Optical short pulse generating device and optical short pulse generating method

Abstract

The purpose of the present invention is to provide a short optical pulse generation device, a short optical pulse generation method, and a program that generate short optical pulses with less variation in pulse width, chirp, and phase modulation amount.　The short optical pulse generation device comprises: a first optical intensity modulator (2) that outputs an optical pulse in which the signal intensity of the optical carrier outputted by a light source (1) is modulated, in accordance with the magnitude of a first drive signal around an operating bias point; a delay unit (3) that generates a second drive signal by delaying the first drive signal by half a period; and a second optical intensity modulator (4) that outputs a short optical pulse in which the signal intensity of the optical pulse is modulated, in accordance with the magnitude of the second drive signal around the operating bias point.

Description

[Technical Field]

[0001] The present invention relates to an optical short pulse generating device that generates optical pulses (optical short pulses) with high repetition rate and short pulse width. and optical short pulse generation method Regarding. [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).

[0006] Also, Non-Patent Document 1 discloses a pulse generation method that compensates for chirp by phase modulation. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-89176 [Non-patent literature]

[0008] [Non-Patent Document 1] CERogers III, “Characterization and compensation of the residual chirp in a Mach-Zehnder-type electro-optical intensity modulator” Optics Express Vol. 18, Issue 2, pp. 1166-1176 (2010) Summary of the Invention [Problem to be solved by the invention]

[0009] Consider the case of generating pulses by aligning the bias point with the peak of the intensity modulation characteristics and modulating with a square wave of double the half-wave voltage (2Vπ), as in the method of Patent Document 1. In this case, since the square wave contains high-frequency components, the electrical waveform can be dulled by electrical devices, cables, etc., resulting in variations in the intervals and widths of the generated pulses. Furthermore, in an ideal push-pull intensity modulator, the phase changes are equal in amount but of opposite sign, canceling out the phase changes and enabling chirp-free modulation.

[0010] However, in an actual push-pull intensity modulator, a slight residual chirp occurs due to variations in the splitting ratio of the coupler and the amount of phase modulation on both sides.

[0011] When pulses are generated using an intensity modulator with residual chirp, the optical pulses generated by the rising edge of the drive signal may have a larger chirp than the optical pulses generated by the falling edge of the electrical square wave. The opposite may also be true. This means that there is a problem in that the chirp and phase modulation amount differ for each optical pulse. The method of Non-Patent Document 1 cannot compensate for chirp if the phase amount differs for each optical pulse.

[0012] The present invention has been made in consideration of this problem, and aims to provide an optical short pulse generation device, an optical short pulse generation method, and a program that generate optical short pulses with little variation in pulse width, chirp, and phase modulation amount. [Means for solving the problem]

[0013] An optical short pulse generating device according to one aspect of the present invention includes a first optical intensity modulator that outputs an optical pulse obtained by modulating the signal intensity of an optical carrier output by a light source in accordance with the magnitude of a first drive signal centered on an operating bias point; a delay unit that generates a second drive signal by delaying the first drive signal by a half period; and a second optical intensity modulator that outputs an optical short pulse obtained by modulating the signal intensity of the optical pulse in accordance with the magnitude of the second drive signal centered on an operating bias point. the first optical intensity modulator and the second optical intensity modulator have similar chirp characteristics; The gist of this is as follows.

[0014] Furthermore, a method for generating short optical pulses according to one aspect of the present invention includes the steps of: by the first optical intensity modulator; a first optical intensity modulation step of outputting 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 first drive signal centered on an operating bias point; and a delay step of generating a second drive signal by delaying the first drive signal by half a period. by the second optical intensity modulator; a second optical intensity modulation step of outputting an optical short pulse obtained by modulating the signal intensity of the optical pulse in accordance with the magnitude of the second drive signal around an operating bias point; wherein the first optical intensity modulator and the second optical intensity modulator have similar chirp characteristics. The gist of this is as follows. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide an optical short pulse generating device, an optical short pulse generating method, and a program that can generate optical short pulses with little variation in pulse width, chirp, and phase modulation amount. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a block diagram showing an example of the configuration of an optical short pulse generating device according to a first embodiment of the present invention. [Figure 2] 2 is a schematic diagram for explaining the operation of the optical short pulse generating device shown in FIG. 1. FIG. [Figure 3] FIG. 10 is a block diagram showing an example of the configuration of an optical short pulse generating device according to a second embodiment of the present invention. [Figure 4] FIG. 10 is a block diagram showing an example of the configuration of an optical short pulse generating device according to a third embodiment of the present invention. [Figure 5] 5 is a flowchart showing an operation procedure of the optical short pulse generating device shown in FIG. [Figure 6] FIG. 10 is a block diagram showing an example of the configuration of an optical short pulse generating device according to a fourth embodiment of the present invention. [Figure 7] 7 is a flowchart showing an operation procedure of the optical short pulse generating device shown in FIG. [Figure 8] FIG. 10 is a block diagram showing an example of the configuration of an optical short pulse generating device according to a fifth embodiment of the present invention. [Figure 9] 9 is a flowchart showing an operation procedure of the optical short pulse generating device shown in FIG. 8. [Figure 10] 10A and 10B are diagrams illustrating the difference in optical pulses depending on the magnitude of the extinction ratio. [Figure 11] FIG. 1 is a block diagram illustrating an example of the configuration of a general-purpose computer system. DETAILED DESCRIPTION OF THE INVENTION

[0018] 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.

[0019] (First embodiment) Fig. 1 is a block diagram showing an example of the configuration of an optical short pulse generator according to a first embodiment of the present invention. The optical short pulse generator 10 shown in Fig. 1 generates optical short pulses with a short pulse width for use in optical communications, optical measurement, and other applications. Specific examples of optical short pulses will be described later.

[0020] The optical short pulse generating device 10 includes a light source 1, a first optical intensity modulator 2, a delay unit 3, and a second optical intensity modulator 4. In Fig. 1, thick lines represent the paths of optical signals, and thin lines represent the paths of electrical signals.

[0021] 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.

[0022] The first optical intensity modulator 2 outputs an optical pulse obtained by modulating the signal intensity of the optical carrier output by the light source 1 in accordance with the magnitude of the first drive signal centered around the operating bias point. As the first optical intensity modulator 2, a push-pull MZ type optical intensity modulator or a directional coupler type optical intensity modulator can be used.

[0023] The MZ-type optical intensity modulator is configured to give a phase difference corresponding to a drive signal to light branched into two optical waveguides at a Y-branch waveguide (not shown) on the input side, and to modulate the output light intensity by utilizing the interference effect when the light is combined at a Y-branch waveguide on the output side.

[0024] The first and second optical intensity modulators 2 and 4 may have a function of adjusting the optical intensity after branching into two waveguides, and may correct variations in the branching ratio of the optical intensity based on the waveform after combining. Also, the first and second optical intensity modulators 2 and 4 may be push-pull MZ intensity modulators, and multiple MZ intensity modulators may be mounted on one housing. The operation of modulating the output light intensity will be described later.

[0025] The delay unit 3 generates a second drive signal by delaying the first drive signal by half a period. The delay unit 3 can use various common phase shifters.

[0026] The second optical intensity modulator 4 outputs short optical pulses obtained by modulating the signal intensity of the optical pulses output by the first optical intensity modulator 2 in accordance with the magnitude of the second drive signal centered around the operating bias point. The second optical intensity modulator 4 is the same as the first optical intensity modulator 2.

[0027] (Operation of the optical short pulse generator) FIG. 2 is a schematic diagram for explaining the operation of the optical short pulse generating device 10. As shown in FIG.

[0028] In Figure 2, the horizontal sine wave on the left side indicates the change in the optical transmittance of the first and second optical intensity modulators 2 and 4. The waveform on the left side of the vertical direction (solid line) indicates the change in the first drive signal applied to the first optical intensity modulator 2, with the right direction defined as positive and the left direction defined as negative. The diagram on the top left also shows the phase chirp. The horizontal direction is voltage, and the vertical direction is the amount of phase change.

[0029] 2, the intermediate potential α of the first drive signal is set to coincide with the maximum value of the light transmittance, and the amplitude β of the first drive signal is set to coincide with one period of the light transmittance characteristic. The intermediate potential α of the first drive signal is hereinafter referred to as the operating bias point α.

[0030] The first drive signal is a signal of frequency f having 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 transmittance characteristic of the first optical intensity modulator 2.

[0031] Point a of the first drive signal, where the amplitude of the first drive signal coincides with the operating bias point α, corresponds to point a of the optical pulse. Similarly, points b, c, d, ... of the drive signal correspond to points b, c, d of the optical pulse, respectively.

[0032] In this example, the amount of phase change when the first drive signal changes from 0 to Vπ is represented by Cπ, and the amount of phase change when the first drive signal changes from Vπ to 2Vπ is represented by C2π. Even if the same device (model) is used for the first optical intensity modulator 2 and the second optical intensity modulator 4, the amounts of phase change in the two optical waveguides of the Y-branch waveguide may differ from each other due to manufacturing variations or the like.

[0033] In the case of the phase change amount shown in Figure 2 (upper left diagram), the phase delay of the rising edge of optical pulse a is small, and the phase delay of the falling edge of optical pulse a is large. In Figure 2, this optical pulse a (with a small phase delay on the rising edge and a large phase delay on the falling edge) is represented as an optical pulse with a short pulse width.

[0034] Next, at point b of the first drive signal, the voltage changes from 2Vπ to 0. Therefore, the phase delay of the rising edge of light pulse b increases, and the phase delay of the falling edge of light pulse b decreases. This light pulse b (with a large phase delay on the rising edge and a small phase delay on the falling edge) is represented as an optical pulse with a wide pulse width.

[0035] In this way, the pulse widths of the optical pulses output from the first optical intensity modulator 2 are not uniform. In this example, optical pulses a and b are output alternately and repeatedly (a=c, b=d).

[0036] Therefore, in this embodiment, the second drive signal that changes the optical transmittance of the second optical intensity modulator 4 is a signal that is delayed by half a period with respect to the first drive signal. As shown by the dashed line on the right side of the vertical direction in Fig. 2, the second drive signal is a signal that is delayed by half a period, Δt / 2, with respect to the first drive signal.

[0037] The second optical intensity modulator 4 modulates the signal intensity of the optical pulse output by the first optical intensity modulator 2 with the second drive signal. As a result, optical pulse b is affected by a phase change amount Cπ at its rising edge and by a phase change amount C2π at its falling edge. In other words, with the configuration of this embodiment, each of the optical short pulses a, b, c, and d is affected by the same phase change.

[0038] Therefore, according to the optical short pulse generating device 10, each optical pulse is affected by the same phase change, and therefore uniform optical short pulses can be generated as shown in Fig. 2. Each of the optical short pulses a to d has an optical output pulse width of, for example, about 1 / 3 of the period of the first and second drive signals. It is a force pulse.

[0039] As described above, the optical short pulse generation device 10 according to this embodiment includes a first 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 correspondence with the magnitude of the first drive signal centered around the operating bias point α, a delay unit 3 that generates a second drive signal by delaying the first drive signal by half a period, and a second optical intensity modulator 4 that outputs optical short pulses obtained by modulating the signal intensity of the optical pulse in correspondence with the magnitude of the second drive signal centered around the operating bias point α. This makes it possible to generate optical short pulses with a constant pulse width, chirp, and amount of phase modulation.

[0040] The first optical intensity modulator 2 and the second optical intensity modulator 4 must have similar residual chirp characteristics. While the preferred example has been described using the same modulator, they do not have to be the same. For example, the first optical intensity modulator 2 and the second optical intensity modulator 4 may be different products (models, etc.). Even if the models are different, as long as the chirp characteristics of the modulators are similar, each optical short pulse is affected by the same amount of phase change, allowing the generation of uniform optical short pulses. While the first and second drive signals have been described using waveforms with both the upper and lower limits dulled, they may also be rectangular waves. Furthermore, the first and second drive signals may be sinusoidal or sawtooth waves.

[0041] Also, while the configuration using two intensity modulators is shown, three or more can be connected in series. When two intensity modulators are used, the chirp characteristics of the intensity modulators must be similar, but when three or more are used, the amount of residual chirp is averaged out, ultimately reducing chirp variation. In this case, the delay unit 3 adjusts the drive voltage so that it has an opposite phase to the rising (or falling) edge of the electrical pulse with deteriorated pulse characteristics, i.e., its falling (or rising) edge.

[0042] (Second embodiment) 3 is a block diagram showing an example of the configuration of an optical short pulse generation device according to a second embodiment of the present invention. Optical short pulse generation device 20 shown in FIG. 3 differs from optical short pulse generation device 10 in that it includes a delay adjustment unit 5.

[0043] The delay adjustment unit 5 increases or decreases the delay amount by which the first drive signal is delayed by the delay unit 3. The delay amount is input from outside to the delay adjustment unit 5. Thus, in the optical short pulse generation device 10, the delay amount of the second drive signal, which has a fixed delay amount relative to the first drive signal, can be adjusted forward or backward (advance or lag).

[0044] The delay adjustment unit 5 may be configured, for example, by preparing a plurality of waveguides (not shown) with different line lengths and selecting each waveguide with a switch (not shown) to adjust the delay amount (phase amount). The delay adjustment unit 5 may also use an electrical buffer memory or may be configured using various general phase shifters.

[0045] As described above, the optical short pulse generating device 20 includes a delay adjustment unit 5 that increases or decreases the amount of delay applied to the first drive signal by the delay unit 3. This allows the optical short pulses to be optimized. Specifically, adjustments are made so that both the pulse width and period of the optical short pulses are uniform. Note that adjustments may also be made so that only one of the pulse width or period of the optical short pulses is uniform.

[0046] (Third embodiment) Fig. 4 is a block diagram showing an example of the configuration of an optical short pulse generation device according to a third embodiment of the present invention. The optical short pulse generation device 30 shown in Fig. 4 differs from the optical short pulse generation device 20 in that it includes an optical coupler 6, an optical intensity measurement unit 31, and a delay adjustment unit 35.

[0047] The optical coupler 6 branches a part of the short optical pulse output from the second optical intensity modulator 4. The optical coupler 6 is a general type.

[0048] The optical intensity measurement unit 31 converts the optical short pulse branched by the optical coupler 6 into an electrical signal. The optical intensity measurement unit 31 is a photoelectric element such as a photodiode or a phototransistor. The optical intensity measurement unit 31 measures the time waveform of the optical short pulse.

[0049] The delay adjustment unit 35 adjusts the delay amount of the delay unit 3 so that the pulse width of the optical short pulse becomes constant. In other words, the delay adjustment unit 35 controls the delay amount of the delay unit 3 so that the time waveform of the optical short pulse fed back by the optical coupler 6 and the optical intensity measurement unit 31 becomes constant.

[0050] As a result, the pulse width of the short optical pulse is automatically adjusted by feedback control.

[0051] (Method for generating short optical pulses) 5 is a flowchart showing the operation procedure of the optical short pulse generating device 30 (FIG. 4). Each step of this flowchart is executed mainly by a control unit (not shown) and a delay adjustment unit 35.

[0052] When the process of adjusting the optical pulse is started, the control unit first sets the amplitudes of the first drive signal and the second drive signal that drive the first and second optical intensity modulators 2 and 4 to 0 (step S1).

[0053] Next, the control unit increases the bias voltage of the first drive signal (step S2) so that the signal intensity of the optical signal output from the first optical intensity modulator 2 becomes maximum (until the transmittance becomes maximum (Yes in step S3)).

[0054] Next, the control unit increases the bias voltage of the second drive signal so that the signal intensity of the optical signal output from the second optical intensity modulator 4 becomes maximum (until the transmittance becomes maximum (Yes in step S5)) (step S4).

[0055] Next, the control unit increases the amplitude of the drive signal that drives the first optical intensity modulator 2 (step S6) so that the signal level between optical pulses becomes 0 (Yes in step S7).

[0056] Next, the control unit increases the amplitude of the drive signal that drives the second optical intensity modulator 4 so that the signal level between the short optical pulses becomes 0 (Yes in step S9) (step S8).

[0057] Next, the delay adjustment unit 35 adjusts the delay amount of the second drive signal (step S10) so that the amplitude and pulse width of each short optical pulse are the same (Yes in step S11).

[0058] In this way, the optical short pulse generation device 30 automatically adjusts the amplitude and pulse width of the optical short pulses so that they are the same. Note that it is also possible to adjust either the amplitude or the pulse width of the optical short pulses with priority.

[0059] The bias control of the first optical intensity modulator 2 (steps S2 and S3) and the bias control of the second optical intensity modulator 4 (steps S4 and S5), and the drive signal control of the first optical intensity modulator 2 (steps S6 and S7) and the bias control of the second optical intensity modulator 4 (steps S8 and S9) can be performed in any order. They can also be performed in parallel. When the pulse tail is zero (steps S7 and S9), the time waveform can be observed, or the intensity of the pulse tail can be extracted using a switch. Furthermore, the component where the pulse tail is zero can be extracted using an interferometer with a period half the pulse interval.

[0060] (Fourth embodiment) Fig. 6 is a block diagram showing an example of the configuration of an optical short pulse generation device according to a fourth embodiment of the present invention. Optical short pulse generation device 40 shown in Fig. 6 differs from optical short pulse generation device 30 (Fig. 4) in that it includes a dispersing device 41 that disperses light between optical coupler 6 and optical intensity measurement unit 31.

[0061] The dispersive device 41 is, for example, an optical fiber, a diffraction grating, or a fiber Bragg grating with refractive index modulation in the fiber.

[0062] In this way, optical short pulse generating device 40 controls the pulse width of the optical short pulses that pass through dispersive device 41 so as to be constant, thereby canceling out the influence of the optical fiber between optical short pulse generating device 40 and the receiving device.

[0063] Fig. 7 is a flowchart showing the operation procedure of the optical short pulse generation device 40 (Fig. 6). The only difference between the operation procedures of the optical short pulse generation device 40 is the inclusion of step S40 of transmitting optical short pulses to the dispersion device 41. Therefore, a detailed description of Fig. 7 will be omitted.

[0064] (Fifth embodiment) Fig. 8 is a block diagram showing an example configuration of an optical short pulse generator according to a fifth embodiment of the present invention. Optical short pulse generator 50 shown in Fig. 8 differs from optical short pulse generator 10 in that it includes an optical coupler 6, a delay unit 51, a phase modulation unit 52, a one-pulse delay MZ interferometer 53, and a delay amount generation unit 54. As is clear from the reference numeral, optical coupler 6 is the same as in optical short pulse generators 30 and 40.

[0065] The delay unit 51 delays the first drive signal by Δt.

[0066] The phase modulation section 52 performs phase modulation so that the phase of the short optical pulse repeats 0 and π for each pulse.

[0067] The one-pulse delay MZ interferometer 53 is an MZ interferometer that splits the optical pulse into two and then combines it with a waveguide that is delayed by one pulse. It may be possible to delay more than one pulse. It measures the interference amount of the short optical pulse phase-modulated by the phase modulation unit 52.

[0068] The delay amount generation unit 54 generates a delay amount of the second drive signal relative to the first drive signal based on an electrical signal obtained by converting the optical output of the one-pulse delay MZ interferometer 53. The delay unit 3 (FIG. 1) delays the first drive signal by the delay amount generated by the delay amount generation unit 54.

[0069] 9 is a flowchart showing the operation procedure of the optical short pulse generation device 50 (FIG. 8). The operation procedure of the optical short pulse generation device 50 differs from that of the optical short pulse generation device 30 only in that steps S10 to S11 are replaced with steps S50 to S53.

[0070] The different operational steps will be described with reference to FIG.

[0071] The phase modulation unit 52 adjusts the amount of phase modulation (step S50) so that the output of the one-pulse delay MZ interferometer 53 becomes maximum (Yes in step S51).

[0072] The delay amount generating unit 54 generates a delay amount (step S52) so that the extinction ratio of the one-pulse delay MZ interferometer 53 becomes maximum (Yes in step S53).

[0073] Figure 10(a) shows a schematic diagram of the variation in the amount of phase modulation when the extinction ratio is poor. Figure 10(b) shows a schematic diagram of the variation in the amount of phase modulation when the extinction ratio is good. As can be seen, when the extinction ratio is poor, the amount of phase modulation of the phase π increases.

[0074] As described above, the delay adjustment unit 5 (FIG. 3) includes a phase modulation unit 52 that modulates the phase of an optical short pulse, a one-pulse delay MZ interferometer 53 that receives the optical short pulse via the phase modulation unit 52 as input, and a delay amount generation unit 54 that generates a delay amount based on the output of the one-pulse delay MZ interferometer 53. This makes it possible to generate optical short pulses with a constant pulse width, chirp, and amount of phase modulation, and in particular to reduce variations in the amount of phase modulation.

[0075] The minimum configuration of an optical short pulse generator according to the present invention is the configuration of the first embodiment ( FIG. 1 ). Specifically, optical short pulse generator 10 includes a first optical intensity modulator 2 that outputs optical pulses obtained by modulating the signal intensity of an optical carrier output by light source 1 in correspondence with the magnitude of a first drive signal centered around an operating bias point α; a delay unit 3 that generates a second drive signal by delaying the first drive signal by half a period; and a second optical intensity modulator 4 that outputs optical short pulses obtained by modulating the signal intensity of an optical pulse in correspondence with the magnitude of the second drive signal centered around the operating bias point α. This makes it possible to provide an optical short pulse generator that can generate optical short pulses with little variation in pulse width, chirp, and phase modulation amount.

[0076] Furthermore, the simplest method for generating optical short pulses according to the present invention includes a first 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 first drive signal centered on an operating bias point, a delay step of generating a second drive signal by delaying the first drive signal by half a period, and a second optical intensity modulation step of outputting optical short pulses obtained by modulating the signal intensity of the optical pulses in correspondence with the magnitude of the second drive signal centered on an operating bias point. This makes it possible to provide an optical short pulse generator capable of generating optical short pulses with little variation in pulse width, chirp, and phase modulation amount.

[0077] The control unit (not shown) and delay adjustment unit 5 of optical short pulse generation device 10 can be realized by a general-purpose computer system as shown in Fig. 11. For example, in a general-purpose computer system including a CPU 90, memory 91, storage 92, communication unit 93, input unit 94, and output unit 95, the CPU 90 executes a predetermined program loaded onto memory 91, thereby realizing the functions of the control unit and delay adjustment unit 5 of optical short pulse generation device 10. The predetermined program can be recorded on a computer-readable recording medium such as an HDD, SSD, USB memory, CD-ROM, DVD-ROM, or MO, or can be distributed via a network. Note that a GPU may be used instead of a CPU.

[0078] In the above embodiment, the first drive signal and the second drive signal are directly input to the first and second optical intensity modulators 2 and 4, respectively. However, the present invention is not limited to this example. The first and second drive signals may be input to the first and second optical intensity modulators 2 and 4 via an amplifier (not shown). The same applies to the relationship between the phase modulation unit 52 and the delay unit 51 shown in FIG. 8. Furthermore, a directional coupler-type optical intensity modulator may be used instead of the MZ-type optical intensity modulator.

[0079] 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]

[0080] 1: Light source 2: First optical intensity modulator 3,51: Delay section 4: Second optical intensity modulator 5: Delay adjustment section 6: Optical coupler 10, 20, 30, 40, 50: Optical short pulse generator 52: Phase modulation section 53:1 pulse delay MZ interferometer 54: Delay amount generation unit

Claims

1. a first 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 first drive signal centered on an operating bias point; a delay unit that generates a second drive signal by delaying the first drive signal by half a period; a second optical intensity modulator that outputs an optical short pulse obtained by modulating the signal intensity of the optical pulse in accordance with the magnitude of the second drive signal around an operating bias point, the first optical intensity modulator and the second optical intensity modulator have similar chirp characteristics; Optical short pulse generator.

2. a delay adjusting unit that increases or decreases the delay amount by which the first drive signal is delayed by the delay unit; The optical short pulse generating device according to claim 1 .

3. The delay adjustment unit The delay amount is adjusted so that the pulse width of the optical short pulse is constant. The optical short pulse generating device according to claim 2 .

4. The delay adjustment unit The delay amount is adjusted so that the pulse width of the optical short pulse that has passed through the dispersion device is constant. The optical short pulse generating device according to claim 3 .

5. The delay adjustment unit a phase modulator that modulates the phase of the short optical pulse; a one-pulse delay interferometer to which the short optical pulse is input via the phase modulator; a delay amount generating unit that generates the delay amount based on an output of the one-pulse delay interferometer; The optical short pulse generating device according to claim 2 , comprising:

6. A first optical intensity modulation step of outputting an optical pulse by a first optical intensity modulator in which the signal intensity of the optical carrier output by the light source is modulated in accordance with the magnitude of the first drive signal centered on an operating bias point; a delay step of generating a second drive signal by delaying the first drive signal by half a period; a second optical intensity modulation step of outputting an optical short pulse obtained by modulating the signal intensity of the optical pulse by a second optical intensity modulator in accordance with the magnitude of the second drive signal around an operating bias point, the first optical intensity modulator and the second optical intensity modulator have similar chirp characteristics; A method for generating short optical pulses.

7. a delay adjusting step of increasing or decreasing the delay amount by which the first drive signal is delayed; The method for generating short optical pulses according to claim 6 , comprising:

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