JP4680223B2 - Chromatic dispersion measurement device - Google Patents

Description

  The present invention relates to a chromatic dispersion measuring apparatus that measures, for example, chromatic dispersion of an optical signal propagating in an optical fiber.

  In recent years, with an increase in communication demand due to the rapid spread of the Internet, further increase in transmission speed in optical fiber transmission is required. Currently, optical transmission systems with a transmission speed of 10 gigabits / second have been realized, the next generation optical transmission system with 40 gigabits / second, and the next generation of light with a transmission speed exceeding 100 gigabits / second. Transmission systems are being considered. As the transmission speed is increased, the time interval between adjacent bits of the optical signal is narrowed. Therefore, when the optical signal is affected by some influence during transmission and the signal quality deteriorates, the optical signal cannot be identified.

  One of the influences when an optical signal is transmitted is chromatic dispersion. This chromatic dispersion is a phenomenon in which the speed at which light travels differs depending on the wavelength, and the propagation speed differs for each wavelength component (optical frequency component) that constitutes an optical pulse, resulting in waveform distortion and spreading of the pulse after propagation. Since the waveform distortion and the spread of the pulse limit the transmission speed of the optical signal, the technique for accurately evaluating the chromatic dispersion has become very important as the transmission speed is increased.

  As a method for measuring chromatic dispersion, a phase shift method, an optical pulse method, an interference method, and the like are known (see Patent Documents 1 and 2). However, Patent Documents 1 and 2 measure chromatic dispersion using a dedicated light source, and are transmission lines used in actual communication (hereinafter referred to as “actual transmission lines”). There has been a problem that the chromatic dispersion of the transmitted optical signal cannot be measured.

  In order to solve this problem, for example, a chromatic dispersion measuring device shown in FIGS. 15A and 15B has been proposed (see, for example, Non-Patent Document 1).

  First, what is shown in FIG. 15A is an optical transmission signal in which an optical signal component in the upper sideband and lower sideband is selected and extracted by a wavelength tunable optical filter (Optical Filter), and a high-speed light receiving circuit (O / E) and the phase of the optical signal component in the upper sideband and the phase of the optical signal component in the lower sideband with reference to the phase of the clock signal extracted from the optical transmission signal in the high-speed phase detector (Phase Detector). Is detected, and chromatic dispersion is obtained from the phase difference.

Next, what is shown in FIG. 15 (b) is that after selecting and extracting the optical signal component of the upper sideband and the lower sideband from the optical transmission signal with a wavelength tunable optical filter and photoelectrically converting it with a high-speed light receiving circuit. The phase difference between the clock signal recovered by the high-speed clock recovery circuit (Clock Recovery) and extracted from the optical transmission signal by the high-speed phase comparator and the clock recovery signal of the optical signal component of the upper sideband and the lower sideband is obtained. The wavelength dispersion is detected and the chromatic dispersion is obtained from the phase difference.
JP 2000-105169 A JP 2002-107271 A Qian Yu, et al. “Chromatic dispersion monitoring technical using sideband optical filtering and clock phase-shift detection”, JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 20, NO. 12, DECEMBER 2002

  However, the conventional one shown in FIG. 15 has a high-speed light receiving circuit, a high-speed phase comparator, and a high-speed clock recovery circuit as the optical transmission signal speeds up. There was a problem that it was complicated and the manufacturing cost increased significantly.

  The present invention has been made to solve the conventional problems, and can measure the chromatic dispersion of an ultrahigh-speed optical signal transmitted through an actual transmission path, and further reduces the manufacturing cost compared to the conventional one. An object of the present invention is to provide a chromatic dispersion measuring apparatus capable of performing the above.

The chromatic dispersion measuring apparatus of the present invention includes an optical demultiplexer (11) that demultiplexes an incident optical signal to be measured into first and second optical paths, and one of the first and second optical paths. A USB carrier component extracting means (12) for extracting from the measured optical signal a USB carrier component indicating a carrier component of the measured optical signal and an upper sideband component of the carrier component; and the first and second optical paths On the other hand, LSB carrier component extraction means (15) for extracting a LSB carrier component indicating the carrier component of the measured optical signal and the lower sideband component of the carrier component from the measured optical signal, the USB carrier component and the USB carrier component An optical delay means (13) that delays any one of the LSB carrier components, and one optical signal delayed by the optical delay means (13) and the other optical signal that is not delayed are incident to the optical signal under measurement. Self An autocorrelation intensity signal output means (70) for outputting a correlation intensity signal, and a position of the optical delay means (13) at which the relative intensity of the autocorrelation intensity signal is maximized, and the predetermined optical delay means (13). Group delay time acquisition means (16) for acquiring a group delay time of the measured optical signal based on a reference position of the measured optical signal, and the measured optical signal is input with pulsed light of a random pattern having zero chromatic dispersion In this case, the position of the optical delay unit (13) where the autocorrelation intensity signal is maximized is determined as the reference position .

  With this configuration, the chromatic dispersion measuring apparatus of the present invention receives one optical signal delayed by the optical delay means (13) and the other optical signal not delayed, and outputs an autocorrelation intensity signal of the optical signal to be measured. The group delay time of the optical signal to be measured is obtained based on the position of the optical delay means (13) where the relative intensity of the autocorrelation intensity signal is maximum and the reference position of the predetermined optical delay means (13). Therefore, unlike conventional ones, it is possible to measure the chromatic dispersion of an ultrafast optical signal transmitted through an actual transmission path without using a dedicated light source.

  In addition, with this configuration, the chromatic dispersion measuring device of the present invention does not require a high-speed light receiving circuit, a high-speed phase comparator, and a high-speed clock recovery circuit, unlike the conventional one, so that the manufacturing cost is reduced as compared with the conventional one. can do.

Also, with this configuration, the chromatic dispersion measuring apparatus of the present invention performs actual transmission based on the position of the optical delay means (13) where the relative intensity of the autocorrelation intensity signal is maximum and the reference position of the optical delay means (13). It is possible to measure the chromatic dispersion of an ultrahigh-speed optical signal transmitted through a path.

  Furthermore, the chromatic dispersion measuring apparatus of the present invention includes an optical demultiplexer (11) that demultiplexes an incident optical signal to be measured into the first and second optical paths, and one of the first and second optical paths. And the USB carrier component indicating the carrier component of the measured optical signal and the upper sideband component of the carrier component, and the LSB carrier component indicating the carrier component of the measured optical signal and the lower sideband component of the carrier component. Optical signal component extraction means (21) for extracting the signal from the optical signal to be measured, and the USB carrier component or the LSB carrier component and the optical signal to be measured in any one of the first and second optical paths. An optical delay means (13) for delaying either one of the optical carrier signal delayed by the optical delay means (13) and one of the optical signals to be measured and the other optical signal not delayed are incident. When The first autocorrelation strength signal of the optical signal to be measured is output, and the LSB carrier component delayed by the optical delay means (13) and the other optical signal that is not delayed with one optical signal of the optical signal to be measured An autocorrelation intensity signal output means (70) for outputting a second autocorrelation intensity signal of the optical signal to be measured when the signal is incident thereon, and the light having the maximum relative intensity of the first autocorrelation intensity signal. A group delay for obtaining a group delay time of the optical signal under measurement based on the position of the delay means (13) and the position of the optical delay means (13) at which the relative intensity of the second autocorrelation intensity signal is maximum. And a time acquisition means (16).

  With this configuration, the chromatic dispersion measuring apparatus of the present invention has the position of the optical delay means (13) at which the relative intensity of the first autocorrelation intensity signal is maximum and the relative intensity of the second autocorrelation intensity signal is maximum. Since the group delay time of the optical signal to be measured is acquired based on the position of the optical delay means (13), it is different from the conventional one, and it is not necessary to use a dedicated light source. The chromatic dispersion of a high-speed optical signal can be measured.

  Furthermore, in the chromatic dispersion measuring apparatus of the present invention, the autocorrelation strength signal output means (70) combines one optical signal delayed by the optical delay means (13) and the other optical signal not delayed. An optical multiplexer (73), and a sum frequency indicating light having a frequency that is the sum of the frequency of the one optical signal and the frequency of the other optical signal upon incidence of light emitted from the optical multiplexer (73) A sum frequency light emitting section (74) for emitting light and a photoelectric conversion section (76) for converting the sum frequency light into an electric signal are provided.

  With this configuration, the chromatic dispersion measuring apparatus according to the present invention enables the actual transmission based on the relative strength of the autocorrelation strength signal because the electrical signal obtained from the sum frequency light corresponds to the autocorrelation strength signal of the optical signal to be measured. It is possible to measure the group delay time of an ultrafast optical signal transmitted on a path.

  Furthermore, the chromatic dispersion measuring apparatus of the present invention has a configuration in which the sum frequency light emitting section (74) is formed of a nonlinear optical material.

  With this configuration, the chromatic dispersion measuring apparatus according to the present invention allows the relative intensity of the sum frequency light emitted from the nonlinear optical material to correspond to the relative intensity of the autocorrelation intensity signal of the optical signal to be measured. Based on the intensity, it is possible to measure the group delay time of the ultrafast optical signal transmitted through the actual transmission path.

  Further, in the chromatic dispersion measuring apparatus according to the present invention, the autocorrelation intensity signal output means (41) receives one optical signal delayed by the optical delay means (13) and the other optical signal not delayed. An optical gate device (42) that emits an optical signal indicating autocorrelation of the optical signal to be measured, and a photoelectric conversion unit (44) that converts the optical signal emitted from the optical gate device (42) into an electrical signal. It has a configuration.

  With this configuration, the chromatic dispersion measuring apparatus of the present invention has the relative intensity of the optical signal emitted from the optical gate device (42) corresponding to the relative intensity of the autocorrelation intensity signal of the optical signal to be measured. Based on the relative intensity, the group delay time of the ultrahigh-speed optical signal transmitted through the actual transmission path can be measured.

  Furthermore, the chromatic dispersion measuring apparatus of the present invention includes a light receiving unit (55) that receives at least a part of the emitted light from the USB carrier component extracting means (12), and the emitted light from the LSB carrier component extracting means (15). And a light receiving portion (57) for receiving at least a part of the light receiving portion.

  With this configuration, the chromatic dispersion measuring apparatus of the present invention monitors the emitted light from the USB carrier component extracting means (12) and the LSB carrier component extracting means (15) by the light receiving part (55) and the light receiving part (57), respectively. The optical spectrum of each optical signal is obtained by sweeping the wavelength of the USB carrier component extracting means (12) and the LSB carrier component extracting means (15), and the USB carrier component extracting means (12) and the LSB carrier component extracting means (15 ) Is determined, and a necessary optical signal can be accurately extracted from the optical signal transmitted through the actual transmission path.

  Furthermore, the chromatic dispersion measuring apparatus of the present invention has a configuration including a light receiving part (32) for receiving at least a part of the emitted light of the optical signal component extracting means (21).

  With this configuration, the chromatic dispersion measuring apparatus of the present invention performs light sweep by wavelength sweeping the optical signal component extraction means (21) while monitoring the emitted light of the optical signal component extraction means (21) by the light receiving section (32). A spectrum is obtained, a set wavelength to be set in the optical signal component extracting means (21) is determined, and the chromatic dispersion of the ultrafast optical signal transmitted through the actual transmission path can be measured.

  Furthermore, the chromatic dispersion measuring apparatus of the present invention is characterized in that the optical signal under measurement is a wavelength division multiplexed optical signal, the transmission path through which the optical signal under measurement is wavelength division multiplexed and transmitted, and the optical demultiplexer (11). Wavelength division multiplexed optical signal extraction means (51) for extracting a wavelength division multiplexed optical signal of an arbitrary wavelength from the measured optical signal, and at least one of the emitted lights of the wavelength division multiplexed optical signal extraction means (51) And a light receiving part (53) for receiving the light.

  With this configuration, the wavelength dispersion measuring apparatus of the present invention sweeps the wavelength division multiplexed optical signal extraction means (51) while monitoring the outgoing light of the wavelength division multiplexed optical signal extraction means (51) by the light receiving unit (53). Thus, the optical spectrum can be observed, the set wavelength to be set in the wavelength division multiplexing optical signal extraction means (51) is determined, and the wavelength dispersion of the ultrahigh-speed optical signal transmitted by wavelength division multiplexing on the actual transmission path is determined. Can be measured.

  The present invention provides a chromatic dispersion measuring apparatus capable of measuring the chromatic dispersion of an ultrahigh-speed optical signal transmitted through an actual transmission line and having the effect of reducing the manufacturing cost as compared with the conventional one. Is something that can be done.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
First, the configuration of the chromatic dispersion measuring apparatus according to the first embodiment of the present invention will be described. Note that the chromatic dispersion measuring device according to the present embodiment is such that, for example, a light intensity modulation signal is branched and incident from a tap that branches an optical signal on an actual transmission path.

  As shown in FIG. 1, a chromatic dispersion measuring apparatus 10 according to the present embodiment includes an optical demultiplexer 11 that demultiplexes light under measurement into two light beams, and a wavelength tunable light that is incident on light transmitted through the optical demultiplexer 11. A filter 12, an optical delay device 13 that delays an optical signal by a predetermined amount, a mirror 14 that receives and reflects the reflected light of the optical demultiplexer 11, a wavelength variable optical filter 15 that receives the reflected light of the mirror 14, An autocorrelation intensity signal output unit 70 that outputs an autocorrelation intensity signal of the light to be measured, a signal processing unit 16 that processes an output signal of the autocorrelation intensity signal output unit 70, and a control unit 17 that outputs a control signal are provided. ing.

  The optical demultiplexer 11 demultiplexes the incident light intensity modulation signal, which is the light to be measured, into two light beams, and emits the transmitted light to the wavelength tunable optical filter 12 and the reflected light to the mirror 14. Yes. Here, the optical path from the transmitted light of the optical demultiplexer 11 to the optical multiplexer 73 of the autocorrelation intensity signal output unit 70 is hereinafter referred to as “first optical path”. On the other hand, the optical path from the reflected light of the optical demultiplexer 11 to the optical multiplexer 73 of the autocorrelation intensity signal output unit 70 is hereinafter referred to as a “second optical path”.

  The wavelength tunable optical filter 12 can extract an optical signal component having a predetermined wavelength from incident light to be measured based on a control signal from the control unit 17. An optical signal component including the upper sideband (USB) or an optical signal component including the carrier component and the lower sideband (LSB) can be selected and transmitted. ing. The transmitted optical signal is output to the optical multiplexer 73 of the autocorrelation intensity signal output unit 70.

  The optical signal component including the carrier wave component and the USB component is hereinafter referred to as “USB carrier wave component”, and the optical signal component including the carrier wave and the LSB component is hereinafter referred to as “LSB carrier wave component”. In the present embodiment, it is assumed that the wavelength tunable optical filter 12 transmits the USB carrier wave component of the measured light. The wavelength tunable optical filter 12 corresponds to the USB carrier component extraction means of the present invention.

  The optical delay device 13 includes a corner mirror 13a that can be translated in the movement direction indicated by the arrow in the drawing, a mirror 13b that reflects the light emitted from the wavelength tunable optical filter 12 toward the corner mirror 13a, and the corner mirror 13a. And a mirror 13 c that reflects the light and emits it to the optical multiplexer 73 of the autocorrelation intensity signal output unit 70. Further, the optical delay device 13 is held by a parallel holding portion (not shown) that can move in the moving direction indicated by the arrow in the drawing, and this parallel holding portion is indicated by an arrow according to a control signal from the control portion 17. It can be moved in the direction. With this configuration, the optical delay device 13 can vary the optical path length of the first optical path. The optical delay device 13 corresponds to the optical delay means of the present invention.

  The mirror 14 receives and reflects the reflected light of the optical demultiplexer 11 and emits it to the wavelength tunable optical filter 15.

  The wavelength tunable optical filter 15 can extract an optical signal component having a predetermined wavelength from the reflected light of the mirror 14, that is, incident light to be measured, based on a control signal from the control unit 17. The optical USB carrier component or LSB carrier component can be selected and transmitted. The transmitted optical signal component is emitted to the half-wave plate 71 of the autocorrelation intensity signal output unit 70. In the present embodiment, it is assumed that the wavelength tunable optical filter 15 transmits the LSB carrier component in the measured light. The tunable optical filter 15 corresponds to the LSB carrier component extraction means of the present invention.

  The autocorrelation intensity signal output unit 70 includes a half-wave plate 71 that rotates the polarization plane of the optical signal from the wavelength tunable optical filter 15, a mirror 72 that reflects the light transmitted through the half-wave plate 71, and a USB carrier wave. Optical multiplexer 73 that combines the component and the LSB carrier component, type 2 nonlinear optical material 74 that emits sum frequency light by the second type phase matching, and an optical filter that blocks unnecessary optical signals other than autocorrelation signals 75, a light receiver 76 that converts an optical signal into an electrical signal, a low-pass filter (hereinafter referred to as “LPF”) 77 that smoothes the electrical signal, and an AD converter 78 that converts an analog signal into a digital signal. ing. The autocorrelation strength signal output unit 70 corresponds to the autocorrelation strength signal output means of the present invention.

  The half-wave plate 71 rotates the polarization plane of the optical signal emitted from the wavelength tunable optical filter 15 by 90 ° and emits it to the mirror 72.

  The mirror 72 reflects the optical signal from the half-wave plate 71 and emits it to the optical multiplexer 73.

  The optical multiplexer 73 multiplexes the optical signal from the first optical path and the optical signal from the second path, and outputs the combined optical signal to the type 2 nonlinear optical material 74.

The type 2 nonlinear optical material 74 performs the second type phase matching. As shown in FIG. 2, the USB carrier component (frequency ω _U ) and the LSB carrier component (frequency ω _L ) having polarization planes orthogonal to each other. When the two light beams are incident, the sum frequency light (SFG light: frequency ω _U + ω _L ) proportional to the product of the intensity of the two incident light beams is emitted only when the two incident light beams overlap at the same time. . In this embodiment, since the two incident lights are the same measured light, the light emitted from the type 2 nonlinear optical material 74 generates a sum frequency light having a frequency twice that of the measured light. The type 2 nonlinear optical material 74 corresponds to the sum frequency light emitting portion of the present invention.

  Here, the function of the type 2 nonlinear optical material 74 will be described in more detail with reference to FIG. Note that since there are types of nonlinear optical materials that perform first-type phase matching (hereinafter referred to as “type 1 nonlinear optical materials”), both will be described. FIGS. 3A and 3B are diagrams illustrating functions of the type 1 nonlinear optical material and the type 2 nonlinear optical material, respectively. Here, the fundamental wave light a having a wavelength of 1540 nm and the fundamental wave light b having a wavelength of 1560 nm are taken as an example, and the arrow direction in the figure indicates the direction of the polarization plane of each light.

  As shown in FIG. 3 (a), when the polarization planes of the incident fundamental wave lights a and b are parallel to each other, the type 1 nonlinear optical material has fundamental wave lights a and b, SFG light (775 nm), and two SHGs. Light (770 nm and 780 nm) is emitted.

  On the other hand, as shown in FIG. 3B, the type 2 nonlinear optical material emits the fundamental wave light a and b and the SFG light (775 nm) when the polarization planes of the incident fundamental wave lights a and b are orthogonal to each other. To do. Therefore, unlike the type 1 nonlinear optical material, the SHG light is not generated in the type 2 nonlinear optical material, so that the SN ratio at the time of outputting the autocorrelation intensity signal can be improved.

  In the present embodiment, the sum frequency light is obtained only when the USB carrier component and the LSB carrier component enter the type 2 nonlinear optical material 74 at the same time. Therefore, the relative intensity of the sum frequency light is maximized when the USB carrier component and the LSB carrier component of the light to be measured coincide with each other in time, and becomes smaller as the two are shifted in time. That is, the relative intensity of the sum frequency light indicates an autocorrelation indicating the degree of temporal coincidence between the USB carrier component and the LSB carrier component of the light to be measured.

  In place of the type 2 nonlinear optical material 74, a type 1 nonlinear optical material may be used. In this case, as described with reference to FIG. 3A, the polarization directions of the light incident on the type 1 nonlinear optical material must be parallel to each other. For example, the half-wave plate 71 shown in FIG. Should be abolished. Also in this configuration, since the sum frequency light is emitted from the type 1 nonlinear optical material, the same effect as that of the type 2 nonlinear optical material 74 can be obtained.

  Returning to FIG. 1, the description of the configuration of the chromatic dispersion measuring apparatus 10 will be continued.

  The optical filter 75 transmits only the sum frequency light among the USB carrier component of the light to be measured emitted from the type 2 nonlinear optical material 74, the LSB carrier component of the light to be measured, and the sum frequency light.

  The light receiver 76 includes, for example, a photodiode, converts the sum frequency light from the optical filter 75 into an electrical signal, and outputs the electrical signal to the LPF 77. Here, the light receiver 76 corresponds to the photoelectric conversion unit of the present invention. When the wavelength of the light to be measured is in the 1.5 μm band, the silicon photo diode (Si-PD) is provided in the light receiver 76, so that the sensitivity of the Si-PD in the 1.5 μm band is extremely low. Since the LSB carrier component is removed and only the sum frequency light is received, the optical filter 75 can be omitted.

  The LPF 77 smoothes an electrical signal corresponding to the sum frequency light (hereinafter referred to as “sum frequency signal”).

  The AD converter 78 receives the sum frequency signal which is an analog signal, converts it into a digital signal, and outputs it to the signal processing unit 16.

  The signal processing unit 16 has a waveform indicating the autocorrelation of the measured light from the autocorrelation strength signal obtained by the autocorrelation strength signal output unit 70 for each delay amount of the optical delay device 13 (hereinafter referred to as “autocorrelation waveform”). And the group delay is acquired based on the autocorrelation waveform. Here, the autocorrelation waveform is a waveform in which the movement distance data acquired from the control unit 17 and the relative intensity of the autocorrelation intensity signal are related to each other on the time axis of the USB carrier component and the LSB carrier component of the measured light. The maximum value of the relative intensity is shown when the positions of the two coincide. The signal processing unit 16 corresponds to the group delay time acquisition unit of the present invention.

  The control unit 17 outputs a control signal for operating each of the wavelength tunable optical filter 12, the optical delay device 13, the wavelength tunable optical filter 15, and the signal processing unit 16. Further, the control unit 17 acquires data indicating the moving distance of the corner mirror 13 a (hereinafter referred to as “moving distance data”) from the optical delay device 13 that delays the USB carrier wave component, and outputs the data to the signal processing unit 16. It has become.

  Next, the operation principle of the chromatic dispersion measuring apparatus 10 according to the present embodiment will be described with reference to FIG. FIG. 4A shows an optical transmission signal pattern along the time axis of the USB carrier component and LSB carrier component of the light to be measured incident on the optical demultiplexer 11. In FIG. 4A, in order to display each optical transmission signal pattern of the USB carrier component and the LSB carrier component in an easy-to-understand manner, the vertical directions are different from each other. FIG. 4B shows an example of an autocorrelation waveform. The reference position shown in FIG. 4B refers to a position of the optical delay device 13 that is determined in advance using a light intensity modulation signal with zero chromatic dispersion.

  In FIG. 4A, the optical transmission signal pattern of the LSB carrier component of the measured light is delayed by Δτ from the optical transmission signal pattern of the USB carrier component. Since this optical transmission signal is a random pattern signal, as shown in FIG. 4B, the signal pattern of the LSB carrier component and the signal pattern of the USB carrier component incident on the autocorrelation strength signal output unit 70 are time axes. When they match, the autocorrelation strength signal becomes maximum, and the autocorrelation strength signal becomes smaller as the two signal patterns are shifted.

  When the position of the optical delay unit 13 is changed from the reference position of the optical delay unit 13 so as to increase the optical path length of the first optical path through which the USB carrier component propagates, the USB incident on the autocorrelation intensity signal output unit 70 When a delay amount is given to the carrier wave component, and this delay amount becomes Δτ, that is, when the signal pattern of the LSB carrier wave component and the signal pattern of the USB carrier wave component coincide with each other, as shown in FIG. The relative intensity in the correlation waveform becomes a peak, and the autocorrelation intensity signal output from the autocorrelation intensity signal output unit 70 is maximized. Furthermore, if a delay amount of Δτ or more is given, the signal pattern of the LSB carrier component and the signal pattern of the USB carrier component shift, and the autocorrelation strength signal gradually decreases.

Accordingly, the position of the optical delay device 13 at which the autocorrelation strength signal is maximized when the optical intensity modulation signal has zero chromatic dispersion is determined in advance as the reference position (L _B ) of the optical delay device 13, and the reference position. By obtaining a moving distance from (L _B ) to the position (L _D ) of the optical delay device 13 where the autocorrelation intensity signal is maximum, and converting this moving distance into time, the group delay of the light to be measured is obtained. Can do. Specifically, the autocorrelation intensity signal is maximized when the optical delay unit 13 is translated from the reference position (L _B ) by d / 2 in the direction of the arrow and the optical path length of the first optical path is increased by d. Assuming that, the group delay time difference Δτ and the group delay D at this time can be calculated by the equations (1) and (2), respectively. Here, c represents the speed of light.

Δτ = (L _D −L _B ) / c
= D / c (1)
D = Δτ / Δλ (2)
Here, Δλ = λ _L −λ _U , λ _U indicates the center wavelength of the USB optical signal component in the wavelength tunable optical filter 12, and λ _L indicates the center wavelength of the LSB optical signal component in the wavelength tunable optical filter 15. Indicates. Note that the wavelength tunable optical filters 12 and 15 may be swept to obtain λ _U and λ _L from the transmitted light spectrum.

  As shown in the equation (1), the detection accuracy of the group delay time difference Δτ is determined by the setting accuracy of the optical delay device 13. When the variable accuracy of the optical path length of the optical delay device 13 is 1 μm, for example, it is converted to the time axis. Then, the accuracy becomes as high as about 0.003 ps.

  Next, the operation of the chromatic dispersion measuring apparatus 10 in the present embodiment will be described. Note that the wavelength dispersion of the light to be measured is not zero.

  First, the optical demultiplexer 11 demultiplexes the light intensity modulation signal, which is the light to be measured, into two light beams, and emits the transmitted light to the wavelength variable optical filter 12 and the reflected light to the mirror 14. For example, when an optical phase modulation signal is used as light to be measured, the optical phase modulation signal may be converted into a light intensity modulation signal in advance.

  The transmitted light of the optical demultiplexer 11 enters the wavelength tunable optical filter 12, and the wavelength tunable optical filter 12 transmits the USB carrier component of the light intensity modulation signal, and the USB carrier component passes through the optical delay device 13. Then, the light is incident on the optical multiplexer 73 of the autocorrelation intensity signal output unit 70.

  On the other hand, the reflected light of the optical demultiplexer 11 is reflected by the mirror 14 and enters the wavelength tunable optical filter 15. The tunable optical filter 15 transmits the LSB carrier component of the light intensity modulation signal, and the LSB carrier component is incident on the autocorrelation strength signal output unit 70. The LSB carrier component incident on the autocorrelation intensity signal output unit 70 has its plane of polarization rotated 90 ° by the half-wave plate 71 and enters the optical multiplexer 73 via the mirror 72.

  Subsequently, the optical multiplexer 73 multiplexes the USB carrier component from the first optical path and the LSB carrier component from the second optical path, and outputs them to the type 2 nonlinear optical material 74.

  Further, the type 2 nonlinear optical material 74 emits the USB carrier component and the LSB carrier component and their sum frequency light to the optical filter 75.

  Next, the optical filter 75 transmits only the sum frequency light out of the light emitted from the type 2 nonlinear optical material 74 and emits it to the light receiver 76.

  Subsequently, the light receiver 76 converts the sum frequency light into an electric signal and outputs it to the LPF 77, and the LPF 77 smoothes the sum frequency signal, that is, the autocorrelation intensity signal, and outputs it to the AD converter 78.

  Next, the AD converter 78 performs AD conversion on the autocorrelation strength signal and outputs the signal to the signal processing unit 16. Thus, the autocorrelation intensity signal of the measured light obtained using the USB carrier component and the LSB carrier component is input to the signal processing unit 16. Since the wavelength dispersion of the light to be measured is not zero, there is a signal pattern shift between the USB carrier component and the LSB carrier component as shown in FIG. The relative intensity of the autocorrelation intensity signal is at a level corresponding to the deviation.

When the optical carrier 13 is translated to delay the USB carrier component, the signal processor 16 observes a change in the relative intensity of the autocorrelation intensity signal with respect to the optical delay amount. At this time, the travel distance data is sequentially output from the optical delay device 13 to the signal processing unit 16 via the control unit 17, and the signal processing unit 16 performs relative processing of the autocorrelation strength signal as shown in FIG. The group delay time difference Δτ is obtained by the equation (1) from the difference between the position (L _D ) of the optical delay device 13 where the intensity is maximum and the reference position (L _B ) of the optical delay device 13, and the group is obtained by the equation (2). The delay D is obtained.

As described above, according to the chromatic dispersion measuring apparatus 10 in the present embodiment, the wavelength tunable optical filters 12 and 15 extract the USB carrier component and the LSB carrier component from the measured light on the actual transmission path, respectively. The correlation strength signal output unit 70 outputs an autocorrelation strength signal of the measured light based on the USB carrier component delayed by the optical delay device 13 and the LSB carrier component not delayed, and the signal processing unit 16 outputs the autocorrelation strength signal. Since the group delay time of the light to be measured is acquired based on the position (L _D ) of the optical delay device 13 where the relative intensity is maximum and the reference position (L _B ) of the optical delay device 13, the actual transmission path It is possible to measure the chromatic dispersion of an ultrahigh-speed optical signal transmitted through the network.

  Further, unlike the conventional one, the chromatic dispersion measuring apparatus 10 in the present embodiment does not require a high-speed light receiving circuit, a high-speed phase comparator, and a high-speed clock recovery circuit, so that the manufacturing cost is reduced as compared with the conventional one. In addition, it is possible to measure the group delay time of the ultrahigh-speed optical transmission signal.

  Note that an ultrahigh-speed optical signal transmitted through an actual transmission line is obtained by connecting a display device that displays chromatic dispersion data of the light to be measured to the signal processing unit 16 of the chromatic dispersion measuring device 10 in the present embodiment. It is possible to function as a chromatic dispersion monitor for monitoring the chromatic dispersion.

  Further, in the above-described embodiment, a description is given by taking as an example a configuration in which the wavelength tunable optical filter 12 extracts the USB carrier wave component and the wavelength tunable optical filter 15 extracts the LSB carrier wave component from the measured light on the actual transmission path. However, the present invention is not limited to this.

  In the above-described embodiment, the configuration in which the optical delay device 13 is provided between the wavelength tunable optical filter 12 and the optical multiplexer 73 has been described as an example. However, the present invention is not limited to this. For example, the same effect can be obtained by providing the optical delay device 13 between the wavelength tunable optical filter 15 and the half-wave plate 71.

  Further, in the above-described embodiment, the configuration in which the autocorrelation intensity signal is obtained based on the point where the relative intensity in the autocorrelation waveform reaches a peak has been described. However, the present invention is not limited to this. A similar effect can be obtained even when the autocorrelation intensity signal is obtained using the maximum intensity centroid of the waveform.

(Second Embodiment)
FIG. 5 shows a chromatic dispersion measuring apparatus according to this embodiment. The chromatic dispersion measuring apparatus in the present embodiment is obtained by changing a part of the chromatic dispersion measuring apparatus 10 (see FIG. 1) in the first embodiment, and has the same configuration as the chromatic dispersion measuring apparatus 10. Reference numerals are assigned, and duplicate descriptions are omitted.

  As shown in FIG. 5, the chromatic dispersion measuring device 20 in the present embodiment includes an optical demultiplexer 11 that demultiplexes the light to be measured into two light beams, and a wavelength tunable light that is incident on the light transmitted through the optical demultiplexer 11. Filter 21, mirror 14 that receives and reflects the reflected light of optical demultiplexer 11, optical delay device 13 that receives the reflected light of mirror 14 and delays the optical signal by a predetermined amount, and autocorrelation of the light to be measured An autocorrelation intensity signal output unit 70 that outputs an intensity signal, a signal processing unit 16 that processes an output signal of the autocorrelation intensity signal output unit 70, and a control unit 17 that outputs a control signal are provided.

  In the following description, the USB and LSB optical signal components included in the incident measurement light are referred to as double sideband (DSB) optical signal components, and include an optical signal including a carrier wave component and a DSB component. The component is hereinafter referred to as “DSB carrier component”.

The wavelength tunable optical filter 21 can extract an optical signal component of a predetermined wavelength from incident light to be measured based on a control signal from the control unit 17, for example, a USB carrier component or LSB carrier of the light to be measured. A component can be selected and transmitted. The transmitted optical signal is output to the optical multiplexer 73 of the autocorrelation intensity signal output unit 70. The wavelength tunable optical filter 21 corresponds to the optical signal component extraction unit of the present invention.

  Next, the operation principle of the chromatic dispersion measuring apparatus 20 in the present embodiment will be described with reference to FIG. FIG. 6A illustrates the optical transmission signal pattern along the time axis of the DSB carrier component, the USB carrier component, and the LSB carrier component that are components of the light to be measured incident on the optical demultiplexer 11. ing. In FIG. 6A, in order to display each optical transmission signal pattern in an easy-to-understand manner, only the LSB carrier component is different in the vertical direction. FIG. 6B shows an example of an autocorrelation waveform.

  Let Δτ be the relative group delay time difference between the USB carrier component from the first optical path incident on the autocorrelation strength signal output unit 70 and the DSB carrier component from the second optical path. The optical delay device 13 can give an arbitrary group delay time difference Δτ ′ between the USB carrier component and the DSB carrier component by the movement of the corner mirror 13a. The USB carrier component extracted by the wavelength tunable optical filter 21 on the first optical path and the DSB carrier component to which Δτ ′ is added on the second optical path are input to the autocorrelation strength signal output unit 70, and Δτ ′ is When Δτ is canceled, the autocorrelation signal output from the autocorrelation strength signal output unit 70 is maximized (FIG. 6B). Furthermore, when a group delay amount equal to or greater than Δτ is given, the optical transmission signal pattern of the USB carrier component and the optical transmission signal pattern of the DSB carrier component shift, and the autocorrelation strength signal gradually decreases.

  Similarly to the above, even when the wavelength tunable optical filter 21 extracts the LSB carrier component on the first optical path, Δτ that maximizes the autocorrelation signal output from the autocorrelation strength signal output unit 70 can be obtained. .

Accordingly, when the USB carrier component and the DSB carrier component are input to the autocorrelation strength signal output unit 70, the position (L _U ) of the optical delay unit 13 at which the autocorrelation signal becomes maximum, the LSB carrier component, and the DSB carrier component Is obtained, the position (L _L ) of the optical delay device 13 at which the autocorrelation signal is maximized is obtained, and the distance difference d between the position L _L and the position L _U of the optical delay device 13 is converted into time. Thus, the group delay time of the light to be measured can be obtained.

  That is, the group delay time difference Δτ and the group delay D can be calculated by Expression (3) and Expression (4), respectively. Here, c represents the speed of light.

Δτ = (L _L −L _U ) / c
= D / c (3)
D = Δτ / Δλ (4)
Here, Δλ = λ _L −λ _U , where λ _U indicates the center wavelength of the USB optical signal component emitted from the wavelength tunable optical filter 21, and λ _L is the LSB optical signal emitted from the wavelength tunable optical filter 21. Indicates the center wavelength of the component. The optical delay device 13 outputs data indicating the position L _L and the position L _U to the signal processing unit 16 via the control unit 17. Alternatively, the wavelength tunable optical filter 21 may be swept to obtain λ _U and λ _L from the transmitted light spectrum.

  As shown in equation (3), the detection accuracy of the group delay time difference Δτ is determined by the setting accuracy of the optical delay device 13, and is converted to the time axis when the optical path length variable accuracy of the optical delay device 13 is 1 μm, for example. Then, the accuracy becomes as high as about 0.003 ps.

  Next, the operation of the chromatic dispersion measuring apparatus 20 in the present embodiment will be described. Note that the wavelength dispersion of the light to be measured is not zero.

  First, the optical demultiplexer 11 demultiplexes the light intensity modulation signal, which is the light to be measured, into two light beams, and emits the transmitted light to the wavelength tunable optical filter 21 and the reflected light to the mirror 14.

  The tunable optical filter 21 transmits the USB carrier component or the LSB carrier component of the light intensity modulation signal, and enters the transmitted optical signal component into the optical multiplexer 73 of the autocorrelation strength signal output unit 70.

  On the other hand, the reflected light (DSB carrier component) of the optical demultiplexer 11 is reflected by the mirror 14 and enters the half-wave plate 71 of the autocorrelation intensity signal output unit 70 via the optical delay device 13. The incident DSB carrier component has its plane of polarization rotated by 90 ° by the half-wave plate 71, and enters the optical multiplexer 73 via the mirror 72.

  Subsequently, the optical multiplexer 73 multiplexes the USB carrier component or LSB carrier component from the first optical path and the DSB carrier component from the second optical path, and outputs the resultant to the type 2 nonlinear optical material 74.

  Further, the type 2 nonlinear optical material 74 emits the sum frequency light of the USB carrier component or LSB carrier component and the DSB carrier component to the optical filter 75.

  Next, the optical filter 75 transmits only the sum frequency light out of the light emitted from the type 2 nonlinear optical material 74 and emits it to the light receiver 76.

  Subsequently, the light receiver 76 converts the sum frequency light into an electric signal and outputs it to the LPF 77, and the LPF 77 smoothes the sum frequency signal and outputs it to the AD converter 78.

  Next, the AD converter 78 performs AD conversion on the sum frequency signal and outputs it to the signal processing unit 16. Here, the autocorrelation intensity signal of the measured light obtained using the USB carrier component or the LSB carrier component and the DSB carrier component is input to the signal processing unit 16. Since the wavelength dispersion of the light to be measured is not zero, as shown in FIG. 6A, a signal is transmitted between the USB carrier component and the DSB carrier component and between the DSB carrier component and the LSB carrier component. There is a pattern shift, and the relative intensity of the autocorrelation intensity signal input to the signal processing unit 16 is at a level corresponding to the shift.

When the optical delay unit 13 is translated to delay the DSB carrier component, the signal processor 16 observes a change in the relative intensity of the autocorrelation intensity signal. At this time, data indicating the moving distance of the corner mirror 13 a of the optical delay device 13 that delays the DSB carrier component is sequentially output from the optical delay device 13 to the signal processing unit 16 via the control unit 17. As shown in FIG. 6 (b), the signal processing unit 16 has a maximum autocorrelation signal when the USB carrier component and the DSB carrier component are input to the autocorrelation strength signal output unit 70. From the position (L _U ) and the position (L _L ) of the optical delay unit 13 where the autocorrelation signal is maximized when the LSB carrier component and the DSB carrier component are input, the group delay time difference Δτ is calculated by the equation (3). Then, the group delay D is obtained by the equation (4).

As described above, according to the chromatic dispersion measuring apparatus 20 in the present embodiment, the tunable optical filter 21 extracts the USB carrier component or the LSB carrier component from the measured light on the actual transmission path, and outputs the autocorrelation strength signal. The unit 70 outputs an autocorrelation strength signal of the measured light based on the DSB carrier component and the USB carrier component or the LSB carrier component delayed by the optical delay unit 13, and the signal processing unit 16 outputs the position of the optical delay unit 13 (L _Since the group delay time of the light to be measured is acquired based on _U ) and the position (L _L ), it is possible to measure the chromatic dispersion of the ultrafast optical signal transmitted through the actual transmission path.

  Further, unlike the conventional one, the chromatic dispersion measuring apparatus 20 in the present embodiment does not require a high-speed light receiving circuit, a high-speed phase comparator, and a high-speed clock recovery circuit, so that the manufacturing cost is reduced as compared with the conventional one. In addition, it is possible to measure the group delay time of an ultrafast optical signal.

(Third embodiment)
A chromatic dispersion measuring apparatus according to the present embodiment is shown in FIG. The chromatic dispersion measuring apparatus in the present embodiment is obtained by changing a part of the chromatic dispersion measuring apparatus 20 (see FIG. 5) in the second embodiment, and has the same configuration as the chromatic dispersion measuring apparatus 20. Reference numerals are assigned, and duplicate descriptions are omitted.

  As shown in FIG. 7, the chromatic dispersion measuring device 30 according to the present embodiment includes an optical demultiplexer 31 that demultiplexes part of the light emitted from the wavelength tunable optical filter 21, and the optical demultiplexer 31 demultiplexes. And a light receiving portion (hereinafter referred to as “PD”) 32 for receiving light.

  The optical demultiplexer 31 is provided between the wavelength tunable optical filter 21 and the optical multiplexer 73 of the autocorrelation intensity signal output unit 70, demultiplexes the light emitted from the wavelength tunable optical filter 21, and The light is emitted to the PD 32.

  The PD 32 photoelectrically converts the light emitted from the optical demultiplexer 31 and outputs an electric signal to the signal processing unit 16. Therefore, the signal processing unit 16 can acquire the spectrum information of the optical signal under measurement by sweeping the wavelength tunable optical filter 21 by the control unit 17, and the wavelength tunable optical filter 21 can be obtained based on the spectrum information. The measurement wavelength to be set can be determined.

As described above, the chromatic dispersion measuring device 30 according to the present embodiment can determine the measurement wavelength set by the tunable optical filter 21 even when the wavelength of the optical signal under measurement propagating through the transmission line is unknown. . Therefore, the chromatic dispersion measuring device 30 sets the determined measurement wavelength in the tunable optical filter 21, so that the position (L _U ) of the optical delay device 13 is the same as the chromatic dispersion measuring device 20 in the second embodiment. ) And the position (L _L ), and the chromatic dispersion of the ultrafast optical signal transmitted through the actual transmission path can be measured.

  Also, the chromatic dispersion measuring apparatus 30 in the present embodiment does not require a high-speed light receiving circuit, a high-speed phase comparator, and a high-speed clock recovery circuit unlike the conventional one, so that the manufacturing cost is reduced as compared with the conventional one. In addition, it is possible to measure the group delay time of an ultrafast optical signal.

(Fourth embodiment)
A chromatic dispersion measuring apparatus according to the present embodiment is shown in FIG. The chromatic dispersion measuring apparatus in the present embodiment is obtained by changing the autocorrelation intensity signal output unit 70 of the chromatic dispersion measuring apparatus 20 (see FIG. 5) in the second embodiment, and is the same as the chromatic dispersion measuring apparatus 20. The same reference numerals are used for the same components, and duplicate descriptions are omitted.

  As shown in FIG. 8, the chromatic dispersion measuring apparatus 40 in the present embodiment includes an autocorrelation strength signal output unit 41. The autocorrelation intensity signal output unit 41 includes an optical gate device 42 that transmits or blocks an optical signal based on an optical control signal, a light receiver 44 that converts incident light into an electrical signal, an LPF 45 that smoothes the electrical signal, And an AD converter 46 for converting an analog signal into a digital signal. Since the configuration other than the optical gate device 42 is the same as that of the autocorrelation strength signal output unit 70 in the second embodiment, the description thereof is omitted. The autocorrelation intensity signal output unit 41 and the light receiver 44 correspond to the autocorrelation intensity signal output unit and the photoelectric conversion unit of the present invention, respectively.

  The optical gate device 42 includes, for example, a single traveling carrier photodiode (UTC-PD) characterized by high speed and high output, and a traveling wave electrode electroabsorption modulator (TW-EAM) characterized by high speed and low voltage driving. Is a PD-EAM (photodiode-electro-absorption optical modulator) integrated on a single semiconductor chip, and is an element that directly drives TW-EAM with the output of UTC-PD without using an electric amplifier. .

  The optical gate device 42 includes an optical signal input port 42a that inputs an optical signal, an optical control signal input port 42b that inputs an optical control signal and functions as a gate, and an optical signal output that outputs an optical signal in accordance with the optical control signal Port 42c. In the present embodiment, the optical signal input port 42a inputs a USB carrier component or LSB carrier component (hereinafter referred to as a USB carrier component) emitted from the wavelength tunable optical filter 21, and inputs an optical control signal. The port 42 b is configured to input a DSB carrier component that has passed through the optical delay device 13.

  That is, the optical gate device 42 outputs the optical signal of the USB carrier component during the period in which the DSB carrier component is input and the optical control signal input port 42b is turned on. An optical signal having an optical intensity corresponding to the determined delay amount of the DSB carrier component is output. Therefore, the autocorrelation strength signal output unit 41 in the present embodiment outputs the autocorrelation strength signal of the measured light to the signal processing unit 16 by the DSB carrier component delayed by the optical delay device 13 and the USB carrier component not delayed. Will be.

As described above, according to the chromatic dispersion measuring device 40 in the present embodiment, the tunable optical filter 21 extracts the USB carrier component from the measured light, and the autocorrelation strength signal output unit 70 is an optical delay device. 13 outputs the autocorrelation intensity signal of the measured light by the delayed DSB carrier component and the undelayed USB carrier component, and the signal processing unit 16 outputs the position (L _U ) and position (L _L ) of the optical delay unit 13. Therefore, it is possible to measure the chromatic dispersion of the ultrafast optical signal transmitted through the actual transmission path.

  Further, unlike the conventional one, the chromatic dispersion measuring apparatus 40 in the present embodiment does not require a high-speed light receiving circuit, a high-speed phase comparator, and a high-speed clock recovery circuit, so that the manufacturing cost is reduced as compared with the conventional one. In addition, it is possible to measure the group delay time of an ultrafast optical signal.

(Fifth embodiment)
A chromatic dispersion measuring apparatus according to the present embodiment is shown in FIG. The chromatic dispersion measuring apparatus in the present embodiment is obtained by changing a part of the chromatic dispersion measuring apparatus 10 (see FIG. 1) in the first embodiment, and has the same configuration as the chromatic dispersion measuring apparatus 10. Reference numerals are assigned, and duplicate descriptions are omitted.

  As shown in FIG. 9, the chromatic dispersion measuring device 50 in this embodiment includes an optical demultiplexer 11, a tunable optical filter 12, an optical delay 13, a mirror 14, a tunable optical filter 15, A WDM (Wavelength Division Multiplexing) wavelength selection optical filter 51 provided between an actual transmission path (not shown) and the optical demultiplexer 11 and a part of the output light of the WDM wavelength selection optical filter 51 An optical demultiplexer 52 for demultiplexing and a PD 53 for receiving the light demultiplexed by the optical demultiplexer 52 are provided.

  The chromatic dispersion measuring device 50 includes an optical demultiplexer 54 that demultiplexes a part of the light emitted from the wavelength tunable optical filter 12, a PD 55 that receives the light demultiplexed by the optical demultiplexer 54, and a wavelength tunable light. An optical demultiplexer 56 that demultiplexes a part of the light emitted from the filter 15, a PD 57 that receives the light demultiplexed by the optical demultiplexer 56, an autocorrelation intensity signal output unit 70, a signal processing unit 16, And a control unit 17.

  The WDM wavelength selection optical filter 51 extracts an optical signal having an arbitrary wavelength of a WDM channel from an optical signal transmitted by wavelength division multiplexing. The WDM wavelength selective optical filter 51 corresponds to the wavelength division multiplexed optical signal extraction means of the present invention.

  The optical demultiplexer 52 demultiplexes the optical signal extracted by the WDM wavelength selection optical filter 51 into two light beams, and transmits the transmitted light to the optical demultiplexer 11 and the reflected light to the PD 53, respectively.

  The PD 53 receives the reflected light from the optical demultiplexer 52, performs photoelectric conversion, and outputs an electric signal to the signal processing unit 16. Therefore, by sweeping the wavelength of the WDM wavelength selective optical filter 51, the signal processing unit 16 can acquire the spectral information of the optical signal under measurement, and sets the WDM wavelength selective optical filter 51 based on the spectral information. The measurement wavelength can be determined.

  The optical demultiplexer 54 demultiplexes the optical signal emitted from the wavelength tunable optical filter 12 into two light beams, and emits the transmitted light to the optical delay 13 and the reflected light to the PD 55, respectively.

  The PD 55 receives the reflected light from the optical demultiplexer 54, performs photoelectric conversion, and outputs an electric signal to the signal processing unit 16. Therefore, by sweeping the wavelength of the wavelength tunable optical filter 12, the signal processing unit 16 can acquire the spectrum information of the optical signal under measurement, and the measurement wavelength set in the wavelength tunable optical filter 12 based on the spectrum information. Can be determined.

  The optical demultiplexer 56 demultiplexes the optical signal emitted from the wavelength tunable optical filter 15 into two light beams, transmits the transmitted light to the half-wave plate 71 of the autocorrelation intensity signal output unit 70, and reflects the reflected light to the PD 57. It comes out.

  The PD 57 receives reflected light from the optical demultiplexer 56, performs photoelectric conversion, and outputs an electric signal to the signal processing unit 16. Therefore, by sweeping the wavelength of the wavelength tunable optical filter 15, the signal processing unit 16 can acquire the spectrum information of the optical signal under measurement, and the measurement wavelength set in the wavelength tunable optical filter 15 based on the spectrum information. Can be determined.

  Next, the operation of the chromatic dispersion measuring apparatus 50 in the present embodiment will be described with reference to FIGS. FIG. 10 is a flowchart showing the operation of the chromatic dispersion measuring apparatus 50.

  First, by sweeping the wavelength of the WDM wavelength selection optical filter 51, the spectrum of the WDM signal that is the optical signal to be measured is measured by the PD 53, and n measurement wavelengths are determined based on this spectrum (step S11). Here, n is an integer of 1 or more.

Next, the nth measurement wavelength λn is set in the WDM wavelength selection optical filter 51 (step S12). Since this is the first time, the first measurement wavelength λ ₁ is set as n = 1.

Subsequently, by sweeping the wavelength of the wavelength tunable optical filter 15, the spectrum of the measurement wavelength λ ₁ is measured by the PD 57, a set wavelength for extracting the LSB carrier component is determined based on the spectrum, and the wavelength tunable optical filter 15 is set (step S13).

Additionally, than to the wavelength sweeping tunable optical filter 12, the spectrum of the measurement wavelength lambda ₁ measured by PD55, to determine the setting wavelength for extracting a USB carrier component based on the spectrum, wavelength tunable optical filter 12 (Step S14).

Subsequently, the autocorrelation intensity signal output unit 70 measures the autocorrelation intensity while moving the optical delayer 13 in parallel, and obtains the position (L _D ) of the optical delayer 13 corresponding to the maximum intensity of the obtained autocorrelation waveform ( Step S15).

Then, similarly to the chromatic dispersion measuring apparatus 10 in the first embodiment, the moving distance between the position (L _D ) of the optical delay device 13 and the reference position (L _B ) of the optical delay device 13 is expressed by the equation (1). ) Is converted into the group delay time difference Δτ, and the group delay D ₁ is calculated by the equation (2) (step S16).

  Next, the control unit 17 determines whether or not the calculation of the group delay based on all the measurement wavelengths determined in Step S11 has been completed (Step S17), and if not completed, increments n (Step S18). The process of S12-17 is performed.

On the other hand, if the group delay calculation of by all measurement wavelengths is completed, each carrier wavelength lambda _1, the group delay _D 1 in _{λ 2 ··· λ n, D 2} ··· D n is obtained (step S19).

  Next, the signal processing in each of the above steps will be specifically described with reference to FIGS. FIGS. 11 and 12 conceptually show signal processing in the chromatic dispersion measuring apparatus 50.

In FIG. 11A, the triangle schematically shows a WDM signal. By setting the measurement wavelength λ ₁ determined in step S11 described above to the WDM wavelength selective optical filter 51, the WDM wavelength selective optical filter 51 can extract one WDM signal from a plurality of WDM signals as shown in the figure. it can. The WDM signal waveform extracted by the WDM wavelength selective optical filter 51 is, for example, as shown in FIG. 11B, and includes components of a carrier wave, an upper side wave, and a lower side wave.

  Next, by setting the set wavelength determined in the above-described step S13 in the wavelength tunable optical filter 15, the wavelength tunable optical filter 15 has each component of the carrier wave and the lower side wave, that is, as shown in FIG. The LSB carrier component can be extracted. In addition, it is preferable to use the wavelength tunable optical filter 15 having a half-value width substantially equal to the illustrated modulation frequency (Δfm).

  In addition, by setting the set wavelength determined in the above-described step S14 in the wavelength tunable optical filter 12, the wavelength tunable optical filter 12 causes each component of the carrier wave and the upper wave, that is, the USB carrier wave, as shown in FIG. Ingredients can be removed. Note that it is preferable to use the tunable optical filter 12 having a half-value width substantially equal to the modulation frequency (Δfm) shown in the figure.

  The bit patterns indicated by the LSB carrier component and the USB carrier component extracted as described above are as shown in FIG. 12, for example, and the bit patterns of both are correlated. If only the LSB component and only the USB component are extracted, the correlation between the two bit patterns cannot be obtained. However, in this embodiment, since the LSB component and the USB component each include a carrier wave component, both bit patterns are obtained. Is correlated.

As described above, according to the chromatic dispersion measuring apparatus 50 in the present embodiment, the WDM wavelength selective optical filter 51 extracts an optical signal having an arbitrary WDM channel wavelength, and the tunable optical filters 12 and 15 are respectively The USB carrier component and the LSB carrier component are extracted from the optical signal taken out by the WDM wavelength selection optical filter 51, and the autocorrelation strength signal output unit 70 is delayed by the optical delay unit 13 and the undelayed LSB carrier component. To output the autocorrelation intensity signal of the measured light, and the signal processing unit 16 outputs the position of the optical delay unit 13 (L _D ) where the relative intensity of the autocorrelation intensity signal is maximum and the reference position (L _D of the optical delay unit 13). _B ), the group delay time of the light to be measured is obtained, so that the chromatic dispersion of the ultrafast optical signal transmitted on the actual transmission path can be measured. The

  Further, unlike the conventional one, the chromatic dispersion measuring apparatus 50 in the present embodiment does not require a high-speed light receiving circuit, a high-speed phase comparator, and a high-speed clock recovery circuit, so that the manufacturing cost is reduced as compared with the conventional one. In addition, it is possible to measure the group delay time of an ultrafast optical signal.

(Sixth embodiment)
A chromatic dispersion measuring apparatus according to the present embodiment is shown in FIG. The chromatic dispersion measuring apparatus in the present embodiment is obtained by changing a part of the chromatic dispersion measuring apparatus 30 (see FIG. 7) in the second embodiment, and the chromatic dispersion measuring apparatus 50 in the fifth embodiment. (See FIG. 9). Therefore, the same components as those in the description of the wavelength dispersion measuring devices 30 and 50 are denoted by the same reference numerals, and redundant descriptions are omitted.

  As shown in FIG. 13, the chromatic dispersion measuring device 60 in the present embodiment includes an optical demultiplexer 11, an optical delay 13, a mirror 14, a signal processing unit 16, a control unit 17, and a wavelength tunable light. A filter 21, an optical demultiplexer 31, a PD 32, a WDM wavelength selection optical filter 51, an optical demultiplexer 52, a PD 53, and an autocorrelation strength signal output unit 70 are provided.

  Next, the operation of the chromatic dispersion measuring apparatus 60 in the present embodiment will be described with reference to FIGS. FIG. 14 is a flowchart showing the operation of the chromatic dispersion measuring apparatus 60.

  First, by sweeping the wavelength of the WDM wavelength selection optical filter 51, the spectrum of the WDM signal that is the optical signal to be measured is measured by the PD 53, and n measurement wavelengths are determined based on this spectrum (step S21). Here, n is an integer of 1 or more.

Next, the nth measurement wavelength λn is set in the WDM wavelength selection optical filter 51 (step S22). Since this is the first time, the first measurement wavelength λ ₁ is set as n = 1.

Subsequently, a wavelength tunable optical filter 21 than to the wavelength sweeping, the spectrum of the measurement wavelength lambda ₁ measured at PD 32, to determine the setting wavelength for extracting a USB carrier components and LSB carrier component based on the spectrum ( Step S23).

Furthermore, the set wavelength of the tunable optical filter 21 is set to the extraction wavelength of the LSB carrier component (step S24), and the autocorrelation strength signal output unit 70 uses the DSB carrier component and the LSB carrier component while moving the optical delayer 13 in parallel. The autocorrelation intensity of the light to be measured is measured, and the position (L _L ) of the optical delay device 13 corresponding to the maximum intensity of the obtained autocorrelation waveform is obtained (step S25).

Similarly, the set wavelength of the tunable optical filter 21 is set to the extraction wavelength of the USB carrier component (step S26), and the DSB carrier component and the USB carrier component are output by the autocorrelation strength signal output unit 70 while the optical delayer 13 is translated. Then, the autocorrelation intensity of the light to be measured is measured, and the position (L _U ) of the optical delay device 13 corresponding to the maximum intensity of the obtained autocorrelation waveform is obtained (step S27).

Then, similarly to the chromatic dispersion measuring device 30 in the third embodiment, the group delay time difference Δτ is obtained from the position (L _U ) and the position (L _L ) of the optical delay device 13 by the expression (3), and the expression ( 4) by calculating the group delay _{D 1} (step S28).

  Next, the control unit 17 determines whether or not the calculation of the group delay by all the measurement wavelengths determined in step S21 is completed (step S29), and if not completed, increments n (step S30), and step The process of S22-29 is performed.

On the other hand, if the group delay calculation of by all measurement wavelengths is completed, each carrier wavelength lambda _1, the group delay _D 1 in _{λ 2 ··· λ n, D 2} ··· D n is obtained (step S31).

As described above, according to the chromatic dispersion measuring device 60 in the present embodiment, the WDM wavelength selective optical filter 51 extracts an optical signal having an arbitrary WDM channel wavelength, and the tunable optical filter 21 performs the WDM wavelength selective light. The USB carrier component or LSB carrier component is extracted from the optical signal extracted by the filter 51, and the autocorrelation strength signal output unit 70 receives the DSB carrier component delayed by the optical delay device 13 and the USB carrier component or LSB carrier component not delayed. To output the autocorrelation intensity signal of the measured light, and the signal processing unit 16 acquires the group delay time of the measured light based on the position (L _U ) and the position (L _L ) of the optical delay device 13. Therefore, it is possible to measure the chromatic dispersion of the ultrahigh-speed optical signal transmitted through the actual transmission path.

  Further, unlike the conventional one, the chromatic dispersion measuring device 60 in the present embodiment does not require a high-speed light receiving circuit, a high-speed phase comparator, and a high-speed clock recovery circuit, so that the manufacturing cost is reduced as compared with the conventional one. In addition, it is possible to measure the group delay time of an ultrafast optical signal.

  As described above, the chromatic dispersion measuring apparatus according to the present invention can measure the chromatic dispersion of an ultrahigh-speed optical signal transmitted through an actual transmission line, and can reduce the manufacturing cost as compared with the conventional one. It is effective as a chromatic dispersion measuring apparatus that measures the chromatic dispersion of an ultrafast optical signal propagating in an optical fiber.

The block diagram which shows the structure in 1st Embodiment of the chromatic dispersion measuring apparatus which concerns on this invention. Explanatory drawing of the function of a nonlinear optical material in 1st Embodiment of the wavelength dispersion measuring apparatus which concerns on this invention In the first embodiment of the chromatic dispersion measuring apparatus according to the present invention, an explanatory diagram of the function of the nonlinear optical material (a) an explanatory diagram of the function of the type 1 nonlinear optical material (b) an explanation of the function of the type 2 nonlinear optical material Figure Explanatory drawing of the operation principle in the first embodiment of the chromatic dispersion measuring apparatus according to the present invention. The block diagram which shows the structure in 2nd Embodiment of the chromatic dispersion measuring apparatus which concerns on this invention. Explanatory drawing of the operation principle in the second embodiment of the chromatic dispersion measuring apparatus according to the present invention. The block diagram which shows the structure in 3rd Embodiment of the chromatic dispersion measuring apparatus which concerns on this invention. The block diagram which shows the structure in 4th Embodiment of the chromatic dispersion measuring apparatus which concerns on this invention. The block diagram which shows the structure in 5th Embodiment of the chromatic dispersion measuring apparatus which concerns on this invention. The flowchart which shows each step in 5th Embodiment of the chromatic dispersion measuring apparatus which concerns on this invention. The figure which showed notionally the signal processing in 5th Embodiment of the chromatic dispersion measuring apparatus which concerns on this invention The figure which showed notionally the signal processing in 5th Embodiment of the chromatic dispersion measuring apparatus which concerns on this invention The block diagram which shows the structure in 6th Embodiment of the chromatic dispersion measuring apparatus which concerns on this invention. The flowchart which shows each step in 6th Embodiment of the chromatic dispersion measuring apparatus which concerns on this invention. Block diagram of a conventional chromatic dispersion measuring device

Explanation of symbols

10, 20, 30, 40, 50, 60 Wavelength dispersion measuring device 11 Optical demultiplexer 12 Wavelength variable optical filter (USB carrier wave component extracting means)
13a Corner mirror 13b, 13c Mirror 13 Optical delay device (optical delay means)
14, 72 Mirror 15 Wavelength variable optical filter (LSB carrier component extraction means)
16 Signal processor (group delay time acquisition means)
17 Controller 21 Tunable optical filter (optical signal component extraction means)
31, 52, 54, 56 Optical demultiplexer 32, 53, 55, 57 PD (light receiving unit)
41, 70 Autocorrelation strength signal output section (autocorrelation strength signal output means)
42 Optical Gate Device 42a Optical Signal Input Port 42b Optical Control Signal Input Port 42c Optical Signal Output Port 44, 76 Light Receiver (Photoelectric Conversion Unit)
45, 77 LPF
46, 78 AD converter 51 WDM wavelength selective optical filter (wavelength division multiplexed optical signal extraction means)
71 1/2 wavelength plate 73 Optical multiplexer 74 Type 2 nonlinear optical material (sum frequency light emitting part)
75 Optical filter

Claims (8)

An optical demultiplexer (11) for demultiplexing an incident optical signal to be measured into first and second optical paths; a carrier component of the optical signal to be measured in one of the first and second optical paths; A USB carrier wave component extracting means (12) for extracting a USB carrier wave component indicating an upper sideband component of the carrier wave component from the measured optical signal; and a carrier wave of the measured optical signal on the other of the first and second optical paths. An LSB carrier component extracting means (15) for extracting an LSB carrier component indicating a component and a lower sideband component of the carrier carrier component from the optical signal to be measured, and delaying either the USB carrier component or the LSB carrier component The optical delay means (13) and the optical signal delayed by the optical delay means (13) and the non-delayed optical signal are incident to output an autocorrelation intensity signal of the optical signal to be measured. Based on the relationship strength signal output means (70), the position of the optical delay means (13) at which the relative intensity of the autocorrelation intensity signal is maximum, and the predetermined reference position of the optical delay means (13). Group delay time acquisition means (16) for acquiring a group delay time of the optical signal to be measured, and the optical signal to be measured is the autocorrelation when pulse light having a random pattern with zero chromatic dispersion is input. A chromatic dispersion measuring apparatus characterized in that the position of the optical delay device (13) having the maximum intensity signal is determined as the reference position . An optical demultiplexer (11) for demultiplexing an incident optical signal to be measured into first and second optical paths; a carrier component of the optical signal to be measured in one of the first and second optical paths; Light that extracts either the USB carrier component indicating the upper sideband component of the carrier wave component, the carrier wave component of the measured optical signal, or the LSB carrier component indicating the lower sideband component of the carrier wave component from the measured optical signal Signal component extraction means (21) and optical delay means (13) for delaying either the USB carrier component or the LSB carrier component and the measured optical signal in any of the first and second optical paths And when the optical delay means (13) enters the delayed one of the USB carrier component and the optical signal to be measured and the other optical signal that has not been delayed, the first optical signal to be measured Autocorrelation strength When the LSB carrier component delayed by the optical delay means (13) and one optical signal of the optical signal under measurement and the other optical signal not delayed are incident, the optical signal of the optical signal under measurement An autocorrelation intensity signal output means (70) for outputting a second autocorrelation intensity signal, a position of the optical delay means (13) at which the relative intensity of the first autocorrelation intensity signal is maximized, and the second Group delay time acquisition means (16) for acquiring the group delay time of the optical signal under measurement based on the position of the optical delay means (13) where the relative intensity of the autocorrelation intensity signal is maximum. A characteristic chromatic dispersion measuring device. The autocorrelation intensity signal output means (70) includes an optical multiplexer (73) for multiplexing one optical signal delayed by the optical delay means (13) and the other optical signal not delayed, and the optical multiplexer. A sum frequency light emitting unit (74) for emitting the sum frequency light indicating the light having the frequency which is the sum of the frequency of the one optical signal and the frequency of the other optical signal when the outgoing light of the waver (73) is incident. And a photoelectric conversion unit (76) for converting the sum frequency light into an electric signal . The chromatic dispersion measuring device according to claim 3 , wherein the sum frequency light emitting section (74) is formed of a nonlinear optical material . The autocorrelation intensity signal output means (41) receives the one optical signal delayed by the optical delay means (13) and the other optical signal not delayed, and indicates the autocorrelation of the measured optical signal. 3. An optical gate device (42) for emitting a signal, and a photoelectric conversion unit (44) for converting an optical signal emitted by the optical gate device (42) into an electrical signal. The chromatic dispersion measuring apparatus according to 1. A light receiving unit (55) for receiving at least part of the emitted light from the USB carrier component extracting means (12), and a light receiving unit (57) for receiving at least part of the emitted light from the LSB carrier component extracting means (15). The chromatic dispersion measuring device according to claim 1, wherein the chromatic dispersion measuring device is provided. The chromatic dispersion measuring apparatus according to any one of claims 2 to 5 , further comprising a light receiving unit (32) configured to receive at least a part of the light emitted from the optical signal component extraction unit (21) . The optical signal to be measured is a wavelength division multiplexed optical signal, and an arbitrary optical signal is measured from the optical signal to be measured between the optical demultiplexer (11) and a transmission path through which the optical signal to be measured is wavelength division multiplexed. A wavelength division multiplexed optical signal extracting means (51) for extracting a wavelength division multiplexed optical signal of a wavelength; and a light receiving section (53) for receiving at least a part of the emitted light of the wavelength division multiplexed optical signal extracting means (51). The chromatic dispersion measuring apparatus according to claim 1, further comprising a chromatic dispersion measuring apparatus.

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