Optical pulse generating device and generating method

Abstract

This optical pulse generation device comprises: an optical intensity modulator 2 that outputs an optical pulse obtained by modulating the signal intensity of an optical carrier outputted by a light source 1 according to the magnitude of a drive signal with an operation bias point as a center; a measurement unit 3 that measures an inter-pulse phase component that is the amplitude between optical pulses; a bias control unit 4 that controls the operation bias point on the basis of the magnitude of the inter-pulse phase component; and a drive signal control unit 5 that controls the magnitude of the drive signal on the basis of the magnitude of the inter-pulse phase component. The drive signal control unit 5 performs the control such that the magnitude of the drive signal is twice the magnitude of the amplitude between the maximum value and the minimum value of the transmission characteristic of the optical intensity modulator 2.

Description

[Technical Field]

[0001] The present invention relates to an optical pulse generating device and method for generating optical pulses with high repetition rate and short pulse width. [Background technology]

[0002] In an optical communication system, when transmitting signals by intensity modulation of optical pulses, it is effective to shorten the pulse width of the transmitted optical pulses in order to suppress pulse broadening due to fiber dispersion.

[0003] There are two main methods for generating optical pulses: direct modulation, in which an electrical signal is directly modulated into light, and external modulation, in which an optical signal is modulated by an external modulator.

[0004] Direct modulation methods have the problem of phase variations (phase chirp) due to wavelength fluctuations, as high-speed signals are directly modulated. On the other hand, external modulation methods using the electro-optic effect include electro-absorption and Mach-Zehnder (hereinafter referred to as MZ) optical intensity modulators. Among MZ types, push-pull intensity modulation, which is driven by applying an opposite-phase voltage signal to the phase modulation section of the waveguide, is suitable for high-speed communications because it can suppress frequency chirp.

[0005] A known optical pulse generating device using an MZ-type optical intensity modulator is one that generates optical pulses with any pulse width with little chirp by setting the operating bias point of the optical intensity modulator so that the transmittance of the optical intensity modulator is maximized and applying a sine wave or square wave drive signal with an amplitude of 2Vπ (Vπ is a half-wave voltage indicating the drive amplitude corresponding to the adjacent maximum and minimum transmittances) corresponding to one period of the optical transmittance characteristic of the optical intensity modulator (Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 3524005 Summary of the Invention [Problem to be solved by the invention]

[0007] However, with the method of Patent Document 1, the peak of the optical transmission characteristics of the optical intensity modulator may shift due to the device environment or the application of a large voltage. Such changes pose the problem of generating noise components (hereinafter referred to as inter-pulse phase components) between optical pulses, deteriorating the signal-to-noise ratio. Furthermore, when the repetition frequency of the optical pulses is changed, Vπ changes, which changes the amplitude of the drive signal and generates inter-pulse phase components.

[0008] The present invention has been made in consideration of this problem, and aims to provide an optical pulse generating device and generation method that can suppress the occurrence of inter-pulse phase components and stably generate short pulses with little phase chirp due to wavelength fluctuations. [Means for solving the problem]

[0009] An optical pulse generating device according to one aspect of the present invention comprises an optical intensity modulator that outputs optical pulses obtained by modulating the signal intensity of an optical carrier output by a light source in accordance with the magnitude of a drive signal centered on an operating bias point; a measurement unit that measures an inter-pulse phase component that is the amplitude between the optical pulses; a bias control unit that controls the operating bias point based on the magnitude of the inter-pulse phase component; and a drive signal control unit that controls the magnitude of the drive signal based on the magnitude of the inter-pulse phase component.

[0010] Furthermore, an optical pulse generation method according to one aspect of the present invention is summarized as comprising an optical intensity modulation step of outputting optical pulses obtained by modulating the signal intensity of an optical carrier output by a light source in correspondence with the magnitude of a drive signal centered on an operating bias point; a measurement step of measuring an inter-pulse phase component which is the amplitude between the optical pulses; a bias control step of controlling the operating bias point based on the magnitude of the inter-pulse phase component; and a drive signal control step of controlling the magnitude of the drive signal based on the magnitude of the inter-pulse phase component. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide an optical pulse generating device and a generating method that can suppress the generation of noise and stably generate short pulses with little phase chirp due to wavelength fluctuation. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a block diagram showing an example of the configuration of an optical pulse generating device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram schematically illustrating the operation of the optical intensity modulator shown in FIG. [Figure 3] 10 is a flowchart showing a processing procedure of a step of adjusting a light pulse. [Figure 4] 1A and 1B are diagrams illustrating examples of optical pulses generated in the process of adjusting the optical pulses. [Figure 5] FIG. 5 is a diagram schematically illustrating another example of the light pulse shown in FIG. [Figure 6] FIG. 2 is a diagram schematically illustrating a specific configuration example of the optical pulse generating device shown in FIG. [Figure 7] FIG. 7 is a diagram schematically illustrating a modified example of the measuring unit shown in FIG. 6. [Figure 8] 2 is a block diagram showing a schematic configuration example of a quantum communication system including a transmitter using the optical intensity modulator shown in FIG. 1 and a receiver. FIG. [Figure 9] 10 is a flowchart showing a processing procedure for transmitting a test signal. [Figure 10] 9 is a time chart schematically showing the relationship between communication data and a test signal output by the transmitter shown in FIG. 8. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals are used to denote the same parts, and the description thereof will not be repeated.

[0014] (Configuration of optical pulse generator) Fig. 1 is a block diagram showing an example of the configuration of an optical pulse generating device according to an embodiment of the present invention. The optical pulse generating device 10 shown in Fig. 1 is an optical pulse generating device that generates optical pulses used in optical communications, optical measurement, and the like.

[0015] The optical pulse generating device 10 includes a light source 1, an optical intensity modulator 2, a measurement unit 3, a bias control unit 4, and a drive signal control unit 5. In Fig. 1, thick lines represent the paths of optical signals, and thin lines represent the paths of electrical signals.

[0016] The light source 1 outputs an optical carrier. The light source 1 is composed of, for example, a semiconductor laser. The optical carrier is the signal that forms the source of the optical pulse, and the maximum value of the optical carrier forms the peak value of the optical pulse. Note that the light source 1 is not necessary. It is not necessary if an optical carrier is supplied from an external source.

[0017] The optical intensity modulator 2 sets the operating bias point so that the transmittance of the intensity modulator is maximized, and corresponds to the magnitude of the drive signal, and outputs an optical pulse obtained by modulating the signal intensity of the optical carrier output by the light source 1. As the optical intensity modulator 2, a push-pull MZ type optical intensity modulator or a directional coupler type optical intensity modulator can be used.

[0018] The MZ type optical intensity modulator is configured to give a phase difference according to a drive signal to the light branched into two optical waveguides at the input Y-branch waveguide, and modulate the output light intensity by utilizing the interference effect when the lights are combined at the output Y-branch waveguide. The operation of modulating the output light intensity will be described in detail later.

[0019] The measurement unit 3 measures the inter-pulse phase component, which is the amplitude between optical pulses output by the optical intensity modulator 2. The inter-pulse phase component is noise, and will not be output if the operating bias point of the drive signal and the amplitude of the drive signal are adjusted correctly. A specific configuration example of the measurement unit 3 will be described later.

[0020] The bias control unit 4 controls the operating bias point based on the magnitude of the inter-pulse phase component measured by the measurement unit 3.

[0021] The drive signal control unit 5 controls the magnitude of the drive signal based on the magnitude of the inter-pulse phase component measured by the measurement unit 3.

[0022] The optical coupler 6 branches a part of the optical pulse output from the optical intensity modulator 2 to the measurement unit 3. The optical coupler 6 is a general type.

[0023] (Operation of the optical pulse generator) Fig. 2 is a diagram showing a schematic diagram of the operation of the optical intensity modulator 2. Fig. 2 shows an optical pulse in a state where there is no inter-pulse phase component.

[0024] In Figure 2, the horizontal sine wave indicates the change in the light transmittance of the optical intensity modulator 2. The vertical sine wave indicates the change in the drive signal applied to the optical intensity modulator 2, with the right side defined as the positive direction and the left side defined as the negative direction. The string of tall triangles (optical pulses) on the right side indicates the optical pulse string output from the optical intensity modulator 2.

[0025] As shown in Figure 2, when the midpoint potential α of the drive signal coincides with the maximum value of the optical transmittance and the amplitude β of the drive signal coincides with one period of the optical transmittance characteristic, the inter-pulse phase component, which is the amplitude between optical pulses, is zero. The midpoint potential α of the drive signal is hereinafter referred to as the operating bias point α.

[0026] The drive signal is a signal with a frequency f and an amplitude 2Vπ (Vπ is a half-wave voltage indicating the drive amplitude corresponding to the adjacent maximum and minimum transmittance) corresponding to one period of the transmission characteristic of the optical intensity modulator 2.

[0027] Point a of the drive signal, where the amplitude of the drive signal coincides with the operating bias point α, corresponds to optical pulse a. Similarly, points b, c, and d of the drive signal correspond to optical pulses b, c, and d, respectively. Furthermore, the negative peak between points a and b of the drive signal coincides with the minimum transmittance of the transmission characteristics of the optical intensity modulator 2, so the amplitude between optical pulses a and b (inter-pulse phase component) is zero (0). Furthermore, the positive peak between points b and c of the drive signal coincides with the minimum transmittance of the transmission characteristics of the optical intensity modulator 2, so the amplitude between optical pulses b and c (inter-pulse phase component) is also zero (0).

[0028] In this way, by correctly setting the operating bias point α and amplitude β of the drive signal as shown in FIG. 2, optical pulses with a repetition frequency of 2f and no inter-pulse phase component are output from the optical intensity modulator 2.

[0029] According to the optical pulse generating device 10 of this embodiment, it is possible to accurately and easily adjust the operating bias point α and the amplitude β. The adjustment procedure will be described with reference to FIG.

[0030] 3 is a flowchart showing the procedure for adjusting the optical pulse. The steps of this flowchart are executed by the measurement unit 3, bias control unit 4, and drive signal control unit 5, respectively.

[0031] When the process of adjusting the optical pulse starts, the bias control unit 4 resets the bias adjustment flag indicating that the operating bias point has been adjusted. Also, the drive signal control unit 5 resets the drive signal adjustment flag. In short, the adjustment flag is reset before adjustment (step S1).

[0032] Next, the drive signal control unit 5 sets the drive signal to an intermediate magnitude that does not maximize or minimize the transmission characteristic of the optical intensity modulator 2 (step S2). The drive signal at this time is a constant voltage of an arbitrary magnitude within the range of amplitude β.

[0033] Next, the measuring unit 3 measures the optical intensity of the optical carrier output from the optical intensity modulator 2 by the constant voltage (step S3).

[0034] Next, the drive signal control unit 5 shifts the constant voltage of the drive signal set in step S2 in the negative direction (step S4).

[0035] Next, the measurement unit 3 measures the optical intensity of the optical carrier output from the optical intensity modulator 2. Then, the bias control unit 4 compares the optical intensity measured in step S3 with the optical intensity measured in step S4 (step S5).

[0036] If the comparison result indicates an increase (YES in step S5), it is determined that the drive signal set in step S2 is a voltage that is more positive than the intermediate voltage of the amplitude β. In this case, the bias control unit 4 shifts the voltage of the drive signal in the negative direction so that the optical intensity of the optical carrier output from the optical intensity modulator 2 is maximized (step S6).

[0037] If the comparison result is a decrease (NO in step S5), it is determined that the drive signal set in step S2 is a voltage that is more negative than the intermediate voltage of the amplitude β. In this case, the bias control unit 4 shifts the voltage of the drive signal in the positive direction so that the optical intensity of the optical carrier output from the optical intensity modulator 2 is maximized (step S7).

[0038] The bias control unit 4 sets the constant voltage at which the optical intensity of the photocarriers is maximized as the operating bias point α and sets the bias adjustment flag (step S8). Setting the bias adjustment flag indicates that adjustment of the operating bias point α has been completed.

[0039] Fig. 4 is a diagram showing a schematic diagram of the adjustment of the operating bias point α performed by the bias control unit 4. For the purpose of ease of understanding, Fig. 4 shows the drive signal as a square wave with a frequency f. Note that the drive signal in step S7 above is a DC voltage.

[0040] 4(a) shows that the operating bias point α is located to the left of the maximum value of the transmission characteristic of the optical intensity modulator 2. The drive signal in this example is a square wave whose center is the operating bias point α before adjustment and whose amplitude is smaller than the amplitude between the maximum and minimum values ​​of the transmission characteristic of the optical intensity modulator 2. The reason for showing it as a square wave is for convenience of drawing.

[0041] As shown in Figure 4(a), due to a change in the drive signal at time a, the transmittance of the optical intensity modulator 2 changes in a short time in the following order: small transmittance with a phase difference of π, transmittance 0, maximum transmittance, and small transmittance of the reference phase (0). Due to this change in transmittance, the optical pulse changes from small amplitude to amplitude 0, maximum amplitude (a), and then to small amplitude again. The final small amplitude is maintained for the pulse width of the drive signal.

[0042] Next, due to the change in the drive signal at time point b, the transmittance of the optical intensity modulator 2 changes in a short time in the following order: small transmittance at reference phase (0), maximum transmittance, small transmittance at reference phase (0), and small transmittance with a phase change of π. Due to this change in transmittance, the optical pulse changes from small amplitude to maximum amplitude (a), amplitude 0, and then small amplitude again. The final small amplitude is maintained until time point c of the drive signal. This process is repeated thereafter.

[0043] 4(b) shows that the operating bias point α coincides with the maximum value of the transmission characteristic of the optical intensity modulator 2. However, this is the case when the amplitude β of the drive signal is smaller than the amplitude between the maximum and minimum values ​​of the transmission characteristic of the optical intensity modulator 2.

[0044] In this case, as shown in Figure 4(b), the peak optical intensity of the optical pulse coincides with the maximum value of the optical carrier. However, because the amplitude of the drive signal is small, the tail of the optical pulse does not decrease to 0.

[0045] As described above, when the drive amplitude is the same, the peak optical intensity of the optical pulse remains the same even if the operating bias point α does not coincide with the peak of the transmission characteristic. However, if the drive voltage is set to a drive signal of any intermediate magnitude that does not maximize (drive voltage is 0) or minimize the transmission characteristic of the optical intensity modulator 2, and the peak optical intensity of the optical pulse coincides with the maximum value of the optical carrier. In other words, the bias control unit 4 controls the operating bias point α to set it to the maximum value of the transmission characteristic of the optical intensity modulator 2. This makes it possible to increase the peak optical intensity of the optical pulse and improve the signal-to-noise ratio of the optical pulse.

[0046] As described above, the operating bias point α can be adjusted by adjusting only the voltage value of the drive signal. However, as shown in Figure 4(b), even if the operating bias point α is adjusted correctly, if the amplitude of the drive signal is incorrect, an inter-pulse phase component will be output in the part between optical pulses where the amplitude should be zero. Therefore, the magnitude of the amplitude β of the drive signal is then adjusted.

[0047] The operation of the drive signal control unit 5 will be described with reference to Fig. 3 again. The drive signal control unit 5 in this example starts operation after the bias control unit 4 adjusts the operating bias point α.

[0048] The drive signal control unit 5 increases the amplitude β of the drive signal, which is smaller than the amplitude between the maximum and minimum values ​​of the transmission characteristic of the optical intensity modulator 2 (step S9). In this state, an inter-pulse phase component occurs between the optical pulses, as shown in FIG. 4(b).

[0049] After this inter-pulse phase component disappears once, the drive signal control unit 5 increases the amplitude β of the drive signal until the inter-pulse phase component appears again (loop of NO in step S10).

[0050] FIG. 5 is a diagram showing a schematic diagram of the relationship between the drive signal and the optical pulse in a state where the amplitude β of the drive signal is increased until an inter-pulse phase component appears again (YES in step S10).

[0051] 5, the amplitude β of the drive signal is larger than the amplitude between the maximum and minimum values ​​of the transmission characteristic of the optical intensity modulator 2. As a result, two inter-pulse phase components with a phase difference of π, centered around the phase 0 of the transmission characteristic of the optical intensity modulator 2, are generated between the optical pulses.

[0052] 5 (YES in step S10), the amplitude β of the drive signal is too large, so the drive signal control unit 5 reduces the amplitude β of the drive signal (step S11). The amplitude β is reduced until there is no inter-pulse phase component (loop of NO in step S12).

[0053] When the inter-pulse phase component disappears, the drive signal control unit 5 immediately stops changing the amplitude β and sets the drive signal adjustment flag (step S13).

[0054] In this way, the drive signal control unit 5 controls the drive signal so that it becomes twice the amplitude between the maximum and minimum values ​​of the transmission characteristic of the optical intensity modulator 2. This maximizes the amplitude of the optical pulse and improves its signal-to-noise ratio.

[0055] As described above, the optical pulse generating device 10 according to this embodiment comprises an optical intensity modulator 2 that outputs optical pulses obtained by modulating the signal intensity of the optical carrier output by the light source 1 in accordance with the magnitude of the drive signal centered on the operating bias point α, a measuring unit 3 that measures the inter-pulse phase component, which is the amplitude between optical pulses, a bias control unit 4 that controls the operating bias point α based on the magnitude of the inter-pulse phase component, and a drive signal control unit 5 that controls the magnitude of the drive signal based on the magnitude of the inter-pulse phase component. This makes it possible to suppress noise generation and stably generate short pulses with little phase chirp due to wavelength fluctuations.

[0056] Furthermore, the optical pulse generation method executed by optical pulse generation device 10 includes an optical intensity modulation step of outputting an optical pulse obtained by modulating the signal intensity of the optical carrier output by the light source in correspondence with the magnitude of the drive signal centered on the operating bias point, an inter-pulse phase component measurement step of measuring the inter-pulse phase component which is the amplitude between optical pulses, a bias control step (S1 to S8 in FIG. 3) of controlling the operating bias point α based on the magnitude of the inter-pulse phase component, and a drive signal control step (S9 to S13 in FIG. 3) of controlling the magnitude of the drive signal based on the magnitude of the inter-pulse phase component.

[0057] Furthermore, fine adjustment of the operating bias point α can be performed by measuring the inter-pulse phase component. For example, in Figure 4(a), the phase component between pulse a and pulse b is the same as the reference phase (0), and the phase component between pulse b and pulse c has a phase difference of π, repeating 0 and π for each pulse. In Figure 4(b), the phase component between pulse a and pulse b is 0, and the phase component between pulse b and pulse c is also 0. By measuring the inter-pulse phase component, if 0 and π are repeated, the bias can be adjusted without changing the drive voltage by controlling the operating bias point α so that the noise becomes 0 or the inter-pulse phase component is only 0.

[0058] (Specific configuration example) FIG. 6 is a diagram schematically illustrating a specific configuration example of the optical pulse generating device 10. As shown in FIG.

[0059] As shown in FIG. 6, the optical intensity modulator 2 may be configured as, for example, an MZ type optical intensity modulator.

[0060] Optical intensity modulator 2, which is an MZ-type optical intensity modulator, branches an optical carrier input from light source 1 into two optical waveguides 22a and 22b at Y-branch waveguide 21. Then, a phase difference according to the applied voltage (voltage of the drive signal) is given to the branched light, and the output light intensity is modulated by utilizing the interference effect when the waves are combined at Y-branch waveguide 23, to output an optical pulse train. The optical pulse train is output to the outside, and a part of it is input to measurement unit 3 via optical coupler 6.

[0061] The measurement unit 3 includes a phase separation unit 30 that extracts an inter-pulse phase component, and optical intensity measurement units 31 and 32 that measure the intensity of the optical signal output by the phase separation unit 30.

[0062] The phase separation unit 30 can be configured with an MZ-type optical intensity modulator equipped with two optical waveguides that delay the time equivalent to a 1 / f period, that is, the phase by π. The phase separation unit 30 is the same as the MZ-type optical intensity modulator that configures the optical intensity modulator 2, except that no voltage is applied to the electrodes.

[0063] The phase separation section 30 extracts the inter-pulse phase component, which is the amplitude between optical pulses.

[0064] The inter-pulse phase components are converted into electrical signals by the light intensity measuring units 31 and 32. The light intensity measuring units 31 and 32 are photoelectric elements such as photodiodes and phototransistors.

[0065] The bias control unit 4 controls the operating bias point α based on the magnitude of the inter-pulse phase component.

[0066] The drive signal control unit 5 amplifies the signal of frequency f output from the oscillator 55 based on the magnitude of the inter-pulse phase component using the amplifier 56 to control the magnitude of the amplitude β of the drive signal.

[0067] The operating bias point α and the drive signal are controlled in the manner described with reference to FIG.

[0068] (Modification of Phase Separation Section) FIG. 7 is a diagram schematically showing a modified example of the measuring unit (FIG. 6).

[0069] 7, the measurement unit 3A of the modified example differs in that the phase separation unit 30A is configured by a cascade connection of a first MZ interferometer 34 and a second MZ interferometer 35. The first MZ interferometer 34 delays the time (1 / f) of one period of the frequency f of the optical pulse.

[0070] The second MZ interferometer 35 delays the optical pulse by half the period of frequency f. The second MZ interferometer 35 is connected to the first output (upper side in FIG. 7) of the first MZ interferometer 34 instead of the light intensity measuring unit 31.

[0071] A first output (upper side) of the second MZ interferometer 35 is connected to a light intensity measurement unit 36, and a second output (lower side) thereof is connected to a light intensity measurement unit 37. A second output (lower side) of the first MZ interferometer 34 is connected to a light intensity measurement unit 32.

[0072] In this way, the phase separation unit 30 may be configured with a first MZ interferometer 34 that delays the optical pulse by one period of frequency f, and a second MZ interferometer 35 that is connected to the output of the first MZ interferometer 34 and delays the optical pulse by half the period of frequency f. In this configuration, after adjusting the operating bias point α, if the amplitude β of the drive signal is small, the output of the light intensity measurement unit 37 will be small. Similarly, if the amplitude β of the drive signal is large, the output of the light intensity measurement unit 36 ​​will be small. By checking these changes, the magnitude of the amplitude β of the drive signal can be adjusted.

[0073] In this way, by configuring the phase separation section 30 using an optical device such as an MZ-type optical intensity modulator, the optical pulse generating device can be configured more simply and at lower costs than a configuration in which inter-pulse phase components are extracted using electronic circuits.

[0074] (application) One application of high-repetition short pulses is optical communication systems.

[0075] Because the pulses tend to spread due to the effects of fiber dispersion, they can be used as a light source for RZ modulation (Return-to-Zero) with a small duty ratio. By making the repetition rate variable, the communication rate can be changed according to demand. They can also be used as a light source for fiber sensing. Using pulses with a high repetition rate and a small duty ratio can improve measurement resolution. Furthermore, by making the repetition rate variable, the position of the measurement fiber can be swept over a wide range.

[0076] Furthermore, in quantum communications such as quantum cryptography, the sensitivity of measuring instruments is so high that dark counts occur, where signals are mistakenly counted even when no signals are received. To suppress dark counts, pulses with a small duty ratio are required.

[0077] Fig. 8 is a block diagram showing a schematic configuration example of an optical communication system. The optical communication system 100 shown in Fig. 8 includes a transmitter 50 using the optical pulse generating device 10 according to this embodiment, and a receiver 60. The light source 1 of the optical pulse generating device 10 included in the transmitter 50 is not shown.

[0078] In addition to the optical pulse generating device 10, the transmitter 50 includes a signal generating section 51, a data modulating section 52, a frame synchronization signal generating section 53, and an electrical-to-optical converting section .

[0079] The signal generating unit 51 generates communication data and a test signal indicating that the optical pulse generating device 10 is undergoing adjustment. Here, "under adjustment" means that either the drive signal control step (S9 to S13 in FIG. 3) or the bias control step (S1 to S8 in FIG. 3) is being executed.

[0080] The data modulation unit 52 modulates the optical pulse based on the communication data. The modulation method may be intensity, polarization, phase, etc. The optical signal is attenuated to one photon or less per optical pulse and transmitted to the receiving side.

[0081] In quantum communication, most photons are lost during fiber transmission, so frame headers and other information cannot be sent together with the data. Therefore, the frame synchronization signal is sent via a separate route from the data, or wavelength-multiplexed. The frame synchronization signal generator 53 generates a frame synchronization signal that indicates the beginning of the communication data.

[0082] Information indicating the position of the test signal may be inserted together with the frame synchronization signal of this embodiment.

[0083] The electrical-to-optical converter 54 converts the frame synchronization signal into an optical signal and outputs it to the receiver 60 .

[0084] The receiver 60 includes a data decoding unit 61 , an optical-electrical conversion unit 62 , a photon counting and recording unit 63 , and an optical-electrical conversion unit 64 .

[0085] The data decoding unit 61 demodulates the communication data whose phase has been modulated by the transmitter 50 .

[0086] The optical-electrical converter 62 converts the demodulated communication data into an electrical signal. The optical-electrical converter 62 is, for example, an avalanche photodiode for measuring photons or a superconducting photon measuring device.

[0087] The photon counting and recording unit 63 records the communication data converted into an electrical signal.

[0088] The optical-electrical conversion unit 62 converts the frame synchronization signal transmitted from the transmitter 50 into an electrical signal. The converted frame synchronization signal is output to the photon counting recorder 63. The photon count recorder 63 records the time from the frame synchronization signal to the detection of a photon.

[0089] FIG. 9 is a flowchart showing a processing procedure for transmitting a test signal.

[0090] When the communication system 100 starts communication, communication data is transmitted from the transmitter 50 to the receiver 60 (step S20).

[0091] The communication data is received by the receiver 60 (step S21).

[0092] The receiver 60 decodes the header information of the communication data and shares the basis selection information with the transmitter 50 (step S22). The basis selection information is, for example, phase information and time information used by the receiver 60 for measurement.

[0093] The receiver 60 may obtain whether or not a test signal is present from the transmitter 50 in step S22, or determine whether or not the communication data includes a test signal by obtaining the beginning position of the test signal from the frame synchronization signal as shown in FIG. 8 (step S23).

[0094] If a test signal is included, the receiver 60 acquires the data range to be used for the test signal in step S22, or can know the position of the test signal in the communication data from the frame synchronization signal (step S24).

[0095] The receiver 60 removes the test signal from the communication data (step S25), or deletes the communication data including the test signal. For example, if the data range is known, the receiver 60 decodes the data from the frame synchronization signal to the data range.

[0096] Thereafter, for example, information such as an error correction code is shared to correctly decode the communication data (step S26).

[0097] 10 is a time chart that shows the relationship between the communication data and the test signal output by the transmitter. As shown in FIG. 10, the communication data and the test signal are output in time series.

[0098] As described above, the optical data communication method according to this embodiment includes a test signal transmission step (step S20) of transmitting a test signal indicating that either the drive signal control step or the bias control step is being executed to the receiver, and a test signal notification step (step S24) of notifying the receiver of the start position of the test signal. This allows the receiver 60 to prevent an increase in errors due to unadjusted optical pulses.

[0099] Furthermore, by transmitting a test signal, the optical pulse generating device 10 can be adjusted at any timing, thereby constantly suppressing noise generation and stably generating short pulses with little phase chirp due to wavelength fluctuations.

[0100] As explained above, the inter-pulse phase component, which is the amplitude between optical pulses, is extracted using an optical device such as an MZ-type optical intensity modulator, and the operating bias point α of the optical intensity modulator 2 and the amplitude β of the drive signal are controlled so that the inter-pulse phase component does not occur, thereby suppressing noise. Therefore, stable optical communication can be performed using optical pulses with a good S / N ratio.

[0101] Furthermore, since a test signal indicating that the optical pulse is being adjusted or not adjusted is sent to the receiver, communication using an unstable optical pulse can be prevented.

[0102] 6 shows an example in which the optical intensity modulator 2 and the phase separation unit 30 of the measurement unit 3 are configured as separate MZ-type optical intensity modulators, but the present invention is not limited to this example. The optical intensity modulator 2 and the phase separation unit 30 may be arranged on the same chip. This can improve stability against disturbances such as temperature changes. Also, a directional coupler-type optical intensity modulator may be used instead of the MZ-type optical intensity modulator.

[0103] As explained above, the present invention naturally includes various embodiments not described herein. Therefore, the technical scope of the present invention is defined only by the invention-specifying matters according to the scope of the claims that are appropriate from the above explanation. [Explanation of symbols]

[0104] 1:Light source 2: Optical intensity modulator 3,3A: Measuring part 4: Bias control section 5: Drive signal control section 10: Optical pulse generator 30,30A: Phase separation section 31, 32, 36, 37: Light intensity measurement unit 34: First Mach-Zehnder interferometer 35: Second Mach-Zehnder interferometer

Claims

1. an optical intensity modulator that outputs an optical pulse obtained by modulating the signal intensity of an optical carrier output from a light source in accordance with the magnitude of a drive signal centered on an operating bias point; a measurement unit for measuring an inter-pulse phase component which is an amplitude between the optical pulses; a bias control unit that controls the operating bias point based on the magnitude of the inter-pulse phase component; a drive signal control unit that controls the magnitude of the drive signal based on the magnitude of the inter-pulse phase component, The measurement unit a phase separation unit that extracts the inter-pulse phase component; an optical intensity measurement unit that measures the intensity of the optical signal output from the phase separation unit, The phase separation unit is a first Mach-Zehnder interferometer to which the optical pulse is input and which delays the optical pulse by one period of its frequency; a second Mach-Zehnder interferometer connected to the output of the first Mach-Zehnder interferometer and delaying the frequency by half a period of the frequency; The inter-pulse phase component is calculated based on an output from the second Mach-Zehnder interferometer. Optical pulse generator.

2. The drive signal control unit controls the drive signal so that the amplitude is twice the amplitude between the maximum and minimum values ​​of the transmission characteristic of the optical intensity modulator.

2. The optical pulse generating device according to claim 1.

3. The bias control unit controls the operating bias point to be set to a maximum value of the transmission characteristic of the optical intensity modulator.

3. The optical pulse generating device according to claim 1 or 2.

4. an optical intensity modulation step of outputting an optical pulse obtained by modulating the signal intensity of the optical carrier output from the light source in accordance with the magnitude of the drive signal centered on the operating bias point; a measuring step of measuring an inter-pulse phase component which is an amplitude between the optical pulses; a bias control step of controlling the operating bias point based on the magnitude of the inter-pulse phase component; a drive signal control step of controlling the magnitude of the drive signal based on the magnitude of the inter-pulse phase component; a transmitting step of transmitting communication data including a test signal indicating that either the drive signal control step or the bias control step is being performed to a receiver; a notification step of transmitting a frame synchronization signal notifying the receiver of the position of the test signal; The test signal is filtered out or eliminated by the receiver. Optical pulse generation method.

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