JP2009014641A - Timing adjustment device and light sampling device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stabilize for a long time continuously the accuracy of time of light to be measured and pulse light sampling the light to be measured. <P>SOLUTION: A timing adjustment device outputting a phase difference of 2 given pulse lights includes: a variably delaying light section, adjusting the phase difference by delaying at least 1 of the 2 pulse lights; a photoelectric transducer, generating 2 adjustment signals by converting each of the 2 pulse signals with the phase difference adjusted by the variably delaying light unit to electric signals; and a phase comparison section, detecting the phase difference between the 2 adjustment signals and adjusting the delay at the variably delaying light section so that the detected phase difference approaches to a predetermined phase difference. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a timing adjustment device and an optical sampling device. The present invention particularly relates to a timing adjustment device that adjusts and outputs a phase difference between two given pulse lights, and an optical sampling device that is used for measurement of an optical pulse waveform by an optical sampling oscilloscope or the like.

  Optical pulse waveform measurement is not only necessary for evaluating the quality of optical signals at the receiving end in optical communications, but can also be applied to monitoring signal quality at signal repeaters and nodes in optical networks. it can. By the way, with the increase in capacity of optical fiber communication, practical application of a next-generation optical fiber communication system capable of transmitting and receiving signal light at a bit rate of 160 Gb / s or more is being promoted. In order to realize such a large-capacity communication system, an apparatus for measuring the pulse waveform of an optical signal having a high bit rate as described above with high accuracy is indispensable.

As an apparatus for measuring an optical pulse waveform with a bit rate of 160 Gb / s or more, a non-linear optical effect is produced by combining the light to be measured and the pulsed light so as to be incident on a non-linear medium. Is known (see, for example, Patent Document 1).
JP 2006-194842 A

  In the measurement by the above apparatus, in order to measure the pulse waveform of the light to be measured with high time resolution, it is necessary to make the pulse light with a narrower pulse width incident. However, the intensity correlation signal obtained by such a pulse light having a narrow pulse width and the light to be measured has a low signal intensity, so the S / N ratio is low, and as a result, measurement with high sensitivity is difficult.

  Therefore, it is conceivable to amplify the signal intensity of the intensity correlation signal by sampling the intensity correlation signal again with pulse light different from the pulse light. However, in this case, it is necessary to synchronize the intensity correlation signal and the pulsed light with high time accuracy and enter the nonlinear medium. However, it is difficult to stabilize the time accuracy for a long time.

  In order to solve the above-described problem, according to the first aspect of the present invention, there is provided a timing adjustment device that adjusts and outputs the phase difference between two given pulse lights, and includes at least one pulse of the two pulse lights. Two adjustment signals are generated by converting the optical variable delay unit that delays the light and adjusting the phase difference and the two pulse lights whose phase difference is adjusted by the optical variable delay unit into electrical signals. And a photoelectric converter that detects the phase difference between the two adjustment signals and a phase comparison unit that controls a delay amount in the optical variable delay unit so as to bring the detected phase difference closer to a predetermined phase difference An adjustment device is provided.

  According to the second aspect of the present invention, there is provided an optical sampling device for sampling the light to be measured, which is light corresponding to a portion of the light to be measured that has a temporal overlap with the first pulse light to be applied. Are output as the first output light, the first output light, and the second pulse light to be applied have a temporal overlap, the second output is the light amplified from the first output light. A second sampling unit that outputs as light, and a timing adjustment unit that adjusts a phase difference between the first pulsed light and the second pulsed light and inputs the light to the first sampling unit and the second sampling unit. The optical variable delay unit that delays at least one of the first pulse light and the second pulse light to adjust the phase difference, and the first pulse light and the second pulse light that have the phase difference adjusted by the optical variable delay unit , Detecting a phase difference between the first adjustment signal and the second adjustment signal, a photoelectric converter that generates a first adjustment signal and a second adjustment signal obtained by converting at least a part of each into an electric signal; An optical sampling device is provided that includes a phase comparison unit that controls a delay amount in the optical variable delay unit so that the detected phase difference becomes a predetermined phase difference.

  The above summary of the invention does not enumerate all the necessary features of the present invention, and sub-combinations of these feature groups can also be the invention.

  Hereinafter, the present invention will be described through embodiments of the invention. However, the following embodiments do not limit the invention according to the scope of claims, and all combinations of features described in the embodiments are included. It is not necessarily essential for the solution of the invention.

  FIG. 1 is a schematic diagram showing the configuration of the optical sampling device 10. The optical sampling device 10 is a device capable of sampling measured light (signal light) having a pulse waveform. As shown in FIG. 1, the optical sampling device 10 includes a pulsed light output unit 20, a first sampling unit 101, and a second sampling unit. A sampling unit 106, a photoelectric converter 60, and a waveform display 70 are provided. As shown in FIG. 1, the pulsed light output unit 20 includes amplifiers 31 and 32, a pulse width adjustment unit 40, a timing adjustment unit 500, an optical branching unit 80, a laser light source 200, a high-frequency current output unit 260, and a modulation unit 400. And a frequency dividing circuit 410.

  FIG. 2 is a schematic diagram showing the laser light source 200, the high-frequency current output unit 260, the modulation unit 400, and the vicinity of the frequency divider 410 in the pulsed light output unit 20. The laser light source 200 is a pulse light source that outputs single-mode pulsed light, and includes a laser diode 210, a collimating lens 220, a condenser lens 222, a mirror 230, an optical bandpass filter 240, a bias current output unit 250, and a current amplification circuit. 270.

  The high-frequency current output unit 260 is electrically connected to the current amplifier circuit 270 and the frequency divider circuit 410 of the laser light source 200, respectively. The high frequency current output unit 260 outputs a high frequency current having a specific frequency. In addition, the frequency of the high frequency current which the high frequency current output part 260 outputs can be changed as desired.

  The bias current output unit 250 outputs a direct current having a specific magnitude as a bias current. Note that the magnitude of the bias current output from the bias current output unit 250 can be changed as desired. The current amplifying circuit 270 adds a current obtained by superimposing the high-frequency current output from the high-frequency current output unit 260 on the bias current output from the bias current output unit 250 to the laser diode 210.

  The laser diode 210 emits a pulse of laser light (hereinafter referred to as “pulse light”) by the current applied from the current amplification circuit 270. The pair of end faces of the laser diode 210 are a low reflection surface 211 that hardly causes reflection and a high reflection surface 212 with a reflectance of 30% or more, and pulsed light oscillated by the laser diode 210 is transmitted from the low reflection surface 211. Output to the outside of the laser diode 210.

  The collimating lens 220 is disposed on the low reflection surface 211 side of the laser diode 210 and collimates the pulsed light output from the low reflection surface 211 side of the laser diode 210. The mirror 230 has a total reflection surface 232 formed on one surface, and totally reflects the collimated pulsed light on the total reflection surface 232. The optical bandpass filter 240 is disposed on the optical path of the pulsed light between the collimating lens 220 and the mirror 230, and transmits the band component centered on the oscillation wavelength among the spectral components of the pulsed light. The optical bandpass filter 240 is rotatably mounted, and the angle of the transmission surface with respect to the optical path can be changed so that the pulsed light is incident on the transmission surface of the optical bandpass filter 240 from an oblique direction. . Therefore, the optical bandpass filter 240 can set the band of light to be transmitted according to this angle.

  The pulsed light emitted by the laser diode 210 is transmitted through the collimating lens 220 and the optical bandpass filter 240 and totally reflected by the total reflection surface 232 of the mirror 230 as described above, and then again the high reflection of the laser diode 210. Reflected by surface 212. Therefore, the pulsed light reciprocates between the high reflection surface 212 of the laser diode 210 and the total reflection surface 232 of the mirror 230. Here, the interval between the high reflection surface 212 and the total reflection surface 232 is synchronized so that the cycle in which the pulsed light reciprocates between the high reflection surface 212 and the total reflection surface 232 and the pulse emission cycle of the laser diode 210 are synchronized. , The pulsed light is amplified, and a part of the pulsed light is output from the highly reflective surface 212 side of the laser diode 210.

  The condensing lens 222 is disposed on the high reflection surface 212 side of the laser diode 210 and condenses the pulsed light output from the high reflection surface 212 side of the laser diode 210 to enter the optical fiber 290. The optical fiber 290 is connected to the outside of the laser light source 200, and outputs the pulsed light to the outside of the laser light source 200.

The modulation unit 400 is disposed on the optical path of the pulsed light output from the laser light source 200 and is electrically connected to the frequency dividing circuit 410. The frequency dividing circuit 410 divides the high frequency electric signal output from the high frequency current output unit 260 by N (N is a positive integer) and outputs the result to the modulation unit 400. The modulation unit 400 outputs pulsed light obtained by dividing the repetition frequency of the pulsed light by 1 / n according to the frequency of the electric signal input from the frequency dividing circuit 410. Here, the repetition frequency of the pulsed light is defined by the reciprocal of the repetition period of the pulsed light. The modulator 400 is, for example, an LN intensity modulator using a LiNbO ₃ optical waveguide, and can divide the repetition frequency of the pulsed light in response to a high-frequency electric signal having a frequency of about several tens of GHz. it can.

The oscillation wavelength of the laser diode 210, that is, the wavelength of the pulsed light output from the laser light source 200 is blocked by a first color filter 141 described later in the first sampling unit 101 and a second color filter 142 described later in the second sampling unit 106. The wavelength of the band is preferably close to the oscillation wavelength of the light to be measured sampled by the optical sampling device 10. The repetition frequency of the pulsed light output from the laser light source 200 is a frequency for sweeping (Δf) from a frequency obtained by dividing the frequency by N when the frequency of the light to be measured sampled by the optical sampling device 10 is f _0. ) Is preferably shifted frequency.

  The optical splitter 80 receives the pulsed light output from the optical sampling device 10, splits the pulsed light, outputs one of the light to the amplifier 31, and outputs the other to the amplifier 32. As the optical branching device 80, for example, a spectroscope such as a non-polarizing beam splitter is used. In the following, among the pulsed light split by the optical splitter 80, the one light input to the amplifier 31 is referred to as a first pulse light, and the other light input to the amplifier 32 is referred to as a second pulse. Called light.

  The amplifier 31 amplifies the peak intensity of the first pulse light when the first pulse light split by the optical splitter 80 is input. The amplifier 32 amplifies the peak intensity of the second pulse light when the second pulse light split by the optical splitter 80 is input. As the amplifier 31 and the amplifier 32, for example, an erbium-doped optical fiber amplifier (EDFA) is used.

  The pulse width adjustment unit 40 includes a spectrum spreading unit 42 and a pulse compression unit 44, and adjusts the pulse width of the first pulse light. For example, a highly nonlinear fiber (HNLF) is used for the spectrum spreading unit 42, and self-phase modulation is generated in the first pulse light whose peak intensity is amplified by the amplifier 31 to spread the spectrum. Further, a single mode fiber (SMF) is used for the pulse compression unit 44, and the pulse width of the first pulse light whose spectrum is diffused in the spectrum spreading unit 42 is reduced by dispersion compensation. The length of the highly nonlinear fiber used for the spread spectrum unit 42 and the length of the single mode fiber used for the pulse compression unit 44 are, for example, 10 m for the former and 15 m for the latter.

  FIG. 3 shows the result of a non-linear transmission simulation in which the pulse width of the first pulse light input from the spectrum spreading unit 42 side in the pulse width adjustment unit 40 is compressed. In FIG. 3, “A” indicates a time waveform and a spectrum waveform of the first pulse light input to the spectrum spreading unit 42. “B” indicates a time waveform and a spectrum waveform of the first pulsed light output from the spectrum spreading unit 42 and input to the pulse compression unit 44. “C” indicates a time waveform and a spectrum waveform of the first pulse light output from the pulse compression unit 44. As shown in FIG. 3, the time width of the first pulse light is compressed to about 0.7 psec by the pulse width adjustment unit 40. As described above, the pulse width adjustment unit 40 can compress and output the pulse width of the first pulse light to the order of sub-picoseconds.

  FIG. 4 is a diagram illustrating a configuration of the timing adjustment unit 500. As shown in FIG. 4, the timing adjustment unit 500 includes a first optical coupler 511, a second optical coupler 512, a first photoelectric converter 521, a second photoelectric converter 522, amplifiers 531, 532, 1 filter 541, second filter 542, variable optical delay unit 600, and phase comparison unit 700. The timing adjustment unit 500 adjusts the phase difference between the first pulse light output from the pulse width adjustment unit 40 and the second pulse light output from the amplifier 32 and inputs the phase difference to the first sampling unit 101 and the second sampling unit 106. .

  The first optical coupler 511 inputs a part of the first pulse light output from the pulse width adjustment unit 40 to the first photoelectric converter 521. The first photoelectric converter 521 generates a first adjustment signal by converting one of the first pulse lights dispersed by the first optical coupler 511 into an electric signal. The amplifier 531 amplifies the first adjustment signal generated by the first photoelectric converter 521 and outputs the amplified signal to the first filter 541. The first filter 541 removes a frequency component smaller than a predetermined frequency in the first adjustment signal, and inputs it to the phase comparison unit 700. Specifically, when the repetition period of the first pulsed light output from the pulse width adjustment unit 40 is 156.25 MHz, the first filter 541 includes the first component of the frequency components included in the first adjustment signal. The third-order (468.75 MHz) or fifth-order (781.25 MHz) harmonic of the repetition period (156.25 MHz) of the pulsed light is selectively transmitted, and frequency components other than the frequency of the transmitted harmonic are absorbed. .

  The second optical coupler 512 inputs a part of the second pulsed light output from the optical variable delay unit 600 described later to the second photoelectric converter 522. The second photoelectric converter 522 generates a second adjustment signal by converting one second pulsed light split by the second optical coupler 512 into an electric signal. The amplifier 532 amplifies the second adjustment signal generated by the second photoelectric converter 522 and outputs the amplified signal to the second filter 542. The second filter 542 removes a frequency component smaller than a predetermined frequency in the second adjustment signal, and inputs it to the phase comparison unit 700. Specifically, the second filter 542 is included in the second adjustment signal when the repetition period of the second pulse light output from the optical variable delay unit 600 is 156.25 MHz as in the first pulse light. Of the frequency components, the harmonics having the same frequency as the harmonics transmitted by the first filter 541 are transmitted, and the frequency components other than the frequencies of the transmitted harmonics are absorbed.

  FIG. 5 is a diagram illustrating a configuration of the optical variable delay unit 600. As illustrated in FIG. 5, the optical variable delay unit 600 includes a first delay unit 610 and a second delay unit 620.

  The first delay unit 610 includes fixed reflection surfaces 611 and 612 and a movable reflection surface 615. In the first delay unit 610, the fixed reflection surface 611 is fixedly disposed on the optical path of the second pulse light output from the amplifier 32, and reflects the second pulse light toward the movable reflection surface 615. The movable reflecting surface 615 reflects the second pulse light reflected by the fixed reflecting surface 611 toward the fixed reflecting surface 612. The fixed reflection surface 612 inputs the second pulse light reflected by the movable reflection surface 615 to the optical fiber 621 of the second delay unit 620.

  Here, the movable reflective surface 615 moves in a direction in which the movable reflective surface 615 moves away from (or approaches) the fixed reflective surface 611 and the fixed reflective surface 612, so that the movable reflective surface 615, the fixed reflective surface 611, and the fixed reflective surface 612 are moved. The distance between them (hereinafter abbreviated as “distance between reflecting surfaces”) can be changed by, for example, a stroke having a size “L”. Therefore, the first delay unit 610 can change the optical path length from the input second pulsed light from the fixed reflecting surface 611 to the fixed reflecting surface 612 through the movable reflecting surface 615 by a maximum size “2L”. . Accordingly, the first delay unit 610 can delay the second pulse light input to the second sampling unit 106 by increasing the optical path length by an amount corresponding to the increase in the optical path length. The distance between the reflection surfaces in the first delay unit 610 is set to a predetermined value by, for example, manually moving the movable reflection surface 615 in the initial setting of the timing adjustment unit 500 when the optical sampling device 10 is used for sampling the light to be measured. Set to the size (initial setting value). This initial set value will be described later. The movable reflecting surface 615 has a driving mechanism (not shown) such as a motor, and is moved by a control signal input from the control unit 730 of the phase comparison unit 700 described later. Note that the first delay unit 610 is not limited to the form shown above and shown in FIG. The first delay unit 610 may include, for example, two collimating lenses that are arranged at an interval on the optical path of the second pulse light output from the amplifier 32. In this case, the second pulse light propagated through the optical fiber from the amplifier 32 is diffused and output from the optical fiber toward one lens surface of the two collimating lenses, and then the one collimating lens. Is converted into parallel light. Further, the second pulse light converted into the parallel light propagates in the air, for example, enters the other lens surface of the two collimating lenses, and then enters an optical fiber 621 (described later) in the second delay unit 620. Input at the end. Here, the first delay unit 610 has a configuration in which the interval between the two collimating lenses is changed, and the optical path length of the second pulsed light can be changed by changing the interval.

  The second delay unit 620 includes an optical fiber 621, a piezo element 622, electrodes 623 and 624, and a high voltage power source 625. In the second delay unit 620, the optical fiber 621 is wound around a substantially cylindrical piezo element 622. More specifically, the optical fiber 621 is fixed to the electrode 623 disposed on the outer peripheral surface of the substantially cylindrical piezo element 622. An electrode 624 is disposed on the inner peripheral surface of the piezo element 622. The high-voltage power source 625 is a DC voltage source whose output voltage is variable, for example, in the range of 0 to 2 kV, and one of the positive and negative output terminals is connected to the electrode 623 and the other output terminal is connected to the electrode 624. To do. The high voltage power source 625 applies a voltage having a magnitude corresponding to the magnitude of the control voltage input from the control voltage output unit 720 of the phase comparison unit 700 described later between the electrode 623 and the electrode 624.

  The piezo element 622 is deformed according to the magnitude of the voltage applied between the electrode 623 and the electrode 624. Specifically, when the voltage is applied to the piezo element 622, the radius of the cross section changes in accordance with the magnitude of the voltage. In this case, since the area of the outer peripheral surface on which the electrode 623 is disposed in the piezo element 622 also changes, the length of the optical fiber 621 fixed to the electrode 623 also changes accordingly. As a result, the optical path length of the second pulsed light passing through the optical fiber 621 changes.

  As described above, the second delay unit 620 applies the control voltage between the electrode 623 and the electrode 624, so that the optical path length of the second pulsed light passing through the optical fiber 621 in accordance with the magnitude of the voltage. Can be changed. Therefore, for example, the second pulse light input to the second sampling unit 106 can be delayed by an amount corresponding to the increase in the optical path length. The second delay unit 620 changes the optical path length of the second pulse light by extending or contracting the optical fiber 621 by deformation of the piezo element 622. Therefore, the optical path of the second pulse light by the reciprocating movement of the movable reflecting surface 615. The timing at which the second pulse light is input to the second sampling unit 106 can be delayed or advanced with a finer resolution than the first delay unit 610 that changes the length.

  FIG. 6 is a diagram illustrating a configuration of the phase comparison unit 700. As shown in FIG. 6, the phase comparison unit 700 includes a phase difference detection unit 710, a control voltage output unit 720, and a control unit 730. The phase comparison unit 700 includes a first adjustment signal and a second adjustment signal that are input. The phase difference between the two adjustment signals is detected, and the delay amount in the optical variable delay unit 600 is controlled so that the detected phase difference approaches a predetermined phase difference.

  The phase difference detection unit 710 includes a first flip-flop 711, a second flip-flop 712, and an AND circuit 715, and detects a phase difference between the input first adjustment signal and the second adjustment signal. Specifically, the first flip-flop 711 outputs the logic H to the control voltage output unit 720 when the signal level of the first adjustment signal input from the first filter 541 becomes a signal level corresponding to the logic H. And output to the AND circuit 715. The second flip-flop 712 also outputs the logic H to the control voltage output unit 720 and the AND circuit when the signal level of the second adjustment signal input from the second filter 542 becomes a signal level corresponding to the logic H. Output to 715. The AND circuit 715 resets the outputs of the first flip-flop 711 and the second flip-flop 712 to logic L when both the first flip-flop 711 and the second flip-flop 712 output logic H.

  In the phase difference detection unit 710, the first adjustment signal and the second adjustment signal are between the timing at which the first flip-flop 711 outputs logic H and the timing at which the second flip-flop 712 outputs logic H. A time lag of a magnitude corresponding to the phase difference occurs. Further, as described above, the first flip-flop 711 and the second flip-flop 712 are reset from the state of outputting the logic H at the same timing to the state of outputting the logic L. Therefore, the magnitude of the above time shift is substantially equal to the difference in time width in which the logic H is continuously output until the first flip-flop 711 and the second flip-flop 712 are reset. The difference between the output time widths of the first flip-flop 711 and the second flip-flop 712 is that the first pulse light split by the first optical coupler 511 and the second optical coupler 512 of the timing adjusting unit 500 are split. This corresponds to the phase difference with the second pulsed light. Therefore, the phase difference detection unit 710 converts the phase difference between the first pulse light and the second pulse light into a difference in output time width corresponding to the phase difference, and outputs it to the control voltage output unit 720. The control voltage output unit 720 outputs a voltage having a magnitude corresponding to each logic value of logic H and logic L.

  The control voltage output unit 720 includes capacitors 721 and 722, a comparator 725, and an offset voltage application unit 727, and outputs a control voltage corresponding to the difference between the phase difference between the two adjustment signals and a predetermined phase difference. Output. Specifically, a voltage having a magnitude corresponding to the logic H is input to the capacitor 721 for the time width during which the first flip-flop 711 continuously outputs the logic H, and the second flip-flop When a voltage having a magnitude corresponding to the logic H is input to the capacitor 722 for the time width in which the logic 712 continuously outputs the logic H, the time of the input voltage is input to the capacitor 721 and the capacitor 722, respectively. A voltage having a magnitude corresponding to the width is generated.

  The comparator 725 compares the magnitudes of the voltages generated in the capacitor 721 and the capacitor 722 and outputs a voltage having a magnitude corresponding to the difference in the magnitude of the voltage to the offset voltage applying unit 727. Here, the magnitude of the voltage output from the comparator 725 is a magnitude corresponding to the phase difference between the first adjustment signal and the second adjustment signal. The offset voltage application unit 727 outputs a control voltage obtained by adding an offset voltage having a predetermined magnitude to the voltage output from the comparator 725 to the second delay unit 620 and the control unit 730.

  Here, the magnitude of the offset voltage applied by the offset voltage application section 727 is a predetermined magnitude (initial setting value) in the initial setting of the timing adjustment section 500 when the optical sampling device 10 is used for sampling the light to be measured. ). This initial set value will be described later. In this case, the control voltage output from the offset voltage application unit 727 is a voltage that fluctuates within a certain range according to the phase difference between the first adjustment signal and the second adjustment signal with the offset voltage as the center. .

  The control unit 730 detects the control voltage output from the control voltage output unit 720, and determines whether the control voltage is approximately the center of a predetermined voltage range, that is, whether the control voltage is close to the offset voltage. Determine. Here, when the control voltage is a value greatly different from the offset voltage, a control signal is output to the first delay unit 610 of the optical variable delay unit 600 in order to bring the control voltage close to the offset voltage.

  When a control signal is input from the control unit 730, the first delay unit 610 drives the movable reflection surface 615 according to the control signal to change the distance between the reflection surfaces, thereby causing the second sampling unit 106 to The amount of delay given to the input second pulse light is changed. As a result, the phase difference generated between the first pulse light input to the first sampling unit 101 and the second pulse light input to the second sampling unit 106 changes. As described above, the control unit 730 controls the delay amount of the first delay unit 610 for each predetermined period in order to bring the control voltage close to the offset voltage. When the control voltage is input from the control voltage output unit 720, the second delay unit 620 changes the length of the optical path length of the second pulsed light according to the magnitude of the control voltage, as described above. By doing so, the second pulsed light input to the second sampling unit 106 can be delayed or advanced.

  Thus, the phase comparison unit 700 detects the phase difference between the two adjustment signals, the first adjustment signal and the second adjustment signal, and brings the detected phase difference close to a predetermined phase difference. By outputting a control signal and a control voltage to the optical variable delay unit 600, the phase difference between the first pulse light split by the first optical coupler 511 and the second pulse light split by the second optical coupler 512 is constant. It is possible to control the amount of delay that the optical variable delay unit 600 gives to the second pulsed light so as to be held at the same time. Therefore, the optical sampling device 10 including the timing adjustment unit 500 including the optical variable delay unit 600 and the phase comparison unit 700 is input to the first pulse light input to the first sampling unit 101 and the second sampling unit 106. The time accuracy of these two pulsed lights based on the phase difference from the second pulsed light can be stabilized continuously for a long time.

  Further, the phase comparison unit 700 uses the first adjustment light and the second adjustment signal generated from the first pulse light and the second pulse light as described above to use the first pulse light and the second adjustment signal. The phase difference of the second pulse light is detected. Therefore, the detection resolution is improved as compared with the case where the phase difference is detected from the repetition frequency of the first pulse light and the second pulse light.

  Further, even when the timing adjustment unit 500 holds the phase difference between the first pulse light and the second pulse light at a predetermined phase difference, for example, the optical path of the first pulse light due to environmental changes such as temperature over time. The length may change. In such a case, the control voltage output from the offset voltage application unit 727 may deviate greatly from the offset voltage. However, the control unit 730 of the phase comparison unit 700 detects the voltage shift for each predetermined period, and the optical variable delay unit 600 uses the control signal based on the detection result to detect the first pulse of the second pulse light. The phase difference with respect to light can be controlled.

  In the present embodiment, it is preferable that the optical path length from the first optical coupler 511 to the first sampling unit 101 is substantially equal to the optical path length from the second optical coupler 512 to the second sampling unit 106. Further, for example, an optical variable delay unit similar to the optical variable delay unit 600 may be provided between the pulse width adjustment unit 40 and the first optical coupler 511 on the optical path of the first pulse light. In this case, the phase difference between the first pulsed light and the second pulsed light can be controlled separately.

  FIG. 7 is a block diagram illustrating a configuration of the first sampling unit 101. FIG. 8 is a schematic diagram showing how the first sampling unit 101 samples the measured light with the first pulsed light. As shown in FIG. 7, the first sampling unit 101 includes a first input side polarization control unit 111, an optical coupler 118, a first optical fiber 121, a first output side polarization unit 131, and a first color filter 141. Of the light to be measured input from the outside, light corresponding to a portion having a temporal overlap with the first pulsed light input from the pulsed light output unit 20 is output as the first output light.

  The first input side polarization control unit 111 includes a polarization control element 113 and a polarization control element 114. Light to be measured input from the outside to the first sampling unit 101 is input to the polarization control element 113. Further, the first pulsed light output from the pulsed light output unit 20 and input to the first sampling unit 101 is input to the polarization control element 114. The first input side polarization control unit 111 converts the measured light input to the polarization control element 113 and the first pulse light input to the polarization control element 114 into linearly polarized light whose polarization directions are at an angle of 40 to 50 degrees. Each polarization direction is controlled so that it becomes. The light under measurement and the first pulsed light whose polarization directions are controlled by the first input side polarization control unit 111 are output from the polarization control element 113 and the polarization control element 114 to the optical coupler 118, respectively.

  In FIG. 7, on the output side of the polarization control element 113 and the polarization control element 114, the polarization directions of the light to be measured and the first pulse light output from them are indicated by the directions of arrows surrounded by circles. As shown in FIG. 7, in this embodiment, the polarization directions of the light to be measured and the first pulsed light output from the polarization control element 113 and the polarization control element 114 of the first input side polarization control unit 111 are substantially the same. It has an angle of 45 degrees. At this time, the polarization direction of the light to be measured output from the polarization control element 113 is substantially horizontal, and the polarization direction of the first pulsed light output from the polarization control element 114 is approximately 45 degrees with respect to the horizontal direction. Have an angle of

  The optical coupler 118 combines the measured light output from the polarization control element 113 and the first pulsed light output from the polarization control element 114 and outputs the combined light to the first optical fiber 121. As the optical coupler 118, for example, a half mirror or a beam splitter is used.

  The first optical fiber 121 has an optical Kerr effect and a four-wave wave between the light to be measured and the first pulsed light when they pass through the light with at least partly overlapping in time. Produces nonlinear optical effects including mixing. More specifically, as shown in FIG. 8, when the specific pulse of the light to be measured passing through the inside of the first optical fiber 121 and the specific pulse of the first pulse light overlap at least partially in time. The pulse of the light to be measured has a polarization direction substantially the same as the polarization direction of the pulse of the first pulse light by rotating the polarization axis by the optical Kerr effect. As the first optical fiber 121, for example, a highly nonlinear fiber having an average zero dispersion wavelength substantially equal to the wavelength of the first pulsed light and a nonlinear constant of about 20 (/ W / km) is used.

  Here, the rotation of the polarization axis as described above in the measured light does not occur in the entire measured light, but occurs only in a portion where the measured light and the first pulse light overlap in time. Therefore, for example, when the pulse width of the pulse of the first pulse light is shorter than the pulse width of the pulse of the light to be measured, only a part of the pulse of the light to be measured that overlaps with the pulse of the first pulse light in time Thus, the polarization axis rotates, and the polarization direction becomes substantially the same polarization direction as the first pulsed light.

FIG. 9 illustrates the intensity of light passing through the positions indicated by the circled numbers 1 to 4 in the block diagram of the first sampling unit 101 illustrated in FIG. Shown for each frequency. In FIG. 9, the horizontal axis represents the optical frequency, and ω ₀ , ω _1, and ω ₂ are the optical frequencies of the first pulsed light, the measured light (circled number 4 is the first output light), and the idler light, respectively. Indicates. In FIG. 9, the length of the arrow extending in the direction orthogonal to the horizontal axis represents the light intensity at each optical frequency.

  When the intensity of the first pulse light is very large compared to the light to be measured, as shown in the circled numbers 2 and 3 in FIG. 9, as described above in the light to be measured that passes through the first optical fiber 121. The intensity of the portion where the polarization axis rotates, that is, the portion of the light to be measured that overlaps the first pulsed light in time is amplified. This is because the portion of the light to be measured is amplified in the first optical fiber 121 by optical parametric amplification by four-wave mixing. Here, the light in which the portion of the light to be measured is amplified by optical parametric amplification is linearly polarized light having the same optical frequency (wavelength) as that of the light to be measured, and the polarization direction is substantially the same as the polarization direction of the first pulsed light. The same direction. Therefore, the polarization direction of the amplified portion in the light to be measured has an angle of 45 degrees with respect to the horizontal direction.

  As described above, when there is a portion having a temporal overlap in the light to be measured and the first pulsed light passing through the first optical fiber 121, the portion in the light to be measured that has passed through the first optical fiber 121 is The intensity of the light is amplified in substantially the same polarization direction as the one-pulse light. The intensity of the amplified portion of the measured light has a correlation with the intensity of the portion of the measured light before amplification when the intensity of the first pulse light is constant.

  Further, as described above, when there is a portion where the measured light and the first pulsed light passing through the first optical fiber 121 have temporal overlap with each other, as shown in FIG. 9, the measured light and the first pulse Idler light having a temporal overlap with the above portion of light is newly generated by four-wave mixing. The idler light is generated as linearly polarized light having substantially the same polarization direction as the first pulsed light. Therefore, the polarization direction of the idler light has an angle of about 45 degrees with respect to the horizontal direction. The intensity of the idler light is the same as that of the portion of the light to be measured amplified by rotating the polarization direction in substantially the same direction as the polarization direction of the first pulsed light. Therefore, the intensity of the idler light also has a correlation with the intensity before amplification of the portion of the light to be measured when the intensity of the first pulse light is constant.

Further, the difference between the optical frequency ω _{1 of the} measured light and the optical frequency ω ₀ of the first pulsed light is the difference between the optical frequency ω _{2 of the} idler light and the optical frequency ω ₀ of the first pulsed light. equal.

  The first output side polarization unit 131 includes a polarization element 133 disposed on the optical path of light passing through the first optical fiber 121. The polarizing element 133 absorbs light having a horizontal polarization component in incident light and transmits light having a vertical component (a direction perpendicular to the horizontal direction). Therefore, as shown in FIG. 8, the vertical component of the first pulsed light that has passed through the first optical fiber 121 passes through the polarizing element 133. Further, the portion of the measured light that has passed through the first optical fiber 121 that is not temporally overlapped with the first pulsed light in the first optical fiber 121 is absorbed by the polarization element 133.

  On the other hand, the portion of the measured light that overlaps the first pulsed light in time in the first optical fiber 121 is substantially the same in the polarization direction as the first pulsed light as described above, that is, substantially in the horizontal direction. Since it rotates in the direction of 45 degrees, the vertical component passes through the polarizing element 133. Further, the idler light generated in the first optical fiber 121 has the same polarization direction as the polarization direction of the first pulsed light, and thus the vertical component is transmitted through the polarization element 133.

Characteristics first color filter 141, which is disposed on the optical path of the light transmitted through the polarizing element 133 of the first output-side polarization unit 131, transmits only light of wavelengths in the same band as the wavelength lambda ₁ of the light to be measured Have Therefore, the components of the first pulse light and the idler light, which are light having a wavelength different from the wavelength λ _{1 of the} light to be measured, among the light transmitted through the polarizing element 133 are absorbed by the first color filter 141, and the light to be measured Only the component having the same wavelength as the wavelength λ ₁ (optical frequency ω ₁ ) of the first color filter 141 is transmitted. Hereinafter, the light transmitted through the first color filter 141 is referred to as first output light.

The first color filter 141 may have a characteristic of transmitting only light having a wavelength in the same band as the wavelength λ _{2 of the} idler light. In this case, since the first pulse light and the component of the light to be measured are absorbed by the first color filter 141, the component of the idler light transmitted through the first color filter 141 becomes the first output light. Even in this case, since the intensity and wavelength of the idler light have a correlation with the measured light as described above, the first output light composed of the idler light component can be made to correspond to the measured light.

  As described above, in the first sampling unit 101, a portion of the measured light that does not overlap with the first pulsed light in the first optical fiber 121 is absorbed by the polarizing element 133. Therefore, the SN ratio of the first output light obtained by sampling the pulse waveform of the light to be measured can be further increased.

  Further, for example, when the pulsed light output unit 20 outputs sub-picosecond order pulsed light as the first pulsed light, the first sampling unit 101 samples the measured light with the first pulsed light having a very short pulse width. Therefore, the time resolution of sampling of the light to be measured in the first sampling unit 101 can be increased to the order of subpicoseconds.

  FIG. 10 is a block diagram illustrating a configuration of the second sampling unit 106. In FIG. 10, the direction of the arrow surrounded by a circle indicates the polarization direction of the first output light and the second pulsed light output from the polarization control element 115 described later. FIG. 11 is a schematic diagram showing a state in which the first output light is optically parametrically amplified by the second pulsed light in the second sampling unit 106. As shown in FIG. 10, the second sampling unit 106 includes a second input side polarization control unit 112, an optical coupler 119, a second optical fiber 122, and a second color filter 142, and inputs from the first sampling unit 101. The first output light is amplified when the first output light and the second pulse light input from the timing adjustment unit 500 of the pulse light output unit 20 to the second sampling unit 106 have a temporal overlap. Light is output as the second output light.

  The second input side polarization control unit 112 includes a polarization control element 115. The polarization control element 115 receives the second pulsed light output from the timing adjustment unit 500 of the pulsed light output unit 20 and input to the second sampling unit 106. The second input side polarization controller 112 controls the polarization direction of the second pulse light so that the polarization direction of the second pulse light input to the polarization control element 115 is substantially the same as the polarization direction of the first output light. . In the present embodiment, since the polarization direction of the first output light is the vertical direction, the second input side polarization control unit 112 receives the second pulse light input to the polarization control element 115 and the polarization direction thereof is substantially vertical. Control to be in the direction.

  The second pulsed light whose polarization direction is controlled by the second input side polarization control unit 112 is output from the polarization control element 115 toward the optical coupler 119. Note that the second input side polarization control unit 112 does not have to be the case where the polarization direction of the second pulsed light output from the pulsed light output unit 20 is substantially the same as the polarization direction of the first output light. In this case, the number of parts of the first sampling unit 101 can be reduced. The optical coupler 119 combines the first output light and the second pulsed light output from the polarization control element 115 and outputs the combined light to the second optical fiber 122. As the optical coupler 119, for example, a half mirror or a beam splitter is used.

  The first output light and the second pulse light combined by the optical coupler 119 are input to the second optical fiber 122. Here, due to the initial setting of the timing adjustment unit 500, the second pulse light input to the second sampling unit 106 has a temporal overlap between the first output light and the second optical fiber 122. Specifically, in the initial setting, the initial setting value of the distance between the reflection surfaces in the first delay unit 610 of the optical variable delay unit 600 and the initial offset voltage applied by the offset voltage application unit 727 of the control voltage output unit 720 are used. The set value is set such that the second pulsed light input from the optical variable delay unit 600 to the second sampling unit 106 has a temporal overlap with the first output light in the second optical fiber 122.

FIG. 12 shows the intensity of light that passes through the positions indicated by the numbers 5 to 7 in the block diagram of the second sampling unit 106 shown in FIG. Is shown for each optical frequency. In FIG. 12, the horizontal axis represents the optical frequency, and ω ₀ , ω ₁ and ω ₂ are the light of the second pulse light, the first output light (circled number 7 is the second output light), and the idler light, respectively. Indicates the frequency. In FIG. 12, the length of the arrow extending in the direction orthogonal to the horizontal axis represents the intensity of light at each optical frequency.

  The second optical fiber 122 generates four-wave mixing, which is a nonlinear optical effect, between the first output light and the second pulsed light that pass through the inside with a temporal overlap. When the intensity of the second pulse light is very large compared to the first output light, it overlaps in time with the second pulse light in the first output light as shown by the circled numbers 5 and 6 in FIG. The intensity of the portion is amplified. This is because the portion of the first output light is amplified in the second optical fiber 122 by optical parametric amplification by four-wave mixing. In the second optical fiber 122, like the first optical fiber 121 and the first optical fiber 121, for example, the mean zero dispersion wavelength is substantially the same as the wavelength of the second pulse light, and the nonlinear constant is about 20 (/ W / km). Some highly nonlinear fiber is used.

  As described above, the first output light that has passed through the second optical fiber 122 becomes light whose intensity is amplified in substantially the same polarization direction as that of the second pulse light. Note that the intensity of the amplified first output light has a correlation with the intensity of the first output light before being amplified when the intensity of the second pulse light is constant.

  Also, as shown in FIG. 12, in the second optical fiber 122, idler light having a temporal overlap with the first output light and the second pulse light is newly generated by four-wave mixing. The idler light is generated as linearly polarized light having substantially the same polarization direction as the first output light and the second pulse light. Therefore, the polarization direction of the idler light has a substantially vertical angle. The intensity of the idler light is the same as that of the first output light amplified by the optical parametric amplification. Therefore, the intensity of the idler light also has a correlation with the intensity of the first output light before being amplified when the intensity of the second pulse light is constant.

The difference between the optical frequency ω ₁ of the first output light and the optical frequency ω ₀ of the second pulse light is the difference between the optical frequency ω _{2 of the} idler light and the optical frequency ω ₀ of the second pulse light. Is equal to

The second color filter 142 is disposed on the optical path of the light that has passed through the second optical fiber 122 and has a characteristic of transmitting light having a wavelength in the same band as the wavelength of the first output light. Accordingly, of the light passing through the second optical fiber 122, components of the second pulse light and the idler light is light having a wavelength lambda ₁ and different from the wavelength of the first output light is absorbed by the second color filter 142, Only the component having the same wavelength as the wavelength λ ₁ (optical frequency ω ₁ ) of the first output light passes through the second color filter 142. Hereinafter, the light transmitted through the second color filter 142 is referred to as second output light.

The second color filter 142 may have a characteristic of transmitting only light having a wavelength in the same band as the wavelength λ _{2 of the} idler light. In this case, since the second pulse light and the first output light component are absorbed by the second color filter 142, the idler light component transmitted through the second color filter 142 becomes the second output light. Even in this case, since the intensity and wavelength of the idler light have a correlation with the light to be measured as described above, the second output light composed of the component of the idler light can be made to correspond to the light to be measured.

When the first output light output from the first sampling unit 101 is a component of idler light generated in the first optical fiber 121 as described above, the wavelength of the first output light is λ ₂ (optical frequency ω _2). Therefore, in the second optical fiber 122, four-wave mixing that occurs between the second pulsed light having the wavelength λ ₀ (optical frequency ω ₀ ) and the first output light having the wavelength λ ₂ (optical frequency ω ₂ ). The wavelength of the generated idler light is λ ₁ (optical frequency ω ₁ ).

  As described above, the second sampling unit 106 can increase the intensity of the first output light input from the first sampling unit 101 by amplifying the first output light in the second optical fiber 122 by optical parametric amplification. Therefore, even when the intensity of the first output light obtained by sampling the light to be measured by the first sampling unit 101 is small, the signal to be measured is not reduced without reducing the SN ratio of the second output light to the first output light. It is possible to amplify the intensity of the second output light, which is light sampling output light, and output it.

  Further, as described above, the second sampling unit 106 includes the second input side polarization control unit 112 so that the polarization direction of the second pulse light and the polarization direction of the first output light are substantially the same. I have control. Therefore, the amplification efficiency when the first output light is amplified by the optical parametric amplification by the four-wave mixing in the second optical fiber 122 is substantially maximized, and the gain in sampling the measured light can be further increased.

  The photoelectric converter 60 is arranged on the optical path of the light transmitted through the second color filter 142, receives the second output light, converts it into an electrical signal corresponding to the time-intensity component, and outputs it to the waveform display 70. To do. For the photoelectric converter 60, for example, a photoelectric conversion element such as a photodiode is used. At this time, it is preferable that the wavelength of the light with the best sensitivity in the photoelectric converter 60 substantially coincides with the wavelength of the second output light. The waveform display unit 70 is electrically connected to the photoelectric converter 60 and displays the electric signal according to the repetition period.

  As described above, the optical sampling apparatus 10 includes the first sampling unit 101 that can sample the measured light with high time resolution, and the first output that is the sampling output obtained by the first sampling unit 101. Since the second sampling unit 106 that efficiently amplifies the light intensity is provided, the pulse waveform of the light to be measured can be observed with high sensitivity and high time resolution.

  In the optical sampling device 10, the first color filter 141 disposed in the first sampling unit 101 is not limited to a form separately disposed on the output side of the first output side polarization unit 131. For example, when the optical coupler 119 of the second sampling unit 106 has a light incident surface for the first output light and a light incident surface for the second pulse light, the first color filter 141 includes the second pulse light in the optical coupler 119. May be formed integrally with the light incident surface.

  FIG. 13 is a block diagram illustrating configurations of the first sampling unit 102 and the second sampling unit 107. The optical sampling apparatus 10 described above and with reference to FIGS. 1 to 12 replaces the first sampling unit 101 and the second sampling unit 106 with the first sampling unit 102 and the second sampling unit 107 shown in FIG. You may prepare. In the first sampling unit 102 and the second sampling unit 107 shown in FIG. 13, the same reference numerals as those of the first sampling unit 101 and the second sampling unit 106 are substantially the same in configuration, and thus the description will be partly described. Omitted.

  As illustrated in FIG. 13, the first sampling unit 102 includes a first input side polarization control unit 111, an optical coupler 118, a first optical fiber 121, and a first color filter 141.

  The first input side polarization control unit 111 converts the measured light input to the polarization control element 113 and the first pulsed light input to the polarization control element 114 into linearly polarized light whose polarization directions are substantially the same. Control the polarization direction. The light under measurement and the first pulsed light whose polarization directions are controlled by the first input side polarization control unit 111 are output from the polarization control element 113 and the polarization control element 114 to the optical coupler 118, respectively.

  In FIG. 13, on the output side of the polarization control element 113 and the polarization control element 114, the polarization directions of the light to be measured and the first pulse light output from them are indicated by the directions of arrows surrounded by circles. As shown in FIG. 13, in this embodiment, the polarization directions of the light to be measured and the first pulsed light output from the polarization control element 113 and the polarization control element 114 of the first input side polarization control unit 111 are substantially vertical. Direction. However, the polarization directions of the light to be measured and the first pulse light are not limited to the vertical direction as in the present embodiment as long as they are controlled in substantially the same direction by the first input side polarization controller 111.

  In the form shown in FIG. 13, the first pulsed light output from the pulsed light output unit 20 has an appropriate timing and timing so as to overlap with the measured light when passing through the first optical fiber 121 described later. It has a sufficient pulse width. The timing and pulse width of the first pulse light are adjusted by the modulation unit 400 and the pulse width adjustment unit 40 of the pulse light output unit 20.

  The first optical fiber 121 generates four-wave mixing, which is a nonlinear optical effect, between the first output light and the second pulse light that pass through the inside with a temporal overlap. When the intensity of the first pulse light is sufficiently larger than the light to be measured, the intensity of the light to be measured is amplified. Thus, the light to be measured that has passed through the first optical fiber 121 becomes light whose intensity is amplified in substantially the same polarization direction as that of the first pulsed light. The intensity of the amplified light to be measured has a correlation with the intensity of the light to be measured before amplification when the intensity of the first pulse light is constant.

  Also, in the first optical fiber 121, idler light having a temporal overlap with the measured light and the first pulsed light is newly generated by four-wave mixing. This idler light is generated as linearly polarized light having substantially the same polarization direction as the light to be measured and the first pulsed light. Therefore, the polarization direction of the idler light has a substantially vertical angle. The intensity of the idler light is the same as that of the light to be measured amplified by the optical parametric amplification. Therefore, the intensity of the idler light also has a correlation with the intensity of the light to be measured before being amplified when the intensity of the first pulse light is constant. The difference between the wavelength of the light to be measured and the wavelength of the first pulsed light is equal to the difference between the wavelength of the idler light and the wavelength of the first pulsed light.

  The first color filter 141 is disposed on the optical path of the light that has passed through the first optical fiber 121 and has a characteristic of transmitting light having a wavelength in the same band as the wavelength of the light to be measured. Therefore, the components of the first pulsed light and the idler light, which are light having a wavelength different from the wavelength of the light to be measured, among the light that has passed through the first optical fiber 121 are absorbed by the first color filter 141, and the light to be measured Only the component having the same wavelength as the first wavelength passes through the first color filter 141. Hereinafter, the light transmitted through the first color filter 141 is referred to as first output light.

  As illustrated in FIG. 13, the second sampling unit 107 includes a second input side polarization control unit 112, an optical coupler 119, a second optical fiber 122, a second output side polarization unit 132, and a second color filter 142.

  The second input side polarization control unit 112 is configured such that the polarization direction of the second pulsed light input to the polarization control element 115 is linearly polarized light having an angle of 40 to 50 degrees with respect to the polarization direction of the first output light. The polarization direction of the second pulse light is controlled. The second pulsed light whose polarization direction is controlled by the second input side polarization control unit 112 is output from the polarization control element 115 toward the optical coupler 119.

  In FIG. 13, on the output side of the polarization control element 115, the polarization direction of the second pulse light output from the polarization control element 115 is indicated by the direction of an arrow surrounded by a circle. As shown in FIG. 13, in this embodiment, for example, when the polarization direction of the first output light is substantially vertical as described above, the first output from the polarization control element 115 of the second input side polarization control unit 112 is performed. The polarization direction of the two-pulse light preferably has an angle of about 45 degrees with respect to the vertical direction.

  When the input first output light and second pulsed light pass through the interior with at least partly overlapping in time, the second optical fiber 122 has an optical Kerr effect and four-way light between these lights. Produces non-linear optical effects including light wave mixing. More specifically, when the specific pulse of the first output light passing through the inside of the second optical fiber 122 and the specific pulse of the second pulse light overlap at least partially in time, the first output light The pulse has a polarization direction substantially the same as the polarization direction of the pulse of the second pulse light by rotating the polarization axis by the optical Kerr effect. Here, the rotation of the polarization axis as described above in the first output light does not occur in the entire first output light, but occurs only in a portion where the first output light and the second pulse light overlap in time.

  When the intensity of the second pulse light is very large compared to the first output light, the portion of the first output light passing through the second optical fiber 122 where the polarization axis rotates, that is, in the first output light. The intensity of the portion overlapping in time with the second pulse light is amplified by optical parametric amplification. Here, the light in which the portion of the first output light is amplified by optical parametric amplification is linearly polarized light having the same wavelength as that of the first output light, and the polarization direction thereof is substantially the same as the polarization direction of the second pulse light. is there. Therefore, in this embodiment, the polarization direction of the amplified portion in the first output light has an angle of about 45 degrees with respect to the vertical direction.

  In this way, when there is a portion having temporal overlap with each other in the first output light and the second pulse light passing through the second optical fiber 122, the portion in the first output light passing through the second optical fiber 122 is The intensity of the light is amplified in substantially the same polarization direction as that of the second pulse light. The intensity of the amplified portion of the first output light has a correlation with the intensity of the portion of the first output light before amplification when the intensity of the second pulse light is constant.

  In addition, as described above, when there is a portion having a temporal overlap in the first output light and the second pulse light that pass through the second optical fiber 122, the above-described portions of the first output light and the second pulse light Idler light having a temporal overlap is newly generated by four-wave mixing. This idler light is generated as linearly polarized light having substantially the same polarization direction as the second pulsed light. Therefore, the polarization direction of the idler light has an angle of about 45 degrees with respect to the vertical direction. The intensity of the idler light is the same intensity as that of the portion of the first output light amplified by rotating the polarization direction in substantially the same direction as the polarization direction of the second pulse light. Therefore, the intensity of the idler light also has a correlation with the intensity of the portion of the first output light before being amplified when the intensity of the second pulse light is constant.

  The second output side polarization unit 132 includes a polarization element 134 disposed on the optical path of light passing through the second optical fiber 122. The polarizing element 134 absorbs light having a vertical polarization component in incident light and transmits light having a horizontal component. Therefore, as shown in FIG. 13, the horizontal component of the second pulse light that has passed through the second optical fiber 122 is transmitted through the polarizing element 134. Further, the portion of the first output light that has passed through the second optical fiber 122 that does not overlap with the second pulsed light in the second optical fiber 122 is absorbed by the polarizing element 134 because the polarization direction is the vertical direction. The

  On the other hand, the portion of the first output light that overlaps the second pulsed light in time in the second optical fiber 122 is substantially the same as the second pulsed light in the polarization direction as described above, that is, in the vertical direction. Since it rotates in the direction of about 45 degrees, the horizontal component passes through the polarizing element 134. Further, the idler light generated in the second optical fiber 122 has the same polarization direction as the polarization direction of the second pulsed light, so that the horizontal component is transmitted through the polarization element 134.

  The second color filter 142 is disposed on the optical path of the light transmitted through the polarizing element 134 of the second output side polarization unit 132, and has a characteristic of transmitting only light having a wavelength in the same band as the wavelength of the first output light. Have. Therefore, the component of the second pulsed light and the idler light, which is light having a wavelength different from the wavelength of the first output light, among the light transmitted through the polarizing element 134 is absorbed by the second color filter 142, and the first output light is obtained. Only the component having the same wavelength as that of the first wavelength is transmitted through the second color filter 142. Hereinafter, the light transmitted through the second color filter 142 is referred to as second output light.

  The second color filter 142 may have a characteristic of transmitting only light having a wavelength in the same band as that of the idler light. In this case, since the second pulse light and the first output light component are absorbed by the second color filter 142, the idler light component transmitted through the second color filter 142 becomes the second output light. Even in this case, since the intensity and wavelength of the idler light have a correlation with the first output light as described above, the second output light composed of the idler light component can correspond to the first output light.

  As described above, in the second sampling unit 107, a portion of the first output light that does not overlap in time with the second pulsed light in the second optical fiber 122 is absorbed by the polarizing element 134. Therefore, the SN ratio of the second output light obtained by sampling the pulse waveform of the first output light can be further increased.

  For example, when the pulsed light output unit 20 outputs sub-picosecond order pulsed light as the second pulsed light, the second sampling unit 107 samples the first output light with the second pulsed light having a very short pulse width. Therefore, the time resolution of the sampling of the first output light in the second sampling unit 107 can be increased to the sub-picosecond order.

  As described above, the optical sampling device 10 includes the first sampling unit 102 and the second sampling unit 107 illustrated in FIG. 13, thereby efficiently amplifying the intensity of the light to be measured in the first sampling unit 102. The first output light amplified in the second sampling unit 107 can be sampled with high time resolution. Therefore, the pulse waveform of the light to be measured can be observed with high sensitivity and high time resolution.

  Note that the optical sampling device 10 described above and with reference to FIGS. 1 to 12 may include a second sampling unit 107 instead of the second sampling unit 106. In this case, the optical sampling device 10 includes a first sampling unit 101 and a second sampling unit 107. The second sampling unit 107 is the same as the second sampling unit 107 described with reference to FIG. 13, and the description is omitted because it has the same configuration and operational effects.

  The optical sampling apparatus 10 includes the first sampling unit 101 and the second sampling unit 107, so that the first sampling unit 101 samples the measured light with high time resolution, and the second sampling unit 107 outputs the first output. Light can be sampled again without reducing its signal-to-noise ratio. Therefore, the light to be measured can be observed with higher time resolution.

  The optical sampling device 10 described above with reference to FIGS. 1 to 12 may include a first sampling unit 102 instead of the first sampling unit 101. In this case, the optical sampling device 10 includes a first sampling unit 102 and a second sampling unit 106. The first sampling unit 102 is the same as the first sampling unit 102 described with reference to FIG. 13, and the description is omitted because it has the same configuration and operational effects.

  The optical sampling apparatus 10 includes the first sampling unit 102 and the second sampling unit 106, thereby efficiently amplifying the intensity of the light to be measured in the first sampling unit 102, and the first sampling unit 106 that has been amplified in the second sampling unit 106. One output light can be amplified more efficiently. Therefore, the gain in sampling the light to be measured can be further increased.

  FIG. 14 is a schematic diagram of the optical sampling apparatus 10 provided with the pulsed light output unit 21. The optical sampling apparatus 10 described above and with reference to FIGS. 1 to 13 may include a pulsed light output unit 21 shown in FIG. 14 instead of the pulsed light output unit 20. In addition, in the optical sampling apparatus 10 shown in FIG. 14, what attached | subjected the same reference number as the optical sampling apparatus 10 shown in FIG. 1 is the same structure, and description is abbreviate | omitted.

  As shown in FIG. 14, the pulsed light output unit 21 includes a high-frequency current output unit 261, a first laser light source 201, a second laser light source 202, and a frequency dividing circuit 411. Both the first laser light source 201 and the second laser light source 202 have the same configuration as the laser light source 200 and are pulse light sources that output single-mode pulse light. The pulsed light output from the first laser light source 201 is input to the first sampling unit 101 (102) as the first pulsed light through the modulation unit 400, the amplifier 31, and the pulse width adjustment unit 40. In addition, the pulsed light output from the second laser light source 202 is input to the second sampling unit 106 (107) as the second pulsed light through the amplifier 32 and the timing adjustment unit 500.

  The high-frequency current output unit 261 is electrically connected to a current amplification circuit (not shown) of the first laser light source 201 and a frequency dividing circuit 411, respectively. Similar to the high-frequency current output unit 260, the high-frequency current output unit 261 outputs a high-frequency current having a specific frequency. Note that the frequency of the high-frequency current output from the high-frequency current output unit 261 can be changed as desired.

  The frequency dividing circuit 411 divides the high-frequency electric signal output from the high-frequency current output unit 261 by N (N is a positive integer) and outputs it to the current amplification circuit (not shown) of the modulation unit 400 and the second laser light source 202. To do. Therefore, the modulation unit 400 outputs pulsed light obtained by dividing the repetition frequency of the pulsed light output from the first laser light source 201 by 1 / n according to the frequency of the electric signal input from the frequency dividing circuit 411. . Further, the second laser light source 202 has a repetition frequency obtained by dividing the frequency of the electric signal input from the frequency dividing circuit 411, that is, the repetition frequency of the high frequency electric signal output from the high frequency current output unit 261 by 1 / n. The pulse light having

  FIG. 15 is a schematic diagram of the optical sampling device 10 including the pulsed light output unit 22. The optical sampling apparatus 10 described above with reference to FIGS. 1 to 13 may include a pulsed light output unit 22 illustrated in FIG. 15 instead of the pulsed light output unit 20. In addition, in the optical sampling apparatus 10 shown in FIG. 15, what attached the same reference number as the optical sampling apparatus 10 shown in FIG.

  As shown in FIG. 15, the pulsed light output unit 22 includes a high-frequency current output unit 262, a first laser light source 201, a second laser light source 202, and a frequency dividing circuit 412. Both the first laser light source 201 and the second laser light source 202 have the same configuration as the laser light source 200 and are pulse light sources that output single-mode pulse light. The pulsed light output from the first laser light source 201 is input to the first sampling unit 101 (102) as the first pulsed light through the modulation unit 400, the amplifier 31, and the pulse width adjustment unit 40. In addition, the pulsed light output from the second laser light source 202 is input to the second sampling unit 106 (107) as the second pulsed light through the modulation unit 400, the amplifier 32, and the timing adjustment unit 500.

  The high-frequency current output unit 262 is electrically connected to the current amplification circuit (not shown) of the first laser light source 201, the current amplification circuit (not shown) of the second laser light source 202, and the frequency dividing circuit 412. The high frequency current output unit 262 outputs a high frequency current having a specific frequency in the same manner as the high frequency current output unit 260. Note that the frequency of the high-frequency current output from the high-frequency current output unit 262 can be changed as desired.

  The frequency dividing circuit 412 divides the high-frequency electric signal output from the high-frequency current output unit 262 by N (N is a positive integer) and outputs it to the modulation unit 400. Therefore, the modulation unit 400 disposed on the output side of each of the first laser light source 201 and the second laser light source 202 has the first laser light source 201 and the second laser light source 201 according to the frequency of the electric signal input from the frequency dividing circuit 412. The pulsed light obtained by dividing the repetition frequency of the pulsed light output from the laser light source 202 by 1 / n is output.

  In the optical sampling device 10 of this embodiment, the laser light source 200 is a common light source for the first pulse light and the second pulse light, but outputs the light source that outputs the first pulse light and the second pulse light. A light source may be provided separately. Further, the pulse width adjustment unit 40 may be arranged on the optical path of the second pulse light to adjust the pulse width of the second pulse light. Further, the pulse width adjustment unit 40 may be arranged on the optical paths of both the first pulse light and the second pulse light, and may adjust the pulse widths of these two pulse lights.

  The timing adjustment unit 500 is not limited to the form used as a part of the optical sampling device 10 of the present embodiment, and is a timing adjustment device that adjusts and outputs the phase difference between two given pulse lights, for example, an optical signal It can also be used for PM modulation.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above-described embodiment. It is apparent from the scope of the claims that the embodiments added with such changes or improvements can be included in the technical scope of the present invention.

1 is a schematic diagram showing a configuration of an optical sampling device 10. FIG. FIG. 3 is a schematic diagram illustrating the laser light source 200, the high-frequency current output unit 260, the modulation unit 400, and the vicinity of the frequency dividing circuit 410 in the pulsed light output unit 20. The result of the nonlinear transmission simulation which compresses the pulse width of the 1st pulsed light input from the spectrum spreading | diffusion part 42 side in the pulse width adjustment part 40 is shown. 2 is a diagram illustrating a configuration of a timing adjustment unit 500. FIG. FIG. 6 is a diagram illustrating a configuration of an optical variable delay unit 600. FIG. 6 is a diagram showing a configuration of a phase comparison unit 700. 2 is a block diagram showing a configuration of a first sampling unit 101. FIG. FIG. 3 is a schematic diagram illustrating a state in which light to be measured is sampled by a first pulsed light in a first sampling unit. In the block diagram of the first sampling unit 101 shown in FIG. 7, the positions indicated by the circled numbers 1 to 4 are shown for each optical frequency with the intensity of light passing with temporal overlap. . 3 is a block diagram showing a configuration of a second sampling unit 106. FIG. FIG. 6 is a schematic diagram illustrating a state in which first output light is optically parametrically amplified by second pulsed light in a second sampling unit. In the block diagram of the second sampling unit 106 shown in FIG. 10, the intensity of light passing with time overlap is shown for each optical frequency at the positions indicated by the numbers 5 to 7 with circles. Shown in FIG. 3 is a block diagram illustrating configurations of a first sampling unit 102 and a second sampling unit 107. 1 is a schematic diagram of an optical sampling device 10 provided with a pulsed light output unit 21. FIG. 1 is a schematic diagram of an optical sampling device 10 provided with a pulsed light output unit 22. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical sampling device 20, 21, 22 Pulse light output part, 31, 32 Amplifier, 40 Pulse width adjustment part, 42 Spread spectrum part, 44 Pulse compression part, 60 Photoelectric converter, 70 Waveform display, 80 Optical branching device , 101, 102 First sampling unit, 106, 107 Second sampling unit, 111 First input side polarization control unit, 112 Second input side polarization control unit, 113, 114, 115 Polarization control element, 118, 119 Optical coupler 121 First optical fiber, 122 Second optical fiber, 131 First output side polarization unit, 132 Second output side polarization unit, 133, 134 Polarization element, 141 First color filter, 142 Second color filter, 200 Laser light source , 201 first laser light source, 202 second laser light source, 210 laser diode, 211 low reflection 212 High reflection surface, 220 Collimating lens, 222 Condensing lens, 230 Mirror, 232 Total reflection surface, 240 Optical band pass filter, 250 Bias current output unit, 260, 261, 262 High frequency current output unit, 270 Current amplification circuit, 290 optical fiber, 400 modulator, 410, 411, 412 frequency divider, 500 timing adjuster, 511 first optical coupler, 512 second optical coupler, 521 first photoelectric converter, 522 second photoelectric converter, 531, 532 Amplifier, 541 First filter, 542 Second filter, 600 Optical variable delay unit, 610 First delay unit, 611, 612 Fixed reflection surface, 615 Movable reflection surface, 620 Second delay unit, 621 Optical fiber, 622 Piezo element , 623, 624 electrode, 625 high voltage power supply, 700 phase ratio Parts, 710 a phase difference detecting unit, 711 first flip-flop, 712 a second flip-flop, 715 the AND circuit, 720 a control voltage output unit, 721, 722 capacitor, 725 comparator, 727 offset voltage applying unit, 730 control unit

Claims (13)

A timing adjustment device that adjusts and outputs a phase difference between two given pulse lights,
An optical variable delay unit that delays at least one of the two pulsed lights to adjust the phase difference;
A photoelectric converter that generates two adjustment signals by converting each of the two pulsed lights having the phase difference adjusted by the optical variable delay unit into an electrical signal;
A timing adjustment device comprising: a phase comparison unit that detects a phase difference between the two adjustment signals and controls a delay amount in the optical variable delay unit so that the detected phase difference approaches a predetermined phase difference. The timing adjustment apparatus according to claim 1, further comprising: a filter that removes a frequency component smaller than a predetermined frequency for each of the two adjustment signals and inputs the signal to the phase comparison unit. The timing adjustment device according to claim 2, wherein the filter extracts a harmonic of a predetermined order for each of the two adjustment signals and inputs the harmonic to a phase comparison unit. A pulse width adjusting unit that adjusts a pulse width of one of the two pulsed lights;
The timing adjustment device according to claim 1, wherein the optical variable delay unit delays the other pulsed light different from the one pulsed light. The phase comparison unit includes:
A phase difference detector for detecting the phase difference between the two adjustment signals;
A control voltage output unit that outputs a control voltage in accordance with a difference between the phase difference between the two adjustment signals and the predetermined phase difference;
The optical variable delay unit is
A first delay unit that delays the pulsed light according to the phase difference detected by the phase difference detection unit;
2. The timing adjustment device according to claim 1, further comprising: a second delay unit that delays the pulsed light with a finer resolution than the first delay unit according to the control voltage output by the control voltage output unit. The second delay unit changes a delay amount according to the control voltage in a predetermined voltage range,
The phase comparison unit further includes a control unit that controls a delay amount of the first delay unit so that the control voltage output from the control voltage output unit is substantially at the center of the predetermined voltage range. The timing adjustment device according to claim 5. The timing adjustment device according to claim 6, wherein the control unit controls a delay amount of the first delay unit for each predetermined period. The first delay unit changes the optical path length of the pulsed light by changing according to the phase difference detected by the phase difference detection unit,
The timing adjustment device according to claim 5, wherein the second delay unit changes an optical path length of the pulsed light according to a magnitude of the control voltage output from the control voltage output unit. The first delay unit has a fixed reflecting surface and a movable reflecting surface,
The fixed reflecting surface reflects the pulsed light toward the movable reflecting surface,
The movable reflecting surface changes the optical path length of the pulsed light by changing the distance between the movable reflecting surface and the fixed reflecting surface according to the phase difference detected by the phase difference detecting unit,
The second delay unit applies the control voltage to a substantially cylindrical piezo element around which an optical fiber that transmits the pulsed light is wound to change the length of the optical fiber. The timing adjustment device according to claim 8, wherein the optical path length of the timing is changed. An optical sampling device for sampling measured light,
A first sampling unit that outputs, as the first output light, light corresponding to a portion of the measured light that has temporal overlap with the given first pulsed light;
A second sampling unit that outputs light obtained by amplifying the first output light as second output light when the first output light and the applied second pulse light have temporal overlap;
A timing adjustment unit that adjusts a phase difference between the first pulsed light and the second pulsed light and inputs the phase difference to the first sampling unit and the second sampling unit;
The timing adjustment unit
An optical variable delay unit that adjusts the phase difference by delaying at least one of the first pulsed light and the second pulsed light;
A first adjustment signal and a second adjustment signal are generated by converting at least a part of each of the first pulse light and the second pulse light, the phase difference of which has been adjusted by the optical variable delay unit, into an electric signal. A photoelectric converter,
A phase comparison for detecting a phase difference between the first adjustment signal and the second adjustment signal and controlling a delay amount in the optical variable delay unit so that the detected phase difference becomes a predetermined phase difference. And an optical sampling device. An optical splitter that receives the pulsed light and outputs the first pulsed light and the second pulsed light obtained by separating the pulsed light;
A pulse width adjusting unit that adjusts a pulse width of the first pulsed light to be smaller than a pulse width of the second pulsed light and inputs the first pulsed light to the first sampling unit;
The optical sampling device according to claim 10, wherein the optical variable delay unit delays the second pulsed light. The timing adjustment unit
A first optical coupler for inputting a part of the first pulsed light output by the pulse width adjusting unit to the photoelectric converter;
The optical sampling device according to claim 11, further comprising: a second optical coupler that inputs a part of the second pulsed light output from the optical variable delay unit to the photoelectric converter. The optical sampling device according to claim 12, wherein an optical path length from the first optical coupler to the first sampling unit is substantially equal to an optical path length from the second optical coupler to the second sampling unit.

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