Broadband isolator device employing non-reciprocal coupling between transmission line modes

Abstract

The present disclosure relates to an isolator device that is implemented by exploiting the non-reciprocal coupling of electromagnetic modes of a transmission line. A device and method are presented that achieve broadband isolation within a bandwidth of interest. This is achieved by controlling a multitude of controllable impedance elements distributed along the transmission line to generate a modulated set of impedances in the transmission line and exploiting the impedance modulation to generate new tones in the electromagnetic waves supported by a first subset of modes propagating in the transmission line. Depending on the direction of propagation of the electromagnetic waves, the new tones can interfere constructively or destructively, leading to parametric coupling from the first subset of modes to a second subset of modes in the transmission line or preventing it, respectively.

Description

Technical Field

[0001] This disclosure relates to isolator devices and transmission lines, wherein the transmission line may be an optical waveguide or an RF transmission line. This disclosure particularly relates to isolator devices implemented by employing non-reciprocal coupling between different electromagnetic modes of the transmission line on a bandwidth of interest. Background Technology

[0002] Non-reciprocal devices are prevalent in many technical applications, such as microwave circuits for antenna multiplexing, reflection-based amplifiers, or signal sources that shield backscattered signals. As an example of a non-reciprocal device, isolators are commonly found in microwave amplification chains in cryogenic devices to shield the device under test, such as quantum circuits.

[0003] Traditionally, isolators rely on ferrites biased by strong magnetic fields to break reciprocity. Due to the ferrites and magnets used to generate the magnetic field, these isolators are bulky, typically measuring in the tens of millimeters. Therefore, they cannot be integrated onto a chip. Furthermore, the considerable magnetic field interferes with superconductivity and thus degrades the performance of superconducting circuits, such as those used in quantum computers or other ultra-low-noise applications.

[0004] Despite the strong research interest generated by the aforementioned drawbacks, no compact, magnetless isolator device has yet been proposed that can provide broadband isolation and ultra-low noise performance as needed, for example, in sensitive cryogenic environments such as superconducting quantum computers. Summary of the Invention

[0005] Therefore, the object of this disclosure is to provide a novel solution: an integrated, and therefore small-sized, non-reciprocal device that can be used as an isolator device. This device should avoid the aforementioned disadvantages. For example, an object is to provide a magnetless device to avoid strong magnetic fields. Another object is to achieve low dissipation, heat generation, and noise. Yet another object is a large operating bandwidth, i.e., providing broadband isolation, and compatibility with existing integration processes, such as semiconductor integration, e.g., CMOS.

[0006] These and other objectives are achieved by the solutions proposed in this disclosure, as described in the independent claims. Advantageous embodiments are described in the dependent claims.

[0007] A first aspect of this disclosure provides an apparatus for broadband isolation in a bandwidth of interest, the apparatus comprising: a transmission line having a set of electromagnetic modes supporting electromagnetic wave propagation, the set of electromagnetic modes including a first subset of modes in the bandwidth of interest and a second subset of modes outside the bandwidth of interest; wherein the transmission line includes a plurality of controllable impedance elements distributed along the transmission line; and a controller configured to control the controllable impedance elements to generate a set of impedance modulations in the transmission line, the impedance modulations generating new frequency modulations in the spectrum of electromagnetic waves propagating in the transmission line; wherein the controller is configured to control the controllable impedance elements to generate a set of impedance modulations having a specific associated phase set, such that: for the transmission line The first mode subset supports a first propagation direction of electromagnetic waves, the new frequency modulated phase constructive interference causes parametric coupling from the first mode subset to the second mode subset, and for the opposite second propagation direction of electromagnetic waves supported by the first mode subset in the transmission line, the new frequency modulated phase destructive interference prevents parametric coupling from the first mode subset to the second mode subset; wherein the transmission line is further designed such that the electromagnetic mode set includes a third mode subset with a frequency lower than the first mode subset and the second mode subset, and such that the phase mismatch between the third mode subset and the first mode subset and the second mode subset prevents parametric coupling from the first mode subset and the second mode subset to the third mode subset.

[0008] The spectrum of an electromagnetic wave propagating in a transmission line can include a set of “frequency moduli,” where these frequency moduli refer to the different frequency components present in the propagating electromagnetic wave. The electromagnetic wave can be a signal transmitted via the transmission line, including, for example, noise. Impedance modulation in the transmission line distorts this signal and generates “new frequency moduli,” that is, new frequency components in the spectrum of the propagating electromagnetic wave. New frequency moduli are new, different frequency components appearing in the propagating electromagnetic wave. The frequencies of these new frequency moduli may depend on the frequencies initially present at the input of the transmission line. New frequency moduli also propagate along the transmission line and may interfere with other new frequency moduli generated downstream of the transmission line by impedance modulation caused by subsequent controllable impedance elements(s). As mentioned above, the interference can be constructive or destructive to enhance or suppress parametric coupling between different subsets of modes of the transmission line.

[0009] A subset of modes may include one or more modes. A first subset of modes may include all modes within the bandwidth of interest. A second subset of modes may include modes at frequencies higher or lower than the bandwidth of interest, and a third subset of modes may include modes at frequencies lower than the first and second subsets. The bandwidth of interest may refer to the frequency range within which the device operates efficiently as an isolator. The bandwidth of interest may be defined by the device's design specifications and application requirements.

[0010] Parametric coupling from the first subset of patterns to the second subset of patterns can refer to coupling from a specific pattern in the first subset to a specific pattern in the second subset.

[0011] Controllable impedance elements are part of a transmission line. Because controllable impedance elements are controllable, they can be modulated over time, thereby generating new frequency modulations. Each impedance modulation can generate a new frequency modulation, but it is also possible for some impedance modulations not to generate a new frequency modulation. Among numerous impedance elements, all impedance elements can be controlled to generate impedance modulation along the entire transmission line or only in a subset of said impedance elements. The more impedance elements controlled to generate impedance modulation, the stronger the non-reciprocity or isolation effect can be. Each controllable impedance element can be controlled individually by a controller, but a controller can also control multiple or even all impedance elements simultaneously. Each controllable impedance element can correspond to one unit cell in a plurality of consecutively arranged unit cells of the transmission line. A new frequency modulation generated in one unit cell of the transmission line propagates from that unit cell to the next unit cell and can be modulated again in the next (or more) unit cells by further impedance modulation, generating a new frequency modulation again, and so on. The new frequency modulation appears in the spectrum of electromagnetic waves within the transmission line.

[0012] The controller can be configured to control a controllable impedance element, for example, via a control signal, and thus be able to control the frequency and phase of the modulation, thereby controlling the frequency and phase of the new modulation. The controller allows for the engineering of desired interference and non-reciprocal parametric coupling in the transmission line.

[0013] As mentioned above, impedance modulation distorts the electromagnetic field in the transmission line, thereby generating a new frequency modulation. It is worth noting that the electromagnetic field can be decomposed into a series of electromagnetic waves, each of which can be considered as the excitation of a mode. Whether the electromagnetic field carries information is irrelevant; therefore, the electromagnetic waves can be signals and / or noise.

[0014] As will be explained in more detail later, the phase mismatch between the third mode subset and the other two mode subsets prevents undesirable parametric amplification.

[0015] The device of the first aspect can be constructed in a compact manner without being as bulky as ferrite-based methods. The device can therefore be an integrated circuit or a part of an integrated circuit, such as a semiconductor integrated circuit. This device is suitable for fabrication using planar layered integration techniques (such as CMOS or other similar techniques).

[0016] Furthermore, this device enables broadband non-reciprocal electromagnetic signal transmission and can be used as an isolator. Isolation properties are enhanced by suppressing parametric amplification. No strong magnetic field is required—the device can be non-magnetic—nor does it require bias transistors, which would cause resistive dissipation, Joule heating, and thermal noise due to bias current.

[0017] In the implementation of this device, the phase mismatch that prevents parametric coupling from the first and second mode subsets to the third mode subset is the phase shift of the transmission line in the dispersion relation between the first and second mode subsets and the third mode subset.

[0018] For example, phase mismatch could be a frequency gap in the dispersion relation of a transmission line between the first two mode subsets and the third mode subset. Therefore, in this case, there is no propagation mode for the frequencies in the frequency gap.

[0019] In one implementation, the device also includes a number of capacitive and / or inductive elements distributed along and connected to the transmission line, configured to generate phase mismatch.

[0020] In the implementation of this device, the transmission line comprises a plurality of continuously arranged unit cells, each unit cell comprising an inductor connected in series with the inductors of other unit cells and a grounded shunt capacitor; and the plurality of capacitors and / or inductors comprises one of the following: a plurality of grounded shunt inductors, wherein each unit cell comprises one shunt inductor; a plurality of grounded shunt inductors, wherein only each unit cell in a subset of unit cells comprises a shunt inductor; a plurality of resonant elements, wherein each unit cell comprises one resonant element connected in series with the inductors and resonant elements of other unit cells; a plurality of resonant elements, wherein only each unit cell in a subset of unit cells comprises a resonant element connected in series with the inductors of other unit cells; a plurality of resonant elements, wherein each unit cell comprises one resonant element connected in parallel with the grounded shunt capacitor; a plurality of resonant elements, wherein only each unit cell in a subset of unit cells comprises a resonant element connected in parallel with the grounded shunt capacitor.

[0021] In the implementation of this device, the parametric coupling from the first mode subset to the second mode subset includes the adiabatic mode conversion from the first mode subset to the second mode subset.

[0022] In the implementation of this device, numerous controllable impedance elements, including more than 100, more than 500, or more than 2000 controllable impedance elements, are distributed along the transmission line to realize the adiabatic mode conversion from the first mode subset to the second mode subset.

[0023] For example, depending on the length of the transmission line, there may be 100-200 impedance elements, or 500-1000 impedance elements, or 1000-2000 impedance elements, or 2000-5000 impedance elements.

[0024] In the implementation of this device, the distance between adjacent controllable impedance elements varies along the transmission line; and / or the size or area occupied by the corresponding controllable impedance element varies along the transmission line.

[0025] This enables quasi-adiabatic conversion between the first and second subset modes.

[0026] In the implementation of this device, a number of controllable impedance elements include one of the following: a superconducting quantum interference device (SQUID) configured to be modulated by a set of external magnetic fluxes as a pump signal; a voltage-controlled capacitor (varactor diode) configured to be modulated by a set of external voltages as a pump signal; a Josephson junction, a dynamic inductor, a material having second- or third-order nonlinearity, or any other nonlinear element configured to be impedance modulated by a pump signal.

[0027] An external magnetic flux or external voltage can be considered a pump signal. Generally, a pump signal can carry information such as a specific frequency and phase. Each modulation may have a different phase. The pump signal is different from the input signal of the transmission line (i.e., the electromagnetic wave in the transmission line) and can be provided on an additional transmission line as described below.

[0028] In the implementation of this device, the controller is configured to induce an adiabatic mode transition from a first subset of modes to a second subset of modes by spatially altering the phase mismatch and / or amplitude of the modulation (e.g., by spatially altering the phase velocity of the pump signal and its coupling with a controllable impedance element).

[0029] In one implementation, the device further includes an additional transmission line extending alongside the transmission line; wherein the plurality of controllable impedance elements are connected to the additional transmission line; and wherein the controller is configured to control the controllable impedance elements by generating a pump signal on the additional transmission line.

[0030] The pump signal generated by the controller corresponds to the pump signals described above for different types of controllable impedance elements (SQUID, varactor diode, Josephson junction, etc.). The pump signal can be supported by and propagate along the additional transmission line. The propagation direction of the pump signal can be selected depending on the direction in which isolation is required. That is, changing the propagation direction of the pump signal can reverse the non-reciprocal characteristics of the device in the first aspect.

[0031] In this implementation, the controller is configured to generate the pump signal on the additional transmission line to modulate the voltage across each of the plurality of varactor diodes, which are controllable impedance elements, to generate a set of impedance modulations; or the controller is configured to generate the pump signal on the additional transmission line to modulate the magnetic flux through the plurality of SQUIDs, which are controllable impedance elements, to generate a set of impedance modulations.

[0032] In the implementation of this device, the controller is configured to control the controllable impedance element to generate a set of impedance modulations with associated phase sets at a first frequency, so as to achieve a non-reciprocal adiabatic conversion between an electromagnetic wave supported by a first mode subset and propagating in a first propagation direction and an electromagnetic wave supported by a second mode subset and propagating in the same first propagation direction.

[0033] Therefore, in the device of the first aspect, non-reciprocal coupling can be achieved between electromagnetic waves propagating in the same direction and supported by different modes of the transmission line.

[0034] In the implementation of this device, the electromagnetic wave is an RF wave and / or RF noise, or the electromagnetic wave is an optical wave or optical noise and the transmission line is a waveguide.

[0035] In the implementation of this device, the transmission line is either an optical waveguide or an RF transmission line. Optical waveguides are considered a subfamily of transmission lines in this disclosure. Similarly, RF transmission lines are considered a subfamily of transmission lines in this disclosure.

[0036] The device in the first aspect can therefore be implemented and used in RF and optical communication applications.

[0037] A second aspect of this disclosure provides a method of operating an apparatus for broadband isolation in a bandwidth of interest according to the first aspect or any implementation thereof, the method comprising: propagating an electromagnetic wave supported by a first mode subset of a transmission line in a first direction or in an opposite second direction; controlling a plurality of controllable impedance elements distributed along the transmission line to generate a set of impedance modulations in the transmission line; wherein the controllable impedance elements are controlled to generate a set of impedance modulations having a specific associated phase set such that: for a first propagation direction of the electromagnetic wave supported by the first mode subset, the new frequency modulation phase modulates constructively interfere and cause parametric coupling from the first mode subset to the second mode subset, and for an opposite second propagation direction of the electromagnetic wave supported by the first mode subset, the new frequency modulation phase modulates destructively interfere and prevent parametric coupling from the first mode subset to the second mode subset.

[0038] The second method can have an implementation corresponding to the implementation of the apparatus of the first aspect. The second method and its implementation achieve the effects and advantages of the apparatus and its implementation of the first aspect described above.

[0039] The apparatus and method of this disclosure solve all the aforementioned problems. Specifically, the solution of this disclosure achieves non-reciprocal transmission—for implementing isolator devices—while avoiding all of the following problems: (i) bulky magnets and strong magnetic fields that hinder the on-chip and / or integration with superconducting circuits of conventional non-reciprocal devices; (ii) the dissipation, heating, and noise inherent in transistor-based solutions; (iii) the dependence on the inherent amplitude of non-reciprocal devices using nonlinear media; and (iv) the limited operating bandwidth of other existing isolator devices based on modulation and interference modes. Attached Figure Description

[0040] The above aspects and implementations are explained in the following description of embodiments with reference to the accompanying drawings: Figure 1 An apparatus for non-reciprocal transmission is shown according to an exemplary embodiment of the present disclosure.

[0041] Figure 2 It shows Figure 1 The phase mismatch exists between the modes of the transmission lines in the device shown.

[0042] Figure 3 Non-reciprocal parametric coupling in an apparatus according to an exemplary embodiment of the present disclosure is illustrated.

[0043] Figure 4 An exemplary implementation of the impedance element of a device according to an exemplary embodiment of the present disclosure is shown.

[0044] Figure 5 An implementation of an impedance element as a superconducting quantum interference device (SQUID) in an apparatus according to an exemplary embodiment of the present disclosure is shown.

[0045] Figure 6 An implementation of an impedance element as a varactor diode in an apparatus according to an exemplary embodiment of the present disclosure is shown.

[0046] Figure 7 An exemplary diagram illustrates energy exchange and amplification in a modulated transmission line.

[0047] Figure 8 Microwave isolation with limited performance due to spurious amplification in an exemplary modulated transmission line is shown.

[0048] Figure 9 An exemplary spurious amplification that is blocked from isolation is shown in a modulated transmission line.

[0049] Figure 10 The results of a dispersion engineering design for parametric amplification in an exemplary transmission line of an apparatus according to this disclosure are shown.

[0050] Figure 11Various exemplary embodiments for implementing dispersion engineering are shown.

[0051] Figure 12 The limited isolation bandwidth characteristics of an exemplary modulated transmission line of an apparatus according to an exemplary embodiment of the present disclosure are shown.

[0052] Figure 13 An exemplary embodiment of the apparatus according to the present disclosure illustrates a (quasi)adiabatic mode transition in a modulated transmission line via (quasi)adiabatic flux modulation.

[0053] Figure 14 The (quasi)adiabatic mode switching in an apparatus according to an exemplary embodiment of the present disclosure is illustrated.

[0054] Figure 15 Various exemplary embodiments for implementing (quasi)adiabatic flux modulation are shown.

[0055] Figure 16 Broadband microwave isolation via (quasi)adiabatic mode switching is shown in an apparatus according to an exemplary embodiment of the present disclosure.

[0056] Figure 17 A method for operating an apparatus for broadband isolation according to this disclosure is shown. Detailed Implementation

[0057] Figure 1 Elements of the device 10 according to this disclosure are schematically illustrated. Device 10 is configured to implement non-reciprocal signal transmission, wherein the signal is provided by electromagnetic wave 13. Non-reciprocal transmission can mean that signal transmission between two ports of device 10 depends on the direction of signal propagation. Device 10 illustrates non-reciprocal characteristics that allow it to be used as an isolator device. Therefore, device 10 is suitable for broadband isolation within a bandwidth of interest. The bandwidth of interest can be, for example, a bandwidth selected based on the application requirements of device 10.

[0058] The non-reciprocal transmission in the device 10 of this disclosure means that the electromagnetic wave 13 can propagate efficiently in only one direction (e.g., with low loss), rather than in the opposite direction. For example, while the electromagnetic wave 13 can pass through in one direction, reflections or other electromagnetic signals can be prevented from propagating in the opposite direction. The device 10 has isolation properties within the bandwidth of interest, which can mean high attenuation (e.g., 20-30 dB) in the opposite direction. The device 10 can have low insertion loss, which can mean minimal power loss in the forward direction (e.g., <1 dB). The device 10 of this disclosure is non-magnetic.

[0059] The device 10 includes a transmission line 11 having a set of electromagnetic modes that support the propagation of electromagnetic waves 13, for example, at a specific phase velocity. The electromagnetic waves 13 can be signals or noise. The electromagnetic waves 13 can be RF waves or light waves. The set of electromagnetic modes includes a first mode subset 21 and a second mode subset 22, the first mode subset 21 including one or more modes within the bandwidth of interest, and the second mode subset 22 including one or more modes outside the bandwidth of interest at frequencies higher than the bandwidth of interest.

[0060] Patterns from these two subsets 21 and 22 are in Figure 2 As shown in the figure, Figure 2 An exemplary dispersion relation for transmission line 11 is roughly illustrated. The dispersion relation shows how the frequency of electromagnetic wave 13 varies with its wavelength and its cumulative phase. It describes the permissible frequencies of transmission line 11 for different wavelength values. That is, transmission line 11 supports many modes corresponding to points on the dispersion curve. Modes in the first subset 21 are within the bandwidth of interest on the dispersion curve, while modes in the second subset 22 are outside the bandwidth of interest on the dispersion curve.

[0061] The transmission line 11 is also designed such that this set of electromagnetic modes of the transmission line 11 includes a third mode subset 23, which includes one or more modes with frequencies lower than the first mode subset 21 and the second mode subset 22. The transmission line 11 is specifically designed (e.g., it may be dispersion-engineered) such that there is a phase mismatch 12 between the third mode subset 23 and the first and second mode subsets 21, 22.

[0062] The device 10 also includes a plurality of controllable impedance elements 14, which are part of the transmission line 11 and are arranged or distributed along the transmission line 11. For example, the impedance elements 14 may be arranged one after another and / or at regular intervals along the extension direction of the first transmission line 11. The impedance elements 14 may all be of the same type.

[0063] Furthermore, the device 10 includes a controller 15 configured to control the controllable impedance elements 14. The controller 15 is configured to control the controllable impedance elements. For example, the controller 15 can be any unit capable of providing a control signal or pump signal to each controllable impedance element 14. The controller can be a processor, but it can also be a voltage source or a current source. The controller 15 is specifically configured to control the impedance elements 14 such that they generate a set of impedance modulations in the transmission line 11. Each impedance modulation in the set of impedance modulations produces a new frequency modulation in the spectrum of the electromagnetic wave 13 propagating in the first transmission line 11. The new frequency modulation is a new frequency in the spectrum. The electromagnetic wave 13 in the transmission line can be a signal and / or noise.

[0064] The controller 15 is configured to control each controllable impedance element 14 to generate a set of impedance modulations with a specific set of associated phases. Therefore, these associated phases (e.g., by the controller 15) are selected such that the coupling between the first and second mode subsets 21, 22 of the transmission line is different for different propagation directions of the electromagnetic wave 13. Specifically, for the first propagation direction of the electromagnetic wave 13 supported by the first mode subset 21 of the transmission line 11, a new frequency modulation phase-constructive interference occurs, resulting in parametric coupling from the first mode subset 21 to the second mode subset 22. For the opposite second propagation direction of the electromagnetic wave 13 supported by the first mode subset 21 in the transmission line 11, a new frequency modulation phase-destructive interference occurs, preventing parametric coupling from the first mode subset 21 to the second mode subset 22. In this way, non-reciprocal transmission of the electromagnetic wave 13 (e.g., a signal) through the transmission line 11 of the device can be achieved within the bandwidth of interest, because parametric coupling depends on the propagation direction.

[0065] Figure 2 As shown, in the positive direction, the first mode subset 21 can be parametrically coupled to the second mode subset 22 (energy can be efficiently transferred between these two modes via impedance modulation through a parametric process, as indicated by the arrows connecting the first and second mode subsets 21 and 22). Furthermore, phase mismatch 12 also... Figure 2 As shown, this prevents parametric coupling from the first and second mode subsets 21, 22 to the third mode subset 23 (e.g., the arrows do not connect the first and third mode subsets 21, 23, i.e., impedance modulation cannot be effectively transferred by impedance modulation). As shown, phase mismatch 12 can be a phase shift in the dispersion relation of transmission line 11 between the first and second mode subsets 21, 22 and the third mode subset 23. For example, phase mismatch can be a frequency gap. However, this disclosure is not limited to such examples, and other examples of phase mismatch engineering designs are possible.

[0066] Figure 3 The non-reciprocal parametric coupling between a first mode subset 21 and a second mode subset 22 in apparatus 10 according to an exemplary embodiment of the present disclosure is shown in more detail.

[0067] Figure 3 In the exemplary device 10, a transmission line 11 comprises a plurality of continuously arranged unit cells. Each unit cell includes an inductor 31 connected in series with inductors 31 of other unit cells and includes a grounded shunt capacitor 32. The inductance of each inductor can be tuned (indicated by the arrow) such that each inductor 31 corresponds to a controllable impedance element 14.

[0068] Multiple impedance modulations generated by the controllable impedance element 14 each distort the signal, specifically the spectrum of the electromagnetic wave 13 propagating in transmission line 11, and generate a series of new frequency moduli within that spectrum. By controlling the phase of the impedance modulations, the phase of these new frequency moduli can be controlled, and they can be made to constructively interfere as they propagate through transmission line 11. Figure 3 In the dispersion diagram shown in (c), modulation is indicated by arrows. If the modulation has an appropriate frequency... f p and associated phase p,n+1 = p,n + Δ p They can then be coupled in the same transmission line 11, but are two modes propagating at different frequencies, for example, in f s (The patterns in the first subset 21) and f ∑ = f s + f p (The pattern in the second pattern subset 22).

[0069] Specifically, such as Figure 3 As shown in (a), the phase of impedance modulation can generate a new frequency modulation of constructive interference when propagating along a propagation direction (positive phase value on the x-axis) on transmission line 11, and as Figure 3 As shown in (b), a new frequency modulation with destructive interference in opposite directions (negative phase value under the x-axis) can be generated, thereby achieving non-reciprocal parametric coupling in transmission line 11. Figure 3 In the dispersion diagram shown in (c), the same modulation, i.e., the arrow, cannot couple two modes in the forward (to the right of zero) and reverse (to the left of zero) directions. f s and f Σ .

[0070] Figure 4 An exemplary implementation of the controllable impedance element 14 of the apparatus 10 according to an exemplary embodiment of the present disclosure is shown. Figure 4 (a)-(d) are shown in detail Figure 1 The controllable impedance element 14 shown can be (a) a superconducting quantum interference device (SQUID) 41 configured to be modulated by an external flux, or (b) a voltage-controlled capacitor (varactor diode) 42 configured to be controlled by an external voltage, or (d) a Josephson junction, or a dynamic inductor, or a material having second- or third-order nonlinearity, or (c) any other nonlinear element configured to be impedance modulated by a pump signal (e.g., provided by controller 15).

[0071] Figure 5 SQUID 41 is shown in apparatus 10 according to an exemplary embodiment of the present disclosure (see reference). Figure 5 (b) Implementation of the controllable impedance element. The closed magnetic flux of SQUID 41 can be achieved by an additional transmission line 51 extending alongside transmission line 11 (see [link to transmission line 11]). Figure 5 Pump signal modulation propagating on (a) and (c)). Controller 15 is configured to generate a pump signal on additional transmission line 51 to modulate the closed magnetic flux of each SQUID 41. If additional transmission line 51 has the correct phase velocity, the pump signal will generate impedance modulation with a sufficient phase set in transmission line 11. As described above, the propagation direction of the pump signal can be selected according to the desired isolation characteristics of device 10.

[0072] Figure 6 The apparatus 10 shown in the present disclosure is a varactor diode 42 (see reference 10). Figure 6 (b) Implementation of the controllable impedance element. Pump signal propagating on additional transmission line 51 (see...) Figure 6 (a) and (c) can modulate the voltage across the varactor diode, thereby changing its capacitance. Controller 15 is configured to generate a pump signal on additional transmission line 51 to modulate the voltage across each varactor diode 42. If additional transmission line 51 has the correct phase velocity, the pump signal will generate impedance modulation with a sufficient phase set in transmission line 11.

[0073] The following provides some further explanation of the design of the transmission line 11 of the apparatus 10 according to this disclosure.

[0074] Figure 7 It shows Figure 7 (a) illustrates the exemplary energy exchange and amplification in a modulated transmission line. Modulated transmission lines with non-reciprocal parametric coupling can exhibit two distinct phenomena. By employing appropriate modulation frequencies and associated phases, non-reciprocal parametric coupling can be used to achieve energy exchange at different frequencies in transmission line 11. f s and f ∑ / Δ Directed energy conversion between the two modes of propagation, such as Figure 7 As shown in (b). Alternatively, by selecting appropriate frequencies and associated phases, it is possible to achieve different frequencies in transmission line 11. f s and f Δ Directed amplification of two modes of propagation, such as Figure 7 As shown in (c).

[0075] Figure 8An exemplary microwave isolation in a modulated transmission line is shown (see Figure 8 (a) Parametric modulation can be used to achieve microwave isolation. By using appropriate modulation frequencies and associated phases, directional parametric coupling can be used to achieve frequency isolation. f s The energy below is converted into modes outside the bandwidth of interest. These modes can then be filtered out, providing direction-dependent attenuation, i.e., isolation. However, as... Figure 8 As shown in (b), the maximum achievable isolation (here, -12 dB) may be limited due to spurious amplification occurring in lower frequency modes. This can be addressed through dispersion engineering, i.e., by introducing a phase mismatch of 12.

[0076] in this regard, Figure 9 An exemplary modulated transmission line is shown without phase mismatch 12 (see Figure 9 (a) prevents the amplification of isolated stray particles. Figure 9 The parametric modulation represented by the arrows in (b) in the dispersion diagram can lead to amplification or mode switching, depending on the frequency of the coupling mode, i.e., respectively. f p = f s + f Δ or f p = | f s - f ∑ | Figure 9 (c) shows the pattern f s and f Δ Parametric amplification causes the number of photons in the mode to increase exponentially during propagation. Parametric mode switching causes frequency... f s and f ∑ Energy exchange between coupling modes. Due to this gain, f s The pattern at a given location cannot be exhausted, nor can high isolation be achieved.

[0077] Therefore, as Figure 10 As shown, dispersion engineering can be used to counteract the exemplary transmission line 11 of the device 10 according to this disclosure (see Figure 10 Parametric amplification in (a)). As previously mentioned, in particular, phase mismatch 12 is used to prevent parametric coupling. Figure 10As shown in (b), the dispersion relation of lower frequency modes (modes in the third mode subset 23) can be engineered to ensure that the parametric modulation has a strong phase mismatch at these frequencies, resulting in weak parametric coupling and limiting the amplification of these modes. Figure 10 As shown in (c), this dispersion engineering design technique prevents parametric amplification and in both coupling modes f s (The patterns in the first subset 21) and f i Only parameter conversion remains between the patterns (in the second pattern subset 22).

[0078] Figure 11 Various exemplary embodiments for implementing dispersion engineering are shown. The engineering design of the dispersion relationship of transmission line 11 can be accomplished by periodically adding a combination of capacitors and / or inductors 101 to transmission line 11 (see also...). Figure 10 (a)). Figure 11 Several examples are shown. In particular, Figure 11 (a) shows that a shunt inductor can be used in each unit cell of transmission line 11 to filter out low-frequency modes and open a bandgap around DC. Figure 11 (b) shows that, as an alternative implementation, a similar shunt inductor can be used only in every five unit cells to open the bandgap around 0 GHz. Figure 10 (c) shows that, as a third option, a series resonant LC resonant circuit can be used in each unit cell to open the bandgap around 1 GHz. In any case, a guaranteed mode can be used. f s Each dispersion engineering design technique for phase mismatch 12 between (first mode subset 21) and low-frequency mode (third mode subset 23).

[0079] The isolation properties of the device 10 according to this disclosure are further discussed below.

[0080] in this regard, Figure 12 An exemplary modulated transmission line 11 according to this disclosure is shown (see Figure 12 (a) Isolation bandwidth properties. By adjusting the strength of parametric coupling to completely exhaust the input mode at the end of transmission line 11. f s (The modes in the first mode subset 21) can achieve maximum isolation. However, the optimal modulation amplitude to fully exhaust the input mode depends on the frequency of the mode. Figure 12(b) shows that after 250 units of transmission line 11, the signal close to 6 GHz is almost completely exhausted, thus achieving an attenuation of close to -10 dB. However, after 250 units of transmission line 11, the signal around 5 GHz does not attenuate, resulting in an isolation closer to -2 dB. Figure 12 (c) shows that optimal modulation can guarantee high isolation over a limited frequency range.

[0081] Figure 13 An exemplary (quasi)adiabatic mode transition via adiabatic modulation in a modulated transmission line according to this disclosure is illustrated. For example... Figure 13 As shown in (b), by adiabatically eliminating the detuning between the two modes, the population of one mode in the first mode subset 21 can be completely converted to the modes in the second mode subset 22 (see [reference]). Figure 13 (a)), without the need for reverse conversion. Figure 13 (c) shows that detuning between two parametric coupling modes can be achieved through phase difference. To control, and can be achieved by spatially changing the phase velocity of the pump signal on the additional transmission line 51. v p = To achieve adiabatic conversion, because . Figure 13 As shown in (d), in order to shorten the required device length, a fast quasi-adiabatic transition can also be achieved by changing the modulation amplitude and coupling strength, so that the phase mismatch at both ends of the line is much greater than the amplitude of parametric coupling.

[0082] Figure 14 Further examples are shown, such as regarding Figure 13 The explanation given is that (quasi-)adiabatic parametric modulation will affect the frequency. f s The input signal at (the mode in the first mode subset 21) is non-reciprocally converted to a mode outside the bandwidth of interest. f ∑ (The modes in the second mode subset 22), where they can be filtered out to provide isolation. No modulation optimization is required, which also makes this approach more robust.

[0083] Figure 15 Various exemplary embodiments for implementing adiabatic flux modulation are shown. Figure 15 (a) shows that a quasi-adiabatic conversion can be achieved simply by changing the phase velocity of the pump signal in space. Figure 15 (c) shows that the flux modulation amplitude can also be changed by altering the physical distance between SQUID 41 (as an example of controllable impedance element 14) and the pumping line. Figure 15(b) shows that alternatively, the distance can remain constant, but the area of ​​SQUID 41 can vary. These two techniques can also be used in combination. Each of the above techniques alters the magnetic coupling between the flux generated in the additional transmission line by the applied pump signal and SQUID 41, thereby achieving (quasi)adiabatic coupling.

[0084] As can be clearly seen from the above, as previously stated, (quasi)adiabatic coupling can also be achieved for different controllable impedance elements 14, although it may require different techniques known to those skilled in the art to achieve this.

[0085] Figure 16 Broadband microwave isolation via adiabatic mode switching is illustrated in an exemplary device 10 according to this disclosure, particularly using a parametric modulation transmission line 11. Dispersion engineering is employed to suppress spurious amplification, and adiabatic modulation is used for broadband mode switching. Overall, a broadband on-chip magnetless isolator device can be obtained.

[0086] Figure 17 A flowchart of method 170 according to this disclosure, specifically method steps 171 and 172, is shown. Method 170 can be performed to operate apparatus 10 for broadband isolation, for example, as shown in the preceding figures.

[0087] Step 171 includes propagating electromagnetic waves (13) supported by a first mode subset 21 of transmission line 11 in a first direction or a second direction opposite to it.

[0088] Step 172 includes controlling a plurality of adjustable impedance elements 14 distributed along transmission line 11 to generate a set of impedance modulations in transmission line 11. Each impedance modulation in this set produces a new frequency modulation in the electromagnetic wave 13 propagating in the transmission line. Step 172 can control the adjustable impedance elements 14 to generate a set of impedance modulations having a specific associated phase set. Step 172 can thus be performed such that, for a first propagation direction of the electromagnetic wave 13 supported by a first mode subset 21 in the first transmission line 11, the new frequency modulations in the electromagnetic wave of the first transmission line 11 constructively interfere and cause parametric coupling from the first mode subset 21 to a second mode subset 22, i.e., they are coupled to the second mode subset 22 of transmission line 11. It also causes the new frequency modulation phase-deactivation interference of the electromagnetic waves 13 in the transmission line 11 to the opposite second propagation direction supported by the first mode subset 21 in the transmission line 11 and prevents parametric coupling from the first mode subset 21 to the second mode subset 22, that is, they do not couple to the second mode subset 22.

[0089] In summary, this disclosure presents an apparatus 10 and a method 170 that rely on non-reciprocal coupling of electromagnetic waves 13 propagating in transmission line 11 induced by impedance modulation. Parametric coupling can be achieved and controlled by controlling controllable impedance elements 14 arranged along transmission line 11. Specifically, impedance modulation can be controlled with a corresponding associated phase such that parametric coupling of the propagating electromagnetic waves 13 occurs only in one propagation direction, rather than in the opposite direction, thereby making transmission line 11 non-reciprocal, which allows for the construction of isolator devices. Furthermore, dispersion engineering can be used to ensure phase mismatch with low-frequency modes and achieve higher isolation.

[0090] In the claims and the description of this disclosure, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude multiple. A single element can perform the function of several entities or items described in the claims. The fact that certain measures are referenced in mutually different dependent claims does not indicate that a combination of these measures cannot be used for advantageous implementations.

Claims

1. An apparatus (10) for broadband isolation in a bandwidth of interest, the apparatus (10) comprising: A transmission line (11) having a set of electromagnetic modes that support the propagation of electromagnetic waves (13), the set of electromagnetic modes including a first subset (21) of modes in the bandwidth of interest and a second subset (22) of modes outside the bandwidth of interest. The transmission line (11) includes a plurality of controllable impedance elements (14) distributed along the transmission line (11); and A controller (15) is configured to control the controllable impedance element (14) to generate a set of impedance modulations in the transmission line (11), the impedance modulations producing new frequency modulations in the spectrum of electromagnetic waves (13) propagating in the transmission line (11). The controller (15) is configured to control the controllable impedance element (14) to generate a set of impedance modulations with a specific associated phase set, such that: For the first propagation direction of the electromagnetic wave (13) supported by the first mode subset (21) of the transmission line (11), the new frequency modulated phase-constructive interference causes parametric coupling from the first mode subset (21) to the second mode subset (22), and For the electromagnetic wave (13) supported by the first mode subset (21) in the transmission line (11) in the opposite second propagation direction, the new frequency modulation phase deactivates and prevents parametric coupling from the first mode subset (21) to the second mode subset (22); The transmission line (11) is further designed such that the electromagnetic mode set includes a third mode subset (23) with a frequency lower than that of the first mode subset (21) and the second mode subset (22), and The phase mismatch (12) between the third mode subset (23) and the first mode subset (21) and the second mode subset (22) prevents parametric coupling from the first mode subset (21) and the second mode subset (22) to the third mode subset (23).

2. The device (10) according to claim 1, characterized in that: The phase mismatch (12) that prevents parametric coupling from the first mode subset (21) and the second mode subset (22) to the third mode subset (23) is the phase shift of the transmission line (11) in the dispersion relation between the first mode subset (21) and the second mode subset (22) and the third mode subset (23).

3. The apparatus (10) according to claim 1, characterized in that, The device further includes: A plurality of capacitive and / or inductive elements (101) distributed along and connected to the transmission line (11) are configured to generate the phase mismatch (12).

4. The device (10) according to claim 3, characterized in that: The transmission line (11) comprises a plurality of continuously arranged unit cells, each unit cell including an inductor (31) and a grounded shunt capacitor (32), the inductor (31) being connected in series with the inductors (31) of other unit cells; and The plurality of capacitor elements and / or inductor elements (101) include one of the following: A number of grounded shunt inductors, wherein each unit cell includes one shunt inductor; Multiple shunt inductor elements grounded, wherein each unit cell in only the unit cell subset includes a shunt inductor element; Numerous resonant elements, wherein each unit cell includes one resonant element, which is connected in series with the inductive elements and resonant elements of other unit cells; Multiple resonant elements, wherein each unit cell in only the unit cell subset includes a resonant element connected in series with the inductive elements of the other unit cells; Numerous resonant elements, wherein each unit cell includes one resonant element connected in parallel with the grounded shunt capacitor element; Multiple resonant elements, wherein only each unit cell in the unit cell subset includes a resonant element connected in parallel with the grounded shunt capacitor.

5. The device (10) according to claim 1, characterized in that: Parametric coupling from the first mode subset (21) to the second mode subset (22) includes adiabatic mode switching from the first mode subset (21) to the second mode subset (22).

6. The device (10) according to claim 1, characterized in that: The plurality of controllable impedance elements (14) includes more than 100, or more than 500, or more than 2000 controllable impedance elements (14) distributed along the transmission line (11) for realizing the adiabatic mode conversion from the first mode subset (21) to the second mode subset (22).

7. The apparatus (10) according to claim 1, characterized in that: The distance between adjacent controllable impedance elements (14) among the plurality of controllable impedance elements (14) varies along the transmission line (11); and / or The size or area occupied by each of the plurality of controllable impedance elements (14) varies along the transmission line (11).

8. The apparatus (10) according to claim 1, characterized in that, The numerous controllable impedance elements (14) include one of the following: A superconducting quantum interference device (41) is configured to be modulated by a set of external magnetic fluxes as a pump signal; A voltage-controlled capacitor (42) is configured to be modulated by a set of external voltages as a pump signal; Josephson junction (44), dynamic inductor, material with second or third order nonlinearity, or any other nonlinear element configured to be impedance modulated by a pump signal (43).

9. The apparatus (10) according to claim 8, characterized in that: The controller (15) is configured to induce an adiabatic mode transition from the first mode subset (21) to the second mode subset (22) by spatially changing the phase mismatch and / or amplitude of the modulation, for example by spatially changing the phase velocity of the pump signal and its coupling with the controllable impedance element (14).

10. The apparatus (10) according to claim 1, characterized in that, The device further includes: An additional transmission line (51) extends alongside the transmission line (11). The numerous controllable impedance elements (14) are connected to the additional transmission line (51); and The controller (15) is configured to control the controllable impedance element (14) by generating a pump signal on the additional transmission line (51).

11. The apparatus (10) according to claim 10, characterized in that: The controller (15) is configured to generate the pump signal on the additional transmission line (51) to modulate the voltage on each of the plurality of varactor diodes (42) that are the controllable impedance elements (14), to generate the set of impedance modulations; or The controller (15) is configured to generate the pump signal on the additional transmission line (51) to modulate the magnetic flux passing through a plurality of SQUIDs (41) that are the controllable impedance elements (14) to generate the set of impedance modulations.

12. The apparatus (10) according to claim 1, characterized in that: The controller (15) is configured to control the controllable impedance element (14) to generate a set of impedance modulations with associated phase sets at a first frequency to achieve a non-reciprocal adiabatic conversion between an electromagnetic wave (13) supported by the first mode subset (21) and propagating in the first propagation direction and an electromagnetic wave (13) supported by the second mode subset (22) and propagating in the same first propagation direction.

13. The apparatus (10) according to claim 1, characterized in that: The electromagnetic wave (13) is radio frequency, RF, wave, or RF noise; or The electromagnetic wave (13) is a light wave or light noise.

14. The apparatus (10) according to claim 1, characterized in that: The transmission line is an optical waveguide or an RF transmission line.

15. A method (170) of operating an apparatus (10) for broadband isolation in a bandwidth of interest according to any one of claims 1 to 13, the method (170) comprising: Electromagnetic waves (13) supported by the first mode subset (21) of the transmission line (11) propagate (171) in the first direction or in the opposite second direction. Control (172) the plurality of controllable impedance elements (14) distributed along the transmission line (11) to generate the set of impedance modulations in the transmission line (11); The controllable impedance element (14) is controlled to generate a set of impedance modulations with a specific associated phase set, such that: For the first propagation direction of the electromagnetic wave (13) supported by the first mode subset (21), the new frequency modulated phase constructive interference results in parametric coupling from the first mode subset (21) to the second mode subset (22), and For the electromagnetic wave (13) supported by the first mode subset (21) in the opposite second propagation direction, the new frequency modulation phase-deactivates and prevents parametric coupling from the first mode subset (21) to the second mode subset (22).

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