Method and apparatus for carrier recovery

Abstract

The invention relates to a method and apparatus for feedforward carrier recovery in coherent optical communications. A method and apparatus for receiving an optical signal from an optical source is disclosed, wherein the optical signal comprises at least one pilot pulse and at least one signal pulse having information. Quadrature values of a plurality of samples of the at least one pilot pulse are determined using a local oscillator signal of a local oscillator source. A phase difference between the received optical signal of the optical source and the local oscillator signal of the local oscillator source is determined using the quadrature values of the plurality of samples, and carrier information of the at least one signal pulse is recovered based on the determined phase difference.

Description

Technical Field

[0001] This invention relates to methods and apparatus for carrier recovery, particularly in coherent optical communication. In particular, the invention relates to methods and apparatus for feedforward carrier recovery, which can allow phase and / or frequency recovery, for example, in coherent optical communication and quantum cryptography. Background Technology

[0002] Quantum key distribution (QKD) allows two parties, often referred to as Alice and Bob, to share and / or generate cryptographic keys by distributing quantum signals via a communication channel. One of the main QKD implementations is continuously variable QKD (CV-QKD). CV-QKD typically uses coherent states of light (e.g., weak optical pulses) as quantum signals, and the information is encoded in the conjugate orthogonality of electromagnetic fields. Orthogonality is related to the amplitude and phase of the signal pulses.

[0003] A typical CV-QKD system may include a transmitter, often referred to as Alice, which sends low-intensity quantum pulses (i.e., coherent states) with encoded random information to a receiver, called Bob, which can measure the quantum pulses using coherent detection. In coherent detection, a high-intensity reference signal, called a local oscillator (LO), can be mixed or interfered with the signal pulses transmitted by Alice to retrieve their orthogonality. The output of the detection can be affected by any phase fluctuations in the Alice symbol signal and the LO signal. More specifically, fluctuations in the phase difference between the LO signal and the Alice signal can affect the detection. For this reason, in some CV-QKD implementations, the LO and quantum signal can be generated from the same laser at Alice, and both signals are transmitted to Bob. Transmitting the LO in the optical channel allows for a constant phase relationship between the high-intensity LO and the low-intensity Alice pulses. However, this can lead to unwanted third-party access to the encryption key, i.e., eavesdropping.

[0004] In some other implementations of CV-QKD, the free-running LO can be locally generated on the Bob side using an additional laser. This use of the free-running LO at the Bob might require a carrier or phase recovery process to compensate for any phase ripples between the quantum signal generated by Alice and the LO. In classical coherent communication, when using high-intensity signal pulses, phase ripples can be compensated for by referencing the transmitted pulse itself. An alternative could be to use a so-called guide signal to avoid any phase ambiguity caused by data modulation.

[0005] Traditional techniques describe methods for recovering phase information of low-intensity signals by estimating the phase and frequency difference between the Alice laser and the LO signal using two or more consecutive guide pulses (also known as reference pulses). However, to obtain an accurate phase estimate, the frequency difference between the Alice laser and the LO may need to be ±1 / 2T. b Within the range, where T b It is the time delay between two consecutive pilot pulses (see Figure 1 For example, in a high-speed CV-QKD system, the pilot pulse can run at a rate of 100 MHz, and in this case, the frequency difference between the Alice laser and the LO may have to be within 50 MHz. This has the disadvantage of requiring a very stable laser source with a complex structure, thus limiting availability and incurring higher costs. For example, atomic transitions can be used to stabilize the laser frequency. However, this may lead to the use of additional components, such as gas-photocells. Even when the laser signal is stable, there may often be a difference in the emission frequency (wavelength) between the Alice laser and the LO. Therefore, additional relative wavelength tuning may become necessary, which is typically achieved by changing the current and / or temperature.

[0006] Furthermore, the aforementioned traditional methods typically use trigonometric functions to measure the phase of the pilot and / or quantum pulse to recover information. As an alternative to trigonometric functions, lookup tables (LUTs) can be used in some implementations. However, both trigonometric function and LUT methods can suffer from large computational time, hardware, and / or resource requirements. LUT-free techniques can be used to implement real-time feedforward and feedback carrier recovery. This technique can recover data based on selecting optimal samples of each symbol (e.g., according to power), thus limiting the frequency range of operation.

[0007] like Figure 1 As shown, a conventional example illustrates a typical experimental setup for CV-QKD with a true local oscillator (LO (so-called free-running)). The transmitter / sender (Alice) 101 can use a continuous-wave laser source 103, where the laser can be modulated by an amplitude modulator (AM) 105 and / or a phase (PM) electro-optic modulator 107 to obtain optical pulses whose orthogonality follows, for example, a Gaussian random distribution. The in-phase and out-of-phase orthogonal signals encoded by the transmitter / sender 101 are referred to as X, respectively. A and P A Subsequently, the attenuator (ATT) 109 can be used to set the signal variance (i.e., the Alice modulator variance) to a value that maximizes or optimizes the encryption key rate. The modulation variance can typically be equal to twice the mean number of photons.

[0008] Modulated optical pulses are sent to receiver (Bob) 201, where they can interfere with the LO signal generated by LO 205 in receiving unit 203. LO 205 can typically operate as a continuous wave. Polarization controller (PC) 207 of receiving unit 203 can be used to align the polarization of the quantum pulses and the local oscillator to maximize or optimize the interference. Interference can occur at a 90° optical blend (90°OH) (part of detector 209), and the output from the optical blend can be measured by detector 209. Receiver 201 can be configured to process the measurement results in real time to obtain the result with the Alice signal X. A and P A The relevant data. Real-time data processing can typically be performed by a control unit such as a digital signal processing (DSP) unit 211.

[0009] The frequency difference Δf between the LO and the received signal from the transmitter / alice laser, and the frequency noise f of the laser. n This can cause phase drift (phase noise) in the measured orthogonality. The in-phase and out-of-phase orthogonality values ​​of the quantum signal received by Bob (called X) B and P B The relationship between the Alice signal and the Alice signal is as follows:

[0010]

[0011]

[0012] Equation (1) corresponds to the noise (Δf+f) n Phase rotation caused by Where N X and N P It is zero-centered Gaussian noise, which can include shot noise and super noise of the system.

[0013] In order to retrieve the X assigned by Alice A and P A Given the value, Bob might need to perform a phase recovery algorithm, which can be executed via coordinate rotation:

[0014]

[0015]

[0016] A pilot pulse (reference pulse) is known to be used for phase recovery in both classical and quantum communication. In classical coherent communication, this is typically achieved by using a scheme such as the Mth power scheme (M... thMethods such as the power scheme directly perform phase recovery from the signal. Therefore, in classical coherent communication, data recovery does not strictly require a pilot pulse. In continuously variable (CV) quantum key distribution, the use of a pilot pulse R may be necessary because the signal pulse(s) S(s) carrying the data may have low intensity, and such low-intensity signal pulses S may not be suitable for accurate phase noise or frequency drift estimation. In this case, data recovery can be exclusively based on the information from the pilot pulse R.

[0017] For example, using Figure 2 The scheme involves interleaving pilot pulses R between signal pulses S. The phase information of the quantum signal pulse S can be obtained by using trigonometric functions and / or linear interpolation to retrieve the phase information of the high-intensity pilot pulses R placed before and after the quantum signal pulse S. Figure 2 In the middle, the guiding pulse R i and quantum pulse S i The time delay between them is T d And two pilot pulses R i and R i+1 The time delay between them is T b Index i refers to the i-th signal or pilot pulse. However, as mentioned above, this conventional technique has several limitations, such as a limited frequency range and hardware implementation complexity. Summary of the Invention

[0018] In view of the foregoing, the object of the present invention is to provide an improved method and / or apparatus to address one or more of the aforementioned challenges, disadvantages, and / or problems. In other words, there is a need for a method and / or apparatus capable of accurately recovering one or more quantum signal pulses in the presence of large frequency drift (of the light source), while simultaneously reducing hardware complexity.

[0019] In one or more specific embodiments, the present invention addresses the above-mentioned objective by providing a method for feedforward carrier recovery. The method includes the steps of: receiving an optical signal from a light source, wherein the optical signal includes at least one pilot pulse and at least one signal pulse containing information; determining orthogonality values ​​of a plurality of samples of the at least one pilot pulse using a local oscillator signal from a local oscillator source; determining a phase difference between the received optical signal from the light source and the local oscillator signal from the local oscillator source using the orthogonality values ​​of the plurality of samples; and recovering carrier information of the at least one signal pulse based on the determined phase difference.

[0020] In this context, the term "pilot pulse" refers to a reference pulse, the term "quadrature value" can refer to in-phase and / or out-of-phase quadrature values, and the term "sample" refers to, for example, a point on the amplitude / intensity / power versus time diagram of the pilot pulse. The term "signal pulse" can refer to a signal pulse that includes carrier information (e.g., encoded communication information or data), where this information can be multiple in nature. Here, "recovering carrier information" means recovering the signal pulse after compensating for the phase difference. The pilot pulse can be periodic or aperiodic with non-uniform time delays.

[0021] According to the method of the invention, an optical signal comprising at least one pilot pulse and at least one signal pulse is received from a light source, and orthogonality values ​​of multiple samples of the at least one pilot pulse are determined using the local oscillator signal of the local oscillator source to determine the phase difference between the received optical signal from the light source and the local oscillator signal of the local oscillator source. Because of the use of orthogonality values ​​of multiple samples of the at least one pilot pulse, carrier information recovery can be improved, for example, by precise determination, particularly over a wide range of frequency drifts between the light source and the local oscillator source, compared to conventional techniques using only one sample (typically the optimal sample) of the pilot pulse. Therefore, it is advantageous that the method of the invention allows for compensation of large frequency drifts in real-time operation and provides a robust yet simplified and / or efficient method for feedforward carrier recovery. Furthermore, since a wide range of frequency drifts can be compensated, expensive and / or complex laser hardware can be avoided, thus enabling cost-effective applications.

[0022] In specific embodiments of the invention, the orthogonality values ​​of at least two adjacent samples, particularly two directly adjacent samples, of at least one pilot pulse can be used to determine the phase difference. In specific embodiments, two adjacent samples of at least one pilot pulse can be used. In this context, the term "two adjacent samples" can refer to "two consecutive samples" having a predetermined sampling frequency, for example, where the predetermined sampling frequency can be a minimum frequency determined by the sampling technique / hardware (e.g., 1 Gsps per second), or a fixed frequency set by the user, for example. By using two adjacent samples, the determination of the orthogonality values ​​and the phase difference can be robust and simplified, which in turn enables accurate recovery of carrier information, particularly over a wide range of frequency drifts, through a simplified process.

[0023] In specific embodiments of the present invention, at least one of the samples of pilot pulses can be selected based on any one of the predetermined time delay between the pilot pulse and the signal pulse, the power, amplitude, intensity, and peak value of the pilot pulse. Selecting at least one of the samples of pilot pulses is not complex and does not require specific hardware, thereby helping to simplify the carrier recovery process.

[0024] In specific embodiments of the invention, the step of recovering carrier information may include calculating a compensation factor to determine the orthogonality value of at least one signal pulse. The calculation of the compensation factor allows for the recovery of carrier information and also allows for the precise determination of the orthogonality value of at least one signal pulse, particularly using simplified hardware procedures. The determination of the compensation factor facilitates real-time feedforward recovery. Therefore, in one specific example, a compensation factor may be calculated to recover quantum signal pulse(s) placed specifically after at least one pilot pulse. However, the invention is not limited thereto. In alternative embodiments, a compensation factor may be calculated to recover quantum signal pulse(s) placed before at least one pilot pulse.

[0025] In specific embodiments of the invention, the compensation factor can be calculated based on any one and / or any combination of the phase difference between two adjacent samples of the pilot pulse, the time delay, the time delay between at least one signal pulse and one of the samples of the pilot pulse. Because parameters such as the phase difference or orthogonality value of the pilot samples, or the time delay between two adjacent samples of the pilot pulse and / or the time delay between at least one signal pulse and one of the samples of the pilot pulse are used, the calculation of the compensation factor takes into account real-time values, thus simplifying the calculation process, as these parameters can be easily extracted from the pilot and signal pulses.

[0026] In specific embodiments of the invention, the compensation factor may be, for example, a coordinate rotation matrix comprising one or more trigonometric coefficients. The coordinate rotation matrix allows for simplified recovery of carrier information (particularly in terms of hardware / software implementation) and the determination of the orthogonality value of at least one signal pulse.

[0027] In specific embodiments of the present invention, block modules can be used to calculate the compensation factor. A block module can be a signal processing module, including components that facilitate simple mathematical operations such as multiplication, addition, or subtraction. Therefore, block modules facilitate real-time implementation using signal processing units and allow the avoidance of computer-required trigonometric functions / calculations or LUTs.

[0028] In specific embodiments of the invention, the optical signal may include a series of signal pulses. By corresponding the series of signal pulses to at least one pilot pulse, the number of pilot or reference pulses can be reduced, which in turn reduces overhead and increases the security key rate, since the pilot pulse may not have coded data information available for key extraction. Here, the term "corresponds to" may mean that, when determining the phase difference, for a given series of signal pulses, at least one pilot pulse is used as a reference pulse. Here, at least one signal pulse in the series of signal pulses may include carrier information.

[0029] In a specific embodiment of the invention, one or more samples of the pilot pulse may be sampled at a sampling frequency at least twice the inverse of the pilot pulse width. In a specific embodiment, each pilot pulse may be sampled at least twice. This applies regardless of the pulse shape or the pulse spacing of the pulse series. This sampling frequency ensures optimal sampling of the pilot pulse, providing at least two samples that may be necessary for accurately estimating the phase difference using multiple samples.

[0030] In a specific embodiment of the invention, at least one pilot pulse may be an optical pulse with an intensity higher than that of at least one signal pulse. Therefore, any phase fluctuations can be compensated for by referencing a high-intensity pilot pulse, thereby preventing the loss of encoded information in one or more signal pulses. Furthermore, by using a pilot pulse with higher intensity, noise caused by the pilot pulse can be minimized, thus contributing to the accurate recovery of the carrier information of the signal pulse.

[0031] In specific embodiments of the invention, at least one pilot pulse may be interleaved with at least one signal pulse. That is, at least one pilot pulse may be interleaved with one or more signal pulses. This may be particularly advantageous in terms of reducing hardware requirements. In one specific example, time-division multiplexing can be used for interleaving. In another specific example, interleaving can be achieved by transmitting multiplexed data consisting of, for example, signal pulses and pilot pulses from a signal source.

[0032] In a specific embodiment of the invention, at least one signal pulse can be transmitted according to a quantum cryptography protocol, particularly a continuous variable quantum key distribution (CV-QKD) protocol. In CV-QKD, low-intensity signal pulses are typically detected. Therefore, advantageously, this embodiment allows for coherent detection of low-intensity signal pulses without the drawback of requiring a stable laser source for detection.

[0033] In a specific embodiment, the present invention addresses the aforementioned objective by providing an apparatus configured for feedforward carrier recovery. The apparatus includes a receiving unit configured to receive an optical signal from a light source, wherein the optical signal includes at least one pilot pulse and at least one signal pulse containing information. The apparatus also includes a control unit configured to determine orthogonality values ​​of a plurality of samples of the at least one pilot pulse using a local oscillator signal from a local oscillator source. The control unit is further configured to: determine a phase difference between the received optical signal from the light source and the local oscillator signal from the local oscillator source using the plurality of sample orthogonality values, and recover carrier information of the at least one signal pulse based on the determined phase difference.

[0034] In the apparatus of the present invention, the control unit uses the local oscillator signal of the local oscillator source to determine the orthogonality values ​​of multiple samples of at least one pilot pulse. Because of the use of the orthogonality values ​​of multiple samples of at least one pilot pulse, carrier information recovery can be improved through this precise determination, particularly over a wide range of frequency drifts between the light source and the local oscillator source, compared to conventional techniques using only one sample of the pilot pulse. Therefore, it is advantageous that the apparatus of the present invention allows for compensation of large frequency drifts in real-time operation and provides a robust yet simplified and / or efficient device for feedforward carrier recovery. Furthermore, because a wide range of frequency drifts can be compensated, expensive and / or complex laser hardware can be avoided, resulting in a cost-effective device.

[0035] In a specific embodiment of the invention, the control unit can be configured to determine the phase difference using the orthogonality values ​​of two adjacent samples of at least one pilot pulse. In this embodiment, two adjacent samples of at least one pilot pulse can be used. By using two adjacent samples, the determination of the orthogonality values ​​and the phase difference can be simplified, and their accuracy can be improved, particularly over a wide range of frequency drifts between the light source and the local oscillator source. This, in turn, allows for accurate recovery of carrier information using a simplified apparatus.

[0036] In a specific embodiment of the invention, the control unit can be configured to calculate a compensation factor to determine the orthogonality value of at least one signal pulse. The calculation of the compensation factor can allow for the recovery of carrier information and can also allow for the precise determination of the orthogonality value of at least one signal pulse, particularly using simplified hardware. In one specific example, the compensation factor can be calculated to recover one or more quantum signal pulses, specifically placed after at least one pilot pulse.

[0037] In a specific embodiment of the invention, the control unit may include a clock recovery circuit configured to receive signal pulses received and / or detected by the receiving unit, and / or at least one pilot pulse (R) for recovering carrier information. The clock recovery circuit may be part of digital signal processing that facilitates carrier recovery. The clock recovery circuit of the control unit may be configured to determine orthogonal values ​​of a plurality of samples of the at least one pilot pulse.

[0038] In a specific embodiment of the invention, the clock recovery circuit can be configured to select at least one of a sample of pilot pulses based on any one of a predetermined time delay between the pilot pulse and the signal pulse, the power, amplitude, and intensity of the pilot pulse, and the peak values ​​of the power, amplitude, and intensity of the pilot pulse. Using a clock recovery circuit to select at least one of the sample of pilot pulses is uncomplicated and does not require specific hardware, thus simplifying carrier recovery. In one specific example, the clock recovery circuit can be configured to use a frequency of 1 / T.s The input processing clock is used to identify the best sample in terms of optical power on the pilot pulse, its neighboring samples, and / or signal pulses / symbols.

[0039] In a specific embodiment of the invention, the control unit can be configured to calculate a compensation factor based on any one and / or any combination thereof, the phase difference or time delay between two adjacent samples of the pilot pulse, and the time delay between at least one sample of the signal pulse and the pilot pulse. The calculation of the compensation factor can be simplified because parameters such as the phase difference or orthogonality value of the pilot sample, or the time delay between two adjacent samples of the pilot pulse and / or the time delay between at least one sample of the signal pulse and the pilot pulse are used, as the control unit can easily extract these parameters from the pilot and signal pulses.

[0040] In specific embodiments of the invention, the compensation factor may be, for example, a coordinate rotation matrix comprising one or more trigonometric coefficients. The coordinate rotation matrix allows for simplified recovery of carrier information (particularly in terms of hardware / software implementation) and the determination of the orthogonality value of at least one signal pulse.

[0041] In a specific embodiment of the invention, the control unit may include a block module configured to calculate a compensation factor. The block module may be a signal processing module that includes simple mathematical operations such as multiplication, addition, or subtraction. Therefore, the block module facilitates real-time implementation using digital signal processing and allows the avoidance of computer-intensive trigonometric functions or LUTs.

[0042] In specific embodiments of the invention, the block module may include at least one adder and at least one multiplier for calculating the compensation factor. By configuring the block module using one or more adders and / or one or more multipliers, the calculation of the compensation factor, which may involve trigonometric coefficients, can be simplified using simple addition and / or multiplication, where adders and multipliers can also be used accordingly for subtraction and division. Thus, simple yet robust feedforward carrier recovery can be achieved through a simplified architecture.

[0043] In specific embodiments of the present invention, a block module may include at least one multiplexer configured to select one or more inputs of the block module, and at least one register buffer configured to process one or more inputs of the block module. The one or more multiplexers and the one or more register buffers facilitate the processing of one or more inputs of the block module, thereby enabling precise determination of the compensation factor with simplified hardware.

[0044] In specific embodiments of the invention, the control unit can be implemented in digital signal processing (DSP) hardware, particularly a field-programmable gate array (FPGA). Therefore, the device of the invention can be applied using an offline processor or a real-time DSP such as an FPGA, providing a cost-effective system with a low-cost laser for both classical communication and quantum cryptography applications. Attached Figure Description

[0045] Figure 1 A traditional experimental setup for CV-QKD with real LO is illustrated.

[0046] Figure 2 The conventional use of the guide pulse (reference pulse) for phase recovery is illustrated.

[0047] Figure 3 A schematic flowchart illustrating a feedforward carrier recovery method according to a specific embodiment of the present invention is shown.

[0048] Figure 4 An example is illustrated by sampling at least one pilot pulse according to a specific embodiment of the present invention to determine the orthogonality value of at least two adjacent / continuous samples.

[0049] Figure 5 The phase of two consecutive / adjacent samples of the i-th pilot pulse in the complex plane is illustrated according to a specific embodiment of the present invention.

[0050] Figure 6 A block module according to a specific embodiment of the present invention is illustrated.

[0051] Figure 7 An apparatus for feedforward carrier recovery according to a specific embodiment is illustrated.

[0052] Figure 8 A portion of an apparatus according to a specific embodiment of the present invention is illustrated, particularly a control unit.

[0053] Figure 9 A portion of a control unit, particularly a block circuit (BC), is illustrated according to a specific embodiment of the present invention.

[0054] Figure 10 Simulation results supporting the method and evaluating the performance of the carrier recovery of the invention are illustrated. Detailed Implementation

[0055] The features and advantageous embodiments of the invention will be described in detail below with reference to the accompanying drawings.

[0056] Figure 3A schematic flowchart of a method 300 for feedforward carrier recovery according to a specific embodiment of the present invention is shown. The method includes step 302 of receiving an optical signal from a light source, wherein the optical signal includes at least one pilot pulse R and at least one signal pulse S containing information. The method further includes step 304, in which orthogonality values ​​of a plurality of samples R0, R1 of the at least one pilot pulse R are determined using a local oscillator source, particularly a local oscillator signal of the local oscillator source. The method further includes step 306, in which a phase difference between the light source (particularly the received optical signal) and the local oscillator source (particularly the local oscillator signal) is determined using the plurality of samples R0, R1. The method further includes step 308 of recovering carrier information of the at least one signal pulse S based on the determined phase difference.

[0057] Figure 3 Step 302 may include receiving an optical signal via an optical path. The optical path may be one or more fiber optic channels. The optical signal can be received from... Figure 1 The signal is received by a transmitter or transmitter light source (such as a continuous laser source). The optical signal includes at least one pilot pulse (i.e., a reference pulse) R and at least one signal pulse S. In embodiments, the signal pulse may be a pulse that includes carrier information (e.g., communication information) or data encoded therein. In an example, the signal pulse S may be phase- and / or amplitude-modulated. The pilot pulse is the reference pulse and may originate from the same source as the signal pulse or from a different source. The pilot pulse R may not include information encoded therein. In an example, the pilot pulse R may be phase- and / or amplitude-modulated.

[0058] In one embodiment, the intensity (e.g., amplitude) of at least one pilot pulse R may be higher than the intensity of at least one signal pulse S. In another embodiment, the ratio between the intensity of the pilot pulse R and the intensity of the signal pulse S may be in the range of 100 to 500. In a specific embodiment, this ratio may be at least 100. In a specific embodiment, according to a quantum cryptography protocol such as Continuously Variable Quantum Key Distribution (CV-QKD), the pilot pulse R may be a high-intensity pilot pulse, and the signal pulse S may be a low-intensity quantum pulse, wherein a predetermined intensity ratio exists between the two pulses.

[0059] Figure 4 (As will be described in detail later) As illustrated, in an embodiment, the optical signal may include a series or sequence of signal pulses S0 to S1 following at least one pilot pulse R. N-I Where N refers to the number of signal pulses in the series / sequence. That is, at least one pilot pulse R can be accompanied by one or more signal pulses S0 to S1. N-IInterleaving. In one specific embodiment, time-division multiplexing can be used for interleaving. In another specific embodiment, interleaving can be achieved by transmitting one or more quantum signal pulses S0 to S0 from a light source. N-I Interleaving is performed using multiplexed data consisting of at least one pilot pulse R.

[0060] Figure 3 Step 304 includes using a local oscillator source to determine the quadrature values ​​of at least one pilot pulse R. Specifically, the local oscillator source, particularly the local oscillator signal of the local oscillator source, is used to determine the quadrature values ​​of a plurality of samples R0, R1 of the at least one pilot pulse R. In an embodiment, the quadrature values ​​refer to in-phase quadrature values ​​and out-of-phase quadrature values. (See reference...) Figure 4 In embodiments of the invention, at least two samples R0 and R1 of at least one pilot pulse R are sampled for orthogonality determination. However, the sampling is not limited to two. Depending on environmental and / or hardware / software limitations, more than two, three, four, etc., samples may also be used. In a specific example, only two adjacent samples are used.

[0061] In a particular embodiment, two samples are adjacent or consecutive to each other at a predetermined sampling frequency / rate. The predetermined sampling frequency can be a minimum frequency determined by the sampling technique / hardware, or a frequency set by the user. In the embodiment, Figure 4 It shows two adjacent samples R 0,i and R 1,i The i-th boot pulse R (or R for the (i-1)-th boot pulse) 0,i-1 and R 1,i-1 In the embodiment, adjacent samples R 0,i and R 1,i Then there are N-1 signal pulses from S0 to S... N-1 The sampling frequencies of adjacent samples R0 and R1 are called 1 / T. s .

[0062] In a preferred embodiment, one or more of the samples R0 and R1 of the pilot pulse R are sampled at a sampling frequency of 1 / T. s The sampling frequency is at least twice the inverse of the pulse width (measured in time units) of the pilot pulse R, thus satisfying the Nyquist theorem. In a specific embodiment, each pilot pulse is sampled at least twice. This also applies to other pulse shapes and the inter-pulse spacing of pulse series. The sampling frequency can be based on a predetermined time delay T between the pilot pulse R and the signal pulse S. d The power, amplitude, intensity, and peak value of the pilot pulse R are used to select at least one of multiple samples R0, R1 of the pilot pulse R. Figure 4In this process, sample R1 is selected as the optimal sample based on the peak power / amplitude / intensity of the pilot pulse R. Sample R0 can be selected based on a predetermined sampling point and / or a predetermined time delay with respect to R1 (the optimal sample) of the pilot pulse R.

[0063] Here, the term "local oscillator source" can refer to a laser source that operates freely at the Bob (receiver) end, and the term "local oscillator" can refer to the output of the laser oscillator source, i.e., the local oscillator signal. The pilot pulse R and the signal pulse S can be interfered with the local oscillator signal to determine the orthogonality value.

[0064] In step 306, the orthogonality values ​​of multiple samples R0, R1 of at least one pilot pulse R are used to determine the phase difference between the received optical signal from the light source and the local oscillator signal from the local oscillator source. In an embodiment, this step of determining the phase difference can provide a function or component of the determined phase difference, which can be used to compensate for phase errors by recovering carrier information and determining the orthogonality values ​​of at least one signal pulse.

[0065] exist Figure 3 In step 308, carrier information of at least one signal pulse S is recovered based on the determined phase difference. This step allows the use of the phase difference / information extracted from at least one pilot pulse in step 306 to compensate for phase errors / mismatches. In a specific example, step 308 may allow feedforward carrier recovery based on sampled low-intensity signal pulse(s) from a high-intensity pilot pulse(s).

[0066] Reference Figure 4 and Figure 5 Specific, non-limiting embodiments of the invention are described. In this specific embodiment, the phase difference is determined using orthogonal values ​​of at least two adjacent / continuous samples R0 and R1 of at least one pilot pulse R.

[0067] exist Figure 4 In this context, the i-th mode corresponds to a pilot pulse R, which is composed of two consecutive samples R. 0,i and R 1,i The sequence consists of a pilot pulse R followed by N-1 signal pulses S. In terms of power, each signal pulse (marked with k) has an optimal sample S. k For example, in terms of power, the optimal sample R l Having relative to the first S0 and the last S0 in the signal pulse respectively N-1 The time delay T of the sample d and NT d In this embodiment, with an equal time delay T d The signal pulses are received periodically. However, the present invention is not limited to periodicity and / or equal time delay T. dThe in-phase quadrature X of the i-th pilot pulse R, measured by Bob (the receiver). R and heterogeneous orthogonal P R It can be given by the following formula:

[0068]

[0069]

[0070] Where A is a coefficient related to the amplitude of the pilot pulse, which is assumed to be 1 for simplicity. However, the present invention is not limited to A = 1. It's phase noise. It is the phase of the transmitted signal from the light source (Alice (transmitter)) on the guiding pulse R. Phase This includes Alice's encoded phase and the phase related to Alice's laser frequency. It is the phase of the light source signal from the local oscillator associated with the LO frequency. Therefore, the pilot pulse R can have The phase difference. For a pilot pulse without Alice's (i.e., the transmitter's) coded information (i.e., unmodulated), the phase... It may have a component related to the Alice laser frequency. However, the invention is not limited thereto.

[0071] According to another embodiment of the present invention, it can be based on a time delay T d The power, amplitude, intensity, and peak value of the pilot pulse R are used to select at least one of the samples R0 and R1 of the pilot pulse R. In a specific example, a frequency of 1 / T is used. s The input processing clock identifies one or more optimal samples in terms of optical power on the pilot pulse R. Similarly, the optimal / best sample of the signal pulse S can also be based on the time delay T between the pilot pulse R and the signal pulse S. d The optimal sample (R) is selected based on the power, amplitude, intensity, and peak value of the signal pulse. In another specific example, the optimal sample (R) is selected based on the power, amplitude, intensity, and peak value of the signal pulse. 1,i The optical power, its neighboring sample R, can be determined by a clock recovery circuit (described later). 0,i (Pre-defined sampling points, and / or with R) 1,i (the predetermined time delay) and signal pulse S k,i The frequency of use is 1 / T s The input processing clock is used to identify / select.

[0072] Furthermore, one or more samples of the pilot pulse R can be sampled at a frequency that is at least twice the inverse of the pulse width of the pilot pulse R. This sampling frequency ensures that the Nyquist theorem is satisfied, thus achieving optimal sampling.

[0073] exist Figure 4 In this embodiment, the optical signal includes a series of signal pulses S between two reference pulses R. k,i (where k is from 1 to N-1). Therefore, for a series of signal pulses corresponding to at least one pilot pulse R, the number of pilot or reference pulses can be reduced, which in turn reduces overhead and increases the security key rate, since the pilot pulse may not have coded data information available for extracting the key.

[0074] Figure 5 This illustrates two consecutive / adjacent samples R of the i-th pilot pulse according to an embodiment of the invention. 0,i and R 1,i The phases in the complex plane each have a phase. and Therefore, the phase of the k-th (k: 0->N-1) signal pulse in the i-th mode can be given by the following formula:

[0075]

[0076] quantity It can be expressed as Δf and f n The associated phase error. In this embodiment, the frequency difference Δf between the local oscillator source and the transmitter (Alice) laser can be higher than the laser's frequency noise f. n And / or the frequency difference Δf can be within the time ((N+1).T) between two consecutive pilot pulses. d The phase of each individual sample in the pattern is constant. Therefore, the phase of each individual sample in the pattern can correspond to the phase associated with the previous sample. The accumulation, for example assuming the reference phase This serves as a starting point. However, the invention is not limited to this relationship, as long as the frequency difference ensures accurate estimation of the phase of the signal pulses following each pilot pulse.

[0077] In this embodiment, the guiding pulse can have a constant envelope and / or a constant radius in the complex plane. Figure 5 The following triangular relationship is obtained (see reference). Figure 6 ):

[0078]

[0079]

[0080]

[0081]

[0082] Using triangulation properties:

[0083]

[0084]

[0085] Equation (7) can be obtained from equation (5).

[0086]

[0087]

[0088] Using equation (7) above, step 306, which uses the orthogonal values ​​of multiple samples R0 and R1 to determine the phase difference between the received optical signal from the light source and the local oscillator signal from the local oscillator source, is thus completed. Figure 3 The phase difference can be determined based on a function or component of the phase difference (here, the sin and cos functions / components). It is evident from equation (7) that the function or component of the phase difference can be determined through simple mathematical operations on the orthogonal values ​​of multiple samples of the pilot pulse R. Furthermore, the function or component of the phase difference (one or more) can be used to compensate for the phase error by recovering the carrier information and determining the orthogonal value of at least one signal pulse S.

[0089] Specifically, the orthogonality of the pilot pulses is used to determine the phase difference between measurements at the receiver from the transmitter laser source and the local oscillator source. This phase difference can then be used to compensate for or align the measurement of the orthogonality of the local oscillator source of the reference transmitter laser source with respect to the signal pulses, thereby allowing the recovery of information about the signal pulses.

[0090] In this regard, according to embodiments of the invention, step 308 of recovering carrier information may include calculating a compensation factor W to determine the orthogonality value of at least one signal pulse S. In a particular embodiment, the compensation factor W may be calculated for, for example, one or more quantum signal pulses S placed after a pilot pulse R.

[0091] The steps for recovering carrier information according to an embodiment of the invention are described below. In this embodiment, an orthogonal value S can be used. i To recover the k-th signal pulse, especially the signal pulse containing information, the orthogonality value S is... i Based on equations (1) and (4), in-phase orthogonal elements in the i-th mode are included. Orthogonal to heterogeneous phase Therefore, the quadrature value S of the recovered signal pulse is... i The orthogonality value S between the received signal pulse and the received signal pulse. i The relationship between them can be given as follows:

[0092] S i ′=W i ·S i (8)

[0093] in

[0094]

[0095]

[0096] Rotation matrix W i The compensation factor W is called the factor used to recover the transmitted information (i.e., the information encoded in the signal pulse S). From the above relation (9) and referring to... Figure 4 As can be seen, according to the embodiments of the invention, the compensation factor W can be based on the time delay T between two adjacent samples R0 and R1 of the guiding pulse R. s And / or the time delay T between one of the samples R0, R1 of at least one signal pulse S and the pilot pulse R, particularly the optimal sample R1. d In other words, the compensation factor W can be based on factors other than the orthogonality value of the guide sample. The compensation factor W can be called the coordinate rotation matrix or its coefficients.

[0097] In the embodiment, to simplify matrix W, assume And (k+1).M = β.

[0098] To obtain matrix W in equation (9) i The trigonometric values ​​of the elements, Figure 6 This refers to a block module (BM) 600 according to an embodiment of the invention. According to the invention, the block module 600 can be implemented as part of a digital signal processing unit. The block module 600 includes one or more inputs In1 to In4 and one or more outputs Out1, Out2, wherein each input may relate to trigonometric coefficients, particularly compensation factors and / or coefficients of the orthogonality values ​​of signal pulses.

[0099] In this embodiment, block module 600 may further include at least one adder 600A1, 600A2 and at least one multiplier 600M1, 600M2, 600M3, 600M4. Block module 600 is not limited to these components and / or functions. For example, the block module may be configured to use adders and / or multipliers to perform subtraction and / or division, respectively. Furthermore, the number of block modules 600 is not limited to one. In specific embodiments, multiple block modules may be provided.

[0100] In this embodiment, input In1 is associated with sin(a), input In2 with sin(b), input In3 with cos(b), and input In4 with cos(a), such that block module 600 can use at least one adder 600A1, 600A2 and at least one multiplier 600M1, 600M2, 600M3, 600M4 to produce outputs Out1 = sin(a+b) and Out2 = cos(a+b). Therefore, by considering:

[0101]

[0102]

[0103] Furthermore, using the functionality of block module 600, particularly simple multiplication and addition, and also from the definitions in equations (5) and (7), W can be obtained as the compensation factor W. i The matrix elements. Therefore, by using block module 600, it is possible to avoid using any lookup table (LUT) or any specific trigonometric calculator when determining the compensation factor.

[0104] Therefore, using equations (5) and (7), and from... Figure 6 The output of block module 600 can be used to obtain the elements of the rotation matrix W of equation (9), thereby solving equation (8) with in-phase and orthogonal S as input. Based on the input and the matrix coefficients from block module 600, the orthogonality value of the signal pulse S and the matrix elements of S' can be recovered corresponding to a given phase fluctuation.

[0105] Hereinafter, an apparatus 700 for feedforward carrier recovery according to the present invention is described with reference to method 300 of the present invention. The apparatus 700 is configured to perform as described above. Figures 3 to 6 The steps of the method 300 for feedforward carrier recovery according to the present invention are described below. Features of method 300 that have already been discussed will not be repeated, but are incorporated herein by reference. Figure 7 An apparatus 700 for feedforward carrier recovery according to a specific embodiment of the present invention is illustrated.

[0106] The device 700 includes a receiving unit 701 configured to receive an optical signal from a light source, wherein the optical signal includes at least one pilot pulse R and at least one signal pulse S. The receiving unit 701 includes a local oscillator source LO. In a specific embodiment, the receiving unit 700 may be a receiver also known as a Bob. For example, the receiving unit 700 may include... Figure 1 The receiver 201 contains some or all of its components. The device may also include a transmitting unit (not shown) having... Figure 1 Some or all of the components of transmitter 101.

[0107] In a specific embodiment, the receiving unit 701 may be configured to receive and detect optical signals transmitted from the light source. The receiving unit 701 may include one or more optoelectronic components. The one or more optoelectronic components of the receiving unit 701 may include, but are not limited to, any combination of interferometers such as 90° optical hybrids, balanced / unbalanced Michelson interferometers or balanced / unbalanced Mach-Zehnder interferometers, one or more beam splitters, polarization controllers such as polarization-maintaining fiber (PMF), polarization controllers for aligning the polarization of signal pulses and local oscillators to maximize or optimize interference, one or more modulators / demodulators, etc.

[0108] The receiving unit 701 may also include, but is not limited to, one or more optoelectronic components, such as one or more single-photon detectors, heterodyne detectors, or homodyne detectors. The receiving unit 701 can use homodyne or heterodyne detection. In homodyne detection, the receiving unit can randomly select X or P orthogonal measurements by adding a 90° phase shift to the local oscillator, while in heterodyne detection, the receiving unit can simultaneously measure two orthogonal components by using, for example, a 90° optical mixing to split the signal into two parts.

[0109] The light source can be a reference. Figure 1 The transmitter 101 is defined as part of the device 700. The light source may be part of the device 700, or separate from and external to the device 700 or transmitter 101. The device 700 or transmitter 101 may include amplitude modulators and / or phase modulators to obtain optical pulses with orthogonal values ​​following a Gaussian random distribution. The transmitter may also include an attenuator to set the signal variance (i.e., the Alice modulator variance) to a value that maximizes or optimizes the encryption key rate. The modulation variance can typically be equal to twice the average photon number. The receiving unit 701 is configured to receive the optical signal from the light source.

[0110] In embodiments of the invention, any conventionally known transmitter, other than or equivalent to transmitter 101, can be used in conjunction with device 700, particularly with… Figure 7 The illustrated receiving unit 701 is used in combination for communication in a fiber optic network (e.g., a CV-QKD network). The invention is not limited thereto. A fiber optic network can have any number of transmitting and receiving devices. The device of the invention can also be part of a transceiver. Furthermore, all or some of the receiving devices in the network can be configured according to the invention.

[0111] The device 700 also includes a control unit 703 configured to use a local oscillator source LO (e.g., similar to...). Figure 1The continuous-wave laser of element 203 is used to determine the orthogonality values ​​of multiple samples R0, R1 of at least one pilot pulse R. In this regard, a sampling unit (not shown) can be used to sample at least one pilot pulse R. Alternatively, control unit 703 can be configured to sample at least one pilot pulse R. For example, control unit 703 may include an analog-to-digital converter at a predetermined sampling frequency 1 / T. s At least one pilot pulse R is sampled, and the sampling frequency can be at least twice the inverse of the pulse width of the pilot pulse R, thereby satisfying the Nyquist theorem. Control unit 703 can be configured to operate based on the time delay T of the pilot pulse (R). d The power, amplitude, intensity, and peak value of the pilot pulse R are selected from at least one of the samples.

[0112] The control unit 703 is also configured to determine the phase difference between the received optical signal from the light source and the local oscillator signal of the local oscillator source LO using orthogonal values ​​of multiple samples R0, R1, and to recover carrier information of at least one signal pulse S based on the determined phase difference. For example, refer to Figure 4 and Figure 5 The control unit 703 is configured to determine the phase difference using the orthogonality values ​​of two adjacent samples R0, R1 of at least one pilot pulse R. The control unit 703 is also configured to calculate a compensation factor W to determine the orthogonality value of at least one signal pulse S. In a specific embodiment, the control unit 703 includes a block module 600 for calculating the compensation factor W, which specifically has one or more trigonometric coefficients of a rotation matrix, as referenced above. Figure 6 As stated above.

[0113] In one embodiment, the receiving unit 701 may be controlled by software, the control unit 703, or a combination thereof. In another specific embodiment, the local oscillator source LO may be part of the receiving unit 701 or the control unit 703. In another specific embodiment, the local oscillator source LO may be separate from the receiving unit 701 and the control unit 703. The control unit 703 may be a hardware and / or software element. In one specific embodiment, the control unit 703 may be controlled by software. In another specific embodiment, the control unit 703 may be configured to control and / or drive components of the receiving unit 701 and the local oscillator source LO.

[0114] Reference Figure 8 and Figure 9 Specific non-limiting embodiments of the present invention are described below. Figure 8An example is shown of a control unit 703 in device 700. In this specific embodiment, control unit 703 includes a clock recovery circuit 803 configured to receive signal pulses received and / or detected by receiving unit 701, and / or at least one pilot pulse R for recovering carrier information. Control unit 703 also includes a carrier recovery circuit 805 for recovering carrier information. Specifically, in this specific embodiment, clock recovery circuit 803 acts as an input circuit to carrier recovery circuit 805 to help compensate for phase differences. However, separate clock recovery circuits and separate carrier recovery circuits are not necessary, as long as the control unit is configured to perform its functions.

[0115] In this specific embodiment, the apparatus 700 and the method 300 of the invention can use the clock recovery circuit 803 and the carrier recovery circuit 805 to perform carrier recovery in order to compensate for the difference between the received data clock or processing speed and the sampling frequency.

[0116] The clock recovery circuit 803 of the control unit 703 can be configured to be based on the time delay T between the boot pulse and the signal pulse. d At least one of multiple samples R0, R1 of the guide pulse R is selected or identified based on any one of the power, amplitude, intensity, and peak value of the guide pulse R. In this specific embodiment, sample R1 is selected as the optimal sample based on the peak power / amplitude / intensity of the guide pulse R, particularly based on the optical power on the guide pulse R. Sample R0 can be selected based on a predetermined sampling frequency and / or based on a predetermined time delay with respect to R1 of the guide pulse R.

[0117] In this embodiment, a carrier recovery circuit 805, using input from a clock recovery circuit 803 and at least one pilot pulse R and its sample, is configured to determine a phase difference and use the phase difference to recover carrier information. A compensation factor W can be calculated using a block module 600.

[0118] In this specific embodiment, the carrier recovery circuit 805 includes one or more block modules, particularly three block modules 807, 809, and 811. Figure 8 Using block module functionality, in Figure 8 The diagram shows a description of the solution formula (8) for carrier recovery according to the present invention, wherein the signal of Bob (i.e., the receiving unit) is... and Preferably, it is provided digitally as an input to the clock recovery circuit 803.

[0119] As described above, the clock recovery circuit 803 can be configured to respond to the boot pulse, i.e., R 1,i The optical power of its neighboring sample R 0,i and quantum signal pulse S k,iThe frequency of use is 1 / T s The input processing clock 4 selects / identifies the best sample. A clock recovery circuit 803, using, for example, a register composed of D flip-flops with control input options, is configured to output and latch the signal. P S，i 9 and X S，i 10, until the next updated pilot pulse (i.e., the (i+1)th) or quantum signal pulse (i.e., the (k+1)th). Using signals 5 to 8 as inputs, block module 807 outputs 12 (referred to as Out1 and Out2) by applying the following diagram (7):

[0120]

[0121]

[0122] The logical NOT operator 13 can be used in, for example 8 is used before to correct any sign mismatch between the functionalized block module 807 and equation (7). However, the position of the logical NOT operator is not limited to this.

[0123] like Figure 8 As shown, output 12 of block module 807 can serve as an input to block circuit BC. Therefore, block circuit BC can be configured to receive two inputs from block module 807, i.e. and

[0124] Figure 8 The block circuit BC in Figure 9 Detailed examples are provided. Block circuit BC is also block module 18, but may additionally include one or more multiplexers 14, 15 configured to select one or more inputs to the block module, and one or more register buffers 21, 25 configured to process one or more inputs to the block module.

[0125] Using optional control signals 16 and 17, multiplexers 14 and 15 can transmit the input of block circuit BC (i.e., the output of block module 807) to block module 18 to obtain... and These are outputs 19 and 20, respectively. Using optional control signal 22, register buffer 21 can latch its input data in response to input processing clock 4. Control signals 16 and 17 can be controlled or changed so that multiplexers 14 and 15 can feed back the obtained outputs to block module 18 for interaction with... and Combine to obtain and Control signals 16 and 17 can preferably be kept in the ON state until the next detected pilot pulse (i.e., the (i+1)th). Block module 18 can obtain signals corresponding to R respectively. 0,i The j-th sample afterwards and In an embodiment, after N quantum signal pulses, controllers 16, 17, and 22 can be reset for the next mode, which has the same functionality as before. For example, if R 0,i If the (j+1)th sample is a quantum pulse, then the second register buffer 25 of block circuit BC and its optional controller 26 can be latched. and Used for Output1 27 and Output2 28, resulting in:

[0126]

[0127]

[0128] Using equations (5) and (6), and by using the signal from the output of the block circuit BC, the rotation matrix W in equation (9) is obtained. i The elements can be implemented by block module 809, with the following outputs as Out′130 and Out′231:

[0129]

[0130]

[0131] Where equation (13) is in phase and orthogonal to S k，i The combination of these elements, as input to block module 811, can solve equation (8), where regarding... 33 and The equivalent value of 34 is:

[0132]

[0133]

[0134] Therefore, in equation (14), the signal pulse can be considered to be rotated based on the estimate in equation (13), and the matrix element S corresponding to the phase fluctuation can be recovered. i In one embodiment, the entire carrier recovery process can be restarted by receiving the next pilot pulse.

[0135] Figure 10 Simulation results supporting this method and evaluating the performance of the carrier recovery method of the present invention are illustrated. Figure 10In (a) and (c), a group of quantum pulses including in-phase X and orthogonal P is simulated, where (Δf+f n = 60MHz(a) and 1060MHz(c), where M = 16, N = 1, T s =1ns, and 2T s The total guidance and quantum pulse width. It can be seen that for (Δf+f) n )>1 / T s , group in T s It can rotate more than 2π during the sampling period. Figure 10 (b) and (d) respectively show the corresponding Figure 10 The recovered quantum pulses of the signals in (a) and (c) are shown. Simulation results indicate that, using the method of the present invention, data can be recovered correctly and accurately even under conditions of very large frequency drift. In this embodiment, there are no theoretical limitations on the selection of M and N. However, since the laser frequency can change even within short time periods in practical applications, it is preferable to limit M and N to the ranges of 2 to 256 and 1 to 256, respectively, to achieve optimal and better performance in carrier data recovery. In the most preferred embodiment, M = 16 and N = 1.

[0136] Such as about Figure 9 As described, in this invention, together with feedforward phase compensation, the feedback signal obtained from the estimate, for example, equation (13), can also be used to minimize the frequency difference of the laser by actively tuning the wavelength of the local oscillator (LO) source. Preferably, simple but robust feedforward carrier recovery can be achieved using a total of 16 multipliers and 8 adders.

[0137] refer to Figures 6 to 9 The described configuration can also be applied by an offline processor or a real-time digital signal processing unit (such as a field-programmable gate array (FPGA)), featuring a low-cost laser for cost-effective systems in both classical communication and quantum cryptography applications. Specifically, according to embodiments of the invention, the control unit 703 can be implemented in digital signal processing hardware / software. In one specific example, the digital signal processing hardware can be a field-programmable gate array (FPGA). Therefore, the present invention can be combined with digital signal processing (DSP) to recover transmitted information.

[0138] This invention provides an improved method and / or apparatus capable of accurately recovering quantum signal pulses in the presence of large frequency drifts (of the light source), while also reducing hardware complexity. In particular, the disclosed method and / or apparatus can allow compensation for large frequency drifts associated with signal instabilities of the light source (e.g., a laser), and also provides the possibility of a simplified hardware / software implementation with real-time operation due to the efficient and improved carrier recovery process. In other words, by using multiple samples of the pilot pulse, compared to conventional techniques using only one sample of the pilot pulse, this invention allows for accurate carrier recovery across a wide range of frequency drifts between the light sources of the transmitter and receiver. The method and / or apparatus of the invention are particularly suitable for quantum cryptography, such as CV-QKD based on coherent detection of low-intensity quantum pulses.

[0139] The present invention also discloses carrier recovery using hardware that relies on simple mathematical operations (including multiplication and addition (or subtraction)), which can therefore facilitate real-time implementation using digital signal processing units and allow avoidance of computer-intensive trigonometric functions or LUTs.

[0140] Furthermore, the method and / or apparatus of the invention can allow phase and / or frequency recovery in coherent optical communication and can be configured with an offline processor and / or a real-time DSP (such as an FPGA), and have a low-cost laser for cost-effective systems in both classical communication and quantum cryptography applications.

[0141] One or more of the above embodiments / steps / examples of the present invention can be fully or partially automated using one or more components such as processing / computing devices and software / programs. One or more steps / embodiments / examples of the present invention can be implemented by using these components.

[0142] It should be understood that the above description has described and illustrated specific embodiments and examples. However, this description is intended to cover any and all variations of the various embodiments and examples of the invention. After reviewing the above description, combinations of the above embodiments / examples / arrangements not specifically described herein will be apparent to those skilled in the art. Therefore, this disclosure is not intended to be limited to the specific embodiments / examples / arrangements disclosed, but rather the invention will include all embodiments and arrangements falling within the scope of the appended claims.

Claims

1. A method for feedforward carrier recovery, comprising the following steps: Receives an optical signal from a light source, the optical signal including at least one pilot pulse (R). i ) and at least one signal pulse (S) containing information k ); The at least one pilot pulse (R) is determined using the local oscillator signal from the local oscillator source. i Multiple samples (R) 0,i R 1,i orthogonal values; Using the multiple samples (R) 0, i, R 1,i The orthogonality value of the received optical signal from the light source and the local oscillator signal from the local oscillator source are used to determine the phase difference between them. as well as The at least one signal pulse (S) is recovered based on the determined phase difference. k ) carrier information.

2. The method according to claim 1, wherein, The at least one pilot pulse (R) i At least two adjacent samples (R) 0,i R 1,i The orthogonal values ​​of ) are used to determine the phase difference.

3. The method according to claim 1 or 2, wherein, At least one of the samples of the guiding pulse is based on the guiding pulse (R) i ) and the at least one signal pulse (S) k The scheduled time delay (T) between ) d The power, amplitude, intensity, and peak value of the guide pulse can be selected from any one of the power, amplitude, and intensity of the guide pulse.

4. The method according to claim 1 or 2, wherein, The step of recovering the carrier information includes calculating a compensation factor (W) to determine the at least one signal pulse (S). k The steps to find the orthogonal values ​​of ).

5. The method according to claim 4, wherein, The compensation factor is based on the phase difference and the guiding pulse (R). i The time delay (T) between two adjacent samples s ), and the at least one signal pulse (S) k ) and the guiding pulse (R) i The time delay (T) between one of the samples d It is calculated using any one of, or any combination thereof.

6. The method according to claim 4, wherein, The compensation factor (W) includes one or more trigonometric coefficients.

7. The method according to claim 4, wherein, The compensation factor (W) is calculated using block modules.

8. The method according to claim 1 or 2, wherein, The optical signal includes a series of signal pulses (S) k ).

9. The method according to claim 1 or 2, wherein, The guiding pulse (R) i One or more of the samples (R0, R1) are guided by the pilot pulse (R). i The sampling frequency (1 / T) is at least twice the reciprocal of the pulse width. s Sampling was performed.

10. The method according to claim 1 or 2, wherein, The at least one pilot pulse (R) i ) is a signal pulse with an intensity higher than the at least one signal pulse (S) k Optical pulses of intensity.

11. The method according to claim 1 or 2, wherein, The at least one pilot pulse (R) i ) and the at least one signal pulse (S) k )staggered.

12. The method according to claim 1 or 2, wherein, The at least one signal pulse (S) k It was sent according to the quantum cryptography protocol.

13. The method according to claim 12, wherein, The at least one signal pulse (S) k The key is sent according to the Continuous Variable Quantum Key Distribution (CV-QKD) protocol.

14. An apparatus configured for feedforward carrier recovery, comprising: A receiving unit is configured to receive an optical signal from a light source, the optical signal including at least one pilot pulse (R) and at least one signal pulse (S) containing information; as well as The control unit is configured to use a local oscillator signal from a local oscillator source to determine multiple samples (R1) of the at least one pilot pulse (R). 0,i R 1,i orthogonal values; The control unit is further configured to: Using the multiple samples (R) 0,i R 1,i The orthogonality value of the received optical signal from the light source and the local oscillator signal from the local oscillator source are used to determine the phase difference between them. as well as The carrier information of the at least one signal pulse (S) is recovered based on the determined phase difference.

15. The apparatus according to claim 14, wherein, The control unit is configured to determine the phase difference using the orthogonality values ​​of two adjacent samples of the at least one pilot pulse (R).

16. The apparatus according to claim 14 or 15, wherein, The control unit is configured to calculate a compensation factor (W) to determine the orthogonality value of the at least one signal pulse (S).

17. The apparatus according to claim 14 or 15, wherein, The control unit includes a clock recovery circuit configured to receive the signal pulses received and / or detected by the receiving unit, and / or the at least one pilot pulse (R), for recovering carrier information.

18. The apparatus according to claim 17, wherein, The clock recovery circuit is configured to operate based on a predetermined time delay (T) between the pilot pulse (R) and the at least one signal pulse (S). d The power, amplitude, intensity, and peak value of the power, amplitude, and intensity of the pilot pulse are used to select at least one of the samples of the pilot pulse (R).

19. The apparatus according to claim 16, wherein, The control unit is configured to, based on the phase difference and the time delay (T) between two adjacent samples of the guide pulse (R), s ), and the time delay (T) between one of the samples of the at least one signal pulse (S) and the pilot pulse (R). d The compensation factor can be calculated using any one of the following, or any combination thereof.

20. The apparatus according to claim 16, wherein, The compensation factor (W) includes one or more trigonometric coefficients.

21. The apparatus according to claim 16, wherein, The control unit includes a block module configured to calculate the compensation factor (W).

22. The apparatus according to claim 21, wherein, The block module includes at least one adder and at least one multiplier for calculating the compensation factor.

23. The apparatus according to claim 21, wherein, The block module includes at least one multiplexer and at least one register buffer, the multiplexer being configured to select one or more inputs for the block module, and the register buffer being configured to process one or more inputs for the block module.

24. The apparatus according to claim 14 or 15, wherein, The control unit is implemented in digital signal processing hardware, i.e., DSP hardware.

25. The apparatus according to claim 24, wherein, The control unit is implemented in a field-programmable gate array (FPGA).

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