a signal component from each parametric device.

[0068] The means to control the relative phase of the pump signals and / or signal branches at each parametric device may be separate to the means to split the input signal into two or more signal branches, the means to combine the output of the parametric devices into an output signal, and the parametric devices.

[0069] The parametric devices may be non-resonance parametric devices. These non-resonance parametric devices may be transmissive or reflective.

[0070] The parametric devices may be resonance parametric devices. These resonance parametric devices may be transmissive or reflective.

[0071] In the above described aspects or any other embodiment discussed herein, any and all nonlinear media may be used in any of the parametric devices in any suitable combination. Examples may include kinetic inductance parametric amplifiers, SQUID parametric amplifiers, JTWPAs and the like. While the above was discussed in view of realising quantum-limited amplifiers and parametric devices, the concepts and methods discussed can be extended to non-quantum limited parametric amplifiers and other parametric devices.

[0072] Features discussed in relation to any aspect or embodiment may be applied, mutatis mutandis, to any other aspect or embodiment.

[0073] Embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0074] Figure 1 show a block diagram of a circuit arrangement according to a first embodiment, employing three port networks for in-phase power division and recombination alongside the TWPAs in parallel;

[0075] Figure 2A illustrates the pump transmission for the circuit of Figure 1;

[0076] Figure 2B illustrates the signal and idler gain as a function of signal frequency for the circuit of Figure 1;

[0077] Figure 3 illustrates a block diagram of a circuit arrangement according to a second embodiment, employing three port networks for in-phase power division and recombination alongside the TWPAs in parallel;

[0078] Figure 4A shows the pump tone cancelation for the circuit of Figure 3;

[0079] Figure 4B shows the gain in signal and idler tones for the circuit of Figure 3;

[0080] Figure 5 illustrates a circuit arrangement according to a third embodiment, employing hybrid couplers as a power divider and combiner alongside the TWPAs in parallel;

[0081] Figure 6A illustrates the pump transmission at port 1 of the power combiner in the circuit of Figure 5;

[0082] Figure 6B illustrates the pump transmission at port 2 of the power combiner in the circuit of Figure 5;

[0083] Figure 6C illustrates the idler gain in the circuit of Figure 5;

[0084] Figure 6D illustrates the signal tone gain in the circuit of Figure 5;

[0085] Figure 7 illustrates a circuit arrangement according to a fourth embodiment, employing hybrid couplers as a power divider and combiner alongside the TWPAs in parallel; Figure 7A illustrates the pump transmission at port 1 of the power combiner of the arrangement in Figure 7;

[0086] Figure 7B illustrates the pump cancellation at port 2 of the power combiner of the arrangement in Figure 7;

[0087] Figure 7C illustrates the idler and signal gain at a first port of the power combiner of the parametric device system of Figure 7;

[0088] Figure 7D illustrates the idler and signal gain at a second port of the power combiner of the parametric device system of Figure 7;

[0089] Figure 8 illustrates a circuit arrangement according to a third embodiment, employing hybrid couplers as a power divider and combiner alongside the TWPAs in parallel;

[0090] Figure 8A illustrates pump cancellation at a port of the power combiner of the circuit shown in Figure 8;

[0091] Figure 8B illustrates pump cancellation at a port of the power combiner of the circuit shown in Figure 8;

[0092] Figure 8C and 8D illustrate idler and signal separation at the output ports of the power combiner of the circuit shown in Figure 8;

[0093] Figure 9 illustrates a circuit arrangement according to a sixth embodiment, employing hybrid couplers as a power divider and combiner alongside the TWPAs in parallel;

[0094] Figure 9A illustrates the pump cancellation at port 48C of the circuit shown in Figure 9;

[0095] Figure 9B illustrates the pump transmission at port 48D of the circuit shown in Figure 9;

[0096] Figure 9C and 9D illustrate idler and signal separation at the output ports of the final power combiner of the circuit shown in Figure 9;

[0097] Figure 10 illustrates a circuit according to a seventh embodiment, in which a planar beam shifter to provide phase difference between pump signals;

[0098] Figure 11 illustrates a circuit according to an eighth embodiment, in which a -90° phase shifter is provided in one of the branches;

[0099] Figure 12 illustrates a circuit according to a ninth embodiment, in which a +90° phase shifter is provided in one of the branches; Figure 13 illustrates a circuit according to a tenth embodiment, in which two -90° phase shifters are provided in one of the branches;

[0100] Figure 14 illustrates a circuit according to an eleventh embodiment, in which a DC bias is applied across the TWPAs, and three port networks for in-phase power division and recombination;

[0101] Figure 15 illustrates a circuit according to a further embodiment, in which a DC bias is applied across the TWPAs, and three port networks for in-phase power division and a hybrid coupler is used for power recombination;

[0102] Figure 16 illustrates a circuit according to a further embodiment, in which a DC bias is applied across the TWPAs, and hybrid couplers are used for power division and recombination;

[0103] Figure 17 illustrates another embodiment, in which a DC bias is applied across the TWPAs, and hybrid couplers are used for power division and recombination;

[0104] Figure 18A,B illustrate embodiments of circuits with TWPAs in parallel, in which the idler or amplified signal is looped back to the input of the circuit;

[0105] Figure 19 illustrates an embodiment of a circuit with parallel TWPAs and mixers provided on the output of the circuit;

[0106] Figure 20 illustrates an embodiment including a cascade circuit;

[0107] Figure 21 shows a model of the real part of the idler amplitude as a function of the position along the length of a TWPA, for different initial pump phases; and

[0108] Figure 22 shows a model of the variation of the idler phase as a function of the initial pump phase, for different signal phases.

[0109] Equal or functionally equivalent components are designated with the same reference numerals in the figures.

[0110] The below examples will relate to amplification, unless explicitly stated otherwise. However, it will be appreciated that the same teaching can also be applied to frequency converters by taking the idler output (or its harmonics). In this case, the system may be optimised to maximise energy transfer to the idler, to increase the amplitude of the recovered signal. Figure 1 schematically illustrates a block diagram circuit of a first embodiment of a TWPA parametric device system 1.

[0111] In the embodiment shown, the parametric device system 1 comprises an in-phase three-port network power divider 2 at a first (input) end of the parametric device system, two TWPAS 3, 4 and a power combiner 16 at a second end (output) of the parametric device systeml. The power divider 2 and combiner 16 are represented as two rectangular blocks.

[0112] The input power divider 2 is a simple power divider dividing an input signal into two or more output signals of lesser power, the ratios of which may be adjustable. In the current example, the output signals 6, 7 are assumed to have equal powers. The three-port network power divider 2 is optionally arranged such that it provides substantially good amplitude and phase balance.

[0113] A signal to be amplified 5 of nominal phase 5A taken to be zero is fed to the input 2A of the in- phase three-port network power divider 2. The signal 5 is split into two signals components 6, 7 having first signal component phase 6A and second signal component phase 7A. A first signal component 6 is provided along an upper branch of the circuit, and a second signal component 7 is provided along a lower branch of the circuit.

[0114] Unless mentioned otherwise, in the drawings the nominal phase of an input signal to be amplified is indicated by a solid chevron. The difference in phase between any given tone and a nominal tone having a phase of 0° is termed <p. The relationship between <p and the direction of the chevron are as follows: a phase difference <p of 0° corresponds to a chevron facing upwards; a phase difference of 90° corresponds to a chevron pointing to the right; a phase difference of 180° (antiphase) corresponds to a chevron pointing downwards; and a phase difference of 270° (-90°) corresponds to a chevron pointing to the left. Similarly, the phase of any pump signals or components are shown by solid arrows or by a solid arrow with a large triangular head, and the phase of any idler signals or components by outline arrows.

[0115] The upper and lower branches lead to the TWPAS 3,4, arranged in parallel to each other. Each TWPA 3, 4 comprises two input ports 3A, 4A, 3B, 4B, and an output port 16A, 16B.

[0116] On the upper branch, the phase 6A of the signal component is still zero, between the power divider 2 and the TWPA 3. This signal is propagated to the first input port 3A of the first TWPA

[0117] 3. A first pump signal 9 having first pump phase 9A is input at the second input port 3B of the TWPA 3. As with the chevron indicating the phase of the input signal, the direction of the arrow indicates the phase of the pump signal relative to a nominal signal having phase of 0. At the inputs 3A, 3B of the first TWPA 3, the signal component 6 and first pump 9 are in phase.

[0118] At the output of the first TWPA 3, the signal 11 on the upper branch comprises a first signal component having phase 6A equal to zero, a pump tone having phase 9A equal to zero and an idler having phase 13A also equal to zero. All the three components in the upper branch between the TWPA 3 and the input of the power combiner 16 are thus in phase.

[0119] As with the upper branch, at the output port 2C of the power divider 2 on the lower branch, there exists only the signal to be amplified, with its phase 7A equal to zero as shown by the upwards facing chevron. This signal is fed to the first input port 4A of the TWPA 4.

[0120] A second pump signal 10 with second pump phase 10A equal to 90°, such that that pump signal 10 is 90° out of phase with the signal to be amplified, is input at the second input port 4B of the TWPA 4. In this example, the second pump is of different frequency to the first pump.

[0121] At the output of the second TWPA 4 the signal 12 comprises an amplified signal having phase 7A equal to zero, a pump component having phase 10A equal to 90°, and an idler tone having phase 14 equal to 180°.

[0122] The signals 11 and 12 produced by the TWPA 3 and 4 respectively on the upper branch and the lower branch are then fed to the inputs 16A and 16B of the power combiner 16.

[0123] The power combiner 16 is a simple three-port power combiner receiving two incident signals and recombining them into one signal, whereupon depending on the phase difference between the two signals destructive or constructive interference occurs. Like the power divider 2, the three-port network power combiner 16 is optionally arranged such that it provides substantially good amplitude and phase balance.

[0124] Upon combination of the signals from the two TWPAs 3 and 4 in the power combiner 16, the phase relationship of the various compounds results in either destructive or constructive interference of different signal components.

[0125] In the mode of operation shown in Figure 1, the two idler tones from the two branches are out of phase and thus destructively interfere. The amplified signal components from the two signal branches are in phase due to the equality of the signal component phases 6A, 7A, and thus the signal components undergo constructive interference. The pump components at the power combiner 16 are out of phase by 90° and thus undergo partial constructive or destructive interference, resulting in at least some of the pump recovered at the output of the parametric device 1.

[0126] Therefore, in this mode of operation, only the pump tone and the signal tone are recovered at the output of the arrangement 1, and the idler tone is cancelled.

[0127] Post processing may be used to separate the pump tones and the signal tones, which may have a significant frequency difference.

[0128] Figure 2A shows the simulated transmitted pump intensity plotted as a function of the signal frequency. Figure 2B shows the simulated gain in the signal and idler intensities as a function of frequency. The idler is attenuated and thus does not appear on the plot, while the gain in the amplified signal is shown with the characteristic zero-gain gap 18.

[0129] A second embodiment is illustrated in Figure 3. The second embodiment is as described above, unless explicitly stated otherwise.

[0130] In the second embodiment, the phase 10A of the second pump 10 on the lower branch is different from the phase 10A of the second pump in the first embodiment shown in Figure 1. In Figure 2, this second pump phase 10A is 180°, i.e., the second pump is completely in antiphase with respect to the first pump 9.

[0131] At the output of the first TWPA 3, the signal 11 on the upper branch comprises an amplified signal component having phase 6A equal to zero, a pump tone having phase 9A equal to zero and an idler having phase 13A also equal to zero. All the three components in the upper branch between the TWPA 3 and the input of the power combiner 16 are thus in phase.

[0132] At the output of the second TWPA 4 the signal 12 comprises an amplified signal component having phase 7A equal to zero, a pump component having phase 10A equal to 180°, and an idler tone having phase 14 equal to 0°.

[0133] The signals 11 and 12 produced by the TWPA 3 and 4 respectively on the upper branch and the lower branch are then respectively fed to the inputs 16A and 16B of the power combiner 16.

[0134] In the mode of operation shown in Figure 2, the two idler tones are in phase and thus constructively interfere. The amplified signal components from the two signal branches are in phase due to the equality of the signal component phases 6A, 7A, and thus the signal components undergo constructive interference.

[0135] The pump components at the power combiner 16 are out of phase by 180° and thus undergo total destructive interference, resulting in at pump cancellation.

[0136] Therefore, in this mode of operation, only the idler tone and the signal tone are recovered at the output of the amplifier arrangement 1, and the pump tone is cancelled.

[0137] Figure 4A shows the simulated transmitted pump intensity plotted as a function of the signal frequency, and said transmission is zero throughout.

[0138] Figure 4B shows the gain as a function of frequency for the signal and the idler, with the zerogain gap 18 shown again for both the signal and idler tones (appearing here at 7.9 GHz).

[0139] Figure 5 shows the circuitry used in a third embodiment of the invention, in which phase control allows correction of impedance mismatch. The third embodiment is the same as the first and second embodiment, unless explained otherwise.

[0140] In the third embodiment, the power divider 2 and power combiner 3 are provided by quadrature hybrid couplers 20, 27. Quadrature hybrid couplers 20, 27 are four port hybrid couplers having two inputs 20A, 20B, 27A, 27B and two outputs 20C, 20D, 27C, 27D.

[0141] When all four ports are matched, a signal 5 incident at either input port 20A, 20B, 27A, 27B is divided between the two output ports 20C, 20D, 27C, 27D. In the example being considered, the power at the two output ports is equal, but this may not necessarily be the case. At a given output port 20C, 20D, 27C, 27D, the signal is a mix of the signals from the two input ports 20A, 20B, 27A, 27B.

[0142] Within the hybrid coupler, the first input 20A, 27A is coupled to the first output 20C, 27C on a first branch, and the second input 20B, 27B is coupled to the second output 20D, 27D on a second branch. When a signal coupled at an input port is split into two signals, a first signal, called the "through" signal, propagates along the same branch as the initial input signal, and a second signal, called the "coupled" signal, propagates onto the opposite branch. This naming convention of the two signals will be adopted in the following.

[0143] Hybrid couplers introduce a phase difference between the through and the coupled signals when measured at the outputs. The hybrid couplers used in the embodiment shown in Figure 5 are directional quadrature hybrids. They are described in this embodiment as four-port devices, but any suitable device may be used instead. The devices employed in this embodiment will be referred to 90° hybrid couplers because they introduce a 90° phase shift between the through and coupled signals. It will be appreciated that the through signals may have the same phase or different phase as the corresponding input. Hybrid couplers designed to introduce any arbitrary phase difference beyond 90° and 180° may be used. Any suitable alternative device may be used in place of the hybrid couplers.

[0144] For illustration, the signal 5A at the first input port 20A of the hybrid coupler 20 is split into two signals, a first signal 6 propagating on the same branch through to the first output port 20C (the "through" signal), and a second signal 7 coupled across to the lower branch to the second output port 20D (the "coupled signal"). The through signal has a 90° phase difference with the coupled signal, at all frequencies. In the embodiment shown in Figure 5, the signal 6 at port 20C has a phase 6A equal of -90°, whereas the signal 7 has a phase 7A of 180°.

[0145] Quadrature hybrid couplers 20, 27 also permit power transfer from the first input port 20A the second input port 20C and the two output ports 20B, 20D and likewise from any other port to the other three ports.

[0146] In the third embodiment, the input signal 5 to be amplified is provided at a first input port 20A of the power divider 20. The second input port 20B is connected to ground. As discussed above, as a result of the operation of the power divider 20 the input signal 5 is split into two signals 6 (with phase 6A, equal to -90°) and 7 (with phase 7A, equal to 180°). The signals 6 and 7 are respectively fed to the input ports 21A and 22A of the TWPAs 21, 22.

[0147] On the upper branch, the second input 21B of the first TWPA 21 receives a first pump tone 9 of first phase 9A, equal to 0°, i.e., in phase with the original signal 5 to be amplified.

[0148] At the output of the first TWPA 21, the resulting signal 25 on the upper branch comprises components including the amplified signal 6 with phase 6A (equal to -90°), the pump tone 10 with phase 10A (equal to 0°) and an idler tone with phase 13 (equal to 90°).

[0149] On the lower branch, at the second input port 22B of the second TWPA 22, a second pump 10, of phase 10A equal to 0° is propagated. At the output port 22C of the second TWPA 22. The signal 26 comprises components including the amplified signal 7 of phase 7A (equal to 180°), the second pump tone 10 of phase 10A equal to 0°, and an idler tone of phase 14 equal to 180°. The signals 25 and 26 are fed respectively to the input ports 27A and 27B of a second 90° hybrid coupler 27 (the power combiner 27).

[0150] The power combiner 1 provides signals at two outputs, one output 27C on the upper branch, and one output 27D on the lower branch.

[0151] At the first output port 27C the output comprises signal components from the upper branch phase shifted by 90° counter-clockwise and signal components from the lower branch phase shifted by 180°.

[0152] Therefore, the first output port 27C of the power combiner 27 includes the amplified signal 20components 6 and 7 which are out of phase with each other, pump tones 9 and 10 which are 90° out of phase with each other and idler tones which are completely in phase with each other. This results in the signal tones cancelling out, the pump tones undergoing partial constructive or destructive interference, and the idler tones constructively interfering with each other. This results in a substantial idler tone output at 27C.

[0153] At the second output port 27D the output comprises signal components from the upper branch phase shifted by 180° and signal components from the lower branch phase shifted by 90° anticlockwise.

[0154] Therefore, at the output port 27D, the signals comprise the amplified signal components 6 and 7 which are in phase, the pump tones, which are 90° out of phase with each other and the idler tones, which are substantially completely out of phase with each other. This results in partial pump cancellation, total idler cancellation and substantial signal tone output at the port 27D.

[0155] Furthermore, as shown in Figure 5, the reflected signals are in antiphase when they arrive back at the input port 20A, as shown by the phases 23 (thin arrows pointing in opposite directions). This results in there not being a surviving back-propagating reflected mode at the first input port 20A. Instead, the reflected signals are in phase at the port 20B (the isolated port), such that the back-propagating signals constructively interfere and build in amplitude at the isolated port 20B.

[0156] Figure 6A shows the transmission of the pump tones measured at the output port 27C. Figure 6B shows the transmitted pump tone as a function of frequency as measured at the output port 27D. The pump is not attenuated and indeed is fully transmitted at either port. However, postprocessing may be used to remove it. This mode of operation resolves the signal / idler degeneracy as shown in Figure 6C and 6D: the idler is recovered at the first output port 27C, whereas the signal is recovered at the second output port 27D. In addition to addressing the signal and idler degeneracy, the embodiment shown in Figure 5 also addresses impedance mismatch and circulator mode issues, retaining the ability to impedance match the parametric device to the surrounding circuitry which is achieved with commonly known balanced semiconductor amplifiers.

[0157] Instead of reading out the signal output at port 27D, one can read the out the idler output at port 27C. This means any reflected idler at port 27C will be directed to port 20B instead of the input at port 20A. Thus, this embodiment operates in a circulator mode.

[0158] Likewise for the impedance mismatch, if any signal is reflected from the TWPAs due to poor impedance matching, the reflected signal would also be directed to port 20B instead of the input and port 20A.

[0159] Figure 7 shows the circuitry used in a fourth embodiment of the invention, in which phase control allows simple pump injection and pump cancellation. The fourth embodiment is the same as the third embodiment, except where stated otherwise.

[0160] In the fourth embodiment, a signal to be amplified 5 and a pump tone 9 are fed to the inputs 20A, 20B of a 90° hybrid coupler 20 (power divider). The outputs 20C, 20D of the power divider 20 are then fed to two TWPAs 21, 22 in the parallel configuration as described above. The outputs of the two TWPAs 21, 22 are then directed to the input ports of another 90° hybrid coupler (power combiner).

[0161] As illustrated in Figure 7, the signal 5 to be amplified, with phase 5A of 0°, is input at the first input port 20A of the 90° power divider 20. This signal, as before, is split into two branches 6 and 7 (not shown) with first phase 6A for the through signal and second phase 7A, for the coupled signal.

[0162] The pump tone 9, of phase 9A substantially equal to that of the signal to be amplified 5 at the first input of the power divider 20, is provided at the second input port 20B of the power divider 20. Similarly, this pump tone 9 is split into two signals 10 with first phase 10A (through) and 10' second phase 10'A (coupled).

[0163] The signal 30 at the first output port 20C of the power divider 20 thus comprises a signal tone with phase 6A (-90°) and a pump tone of phase 10A' (180°). This signal is fed to a first TWPA 21 and undergoes parametric amplification, resulting in an amplified signal tone 6 with unchanged phase 6A (0°), a pump tone with unchanged phase 10'A (180°) and an idler tone with phase 13A of 180° out of phase with the amplified signal tone 6.

[0164] The signal 30 from the output of the first TWPA 21 is then fed to the first input port 27A of the 90° hybrid power combiner 27.

[0165] Similarly, the signal 31 at the second output port 20D of the power divider 20 thus comprises a signal tone with phase 7A (180°) and a pump tone of phase 10A (-90°). This signal is fed to a second TWPA 22 and undergoes parametric amplification, resulting in an amplified signal tone 7 with unchanged phase of 180°, a pump tone with unchanged phase of -90° and an idler of phase 14A 0°, i.e., in phase with the amplified signal tone 7. This is shown as the signal 31.

[0166] The signal 31 from the output of the second TWPA 22 is then fed to the second input port 27B of the 90° power combiner 27.

[0167] At the first output port 27C of the power combiner 27 in Figure 7 the output comprises components from the upper branch phase shifted by 90° counter clockwise, and signal components from the lower branch phase shifted by 180°.

[0168] Therefore, the first output port 27C of the power combiner 27 includes the amplified signals 6, 7 which are out of phase with each other, pump tones 9, 10 which are in phase with each other and idler tones which are completely antiphase with each other. This results in the signal tones cancelling out, the pump tones undergoing constructive interference, and the idler tones cancelling out. This results in a substantial pump tone output at port 27C.

[0169] At the second output port 27D of the power combiner 27 in Figure 7 the output comprises components from the upper branch phase shifted by 180°, and signal components from the lower branch phase shifted by -90°.

[0170] Therefore, the signals at the second output port 27D of the power combiner 27 includes the amplified signals 6 and 7 which are in phase with each other, pump tones 9, 10 which are antiphase with each other and idler tones which are in phase with each other. This results in the pump tones cancelling out, the signal tones undergoing constructive interference, and the idler tones constructively interfering. This results in a substantial signal and idler tone output at port 27C. The circuit in this embodiment thus achieves simple pump injection and pump cancellation. This is shown in the simulated transmitted pump tones at the two output ports 27C and 27D in Figures 7A and 7B: the pump tone is fully transmitted at the output port 27C and completely attenuated at the output port 27D.

[0171] The gain in the signal and idler tones is plotted against frequency in Figures 7C and 7D for the output ports 27C and 27D respectively. As previously stated, there is substantially no signal tone nor idler tone at the output port 27D, whereas there is a gain of up to 20 dB for both signal and idler tones at the output port 27D.

[0172] In another embodiment of the invention, the circuit shown in Figure 7 is used in a different mode of operation. In the current embodiment, a signal to be amplified 5 with signal phase 5A of 0° and a first pump tone 9 with first pump phase 9A of 0° are provided at the first input port 20A of the quadrature power divider 20. A second pump tone 34 with second pump phase 34A of 0° is provided at the second input port 20B of the power divider 20. This is shown in Figure 8.

[0173] As shown in Figure 8, the first signal 440 on the upper branch at the first output port 20C of the power divider 20 comprises a signal component 6 with phase 6A of -90° and a first pump tone 10 with phase 10A of -90° alongside a second pump tone with phase 34A' of 180°. The signal and first pump tones are the through signals from the input 20A, whereas the second pump tone is the coupled pump signal from the second input 20B.

[0174] Similarly, the second signal 442 on the lower branch at the second output port 20D of the power divider 20 comprises a signal component 7 with phase 7A of 180° and a first pump tone 10' with phase 10A' of 180° alongside a second pump tone with phase 34A of -90°. The signal and first pump tones are the coupled signals from the input 20A, whereas the second pump tone with phase 34A is the through pump signal from the second input 20B.

[0175] The signals 440 and 442 are fed to the parallel TWPAs 21 and 22 as described above. The output signal 441 at the output of the first TWPA 21 on the upper branch comprises a second pump tone component with phase 34A' of 180°, an amplified signal component with phase 6A of -90°, a first pump tone component with phase 10A of -90° and an idler tone component with phase 13 of 180°.

[0176] Similarly, the signal 443 at the output of the second TWPA 22 on the lower branch comprises a second pump tone component with phase 34A of -90°, an amplified signal component with phase 7A of 180°, a first pump tone component with phase 10A' of 180° and an idler tone component with phase 14 -90°.

[0177] The signals 441 and 443 are respectively fed to the input ports 27A and 27B of the power combiner 27. The resultant signal at the first output port 27C of the power combiner 27 includes the following components: two signal tones in antiphase, the first being the through signal from the upper branch which has undergone a phase shift of 90°, thus having a phase of 180°, and the second being the coupled signal from the lower branch, which has undergone a phase shift of 180° and thus has a phase of 0°. two first pump tones in antiphase, the first being the through first pump tone from the upper branch, which has undergone a -90° phase shift and thus has a phase of 180°, and the second being the coupled first pump tone from the lower branch, which has undergone a 180° phase shift and thus has a phase of 0°.

[0178] Two second pump tones in phase, the first being the through second pump tone from the upper branch, which has undergone a -90° phase shift and thus has a phase of 90°, and the second being the coupled second pump tone from the lower branch, which has undergone a phase inversion and thus has a phase of 90°; and two idler tones in phase, the first being the through idler tone from the upper branch, which has gone through a -90° phase shift and thus has a phase of 90°, and the second being the coupled idler tone from the lower branch, which has undergone a phase inversion and thus has a phase of 90°.

[0179] As a result, at the port 27C of the power combiner 27, signals components cancel out, first pump components cancel out, second pump components interfere constructively, and idler components interfere constructively, resulting in a substantial idler and second pump output at the port 27C.

[0180] Similarly, the resultant signal at the second output port 27D of the power combiner 27 are: two signal tones in phase, the first being the coupled signal from the upper branch, which has gone through a phase inversion, and thus has a phase of 90°, and the second being the through signal from the lower branch, which has undergone a -90° phase shift and thus has a phase of 90°. two first pump tones in phase, the first being the coupled first pump tone from the upper branch, which has undergone a 180° phase shift and thus has a phase of 90°, and the second being the through first pump tone from the lower branch, which has undergone a -90° phase shift and thus has a phase of 90°; two second pump tones in antiphase, the first being the coupled second pump tone from the upper branch, which has undergone a 180° phase shift and thus has a phase of 0°, and the second being the through second pump tone from the lower branch, which has undergone a -90° phase shift and thus has a phase of 180°; and two idler tones in antiphase, the first being the coupled idler tone from the upper branch, which has gone through a 180° phase shift and thus has a phase of 0°, and the second being the through idler tone from the lower branch, which has undergone a -90° phase shift and thus has a phase of 180°.

[0181] As a result, at the port 27D of the power combiner 27, signals components constructively interfere, first pump components interfere constructively, second pump components cancel out, and idler components destructively interfere, resulting in a substantial signal and first pump output at the port 27D.

[0182] This embodiment of the invention thus serves to cure the signal and idler degeneracy while providing for a simple pump injection mechanism. This embodiment also works in circulator mode. As previously described, if one were to read out the idler at port 27C instead of the signal at port 27D, then any reflection back to port 27C would be directed back to port 20B instead of the signal input at port 20A, thus achieving circulator mode operation.

[0183] The results related to the pump tones are shown in Figures 8A and 8B, which show the transmitted pump tones for the respective first and second output ports respective. The removal of idler and signal degeneracy is shown in Figures 8C and 8D, showing the gain and idler tones at the first and second port respectively. As shown in figure 8C, the signal tone is attenuated at the first output port, and the idler tone provided, whilst at the second output port, the idler is attenuated and the signal provided.

[0184] In a further embodiment the circuit is provided with asymmetrical hybrid couplers to from the power divider 43 and power combiner 48. Asymmetric hybrid couplers, which for reasons explained above will be referred to as 180° hybrid couplers in the embodiments described herein, split an input signal in a similar way to the quadrature hybrid couplers described above, splitting the signals into a through signal and a coupled signal. However, in this case, the power divider 43 and power combiner 48 provide a 180° phase difference between the transmitted (through) and coupled signals.

[0185] Figure 9 shows an example of the circuit using 180° couplers 43, 48. An input signal 5 with phase 5A (0°) is coupled at the first input 43A of the power divider 43 and is split into input signals 6 with phase 6A (transmitted, upper branch) and input signal 7 with phase 7A (coupled, lower branch).

[0186] Similarly, a pump tone 9 of phase 9A (0°) is fed at the input 43B of the power divider 43. This pump tone is split into two pump tones, a through pump tone with phase 9A of 180°, and a coupled pump tone with phase 10A of 0°.

[0187] The signal 44 on the upper branch at the first output 43C of the power divider 43 thus comprise a signal component 6 with phase 6A of 0° and a pump tone 10 with phase 10A of 0°, and similarly the signal 45 on the lower branch at the second output 43D of the power divider 43 comprises a signal tone component 7 with phase 7A of 0° and a pump tone 9 with phase 9A of 180°.

[0188] The signals 44 and 45 are fed to the TWPAs 21 and 22 in parallel configuration, resulting in signal amplification and generation of idler tones with phases 13 and 14 respectively.

[0189] The signal 46 at the output of the first TWPA 21 on the upper branch comprises an amplified signal component with phase 6A of 0°, a pump component with phase 10A of 0°, and an idler tone with phase 13 of 0°.

[0190] The signal 47 at the output of the second TWPA 22 on the lower branch comprises an amplified signal component with phase 7A of 0°, a pump tone with phase 9A of 180° and an idler with phase 14 of 180°.

[0191] The outputs of the TWPAs are recombined with another power combiner 48. At the first output 48C of the power combiner 48, the signals comprise: two signal components in phase with each other, the first being the through amplified signal from the upper branch, which has not undergone any phase shift and thus still has a phase of 0°, and the second being the coupled amplified signal from the lower branch, which has not undergone any phase shift and thus still has a phase of 0°. two pump components in antiphase, the first being the through pump tone from the upper branch, which has not undergone any phase shift and thus still has a phase of 0°, and the second being the coupled pump signal from the lower branch, which has not undergone any phase shift and thus still has a phase of 180°. two idler components in antiphase, the first being the through idler tone from the upper branch, which has not undergone any phase shift and thus still has a phase of 0°, and the second being the coupled idler signal from the lower branch, which has not undergone any phase shift and thus still has a phase of 180°.

[0192] At the first output port 48C of the power combiner 48, the two amplified signal components are in phase, the two pump tones are in antiphase and the two idler tones are in antiphase. As a result, at this port, only a substantial signal output is read.

[0193] At the second output port 48D of the power combiner 48, the signals comprise: two signals components in antiphase with each other, the first being the coupled amplified signal from the upper branch, which has not undergone any phase shift and thus still has a phase of 0°, and the second being the through amplified signal from the lower branch, which has undergone a 180° phase shift and has a phase of 180°. two pump components in phase, the first being the coupled pump tone from the upper branch, which has not undergone any phase shift and thus still has a phase of 0°, and the second being the through pump signal from the lower branch, which has undergone a 180° phase shift and has a phase of 180°. two idler components in phase, the first being the coupled idler tone from the upper branch, which has not undergone any phase shift and thus still has a phase of 0°, and the second being the through idler signal from the lower branch, , which has undergone a 180° phase shift and has a phase of 180°.

[0194] Therefore, at the second output port 48D of the asymmetric power combiner 48, the two input signals are in antiphase, the two pump tones are in phase and the two idler tones are in phase. As a result, at this port, substantial pump and idler output can be measured as the signal components destructively interfere.

[0195] As a result, this configuration allows the separation of the signal tone and the idler tone, while providing a simple pump injection mechanism and pump cancellation (as the pump tones are attenuated and / or non-existent at the port 48C of the power combiner 48. This configuration also provides for the control of the circulator mode. If one were to read the idler at port 48D instead of the signal at 48C, the reflection from port 48D would end up back at port 43B instead of the signal input at port 43A.

[0196] Figures 9A-B show how all of the output pump is present at output port 48D and none is present at 48C for all signal frequencies.

[0197] Figure 10 illustrates another embodiment of the invention comprising a circuit which can enable signal and idler sideband separation. This embodiment is similar to the embodiments shown in Figure 1 and Figure 2, using a three port divider and combiner, unless otherwise stated.

[0198] In the embodiment shown in Figure 10, a signal to be amplified 5 with phase 5A is coupled at the input port 2A of an in-phase power dividing three port network 2, the phase 5A being zero by convention. This result in the input signal being split in two signal branches, a first signal 6 with phase 6A of 0° propagating on the upper branch towards the output port 2B of the signal splitting three-port network 2, and a second signal 7 with phase 7A of 0° on the lower branch directed to the output port 2C of the three-port network. The signal branches are in phase at this stage.

[0199] A planar beam phase shifter 65 is provided between the power divider 2 and the TWPAs 3, 4, between the upper and lower branches. Phase shifter could be a superconducting transmission line with some current-dependent property, such as kinetic inductance. Applying a DC bias to the high kinetic inductance changes the phase velocity of the line and, therefore, the output phase of a signal propagating along it.

[0200] Alternatively, the phase shifter may be implemented by a length of transmission line, with the path difference between the branches providing the phase shift.

[0201] A pump is injected from pump input 9A and is partially coupled to the upper branch (first dotted line), meaning some of the pump power enters first TWPA 3. The rest of the pump then passes through the phase shifter 65. The output of the phase shifter 65 is coupled to the lower branch (second dotted line) so some of the pump power enters second TWPA 4. The rest of the pump power is terminated. The coupling between the pump and the branches is arranged such that the amount of pump power provided to the first TWPA 3 and the second TWPA 4 is the same. Tuning the DC bias applied to the phase shifter 65 allows the pump provided to the second TWPA 4 to be 90 degrees out-of-phase with the pump at TWPA 3. Figure 10 is different from the embodiments in Figure 1 and 3 in that it uses one pump tone, which is split, whereas Figures 1 and 3 involve the injection of two pump tones. Figure 10, therefore, presents a simplification of the embodiments shown in Figures 1 and 3.

[0202] Two pump signals 9 and 10 with respective phase 9A and 10A varied by a planar beam shifter 65 are introduced and fed to the TWPAS 3 and 4 alongside the signals 6 and 7 described above.

[0203] The signal components at the output of the first TWPA 3 comprise an amplified signal component 6, with phase 6A of 0°, the first pump 9, with phase 9A of 45° and an idler tone with phase 13 of 0°. The phases 6A and 13 are substantially equal to the phase 5A of the input signal, whereas the phase 9A of the first pump is shifted by 45° with respect to the phase 5A.

[0204] The signal components at the output of the second TWPA 4 comprise an amplified signal component 7, with phase 6A of 0°, the second pump 10, with phase 10A of 135° and an idler tone with phase 14 of 180°. The phases 7A and 14 are substantially equal to the phase 5A of the input signal, whereas the phase 10A of the second pump is shifted by 135° with respect to the phase 5A.

[0205] The two sets of signal components are then coupled to the input ports 16A and 16B of an in- phase three network 16 to recombine the signals. At the output port of the three-port network 16, the signals comprise: two amplified signal components in phase, the first coming from the upper branch, and the second from the lower branch.

[0206] Two pump tones, one with a phase of 45°, the second with a phase of 135°, the first being the first pump tone and originating from the upper branch, the second being the second pump originating from the lower branch.

[0207] Two idler tones in antiphase, the first being from the upper branch, the second being from the lower branch.

[0208] Upon recombination the signal components are such that the amplified signals constructively interfere, and the idler tone destructively interfere, resulting in idler cancellation. The pump components undergo partial interference and can be separated from the signal via post processing.

[0209] Figure 11 illustrates another embodiment of the parametric device system 1 using four port quadrature couplers as the power divider 20 and power combiner 28. As stated previous the four port quadrature couplers are used as power dividers and combiners by way of example only. Any suitable device may be used instead. The first input port 20A of the power divider receives a signal to be amplified 5 with phase 5A, by convention chosen to be zero. The second input port 20B of the power divider 20 is terminated with a matched load.

[0210] Under the action of the power divider 20, the signal 5 is split into two signals 6 and 7, the first to be propagated along the upper branch, the second to be propagated along the lower branch of the circuit. At the first output port 20C of the power divider 20, the phase 6A of the signal to be amplified is shifted by -90 with respect to the phase 5A of the input signal 5, whereas at the second output port 20D of the power divider 20 the phase 7A of the signal 7 is shifted by 180° with respect to the phase 5A of the input signal 5, such the signals 7 and 5 are in antiphase.

[0211] Both the signals 6, 7 are fed to the first input ports 21A and 22A of the TWPAs 21, 22 respectively. The second input ports 21B and 22B of the TWPAs 21 and 22 each receives a pump signal 9, 10, with pump phases 9A, 10A of 0°, substantially equal to the phase 5A of the signal to be amplified 5 at the first input 20A of the power divider.

[0212] At the output of the first TWPA 21, the signal 88 comprises: an amplified signal component that has phase 6A of -90°. a pump 9 that has phase 9A of 0°. an idler tone generated in the TWPA 21 that has a phase 13 of 90°.

[0213] At the output of the second TWPA 22, the signal 89 comprises: an amplified signal component that has phase 7A of 180°. a pump 10 that has phase 10A of 0°. an idler tone generated in the TWPA 22 that has a phase 14 of 180°.

[0214] The signal 89 from the second TWPA 22 is propagated through a -90° phase shifter 66 which shifts only the phase of the pump, resulting in the phase 10A' of the pump becoming 90° in the signal 90 provided by the phase shifter. The phase shifter 66 does not affect the phases 7A, 14 of the amplified signal or idler.

[0215] The signals 90 and 88 are fed to the input ports 27B and 27A of the power combiner 27. At the first output port 27C of the power combiner 27, the signal comprises: two amplified signal components in antiphase, the first being the through amplified signal from the upper branch, which has undergone a -90° phase shift and thus has phase 180°, and the second being the coupled amplified signal from the lower branch which has seen a phase inversion and thus phase 0°. two pump components in phase, the first being the through pump tone from the upper branch, which after a -90° phase shift has a phase of -90°, and the second being the coupled pump tone from the lower branch, which has seen a phase inversion and thus has a phase of -90°.

[0216] Two idler tones in antiphase with each other, the first being the though idler tone from the upper branch which has seen a -90° phase and has a phase of 0°, and the second being the coupled idler tone from the lower branch, which has seen a phase inversion and thus has a phase of 0°.

[0217] As a result of the above relative phases, the amplified signal components destructively interfere, whereas the idler components constructively interfere and the pump components constructively interfere. This results in idler and pump output at the first output port 27C.

[0218] At the second output port 27D, the signal comprises: two amplified signal components in phase, the first being the coupled amplified signal from the upper branch, which has undergone a 180° phase shift and thus has phase 90°, and the second being the through amplified signal from the lower branch, which has seen a -90 phase shift and thus a phase of 90°. two pump components out of phase with each other, the first being the coupled pump tone from the upper branch, which after a phase inversion has a phase of 180°, and the second being the through pump tone from the lower branch (after having propagated through the phase shifter 66), which has seen a -90° and thus has a phase of 0°.

[0219] Two idler tones in antiphase with each other, the first being the coupled idler tone from the upper branch which has seen a phase inversion and has a phase of -90°, and the second being the through idler tone from the lower branch, which has seen a -90° phase shift and thus has a phase of 90°.

[0220] Therefore, at the second output port 27D of the directional power combiner 27, the signal components undergo constructive interference, while the pump components interfere destructively and the idler components destructively interfere, resulting in substantial signal output at that port 27D. At the first input port 20A of the power divider 20, the reflected signal comprises components having opposing phases 23 at this port, resulting in cancellation of the reflected signal at the port 20A of the power divider 20. This effectively shields the system producing the input signal 5 from any reflected signals.

[0221] At the second input port 20B of the power divider 20 the components of the reflected signal have phases 24 which are substantially equal, allowing constructive interference and thus allowing the reflected signal to be collected from the port 20B of the power divider 20.

[0222] Figure 12 illustrates a variant of the circuit shown in Figure 11, with the difference that the phase shifter 66 is a 90° phase shifter. So, instead of the phase 10A' of the second pump becoming 90° after the phase shifter 66 as it did in Figure 11, in this embodiment, the phase 10A' of the second pump tone in the lower branch changes from 0° after the TWPA 22 to -90° after the phase shifter 66. This difference results in the following: at the first output port 27C of the power combiner 27, signal and pump cancelation occurs whereas the idler tone survives via constructive interference of its components from the signals 88, 90 from the first TWPA 21 and phase shifter 66.

[0223] At the second output port 27D of the power combiner 27, pump cancellation occurs and the signal and idler tone survive via constructive interference of their respective components in the signal 90, 88 from the first TWPA 21 and phase shifter 66.

[0224] The relative phase differences of the components in the reflected signals at both input ports 20A and 20B of the power divider 20 remain unchanged.

[0225] Figure 13 illustrates another embodiment of the parametric device system 1 using quadrature hybrid couplers as the power divider 43 and power combiner 48. Similar to the above, a signal 5 of phase 5A taken to be zero is introduced at the first port 43A of the power divider 43. A pump in phase with the signal 5, such that the pump phase 9A is substantially equal to the phase 5A, is introduced at the port 43B of the power divider 43.

[0226] In the upper branch, related to the first TWPA 21, there is a signal component with phase 6A of -90° and a pump with phase 10A of 180° before the first TWPA 21. The upper branch has amplified signal component with phase 6A of -90°, pump tone with phase 10A of 180°, and idler with phase 13 of 90° after the first TWPA 21. From the power divider 43, the lower branch comprises a signal 45, which has a signal component with phase 7A of 180°, and a pump with phase 9A of -90°. A 90° phase shifter 68 is placed in this lower branch, in the path of the signal 45. After the phase shifter 68, the pump phase 7 A' in the signal 45' changes to 180°, whereas the signal phase remains unchanged at 180°.

[0227] The signal 45' from the phase shifter 68 is fed to the second TWPA 22. At the output of the TWPA 22, the signal 47 comprises an amplified signal component with phase 7A' of 180°, a pump component with phase 9A' of 180°, and an idler with phase 14 of 180°. This signal 47 then goes through a -90° phase shifter 69. The signal 47', after this phase shifter 69, the pump component of the signal 47' has phase 7 A" of 270°. The idler and signal phases are unchanged.

[0228] The signal 47' from the phase shifter 69 and the signal 46 from the first TWPA 21 are then provided to the input ports of the power combiner 48. At the first output port 48C of the power combiner 48, the signal comprises: two amplified signal components in antiphase, the first being the through amplified signal from the upper branch, which has undergone a -90° phase shift and thus has phase 180°, and the second being the coupled amplified signal from the lower branch which has seen a phase inversion and thus phase 0°. two pump components in phase, the first being the through pump tone from the upper branch, which after a -90° phase shift has a phase of 90°, and the second being the coupled pump tone from the lower branch, which has seen a phase inversion and thus has a phase of 90°.

[0229] Two idler tones in phase with each other, the first being the though idler tone from the upper branch which has seen a -90° phase and has a phase of 0°, and the second being the coupled idler tone from the lower branch, which has seen a phase inversion and thus has a phase of 0°.

[0230] Therefore, at the first output port 48C of the power combiner 48, signal cancelation occurs whereas the idler and pump tones survive via constructive interference of their respective components.

[0231] At the second output port 48D, the signals comprise: two amplified signal components in phase, the first being the coupled amplified signal from the upper branch, which has undergone a 180° phase shift and thus has phase -90°, and the second being the through amplified signal from the lower branch, which has seen a -90 phase shift and thus a phase of -90°. two pump components out of phase with each other, the first being the coupled pump tone from the upper branch, which after a phase inversion has a phase of 180°, and the second being the through pump tone from the lower, which has seen a -90° and thus has a phase of 180°.

[0232] Two idler tones in antiphase with each other, the first being the coupled idler tone from the upper branch which has seen a phase inversion and has a phase of -90°, and the second being the through idler tone from the lower branch, which has seen a -90° phase shift and thus has a phase of 90°.

[0233] Therefore, at the output port 27D of the power combiner, pump and idler cancellation occurs and the signal survives via constructive interference.

[0234] Figure 14 illustrates another embodiment of the parametric device system 1 using three-port couplers for the divider 2 and combiner. In this embodiment, a signal to be amplified of phase 5A, taken to be zero, and a pump of phase 9A, also zero, are introduced at the input port 2A of an in-phase three port network 2, at which point the signal and pump are split into two branches, one propagating towards the first output port 2B of the divider 2, and the other propagated to the second output port 2C. The signals are then fed to the input ports of two parallel TWPAs 3 and 4, across which a DC bias is maintained, with the positive polarity at the input port of the TWPAs and the negative polarity at the output port of the TWPAs.

[0235] The effect of the DC bias on the TWPAs 3, 4 is to modify the phase of the idler generated, whilst the phases of the signal and pump remain unchanged. The bias may be applied to one or both of the TWPAs 3, 4. The reversing of the bias on the second TWPA 4 compared to that applied to the first TWPA 3 results in the phase of the idler in the output of TWPA 4 being 180° out of phase with the idler tone in the output of TWPA 3. It will be appreciated that the same effect can be achieved with a magnetic field.

[0236] At the output of the first TWPA 3, the signal on the upper branch comprises a signal component having phase 6A equal to zero, a pump tone having phase 9A equal to zero and an idler having phase 13A also equal to zero. All the three components in the upper branch between the TWPA 3 and the input of the power combiner 16 are thus in phase. At the output of the second TWPA 4, the signal on the lower branch comprises a signal component having phase 6A equal to zero, a pump tone having phase 9A equal to zero and an idler having phase 13A of 180°.

[0237] The output signals from the two TWPAs are then directed to the input ports 16A and 16B of an in-phase three-port device 16. At the output of the three-port network 16, the signals comprise: two amplified signal tones, which are in phase with respect to each other, the first being from the upper branch and the second being from the lower branch. The two signal components constructively interfere, resulting in signal output at this port.

[0238] Two pump components in phase with each other, one from either branch, resulting in the pump tone surviving via constructive interference of its components.

[0239] Two idler components in antiphase, one from either branch, resulting in idler cancellation via destructive interference of its components.

[0240] Figure 15 illustrates a different embodiment of the parametric device system 1 shown in Figure 14, with the difference that the in-phase coupler 2 at the input of the circuit shown in that figure is replaced by a four-port 180° hybrid 43. The signal 5 of phase 5A equal to 0° is fed at the first input port 43A of this 180° hybrid 43, and the pump 9 with phase 9A equal to 0° is coupled at another input port 43B of the 180° hybrid 43. The remainder of the circuit remains unchanged. The signals recombine in the in-phase three-port device 70, resulting in the following: at the output port 70C of the three-port device 70, the idler tone undergoes cancellation via destructive interference of its components. the pump tone undergoes cancellation via destructive interference of its components. the signal survives via constructive interference of its components.

[0241] Figure 16 illustrates another embodiment of the circuit shown in Figure 15, with the difference that the three-port network used to recombine the signals after the TWPAs in the circuits shown in Figure 14 and 15 is replaced with a four-port 180° hybrid 48.

[0242] The circuit shown in Figure 16 is thus such that an 180° hybrid is used both as means to split the signal at input and as a means to combine the signals after amplification in the TWPAs. The resulting signals are as follows: at the port 48C of the 180° hybrid 48, the idler and pump undergo cancellation via destructive interference of their respective components, and the signal undergoes total constructive interference of its components. This allows the signal to be collected at that port 48C. at the port 48D of the 180° hybrid 48, the idler and pump undergo total constructive interference of their respective components, and the signal undergoes total destructive interference of its components. This allows the idler and pump to be collected at that port 48C.

[0243] Figure 17 illustrates another embodiment of the parametric device system 1, this time using 180° hybrid as the power divider and combiner.

[0244] In this example, a signal of phase 5A, taken to be zero, is coupled to the first input port 43A of the power divider 43. A pump signal, of phase 9A equal to the phase 5A of the input signal 5, is also coupled to the same port 43A of the power divider 43. The second input port 43B of the power divider is terminated with an impedance matched load.

[0245] At the first output port 43C of the power divider, the signal 76 on the upper branch comprises components including a signal of phase 6A that is equal to the phase 5A of the signal at the input port 43A, and a pump of phase 10A in phase with the signal at the input port 43A.

[0246] At the second output port 43D of the power divider, the signal 77 on the lower branch comprises components including a signal of phase 7A that is equal to the phase 5A of the signal at the input port 43A, and a pump of phase 9A' in phase with the signal at the first input port 43A.

[0247] The signals 76 and 77 are directed to the input ports of the TWPAs 21, 22 which are arranged in parallel. A DC bias is maintained across the TWPAs, with the positive polarity at the input port of the TWPAs and the negative polarity at the output port of the TWPAs.

[0248] The output signal 78 of at the output port of the first TWPA21 comprises the signal and the pump tones, with their phase 6A and 10A unchanged, as well as an idler tone with phase 13 equal to the phases 6A and 10A (all phases in this signal are 0°).

[0249] On the lower branch, the second TWPA 22 outputs a signal 79 comprising components including a signal tone with phase 7A equal to 0°, a pump component with phase 9A' equal to 0°, and an idler tone with phase 14 equal to 180°. The signals 78 and 79 are respectively fed to the input ports 48A and 48B of the power combiner

[0250] 48. The resulting signals at the output ports 48C, 48D are as follows: at the first output port 48C of the power combiner 48, the idler undergoes cancellation via destructive interference of its components, and the signal and pump undergo total constructive interference of their respective components. This allows the signal and pump to be collected at that port 48C. at the second output port 48D of the power combiner 48, the signal and pump undergo total destructive interference of their respective components, and the idler undergoes total constructive interference of its components. This allows the idler to be collected at that port 48C.

[0251] Figure 18A illustrates a further embodiment of the parametric device system 1 using four-port devices as the divider and combiner. In this example, a signal to be amplified is fed to the first input port 83A of the power combiner. The signal is split into an upper and lower branch, each branch including a TWPA. The amplified signals, are combined at the divider. At the first output port 84C of the power combiner, the amplified signal is provided and the idler is provided at the second output port 84D. The idler 84D is fed back to the second input port 83B of the input four- port devices 83.

[0252] Figure 18B illustrates an alternative operation of the circuit in Figure 18A. In this example, a signal to be amplified is fed to the first input port 83A of a four-port device 83. The signal is split into an upper and lower branch, each branch including a TWPA. The amplified signals, are combined at the divider. As in the example shown in Figure 18A, the amplified signal is collected at the first output port 84C of the four-port device 84, and is fed back to the first input port 83A of the input four-port device 83. The idler, instead, is collected at the second output port 84D of the four-port device. There are several applications for the embodiments described in Figures 18A and 18B, including inter alia the realisation of a broadband parametric oscillator, an instantaneous frequency identifier for dark matter searches or communication, or random number generation.

[0253] Figure 19 illustrates another embodiment of the parametric device system 1 using four-port devices as the divider and combiner (in this case with a 90 degree phase shift between the through and coupled outputs). In this example, a signal 5 of phase 5A (taken to be 0°) is fed to the first input port 20A of the power divider 20. The second input port 20B of the four-port device 20 is terminated with a matched load. At the first output port 20C of the power divider 20, the signal existing in the upper branch comprises a signal with the phase 6A shifted by 90° with respect to the phase 5A of the input signal at the input port 20A. This signal is fed to a first input port of the first TWPA 3. The second input port of the first TWPA 3 receives a pump signal of phase 9A which is shifted by 135° with respect to the phase 5A of the input signal 5 at the first input port 20A of the divider.

[0254] As a result of the relative phase differences between signal and pump, the signal at the output of the first TWPA 3 comprise an amplified signal component of phase 6A equal to 90°, a pump with phase 9A equal to 135°, and an idler with phase 13 equal to 180°.

[0255] At the second output port 20C of the four-port device 20, the signal existing in the lower branch comprises a signal with the phase 7A shifted by 180° with respect to the phase 5A of the input signal at the input port 20A. This signal is fed to a first input port of the second TWPA 4. The second input port of the second TWPA 4 receives a pump signal of phase 10A which is shifted by 135° with respect to the phase 5A of the input signal 5 at the first input port 20A of the divider 20.

[0256] As a result of the relative phase differences between signal and pump, the signal at the output of the TWPA 4 comprise a signal with phase 7A equal to 180°, a pump with phase 9A equal to 135°, and an idler with phase 13 equal to 90°.

[0257] The signal outputs of the two TWPAs 3, 4, are fed to the input ports of the power combiner 20'. The signals at the first output 20'B of the power combiner 20' are then fed to a mixer 113. After the mixer, the components on the upper branch are as follows:

[0258] The amplified signal components are in antiphase with respect to each other, and undergo total destructive interference.

[0259] The pump components are such that one has a phase of -135°, and the other a phase of -45°. The pump thus undergoes partial constructive or constructive interference. The idler components are in phase with each other, allowing the idler to be measured at this mixer 113.

[0260] The signals at the second output 20'D of the power combiner 20' are also fed to a mixer 114.

[0261] After the mixer 114, components on the upper branch are as follows: the amplified signal components are in phase with respect to each other, and undergo total constructive interference, allowing the signal to be measured at the mixer 114.

[0262] The pump components are such that one has a phase of -45°, and the other a phase of -135°. The pump thus undergoes partial constructive or constructive interference. The idler components are in antiphase with each other, resulting in idler cancellation at the mixer 114.

[0263] The signals from the mixers 113 and 114 are then fed to the input ports 20"A and 20"D of a further direction coupler.

[0264] Any suitable arrangement of circuit components of Figure 19 that provides the desired output may be employed.

[0265] Figure 20 illustrates an embodiment of the invention wherein a first parametric device system 1 is used to amplify a signal fed to a first input port 101. A pump signal is fed to the second input port. The amplified signal is collected at the second output port 102 of the parametric device system 1. The pump output of the amplified signal 1, collected at the first output port 103 of parametric device system 1, is coupled to the second input port of a second parametric device system 1', which amplifies another signal, provided at the first input port 101' of the second parametric device system 1'. This is repeated such that this second amplifier 1' outputs an amplified signal that is collected at the second output port 102' of the second parametric device system 1', and the pump output of the parametric device system 1' is coupled to the second input port 101" of a third parametric device system 1". This continues in a cascading chain of parametric device system 1 up to the amplifier 1N. Because the pump is generally much stronger than the signal tone, it needs to be cancelled, as described earlier, so it does not affect the operation of subsequent components. However, the remaining power of the pump can be used to drive a second TWPA and further TWPAs 1 in the cascading chain.

[0266] In this way, a large array of TWPAs 1 can be driven with only one pump source. This is useful for applications where many amplifiers are required, such as large pixel count system e.g., many qubits, many astronomical pixels and the like. This further saves space and cost by using a single pump source rather than multiple pump sources. Any number of successive parametric device systems 1 may be provided. Any of the output signals from any given parametric device system 1 in the chain may be fed as input to any of the succeeding parametric device systems.

[0267] The above embodiments describe systems employing TWPAs arranged in parallel. TWPAs are an example of non-resonance travelling wave amplifiers. The person skilled in the art would understand that the same system may be implemented with resonance or non-resonance parametric devices, either of which can be provided to achieve transmissive or reflective gain.

[0268] In one example, a transmission resonant device may be a kinetic inductance film or SQUIDS. An example of a reflective resonant device is a JPA.

[0269] Non-resonant devices rely on long transmission lines (which provide a transmission delay) to provide the interaction length between the input signal, the device media and pump signal (where present).

[0270] In resonant devices (reflective or transmissive), reflective elements, such as capacitors, are provided at either end of the device to form a resonant cavity, effectively increase the interaction lengths by allowing the various tones to oscillate back and forth several times between the ends of the line.

[0271] In reflective devices (resonant or non-resonant) separate input and output dividers are not needed. Instead, the input divider functions to both split the input signal and combine the output signals.

[0272] The embodiment shown in Figure 7 could be modified to form a reflective resonant device by replacing the TWPAs with two JPAs. The 90° hybrid coupler 27 that forms the output divider, is removed. At the input power divider 20, the signal to be amplified is provided at a first port 20A and the amplified signal is extracted from the second port 20B. The amplified signal must be filtered from the signal at the second input port, in a known manner. Therefore, in this case, the one-port JPAs is turned turn into a two-port device, with the overall gain doubled

[0273] Use of reflective devices removes the need for a circulator / isolator pair which is normally used with a JPA. The hybrid couplet 20 can easily be integrated into the JPA circuit, given there is no need for magnets or equivalent components. The hybrid could also be formed using the superconducting transmission line, allowing for it to be lossless and very small. This would then allow for it to be incorporated on-chip. Such device, being broadband, could then provide for a tunable JPA.

[0274] The modified version of Figure 7 could also be applied to the kinetic inductance thin film version of the JPA.

[0275] In a reflective non-resonant device, the non-linear medium is not operated as a cavity. However, the interaction length is double due to the reflection.

[0276] As can be seen from the above embodiments, various combinations of destructive interference, constructive interference, and partial constructive or destructive interference for the pump, signal and idler and harmonic tones can be achieved by control of the relative phase differences of the one or more pumps and the signals to be amplified (which in turn provides for means to control the phase of the idler tones generated during parametric amplification in the TWPAs).

[0277] Therefore, by splitting the signal to be amplified, amplifying the signal in TWPAs arranged in parallel and controlling the phases of the signal portions and pump tone, any desired signal can be isolated at an output port of the parametric device system 1 and be extricated / measured, independently of the other signals. The amplified signal, a pump tone or an idler tone can be obtained in this way.

[0278] In general, the current passing along a TWPA is the sum of j current components, and is represented by l(z,t) = 5jlj, which is given by:

[0279] Where:

[0280] Aj is the slowly varying complex amplitude of the jthcomponent; coj is the (angular) frequency of the jthcomponent; Yj = otj + iPj is the complex propagation constant of the jthcomponent;

[0281] 6j is the arbitrary initial phase of the jthcomponent; z is position along the transmission line; t is time; c.c. denotes the complex conjugate; and

[0282] The initial conditions for the propagating tones are provided in the complex form as well, i.e.:

[0283] Figure 21 shows the real part of the idler amplitude as a function of the position along the length of a TWPA. This is determined by numerically solving the equation above for a lossless TWPA. In this example, the TWPAs are operating in the degenerate pump four wave mixing mode: ft - 3(->)

[0284] The different lines in Figure 5 show the Real part of the idler amplitude for as the initial pump phase is varied between 0 and n.

[0285] Whilst the magnitude of the idler component remains unchanged as the initial pump phase is varied, as indicated by the positive envelope function of each of the curves, the phase of the idler tone shifts with the initial pump phase. The fact that the magnitude of the idler is unaffected by the pump phase shift is expected, as any (conversion) gain should not be influenced by the initial pump phase. The shift in the phase of the idler tone shows that the idler phase can be controlled by, for example, controlling the phase of the pump.

[0286] Figure 22 shows the variation of the idler phase as a function of the initial pump phase. The different lines show different initial signal phases from 0 to n.

[0287] Figure 22 shows that shifting the pump phase by 6Pshifts the idler phase 26p, and shifting the signal phase by 6Sshifts the idler phase by -6S(therefore 6; = 26p- 6S).

[0288] Although Figures 221 and 22 are modelled based on lossless TWPAs operating in the degenerate pump four wave mixing mode, the principle can be applied to any of the system discussed above and show that the idler can be controlled independently of the signal.

[0289] It will be appreciated that some of the embodiments discussed above make use of the same circuit arrangement, and differ only in the phase of signals provided and / or which ports signals are provided at or extracted from. In such cases, suitable switching systems or external control may allow operation in various different modes providing different functionality.

[0290] In embodiments which use a pump tone, and the idler signal is taken as an output, the system operates as a frequency converter.

[0291] It will be appreciated that while the embodiments described above make use of one or more pump tones, embodiments of the invention may be implemented which do not employ any pump tone. In such examples, the parametric device system 1 functions as a frequency converter, converting the frequency of the input signal into one or more different frequencies. This may be frequency up-conversion, or it may be frequency down-conversion. In the frequency converter, a single input signal is split onto the two branches. As the signal propagates along the TWPA, one or more harmonics (which may incorporate harmonics or sub-harmonics) are generated. The phases of the harmonics, sub-harmonics and input signals can be controlled in a similar manner to the embodiments discussed above.

[0292] While the parametric device system 1 described in the above embodiments employ three-port devices or four port hybrid couplers or a combination of both type of devices, it will be appreciated that any suitable means to split and recombine signals may be used in the parametric device system 1.

[0293] The embodiments shown with three-port devices may be provided with alternative devices that achieve the same functions. Such devices may be employed to prevent or minimise leakage between ports, can in some examples comprise four port devices, with three of the ports used to perform the operations of a three-port network. The fourth port is terminated with an impedance matched load, ensuring minimal interaction and maximising both reverse isolation and isolation between the two or more output signals. Devices with more than four ports may also be used.

[0294] Furthermore, the parametric device system 1 may comprise any number of TWPAs arranged in parallel, with suitable dividers and combiners provided. Therefore, the parametric device system 1 may comprise two or more branches arranged in parallel, each comprising one or more TWPAs arranged in series in their own branch.

[0295] Any suitable TWPA may be used in the parametric device system 1. The TWPA circuitry employed may include any suitable wave mixing transmission line. The wave mixing may be three-wave mixing, or it may be four-wave mixing. The transmission line may be a radiofrequency transmission line. It may be a transmission line operating at any suitable electromagnetic frequencies.

[0296] The parametric device system 1 may comprise a nonlinear medium having an intrinsic dispersion relationship, the medium arranged to allow interaction between the input signal, the one or more pump signals such that the input signal is amplified and an idler signal is generated and amplified.

[0297] The parametric device system 1 may comprise a plurality of dispersion control elements arranged periodically along any suitable microwave frequency transmission line, the dispersion control elements arranged to alter the dispersion relationship of any suitable nonlinear medium, such that said dispersion function can be modulated to achieved desired characteristics. EP 3 424 143 Bl discloses examples of dispersion control elements.

[0298] In embodiments where separate pump signals of the same frequency are provided to each of the TWPAs, the separate pump tones may stem from a single pump tone that has been split using a signal splitter. A phase shifter may be used on one or more of these separate pump tones where a phase difference between the pump tones is required.

[0299] Various embodiments discussed above show one or two pumps provided along each branch. It will be appreciated that multiple pumps of different frequencies may be provided where a single pump is discussed above. Alternatively, multiple pumps at the same or different frequencies may be provided at different points, as shown in various embodiments discussed above. In this way, the TWPAs may operate in any suitable operational mode.

[0300] It will be appreciated the in the above, the absolute values of the phases given in the text above are nominal and for illustrative purposes only. Any suitable phase may be used.

[0301] The system and methods described above significantly simplify the operation of a TWPA system with regards to pump injection and cancellation, and produce a modular and potentially plug- and-play amplifier, meaning the amplifier can easily be fitted into various systems without requiring modification of the system.

[0302] In addition, the parametric device system 1 can also be used to solve the gain ripple problem. One way of doing so is to use a first TWPA with gain peak at for example 1, 1.1, 1.2 GHz and gain lows at 1.05, 1.15 GHz etc ... and a second TWPA with gain peaks at 1.05, 1.15 GHz and gain low at 1, 1.1 and 1.2 GHz etc. In this way, when the two are combined, the gain profile will flatten. This is done by either driving one TWPA with DC current (or other mean such as purposely making the line slightly longer or shorter).

[0303] More generally, gain ripple may be alleviated by using quadrature hybrid couplers as the power divider 20 and power combiner 27. In this case, the two branches have a phase difference of 90 degrees due to the divider 20. The combiner 27 then causes the phase difference of the different components to be 180 degrees. Therefore, any peak from one branch will be aligned with a trough from another branch, flattening the gain curve and addressing the gain ripple problem.

[0304] Further, while the above focused on the different tones, the principle could work with the noise from different frequencies as well. As an example, one could consider an idler frequency band that has no signal at all. It is not completely empty, as it still has the intrinsic quantum or thermal noise. This will be transferred to the signal band, due to the relation between the signal and idler. So by separating out signal and idler, the noise from the idler band may be removed as well, ensuring that the signal band truly has a quantum noise performance.

Claims

Claims1. A parametric system comprising two or more parametric devices, arranged in parallel to each other, the parametric system comprising: a first input arranged to receive an input signal; means to split the input signal into two or more signal branches, wherein each signal branch is provided to one of the parametric devices; means to supply at least one pump signal to each of the parametric devices alongside the input signal, such that each signal branch undergoes an n-wave mixing process at the corresponding parametric device; means to combine the output of the parametric devices into an output signal, wherein the output of each parametric device includes signal components including: an amplified signal portion, one or more pump signal and an idler signal; and means to control the relative phase of the pump signals and / or signal branches at each parametric device such that the output signal includes at least a first output signal component formed by the constructive interference of a signal component from each parametric device and a second output signal component formed by the destructive interference of a signal component from each parametric device.

2. The parametric device system of claim 1 wherein at the means to combine signals one or more additional signal components undergo interference, and wherein this interference is completely destructive, or completely constructive, or partially constructive or partially destructive.

3. The parametric device system of any preceding claim wherein the pump signals provided at the input of each of the parametric devices stem from the splitting of a single pump signal with an external splitting means, and wherein the resulting two pump branches are provided to the parametric device system between the means to split the signals and the parametric devices.

4. The parametric device system of claim 1 or claim 2 wherein the pump signals provided at the input of each of the parametric devices stem from the splitting of a single pump signal provided at an input of the means to split the input signal .

5. The parametric device system of any preceding claim wherein the means to split the signals comprise a power divider comprising a three port network and wherein the means to recombine the signal comprises a three port network.

6. The parametric device system of claim 5 when dependent on claim 4, wherein the means to control the relative phase of the pump signals and / or signal branches comprises means to apply a DC bias or magnetic field or other means across one or more of the parametric devices.

7. The amplifier of claims 1 to 6 wherein the means to split the input signal into two or more signal branches and the means to control the relative phase of the pump signals and / or signal branches is provided by a four port device, and wherein the means to combine the signals comprise a four port device, and wherein each output of the four port device has a phase difference between signal components provided at the same input.

8. The parametric device system of claim 7 when dependent on claim 4 wherein the input signal is provided at a first the input port of the four port device, and the pump signal is provided at a second input of the four port device, and / or wherein an additional pump signal is provided at the first input of the four port device alongside the signal to be processed.

9. The parametric system of any preceding claim wherein the parametric device is a travelling wave parametric amplifier.

10. The parametric device system of any preceding claim wherein the means to control the relative phase of the pump signals and / or signal branches at each parametric device is arranged such that: at a first output, at least some of the output signal components from different parametric devices destructively interfere and at least some of the output signal components from different parametric devices constructively interfere; and at a second output, at least some of the output signal components from different parametric devices destructively interfere and at least some of the output signal components from different parametric devices constructively interfere; and wherein different output signal components constructivelyinterfere at each output of the four port device, and different components destructively interfere at each output of the four port device.

11. The parametric device system of claim 10, wherein at one or both outputs of the four port coupler, one or more additional signal components undergo interference, and wherein this interference is completely destructive, or completely constructive, or partially constructive or partially destructive.

12. The parametric device system of any preceding claim wherein the means to control the relative phase of the pump signals and / or signals comprises a phase shifting means provided between the means to split the signals and the means combine signals on any branch to provide means for modifying the phase of the signal components in that branch.

13. The parametric device system of claim 12 wherein the phase shifting means is provided before or after the parametric device.

14. The parametric device system of claims 7 to 13 wherein the ports of the four port device are A, B, C and D, wherein A is a first input port, B is a first output port, C is a second input port and D is a second output port, wherein port B comprises a through signal from port A and a coupled signal from port C, and port D comprises a through signal from port C and a coupled signal from port A, and wherein a phase difference is introduced between through signals and coupled signals at an output and wherein the signal to be amplified is coupled to port A of the splitting coupler and wherein the output signal is collected from the port C of the combining four port coupler.

15. The parametric device system of any preceding claim wherein at least one output signal component of the parametric device system is fed to another parametric device system to amplify or frequency convert another signal.

16. The parametric device system of any preceding claim wherein at least one output signal component of the parametric device system is fed to another parametric device system in a cascading series of parametric device systems wherein each parametric device system receives at least one signal component from a preceding parametric device system.

17. The parametric device system of any preceding claim wherein one or more signal component at an output of the means to combine signals is redirected to an input port of the means to split signals.

18. The parametric device system of any preceding claim wherein the signals at the output of the means to combine signals propagate through a means to mix signals and then propagate to another mean to combine signals.

19. The parametric device system of any of preceding claim wherein the means to control the relative phase of the pump signals and / or signal branches at each parametric device are separate to the means to split the input signal into two or more signal branches, the means to combine the output of the parametric devices into an output signal, and the parametric devices.

20. A method of processing at least one signal using a parametric system comprising two or more parametric devices, parametric devices, arranged in parallel to each other, the method comprising: splitting an input signal to be amplified or frequency converted into two or more signal branches, and providing each signal branch to one of the parametric devices; supplying at least one pump signal to each of the parametric devices alongside the input signal; at each parametric device performing an n-wave mixing process; and combining the output of the parametric devices into an output signal, wherein the output of each parametric device includes signal components including: an amplified signal portion, one or more pump signal and an idler signal, wherein the method further comprises controlling the relative phase of the pump signals and / or signal branches at each parametric device such that the output signal includes at least a first output signal component formed by the constructive interference of a signal component from each parametric device and a second output signal component formed by the destructive interference of a signal components from each parametric device,and wherein when the output of the parametric devices are combined into an output signal at least some of the signal components from different parametric devices destructively interfere and at least some of the signal component from different parametric devices constructively interfere.

21. The method of claim 20 wherein the method comprises making one or more additional signal components undergo complete or partial constructive or destructive interference.

22. The method of claim 20 or claim 21 wherein the method comprises splitting the input signal using a three port network and combining the signal components with a three port network, or wherein the method comprises splitting and combining the signals using a four port device.

23. The method of any of claims 20 to 22, further comprising amplifying or frequency converting a signal wherein the output signal includes an amplified signal, one or more pumps and an idler, the method comprising separating the pump and the amplified signal, or separating the amplified signal and the idler.

24. The method of claim 22 wherein four port devices are used to split and combined the signals, wherein the ports of the four port device are A, B, C and D, wherein A is a first input port, B is a first output port, C is a second input port and D a second output port, and wherein the input signal is coupled to port A of the splitting coupler and wherein the output signal is collected from the port C of the combining four port coupler.

25. The method of claim 24, comprising controlling the relative phase difference of the signals such that at the port A of the input coupler the reflected signal components are out of phase with each other and destructively interfere, and wherein the phases of the reflected signal components at the port D of the input coupler are such that they constructively interfere.

26. The methods of any of claims 20 to 25 wherein controlling the relative phase of the pump signals and / or signal branches at each parametric device is separate to splitting the input signal into two or more signal branches, combining the output of the parametric devices into an output signal, and the parametric devices.

27. A frequency converter comprising two or more parametric devices, arranged in parallel to each other, the frequency converter comprising: a first input arranged to receive an input signal to be converted; means to split the input signal into two or more signal branches, wherein each signal branch is provided to one of the parametric devices; means to combine the output of the parametric devices into an output signal, wherein the output of each parametric device includes the input signal and one or more harmonics or sub-harmonics of the input signal; and means to control the relative phase of the input signal and harmonics or subharmonics at each parametric device such that the output signal includes at least a first output signal component formed by the constructive interference of a signal component from each parametric device and a second output signal component formed by the destructive interference of a signal component from each parametric device.

28. The frequency converter of claim 27 wherein the means to control the relative phase of the pump signals and / or signal branches at each parametric device are separate to the means to split the input signal into two or more signal branches, the means to combine the output of the parametric devices into an output signal, and the parametric devices.

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