WO2023212771A1

WO2023212771A1 - A photonic phase shifter

Info

Publication number: WO2023212771A1
Application number: PCT/AU2023/050361
Authority: WO
Inventors: Xiaoke Yi; Luke English; Jianfu Wang; Liwei Li
Original assignee: The University Of Sydney
Priority date: 2022-05-04
Filing date: 2023-05-01
Publication date: 2023-11-09

Abstract

A photonic phase shifter for controlling a phase shift of an input optical signal, the photonic phase shifter comprising: an optical circuit formed on an electo-optic layer, the optical circuit comprising: an input port for receiving the input optical signal, an output port for sending an output signal, and a microring resonator comprising an optical microring and an optical waveguide; an electrical circuit formed on a dielectric layer, the electrical circuit comprising: at least two RF electrodes for receiving an input electrical signal, a resonant loop, and a capacitive electrode, wherein the RF electrodes are in electrical communication with the capacitive electrode via the resonant loop; wherein the electrical circuit is positioned relative to the optical circuit to enable the capacitive electrode to interact with the microring resonator based on the input electrical signal.

Description

A PHOTONIC PHASE SHIFTER

Technical Field

[0001] The present invention relates generally to a photonic phase shifter and associated optical phased array and RF phased array.

Background

[0002] Photonic signal processing has lately attracted significant attention to a wide range of applications in the technical areas of space, datacentre, sensors, 6G, navigation and defence. Through naturally manipulating microwave or radiofrequency (RF) signals in the optical domain, microwave (or RF) photonic systems bring supplementary advantages inherent to photonics such as inherent low loss, wide bandwidth, fast response time, and immunity to electromagnetic interference, overcoming electrical bottlenecks.

[0003] Tuneable photonic integrated circuits are used to process high frequency and ultrafast signals. One such example is tuneable microring resonators (MRRs) that are used as building blocks to achieve adaptive photonic signal processing in integrated circuits, which have the advantage of small size and high design flexibility.

[0004] A phase shifter is a component that is used in microwave or optical systems for controlling the relative phase between various elements in the communication links, or managing the signal phase in electronic systems. Due to the advantage of photonic signal processing and microwave photonics, photonic components are used to control the optical or RF phase shift to provide a solution for fast and adaptive beamforming. For example, this may be achieved via tuneable microring resonators. Conventional tunability of MRR-based phase shifter relies on the thermo-optic (TO) effect, commonly employing an external metal heater above the waveguide for centrosymmetric crystal materials like Si and Sisl^ . However, such designs exhibit slow tuning speeds normally in milliseconds or microseconds.

[0005] The usage of silicon-on-insulator (SOI) or hybrid 11 l-V/SOI platforms allows the free- carrier modulation effect to be exploited, as a faster solution than the TO effect to control the phase of an optical signal. However, the intrinsic loss of the free carrier modulation effect is exacerbated by the resonant configuration, producing large power variations around the operating wavelength translating into RF dependent loss. Pockels effect is an ultrafast electrooptic (EO) effect, with a response time of the order of femtoseconds. Pockels effect exists in several third-generation semiconductor materials such as Silicon carbide (SiC) and aluminium nitride (AIN), which are emerging as new solutions for integrated photonics because of their excellent properties such as low optical loss over a broad wavelength spectrum, wide bandgap, and complementary metal-oxide-semiconductor (CMOS) compatibility. However, the main limitation of these semiconductor materials as a practical solution to the tuneable microring resonator is the relatively small Pockels coefficient, leading to a relatively large drive voltage and poor tuning efficiency. The low energy efficiency becomes more problematic for large array applications for Radar, Lidar, and antenna. This presents challenges in providing systems that are capable of processing high frequency and ultrafast signals.

[0006] There is a desire to provide fast reconfigurable, energy-efficient MRR-based phase shifter for high-density phased array applications. This therefore provides greater capacity for information and communication technology (ICT) systems and networks.

Summary

[0007] It is an object of the present invention to meet this desire or to substantially overcome, or at least ameliorate, one or more disadvantages of existing arrangements.

[0008] Disclosed are arrangements which seek to address the above problems by providing a photonic phase shifter that utilises an optical circuit with a microring resonator and an electrical circuit that interacts with the microring resonator, where the optical circuit is formed on an electro-optic layer and the electrical circuit is formed on a dielectric layer. For example, this may be realised by a highly effective and fast tunable circuit based on a microring resonator with an integrated capacitor-drive resonant electrode with on-chip impedance matching (ICRE- IM).

[0009] According to a first aspect of the present disclosure, there is provided a photonic phase shifter for controlling a phase shift of an input optical signal, the photonic phase shifter comprising: an optical circuit formed on an electo-optic layer, the optical circuit comprising: an input port for receiving the input optical signal, an output port for sending an output signal, and a microring resonator comprising an optical microring and an optical waveguide; an electrical circuit formed on a dielectric layer, the electrical circuit comprising: at least two RF electrodes for receiving an input electrical signal, a resonant loop, and a capacitive electrode, wherein the RF electrodes are in electrical communication with the capacitive electrode via the resonant loop; wherein the electrical circuit is positioned relative to the optical circuit to enable the capacitive electrode to interact with the microring resonator based on the input electrical signal. [0010] Other aspects are also disclosed.

Brief Description of the Drawings

[0011] At least one embodiment of the present invention will now be described with reference to the drawings, in which:

[0012] Figs. 1A shows a schematic diagram of an exploded view of an optical circuit and electrical circuit formed as a layered structure according to the present disclosure;

[0013] Fig. 1 B shows a schematic diagram of a photonic phase shifter with input and output optical signals and control signals according to the present disclosure;

[0014] Fig. 1C shows a schematic diagram of a photonic phase shifter with input optical signal, output RF signal and control signals according to the present disclosure;

[0015] Fig. 1 D shows a schematic diagram of a photonic phase shifter with input optical signal, output RF signal and control signals according to the present disclosure;

[0016] Fig. 2A shows a schematic diagram of an optical phased array in a parallel configuration for optical beam steering according to the present disclosure;

[0017] Fig. 2B shows a schematic diagram of an optical phased array in a series configuration for optical beam steering according to the present disclosure;

[0018] Fig. 3A shows a schematic diagram of an RF (microwave) phased array in a parallel configuration for RF beam steering according to the present disclosure;

[0019] Fig. 3B shows a schematic diagram of an RF (microwave) phased array in a series configuration for RF beam steering according to the present disclosure;

[0020] Fig. 4A shows an electrical response (reflection power) of a capacitive electrode with and without an integrated capacitor-drive resonant electrode with on chip impedance matching according to the present disclosure;

[0021] Fig. 4B shows an electrical response (electrical field) of a capacitive electrode with and without an integrated capacitor-drive resonant electrode with on chip impedance matching according to the present disclosure; [0022] Fig. 5A shows a schematic cross-section view of an EO MRR based device;

[0023] Fig. 5B shows the simulated electrical and optical field of the device of Fig. 5A;

[0024] Fig. 6A shows an optical response (amplitude spectrum) of a capacitive electrode with and without an integrated capacitor-drive resonant electrode with on chip impedance matching according to the present disclosure;

[0025] Fig. 6B shows an optical response (phase spectrum) of a capacitive electrode with and without an integrated capacitor-drive resonant electrode with on chip impedance matching according to the present disclosure;

[0026] Fig. 7A shows an RF response (amplitude spectrum) of a capacitive electrode with and without an integrated capacitor-drive resonant electrode with on chip impedance matching according to the present disclosure;

[0027] Fig. 7B shows an RF response (phase spectrum) of a capacitive electrode with and without an integrated capacitor-drive resonant electrode with on chip impedance matching according to the present disclosure;

[0028] Fig. 8 shows electrical responses of an example device according to the present disclosure;

Detailed Description including Best Mode

[0029] Where reference is made in any one or more of the accompanying drawings to steps and/or features, which have the same reference numerals, those steps and/or features have for the purposes of this description the same function(s) or operation(s), unless the contrary intention appears.

[0030] Figs. 1A shows a schematic diagram of an exploded view of an optical circuit and electrical circuit formed as a layered structure to form a photonic phase shifter for controlling a phase shift (and optionally the amplitude) of an input optical signal.

[0031] In this example, the photonic phase shifter 101 is formed from an optical circuit 103 and an electrical circuit 105. The optical circuit 103 is formed on a layer 107 made of an electro-optic material, such as, for example, silicon carbide (SiC). The electrical circuit 105 is formed on a buffer layer 109 made of a dielectric material, such as, for example, silicon dioxide (SiC>2). The silicon carbide layer 107 is formed on top of an insulator layer 111 , which in this example is silicon dioxide (SiC>2). Therefore, the optical circuit 103 with layers 107 and 111 form a SiC-on-insulator (SiCOI) waveguide. This optical circuit 103, and so the photonic phase shifter 101 , is formed on a substrate 113 made of, for example, silicon (Si).

[0032] It will be understood that other materials may be used for the electro-optic layer 107, such as, for example lithium niobate, strained silicon, aluminium nitride, indium phosphide, gallium arsenide and silicon nitride. It will be understood that other materials may be used for the dielectric buffer layer 109, such as, for example silicon dioxide, silicon nitride, sapphire (AI₂O₃), germanium (Ge), aluminium gallium arsenide (AIGaAs), tantalum pentoxide (Ta2Os), organic modified ceramics and halogenated acrylics. It will be understood that other materials may be used for the insulator layer 111 , such as the exemplary materials listed for layer 109. It will be understood that other materials may be used for the substrate 113, such as, for example sapphire (AI₂O₃), germanium (Ge) and lll-V compound semiconductors including, but not limited to, gallium arsenide (GaAs), gallium phosphide (GaP), gallium antimonide (GaSb), indium phosphide (InP) and indium arsenide (InAs).

[0033] The device may be fabricated using any known CMOS photonic process techniques, such as deposition, etching etc.

[0034] The optical circuit 103 has an input port 115 for receiving the input optical signal and an output port 117 for sending an output optical signal. The optical circuit 103 also has a microring resonator 119 comprising an optical microring 121 and an optical waveguide 123. In one example, the input port 115 and output port 117 are a pair of vertical grating couplers. Other suitable input and output ports for optical signals may be used, such as fibre lenses, adiabatic couplers, and edge couplers.

[0035] The electrical circuit 105 has at least two RF electrodes (125A, 125B) with RF pads (126A, 126B), e.g. microwave strip line electrodes, for receiving/delivering an input electrical signal, a resonant loop 127, and a capacitor electrode 129. The RF electrodes (125A, 125B) are in electrical communication with the capacitive electrode 129 via the resonant loop 127. The electrical circuit 105 is positioned relative to the optical circuit 103 to enable the capacitive electrode 129 to interact with the microring resonator 119 based on the input electrical signals being received at the RF electrodes (125A, 125B). That is, the electrical circuit delivers an electrical field upon receiving the input electrical signals, and this electrical field interacts with the optical field being generated by the optical circuit based on the input optical signal. [0036] The RF electrodes (125A, 125B) may be configured to achieve arbitrary input impedance matching of the electrical circuit. For example, an electrical length and characteristic impedance of the RF electrodes is configured to match an input impedance of the resonant loop to an arbitrary value, thereby reducing signal reflection of the electrical circuit.

[0037] The RF electrodes (125A, 125B) may be configured for operation in a superconducting regime. For example, the RF electrodes (125A, 125B) may have a purely real characteristic impedance with equal magnitude to either an on-chip or off-chip terminating impedance, thereby minimizing signal reflection in the electrical circuit. In such a design, the resistor, inductance, capacitor effectively forms an RLC circuit that resonates at a resonant frequency and reduces to a lossless LC circuit.

[0038] In this example, the resonant loop 127 is formed as a polygon (e.g. square or rectangle) shaped loop of track using a conducting material, e.g. gold (Au), aluminium (Al), copper (Cu) or titanium (Ti). Other conductors may be used if the material’s conductivity is sufficiently high to allow for an improved electric field through the electro-optic layer 107. Other suitable shaped loops may also be used, such as, for example circular, elliptical and triangular.

[0039] As seen more clearly in Fig. 1 B, one end 131 of the resonant loop 127 connects to an outer circumferential track 133 and inner circumferential track 135 of the capacitive electrode 129, while the other end 137 of the resonant loop 127 connects to an intermediate circumferential track 139 of the capacitive electrode 129 that is positioned in between the outer and the inner circumferential tracks (133, 135). Other suitable configurations for forming the capacitive electrode may also be used.

[0040] The RF electrodes (125A, 125B), resonant loop 127 and capacitive electrode 129 form a microwave resonator circuit where the RF electrodes (125A, 125B), resonant loop 127 and capacitive electrode 129 form a series resistor, inductance, capacitor (RLC) circuit near resonant frequencies and that resonates at a resonant frequency. At the resonant frequency, the input optical signal has an effective zero-degree shift in phase when passing through the microring resonator, i.e. from the input port 115 to the output port 117. An “effective zerodegree” phase shift means that the phase shift may be 0°. Alternatively, an “effective zerodegree” phase shift may mean that the phase shift is 360° or 720°, or indeed any other integer multiple of 360°. Further, an “effective zero-degree” phase shift may mean that the phase of the input optical signal is p° and the phase of the output optical signal is p° + (n x 360)°, where n is 0, 1 , 2, 3 etc. For example, the phase of the input signal may be 7° and the phase of the output optical signal may be 7°, 367°, 727° etc. [0041] The RF electrodes (125A, 125B) are formed to have a length that is one quarter of a wavelength of the resonant frequency of the RLC circuit. This length may be made from multiple quarter wave sections is to provide impedance matching of the electrical circuit with a connected circuit at the resonant frequency of the electrical circuit.

[0042] The voltage across the capacitive electrode 129, is enhanced by the quality (Q) factor of the microwave resonator circuit at resonance. This improved voltage amplifies the electric field through the electro-optic interaction region (between the electrical circuit 105 and the optical circuit 103 at the microring resonator 119), therefore increasing the electro-optic conversion efficiency of the microring resonator 119. At resonance, the input impedance of the capacitive electrode 129 with the resonant loop 127 is purely real. The method of a quarterwave section, using transmission lines with an electrical length of one-quarter of a wavelength, can be used to match purely real input impedances to any arbitrary value. Therefore, it is suited to match the polygonal resonant loop. By using one or more quarter-wave matching stages, the input impedance of the resonant loop 127 can be matched to a standard 50 Q impedance. This enables a further enhanced electrical field, and reduces electrical reflection, thus achieving ultrafast tunability with high energy efficiency. Since both amplitude and phase of the microring can be altered via the applied input signals to the RF pads (126A, 126B), the device may be used as a tuneable optical or RF phase shifter, depending on the application.

[0043] Fig. 1 B shows a schematic diagram of a photonic phase shifter with input and output optical signals and control signals. The photonic phase shifter is based on a single microring resonator with an ICRE-IM.

[0044] When the input optical signal (i.e. light) passes through the optical microring 121 via the optical waveguide 123, an optical phase shift is introduced to the input optical signal. Since the optical phase change is dependent on the resonance wavelength of the microring resonator 119 (i.e. the optical microring 121 and the optical waveguide 123), a tuneable optical phase shifter is provided that can be controlled by applying input electrical signals (as an electrical voltage) to the RF electrodes (125A, 125B).

[0045] The input optical signal is provided by any suitable light source, such as a laser diode for example. As shown in Fig. 1B, an input optical signal having an optical amplitude and optical phase of A_o and 0_O is launched into the microring resonator 119 via the input port 115. The optical response is modified by the microring resonator optical response in both amplitude and phase, which generates the output optical signal with an optical amplitude A’oand optical phase 9'o. The output optical signal is based on the input electrical signal and the input optical signal and provides an optical photonic phase shifter.

[0046] In Fig. 1 B, Amps is the electrical amplitude. Vo is the input electrical signal (control voltage) applied to the RF electrodes (125A, 125B). ICRE-IM is the enhanced control voltage enhanced by the electrical circuit of the ICRE-IM. Ampo is the amplitude of the optical signal, wo is the optical frequency of the input optical signal, w_RF is the input RF frequency of the input electrical signal. 6 is the phase.

[0047] Fig. 1C shows a schematic diagram of a photonic phase shifter with input optical signal, output RF signal and control signals. An RF (or microwave) photonic phase shifter can be realized by manipulating the optical phase of the carrier and sidebands of the input optical signal.

[0048] The RF (or microwave) photonic phase shifter combines optical single-sideband (OSSB) modulation with an optical microring resonator that has an ICRE-IM and a photodetector 141 (e.g. photodiode). When the OSSB modulated input optical signal is provided via the input port 115 by, for example, a laser diode, it is passed through the optical microring via the optical waveguide (i.e. through the microring resonator) and an optical phase shift is introduced to the carrier and the sideband of the input optical signal. The optical phase change is mapped from the optical domain to the microwave (RF) domain after beating at the photodetector 141. Since the RF phase shift of the output RF signal is achieved by controlling the optical phase of the input optical signal, by tuning the resonance of the microring, advantages are provided such as high-frequency operation and fast tuning speed. That is, the output RF signal is based on the input electrical signal and the input optical signal.

[0049] Fig. 1 D shows a schematic diagram of an exploded view of an alternative electrical circuit for use in an example photonic phase shifter as described herein. In this example, the RF electrodes (125A, 125B) described above, which form a quarter-wave matching section, have been replaced with a coplanar strip line section 151 with smoothly varying geometry. That is, to mitigate signal reflection in the electrical circuit, antireflection of the traveling electromagnetic waves can be achieved through a characteristic impedance gradient.

[0050] The characteristic impedance of coplanar strip, or transmission, lines is dependent on the strip widths and separation. By smoothly varying one or both of these geometries, a characteristic impedance gradient can be created, allowing for antireflective properties. Similar to antireflective coatings, antireflection is achieved for light with a wavelength not significantly larger than nor smaller than the gradient geometries. Therefore, the bandwidth of interest can be tuned by adjusting how quickly the characteristic impedance changes, that is, the change in characteristic impedance per unit length. This bandwidth of interest can therefore be tuned by adjusting the coplanar strip line geometries such as width and/or separation. Thus, a characeristic impedance gradient can be achieved through smoothly varying transmission line geometries.

[0051] In this particular example, each of the strip lines in the coplanar strip line section 151 varies from a first width (w7) nearest the RF pads to a second width (w2) nearest the resonant loop where w1 > w2.

[0052] Fig. 2A shows a schematic diagram of an optical phased array in a parallel configuration for optical beam steering. The optical phased array may be arranged on a single chip or substrate. Multiple photonic phase shifters (201 A, 201 B, 201C, 201 D, 201 E and 201 F) are arranged in a parallel configuration, where the photonic phase shifters have the same, or similar form as that described in relation to Fig. 1A. A beam splitter 203 is arranged to split an optical phased array input signal into multiple input optical signals such that each input optical signal is provided as an input optical signal to each photonic phase shifter. That is, a first input optical signal is provided as an input optical signal to a first photonic phase shifter (e.g. 201A). A second input optical signal is provided as an input optical signal to a second photonic phase shifter (e.g. 201 B), and so on. Although Fig. 2A shows six photonic phase shifters (201 A, 201 B, 201 C, 201 D, 201 E and 201 F), it will be understood that two or more photonic phase shifters may be used in the optical phased array. At least one optical antenna 205 is provided to generate an output signal that can be beam steered based on the cumulative optical output signals being generated by each of the photonic phase shifters (201A, 201 B, 201C, 201 D, 201 E and 201 F).

[0053] Fig. 2A also shows an optical bus waveguide that transmits the optical signal from the laser source (e.g. a laser diode), via a beam splitter to split the optical signal into multiple paths. The microring resonator with an ICRE-IM provides an optical phase shift along each path. The at least one optical antenna 205 may be an array of vertical grating couplers to radiate an output signal outside the device.

[0054] Fig. 2B shows a schematic diagram of an optical phased array in a series configuration for optical beam steering. The optical phased array may be arranged on a single chip or substrate. [0055] Multiple photonic phase shifters (207A, 207B, 207C, 207D, 207E and 207F) are arranged in a series configuration, where the photonic phase shifters have the same, or similar form as that described in relation to Fig. 1A. An optical phased array input signal is applied as an input optical signal to each of the photonic phase shifters in sequence. That is, a first input optical signal is provided as an input optical signal to a first photonic phase shifter (e.g. 207A). The output optical signal of the first photonic phase shifter (e.g. 207A) is provided as a second input optical signal to a second photonic phase shifter (e.g. 207B), and so on in sequence. Multiple optical antenna (209A, 209B, 209C, 209D, 209E, 209F) are provided to generate an output signal that can be beam steered based on the cumulative optical output signals being generated by each of the photonic phase shifters (207A, 207B, 207C, 207D, 207E and 207F).

[0056] Optical couplers are provided between each adjacent photonic phase shifter in order to tap an optimum portion of the phase tuned optical signal into the optical antenna (209A, 209B, 209C, 209D, 209E, 209F). The radiation pattern at the optical antenna (209A, 209B, 209C, 209D, 209E, 209F) output can be steered by changing the relative phases of the optical input signal(s) without mechanically moving the antenna, and therefore leads to many applications due to its agility and reliability.

[0057] Although Fig. 2B shows six photonic phase shifters (207A, 207B, 207C, 207D, 207E and 207F), it will be understood that two or more photonic phase shifters may be used in the optical phased array.

[0058] Therefore, an optical phased array input signal may be applied as the input optical signals of the photonic phase shifters, arranged in parallel or in series, wherein the output signals of the photonic phase shifters are provided to the at least one optical antenna, the optical phased array is arranged to steer an optical phased array output signal based on the optical phased array input signal(s) and each of the input electrical signals being applied to the photonic phase shifters.

[0059] As such, the photonic phase shifter can be extended to an array operation for complicated functions. For instance, optical phased array antennas with beam steering capabilities may be used as key components for chip-scale LIDAR, where the Size, Weight, and Power (SWaP) are the main limiting factors in conventional LIDAR systems.

[0060] Fig. 3A shows a schematic diagram of an RF (microwave) phased array in a parallel configuration for RF beam steering. The RF phased array may be arranged on a single chip or substrate. Multiple photonic phase shifters (301 A, 301 B, 301 C, 301 D, 301 E and 301 F) are arranged in a parallel configuration, where the photonic phase shifters have the same, or similar form as that described in relation to Fig. 1A. A beam splitter 303 is arranged to split an RF phased array optical input signal into multiple input optical signals such that each input optical signal is provided as an input optical signal to each photonic phase shifter. That is, a first input optical signal is provided as an input optical signal to a first photonic phase shifter (e.g. 301A). A second input optical signal is provided as an input optical signal to a second photonic phase shifter (e.g. 301 B), and so on. Although Fig. 3A shows six photonic phase shifters (301 A, 301 B, 301 C, 301 D, 301 E and 301 F), it will be understood that two or more photonic phase shifters may be used in the RF phased array. A photodetector (305A, 305B, 305C, 305D, 305E and 305F) is provided at the output of each of the photonic phase shifters (301 A, 301 B, 301 C, 301 D, 301 E and 301 F) to feed to a respective antenna (307A, 307B, 307C, 307D, 307E, 307F) to generate an RF output signal that can be beam steered based on the cumulative RF output signals being generated at each of the respective photodetectors (305A, 305B, 305C, 305D, 305E and 305F) and at each respective antenna (307A, 307B, 307C, 307D, 307E, 307F).

[0061] Fig. 3A also shows an optical bus waveguide that transmits the optical signal from the laser source (e.g. a laser diode), via a beam splitter to split the optical signal into multiple paths. The microring resonator with ICRE-IM provides an optical phase shift along each path. The at least one photodetector (305A-F) converts the optical signal(s) to electrical signal(s) and the at least one RF antenna (307A-F) radiates an output signal outside the device based on the electrical signal(s).

[0062] Fig. 3B shows a schematic diagram of an RF (microwave) phased array in a series configuration for RF beam steering. The RF phased array may be arranged on a single chip or substrate.

[0063] Multiple photonic phase shifters (309A, 309B, 309C, 309D, 309E and 309F) are arranged in a series configuration, where the photonic phase shifters have the same, or similar form as that described in relation to Fig. 1A. An RF phased array optical input signal is applied as an input optical signal to each of the photonic phase shifters in sequence. That is, a first input optical signal is provided as an input optical signal to a first photonic phase shifter (e.g. 309A). The output optical signal of the first photonic phase shifter (e.g. 309A) is provided as a second input optical signal to a second photonic phase shifter (e.g. 309B), and so on in sequence. Multiple photodetectors (311 A, 311 B, 311C, 311 D, 311 E, 311 F) are provided to generate photodetector output signals based on the output signals of the photonic phase shifters. The photodetector output signals are fed to multiple respective antenna (313A, 313B, 313C, 313D, 313E, 313F) and beam steered based on the cumulative RF output signals being generated at each of the respective photodetectors (311 A, 311 B, 311C, 311D, 311E, 311 F) and at each respective antenna (313A, 313B, 313C, 313D, 313E, 313F).

[0064] Optical couplers are provided between each adjacent photonic phase shifter in order to tap an optimum portion of the phase tuned optical signal into the respective photodiode and RF antenna. The radiation pattern at the RF antenna output can be steered by changing the relative phases of the optical input signal(s) without mechanically moving the antenna, and therefore leads to many applications due to its agility and reliability.

[0065] Although Fig. 3B shows six photonic phase shifters (309A, 309B, 309C, 309D, 309E and 309F), it will be understood that two or more photonic phase shifters may be used in the RF phased array.

[0066] In regard to Fig, 3A and 3B, the radiation pattern of each individual antenna element constructively combines with neighbouring antenna to form an effective radiation pattern, where the direction of the radiation is manipulated by changing the phase of the RF signal via the microring resonator and ICRE-IM.

[0067] The photonic phase shifter can therefore be extended to an array operation for complicated functions. For instance, RF phased array antennas with RF beamforming using RF (microwave) photonic phase shifters offers advantages inherent only to photonics, such as wideband frequency coverage and immunity to electromagnetic interference, and has various applications in satellite communications and 6G.

[0068] Therefore, the RF phased array optical input signal may be applied as the input optical signal to each of the photonic phase shifters in sequence, and the RF antennas are arranged to generate the RF phased array output signal.

[0069] Fig. 4A shows an electrical response (reflection power) of a capacitive electrode with and without an integrated capacitor-drive resonant electrode with on chip impedance matching. Fig. 4B shows an electrical response (electrical field) of a capacitive electrode with and without an integrated capacitor-drive resonant electrode with on chip impedance matching.

[0070] In these examples, the electrodes were constructed using gold strip lines. The gold electrode with ground-signal-ground design was coated on top of the microring structure after inserting SiC>2 buffer layer to avoid optical loss induced by metal. As expected, the resonant electrodes offer significantly increased electric field strength at the resonant frequency which is 15.4 GHz in this design. Note the resonant frequency can be adjusted via the geometry of the polygonal resonant loop by changing length, which provides further design flexibility. It can be seen the conventional capacitive electrodes exhibit a current density of around 5.2 x10⁴ V/m generated from the electric field strength, while the ICRE-IM circuit exhibits a maximum current density of 3x10⁵ V/m, which corresponds to a 570% relative increase in the electric field strength.

[0071] The Pockels effect, as a linear refractive index change based on the electro-optic effect given by the following Equation :

[0072] An « — ^n³rE_RF

[0073] where An is the change in the refractive index of optical waveguide material, r is the linear EO tensor, and E_RF is the applied electric field. The Equation above shows a linear relationship between An and E_RF, indicating that the enlarged electrical field via ICRE-IM will increase the refractive index change, which will result in an enhanced tunability of the microring resonator.

[0074] Fig. 5A shows a schematic cross-section view of an EO MRR based device. Fig. 5B shows the simulated electrical and optical field of the device of Fig. 5A, where the arrows show the electrical field direction.

[0075] To evaluate the effect of the enhanced electrical fields on the microring resonator, simulations were carried out to verify optical responses. Fig. 5A shows a cross-section of MRR waveguide that is designed on a SiCOI platform, as an example. As shown in Fig. 5B, when the voltage is applied across the signal and ground electrodes, a vertical electric field is induced predominantly in the vertical direction overlapping with the optical mode to probe the Pockels effect.

[0076] Fig. 6A shows an optical response (amplitude spectrum) of a capacitive electrode with and without an integrated capacitor-drive resonant electrode with on chip impedance matching when the voltage of the input signal is 4.75V.

[0077] It can be seen that the optical resonance of the microring is shifted according to the voltage level of the input electrical signal (voltage), which correspondingly introduces an optical phase shift to the input optical signal. The optical phase shift introduced by the microring with integrated capacitor-drive resonant electrode with on chip impedance matching is about 30 times of the one introduced by the microring without the ICRE-IM, when the optical carrier is located at 40pm longer wavelength of the resonance position, showing the photonic phase shifter reduces the energy consumption by over 25 times . The optical phase change can be mapped to the RF domain to achieve an RF phase shifter.

[0078] Fig. 6B shows an optical response (phase spectrum) of a capacitive electrode with and without an integrated capacitor-drive resonant electrode with on chip impedance matching.

[0079] As shown in Fig. 6B, this is realized by aligning the carrier wavelength with the resonance of the phase change induced by the microring, so that an optical phase change is induced at the optical carrier. After beating at the photodetector, the resulting RF signal is phase shifted. The effective phase of the output RF signal is therefore dependent on the optical phase difference between the optical carrier and its sideband. By tuning the resonance of the microring with respect to the carrier wavelength, the phase difference can be varied to realize different RF phase shifts.

[0080] Figs. 7A and 7B show the RF response with and without using integrated capacitordrive resonant electrode with on chip impedance matching. Again, a significant enlargement of RF phase shifting can be seen by using the microring resonator with integrated capacitor-drive resonant electrode with on chip impedance matching.

[0081] Fig. 7A shows an RF response (amplitude spectrum) of a capacitive electrode with and without an integrated capacitor-drive resonant electrode with on chip impedance matching.

[0082] Fig. 7B shows an RF response (phase spectrum) of a capacitive electrode with and without an integrated capacitor-drive resonant electrode with on chip impedance matching.

[0083] Fig. 8 shows electrical responses of a phase shifter fabricated on a silicon on insulator wafer via a CMOS compatible process. An experiment was carried out by measuring the electrical reflection (Sn) and transmission (S21) responses of the ICRE-IM via a vector network analyzer (VNA). A Radio Frequency (RF) probe was connected to the port of the VNA through a RF cable, delivering the electrical signals to the electrode pads of the phase shifter.

[0084] Fig. 8 displays the measured electrical frequency responses of the ICRE-IM. Sn response exhibits a deep notch at the resonant frequency of 19 GHz, which suggests that energy is being accumulated at the resonance frequency and there are fewer electrical signal reflections. To further demonstrate the enhanced electrical field, the S21 response of the ICRE- IM is obtained via a free-space coupling measurement. It shows a peak response at the designed resonant frequency, which is believed to be contributed from the polygonal loop. This device provides a large tuning efficiency for EO-based photonic RF phase shifters.

Industrial Applicability

[0085] The arrangements described are applicable to the computer and data processing industries and particularly for the magnetic field sensing industries.

[0086] The foregoing describes only some embodiments of the present invention, and modifications and/or changes can be made thereto without departing from the scope and spirit of the invention, the embodiments being illustrative and not restrictive.

[0087] In the context of this specification, the word “comprising” means “including principally but not necessarily solely” or “having” or “including”, and not “consisting only of”. Variations of the word "comprising", such as “comprise” and “comprises” have correspondingly varied meanings.

Claims

CLAIMS:

1. A photonic phase shifter for controlling a phase shift of an input optical signal, the photonic phase shifter comprising: an optical circuit formed on an electo-optic layer, the optical circuit comprising: an input port for receiving the input optical signal, an output port for sending an output signal, and a microring resonator comprising an optical microring and an optical waveguide; an electrical circuit formed on a dielectric layer, the electrical circuit comprising: at least two RF electrodes for receiving an input electrical signal, a resonant loop, and a capacitive electrode, wherein the RF electrodes are in electrical communication with the capacitive electrode via the resonant loop; wherein the electrical circuit is positioned relative to the optical circuit to enable the capacitive electrode to interact with the microring resonator based on the input electrical signal.

2. The photonic phase shifter of claim 1 , wherein the output port is for sending an output optical signal, wherein the output optical signal is based on the input electrical signal and the input optical signal.

3. The photonic phase shifter of claim 2, wherein the optical input port and the optical output port comprise a vertical grating coupler.

4. The photonic phase shifter of claim 1, wherein the RF electrodes, resonant loop and capacitive electrode form a resistor, inductance, capacitor circuit that resonates at a resonant frequency, wherein at the resonant frequency, the input optical signal has an effective zero-degree shift in phase when passing through the microring resonator.

5. The photonic phase shifter of claim 1, wherein a length of the RF electrodes is one quarter of a wavelength of the resonant frequency for impedance matching the electrical circuit with a connected circuit at a resonant frequency of the electrical circuit.

6. The photonic phase shifter of claim 1, wherein the RF electrodes are formed from a coplanar strip line section with a smoothly varying geometry. The photonic phase shifter of claim 1, further comprising an insulation layer formed on a substrate, wherein the electro-optic layer is formed on the insulation layer, and the dielectric layer is formed on the electro-optic layer. The photonic phase shifter of claim 1 , wherein the output port is for sending an output RF signal, and the optical circuit further comprises a photodetector arranged to generate the output RF signal based on the input optical signal and the input electrical signal. The photonic phase shifter of claim 8, wherein the optical input port comprises a vertical grating coupler. The photonic phase shifter of claim 1, wherein the RF electrodes are configured to achieve arbitrary input impedance matching of the electrical circuit. The photonic phase shifter of claim 10, wherein an electrical length and characteristic impedance of the RF electrodes is configured to match an input impedance of the resonant loop to an arbitrary value, thereby reducing signal reflection of the electrical circuit. The photonic phase shifter of claim 1, wherein the RF electrodes are configured for operation in a superconducting regime. The photonic phase shifter of claim 12, wherein the RF electrodes have a purely real characteristic impedance with equal magnitude to either an on-chip or off-chip terminating impedance, thereby minimizing signal reflection in the electrical circuit. An optical phased array comprising a plurality of the photonic phase shifters of claim 1 and at least one optical antenna, wherein an optical phased array input signal is applied as the input optical signals of the photonic phase shifters, wherein the output signals of the photonic phase shifters are provided to the at least one optical antenna, the optical phased array arranged to steer an optical phased array output signal based on the optical phased array input signal and each of the input electrical signals being applied to the photonic phase shifters. The optical phased array of claim 14 further comprising a beam splitter, wherein the photonic phase shifters are arranged in a parallel configuration, and the beam splitter is arranged to split the optical phased array input signal to provide the input optical signals of the photonic phase shifters. The optical phased array of claim 14 further comprising a plurality of the optical antenna, wherein the photonic phase shifters are arranged in a series configuration and the optical phased array input signal is applied as the input optical signal to each of the photonic phase shifters in sequence, and the optical antennas are arranged to generate the optical phased array output signal. An RF phased array comprising a plurality of the photonic phase shifters of claim 8 and at least one RF antenna, wherein an RF phased array optical input signal is applied as the input optical signals of the photonic phase shifters, wherein the output RF signals of the photonic phase shifters are provided to the at least one RF antenna, the RF phased array arranged to steer an RF phased array output signal based on the RF phased array optical input signal and each of the input electrical signals being applied to the photonic phase shifters. The RF phased array of claim 17 further comprising a beam splitter, wherein the photonic phase shifters are arranged in a parallel configuration, and the beam splitter is arranged to split the RF phased array optical input signal to provide the input optical signals of the photonic phase shifters. The RF phased array of claim 17 further comprising a plurality of the RF antenna, wherein the photonic phase shifters are arranged in a series configuration and the RF phased array optical input signal is applied as the input optical signal to each of the photonic phase shifters in sequence, and the RF antennas are arranged to generate the RF phased array output signal.