An on-chip encoder and method for attenuation equalization
By introducing a phase modulator into the on-chip encoder for attenuation pre-compensation, the problem of uneven attenuation of the on-chip encoder under different polarization states is solved, optical signal power equalization is achieved, and the stability and efficiency of quantum key distribution are improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- QUANTUMCTEK CO LTD
- Filing Date
- 2021-12-31
- Publication Date
- 2026-07-17
Smart Images
Figure CN116418406B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of quantum secure communication, and specifically to an on-chip encoder with attenuation equalization and its encoding method. 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 provable unconditionally secure key distribution system.
[0003] Quantum key distribution often involves complex optical signal encoding and decoding processes. Currently, the required encoders and decoders are often based on a combination of traditional fiber optic devices, which are large in size and expensive.
[0004] Polarization coding schemes are one of the mainstream quantum key distribution schemes. They are mainly implemented through a phase modulation-based polarization coding process, that is, for two light components with polarization states of |H> and |V> respectively, a phase difference is formed between the two light components through phase modulation. The two components, after being vector-composed, will form a polarization state as follows: The polarized light signal. Therefore, it can be seen that the phase difference between the two components of the input light signal can be adjusted using a phase modulator. The required polarization coding is implemented on the optical signal.
[0005] Currently, mainstream polarization encoders are implemented using a combination of fiber optic devices and polarization-maintaining phase modulators, which generally result in large size and high cost. To address this, existing technologies have proposed solutions for implementing optical signal encoding and decoding on optical chips, thus providing an important approach to achieving small-size, low-cost, and highly stable quantum key distribution devices.
[0006] Figure 1 The present invention illustrates a silicon-based integrated polarization modulation device, which is implemented by a polarization beam splitter, a polarization beam combiner, and a silicon-based phase shifter, wherein the silicon-based phase shifter is typically based on the thermo-optical effect principle or the plasma dispersion effect principle.
[0007] In this on-chip coding scheme, silicon-based phase modulators based on the plasmon dispersion effect generally suffer from modulation-dependent loss, meaning that the attenuation varies depending on the phase being modulated. Therefore, this on-chip encoder will produce different attenuations of the input optical signal when modulating different polarization states, ultimately leading to unbalanced power in the output polarized optical signal. However, in this quantum key distribution, theoretically, all dimensions other than polarization state must be indistinguishable.
[0008] Therefore, existing technologies have proposed a solution to this problem by sacrificing a certain security key generation rate, but this reduction in key generation rate is also detrimental to quantum key distribution. Summary of the Invention
[0009] To address the aforementioned problems in the prior art, this invention proposes an on-chip encoder and method for attenuation equalization. A phase modulator is placed outside the polarization encoding unit to induce a certain pre-attenuation in the optical signal through phase modulation. Furthermore, based on the attenuation value generated by the polarization encoding unit on the optical signal, the pre-attenuation value is adjusted by regulating the modulation phase, thereby ensuring that the total attenuation value of the optical signal output by the on-chip encoder is a fixed value. Thus, an on-chip encoder and method for attenuation equalization are achieved.
[0010] The first aspect of the present invention relates to an on-chip coding method for attenuation equalization, which includes a pre-compensation step and a coding step;
[0011] In the pre-compensation step, a first silicon-based phase modulator is used to provide a first modulation phase for the input optical signal. j = 1, ..., M;
[0012] In the encoding step, an optical beam splitter is used to divide the phase-modulated input optical signal into first and second components, and a second silicon-based phase modulator is used to provide a second modulation phase for the first or second component. The first and second components are combined using a polarization beam combiner to form a polarized light signal;
[0013] Wherein, the first modulation phase The second modulation phase is configured such that the total attenuation value IL of the polarized light signal relative to the input light signal is a fixed value. Selected from the first phase set.
[0014] Furthermore, the on-chip coding method of the present invention further includes a fixed value setting step, wherein the first modulation phase is set... If the value is zero, select N second modulation phase scan points within the first phase range. i = 1, ..., N, record the second modulation phase scan point The total attenuation value IL(i) is used to obtain the maximum total attenuation value, and this maximum total attenuation value is set as the fixed value.
[0015] Furthermore, the on-chip coding method of the present invention further includes pre-coding each second modulation phase in the first phase set. Determine the first modulation phase that makes the total attenuation value IL equal to the fixed value. The steps.
[0016] Preferably, the first phase set includes 0, π / 2, π, and 3π / 2; and / or, the optical beam splitter is a multimode interferometer or a directional coupler; and / or, the polarization beam combiner is a two-dimensional grating; and / or, the silicon-based phase modulator is formed based on the principle of plasma dispersion effect.
[0017] Optionally, the first phase range is 0-2π.
[0018] A second aspect of the invention relates to an attenuation-equalized on-chip encoder comprising a first phase modulator, an optical beam splitter, a second phase modulator, and a polarization beam combiner connected via waveguides.
[0019] The first phase modulator is configured to provide a first modulation phase for the input optical signal.
[0020] The optical beam splitter is configured to split the phase-modulated input optical signal into first and second components;
[0021] The second phase modulator is configured to provide a second modulation phase for the first or second component. It is selected from the first phase set;
[0022] The polarization beam combiner is configured to combine the first and second components to form a polarized light signal.
[0023] Wherein, the first modulation phase It is set to make the total attenuation value IL of the polarized light signal relative to the input light signal a fixed value.
[0024] Furthermore, the fixed value is in the first modulation phase. When it is zero, the second modulation phase within the first phase range is used. The maximum value in the total attenuation value IL obtained.
[0025] Optionally, the first phase set includes 0, π / 2, π, and 3π / 2.
[0026] Optionally, the first phase range is 0-2π.
[0027] Preferably, other devices or functional units are provided between the first phase modulator and the optical beam splitter; and / or, the optical beam splitter is a multimode interferometer or a directional coupler; and / or, the polarization beam combiner is a two-dimensional grating; and / or, the phase modulator is a carrier deposition type, a carrier injection type, or a carrier depletion type; and / or, the first phase modulator, the optical beam splitter, the second phase modulator, the polarization beam combiner, and the waveguide are made of silicon. Attached Figure Description
[0028] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.
[0029] 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.
[0030] Figure 1 This illustrates a silicon-based integrated polarization modulation device in the prior art;
[0031] Figure 2 An example of an on-chip encoder with attenuation equalization according to the present invention is shown;
[0032] Figure 3 Another example of an on-chip encoder with attenuation equalization according to the present invention is shown. Detailed Implementation
[0033] 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.
[0034] Considering that the uneven attenuation of existing on-chip encoders is due to the different attenuations introduced into the optical signal when performing polarization encoding, this invention proposes to add an attenuation pre-compensation step to the original polarization encoding process. By compensating for the attenuation differences during the polarization encoding process in the pre-compensation step, it is ensured that the total attenuation value generated by the on-chip encoder on the input optical signal is a fixed value when encoding different polarization states. That is, the different polarization optical signals output by its polarization encoding have the same power (light intensity).
[0035] More importantly, in implementing this attenuation pre-compensation, this invention does not employ conventional intensity modulation devices or functional structures such as intensity modulators. Instead, it proposes an attenuation pre-compensation structure using phase modulators, specifically tailored to the unique application scenario of on-chip encoders. While conventional devices like intensity modulators offer power regulation, they are not entirely suitable for addressing the attenuation imbalance problem in on-chip encoders. In existing on-chip encoders, the attenuation differences of phase modulators corresponding to different modulation phases are relatively small, thus requiring high power regulation accuracy to compensate for these differences. In contrast, conventional power regulation devices, such as intensity modulators, have excessively large adjustment ranges, necessitating complex control processes to achieve the required attenuation compensation for on-chip encoders. Furthermore, the relatively complex structure of these power regulation devices unnecessarily increases the complexity of on-chip encoder fabrication and hinders miniaturization. Therefore, this invention, through analysis of the on-chip encoder structure, innovatively proposes the concept of similar compensation. Utilizing the correlation between attenuation value and modulation phase in the phase modulator, it uses the active change of one phase modulator to compensate for the passive change in another, thereby overcoming the attenuation imbalance problem caused by undesirable attenuation value changes. Furthermore, the attenuation compensation structure in this invention possesses the same characteristics as the phase modulator in the polarization coding unit, allowing for the provision of the required attenuation compensation in a very simple manner; its compensation accuracy is consistent with the attenuation variation accuracy in the polarization coding unit, enabling very precise attenuation compensation; and both exhibit consistent environmental stability, thus allowing for stable compensation effects. Simultaneously, the attenuation compensation structure implemented using a phase modulator requires a relatively simple manufacturing process and a relatively small size, which is highly advantageous for on-chip encoders.
[0036] Figure 2 An example of an on-chip encoder with attenuation equalization according to the present invention is shown.
[0037] like Figure 2 As shown, the on-chip encoder may include a first phase modulator 200, an optical beam splitter 300, a second phase modulator 400, and a polarization beam combiner 500. The first phase modulator 200 is used to implement attenuation compensation, while the optical beam splitter 300, the second phase modulator 400, and the polarization beam combiner 500 together implement polarization encoding.
[0038] The input terminal of the first phase modulator 200 is connected to the input waveguide 100 to receive the input optical signal and modulate the first phase. The first phase modulation is applied to it, thus providing a phase with the first modulation on the input optical signal. The corresponding attenuation value serves as pre-compensation.
[0039] The optical beam splitter 300, the second phase modulator 400, and the polarization beam combiner 500 constitute a polarization encoding unit. The output of the first phase modulator 200 is connected to the input of the optical beam splitter 300 via a waveguide, so that the pre-compensated input optical signal is input into the polarization encoding unit for polarization encoding to generate a polarized optical signal.
[0040] In the polarization coding unit, the optical beam splitter 300 splits the input optical signal into a first component and a second component.
[0041] The first and second components each propagate along a waveguide toward the polarization combiner 500. During this propagation, the second phase modulator 400 is in the second modulation phase. The first component is then subjected to a second phase modulation. Therefore, when the first and second components are combined at polarization combiner 500 to form a polarized light signal, the polarization state of the polarized light signal will be synchronized with the second modulation phase. related.
[0042] like Figure 2 As shown, the output of the polarization combiner 500 can be connected to the output waveguide 600 to output polarized light signals.
[0043] In this invention, a second modulation phase can be set according to the polarization state to be encoded. Simultaneously, based on the second modulation phase Set the first modulation phase This ensures that the attenuation value IL of the polarized light signal relative to the input light signal (i.e., the total attenuation value of the on-chip encoder) is a preset fixed value.
[0044] The following will combine Figure 2 The on-chip coding method for attenuation equalization of the present invention is further described in order to, for example, better understand the first modulation phase. Second modulation phase The process of setting the fixed total attenuation value IL of the on-chip encoder.
[0045] The on-chip encoding method for attenuation equalization according to the present invention may include a fixed value setting step, a pre-compensation step, and an encoding step.
[0046] The fixed value setting step is used to set a suitable fixed total attenuation value IL for the on-chip encoder.
[0047] In this fixed value setting step, the first modulation phase is set... If the value is zero, select N second modulation phase scan points within the first phase range. i = 1, ..., N, and recorded at each second modulation phase scan point. Next, the total attenuation value IL(i) of the on-chip encoder is obtained. Finally, using the obtained N total attenuation values IL(i), the maximum total attenuation value within the first phase range is calculated and set as a fixed value.
[0048] In this invention, the second modulation phase used for polarization coding can be used as a basis. Determine the first phase range. As an example, the first phase range can be set to 0-2π.
[0049] After setting a fixed value, multiple first modulation phases can be obtained in advance to make the total attenuation value IL of the on-chip encoder a fixed value. Second modulation phase The phase combination. Therefore, it is convenient to determine the second modulation phase used for polarization coding. Determine the first modulation phase used to provide attenuation precompensation.
[0050] For example, this can be applied to each of the second modulation phases in the first phase set. The first modulation phase that makes the total attenuation value IL a fixed value is calculated separately. This results in the formation of corresponding phase combinations.
[0051] As an example, the first phase set may include four modulation phases, such as 0, π / 2, π, and 3π / 2, for implementing four polarization states, such as |+>, |R>, |->, and |L>, in the on-chip encoder.
[0052] Therefore, in the pre-compensation step, the second modulation phase used for polarization coding can be used as a reference. For example, the first modulation phase that matches the pre-formed phase combination is obtained. The first phase modulator 200 provides the first modulation phase for the input optical signal. Provide a corresponding attenuation value to the input optical signal to perform attenuation pre-compensation.
[0053] In the encoding step, the optical beam splitter 300 can be used to split the input optical signal, which has undergone the first phase modulation (attenuation pre-compensation), into first and second components, and the second phase modulator 400 can be used to provide a second modulation phase on the first or second component. The polarization of the two components is ultimately combined by the polarization combiner 500 to form a polarized light signal with the desired polarization state. Furthermore, the total attenuation IL of the polarized light signal relative to the input light signal must be a preset fixed value, thereby allowing the on-chip encoder to stably output polarized light signals with different polarization states but the same power.
[0054] In this invention, the first phase modulator 200, the optical beam splitter 300, the second phase modulator 400, and the polarization beam combiner 500, as well as the waveguide connected to these devices, can preferably be implemented using silicon material.
[0055] Preferably, the first and second phase modulators can be formed based on the principle of plasma dispersion effect.
[0056] Furthermore, the phase modulator of the present invention can be a carrier deposition type, a carrier injection type, or a carrier depletion type.
[0057] Preferably, the optical beam splitter 300 may include a multimode interferometer or a directional coupler.
[0058] Preferably, the polarization combiner 500 may include a polarization rotation combiner, such as a two-dimensional grating.
[0059] although Figure 2 The on-chip encoder shown only includes a first phase modulator 200 and a polarization encoding unit. However, those skilled in the art will understand that in the on-chip encoder according to the present invention, any necessary optical devices or functional modules can be arranged between the first phase modulator 200 and the polarization encoding unit without affecting the stable output of attenuated and balanced polarized light signals by the on-chip encoder.
[0060] Figure 3 Another example of an on-chip encoder according to the present invention is shown.
[0061] like Figure 3 As shown, with Figure 2 Compared to the on-chip encoder shown, this on-chip encoder also has an optical beam splitting ratio adjustment unit between the first phase modulator 200 and the optical beam splitter 300 (i.e., polarization encoding unit), which includes an optical beam splitter 700 and a phase modulator 800, for adjusting the beam splitting ratio of the optical beam splitter 300.
[0062] Those skilled in the art will understand that, Figure 3 In the on-chip encoder shown, while increasing the power adjustment function of the polarized light signal by means of the intensity modulator, it is still possible to eliminate the attenuation imbalance in the on-chip encoder caused by the imperfection of the phase modulator (i.e., the attenuation value changes with the modulation phase) by means of the pre-compensation of the phase modulator 200.
[0063] 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. An on-chip coding method for attenuation equalization, comprising a pre-compensation step and a coding step; In the pre-compensation step, a first silicon-based phase modulator is used to provide a first modulation phase for the input optical signal. In the encoding step, an optical beam splitter is used to divide the phase-modulated input optical signal into first and second components, and a second silicon-based phase modulator is used to provide a second modulation phase for the first or second component. The first and second components are combined using a polarization beam combiner to form a polarized light signal; in, First modulation phase The second modulation phase is set such that the total attenuation value IL of the polarized light signal relative to the input light signal is a fixed value. Selected from the first phase set.
2. The on-chip encoding method as described in claim 1, further comprising a fixed value setting step, wherein, Make the first modulation phase If the value is zero, select N second modulation phase scan points within the first phase range. Record the second modulation phase scan point The total attenuation value IL(i) is used to obtain the maximum total attenuation value, and this maximum total attenuation value is set as the fixed value.
3. The on-chip coding method as described in claim 2, further comprising pre-coding each of the second modulation phases in the first phase set. Determine the first modulation phase that makes the total attenuation value IL equal to the fixed value. The steps.
4. The on-chip coding method according to any one of claims 1-3, wherein: The first phase set includes 0, π / 2, π, and 3π / 2; and / or, The optical beam splitter is a multimode interferometer or a directional coupler; and / or... The polarization beam combiner is a two-dimensional grating; and / or The silicon-based phase modulator is based on the principle of plasma dispersion effect.
5. The on-chip coding method as described in claim 2 or 3, wherein, The first phase range is 0-2π.
6. An attenuation-equalized on-chip encoder, comprising a first phase modulator, an optical beam splitter, a second phase modulator, and a polarization beam combiner connected via waveguides; The first phase modulator is configured to provide a first modulation phase for the input optical signal. The optical beam splitter is configured to split the phase-modulated input optical signal into first and second components; The second phase modulator is configured to provide a second modulation phase for the first or second component. It is selected from the first phase set; The polarization beam combiner is configured to combine the first and second components to form a polarized light signal. in, First modulation phase It is set to make the total attenuation value IL of the polarized light signal relative to the input light signal a fixed value.
7. The on-chip encoder as described in claim 6, wherein, The fixed value is in the first modulation phase. When it is zero, the second modulation phase within the first phase range is used. The maximum value of the total attenuation value IL obtained by 2(j).
8. The on-chip encoder as claimed in claim 6, wherein, The first phase set includes 0, π / 2, π, and 3π / 2.
9. The on-chip encoder as claimed in claim 7, wherein, The first phase range is 0-2π.
10. The on-chip encoder as described in any one of claims 6-9, wherein: Other devices or functional units are also provided between the first phase modulator and the optical beam splitter; and / or, The optical beam splitter is a multimode interferometer or a directional coupler; and / or... The polarization beam combiner is a two-dimensional grating; and / or The phase modulator is a carrier deposition type, a carrier injection type, or a carrier depletion type; and / or... The first phase modulator, the optical beam splitter, the second phase modulator, the polarization beam combiner, and the waveguide are made of silicon.