Method for adjusting delay difference of unequal arm interferometer chip and time phase encoding chip

Abstract

The application discloses a delay difference adjustment method for an unequal-arm interferometer chip and a time phase encoding chip, wherein by introducing an adjustable optical delay module realized by means of an interferometer structure in the optical arm of the unequal-arm interferometer chip (module), the optical transmission path of the optical signal can be switched, the time delay realized by the adjustable optical delay module can be adjusted, and the adjustment of the delay difference of the unequal-arm interferometer chip and the time phase encoding chip is realized by changing the parameters (such as a modulation phase, an optical attenuation value, etc.) of the interferometer structure, so that the problem that the productization of the time phase encoding chip is limited due to the too large actual delay line length difference between different batches or different chips in the same batch in the prior art is effectively solved.

Description

Delay difference adjustment method for unequal arm interferometer chip and time phase encoding chip Technical Field

[0001] This invention relates to the field of quantum secure communication, and in particular to a method for adjusting the delay difference of unequal-arm interferometer chips and time phase encoding chips. Background Technology

[0002] Quantum key distribution (QKD) is based on the principles of quantum mechanics. Due to the quantum no-cloning and uncertainty principles, it is a theoretically provably unconditionally secure key distribution system. With the development of quantum key distribution technology, providing small-sized, low-cost, and highly stable quantum key distribution devices will become more competitive. Quantum key distribution often involves complex optical signal encoding and decoding. Currently, its encoding and decoding structures are often formed by combining traditional fiber optic devices, resulting in large size and high cost. Implementing optical signal encoding and decoding on optical chips is one of the important solutions for small-sized, low-cost, and highly stable quantum key distribution devices.

[0003] Figure 1 illustrates a transmitter encoding module of an integrated time-phase quantum key distribution system in the prior art. As shown in Figure 1, the encoding module utilizes optical beamsplitter one, optical beamsplitter two, phase modulation module one, and phase modulation module two to form an equal-arm interferometer, and utilizes optical beamsplitter two, an optical waveguide delay module, and a beam combiner to form an unequal-arm interferometer. By modulating the phase difference in the equal-arm interferometer, the output port of the optical signal can be dynamically modulated so that the optical signal travels only along the long arm or the short arm in the unequal-arm interferometer, or simultaneously along both arms, thereby preparing four states conforming to the BB84 protocol.

[0004] Figure 2 illustrates another packaging structure for a time-phase encoded quantum key distribution system in the prior art. As shown in Figure 2, the packaging structure utilizes optical beamsplitter BS1, Heater1, and optical beamsplitter BS2 to form an equal-arm MZ interferometer, and connects the equal-arm interferometer to an unequal-arm interferometer. Similarly, by modulating the phase difference in the equal-arm interferometer with Heater1, the output port of the optical signal is dynamically modulated so that the optical signal travels only along the long arm or the short arm in the unequal-arm interferometer, or simultaneously along both arms, thereby preparing four states conforming to the BB84 protocol.

[0005] Therefore, time-phase encoding schemes typically require the use of unequal-arm interferometers, where even minute deviations in arm length can alter the interference results. Deviations reaching the hundreds of nanometers level can lead to completely opposite interference outcomes. For example, if the inherent bias in the interferometer is too large, exceeding the coherence length of the light source, it will directly prevent the measurement of interference phenomena. In addition to controlling the inherent bias of the interferometer, it is also necessary to control random biases caused by environmental changes (which cause phase fluctuations in the light pulses passing through the interferometer). This is often achieved through real-time closed-loop compensation using phase modulators / phase shifters and detectors. However, while phase modulators / phase shifters offer relatively fast adjustment rates, their adjustment range is limited to a few π phases (corresponding to optical path lengths on the order of several micrometers), which is insufficient to handle situations with large inherent biases in the interferometer arm length differences.

[0006] To reduce the impact of arm length difference deviations in interferometers, the main approach currently is to precisely control the arm length difference using processes such as fiber polishing, keeping the inherent deviation of the arm length difference between two or a batch of interferometers to a small level. Simultaneously, vibration damping and thermal insulation designs can be introduced into the interferometer to reduce the impact of environmental disturbances, and real-time compensation can be achieved using devices such as phase modulators / phase shifters, as disclosed in existing technologies such as "Faraday-Michelson system for quantum cryptography," CN201822228162.7, and CN201822226830.2. However, it is noteworthy that these solutions often result in interferometers with large size, poor stability, and complex systems.

[0007] Figure 1 illustrates a solution where the long arm of the interferometer is implemented using a waveguide delay module formed by a segment of waveguide. This solution achieves a small size and good resistance to environmental disturbances, but it is in chip form. Once the chip is fabricated, it is difficult to adjust the interferometer arm length difference, thus requiring high consistency in chip fabrication processes. In fact, due to limitations in chip fabrication processes, interferometers from different wafers, and even those from the same wafer, can have significant differences. This leads to a large inherent deviation in the interferometer arm length difference, far exceeding the adjustment range of phase modulators / phase shifters, and even exceeding the coherence length of general light sources. This makes it impossible to measure interference phenomena using conventional light sources. Furthermore, once the chip is fabricated, it cannot be adjusted, which limits its practical application and large-scale networking (requiring interferometers to be arbitrarily paired with minimal difference in arm length difference after pairing). This may be one of the main reasons hindering the large-scale deployment of on-chip interferometer products.

[0008] Figure 3 illustrates another solution proposed in the prior art: designing an adjustable delay unit at the receiver. As shown in Figure 3, this solution requires the design of active devices (e.g., phase modulators) at the receiver. However, typical active devices are polarization-sensitive, and fiber optic links cause random polarization variations. Therefore, a polarization-independent receiver or a polarization compensation device needs to be designed accordingly, which significantly increases system complexity and technical difficulty. Furthermore, designing a correlated adjustable delay unit at the receiver increases losses and reduces the performance of the quantum key distribution device. Summary of the Invention

[0009] To address the aforementioned problems in the prior art, this invention discloses a method for adjusting the delay difference of unequal-arm interferometer chips and time-phase encoding chips. By introducing an adjustable optical delay module implemented using an interferometer structure onto the optical arm of the unequal-arm interferometer chip (module), the waveguide length used for the optical signal can be switched by simply changing the parameters of the interferometer structure (e.g., modulation phase, optical attenuation value, etc.), thereby adjusting the delay amount introduced by the adjustable optical delay module on the optical arm. This effectively solves the problem of excessively large differences in actual delay line length between different batches or different chips within the same batch, which limits the commercialization of time-phase encoding chips.

[0010] The first aspect of the present invention relates to a method for adjusting the delay difference of an unequal-arm interferometer chip, wherein,

[0011] The unequal-arm interferometer chip includes a first optical beam splitter and a first optical beam combiner. The two outputs of the first optical beam splitter are respectively connected to the two inputs of the first optical beam combiner through first and second waveguides.

[0012] At least one of the first and second waveguides is provided with an adjustable optical delay module for providing a time delay for optical signals propagating along the waveguide;

[0013] The tunable optical delay module includes one or more cascaded delay switching units, which are implemented based on an interferometer structure.

[0014] The delay difference adjustment method includes an adjustment step, which is used to switch the transmission path for the optical signal by changing the parameters of the interferometer structure, so as to adjust the delay difference of the unequal arm interferometer chip.

[0015] Furthermore, the delay switching unit includes an equal-arm MZ interferometer with an input end and two output ends. The phase difference between the two arms of the equal-arm MZ interferometer is adjustable, and the two output ends are respectively connected to the two input ends of the second optical beam combiner through a third and a fourth waveguide. The third and fourth waveguides have different optical path lengths.

[0016] In the adjustment step, by adjusting the phase difference between the two arms of the equal-arm MZ interferometer, one of the two output terminals of the equal-arm MZ interferometer is selected for outputting an optical signal.

[0017] Furthermore, tunable optical attenuators are respectively provided on the third and fourth waveguides; and,

[0018] The adjustment step also includes adjusting the attenuation value of the adjustable optical attenuator to cause the optical signal to be extinguished on the third or fourth waveguide.

[0019] Furthermore, the method may also include a preset step for pre-setting a lookup table between the delay difference of the unequal-arm interferometer chip and the phase difference between the two arms of the equal-arm MZ interferometer;

[0020] In the adjustment step, the phase difference between the two arms of the equal-arm MZ interferometer is obtained using the lookup table.

[0021] Furthermore, the delay switching unit includes a third optical beam splitter and a third optical beam combiner. The two outputs of the third optical beam splitter are connected to the two inputs of the third optical beam combiner through a seventh waveguide and an eighth waveguide, respectively. Adjustable optical attenuators are provided on the seventh waveguide and the eighth waveguide, and the seventh waveguide and the eighth waveguide have different optical path lengths.

[0022] In the adjustment step, the optical signal is extinguished on the seventh or eighth waveguide by adjusting the attenuation value of the adjustable optical attenuator.

[0023] Furthermore, at least one of the first and second waveguides is provided with an attenuation control module for providing controllable attenuation of the optical signal propagating along the waveguide;

[0024] The delay difference adjustment method further includes a power control step, used to adjust the attenuation amount of the attenuation control module according to the time delay of the adjustable optical delay module.

[0025] Optionally, the attenuation control module includes a carrier injection attenuator.

[0026] Preferably, the optical beam splitter and optical beam combiner are multimode interferometers or directional couplers; and / or, the optical beam splitter, optical beam combiner and waveguide are made of silicon.

[0027] Optionally, the third waveguides in different delay switching units have the same or different optical path lengths, and the fourth waveguides in different delay switching units have the same or different optical path lengths.

[0028] Optionally, the seventh waveguides in different delay switching units have the same or different optical path lengths, and the eighth waveguides in different delay switching units have the same or different optical path lengths; and / or, the adjustable optical attenuator is implemented based on the carrier injection principle or based on the MZ interferometer principle.

[0029] A second aspect of the present invention relates to a delay difference adjustment method for a time phase encoding chip, wherein,

[0030] The time phase encoding chip includes a second optical beam splitter, a first optical beam splitter, and a first optical beam combiner;

[0031] The two outputs of the second optical beam splitter are connected to the two inputs of the first optical beam splitter through the fifth and sixth waveguides, respectively. At least one of the fifth and sixth waveguides is provided with a phase adjustment module for phase modulation of the optical signal, thereby forming an equal-arm interferometer chip module.

[0032] The two outputs of the first optical beam splitter are respectively connected to the two inputs of the first optical beam combiner through the first and second waveguides. At least one of the first and second waveguides is provided with an adjustable optical delay module for providing time delay for the optical signal, thereby forming an unequal arm interferometer chip module.

[0033] The tunable optical delay module includes one or more cascaded delay switching units, which are implemented based on an interferometer structure.

[0034] The delay difference adjustment method includes an adjustment step, which is used to switch the transmission path for the optical signal by changing the parameters of the interferometer structure, so as to adjust the delay difference of the unequal arm interferometer chip module.

[0035] Furthermore, the delay switching unit includes an equal-arm MZ interferometer with an input end and two output ends. The phase difference between the two arms of the equal-arm MZ interferometer is adjustable, and the two output ends are respectively connected to the two input ends of the second optical beam combiner through a third and a fourth waveguide. The third and fourth waveguides have different optical path lengths.

[0036] In the adjustment step, by adjusting the phase difference between the two arms of the equal-arm MZ interferometer, one of the two output terminals of the equal-arm MZ interferometer is selected for outputting an optical signal.

[0037] Furthermore, tunable optical attenuators are respectively provided on the third and fourth waveguides; and,

[0038] The adjustment step also includes adjusting the attenuation value of the adjustable optical attenuator to cause the optical signal to be extinguished on the third or fourth waveguide.

[0039] Preferably, the method may further include a preset step for setting a lookup table between the delay difference of the unequal-arm interferometer chip module and the phase difference between the two arms of the equal-arm MZ interferometer in advance;

[0040] In the adjustment step, the phase difference between the two arms of the equal-arm MZ interferometer is obtained using the lookup table.

[0041] Furthermore, the delay switching unit includes a third optical beam splitter and a third optical beam combiner. The two outputs of the third optical beam splitter are connected to the two inputs of the third optical beam combiner through a seventh waveguide and an eighth waveguide, respectively. Adjustable optical attenuators are provided on the seventh waveguide and the eighth waveguide, and the seventh waveguide and the eighth waveguide have different optical path lengths.

[0042] In the adjustment step, the optical signal is extinguished on the seventh or eighth waveguide by adjusting the attenuation value of the adjustable optical attenuator.

[0043] Furthermore, at least one of the first and second waveguides is provided with an attenuation control module for providing controllable attenuation of the optical signal propagating along the waveguide;

[0044] The delay difference adjustment method further includes a power control step, used to adjust the attenuation amount of the attenuation control module according to the time delay of the adjustable optical delay module.

[0045] Optionally, the attenuation control module includes a carrier injection attenuator.

[0046] Preferably, the phase adjustment module is a carrier deposition type, a carrier injection type, or a carrier depletion type; and / or, the optical beam splitter and optical beam combiner are multimode interferometers or directional couplers; and / or, the optical beam splitter, optical beam combiner, and waveguide are made of silicon.

[0047] Optionally, the third waveguides in different delay switching units have the same or different optical path lengths, and the fourth waveguides in different delay switching units have the same or different optical path lengths.

[0048] Optionally, the seventh waveguides in different delay switching units have the same or different optical path lengths, and the eighth waveguides in different delay switching units have the same or different optical path lengths. Attached Figure Description

[0049] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0050] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0051] Figure 1 shows the transmitter encoding module of an integrated time-phase quantum key distribution system in the prior art;

[0052] Figure 2 shows the packaging structure for a time-phase encoded quantum key distribution system in the prior art;

[0053] Figure 3 shows a receiver structure with an adjustable delay unit in the prior art;

[0054] Figure 4 shows an example of the adjustable delay difference unequal arm interferometer chip module and time phase encoding chip of the present invention;

[0055] Figure 5 schematically illustrates the cascaded configuration of the tunable delay module of the present invention;

[0056] Figure 6 schematically illustrates an example of the delay switching unit of the present invention;

[0057] Figure 7 schematically illustrates an example of a cascaded implementation of a tunable delay module;

[0058] Figure 8 shows a further example of the delay switching unit and tunable delay module shown in Figures 6-7;

[0059] Figure 9 shows another example of the delay switching unit and tunable delay module of the present invention. Detailed Implementation

[0060] In the following description, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided by way of example in order to fully convey the spirit of the invention to those skilled in the art. Therefore, the invention is not limited to the embodiments disclosed herein.

[0061] In this invention, the time-phase encoding chip can be implemented using an equal-arm interferometer chip module and an unequal-arm interferometer chip module. The input terminal of the equal-arm interferometer chip module is used to receive the optical signal to be encoded, and the output terminal of the unequal-arm interferometer chip module is used to output the time-phase encoded optical signal.

[0062] When the optical signal enters the time-phase encoding chip through the optical waveguide, it first enters the equal-arm interferometer chip module.

[0063] By adjusting the phase difference between the two arms in the equal-arm interferometer chip module, the optical signal can be controlled to be output from only one output terminal of the equal-arm interferometer chip module, or simultaneously output from both output terminals of the equal-arm interferometer chip module with a preset phase difference.

[0064] Furthermore, by utilizing the arm length difference (i.e., delay difference) of the unequal-arm interferometer chip module, information under the time basis can be applied to the optical signal. This enables time-phase encoding of the optical signal.

[0065] For example, the phase difference between the two arms of the equal-arm interferometer chip module can be adjusted to be 0, so that the optical signal is output from the first output terminal of the equal-arm interferometer chip module and enters the long arm of the unequal-arm interferometer chip module, thereby preparing the |Z1> state on the optical signal; or, the phase difference between the two arms of the equal-arm interferometer chip module can be adjusted to be π, so that the optical signal is output from the second output terminal of the equal-arm interferometer chip module and enters the short arm of the unequal-arm interferometer chip module, thereby preparing the |Z0> state; or, the phase difference between the two arms of the equal-arm interferometer chip module can be adjusted to be π. In the equal-arm interferometer chip module, the phase difference between the two arms is π / 2, so that the optical signal is equally distributed and simultaneously output from the two output terminals of the equal-arm interferometer chip module and enters the long arm and short arm of the unequal-arm interferometer chip module respectively. At this time, the |X0> state is prepared. Alternatively, the phase difference between the two arms in the equal-arm interferometer chip module can be adjusted to 3π / 2, so that the optical signal is equally distributed and simultaneously output from the two output terminals of the equal-arm interferometer chip module and enters the long arm and short arm of the unequal-arm interferometer chip module respectively. At this time, the |X1> state is prepared.

[0066] As mentioned earlier, in time-phase coding schemes, the consistency of the arm length difference (delay difference) between the unequal-arm interferometer chip modules in the transmitter and receiver has a significant impact on quantum key distribution performance. Therefore, this invention discloses a delay difference adjustment method for unequal-arm interferometer chips and time-phase coding chips. This method allows for a wide range of adjustment of the delay difference between the long and short arms in the unequal-arm interferometer chip module using control signals (e.g., phase drive signals and / or adjustable attenuator drive signals), achieving consistency of the arm length difference between the transmitter and receiver. Therefore, it allows for a reduction in the consistency requirements of the unequal-arm interferometer arm length difference during chip fabrication and a reduction in the requirements for the environmental disturbance resistance of the unequal-arm interferometer during the design phase.

[0067] Figure 4 schematically illustrates the unequal-arm interferometer chip module with adjustable delay difference according to the present invention.

[0068] As shown in the figure, the unequal arm interferometer chip module may include a first optical beam splitter 202, a first optical beam combiner 203, and first and second waveguides connected between the first optical beam splitter 202 and the first optical beam combiner 203.

[0069] For example, the first output terminal of the first optical beam splitter 202 is connected to the first input terminal of the first optical beam combiner 203 through the first waveguide, and the second output terminal of the first optical beam splitter 202 is connected to the second input terminal of the first optical beam combiner 203 through the second waveguide. The input terminal of the first optical beam splitter 202 is used as the input terminal of the unequal-arm interferometer chip module, and the output terminal of the first optical beam combiner 203 is used as the output terminal of the unequal-arm interferometer chip module.

[0070] Furthermore, an adjustable optical delay module 401 is provided on at least one of the first and second waveguides of the unequal-arm interferometer chip module (e.g., the first waveguide in FIG4) for providing an adjustable time delay for the optical signal propagating along the waveguide in which it is located, thereby enabling the unequal-arm interferometer chip module to have an adjustable arm length difference (i.e., a delay difference with respect to the optical signal).

[0071] Specifically, the tunable optical delay module 401 may include one or more delay switching units, each of which can switch between multiple different operating states based on a control signal, and can provide different time delays to the optical signal in different operating states. In a preferred example, in different operating states, the optical signal will propagate along different waveguides in the delay switching units, wherein the different waveguides may have different lengths (optical path lengths).

[0072] Figure 5 illustrates an example of a tunable optical delay module, which is a cascaded structure formed by N delay switching units (N being an integer greater than 1) connected sequentially via waveguides. In this cascaded implementation, if a single delay switching unit has M operating states (i.e., allows switching between M time delay values), the tunable optical delay module can provide M... N Different time delay values ​​are possible. Clearly, by using this cascading method, theoretically, the tunable delay module can achieve any desired range of delay adjustment.

[0073] For example, assuming that the i-th delay switching unit has the longest and shortest delay values ​​Li1 and Li2 respectively, the dimmable delay module can have the longest and shortest delay values ​​(L11+L21+…+LN1) and (L12+L22+…+LN2) respectively, and can also have multiple selectable delay values ​​between the longest and shortest delay values.

[0074] Figure 6 schematically illustrates an example of a delay switching unit.

[0075] As shown in the figure, the delay switching unit may include an input waveguide 111, an optical path selection component 211, a third waveguide 311, a fourth waveguide 312, a second optical beam combiner 212, and an output waveguide 112.

[0076] The input waveguide 111 is connected to the input of the optical path selection component 211 to allow optical signals to enter the optical path selection component 211.

[0077] The optical path selection component 211 may have a first output terminal and a second output terminal, which are used to connect the third waveguide 311 and the fourth waveguide 312, respectively.

[0078] According to the present invention, the third waveguide 311 and the fourth waveguide 312 will be configured to have different lengths (optical path). For example, as shown in FIG6, the third waveguide 311 and the fourth waveguide 312 are a long waveguide and a short waveguide, respectively.

[0079] Furthermore, the optical path selection component 211 can be configured to switch between a first operating state where the input optical signal is output from the first output terminal and a second operating state where the input optical signal is output from the second output terminal, based on a control signal. Since the third and fourth waveguides connected to the first and second output terminals respectively have different lengths, different time delays can be provided for the optical signal in different operating states.

[0080] Referring to Figure 6, the third waveguide 311 and the fourth waveguide 312 are respectively connected to the two input ends of the second optical combiner 212 at the other end. Therefore, with the help of the beam combining effect of the second optical combiner 212, the optical signals in the optical path selection component 211 are allowed to be output from the same output end of the second optical combiner 212 and enter the output waveguide 112.

[0081] Those skilled in the art will understand that, in the cascaded implementation of tunable optical delay modules, for N delay switching units, the third waveguide in different delay switching units can have the same length or different lengths; similarly, the fourth waveguide in different delay switching units can have the same length or different lengths.

[0082] Furthermore, although the optical path selection component 211 can be implemented using any device with optical path selection switching function, this invention also proposes a new optical path selection component implementation scheme specifically for chip implementation scenarios. In this scheme, the optical path selection switching function is achieved through a simple control process by using an MZ interferometer structure that can be implemented on a chip with mature chip processing technology. This is extremely advantageous for chip design.

[0083] Figure 7 schematically illustrates an adjustable optical delay module implemented by cascading three delay switching units, wherein the optical path selection component in the delay switching unit is implemented by an equal-arm interferometer.

[0084] As shown in the figure, the optical path selection component 211 adopts an equal-arm interferometer structure, which has an optical beam splitter, an optical beam combiner, and first and second arms formed between the two by means of a waveguide. At least one of the first and second arms is provided with a phase shifter 321, 322, 323, thereby allowing the selection of different output terminals for the input optical signal by adjusting the phase difference between the two arms, and realizing the switching between two different working states.

[0085] Specifically, in the equal-arm interferometer for the optical path selection component shown in Figure 7: the input end of the optical beam splitter serves as the input end of the optical path selection component and is used to receive optical signals; the two output ends of the optical beam combiner serve as the two output ends of the optical path selection component and are used to connect the third and fourth waveguides, respectively.

[0086] Therefore, by using the driving signals for phase shifters 321, 322, and 323, the optical signal can be controlled to enter the third or fourth waveguide to obtain the selected time delay. Phase shifters 321, 322, and 323 can preferably be thermally tunable phase shifters.

[0087] The working process of the adjustable optical delay module implemented by means of the equal-arm MZ interferometer will be further explained below with reference to Figure 7, so as to better understand the delay difference adjustment principle of the unequal-arm interferometer chip module of the present invention.

[0088] In the example of Figure 7, the tunable delay module 401 includes a first delay switching unit, a second delay switching unit, and a third delay switching unit cascaded through waveguides.

[0089] The first delay switching unit includes an interferometer with a phase shifter 321 on its arm, a third waveguide with an optical path length L11, a fourth waveguide with an optical path length L12, and a second optical beam combiner.

[0090] The second delay switching unit includes an interferometer with a phase shifter 322 on its arm, a third waveguide with an optical path length L21, a fourth waveguide with an optical path length L22, and a second optical combiner.

[0091] The third delay switching unit includes an interferometer with a phase shifter 323 on its arm, a third waveguide with an optical path length L31, a fourth waveguide with an optical path length L32, and a second optical combiner.

[0092] For each delay switching unit, an external DC drive signal can be used to control the phase shifters 321 / 322 / 323 to direct the optical signal into the third or fourth waveguide. For example, the phase difference between the upper and lower arms of the equal-arm interferometer can be adjusted to 0, causing the entire optical signal to enter the longer third waveguide; or the phase difference between the upper and lower arms of the interferometer can be adjusted to π, causing the entire optical signal to enter the shorter fourth waveguide. This adjusts the amount of delay provided to the optical signal by the adjustable optical delay module 401.

[0093] Table 1 below shows the target delay amount ultimately achieved by the tunable delay module 401 when different phase differences are modulated between the two arms of each delay switching unit by means of a phase shifter at L11=3ps, L12=1ps, L21=5ps, L22=1ps, L31=9ps, and L32=1ps.

[0094]

[0095] (Table 1)

[0096] As can be seen from Table 1, by freely controlling the phase difference between the two arms of the interferometer in each delay switching unit, the delay amount in each delay switching unit can be switched, and after three levels of delay accumulation, the delay amount adjustment capability from 3ps to 17ps, in steps of 2ps, is obtained.

[0097] Those skilled in the art will understand that a lookup table of the phase difference between the two arms of the interferometer and the target delay amount can be established in advance in each stage of the delay switching unit. This allows the phase shifter to be used to conveniently achieve the required phase difference between the two arms in each stage of the delay switching unit, thereby providing the desired delay amount for the optical signal.

[0098] Figure 8 schematically illustrates a further example of the delay switching unit shown in Figures 6-7.

[0099] As shown in Figure 8, the delay switching unit may also include adjustable optical attenuators (VOAs) respectively disposed on the third and fourth waveguides. Therefore, when the optical signal is transmitted into the third (or fourth) waveguide by means of the phase modulation selection in the optical path selection component, the attenuation value of the adjustable optical attenuator (VOA) on the fourth (or third) waveguide can be controlled to attenuate the optical signal on the fourth (or third) waveguide to the extinction state, thereby allowing a reduction in the extinction ratio requirement of the phase shifter (or phase modulator) in the MZ interferometer.

[0100] Figure 9 schematically illustrates another example of the delay switching unit according to the present invention.

[0101] As shown in Figure 9, the delay switching unit may include a third optical beam splitter BS and a third optical beam combiner BS. The two outputs of the third optical beam splitter are connected to the two inputs of the third optical beam combiner through the seventh waveguide and the eighth waveguide, respectively, to form an interferometer structure. The input of the third optical beam splitter is used as the input of the delay switching unit, and the output of the third optical beam combiner is used as the output of the delay switching unit.

[0102] As an example, the seventh waveguide and the eighth waveguide have different optical path lengths, for example, the seventh waveguide has a time delay dT1, dT2, dT3... relative to the eighth waveguide.

[0103] To achieve the time delay switching function, adjustable optical attenuators (VOAs) can be installed on the seventh and eighth waveguides respectively. Therefore, by controlling the attenuation value of the adjustable optical attenuator (VOA) on the seventh (or eighth) waveguide to approximately disconnect the optical path, the optical signal can pass through only the eighth (or seventh) waveguide and be output from the delay switching unit, thereby achieving the switching of the time delay for the optical signal.

[0104] In this invention, the tunable optical attenuator (VOA) can be based on the carrier injection principle or on the MZ interferometer principle.

[0105] Similarly, the tunable attenuator (VOA) can be formed from silicon material.

[0106] Referring again to Figure 4, in the unequal arm interferometer chip module of the present invention, an attenuation control module 501 can also be provided on at least one of the first waveguide and the second waveguide to provide controllable attenuation for the optical signal propagating along the waveguide in which it is located, for example, to compensate for the power difference formed by the optical signal propagating along the unequal arm due to different attenuations, so that the attenuation of the optical signal in the unequal arm interferometer chip module is consistent.

[0107] For example, in the quantum key distribution process based on the time-phase encoding scheme, after the delay of the long and short arms in the unequal-arm interferometer chip module is calibrated, the attenuation of the long and short arms can be made consistent by adjusting the working state of the attenuation control module. This ensures the power balance of the optical signal in the time-phase encoding process and prepares a quantum state with the expected delay.

[0108] Preferably, the attenuation control module 501 may include a carrier injection type attenuator.

[0109] Preferably, the unequal-arm interferometer chip module can be implemented on a silicon-based chip. Therefore, the optical beamsplitters (e.g., the first optical beamsplitter 202 and the third optical beamsplitter), optical beam combiners (e.g., the first optical beam combiner 203, the second optical beam combiner 212 and the third optical beam combiner), and waveguides (e.g., the first waveguide, the second waveguide, the third waveguide, the fourth waveguide, the input waveguide, the output waveguide, etc.) can all be formed of silicon material.

[0110] Preferably, the optical beam splitters (e.g., the first optical beam splitter 202 and the third optical beam splitter) and the optical beam combiners (e.g., the first optical beam combiner 203, the second optical beam combiner 212 and the third optical beam combiner) can be multimode interferometers or directional couplers.

[0111] Furthermore, the aforementioned unequal-arm interferometer chip module can also be implemented as a separate chip, resulting in an unequal-arm interferometer chip.

[0112] The following will continue to describe a method for adjusting the delay difference of an unequal-arm interferometer chip based on the present invention.

[0113] As can be seen from the above, the present invention utilizes an interferometer structure (such as the combination of equal-arm MZ interferometer and unequal-arm interferometer in Figures 6-8, or the unequal-arm interferometer with attenuators on both arms in Figure 9) to realize a delay switching unit that can provide time delay switching by switching the optical signal transmission path.

[0114] Therefore, in the delay difference adjustment method of the present invention, the transmission path for optical signals can be switched by changing the parameters of the interferometer structure used to realize the delay switching unit (e.g., phase difference between the two arms, attenuation value on the optical arm, etc.) to realize the adjustment step, which is used to adjust the delay difference of the unequal arm interferometer chip.

[0115] Specifically, when the interferometer structure includes a combination of the equal-arm MZ interferometer and the unequal-arm interferometer described above with respect to Figures 6-7, in the adjustment step, for the optical signal entering the delay switching unit, by controlling the phase difference between the two arms of the equal-arm MZ interferometer, one of the two output terminals of the equal-arm interferometer can be selected to output the optical signal, so that it propagates along the third waveguide or the fourth waveguide, thereby obtaining different delay amounts. This controls the delay amount of the arm where the delay switching unit (adjustable optical delay module 401) is located, thereby realizing the adjustment of the delay difference of the unequal-arm interferometer chip.

[0116] When the interferometer structure adopts the combination of the equal-arm MZ interferometer, the unequal-arm interferometer, and the adjustable optical attenuator (VOA) shown in Figure 8, the adjustment steps may further include adjusting the attenuation value of the adjustable optical attenuator (VOA) in the unequal-arm interferometer to extinct the optical signal on the third or fourth waveguide. As mentioned earlier, this allows for a relaxation of the extinction ratio requirement in the equal-arm MZ interferometer, achieving the purpose of optical transmission path selection by increasing the optical attenuation value on the third or fourth waveguide to achieve the extinction state of the optical signal.

[0117] At this point, the delay difference adjustment method of the present invention may preferably include a preset step. In the preferred preset step, the correspondence between the delay difference of the unequal-arm interferometer chip and the phase difference between the two arms of the equal-arm MZ interferometer in the delay switching unit can be determined in advance, and a corresponding lookup table can be established accordingly. This allows the phase difference between the two arms of the equal-arm MZ interferometer in the corresponding delay switching unit to be directly obtained by looking up the lookup table according to the target delay amount during the adjustment step. This allows for convenient adjustment of the phase difference between the two arms of the equal-arm MZ interferometer to achieve the required delay difference.

[0118] When the interferometer structure adopts the unequal-arm interferometer shown in Figure 9, which is formed by the third optical beam splitter and the third optical beam combiner and has adjustable optical attenuators (VOAs) on both arms, the optical signal can be extinct on the seventh or eighth waveguide by adjusting the attenuation value of the adjustable optical attenuators (VOAs) in the unequal-arm interferometer, so as to select the optical transmission path and thus realize the delay difference adjustment function.

[0119] Furthermore, since the delay is achieved by changing the length of the waveguide used for optical signal propagation, the delay difference adjustment method of the present invention may also include a power control step to compensate for the fluctuation in optical signal attenuation (intensity) caused by the change in delay.

[0120] In the power control step, the attenuation of the attenuation control module 501 can be adjusted according to the delay of the adjustable optical delay module 401, so that for the same input optical signal, the optical signal output by the unequal arm interferometer chip has a balanced power, which is beneficial for its application in time phase coding schemes.

[0121] Referring again to Figure 4, a time-phase encoding chip with adjustable delay difference is shown. As shown, the time-phase encoding chip includes an equal-arm interferometer chip module and the aforementioned unequal-arm interferometer chip module with adjustable delay difference. The optical beam combiner of the equal-arm interferometer chip module and the optical beam splitter of the unequal-arm interferometer chip module share the same optical beam splitter 202 (optical beam combiner).

[0122] Specifically, the first optical beam splitter 202 in the unequal arm interferometer chip module has two input terminals, namely the first input terminal and the second input terminal.

[0123] In the equal-arm interferometer chip module, the first output terminal of the second optical beamsplitter 201 is connected to the first input terminal of the first optical beamsplitter 202 via a fifth waveguide, and the second output terminal of the second optical beamsplitter 201 is connected to the second input terminal of the first optical beamsplitter 202 via a sixth waveguide. Phase adjustment modules 301 / 302 are provided on at least one of the fifth and sixth waveguides, as shown in Figure 4, for example, on the fifth and sixth waveguides respectively. Thus, an equal-arm interferometer chip module with the input terminal of the second optical beamsplitter 201 as its input terminal can be realized, while simultaneously enabling the connection between the equal-arm interferometer chip module and an unequal-arm interferometer chip module (with adjustable delay difference), thereby obtaining a time-phase encoding chip with adjustable delay difference.

[0124] Accordingly, in the time phase encoding chip, the input end of the second optical beam splitter 201 can be connected to the input waveguide 101 to receive the optical signal to be encoded; the output end of the first optical beam combiner 203 can be connected to the output waveguide 102 to output the encoded optical signal.

[0125] Therefore, when the optical signal enters the equal-arm interferometer chip module through the input waveguide 101, the phase shift state of the phase adjustment modules 301 / 302 can be driven by an external pulse voltage signal to adjust the phase difference between the two arms in the equal-arm interferometer chip module to 0, so that all the optical signal is output from the first output terminal of the first optical beamsplitter 202 (which is multiplexed as the optical beam combiner in the equal-arm interferometer chip module) and enters the first waveguide of the unequal-arm interferometer chip module, thereby preparing the |Z1> state on the optical signal; or, the phase difference between the two arms in the equal-arm interferometer chip module can be adjusted to π, so that all the optical signal is output from the second output terminal of the first optical beamsplitter 202. The output signal enters the second waveguide of the unequal-arm interferometer chip module, thus preparing the |Z0> state; or, the phase difference between the two arms in the equal-arm interferometer chip module can be adjusted to π / 2, so that the optical signal is equally divided and simultaneously output from the two outputs of the first optical beamsplitter 202 to enter the first and second waveguides of the unequal-arm interferometer chip module respectively, thus preparing the |X0> state; or, the phase difference between the two arms in the equal-arm interferometer chip module can be adjusted to 3π / 2, so that the optical signal is equally divided and simultaneously output from the two outputs of the first optical beamsplitter 202 to enter the first and second waveguides of the unequal-arm interferometer chip module respectively, thus preparing the |X1> state.

[0126] During this process, the optical signal can be switched to different transmission paths by controlling the working state of the delay switching unit in the adjustable optical delay module 401 within the unequal-arm interferometer chip module, thereby achieving the desired delay difference between the two arms within the unequal-arm interferometer chip module. For details, please refer to the above text; further explanation is omitted here.

[0127] Meanwhile, the working state of the attenuation control module 501 can be controlled in the unequal arm interferometer chip module to ensure that the optical signal is attenuated uniformly on both arms, thereby preparing a quantum state with balanced power and expected delay.

[0128] Preferably, the time phase encoding chip can be implemented using a silicon-based chip. Accordingly, all optical beam splitters, optical beam combiners, and waveguides are formed of silicon material.

[0129] Preferably, the second optical beam splitter 201 can be a multimode interferometer or a directional coupler.

[0130] Preferably, the phase adjustment modules 301 and 302 can be carrier deposition type, carrier injection type or carrier depletion type.

[0131] Similarly, the present invention also discloses a delay difference adjustment method for a time phase encoding chip, which may include an adjustment step and a power control step.

[0132] Specifically, the adjustment step and the power control step can be implemented using the adjustment step and the power control step described above in the method for adjusting the delay difference of unequal arm interferometer chips, so they will not be repeated here.

[0133] Furthermore, the delay difference adjustment method for time phase encoding chips of the present invention may also include a preset step, which can also be implemented by means of the preset step in the delay difference adjustment method for unequal arm interferometer chips described above, and therefore will not be repeated here.

[0134] In summary, this invention proposes a method for adjusting the delay difference between unequal-arm interferometer chips and time-phase encoding chips by introducing an adjustable optical delay module based on an interferometer structure onto the optical arm of the unequal-arm interferometer chip / chip module. By simply changing certain parameters of the interferometer structure (e.g., modulation phase, optical attenuation value, etc.), the delay difference can be adjusted over a wide range and with controllable precision. This effectively solves the problem of uncontrollable delay differences between chips caused by process errors in existing technologies, which is beneficial for the engineering application of time-phase encoding chips. Furthermore, this invention allows for the introduction of redundant designs with long delays, and the total delay and delay adjustment precision can be easily and freely defined, making the solution of this invention applicable to a wider range of situations.

[0135] Although the present invention has been described above with reference to the accompanying drawings and specific embodiments, those skilled in the art will readily recognize that the above embodiments are merely exemplary and used to illustrate the principles of the present invention. They do not limit the scope of the present invention. Those skilled in the art can make various combinations, modifications and equivalent substitutions to the above embodiments without departing from the spirit and scope of the present invention.

Claims

1. A method for adjusting the delay difference of a chip in an unequal-arm interferometer, wherein, The unequal-arm interferometer chip includes a first optical beamsplitter and a first optical beam combiner. The two outputs of the first optical beamsplitter are respectively connected to the two inputs of the first optical beam combiner via first and second waveguides. At least one of the first and second waveguides is provided with an adjustable optical delay module for providing a time delay for the optical signal propagating along the waveguide. The adjustable optical delay module includes one or more cascaded delay switching units, which are implemented based on the interferometer structure. The delay difference adjustment method includes an adjustment step for switching the transmission path for the optical signal by changing the parameters of the interferometer structure, thereby adjusting the delay difference of the unequal-arm interferometer chip.

2. The delay difference adjustment method as described in claim 1, wherein, The delay switching unit includes an equal-arm MZ interferometer with an input end and two output ends. The phase difference between the two arms of the equal-arm MZ interferometer is adjustable, and the two output ends are respectively connected to the two input ends of the second optical beam combiner through a third and a fourth waveguide, respectively. The third and fourth waveguides have different optical path lengths. In the adjustment step, by adjusting the phase difference between the two arms of the equal-arm MZ interferometer, one of the two output ends of the equal-arm MZ interferometer is selected for outputting an optical signal.

3. The delay difference adjustment method as described in claim 2, wherein, The third and fourth waveguides are respectively provided with adjustable optical attenuators; and the adjustment step further includes the step of adjusting the attenuation value of the adjustable optical attenuator to make the optical signal extinct on the third or fourth waveguide.

4. The delay difference adjustment method as described in claim 2 further includes a preset step for setting a lookup table between the delay difference of the unequal-arm interferometer chip and the phase difference between the two arms of the equal-arm MZ interferometer; in the adjustment step, the phase difference between the two arms of the equal-arm MZ interferometer is obtained by using the lookup table.

5. The delay difference adjustment method as described in claim 1, wherein, The delay switching unit includes a third optical beam splitter and a third optical beam combiner. The two outputs of the third optical beam splitter are connected to the two inputs of the third optical beam combiner through a seventh waveguide and an eighth waveguide, respectively. The seventh waveguide and the eighth waveguide are respectively equipped with adjustable optical attenuators, and the seventh waveguide and the eighth waveguide have different optical path lengths. In the adjustment step, the optical signal is extinct on the seventh waveguide or the eighth waveguide by adjusting the attenuation value of the adjustable optical attenuator.

6. The delay difference adjustment method according to any one of claims 1-5, wherein, At least one of the first and second waveguides is further provided with an attenuation control module for providing controllable attenuation for optical signals propagating along the waveguide; the delay difference adjustment method further includes a power control step for adjusting the attenuation amount of the attenuation control module according to the time delay of the adjustable optical delay module.

7. The delay difference adjustment method as described in claim 6, wherein, The attenuation control module includes a carrier injection attenuator.

8. The delay difference adjustment method as described in claim 1, wherein, The optical beam splitter and optical beam combiner are multimode interferometers or directional couplers; and / or, the optical beam splitter, optical beam combiner and waveguide are made of silicon.

9. The delay difference adjustment method as described in claim 2, wherein, The third waveguides in different delay switching units have the same or different optical path lengths, and the fourth waveguides in different delay switching units have the same or different optical path lengths.

10. The delay difference adjustment method as described in claim 5, wherein, The seventh waveguide in different delay switching units has the same or different optical path lengths, and the eighth waveguide in different delay switching units has the same or different optical path lengths; and / or, the adjustable optical attenuator is implemented based on the carrier injection principle or based on the MZ interferometer principle.

11. A method for adjusting the delay difference in a time-phase encoding chip, wherein, The time-phase encoding chip includes a second optical beamsplitter, a first optical beamsplitter, and a first optical beam combiner. The two outputs of the second optical beamsplitter are respectively connected to the two inputs of the first optical beamsplitter via fifth and sixth waveguides. At least one of the fifth and sixth waveguides is provided with a phase adjustment module for phase modulation of the optical signal, thereby forming an equal-arm interferometer chip module. The two outputs of the first optical beamsplitter are respectively connected to the two inputs of the first optical beam combiner via first and second waveguides. At least one of the first and second waveguides is provided with an adjustable optical delay module for providing time delay for the optical signal, thereby forming an unequal-arm interferometer chip module. The adjustable optical delay module includes one or more delay switching units cascaded together, the delay switching units being implemented based on an interferometer structure; the delay difference adjustment method includes an adjustment step, used to switch the transmission path for the optical signal by changing the parameters of the interferometer structure, so as to adjust the delay difference of the unequal arm interferometer chip module.

12. The delay difference adjustment method as described in claim 11, wherein, The delay switching unit includes an equal-arm MZ interferometer with an input end and two output ends. The phase difference between the two arms of the equal-arm MZ interferometer is adjustable, and the two output ends are respectively connected to the two input ends of the second optical beam combiner through a third and a fourth waveguide, respectively. The third and fourth waveguides have different optical path lengths. In the adjustment step, by adjusting the phase difference between the two arms of the equal-arm MZ interferometer, one of the two output ends of the equal-arm MZ interferometer is selected for outputting an optical signal.

13. The delay difference adjustment method as described in claim 12, wherein, The third and fourth waveguides are respectively provided with adjustable optical attenuators; and the adjustment step further includes the step of adjusting the attenuation value of the adjustable optical attenuator to make the optical signal extinct on the third or fourth waveguide.

14. The delay difference adjustment method as described in claim 12, further comprising a preset step for pre-setting a lookup table between the delay difference of the unequal-arm interferometer chip module and the phase difference between the two arms of the equal-arm MZ interferometer; in the adjustment step, the phase difference between the two arms of the equal-arm MZ interferometer is obtained by using the lookup table.

15. The delay difference adjustment method as described in claim 11, wherein, The delay switching unit includes a third optical beam splitter and a third optical beam combiner. The two outputs of the third optical beam splitter are connected to the two inputs of the third optical beam combiner through a seventh waveguide and an eighth waveguide, respectively. The seventh waveguide and the eighth waveguide are respectively equipped with adjustable optical attenuators, and the seventh waveguide and the eighth waveguide have different optical path lengths. In the adjustment step, the optical signal is extinct on the seventh waveguide or the eighth waveguide by adjusting the attenuation value of the adjustable optical attenuator.

16. The delay difference adjustment method according to any one of claims 11-15, wherein, At least one of the first and second waveguides is further provided with an attenuation control module for providing controllable attenuation for optical signals propagating along the waveguide; the delay difference adjustment method further includes a power control step for adjusting the attenuation amount of the attenuation control module according to the time delay of the adjustable optical delay module.

17. The delay difference adjustment method as described in claim 16, wherein, The attenuation control module includes a carrier injection attenuator.

18. The delay difference adjustment method as described in claim 11, wherein, The phase adjustment module is a carrier deposition type, a carrier injection type, or a carrier depletion type; and / or, the optical beam splitter and optical beam combiner are multimode interferometers or directional couplers; and / or, the optical beam splitter, optical beam combiner, and waveguide are made of silicon.

19. The delay difference adjustment method as described in claim 12, wherein, The third waveguides in different delay switching units have the same or different optical path lengths, and the fourth waveguides in different delay switching units have the same or different optical path lengths.

20. The delay difference adjustment method as described in claim 15, wherein, The seventh waveguide in different delay switching units has the same or different optical path lengths, and the eighth waveguide in different delay switching units has the same or different optical path lengths.

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