Optical coupling device with adjustable coupling coefficient

Abstract

An optical coupling device is presented. The optical coupling device (400) comprises a plurality of input channels (410... 40M); a plurality of output channels (491... 49M); and a plurality of input coupling devices (451a... 45Na), or a plurality of output coupling devices (451b... 45Nb), or a combination of both. Each input coupling device has a coupling channel (411, 421... 4N1) and is configured to couple an optical signal propagating through the respective input channel into the coupling channel with an adjustable coupling coefficient. Each output coupling device has a coupling channel and is configured to couple an optical signal propagating through the coupling channel into a corresponding output channel at an adjustable coupling coefficient.

Description

TECHNICAL FIELD

[0001] The present invention relates to optical coupling devices with tunable coupling coefficients. In particular, the present disclosure relates to configurable optical coupling devices with multiple coupling devices with tunable coupling coefficients. BACKGROUND

[0002] Optical matrix structures comprising matrix multiplication units have been reported for implementing photonic computing, see for example Feldmann, J., Youngblood, N., Karpov, M. et al. Parallel convolutional processing using an integrated photonic tensor core. Nature 589, 52-58 (2021). https: / / doi.org / 10.1038 / s41586-020-03070-1 .

[0003] Conventional optical coupling devices such as optical switches are based on electro-optical conversion. In this approach, an optical input signal is converted into an electrical signal, re-routed, and converted back to an optical signal at the output. Such switch devices are typically slow and can be described as having a high latency. Alternative approaches have been proposed based on fiber architectures and / or using microelectromechanical system (MEMS) modulators. Such systems are still limited by relatively high latency, low efficiency due to optical losses, and lack of flexibility of use. Some MEMS can be designed to have relatively low latency and optical losses, but are typically difficult to manufacture and have a limited number of switching cycles. Current systems can not be designed to perform signal replication.

[0004] Depending on their implementation, some photonic matrix multipliers can have an intrinsic optical loss factor of 1 / (MN), where MxN is the matrix / switch size, plus additional component losses. This loss is introduced by the requirement to split the incident light equally between all columns of the matrix (1 / N) and the incoherent addition of individual matrix multiplication results (1 / M).

[0005] It is an object of the present disclosure to address one or more of the above-mentioned limitations. SUMMARY

[0006] According to a first aspect of the present disclosure, there is provided an optical coupling device comprising: a plurality of input channels; a plurality of output channels; and at least one of a plurality of input coupling arrangements and a plurality of output coupling arrangements; wherein each input coupling arrangement comprises a coupling channel, the input coupling arrangement being configured to couple an optical signal propagating through a corresponding input channel into the coupling channel with an adjustable coupling coefficient; and wherein each output coupling arrangement comprises a coupling channel, the output coupling arrangement being configured to couple an optical signal propagating through the coupling channel into a corresponding output channel with an adjustable coupling coefficient.

[0007] Optionally, the input coupling arrangements and / or the output coupling arrangements comprise a phase shifting element.

[0008] Optionally, the phase shifting element comprises an optical modulator.

[0009] For example, the optical modulator can be a thermal modulator, or a forward-biased electro-absorption modulator (EAM), or a phase change material (PCM) modulator, or a PN phase shifter.

[0010] Optionally, one or more of the plurality of input coupling arrangements and output coupling arrangements are implemented as an interferometer.

[0011] For example, the interferometer can be a Mach-Zehnder interferometer.

[0012] Optionally, the interferometer has a first arm and a second arm, the first arm and the second arm being arranged to form an input combiner-splitter and an output combiner-splitter.

[0013] For example, the input combiner-splitter and the output combiner-splitter can be implemented using a directional coupler or a multimode interference, MMI, coupler.

[0014] Optionally, the coupling channel extends between a first end and a second end.

[0015] Optionally, each input channel extends along a corresponding longitudinal axis, and wherein the input channels are arranged substantially parallel to each other; and wherein the coupling channel is substantially perpendicular to the input channels.

[0016] Optionally, the coupling channel forms part of an input coupling arrangement at the first end, and the coupling channel forms part of an output coupling arrangement at the second end.

[0017] Optionally, the coupling channel forms part of an input coupling arrangement or an output coupling arrangement at the first end, and the coupling channel is coupled to a directional coupler at the second end.

[0018] Optionally, the directional coupler is designed to combine the optical signals in a predetermined ratio, or to separate the optical signals in a predetermined ratio.

[0019] For example, the predetermined ratio can be chosen to obtain equal contributions from each input / output channel.

[0020] Optionally, the plurality of coupling channels forms at least one main group of coupling channels configured to couple a plurality of input channels to a single output channel; and wherein the plurality of coupling channels forms at least one secondary group of coupling channels configured to couple a single input channel to a plurality of output channels.

[0021] Optionally, one or more of the coupling channels is provided with an optical amplifier.

[0022] Optionally, the coupling channel is a closed channel provided with an optical modulator to form a ring resonator.

[0023] Optionally, the ring resonator has an optical path length, and wherein the input optical signal is coupled to the ring resonator when the optical path length is a multiple of an input wavelength of the input optical signal propagating through the corresponding input channel.

[0024] For example, the modulator can be operable to change the optical path length of the ring resonator.

[0025] Optionally, the optical device comprises at least two groups of ring resonators, wherein each group comprises a plurality of ring resonators having the same resonant wavelength, and wherein the ring resonators of different groups have different resonant wavelengths.

[0026] Optionally, the optical device comprises a plurality of wavelength multiplexers, wherein each wavelength multiplexer is coupled to a channel of a specific wavelength.

[0027] Optionally, one or more of the input or output channels is provided with an optical amplifier.

[0028] Optionally, the optical coupling device comprises a controller configured to control the operation of the plurality of phase shifting elements or optical modulators and / or optical amplifiers.

[0029] Optionally, the optical coupling device is bidirectional.

[0030] According to a second aspect of the disclosure, there is provided a system comprising a plurality of optical coupling devices according to the first aspect, wherein each optical coupling device is configured to receive an optical input signal of a specific wavelength.

[0031] Optionally, the system comprises a plurality of wavelength demultiplexers coupled to the input ports of the plurality of optical coupling devices and a plurality of wavelength multiplexers coupled to the output ports of the plurality of optical coupling devices.

[0032] According to a third aspect of the present disclosure, there is provided an integrated optical chip comprising an optical coupling device according to the first aspect.

[0033] According to a fourth aspect of the present disclosure, there is provided a method of manipulating an optical signal, the method comprising: providing an optical coupling device comprising a plurality of input channels, a plurality of output channels, and at least one of a plurality of input coupling devices and a plurality of output coupling devices; wherein each input coupling device comprises a coupling channel, the input coupling device being configured to couple an optical signal propagating through a corresponding input channel into the coupling channel with an adjustable coupling coefficient; and wherein each output coupling device comprises a coupling channel, the output coupling device being configured to couple an optical signal propagating through the coupling channel into a corresponding output channel with an adjustable coupling coefficient; sending the optical signal through the input channels; and operating the plurality of coupling devices to manipulate the optical signal.

[0034] For example, manipulating the optical signal can comprise performing a computational operation or copying the signal. For example, the method can comprise combining several input signals to perform a computational operation.

[0035] According to a fifth aspect of the present disclosure, there is provided a system comprising a plurality of optical coupling devices, a plurality of wavelength demultiplexers coupled to input ports of the plurality of optical coupling devices, and a plurality of wavelength multiplexers coupled to output ports of the plurality of optical coupling devices; wherein each optical coupling device is configured to receive an optical input signal of a specific wavelength.

[0036] The optical coupling device can be any optical switch configured to connect M optical input ports to N optical output ports in a configurable way. The optical coupling device can be implemented in different ways, for example, the optical coupling device can be implemented as described in any one of Figure 2 、 Figure 3 、 Figure 4A 、 Figure 6A 、 Figure 6B 、 Figure 7 or Figure 9 .

[0037] The options described in relation to the first aspect of the present disclosure are also common to the second aspect, the third aspect, the fourth aspect, and the fifth aspect of the present disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0038] The present disclosure is described in more detail below, by way of example and with reference to the accompanying drawings, in which: Figure 1 is a schematic illustration of an optical coupling device; Figure 2 isFigure 1 Figure 1 is a diagram of an exemplary embodiment of an optical coupling device; Figure 3 yes Figure 1 FIG. 1 is a diagram of another exemplary embodiment of an optical coupling device; Figure 4A is a diagram of an optical coupling device with adjustable coupling coefficient; Figure 4B yes Figure 4A a selected portion of an optical coupling device showing an input channel coupled to an output channel; Figure 5 is a diagram of a coupling device implemented as a Mach-Zehnder interferometer; Figure 6A is a diagram of another optical coupling device with adjustable coupling coefficient; Figure 6B yes Figure 6A FIGURE 1 shows a modified version of an optical coupling device; Figure 7 is a diagram of another optical coupling device with adjustable coupling coefficient; Figure 8A is a diagram illustrating the operation of a ring resonator in an add-drop configuration; Figure 8B yes Figure 8A The transmission spectrum of the ring resonator is shown in Figure 2. Figure 9 yes Figure 7 A modified version of the optical coupling device; Figure 10 is a schematic diagram of a system for wavelength selective switching; Figure 11 is a flow chart of a method for manipulating an optical signal. describe

[0039] Figure 1 FIG2 is a schematic diagram of an optical coupling device. An optical coupling device 100 (also known as an optical switch) can be used to connect M optical input ports to N optical output ports in a configurable manner. The coupling device has M input channels and N output channels.

[0040] A plurality of coupling channels (not shown) are also provided. Each coupling channel is configured to couple an input channel to an output channel. Each coupling channel is provided with a dedicated amplitude modulator configured to attenuate or amplify the optical signal. The amplitude modulator may be an optical modulator or an optical amplifier, or a combination of both. A controller, such as an electronic controller or an optical controller, is provided to control the operation of the amplitude modulator.

[0041] The input ports are designed to receive optical input signals labeled Sin_1 - Sin_M. The optical input signals can be generated by one or more light sources and coupled to the input ports. Depending on the type of light source selected, optical coupling can be achieved using optical fibers (e.g., via a grating coupler or edge coupling). Similarly, the output ports are configured to provide optical output signals Sout_1 through Sout_N. The optical coupling device 100 can be used to manipulate the optical signals in various ways. For example, amplitude adjusters can be operated to replicate or duplicate one or more optical signals. The amplitude adjusters can also be operated to perform computational tasks. For example, the controller can be configured to perform addition and / or multiplication of optical signals.

[0042] The optical input signals include information or data to be transmitted. The optical signals can be generated using light sources such as lasers, which are then modulated with the data to be transmitted. The device 100 is designed to route the input optical signals independent of the information or data present in the input optical signals. The device / controller can be configured to route the signals in a predetermined manner depending on the application. Such a device can be referred to as a layer 1 (LI) switch.

[0043] Figure 2 is Figure 1 A diagram of an exemplary embodiment of an optical coupling device. The optical coupling device 200 has four input ports coupled to four input channels 201-204 and four output ports coupled to four output channels 291-294.

[0044] The coupling between the input channels and the output channels is provided by four sets of coupling channels labeled 210, 220, 230, 240 (referred to as main sets). In each main set, the coupling channels are configured to couple multiple input channels to a single output channel.

[0045] The first set 210 has four coupling channels 211, 212, 213, and 214 configured to couple the input channels 201, 202, 203, and 204 to the first output channel 291. The coupling channel 211 is disposed between the first input channel 201 and the first output channel 291; the coupling channel 212 is disposed between the second input channel 202 and the first output channel 291; the coupling channel 213 is disposed between the third input channel 203 and the first output channel 291; and the coupling channel 214 is disposed between the fourth input channel 204 and the first output channel 291.

[0046] Similarly, the second group 220 has four coupling channels 221, 222, 223, and 224 configured to couple the input channels 201, 202, 203, and 204 to the second output channel 292. The third group 230 has four coupling channels 231, 232, 233, and 234 configured to couple the input channels 201, 202, 203, and 204 to the third output channel 293. The fourth group 240 has four coupling channels 241, 242, 243, and 244 configured to couple the input channels 201, 202, 203, and 204 to the fourth output channel 294.

[0047] The device 200 is also provided with four sub-groups. In a sub-group, a coupling channel is configured to couple a single input channel to multiple output channels. The coupling channels 211, 221, 231, and 241 form a first sub-group. The channels 212, 222, 232, and 242 form a second sub-group. The channels 213, 223, 233, and 243 form a third sub-group. The channels 214, 224, 234, and 244 form a fourth sub-group.

[0048] In this way, each input channel can be coupled to multiple outputs. For example, the first channel 201 is coupled to the first output channel 291 via the coupling channel 211, to the second output channel 292 via the coupling channel 221, to the third output channel 293 via the coupling channel 231, and to the fourth output channel 294 via the coupling channel 241.

[0049] It will be appreciated that the above arrangement can be extended to M input channels and N output channels, where M and N are integers. Thus, more generally, each input channel is provided with N coupling channels for coupling to N output channels.

[0050] Each coupling channel extends between a first coupler (also referred to as an input coupler) coupled to an input channel and a second coupler (also referred to as an output coupler) coupled to a corresponding output channel. For example, the coupling channel 211 extends between an input coupler Cia at the input channel 201 and an output coupler Coutla at the output channel 291. Similarly, the coupling channel 214 extends between an input coupler Cid at the input channel 204 and an output coupler Coutld at the output channel 291.

[0051] The couplers can be implemented as directional couplers, or multi-mode interference splitters (MMIS) or Y-splitters. The input coupler is designed to split an input optical signal propagating through the input channel, such that a portion of the signal (also referred to as an intermediate signal) is directed to the coupling channel, while the remaining portion continues to be transmitted through the input channel. Similarly, the output coupler is designed to combine an optical signal propagating through the coupling channel with another optical signal transmitted through the output channel.

[0052] The splitting ratios of the input couplers of the sub-group can be selected so that each of the coupling channels provided along the input channel obtains the same amount or same amplitude of optical signal, so that the input signal is evenly distributed between the N coupling channels of the sub-group. For the sub-group formed by 211, 221, 231 and 241, and assuming no losses, this would mean that coupler Cia couples ¼ of the input optical signal to channel 211, coupler C2acouples 1 / 3 of the remaining optical signal to channel 221, coupler C3acouples ½ of the remaining optical signal to channel 231, and coupler C4acouples all (1 / 1) of the remaining optical signal to channel 241. In this way, each of the coupling channels 211, 221, 231 and 241 receives one quarter of the total input optical signal received at the input port.

[0053] The splitting ratios of the output couplers of the main group can be selected so that the contribution of the M input pairs to the output signal provided at the output port of the main group is equal. For the main group 210, the splitting ratios of the output couplers Coutia, Coutib, Coutic and Coutidcoupled to the first output channel 291 can be ¼, 1 / 3, ½ and 1 / 1, respectively.

[0054] In this example, the output signal received at the output port consists of 3 / 4 of the signal from coupling channels 212, 213 and 214 and 1 / 4 of the signal from coupling channel 211. The signal received by output channel 291 at the output of 212 consists of 2 / 3 of the signal from coupling channels 213 and 214 and 1 / 3 of the signal from coupling channel 212. The signal received by output channel 291 at the output of 213 consists of ½ of the signal from coupling channel 214 and ½ of the signal from coupling channel 213. The signal received by output channel 291 at the output of 214 is 100% (1 / 1) of the signal from coupling channel 214.

[0055] Depending on the device implementation, further adjustments can be required to account for optical losses at the intersection points between the input channels and the coupling channels and optical losses associated with the couplers. Overall, the ratios can be adjusted so that each input contributes the same amount of optical signal to each output.

[0056] Each coupling channel includes an amplitude adjuster, which can be an optical attenuator or an optical amplifier or a combination of both. A controller (not shown) is provided to control the operation of the optical attenuators and / or optical amplifiers as dictated by the selected design.

[0057] In Figure 2In the example, each coupling channel is provided with an amplitude modulator for modulating the optical signal transmitted through the coupling channel. For example, coupling channels 211, 212, 213, and 214 are provided with modulators M1, M2, M3, and M4, respectively. In this configuration, the modulators can be densely packed, thereby reducing the device's footprint. In another embodiment, each modulator can be replaced by or used in combination with an optical amplifier.

[0058] Modulators and / or amplifiers are used to control the degree of transmission of the signal passing through the coupling channel. This allows the configuration of the coupling device to be varied. The modulator is configured to attenuate the optical signal with an adjustable attenuation factor. When the attenuation factor is maximum, the optical signal is extinguished and cannot propagate. Similarly, if the attenuation factor is minimum (e.g., zero), the entire optical signal can propagate. In the case of an optical amplifier, the optical amplifier can have a transmission factor greater than 1, which accounts for the gain of the optical amplifier.

[0059] The output coupler is used to combine the modulated signal transmitted through the coupling channel with other modulated signals transmitted through other coupling channels.

[0060] exist Figure 2 In an example, the input channels are linear channels arranged substantially parallel to one another. The coupling channel has a linear portion disposed between two curved portions of the input coupler and the output coupler. The linear portions of the coupling channel are substantially parallel to one another and perpendicular to the input channels.

[0061] Depending on the design, the input channel and the coupling channel may cross at several intersection points. Alternatively, the input channel and the coupling channel may be arranged in different planes so that they do not cross.

[0062] Optical coupling device 200 can function as an optical switch, connecting M optical input ports to N optical output ports in a reconfigurable manner with ultra-low latency. Device 200 also enables duplication of an input signal from one to multiple connections. The selection of which input is connected to which output can be freely reconfigured at high speed (e.g., at GHz frequencies) by controlling attenuators and / or amplifiers. The device avoids electro-optical conversion of the input signal, thus achieving ultra-low latency (only the time-of-flight of the optical signal, e.g., less than 1 ns). Another advantage is the ability to duplicate signals. In other words, an input optical signal at one input port can be sent to multiple output ports. This can be achieved while compensating for optical losses, ensuring that the intensity of the duplicated output optical signal is sufficient for detection or further processing.

[0063] Figure 3 yes Figure 1 FIG. 300 is another exemplary embodiment of an optical coupling device having aFigure 2 The apparatus 200 of this embodiment has the same architecture as the apparatus 200 of Figure 1, and uses the same reference numerals to label the corresponding components. In this embodiment, each coupling channel is provided with an optical amplifier and an optical attenuator. For example, the coupling channel 211 is provided with an optical amplifier 361a and an optical attenuator 371a. Similarly, the coupling channel 214 is provided with an optical amplifier 361d and an optical attenuator 371d.

[0064] The optical amplifiers can be implemented as semiconductor optical amplifiers SOA. The optical attenuators can be Mach-Zehnder modulators (MZM), also known as Mach-Zehnder interferometers (MZI), or electro-absorption modulators (EAM), or micro-ring resonators, or phase change material (PCM) modulators.

[0065] The attenuators can be used to cancel or cancel out optical signals that should not be transmitted to the output ports. In this scenario, the amplifiers are off and the attenuators are on. The amplifier / attenuator combination can be implemented using the same component or as two separate components. The modulator component (e.g. SOA) can be designed to perform signal amplification when a positive voltage is applied to it, and to perform signal attenuation when a negative voltage is applied to it.

[0066] In operation, an optical input signal propagates through the input channel (e.g. input channel 201), and the input couplers C1a-C4a direct a portion of the optical input signal to the coupling channels 211, 221, 231 and 241, respectively. When the optical amplifier located on one of these coupling channels is turned on, the optical signal propagating through that channel is amplified. This can be used to recover optical losses in the optical path. By turning on multiple optical amplifiers connected to the same input port, multiple output ports can be addressed to perform signal replication.

[0067] As explained above with reference to Figure 2 The splitting ratios of the input couplers C1a, C2a, C3a and C4a can be chosen such that each coupling channel receives ¼ of the input optical signal. If the optical amplifiers 361a, 362a, 363a and 364a are all turned on, each of the coupling channels 211, 221, 231 and 241 can provide the same amplified optical signal at the output channels 291, 292, 293 and 294. This can be achieved by using the same amplification factor for each of the amplifiers 361a-364a, assuming the same optical losses in each coupling channel. Alternatively, different amplification factors can be used to compensate for different optical losses.

[0068] Optical attenuators can be used to prevent optical signals propagating through coupling channels from being transmitted to output channels. For example, optical attenuators 371a, 372a, 373a, and 374a can be disabled, while all other remaining attenuators are enabled to block the propagation of input signals originating from input channels 202, 203, and 204, thereby affecting the output signals at output ports 1-4. In this example, the input optical signal received at input channel 201 will be replicated four times at output ports 1 through 4.

[0069] The replicated output signal has the same waveform profile as the input signal, but can have a different amplitude. As described above, the amplifier configuration allows for compensating for optical losses and even amplifying the signal to levels higher than the input signal. The level of amplification can be selected based on the sensitivity of the optical detector used to sense the output signal.

[0070] It should also be understood that Figure 3 The circuit can be implemented using only optical attenuators without optical amplifiers, although in this case the input signal amplitude will be reduced by >1 / (N*M).

[0071] Figure 2 and Figure 3 An optical switch splits the input signal into N parts, regardless of where the light needs to go. This introduces an undesirable system loss factor of 1 / N. By combining channels with equal split ratios at the output, another loss factor of 1 / M is introduced.

[0072] Figure 4A is a diagram of an optical coupling device with adjustable coupling coefficient. The optical coupling device 400 is similar to Figure 2 or Figure 3 However, in this case, the input and output couplers have been replaced by coupling devices with adjustable coupling coefficients.

[0073] The optical coupling device 400 has M input ports coupled to M input channels 401-40M, and N output ports coupled to N output channels 491-49N. The reference numerals are provided for clarity only, and it is understood that the number of input ports and output ports can be any integer required by the application of the optical coupling device.

[0074] The coupling between the input channels and the output channels is provided by N groups of coupling channels, referred to as main groups. In each main group, the coupling channels are configured to couple multiple input channels to a single output channel.

[0075] The first group has M coupling channels 411, 412...41M configured to couple the input channels 401, 402...40M to the first output channel 491. Coupling channel 411 is arranged between the first input channel 401 and the first output channel 491; coupling channel 412 is arranged between the second input channel 402 and the first output channel 491; and coupling channel 41M is arranged between the input channel 40M and the first output channel 491. Similarly, the second group of main channels couples the input channels 401, 402...40M to the second output channel 492.

[0076] The device 400 is further provided with M sub-groups. In the sub-groups, the coupling channels are configured to couple a single input channel to multiple output channels. For example, coupling channels 411, 421...4N1 form a first sub-group. In this way, each input channel can be coupled to multiple outputs. For example, the first channel 401 is coupled to the first output channel 491 via coupling channel 411, to the second output channel 492 via coupling channel 421, and to the Nth output channel 49N via coupling channel 4N1.

[0077] Each coupling channel extends between a first coupling device (also referred to as an input coupling device) coupled to an input channel and a second coupling device (also referred to as an output coupling device) coupled to a respective output channel.

[0078] For example, coupling channel 411 extends between an input coupling device 451a at input channel 401 and an output coupling device 451b at output channel 491. Similarly, coupling channel 4N1 extends between an input coupling device 45Na at input channel 401 and an output coupling device 45Nb at output channel 49N.

[0079] Each coupling channel can be provided with an optical amplifier 460. The optical amplifier can be implemented as a semiconductor optical amplifier SOA. The SOA is used to recover optical losses, but since the large loss factor of 1 / (MN) is reduced, the required gain is much smaller than the gain in an optical switch of Figure 2 and Figure 3 The position and number of optical amplifiers can vary depending on how much loss can be tolerated.

[0080] Figure 4B is Figure 4Aselected portion of the circuit of Fig. 1, showing the input channel coupled to the output channel. The coupling channel 411 extends between a first end and a second end. The coupling channel 411 forms part of an input coupling device 451a at the first end and part of an output coupling device 451b at the second end. The coupling devices are implemented as interferometers. For example, the input coupling device 451a has two arms: a first arm provided by the input channel 401 and a second arm provided by the coupling channel 411. The second arm comprises an optical phase shifter PS. Thus, the input coupling device 451a is configured to couple the optical signal propagating through the input channel 401 into the coupling channel 411 with an adjustable coupling coefficient.

[0081] Similarly, the output coupling device 451b has a first arm provided by the output channel 491 and a second arm provided by the coupling channel 411. The second arm comprises an optical phase shifter PS. Thus, the output coupling device 451b is configured to couple the optical signal propagating through the coupling channel 411 into the output channel 491 with an adjustable coupling coefficient.

[0082] Figure 5 is a diagram of a coupling device implemented as a Mach-Zehnder interferometer. The coupling device 500 has a first arm 510 and a second arm 520. The second arm 520 comprises an optical phase shifter 530. The coupling device 500 can be used in Figure 4A the circuit of Fig. 1.

[0083] It is to be understood that, in another embodiment, the optical phase shifter 530 can be provided in the first arm 510. In yet another embodiment, two phase shifters can be provided, one in each arm.

[0084] An input combiner-splitter 542 is provided at the input of the coupling device 500 for splitting the input optical signal S0 propagating along the first arm 510 into a first signal S0’ propagating along the first arm 510 and a second signal S0” propagating along the second arm 520. The input combiner-splitter 542 can provide a 50:50 splitting ratio so that S0’ and S0” have the same intensity. Similarly, an output combiner-splitter 544 is provided at the output of the coupling device 500.

[0085] The input combiner-splitter 542 and the output combiner-splitter 544 can be implemented in different ways. For example, using a directional coupler or a multimode interference, MMI, coupler.

[0086] In operation, the phase shifter 530 causes a phase shift between the signal S0’ and the signal S0”. The output combiner-splitter 544 receives the signals S0’ and S0” and generates an interference signal S Int. Depending on their phase difference, the signals S0’ and S0” interfere constructively or destructively.

[0087] Various scenarios can be envisaged. When constructive interference occurs on the second arm 520 and destructive interference occurs on the first arm 510, then the interference signal S Int propagates through the second arm 520 and no signal propagates via the first arm 510. When constructive interference occurs on the first arm 510 and destructive interference occurs on the second arm 520, then the interference signal S Int propagates through the first arm 510 and no signal propagates via the second arm 520.

[0088] Some constructive interference can also occur on both arms 510 and 520, in which case the interference signal S Int is split by the output combiner-beamsplitter 544 between the first and second arms. Depending on the degree of interference in each arm, various splitting ratios are possible. Thus, since the coupling coefficient is adjustable, so is the splitting ratio.

[0089] The signals S1 and S2 have optical powers P 1 and P 2, respectively, defined as: and , P 0 is the optical power of the signal S0, and is the phase difference between S0' and S0". Thus, the splitting ratio between the signals S1 and S2 depends on the phase difference A controller (not shown) is provided to operate the phase shifter and determine the phase shift to be introduced between S0' and S0".

[0090] Thus, the coupling device 500 is configured to couple the input optical signal into the coupling channel 520 with an adjustable coupling coefficient. When the coupling coefficient is 1, 100% of the input signal is coupled into the coupling channel 520. When the coupling coefficient is 0, 100% of the input signal is transmitted through the input channel 510. When the coupling coefficient is 50, 50% of the input signal is coupled into the coupling channel 520 and the remaining 50% is transmitted through the input channel 510.

[0091] The coupling device 500 can be used to implement various input and output coupling devices in the circuit of Figure 4A .

[0092] The phase shifter 530 can be implemented in different ways. For example, the phase shifter 530 can be a PN phase shifter, or a thermal modulator, or a forward-biased electro-absorption modulator (EAM), or a phase change material (PCM) modulator. The phase shift modulator 530 can be made of different materials, including for example silicon, silicon nitride, InP, lithium niobate, polymers, graphene, etc.

[0093] The optical arrangement 500 forms an interferometer structure which can be referred to as a Mach-Zehnder modulator (MZM) structure or a Mach-Zehnder interferometer (MZI) structure. The MZM acts as a tunable beam splitter. In this way, light is not always split equally to all columns but is specifically directed to the desired output. It reduces the loss and also the cross-talk between channels.

[0094] In Figure 4A The use of optical arrangements 451a, 452A...45NA allows to direct the desired amount of signal to the coupling channels 411, 421...4N1 by adjusting the coupling factor of each optical arrangement.

[0095] The default state can be chosen such that light is transmitted directly through the optical arrangement. When the correct coupling channel is reached, the coupling arrangement is operated to transfer the optical signal to the coupling channel. If the optical signal needs to be transferred to multiple output ports, the coupling factor / splitting ratio of the coupling arrangement is adjusted accordingly.

[0096] The optical arrangements 451a, 452a... 45Na can for example be controlled such that 100% of the input signal received at the input channel 401 is coupled to the coupling channel 421. Alternatively, the optical arrangements 451a, 452a... 45Na can be controlled such that 50% of the input signal is coupled to the coupling channel 411 and 50% of the input signal is coupled to the coupling channel 421. This approach allows to direct the input signal directly to a specific output without splitting the light to any other output which is not needed. To recover the optical loss, the signal is passed through a SOA. At the output stage, M column channels can be combined into one output. In Figure 2 In an implementation, this is achieved by setting equal splitting ratios between all of them such that a loss of 1 / M is introduced in total.

[0097] Since only one input at a time is transmitted to a certain output, this loss factor can be removed in the same way as the input and the splitting ratio of the coupling arrangement is adjusted to couple only the correct input to the output channel. A further stage of optical amplifiers 460 at the output can be used to further reduce or compensate the optical loss. The reduction of the optical loss means that less gain is needed which reduces the requirements on the SOA. In turn, this reduces the power consumption and allows to implement a device with a smaller footprint.

[0098] Figure 6A is another schematic diagram of an optical coupling device with adjustable coupling factors. The optical coupling device 600A is similar to the optical coupling device 400 of Fig. 4, however in this case the optical coupling arrangements 451b, 452b and 45Nb are replaced by output couplers with fixed splitting ratios. This reduces the number of phase shifters needed and the footprint of the device.

[0099] Figure 6B is Figure 6A a modified version of the optical coupling device of

[0100] Of course, it will be appreciated that further variations of the optical switch shown in Fig. 4, Figure 5 and Fig. 6 can be envisaged, including the number and location of fixed couplers, the number and location of optical amplifiers, etc.

[0101] Figure 6A and Figure 6B The optical switches of

[0102] It will be appreciated that Figure 6A and Figure 6B The devices of

[0103] In applications involving signal replication, it can be beneficial to have a fixed splitting ratio at the input stage. In a standard implementation with tunable splitting at the input, the signal reaching the respective SOA decreases with the number of replications (as the initial MZM only couples part of the light to the column). This has to be corrected by the SOA at the output (by increasing the gain).

[0104] Figure 7 is another schematic of an optical coupling device with tunable coupling coefficients. The optical coupling device 700 has M input ports coupled to M input channels 701-70M, and N output ports coupled to N output channels 791-79N. The coupling between the input channels and the output channels is provided by N groups of coupling channels, referred to as main groups. In each main group, the coupling channels are configured to couple multiple input channels to a single output channel. The first group has M coupling channels 711, 712...71M, which are configured to couple the input channels 701, 702...70M to a first output channel 791. Similarly, the second group of main channels couples the input channels 701, 702...70M to a second output channel 792.

[0105] The device 700 further comprises M sub-groups. In the sub-groups, the coupling channels are configured to couple a single input channel to multiple output channels. For example, the coupling channels 711, 721...7N1 form a first sub-group. In this way, each input channel can be coupled to multiple outputs. For example, the first channel 701 is coupled to the first output channel 791 via the coupling channel 711, to the second output channel 792 via the coupling channel 721, to the Nth output channel 79N via the coupling channel 7N1.

[0106] Each coupling channel is a closed channel with a modulator Md to form a ring resonator, also called optical micro-ring modulator. Each ring resonator is arranged in a so-called add-drop configuration, which means that two channels are coupled to the ring resonator (in this case a horizontal input channel and a vertical output channel). For example, the coupling channel 711 is a ring channel for coupling the first input channel 701 to the first output channel 791. Similarly, the coupling channel 712 is a ring channel for coupling the second input channel 702 to the first output channel 791, and so on.

[0107] Each ring resonator forms a coupling device configured to couple an optical signal propagating through the corresponding input channel into the coupling channel with an adjustable coupling coefficient. Each output channel can be provided with an optical amplifier 760, such as a SOA. The ring-based implementation also eliminates the 1 / (M*N) loss factor.

[0108] In operation, if an input signal with a wavelength λ1 is in resonance with the ring resonator, the signal is coupled into the ring resonator and transmitted to the corresponding output channel. On the other hand, if the input signal is not in resonance with the ring resonator, the input signal is transmitted through the input channel. The modulator Md allows to tune the resonance of the ring resonator, and thus the coupling coefficient of the coupling device. Various coupling coefficients can be obtained. This is because the resonance peak has a certain width according to the quality factor of the resonator. A resonance response zone (slope) can be defined between the off-resonance and the full on-resonance. Along this resonance response zone different splitting ratios can be achieved.

[0109] The optical amplifier 760 is used to recover the losses in the ring resonator.

[0110] This approach is ideally used for a single input wavelength. If the input signal has multiple wavelengths, the ring resonators need to be carefully designed and tuned so that the free spectral range (FSR) of the ring resonator matches the wavelength spacing. The free spectral range can be defined as the distance in the spectrum (optical frequency or optical wavelength) of the resonance repetition (optical maximum) of the ring.

[0111] Depending on the application, the optical signals received at the input channels 701-70M can have the same wavelength λ1 (or wavelength range), or different wavelengths λi (or wavelength ranges). For example, when using the circuit 700 as a matrix multiplier, the input optical signals can all have different input wavelengths.

[0112] Figure 8A is a diagram illustrating the operation of a ring resonator in an add-drop configuration. The ring resonator 810 is coupled to a first (input) waveguide 820 and a second (output) waveguide 830. In this example, the first and second waveguides are parallel to each other, but can be arranged differently, for example as in Figure 7 The ring waveguide 810 is provided with a modulator Md. The modulator can be operated to change the refractive index of the ring waveguide and thus its optical path length.

[0113] The input waveguide 820 is in close proximity (typically <1 μιη) to the ring waveguide 810, so that light can be evanescently coupled to the ring. Similarly, the output waveguide 830 is also provided in close proximity to the ring waveguide 810. The input waveguide 820 extends between an input port and a through port. Similarly, the output waveguide 830 extends between an add port and a drop port.

[0114] In operation, an input optical signal received at the input port exits at the through port of the waveguide 820 or at the drop port of the waveguide 830.

[0115] For a resonant condition, the optical path length of the ring resonator matches a multiple of the wavelength of the input optical signal, following the equation where is the effective refractive index of the waveguide. Thus, the optical signal is coupled to the ring resonator and exits at the drop port.

[0116] For a non-resonant condition, the optical path length of the ring resonator does not match a multiple of the wavelength of the input optical signal. As a result, the optical signal is not coupled to the ring resonator (destructive interference), and all the light exits at the through port.

[0117] In a simple picture, the first arriving photons split between the through port and the ring (as in a directional coupler). After a while, when the first photons in the ring have made one round trip and arrive at the coupling point, they interfere with the light from the input. If the light now coupled out of the ring destructively interferes with the light of the through port, no light exits the through port. Similarly, if the light is in resonance with the ring, constructive interference occurs inside the ring, and light can exit at the drop port.

[0118] Figure 8B isFigure 8A A plot of the transmission spectrum of a ring resonator; the transmission spectrum shows that non-resonant wavelengths are transmitted to the through port, and resonant light exits at the drop port. Resonances repeat at a certain distance, called the free spectral range (FSR).

[0119] The complex mode amplitudes (E-field) at the through and drop ports can be expressed as:

[0120] .

[0121] where t1and t2are the complex coupling factors, a is the ring resonator loss factor, and 0 is a geometric factor expressed as a function of the radius r and the wavelength l .

[0122] This translates into optical power: P 直通 =

[0123] P 分出 = .

[0124] Figure 9 is a modified version of the optical coupling device of Figure 7 The optical coupling device 900 is similar to the device 700 of Figure 7 In this case, multiple ring resonators with different resonant wavelengths are provided.

[0125] For example, the input channel 901 is provided with a first ring resonator 911' coupled to the output channel 991a and a second ring resonator 911" coupled to the output channel 991b. The ring resonator 911' has a resonant wavelength l1, while the ring resonator 911" has a resonant wavelength l2.

[0126] Similarly, the input channel 902 is provided with a first ring resonator 912' coupled to the output channel 991a and a second ring resonator 912" coupled to the output channel 991b, etc.

[0127] The output channels 991a and 991b are coupled to a wavelength multiplexer 971. The output of the multiplexer is coupled to a single output channel 991, which can be provided with an amplitude amplifier 960. Similarly, the output channels 992a and 992b are coupled to a wavelength multiplexer 972, etc.

[0128] It will be appreciated that the architecture of the optical switch 900 can be extended to more wavelengths by adding additional output channels and additional ring resonators with different resonant wavelengths.

[0129] The topology of the optical switch 900 eliminates the need for precise alignment of the FSR with the channel spacing. It also enables wavelength selective switching.

[0130] Figure 10 is a schematic diagram of a system for wavelength selective switching. The system 1000 includes a first optical switch 1010 and a second optical switch 1020. The first optical switch 1010 is configured to receive optical input signals of wavelength λ1, while the second optical switch 1020 is configured to receive optical input signals of wavelength λ2. The first optical switch 1010 can be implemented as an optical switch 700 with a ring resonator having a resonance wavelength λ1. Figure 7 Similarly, the second optical switch 1020 can be implemented as an optical switch 700 with a ring resonator having a resonance wavelength λ2.

[0131] A set of wavelength demultiplexers 1031, 1032, 1033 is provided to deliver optical input signals of wavelength λ1 to the first optical switch 1010 and optical input signals of wavelength λ2 to the second optical switch 1020. Similarly, a set of wavelength multiplexers 1041, 1042, 1043 is provided to collect optical output signals of wavelength λ1 from the first optical switch 1010 and optical output signals of wavelength λ2 from the second optical switch 1020.

[0132] The system 1000 is shown as a 3x3 optical switch with 2 wavelengths, however the system can be extended to a larger number of wavelengths. This can be achieved by providing one NXM optical switch per wavelength. Different architectures can be used to implement the NXM optical switch, for example the optical switches described above with reference to Figure 2 , Figure 3 , Figure 4A , Figure 6A , Figure 6B and Figure 7 .

[0133] The system 1000 allows input signals with different wavelengths to be separated and switched individually. The system adds wavelength selective switching (each wavelength in the input fiber can be routed independently) and simplifies support for a larger wavelength range. Furthermore, the SOA design is simplified and crosstalk (cross-gain modulation) is reduced.

[0134] Figure 11 is a flow diagram of a method for manipulating optical signals. The method includes steps 1110 to 1130. The optical coupling device as described with reference to Figures 1 to 10 may be implemented using integrated optical circuits such as photonic integrated circuits (PICs) or with fiber-based components.

[0135] The input channels, coupling channels and output channels can be implemented in a single layer. In this case, the input channels and coupling channels can cross at several cross-overs. This can result in some signal loss and optical cross-talk. For example, optical signals can be scattered into another (perpendicular) channel at the cross-overs. Alternatively, the input channels can be formed within a first layer, while the coupling channels and output channels are formed within a second layer. The first layer can be arranged in a first plane, and the second layer can be arranged in a second plane substantially parallel to the first plane. For example, the second layer can be arranged above or below the first layer. In this way, channel crossings can be avoided, thus reducing optical loss.

[0136] The various channels can be implemented as waveguides, such as integrated waveguides. The waveguides can be made of the same or different materials. In a particular example, the input waveguides can be implemented in a silicon nitride layer, while the coupling waveguides can be implemented in a silicon layer. The silicon layer can be arranged underneath the silicon nitride layer. This approach allows to build compact devices with fast signal transmission times between the input port and the output port. For example, a compact photonic integrated circuit of less than 2x2 cm2may be implemented, thus reducing the flight time to achieve ultra-low latency and recover signal loss via optical amplifiers.

[0137] The optical coupling device can be designed to operate at different wavelengths depending on the application. For example, the optical coupling device can be designed to operate across the main telecommunication window of wavelengths of about 1200-1600 nm.

[0138] The optical coupling device of the present disclosure can be used for different applications. As mentioned above, the optical coupling device can be used to replicate an input optical signal multiple times and distribute the replicated signals at multiple outputs.

[0139] The optical coupling device can also be used as a computing device for performing computational tasks, e.g. as a multiplication matrix. Modulation of the optical signals can be used to perform a multiplication operation of the optical signals by a predetermined coefficient. While accumulation of the modulated signals can be used to perform a multiply-accumulate (MAC) operation. The accumulation is performed by superimposing the signals over time. For example, an amplitude adjuster can be operated to accumulate several optical signals. By connecting multiple optical coupling devices together, the size of the matrix can be increased.

[0140] With reference to Figures 4 to Figure 10 The described optical switch allows to reduce or eliminate the 1 / (MN) loss factor by directing the light through only the required paths. This results in lower power consumption, as less on-chip gain is needed, allowing to build larger switches (higher port count). The cross-talk between channels is also reduced.

[0141] Figure 2 、 Figure 3 、 Figure 4A 、 Figure 6A 、Figure 6B 、 Figure 7 、 Figure 9 The device described in the above is a bidirectional device that can operate in two directions. This means that the input signal can be sent through the output channel. In other words, the input and output channels can be exchanged so that the output channel becomes the input channel and the input channel becomes the output channel.

[0142] The skilled person will understand that variations of the disclosed arrangements are possible without departing from the disclosure. The above description of specific embodiments is therefore to be taken only by way of example and not for the limitation purposes. The skilled person will be aware that small modifications can be made without significantly altering the described operation.

Claims

1. An optical coupling device, comprising: Multiple input channels; Multiple output channels; and at least one of a plurality of input coupling means and a plurality of output coupling means; wherein each input coupling device comprises a coupling channel, and the input coupling device is configured to couple an optical signal propagating through the corresponding input channel into the coupling channel with an adjustable coupling coefficient; and Each output coupling device includes a coupling channel, and the output coupling device is configured to couple the optical signal propagating through the coupling channel into the corresponding output channel with an adjustable coupling coefficient.

2. The optical coupling device according to claim 1, wherein The input coupling means and / or the output coupling means comprise a phase shifting element.

3. The optical coupling device according to claim 2, wherein: The phase shift element includes a light modulator.

4. The optical coupling device according to claim 2 or 3, wherein: One or more coupling means of the plurality of input coupling means and the plurality of output coupling means are implemented as an interferometer.

5. The optical coupling device according to claim 4, wherein: The interferometer has a first arm and a second arm arranged to form an input combiner-beamsplitter and an output combiner-beamsplitter.

6. An optical coupling device according to any one of the preceding claims, wherein The coupling channel extends between a first end and a second end.

7. The optical coupling device according to claim 6, wherein: Each input channel extends along a corresponding longitudinal axis, and wherein the input channels are arranged substantially parallel to each other; and wherein the coupling channel is substantially perpendicular to the input channels.

8. The optical coupling device according to claim 6 or 7, wherein: The coupling channel forms part of an input coupling arrangement at the first end, and wherein the coupling channel forms part of an output coupling arrangement at the second end.

9. The optical coupling device according to claim 6 or 7, wherein: The coupling channel forms part of an input coupling arrangement or an output coupling arrangement at the first end, and wherein the coupling channel is coupled to a directional coupler at the second end.

10. The optical coupling device according to claim 9, wherein: The directional coupler is designed to combine optical signals at a predetermined ratio, or to separate optical signals at a predetermined ratio.

11. An optical coupling device according to any one of the preceding claims, wherein The plurality of coupling channels form at least one main group of coupling channels configured to couple the plurality of input channels to a single output channel; and wherein the plurality of coupling channels form at least one secondary group of coupling channels configured to couple the single input channel to a plurality of output channels.

12. An optical coupling device according to any one of the preceding claims, wherein One or more coupling channels are provided with an optical amplifier.

13. The optical coupling device according to claim 1, wherein: The coupling channel is a closed channel provided with an optical modulator to form a ring resonator.

14. The optical device according to claim 13, wherein The ring resonator has an optical path length, and wherein the input optical signal is coupled to the ring resonator when the optical path length is a multiple of an input wavelength of the input optical signal propagating through a corresponding input channel.

15. The optical device according to claim 13 or 14, comprising at least two groups of ring resonators, wherein: Each group includes a plurality of ring resonators having the same resonant wavelength, and the ring resonators of different groups have different resonant wavelengths.

16. The optical device according to claim 15, comprising a plurality of wavelength multiplexers, wherein Each wavelength multiplexer is coupled to a channel of a specific wavelength.

17. An optical coupling device according to any one of the preceding claims, wherein One or more input channels or output channels are provided with optical amplifiers.

18. An optical coupling device according to any preceding claim, comprising a controller configured to control the operation of the plurality of phase shifting elements or optical modulators and / or optical amplifiers.

19. An optical coupling device according to any one of the preceding claims, wherein The optical coupling device is bidirectional.

20. A system comprising a plurality of optical coupling devices according to any one of the preceding claims, wherein: Each optical coupling device is configured to receive an optical input signal of a specific wavelength.

21. The system of claim 20, comprising a plurality of wavelength demultiplexers coupled to input ports of the plurality of optical coupling devices and a plurality of wavelength multiplexers coupled to output ports of the plurality of optical coupling devices.

22. An integrated optical chip comprising the optical coupling device according to any one of claims 1 to 19.

23. A method of manipulating an optical signal, the method comprising: Providing an optical coupling device, the optical coupling device comprising: a plurality of input channels; a plurality of output channels; and at least one of a plurality of input coupling means and a plurality of output coupling means; wherein each input coupling device comprises a coupling channel, and the input coupling device is configured to couple an optical signal propagating through the corresponding input channel into the coupling channel with an adjustable coupling coefficient; and Each output coupling device includes a coupling channel, and the output coupling device is configured to couple the optical signal propagating through the coupling channel into the corresponding output channel with an adjustable coupling coefficient; sending the optical signal through an input channel; and The plurality of coupling devices are operated to manipulate the optical signal.

24. A system comprising a plurality of optical coupling devices, a plurality of wavelength demultiplexers coupled to input ports of the plurality of optical coupling devices, and a plurality of wavelength multiplexers coupled to output ports of the plurality of optical coupling devices; wherein Each optical coupling device is configured to receive an optical input signal of a specific wavelength.

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