CN116418494A - On-chip encoder with low driving voltage and encoding method - Google Patents

On-chip encoder with low driving voltage and encoding method Download PDF

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CN116418494A
CN116418494A CN202111672173.4A CN202111672173A CN116418494A CN 116418494 A CN116418494 A CN 116418494A CN 202111672173 A CN202111672173 A CN 202111672173A CN 116418494 A CN116418494 A CN 116418494A
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phase
chip
encoder
polarization
components
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刘仁德
陶俊
唐世彪
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Quantumctek Co Ltd
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Quantumctek Co Ltd
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Abstract

The invention discloses an on-chip encoder and an encoding method, which modulate the phase difference required by polarization encoding between a first component and a second component of an input optical signal by combining three phase modulators, can allow the maximum driving voltage to be reduced to 1/3 of the original driving voltage, and reduce the number of different levels required to be switched to 1/2 of the original driving voltage, thereby obviously reducing the technical complexity and cost of a driving circuit, improving the high-low temperature stability, eliminating the need of using a monitoring and compensating unit, effectively reducing the complexity and cost of the system, and obviously increasing the volume and cost of the on-chip encoder.

Description

On-chip encoder with low driving voltage and encoding method
Technical Field
The invention relates to the field of quantum secret communication, in particular to an on-chip encoder with low driving voltage and an encoding method.
Background
Quantum Key Distribution (QKD) is based on quantum mechanics principles, which is a key distribution system that can prove unconditionally secure by theory due to quantum unclonable and mismeasurable principles.
Quantum key distribution often involves complex optical signal encoding and decoding processes, and currently often implements the required encoder and decoder based on a combination of conventional fiber optics, which is bulky and costly.
Polarization encoding schemes are one of the mainstream quantum key distribution schemes,it is realized mainly by means of a polarization encoding process based on phase modulation, namely: for two component lights with polarization states of |H > and |V >, respectively, a phase difference is formed between the two component lights by phase modulation
Figure BDA0003453338570000011
The two components will form a polarization state of +.>
Figure BDA0003453338570000012
Is provided. It follows that the phase difference between the two components of the input optical signal can be adjusted by the phase modulator +.>
Figure BDA0003453338570000013
The desired polarization encoding is achieved on the optical signal.
Currently, the mainstream polarization encoder is realized by means of a combination of an optical fiber device and a polarization-preserving phase modulator, and the polarization encoder is generally large in size and high in cost. For this reason, solutions for implementing optical signal encoding and decoding on optical chips are proposed in the prior art, thereby providing an important solution idea for implementing a small-volume, low-cost and highly stable quantum key distribution device.
Fig. 1 shows a silicon-based integrated polarization modulation device of the prior art, which is realized by a polarization beam splitter, a polarization beam combiner and a silicon-based phase shifter.
Fig. 2 shows a prior art polarization encoding QKD system based on a silicon-based integrated chip, in which a polarization encoder is still constructed from a beam splitter, a polarization rotating combiner, and a silicon-based phase shifter, with the addition of a first-order mach-zehnder interferometer to adjust the proportion of optical power into the optical path shown in fig. 2 at reference numerals 3 and 4, as compared to the structure shown in fig. 1.
The polarization modulation of the on-chip encoder is based on phase adjustment, and the output light polarization state can be written as
Figure BDA0003453338570000021
Which is related to the modulated phase difference. Current silicon-based phaseThe half-wave voltage of the modulator (the driving voltage required to achieve pi phase shift) is typically large. For quantum key distribution it is generally at least necessary to encode with 4 polarization states, e.g.>
Figure BDA0003453338570000022
When the encoder outputs |+ >; />
Figure BDA0003453338570000023
When the encoder outputs |R >; />
Figure BDA0003453338570000024
When the encoder outputs >; />
Figure BDA0003453338570000025
When the encoder outputs |L >. For this reason, the maximum driving voltage often needs to reach 1.5 times the half-wave voltage, and it is also necessary that high-speed switching between 4 different levels (0, 0.5 times the half-wave voltage, and 1.5 times the half-wave voltage) can be achieved.
As such, high demands are placed on the driving circuitry, requiring the use of complex schemes and expensive devices, and even being impractical. Further, as the driving voltage increases, devices such as a power amplifier are often required. When a level 4 is required in quantum key distribution, the power amplifier works at different working points, and finally the output driving voltage is influenced by environmental factors such as temperature, so that a large coding error can be introduced, which often requires a monitoring and compensating unit to be designed for compensation, but the monitoring and compensating unit has high technical complexity and cost.
Disclosure of Invention
In view of the above-mentioned problems in the prior art, the present invention proposes an on-chip encoder and an encoding method, in which, by using three phase modulators in combination, a phase difference required for polarization encoding is modulated between first and second components of an input optical signal, which can allow a maximum driving voltage required for phase modulation to be reduced to 1/3 of an original half-wave voltage, and simultaneously, the number of different level signals required to be used is reduced to half of an original half-wave voltage, and only switching between two level signals of half-wave voltage of 0 and 0.5 times is required, which can significantly reduce technical complexity and cost of a driving circuit and improve high-low temperature stability; and moreover, a monitoring and compensating unit is not needed, so that the complexity and cost of the system can be effectively reduced, and meanwhile, the volume and cost of the on-chip encoder are not obviously increased.
In particular, a first aspect of the present invention relates to a low drive voltage on-chip encoder comprising an optical beam splitter, a first phase modulator, a second phase modulator, a third phase modulator and a polarization beam combiner;
the optical splitter is arranged to split an input optical signal into first and second components;
the first, second and third phase modulators are disposed between the optical beam splitter and the polarization beam combiner, wherein the first phase modulator is configured to modulate a first phase on the first component
Figure BDA0003453338570000031
Said second phase modulator for modulating a second phase +.>
Figure BDA0003453338570000032
Said third phase modulator for modulating a third phase +.>
Figure BDA0003453338570000033
The polarization beam combiner is configured to combine the first and second components to form a polarized optical signal.
Further, the first phase
Figure BDA0003453338570000034
Second phase->
Figure BDA0003453338570000035
And a third phase->
Figure BDA0003453338570000036
Is arranged to form a phase difference between said first and second components>
Figure BDA0003453338570000037
Said phase difference->
Figure BDA0003453338570000038
Figure BDA0003453338570000039
Selected from the first set of phases.
Alternatively, the first set of phases may include 0, pi/2, pi, and 3 pi/2. Wherein the phase combination formed by the first phase, the second phase and the third phase
Figure BDA00034533385700000310
Figure BDA00034533385700000311
Selected from the group of phase groups [ (0, 0), (0, pi/2, 0), (pi/2, 0), (0, pi/2)]。
Preferably, 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 formed based on the principle of plasma dispersion effect; and/or the first, second and third phase modulators, the optical beam splitter and the polarization beam combiner are made of silicon materials.
A second aspect of the invention relates to a low driving voltage on-chip encoding method comprising the steps of:
splitting an input optical signal into first and second components;
performing two-time phase modulation on the first component, wherein the modulation phases are respectively the first phase
Figure BDA00034533385700000312
And second phase->
Figure BDA00034533385700000313
Performing primary phase modulation on the second component, wherein the modulation phase is a third phase
Figure BDA00034533385700000314
Figure BDA00034533385700000315
The method comprises the steps of,
the phase modulated first and second components are polarization combined to form a polarized optical signal.
Further, a first phase
Figure BDA00034533385700000316
Second phase->
Figure BDA00034533385700000317
And a third phase->
Figure BDA00034533385700000318
Is arranged to form a phase difference between said first and second components>
Figure BDA00034533385700000319
Said phase difference->
Figure BDA00034533385700000320
Selected from the first set of phases.
Optionally, the first set of phases includes 0, pi/2, pi, and 3 pi/2. A phase combination formed by the first phase, the second phase and the third phase
Figure BDA0003453338570000041
May be selected from the group of phase groups [ (0, 0), (0, pi/2, 0), (pi/2, 0), (0, pi/2)]。
Preferably, the on-chip encoding method of the present invention may be implemented by means of an on-chip encoder as described above.
Drawings
The following describes the embodiments of the present invention in further detail with reference to the drawings.
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 illustrates a silicon-based integrated polarization modulation device of the prior art;
FIG. 2 shows a prior art polarization encoded QKD system based on a silicon-based integrated chip;
fig. 3 shows an example of a low driving voltage on-chip encoder according to the present invention.
Detailed Description
Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following examples are provided by way of illustration to fully convey the spirit of the invention to those skilled in the art to which the invention pertains. Thus, the present invention is not limited to the embodiments disclosed herein.
Fig. 3 shows an example of a low driving voltage on-chip encoder according to the present invention.
As shown in fig. 3, the on-chip encoder includes an optical beam splitter 200, a polarization beam combiner 400, and first, second, and third phase modulators 301, 302, and 303 disposed between the optical beam splitter 200 and the polarization beam combiner 400.
The optical splitter 200 has an input end, a first splitting end, and a second splitting end. Wherein the input waveguide 100 is connected to an input end of the optical splitter 200 to input an input optical signal to the optical splitter 200; the input optical signal is split in the optical splitter 200 to form first and second components, which are output from the first and second splitting ends of the optical splitter 200, respectively.
The first beam splitting end of the optical beam splitter 200 is connected to a first input end of the polarization beam combiner 400 through a first waveguide, and the second beam splitting end is connected to a second input end of the polarization beam combiner 400 through a second waveguide, thereby allowing the first and second components to be transmitted to the polarization beam combiner 400.
The polarization beam combiner 400 may polarization-combine the first and second components to form a polarized optical signal and output the polarized optical signal through the output waveguide 500 connected to an output terminal thereof.
It is noted that unlike the prior art, the present invention forms first and second phase modulators 301, 302 on the first waveguide, allowing the first component to be phase modulated twice before it reaches the polarization beam combiner 400, wherein the first phase modulator 301 modulates the first phase on the first component
Figure BDA0003453338570000051
Second phase modulator 302 modulates the second phase on the first component>
Figure BDA0003453338570000052
Meanwhile, a third phase modulator 303 is formed on the second waveguide for modulating a third phase +.>
Figure BDA0003453338570000053
Therefore, the first phase can be reasonably set in the polarization encoding process
Figure BDA0003453338570000054
First phase->
Figure BDA0003453338570000055
And a third phase->
Figure BDA0003453338570000056
Is a combination of the first and second components, a phase difference corresponding to the polarization encoding is formed between the first and second components>
Figure BDA0003453338570000057
For a better understanding of the working principle of the present invention, the low driving voltage on-chip encoding method of the present invention will be described in detail with reference to fig. 3.
In polarization encoding, an input optical signal will enter the optical splitter 200 through the input waveguide 100.
In the optical splitter 200, an input optical signal is split to form first and second components having polarization states perpendicular to each other, and the first and second components are transmitted toward the polarization beam combiner 400 along first and second waveguides, respectively.
The first phase may be modulated on the first component by means of a first phase modulator 301 and a second phase modulator 302, respectively, during transmission of the first and second components along the first and second waveguides, respectively
Figure BDA0003453338570000058
And second phase->
Figure BDA0003453338570000059
And modulates a third phase +_ on the second component by means of a third phase modulator 303>
Figure BDA00034533385700000510
Thereby forming a phase difference +_ between the first and second components>
Figure BDA0003453338570000061
In polarization encoding schemes, it is often desirable to encode four or more polarization states, such as |++ >, |R >, |- > and |L >. When coding of four polarization states, |++ >, R >, |-, and L > is to be implemented on a polarized optical signal, a phase difference between the first and second components is required
Figure BDA0003453338570000062
Corresponding to 0, pi/2, pi and 3 pi/2, i.e. +.>
Figure BDA0003453338570000063
Selected from the phase set [0, pi/2, pi, 3 pi/2]。
In the present invention, the first phase can be properly utilized
Figure BDA0003453338570000064
Second phase->
Figure BDA0003453338570000065
And a third phase->
Figure BDA0003453338570000066
Is to achieve this phase difference +.>
Figure BDA0003453338570000067
The first phase is shown in
Figure BDA0003453338570000068
Second phase->
Figure BDA0003453338570000069
And a third phase->
Figure BDA00034533385700000610
By means of which the phase difference required for polarization encoding can be achieved>
Figure BDA00034533385700000611
Figure BDA00034533385700000612
(which is selected from the phase set [0, pi/2, pi, 3 pi/2 ]])。
Figure BDA00034533385700000613
(Table I)
It can be seen that with the on-chip encoder of the present invention provided with three phase modulators, the phase modulators provide a maximum of pi/2 modulation phase when implementing the four polarization states required for a polarization encoding scheme. Therefore, the maximum driving voltage required by the on-chip encoder is only 0.5 times of half-wave voltage, and the half-wave voltage is reduced to 1/3 of the maximum driving voltage required by the existing on-chip encoder, so that the driving voltage of the on-chip encoder can be obviously reduced, and the requirement on a driving circuit is reduced. At the same time, it is also noted that in the on-chip encoder of the present invention, the modulation phase of each phase modulator only needs to be switched between 0 and pi/2, in other words, the driving signal for the phase modulator only needs to be switched between two different levels, which is only half of the four level signals required by the existing scheme in number, which significantly reduces the complexity of the driving circuit control process, improving its usability and stability. Therefore, the on-chip encoder provided by the invention needs lower driving voltage, is easier to realize, has good high-low temperature stability, and does not need complex monitoring and compensation. Furthermore, the encoder of the present invention is implemented on-chip, increasing the number of phase modulators does not significantly increase cost and bulk.
In a preferred example of the present invention, the input waveguide 100, the optical beam splitter 200, the first phase modulator 301, the second phase modulator 302, the third phase modulator 303, the polarization beam combiner 400, the output waveguide 500, and the first and second waveguides may be implemented with silicon materials.
Preferably, the first, second and third phase modulators 301, 302, 303 may be formed based on the principle of the plasma dispersion effect. Further, these phase modulators may be of a carrier deposition type, a carrier injection type, or a carrier depletion type.
Preferably, the optical splitter 200 may be a multimode interferometer or a directional coupler.
Preferably, the polarization beam combiner 400 may be a polarization rotating beam combiner such as a two-dimensional grating.
While the invention has been described in connection with the specific embodiments illustrated in the drawings, it will be readily appreciated by those skilled in the art that the above embodiments are merely illustrative of the principles of the invention, which are not intended to limit the scope of the invention, and various combinations, modifications and equivalents of the above embodiments may be made by those skilled in the art without departing from the spirit and scope of the invention.

Claims (10)

1. An on-chip encoder with low driving voltage comprises an optical beam splitter, a first phase modulator, a second phase modulator, a third phase modulator and a polarization beam combiner;
the optical splitter is arranged to split an input optical signal into first and second components;
the first, second and third phase modulators are disposed between the optical beam splitter and the polarization beam combiner, wherein the first phase modulator is configured to modulate a first phase on the first component
Figure FDA0003453338560000011
Said second phase modulator for modulating a second phase +.>
Figure FDA0003453338560000012
Said third phase modulator for modulating a third phase +.>
Figure FDA0003453338560000013
The polarization beam combiner is configured to combine the first and second components to form a polarized optical signal.
2. The on-chip encoder of claim 1, wherein the first phase
Figure FDA0003453338560000014
Second phase->
Figure FDA0003453338560000015
And a third phase->
Figure FDA0003453338560000016
Is arranged to form a phase difference between said first and second components>
Figure FDA0003453338560000017
Said phase difference->
Figure FDA0003453338560000018
Selected from the first set of phases.
3. The on-chip encoder of claim 2, wherein the first set of phases comprises 0, pi/2, pi, and 3 pi/2.
4. The on-chip encoder of claim 3, wherein the phase combination formed by the first phase, the second phase, and the third phase
Figure FDA0003453338560000019
Selected from the group of phase groups [ (0, 0), (0, pi/2, 0), (pi/2, 0), (0, pi/2)]。
5. The on-chip encoder of any of claims 1-4, wherein:
the optical beam splitter is a multimode interferometer or a directional coupler; and/or the number of the groups of groups,
the polarization beam combiner is a two-dimensional grating; and/or the number of the groups of groups,
the phase modulator is formed based on the principle of plasma dispersion effect; and/or the number of the groups of groups,
the first, second and third phase modulators, the optical beam splitter and the polarization beam combiner are made of silicon materials.
6. An on-chip encoding method of low driving voltage, comprising the steps of:
splitting an input optical signal into first and second components;
performing two phase modulations on the first component, whichThe modulation phases are respectively the first phases
Figure FDA00034533385600000110
And a second phase
Figure FDA00034533385600000111
Performing primary phase modulation on the second component, wherein the modulation phase is a third phase
Figure FDA0003453338560000021
3 (i) The method comprises the steps of carrying out a first treatment on the surface of the The method comprises the steps of,
the phase modulated first and second components are polarization combined to form a polarized optical signal.
7. The on-chip encoding method of claim 6, wherein the first phase
Figure FDA0003453338560000022
Second phase->
Figure FDA0003453338560000023
And a third phase->
Figure FDA0003453338560000024
Is arranged to form a phase difference between said first and second components>
Figure FDA0003453338560000025
Said phase difference->
Figure FDA0003453338560000026
Selected from the first set of phases.
8. The on-chip encoding method of claim 7, wherein the first set of phases comprises 0, pi/2, pi, and 3 pi/2.
9. The on-chip encoding method of claim 8, wherein a phase combination formed by the first phase, the second phase, and the third phase
Figure FDA0003453338560000027
Selected from the group of phase groups [ (0, 0), (0, pi/2, 0), (pi/2, 0), (0, pi/2)]。
10. An on-chip encoding method as claimed in claim 6, which is implemented by means of an on-chip encoder as claimed in any of claims 1-5.
CN202111672173.4A 2021-12-31 2021-12-31 On-chip encoder with low driving voltage and encoding method Pending CN116418494A (en)

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