WO2023246768A1

WO2023246768A1 - Method for adjusting time delay difference between unequal-arm interferometer chip and time phase coding chip

Info

Publication number: WO2023246768A1
Application number: PCT/CN2023/101355
Authority: WO
Inventors: 刘仁德; 马昆; 唐世彪
Original assignee: 科大国盾量子技术股份有限公司
Priority date: 2022-06-22
Filing date: 2023-06-20
Publication date: 2023-12-28
Also published as: CN117318828A

Abstract

Disclosed in the present invention is a method for adjusting a time delay difference between an unequal-arm interferometer chip and a time phase coding chip. An adjustable optical delay module realized by means of an interferometer structure is introduced into an optical arm of an unequal-arm interferometer chip (module), such that parameters (e.g. a modulation phase and a light attenuation value) of the interferometer structure can be simply changed, an optical transmission path of an optical signal is switched, and a time delay realized by the adjustable optical delay module is adjusted, and thus a time delay difference between the unequal-arm interferometer chip and a time phase coding chip is adjusted, thereby effectively solving the problems in the prior art of productization of a time phase coding chip being limited caused by an excessively large difference between lengths of actual delay lines between different chips of different batches or of the same batch, etc.

Description

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

This application requests the priority of the Chinese patent application submitted to the China Patent Office on June 22, 2022, with the application number 202210720770.8 and the invention name "Delay difference adjustment method of unequal arm interferometer chip and time phase encoding chip", The entire contents of which are incorporated herein by reference.

Technical field

The invention relates to the field of quantum secure communication, and in particular to a delay difference adjustment method for an unequal arm interferometer chip and a time phase encoding chip.

Background technique

Quantum key distribution (QKD) is based on the principles of quantum mechanics. Due to the principles of quantum non-cloning and uncertainty, it is a key distribution system that can be theoretically proven to be unconditionally secure. With the development of quantum key distribution technology, it will become more competitive to provide small-sized, low-cost and highly stable quantum key distribution equipment. Quantum key distribution often involves more complex optical signal encoding and decoding. At present, its encoding and decoding structure is often formed by a combination of traditional optical fiber devices, which is larger and more costly. Encoding and decoding optical signals on optical chips is one of the important solutions for small-sized, low-cost and highly stable quantum key distribution equipment.

Figure 1 shows an integrated time phase quantum key distribution system transmitter encoding module in the prior art. As shown in Figure 1, the encoding module uses optical beam splitter one, optical beam splitter two, phase modulation module one and phase modulation module two to form an equal-arm interferometer, and uses optical beam splitter two, optical waveguide delay module and beam combiner The device constitutes an unequal arm interferometer. By modulating the phase difference in the unequal-arm interferometer, the output port of the optical signal can be dynamically modulated, so that the optical signal only travels along the long arm or the short arm, or along the long and short arms in the unequal-arm interferometer, thus preparing Output 4 states that comply with the BB84 protocol.

Figure 2 shows another packaging structure for a time phase encoding quantum key distribution system in the prior art. As shown in Figure 2, the package structure uses beam splitters BS1, Heater1 and beam splitter BS2 to form an equal-arm MZ interferometer, and the equal-arm interferometer is connected to an unequal-arm interferometer. similar Ground, with the help of the phase difference in the Heater1 modulated equal-arm interferometer, the output port of the optical signal is dynamically modulated, so that the optical signal only travels along the long arm or the short arm in the unequal-arm interferometer, or travels along the long and short arms at the same time, by This prepares 4 states that comply with the BB84 protocol.

It can be seen that time phase encoding schemes usually require the use of unequal arm interferometers, and slight deviations in the arm length difference may cause changes in the interference results. This deviation reaching the level of hundreds of nanometers may cause completely opposite interference to be obtained. result. For example, if the inherent deviation in the interferometer is too large and exceeds the coherence length of the light source, it will directly lead to the inability to measure the interference phenomenon. On the premise of controlling the inherent deviation of the interferometer, it is also necessary to control the random deviation caused by environmental changes (which will cause phase fluctuations of the light pulses passing through the interferometer). This is often done with the help of phase modulators/phase shifters and detectors. Real-time closed-loop compensation. However, although the phase modulator/phase shifter can have a fast adjustment rate, its adjustment range is only a few π phases (corresponding to an optical path of several microns), and it cannot cope with the large inherent difference in the arm length of the interferometer. deviation situation.

In order to reduce the influence of the arm length difference deviation in the interferometer, the current main method is to accurately control the arm length difference of the interferometer by means of fiber polishing and other processes, and control the inherent deviation of the arm length difference of two or a batch of interferometers to a minimum. At a small level. At the same time, shock absorption and thermal insulation designs can also be introduced into the interferometer to reduce the impact of environmental disturbances, and devices such as phase modulators/phase shifters can be used for real-time compensation. For example, see "Faraday-Michelson system for quantum cryptography", CN201822228162 .7 and CN201822226830.2 and other solutions disclosed by existing technologies. However, it can be clearly noticed that such solutions often result in larger interferometers, poor stability and more complex systems.

A solution is presented in the structure shown in Figure 1, where the long arm of the interferometer is realized using a waveguide delay module implemented by a length of waveguide wire. In this solution, a small size and good anti-environmental disturbance performance can be achieved, but it is in the form of a chip. Once the chip is processed, it is difficult to adjust the interferometer arm length difference. Therefore, the chip processing technology is greatly affected. Consistency is very demanding. In fact, due to chip processing technology, interferometers from different wafers or even the same wafer may have large differences, which will lead to a large inherent deviation in the arm length difference of the interferometer, which is much larger than that of the phase modulator/phase shifter. The adjustment range of the detector even exceeds the coherence length of general light sources, making it impossible to use normal The interference phenomenon is measured by the standard light source, but it cannot be adjusted after the chip is produced, which limits its practical application and large-scale networking (interferometers need to be paired arbitrarily, and the difference in arm length between the two interferometers after pairing is small) , may also be one of the main reasons hindering the large-scale deployment of current on-chip interferometer products.

Figure 3 shows another solution proposed in the prior art, that is, designing an adjustable delay unit at the receiving end. As shown in Figure 3, this solution requires the design of active devices (such as phase modulators) at the receiving end, but general active devices are sensitive to polarization, and fiber links can cause random polarization changes, so the polarization needs to be designed accordingly Irrelevant receiving ends or adding polarization compensation devices will greatly increase the system complexity and technical difficulty. In addition, the design of relevant adjustable delay units at the receiving end will also increase losses and reduce the performance of quantum key distribution equipment.

Contents of the invention

In view of the above-mentioned problems existing in the prior art, the present invention discloses a delay difference adjustment method for an unequal arm interferometer chip and a time phase encoding chip, in which the delay difference adjustment method of the unequal arm interferometer chip (module) is The introduction of an adjustable optical delay module implemented with the help of an interferometer structure on the optical arm allows the waveguide length for the optical signal to be switched simply by changing the parameters of the interferometer structure (such as modulation phase, light attenuation value, etc.), making the adjustment adjustable The delay amount introduced by the optical delay module on the optical arm realizes the adjustment of the delay difference between the unequal arm interferometer chip and the time phase encoding chip, effectively solving the problem of actual delay lines between different batches or different chips in the same batch. Excessive length difference limits the commercialization of time phase encoding chips.

A first aspect of the present invention relates to a delay difference adjustment method for an unequal arm interferometer chip, wherein,

The unequal arm interferometer chip includes a first optical beam splitter and a first optical beam combiner. The two output ends of the first optical beam splitter are connected to the first optical beam combiner through first and second waveguides respectively. Two input terminals;

An adjustable optical delay module is provided on at least one of the first and second waveguides for providing time delay for the optical signal propagating along the waveguide;

The adjustable light delay module includes one or multiple delay switching units in cascade, and the delay switching unit is implemented based on an interferometer structure;

The delay difference adjustment method includes an adjustment step for adjusting the delay difference of the unequal arm interferometer chip by changing the parameters of the interferometer structure and switching the transmission path for the optical signal.

Further, the delay switching unit includes an equal-arm MZ interferometer having an input end and two output ends. The phase difference of the two arms of the equal-arm MZ interferometer is adjustable, and the two output ends pass through the third and fourth terminals respectively. The waveguide is connected to the two input ends of the second optical beam combiner, and 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 terminals of the equal-arm MZ interferometer is selected for outputting an optical signal.

Furthermore, the third waveguide and the fourth waveguide are respectively provided with adjustable optical attenuators; and,

The adjusting step further includes the step of extinguishing the optical signal on the third waveguide or the fourth waveguide by adjusting the attenuation value of the adjustable optical attenuator.

Further, the method may also include a preset step for setting a lookup table in advance between the delay difference of the unequal-arm interferometer chip and the phase difference of the two arms of the equal-arm MZ interferometer;

In the adjustment step, the look-up table is used to obtain the phase difference between the two arms of the equal-arm MZ interferometer.

Further, the delay switching unit includes a third optical beam splitter and a third optical beam combiner, and the two output ends of the third optical beam splitter are respectively connected to the third optical beam combiner through a seventh waveguide and an eighth waveguide. The two input ends of the seventh waveguide and the eighth waveguide are respectively provided with adjustable optical attenuators, and the seventh waveguide and the eighth waveguide have different optical path lengths;

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

Further, at least one of the first and second waveguides is also provided with an attenuation control module for providing controllable attenuation for the optical signal 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 light delay module.

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

Preferably, the optical beam splitter and optical beam combiner are multi-mode interferometers or directional couplers; and/or the optical beam splitter, optical beam combiner and waveguide are made of silicon.

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.

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 It is realized based on the principle of carrier injection, or based on the principle of MZ interferometer.

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

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

The two output ends of the second optical beam splitter are respectively connected to the two input ends of the first optical beam splitter through fifth and sixth waveguides, and at least one of the fifth and sixth waveguides is provided with a A phase adjustment module that performs phase modulation on optical signals to form an equal-arm interferometer chip module;

The two output ends of the first optical beam splitter are respectively connected to the two input ends of the first optical beam combiner through first and second waveguides, and at least one of the first and second waveguides is provided with a The optical signal provides an adjustable optical delay module with time delay, thus forming an unequal arm interferometer chip module;

The delay difference adjustment method includes an adjustment step for adjusting the delay difference of the unequal arm interferometer chip module by changing the parameters of the interferometer structure and switching the transmission path for the optical signal.

In the adjustment step, by adjusting the phase difference between the two arms of the equal-arm MZ interferometer, from Select one of the two output terminals of the equal-arm MZ interferometer to output an optical signal.

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

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 multi-mode interferometers or directional couplers; And/or the optical beam splitter, optical beam combiner and waveguide are made of silicon.

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.

Description of the drawings

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

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are only For some embodiments of the present invention, those of ordinary skill in the art can also obtain other drawings based on these drawings without exerting creative efforts.

Figure 1 shows the transmitter encoding module of the integrated time phase quantum key distribution system in the prior art;

Figure 2 shows a packaging structure for a time phase encoding quantum key distribution system in the prior art;

Figure 3 shows a receiving end structure with an adjustable delay unit in the prior art;

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

Figure 5 schematically shows the cascade form of the adjustable light delay module of the present invention;

Figure 6 schematically shows an example of the delay switching unit of the present invention;

Figure 7 schematically shows an example of an adjustable light delay module implemented in a cascade form;

Figure 8 shows a further example of the delay switching unit and the dimmable light delay module shown in Figures 6-7;

Figure 9 shows another example of the delay switching unit and the dimmable light delay module of the present invention.

Detailed ways

Hereinafter, 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 present invention to those skilled in the art to which this invention belongs. Therefore, the invention is not limited to the embodiments disclosed herein.

In the present invention, the time phase encoding chip can be implemented by means of an equal-arm interferometer chip module and an unequal-arm interferometer chip module. The input end of the equal-arm interferometer chip module is used to receive the optical signal to be encoded. The output end of the arm interferometer chip module is used to output a time-phase-encoded optical signal.

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

By adjusting the phase difference between the two arms in the equal-arm interferometer chip module, the optical signal can be controlled The output is only output from a certain output terminal of the equal-arm interferometer chip module, or is output from two output terminals of the equal-arm interferometer chip module at the same time with a preset phase difference.

Furthermore, with the help of the arm length difference (ie delay difference) of the unequal arm interferometer chip module, information under the time basis can be applied to the optical signal. Thus, time phase encoding of the optical signal is achieved.

For example, the phase difference between the two arms in the equal-arm interferometer chip module can be adjusted to 0, so that all optical signals are output from the first output end of the equal-arm interferometer chip module and enter the long end of the unequal-arm interferometer chip module. arms, thereby preparing the |Z1> state on the optical signal; alternatively, the phase difference between the two arms in the equal-arm interferometer chip module can be adjusted to π, so that all optical signals are transmitted from the second end of the equal-arm interferometer chip module. The output end outputs and enters the short arm of the unequal-arm interferometer chip module. At this time, the |Z0> state is prepared; alternatively, the phase difference between the two arms in the equi-arm interferometer chip module can be adjusted to π/2, so that the light The signal is output equally from the two output terminals of the equal-arm interferometer chip module at the same time 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, it can be adjusted to make equal arms The phase difference between the two arms in the interferometer chip module is 3π/2, so that the optical signal is output equally from the two output terminals of the equal-arm interferometer chip module at the same time and enters the long arm of the unequal-arm interferometer chip module respectively. and short arm, the |X1> state is prepared at this time.

As mentioned before, in the time phase encoding scheme, the consistency of the arm length difference (delay difference) of the unequal arm interferometer chip modules in the sender and receiver has a very significant impact on the quantum key distribution performance. Therefore, the present invention discloses a delay difference adjustment method for an unequal arm interferometer chip and a time phase encoding chip, which will allow the use of a control signal (such as a phase drive signal and/or an adjustable attenuator drive signal). The delay difference between the long and short arms in the unequal arm interferometer chip module is adjusted within a wide range to achieve consistency in the arm length difference between the sender and the receiver. Therefore, it is possible to reduce the consistency requirements of the chip processing link for the arm length difference of the unequal arm interferometer, and reduce the requirements for the anti-environmental disturbance resistance of the unequal arm interferometer in the design link.

Figure 4 schematically shows an unequal arm interferometer chip module with adjustable delay difference according to the present invention.

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 a third optical beam splitter 202 connected between the first optical beam combiner 203. First and second waveguides.

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

Further, an adjustable light delay module 401 is provided on at least one of the first and second waveguides of the unequal arm interferometer chip module (for example, the first waveguide in FIG. 4), for providing the signal along the The optical signal propagated through the waveguide provides an adjustable time delay, thereby allowing the unequal arm interferometer chip module to have an adjustable arm length difference (ie, a delay difference with respect to the optical signal).

Specifically, the dimmable delay module 401 may include one or more delay switching units, wherein each delay switching unit may switch between a plurality of different working states based on a control signal, and in different working states can provide different time delays for optical signals. In a preferred example, under different working states, the optical signal will propagate along different waveguides in the delay switching unit, where the different waveguides may have different lengths (optical paths).

Figure 5 shows an example of an adjustable optical delay module, which is a cascade structure formed by N (N is an integer greater than 1) delay switching units connected in sequence through waveguides. In this cascade implementation, if a single delay switching unit has M working states (that is, allows switching between M time delay amounts), the adjustable optical delay module will be able to provide M ^N different modes for the optical signal. The amount of time delay. Obviously, with this cascading method, the adjustable light delay module can theoretically achieve any desired delay difference adjustment range.

For example, assuming that the i-th delay switching unit has the longest and shortest delay amounts of Li 1 and Li2 respectively, the dimmable delay module can have (L11+L21+…+LN1) and (L12+L22+…+LN2) respectively. ), and there can be multiple optional delay amounts between the longest and shortest delay amounts.

Figure 6 schematically shows an example of a delay switching unit.

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.

The input waveguide 111 is connected to the input end of the optical path selection component 211 to allow the optical signal to enter the optical Road selection component 211.

The optical path selection component 211 may have a first output end and a second output end for connecting the third waveguide 311 and the fourth waveguide 312 respectively.

According to the present invention, the third waveguide 311 and the fourth waveguide 312 will be provided with different lengths (optical paths). For example, as shown in Figure 6, the third waveguide 311 and the fourth waveguide 312 are long waveguides and short waveguides respectively.

Further, the optical path selection component 211 may be configured to be able to operate in a first working state in which the input optical signal is output from the first output terminal and in a second working state in which the input optical signal is output from the second output terminal according to the control signal. switch between. Since the third and fourth waveguides respectively connected to the first and second output ends have different lengths, different time delay amounts can be provided for the optical signal in different working states.

Continuing to refer to FIG. 6 , the third waveguide 311 and the fourth waveguide 312 are respectively connected to the two input ends of the second optical beam combiner 212 at the other end. Therefore, with the beam combining function of the second optical beam combiner 212 , the optical path selection component 211 is allowed to The optical signals in are finally output from the same output end of the second optical beam combiner 212 and enter the output waveguide 112 .

Those skilled in the art can understand that in the cascade implementation of the adjustable optical delay module, for N delay switching units, the third waveguides in different delay switching units can have the same length or different lengths; similarly Ground, the fourth waveguides in different delay switching units may have the same length, or may have different lengths.

In addition, although the optical path selection component 211 can be implemented with the help of any device with an optical path selection switching function, in the present invention, a new optical path selection component implementation scheme is proposed especially for the chip implementation scenario, in which the optical path selection component 211 can be implemented with the help of mature technology. The MZ interferometer structure implemented on the chip using advanced chip processing technology can realize the above-mentioned optical path selection and switching function through a simple control process, which is extremely beneficial for chip design.

Figure 7 schematically shows an adjustable optical delay module implemented by a cascade of three delay switching units, where the optical path selection component in the delay switching unit is implemented by an equal-arm interferometer.

As shown in the figure, the optical path selection component 211 adopts an equal-arm interferometer structure, which has a light beam splitter, a light combiner, and first and second arms formed between them by means of a waveguide, wherein the first and second arms are At least one of the two arms is provided with a phase shifter 321, 322, 323, which allows the input optical signal to be selected from different output terminals by adjusting the phase difference between the two arms to achieve one of two different working states. switching between.

Specifically, in the equal-arm interferometer used 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 The two output ends of the optical path selection component are respectively used to connect the third and fourth waveguides.

Therefore, with the help of the driving signals for the phase shifters 321, 322, 323, the optical signal can be controlled to enter the third waveguide or the fourth waveguide to obtain the selected time delay amount. Among them, the phase shifters 321, 322, and 323 may preferably be thermally tuned phase shifters.

The working process of the adjustable light delay module implemented by the equal-arm MZ interferometer will be further explained below in conjunction with FIG. 7 to more clearly understand the delay difference adjustment principle of the unequal-arm interferometer chip module of the present invention.

In the example of FIG. 7 , the adjustable light delay module 401 includes a first delay switching unit, a second delay switching unit and a third delay switching unit cascaded through a waveguide.

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

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

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

For each delay switching unit, an external DC driving signal can be used to control the phase shifter 321/322/323 therein, so that the optical signal enters the third waveguide or the fourth waveguide. For example, the phase difference between the upper and lower arms of the equal-arm interferometer can be adjusted to 0, so that all optical signals enter the longer third waveguide, or the phase difference between the upper and lower arms of the interferometer can be adjusted to π, so that The optical signals all enter the shorter fourth waveguide. Thereby, the amount of delay provided by the adjustable light delay module 401 to the optical signal is adjusted.

Table 1 below shows the different modulations between the two arms of the delay switching units at all levels with the help of phase shifters when L11=3ps, L12=1ps, L21=5ps, L22=1ps, L31=9ps, L32=1ps. When the phase difference is , the adjustable light delay module 401 finally achieves the target delay amount.

(Table I)

As can be seen from Table 1, by freely controlling the phase difference between the two arms of the interferometer in the delay switching units at all levels, the delay amount in the delay switching units at all levels can be switched, and after three levels of delay accumulation, a value of 3ps to 17ps, delay adjustment capability in steps of 2ps.

Those skilled in the art can understand that a lookup table of the phase difference between the two arms of the interferometer and the target delay amount in the delay switching unit at each level can be established in advance, so as to allow convenient delay switching at all levels with the help of a phase shifter according to the lookup table. The required phase difference between the two arms is realized in the unit to provide the desired delay amount for the optical signal.

Figure 8 schematically shows a further example of the delay switching unit shown in Figures 6-7.

As shown in FIG. 8 , the delay switching unit may further include adjustable optical attenuators VOA respectively provided on the third waveguide and the fourth waveguide. Therefore, when the optical signal enters the third waveguide (or fourth waveguide) for transmission 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 waveguide (or third waveguide) can also be controlled. , so that the fourth waveguide (or third waveguide) The optical signal attenuates to the extinction state, thereby allowing the extinction ratio requirement of the phase shifter (or phase modulator) in the MZ interferometer to be reduced.

Figure 9 schematically shows another example of a delay switching unit according to the present invention.

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 output ends of the third optical beam splitter are respectively connected to the third optical combiner through a seventh waveguide and an eighth waveguide. The two input ends of the beam splitter form an interferometer structure, in which the input end of the third optical beam splitter is used as the input end of the delay switching unit, and the output end of the third optical beam combiner is used as the output end of the delay switching unit.

As an example, the seventh waveguide and the eighth waveguide have different optical paths. For example, the seventh waveguide has time delays dT1, dT2, dT3... relative to the eighth waveguide.

In order to realize the time delay switching function, the adjustable optical attenuator VOA can be set on the seventh waveguide and the eighth waveguide respectively. Therefore, the attenuation value of the adjustable optical attenuator VOA on the seventh (or eighth) waveguide can be increased to approximately disconnect the optical path through control, so that the optical signal only passes through the eighth (or seventh) waveguide and is delayed from The switching unit outputs, thereby realizing switching of the time delay amount for the optical signal.

In the present invention, the adjustable optical attenuator VOA may be based on the carrier injection principle or may be implemented based on the MZ interferometer principle.

Similarly, the adjustable optical attenuator VOA may be formed of silicon material.

Continuing to refer 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, for providing light propagation along the waveguide where it is located. The signal provides controllable attenuation, such as compensating the power difference caused by different attenuation of the optical signal propagating along the unequal arms, so that the attenuation amount of the optical signal in the unequal arm interferometer chip module is consistent.

For example, in the quantum key distribution process based on the time phase encoding scheme, after completing the calibration of the delay amount of the long and short arms in the unequal arm interferometer chip module, the working status of the attenuation control module can be adjusted to make the long and short arms The attenuation amount is consistent, thereby ensuring the power balance of the optical signal during the time phase encoding process, and preparing a quantum state with an expected delay.

Preferably, the attenuation control module 501 may include a carrier injection attenuator.

Preferably, the unequal arm interferometer chip module can be implemented on a silicon-based chip. Therefore, light beam splitters (such as the first light beam splitter 202 and the third light beam splitter), light beam combiners (such as the first light beam combiner 203, the second light beam combiner 212 and the third light beam combiner), and The waveguides (eg, the first waveguide, the second waveguide, the third waveguide, the fourth waveguide, the input waveguide, the output waveguide, etc.) may be formed of silicon material.

Preferably, a light beam splitter (such as the first light beam splitter 202 and the third light beam splitter), a light beam combiner (such as the first light beam combiner 203, the second light beam combiner 212 and the third light beam combiner) Can be a multimode interferometer or directional coupler.

Furthermore, the above-mentioned unequal arm interferometer chip module can also be implemented as a separate chip to obtain an unequal arm interferometer chip.

The following will continue to describe the method for adjusting the delay difference of the unequal arm interferometer chip based on the unequal arm interferometer chip of the present invention.

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

Therefore, in the delay difference adjustment method of the present invention, the parameters used for the optical signal can be switched by changing the parameters of the interferometer structure used to implement the delay switching unit (such as the phase difference between the two arms, the attenuation value on the optical arm, etc.) The transmission path implements the adjustment step, which is used to adjust the delay difference of the unequal arm interferometer chip.

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 Control the phase difference between the two arms of the equal-arm MZ interferometer, and select one of the two output terminals of the equal-arm interferometer to output the optical signal so that it propagates along the third waveguide or the fourth waveguide, thereby obtaining different delays. Thus, the delay amount of the arm where the delay switching unit (adjustable light delay module 401) is located is controlled, and the delay difference of the unequal arm interferometer chip is adjusted.

When the interferometer structure adopts the equal-arm MZ interferometer, unequal-arm interferometer and adjustable light shown in Figure 8 When combining the attenuator VOA, the adjustment step may also include the step of adjusting the attenuation value of the adjustable optical attenuator VOA in the unequal arm interferometer so that the optical signal is extinguished on the third waveguide or the fourth waveguide. As mentioned before, this allows relaxing the requirements on the extinction ratio in the equal-arm MZ interferometer. By increasing the optical attenuation value on the third or fourth waveguide to make the optical signal reach the extinction state, the selection of the optical transmission path can be achieved. Purpose.

At this time, the delay difference adjustment method of the present invention may also preferably include preset steps. In a preferred preset step, the corresponding relationship between the delay difference of the unequal arm interferometer chip and the phase difference of the two arms of the medium-arm MZ interferometer of the delay switching unit can be determined in advance, and a corresponding lookup table can be established accordingly, so that In the adjustment step, the phase difference between the two arms of the equal-arm MZ interferometer of the corresponding delay switching unit can be directly obtained by querying the lookup table according to the target delay amount, thereby allowing the two arms of the equal-arm MZ interferometer to be conveniently adjusted. arm phase difference to achieve the required delay difference.

When the interferometer structure adopts an unequal arm interferometer formed by a third optical beam splitter and a third optical beam combiner as shown in Figure 9 and with adjustable optical attenuators VOA provided on both arms, the unequal arm interferometer can be adjusted by The attenuation value of the adjustable optical attenuator VOA in the arm interferometer causes the optical signal to be extinguished on the seventh waveguide or the eighth waveguide to select the optical transmission path, thereby realizing the delay difference adjustment function.

Furthermore, since the delay amount is achieved by changing the length of the waveguide used for optical signal propagation, in order to compensate for fluctuations in the attenuation (intensity) of the optical signal caused by changes in the delay amount, the delay difference adjustment method of the present invention may also include Power control steps.

In the power control step, the attenuation amount of the attenuation control module 501 can be adjusted according to the delay amount 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 balanced power. , which is advantageous for its application in temporal phase encoding schemes.

Continuing to refer to Figure 4, which shows a time phase encoding chip with an adjustable delay difference. As shown in the figure, the time phase encoding chip includes an equal-arm interferometer chip module, and the above-mentioned unequal-arm interferometer chip module with adjustable delay difference. Among them, the optical beam combiner and unequal-arm interference of the equal-arm interferometer chip module The optical beam splitter of the instrument chip module multiplexes the same optical beam splitter 202 (optical beam combiner).

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

In the equal-arm interferometer chip module, the first output end of the second optical beam splitter 201 is connected to the first input end of the first optical beam splitter 202 through the fifth waveguide, and the second output end of the second optical beam splitter 201 The end is connected to the second input end of the first optical beam splitter 202 through the sixth waveguide, and a phase adjustment module 301/302 is provided on at least one of the fifth waveguide and the sixth waveguide, for example, as shown in Figure 4, respectively. Phase adjustment modules 301 and 302 are provided on the fifth and sixth waveguides. Thus, an equal-arm interferometer chip module using the input end of the second optical beam splitter 201 as an input end can be realized, and an equal-arm interferometer chip module and an unequal-arm interferometer chip module (with adjustable delay difference) can be realized simultaneously. connection, thus obtaining a time phase encoding chip with adjustable delay difference.

Correspondingly, 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 receive Outputs an encoded optical signal.

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 module 301/302 can be driven by the external pulse voltage signal, and the phase difference between the two arms in the equal-arm interferometer chip module can be adjusted. Adjust to 0, so that all optical signals are output from the first output end of the first optical beam splitter 202 (which is multiplexed as the optical beam combiner in the equal-arm interferometer chip module) and enter the unequal-arm interferometer chip module. The first waveguide, thereby preparing the |Z1> state on the optical signal; alternatively, the phase difference between the two arms in the equal-arm interferometer chip module can be adjusted to π, so that the optical signal all passes from the first optical beam splitter 202 The second output end of the output terminal is output and enters the second waveguide of the unequal-arm interferometer chip module. At this time, the |Z0> state is prepared; alternatively, the phase difference between the two arms in the unequal-arm interferometer chip module can be adjusted to π/ 2. Make the optical signal equally divided and simultaneously output from the two output ends of the first optical beam splitter 202 to enter the first and second waveguides of the unequal arm interferometer chip module respectively, and prepare the |X0> state at this time; 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 signals are output equally from the two output ends of the first optical beam splitter 202 at the same time to enter the unequal arms respectively. The first and second waveguides of the interferometer chip module are now in the |X1> state.

During this period, in the unequal arm interferometer chip module, the working state of the delay switching unit in the adjustable optical delay module 401 can be controlled to switch different transmission paths for the optical signal, so as to realize the unequal arm interferometer chip module. The desired delay difference between the two arms. Please refer to the above for details and will not be repeated here.

At the same time, the working state of the attenuation control module 501 can also be controlled in the unequal arm interferometer chip module so that the optical signal is uniformly attenuated on both arms, thereby preparing a quantum state with balanced power and expected delay.

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

Preferably, the second optical beam splitter 201 may be a multi-mode interferometer or a directional coupler.

Preferably, the phase adjustment modules 301 and 302 may be carrier deposition type, carrier injection type or carrier depletion type.

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.

Specifically, the adjustment step and the power control step can be realized respectively by means of the adjustment step and the power control step in the delay difference adjustment method for the unequal arm interferometer chip mentioned above, and therefore will not be described again.

Furthermore, the delay difference adjustment method for the time phase encoding chip of the present invention can also include a preset step, which can also be based on the preset steps in the delay difference adjustment method for the unequal arm interferometer chip. There are several steps to achieve this, so they will not be described again here.

In summary, the present invention proposes an unequal arm interferometer chip and time phase encoding chip by introducing an adjustable light delay module based on the interferometer structure into the optical arm of the unequal arm interferometer chip/chip module. The delay difference adjustment method can realize delay difference adjustment within a wide range and with controllable adjustment accuracy by simply changing certain parameters of the interferometer structure (such as modulation phase, light attenuation value, etc.). This effectively solves the uncontrollable delay difference between chips caused by process errors in the existing technology, and is beneficial to the engineering application of time phase encoding chips. At the same time, the present invention also allows the introduction of redundant designs with long delays, and the total delay and delay adjustment accuracy can be conveniently and freely defined, so that the solution of the present invention can have a wider scope of application.

Although the present invention has been described above through specific embodiments in conjunction with the accompanying drawings, those skilled in the art can easily realize that the above embodiments are only exemplary and are used to illustrate the principles of the present invention and do not limit the scope of the present invention. Without limitation, those skilled in the art can make various combinations, modifications and equivalent substitutions of the above embodiments without departing from the spirit and scope of the present invention.

Claims

A delay difference adjustment method for unequal arm interferometer chips, wherein,

The unequal arm interferometer chip includes a first optical beam splitter and a first optical beam combiner. The two output ends of the first optical beam splitter are connected to the first optical beam combiner through first and second waveguides respectively. Two input terminals;

An adjustable optical delay module is provided on at least one of the first and second waveguides for providing time delay for the optical signal propagating along the waveguide;

The adjustable light delay module includes one or multiple delay switching units in cascade, and the delay switching unit is implemented based on an interferometer structure;

The delay difference adjustment method includes an adjustment step for adjusting the delay difference of the unequal arm interferometer chip by changing the parameters of the interferometer structure and switching the transmission path for the optical signal.
The delay difference adjustment method according to claim 1, wherein the delay switching unit includes an equal-arm MZ interferometer with an input end and two output ends, and 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 third and fourth waveguides, and 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 terminals of the equal-arm MZ interferometer is selected for outputting an optical signal.
The delay difference adjustment method according to claim 2, wherein the third waveguide and the fourth waveguide are respectively provided with adjustable optical attenuators; and,

The adjusting step further includes the step of extinguishing the optical signal on the third waveguide or the fourth waveguide by adjusting the attenuation value of the adjustable optical attenuator.
The delay difference adjustment method according to claim 2, further comprising a preset step for setting in advance the difference between the delay difference of the unequal arm interferometer chip and the phase difference of the two arms of the equal-arm MZ interferometer. query table between;

In the adjustment step, the look-up table is used to obtain the phase difference between the two arms of the equal-arm MZ interferometer.
The delay difference adjustment method according to claim 1, wherein the delay switching unit includes including a third optical beam splitter and a third optical beam combiner, the two output ends of the third optical beam splitter are respectively connected to the two input ends of the third optical beam combiner through a seventh waveguide and an eighth waveguide, the Adjustable optical attenuators are respectively provided on the seventh waveguide and the eighth waveguide, and the seventh waveguide and the eighth waveguide have different optical path lengths;

In the adjustment step, by adjusting the attenuation value of the adjustable optical attenuator, the optical signal is extinguished on the seventh waveguide or the eighth waveguide.
The delay difference adjustment method according to any one of claims 1 to 5, wherein at least one of the first and second waveguides is further provided with an attenuation control module for adjusting the optical signal propagating along the waveguide. Provide controllable attenuation;

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 light delay module.
The delay difference adjustment method according to claim 6, wherein the attenuation control module includes a carrier injection attenuator.
The delay difference adjustment method according to claim 1, wherein the optical beam splitter and optical beam combiner are multi-mode interferometers or directional couplers; and/or the optical beam splitter, optical beam combiner and waveguide are made of silicon. .
The delay difference adjustment method according to 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.
The delay difference adjustment method according to claim 5, wherein 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.
A delay difference adjustment method for time phase encoding chips, wherein,

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

The two output ends of the second optical beam splitter are respectively connected to the two input ends of the first optical beam splitter through fifth and sixth waveguides, and at least one of the fifth and sixth waveguides is provided with a to light The phase adjustment module performs phase modulation on the signal to form an equal-arm interferometer chip module;

The two output ends of the first optical beam splitter are respectively connected to the two input ends of the first optical beam combiner through first and second waveguides, and at least one of the first and second waveguides is provided with a The optical signal provides an adjustable optical delay module with time delay, thus forming an unequal arm interferometer chip module;

The adjustable light delay module includes one or multiple delay switching units in cascade, and the delay switching unit is implemented based on an interferometer structure;

The delay difference adjustment method includes an adjustment step for adjusting the delay difference of the unequal arm interferometer chip module by changing the parameters of the interferometer structure and switching the transmission path for the optical signal.
The delay difference adjustment method according to claim 11, wherein the delay switching unit includes an equal-arm MZ interferometer having an input end and two output ends, and 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 third and fourth waveguides, and 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 terminals of the equal-arm MZ interferometer is selected for outputting an optical signal.
The delay difference adjustment method according to claim 12, wherein the third waveguide and the fourth waveguide are respectively provided with adjustable optical attenuators; and,

The adjusting step further includes the step of extinguishing the optical signal on the third waveguide or the fourth waveguide by adjusting the attenuation value of the adjustable optical attenuator.
The delay difference adjustment method according to claim 12, further comprising a preset step for setting the delay difference of the unequal arm interferometer chip module and the two-arm phase difference of the equal-arm MZ interferometer in advance lookup table between;

In the adjustment step, the look-up table is used to obtain the phase difference between the two arms of the equal-arm MZ interferometer.
The delay difference adjustment method according to claim 11, wherein the delay switching unit includes a third optical beam splitter and a third optical beam combiner, and the two output ends of the third optical beam splitter pass through a third optical beam splitter respectively. The seventh waveguide and the eighth waveguide are connected to the two input ends of the third optical beam combiner. The seventh waveguide and the eighth waveguide are respectively provided with adjustable optical attenuators, and the seventh waveguide and the eighth waveguide have different optical path lengths;

In the adjusting step, by adjusting the attenuation value of the adjustable optical attenuator, the optical signal is extinguished on the seventh waveguide or the eighth waveguide.
The delay difference adjustment method according to claims 11-15, wherein at least one of the first and second waveguides is further provided with an attenuation control module for providing controllable damping for optical signals propagating along the waveguide. attenuation;

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 light delay module.
The delay difference adjustment method according to claim 16, wherein the attenuation control module includes a carrier injection attenuator.
The delay difference adjustment method according to claim 11, wherein the phase adjustment module is a carrier deposition type, a carrier injection type or a carrier depletion type; and/or, an optical beam splitter and a photosynthetic The beam device is a multi-mode interferometer or a directional coupler; and/or the optical beam splitter, optical beam combiner and waveguide are made of silicon.
The delay difference adjustment method according to 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.
The delay difference adjustment method according to claim 15, wherein seventh waveguides in different delay switching units have the same or different optical path lengths, and eighth waveguides in different delay switching units have the same or different optical path lengths.