JP6010407B2 - Optical signal measuring device - Google Patents

Description

  The present invention relates to an optical signal measuring apparatus, and more particularly to an improvement of a measuring apparatus used for measuring characteristics of multiplexed optical signals in WDM or the like.

  Along with the dramatic increase in information transmission in information communication in recent years, WDM (Wavelength Division Multiplexing) technology using an optical fiber as a transmission line is attracting attention as a means for realizing high-speed and large-capacity transmission.

  WDM is a system that uses a single optical fiber in a multiplexed manner by utilizing the property that light having different wavelengths does not interfere with each other and simultaneously transmitting a plurality of optical signals having different wavelengths. According to a transmission system using WDM, for example, a transmission capacity of terabits per second can be realized by multiplexing a 128-wave optical signal of 10 Gbps.

  In such WDM transmission, for example, if the wavelength of each multiplexed optical signal fluctuates beyond the specification range, the signal quality at the receiving unit is significantly degraded.

  Therefore, in order to monitor whether or not an abnormality has occurred in each multiplexed optical signal, for example, a wavelength meter configured as described in Patent Document 1 has been proposed.

  Patent Document 2 describes a wavelength meter technique that can be easily averaged in order to more accurately measure the noise power level between optical signals by reducing device noise.

  FIG. 3 is a block diagram illustrating a configuration example of the wavelength meter described in Patent Document 1. In FIG. 3, the measurement light input unit 1 outputs to the interferometer 3 light to be measured in which a plurality of optical signals having different wavelengths transmitted by WDM transmission via an optical fiber cable are multiplexed.

  The reference light source 2 is composed of a helium neon (HeNe) laser or the like, and is a light source that generates reference light having a predetermined wavelength for measuring the optical frequency, optical wavelength, and power of the light to be measured. The light is output to the interferometer 3.

  The interferometer 3 is a device that converts the measured light input from the measurement light input unit 1 or the reference light input from the reference light source 2 into an electrical signal proportional to the optical frequency and outputs the electrical signal, and creates an interference waveform. A prism lens, a reflection mirror, and a PD (Photo Diode) for converting an interference waveform into an electric signal.

  The interferometer 3 first creates an interference waveform by amplifying and interfering the measured light input from the measurement light input unit 1 or the reference light input from the reference light source 2 with a prism lens, a reflection mirror, or the like. Then, the PD detects the light amount of the interference waveform and converts it to an electric signal having a frequency proportional to the optical frequency (optical wavelength), and outputs the converted electric signal to the calculation unit 4.

  The calculation unit 4 decomposes the electric signal input from the interferometer 3 into each frequency component and outputs it to the CPU 5.

The CPU 5 calculates (measures) the optical frequency, the optical wavelength, and the power of the light under measurement based on the electric signal with respect to the reference light and the electric signal with respect to the light under measurement which are decomposed into frequency components, and the measurement results It is displayed on the display unit 7. The measurement principle of this optical frequency and optical wavelength is derived from the following equations (1) and (2).
Optical frequency of light to be measured = (speed of light / frequency of interference waveform of reference light) × optical frequency of reference light (1)
Light wavelength of light to be measured = light speed / light frequency of light to be measured (2)

  Further, the CPU 5 calculates (measures) the optical frequency of the light to be measured and performs monitoring processing of the light to be measured.

  First, when a WDM optical signal serving as a reference wave for monitoring is input to the measurement light input unit 1, each unit performs the same operation as the measurement of measured light, and finally an electrical signal is input to the CPU 5. The Then, the CPU 5 measures power (amount of power) and wavelength in each frequency component of the optical signal that becomes the monitoring reference wave, and stores the measured value in a storage unit (not shown).

  Next, after each value of the monitoring reference wave is set, when measured light during WDM transmission is input to the measuring light input unit 1, the CPU 5 measures the power and wavelength of the measured light, The measured light is monitored by comparing with the power and wavelength of the set reference wave for monitoring.

  At this time, if the power and wavelength of the light to be measured are different from the power and wavelength of the reference wave for monitoring and the fluctuation amount (deviation) is equal to or greater than a predetermined threshold, the CPU 5 has an abnormality in the WDM transmission. It determines with having generate | occur | produced, and the display to that effect is output to the display part 7. FIG.

  FIG. 4 is an explanatory diagram of the power fluctuation amount of each multiplexed optical signal in WDM transmission. In FIG. 4, the horizontal axis represents a wavelength in units of nm (nanometers), for example, and the vertical axis represents power in units of dBm, for example. Further, the solid line is the waveform of the light under measurement during measurement, and the broken line is the waveform of the monitoring reference wave.

  In FIG. 4, three peaks 1 to 3 indicate WDM transmission in which three optical signals in which optical signals of three different wavelengths are included in the measured light are multiplexed. A miscellaneous signal (noise) is transmitted / propagated between valleys when these peaks 1 to 3 are peaks, for example, between peak 1 and peak 2 or between peak 2 and peak 3.

  The difference in power between the waveform of the light under measurement at these three peaks 1 to 3 and the waveform of the reference wave for monitoring, that is, fluctuations 1 to 3 in FIG. It is.

  FIG. 5 is an explanatory diagram of the wavelength variation of each multiplexed optical signal in WDM transmission. As in FIG. 4, three peaks 4 to 6 are included, the solid line is the waveform of the light under measurement being measured, and the broken line is the waveform of the monitoring reference wave. The difference in wavelength between the waveform of the light under measurement and the waveform of the monitoring reference wave at the three peaks 4 to 6, that is, the fluctuations 4 to 6 in FIG. 5 are the fluctuation amounts of the wavelengths of the multiplexed optical signals in the WDM transmission. is there. The power fluctuation amount in FIG. 4 and the wavelength fluctuation amount in FIG. 5 are monitored by the CPU 5.

  FIG. 6 is a flowchart showing the operation of the monitoring process by the CPU 5. In FIG. 6, when a threshold value of the amount of variation of light to be monitored to be monitored, that is, an allowable range of fluctuation is input from the input unit (step S1), the CPU 5 stores the allowable range in the storage unit.

  When a WDM optical signal serving as a monitoring reference wave is input to the measurement light input unit 1, an interference waveform of the monitoring reference wave is created by the interferometer 3 and converted into an electric signal. The calculation unit 5 decomposes each frequency component.

  The CPU 5 calculates (measures) the frequency (wavelength) and power from the electrical signal for each frequency component, and stores and sets the wavelength and power in the storage unit as a predetermined reference value of the monitoring reference wave (step S2). .

  When the light to be measured is input from the measurement light input unit 2 after the monitoring reference wave is set, an electrical signal is input to the CPU 5 via the interferometer 3 and the like, as in the measurement of the monitoring reference wave. The CPU 5 measures the light to be measured and displays the measurement result on the display unit 6 (step S3).

  Further, the CPU 5 detects a peak representing each optical signal multiplexed in the measured light, and compares it with the wavelength and power at the peak of the monitoring reference wave. Then, it is determined whether the difference between the wavelength and power at the peak of the monitoring reference wave and the value of the wavelength and power at the peak of the light to be measured exceeds the allowable range set in step S1 (step S4). .

  If it is within the allowable range, the CPU 5 proceeds to step S3 and continues the measurement of the light to be measured, and if it exceeds the allowable range, an alarm message indicating that the allowable range has been exceeded is displayed on the display unit 6. Display (step S5), stop the measurement of the light to be measured (step S6), and end the monitoring process.

  FIG. 7 is a block diagram showing a configuration example of a wavelength meter using a Michelson interferometer described in Patent Document 2. In FIG. 7, the optical signal 12 to be analyzed is input to the beam splitter 13 and is decomposed into a first light beam reflected by the fixed reflecting mirror 14 and a second light beam reflected by the movable reflecting mirror 15.

  The first and second light beams are combined again at the beam splitter 13 and interfere with each other to generate an optical signal applied to the light receiving element 18. When the input optical signal consists of a single wavelength signal, the optical signal detected by the light receiving element 18 changes sinusoidally as the actuator 16 moves the reflecting mirror 15 at a constant speed.

  This signal is sampled by the sampling circuit 17. The point at which the signal is sampled is determined by the second signal generated based on the reference light beam 11 output from a high-precision light source such as a normal He-Ne laser. The reference light beam 11 is divided into two light beams by the beam splitter 13. These light beams are respectively reflected by the fixed and movable reflecting mirrors 14 and 15 and are combined again by the beam splitter 13.

  The combined light flux is input to the light receiving element 19. The output of the light receiving element 19 has a reference signal amplitude that changes sinusoidally, and changes one cycle each time the movable reflecting mirror 15 moves a distance equal to a half wavelength of the reference signal. The sampling circuit 17 triggers sampling of the signal from the detector 18 using this fixed point of the reference signal amplitude.

  The reference signal 11 indicates the change in the position of the reflector very precisely, but does not give any information about the absolute position of the reflector. In order to average the sampled signal from the detector 18, this sampled signal must start at the same point in the reflector stroke in the sequential sweep of the reflector. In principle, the reflector actuator can include an encoder that provides a signal that gives the absolute position of the actuator mechanism and consequently the position of the reflector to be determined.

  However, since the actuator has a large backlash that is a fraction of the wavelength of the reference beam, the encoder cannot provide the accuracy required for determining the absolute position of the reflecting mirror.

  In the configuration of FIG. 7, this problem is solved by providing a position detector for determining when the reflecting mirror passes through the fixed point during movement in a predetermined direction.

  That is, every time the reflecting mirror passes this position, the controller 20 starts a new series of measurements. The resulting series of measurements is then averaged before applying the FFT to the averaged series of measurements. Therefore, a base mark detection unit 23 for detecting the base mark 22 on the stage holding the reflecting mirror 15 is used.

JP 2001-66220 A JP2002-333371

  However, since the wavelength meters described in Patent Document 1 and Patent Document 2 only calculate the wavelength at an arbitrary measurement time, for example, optical signals having wavelength fluctuations in the medium to long term are representative thereof. It is difficult to measure the value.

  The present invention solves such a problem, and an object of the present invention is to realize an optical signal measuring apparatus capable of measuring a representative value of a wavelength in a stable state, for example, in the case of an optical signal having a fluctuation in wavelength. There is to do.

In order to achieve such an object, the invention described in claim 1 of the present invention is
In the optical signal measuring apparatus configured to obtain the wavelength and power of the measured light based on a plurality of waveform data obtained by performing FFT on the interference fringes of the measured light,
Waveform data storage means for sequentially storing waveform data such as wavelength data and power data of measured light calculated by FFT together with measurement target attribute data such as measurement time data and measurement channel data;
Waveform data selection means for selecting desired waveform data based on the measurement target attribute data from the waveform data storage means ;
Statistical calculation means for performing desired statistical calculation using the waveform data selected by the waveform data selection means,
Is provided.

The invention according to claim 2 is the optical signal measuring device according to claim 1,
The desired statistical calculation includes at least one of an average wavelength, average power, maximum wavelength, minimum wavelength, maximum power, minimum power, wavelength standard deviation, and power standard deviation of the light to be measured. .

The invention described in claim 3 is the optical signal measuring device according to claim 1 or 2, wherein
The measured light is a multiplexed optical signal.

The invention according to claim 4 is the optical signal measuring device according to any one of claims 1 to 3,
The waveform data selected by the waveform data selection means is a channel having a wavelength closest to the (m-1) th waveform data and the mth measurement result.

  According to such a configuration, for example, the center wavelength of an optical signal having a fluctuation in wavelength can be measured.

It is a block diagram which shows one Example of this invention. It is an example figure of the waveform data used as the object of the statistical calculation of this invention. It is a block diagram which shows the structural example of the conventional wavelength meter. It is explanatory drawing of the power fluctuation amount of each optical signal multiplexed in WDM transmission. It is explanatory drawing of the amount of wavelength fluctuations of each multiplexed optical signal in WDM transmission. It is a flowchart which shows the operation | movement of the monitoring process by CPU5 of FIG. It is a block diagram which shows the structural example of the conventional wavelength meter using a Michelson interferometer.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention, and the same reference numerals are given to portions common to FIG. In FIG. 1, the FFT calculation unit 24 calculates the wavelength and power of light output from the light source 1 to be measured by performing fast Fourier transform (hereinafter referred to as FFT) on the interference fringes detected and output from the optical unit 3. In the waveform data storage unit 25, waveform data such as wavelength data and power data of light output from the light source 1 to be measured calculated by the FFT calculation unit 24 are measured attributes such as measurement time data and measurement channel data. Stored sequentially with data.

  The statistical calculation target selection unit 26 includes a plurality of waveform data stored in the waveform data storage unit 25 as a target of waveform data for a plurality of times for which statistical calculation such as averaging calculation is performed by the statistical calculation unit 27 in the subsequent stage. To determine which measurement channel waveform data is to be selected.

  The waveform data calculated by the FFT calculation unit 24 is not limited to a single channel measurement result, but may be a measurement result of a plurality of channels. In these statistical calculations, for example, the waveform data of which channel in the (m-1) th measurement as shown in FIG. 2 (A) and the waveform data of which channel in the mth measurement as shown in FIG. 2 (B). It is necessary to determine whether to perform statistical calculation. The statistical calculation target selection unit 26 has a function of selecting and determining these averaging targets.

  For example, in the averaging calculation, basically, the channel having the closest wavelength in the m-1th waveform data and the mth measurement result is set as the averaging target. As this calculation method, for example, a method for determining the identity of a WDM channel described in JP-A-2002-290346 can be applied.

  For the calculation of the average wavelength λave (j, m) of m times for channel j in the statistical calculation unit 27, the following equation is used. Note that λ (j, m) is a wavelength that is the mth measurement result of channel j.

  Note that the following equation may be used in the same manner as the normal average calculation.

  In calculating the averaged power Pave (j, m), the following equation is used.

  Or you may use the following formula | equation.

  The calculation results of the average wavelength λave (j, m) and average power Pave (j, m) calculated by the statistical calculation unit 27 based on these equations are visualized and displayed on the display screen of the display unit 6.

  Thereby, it is possible to measure the average wavelength and the average power of light having fluctuations in wavelength.

  In addition, although the example which calculates an average wavelength and average power by the statistical calculation part 27 was demonstrated in the said Example, it is not restricted to these, The maximum wavelength, the minimum wavelength, the maximum power, the minimum power, the standard deviation of a wavelength, It is also possible to know the stability of the channel by calculating the standard deviation of the power.

  By using such an optical signal measuring device, it is possible to efficiently monitor whether or not an abnormality has occurred in a multiplexed optical signal such as WDM.

  Further, the optical signal measuring device according to the present invention is not limited to monitoring the occurrence of abnormality of multiplexed optical signals, but is also effective for measuring the characteristic change of a single optical signal.

  As described above, according to the present invention, it is possible to realize an optical signal measuring apparatus capable of measuring a representative value of a wavelength in a stable state even in the case of an optical signal having a fluctuation in wavelength, for example.

1 Light source to be measured 3 Optical part (interferometer)
6 Display Unit 24 FFT Operation Unit 25 Waveform Data Storage Unit 26 Statistical Operation Target Selection Unit 27 Statistical Operation Unit

Claims (4)

In the optical signal measuring apparatus configured to obtain the wavelength and power of the measured light based on a plurality of waveform data obtained by performing FFT on the interference fringes of the measured light,
Waveform data storage means for sequentially storing waveform data such as wavelength data and power data of measured light calculated by FFT together with measurement target attribute data such as measurement time data and measurement channel data;
Waveform data selection means for selecting desired waveform data based on the measurement target attribute data from the waveform data storage means ;
Statistical calculation means for performing desired statistical calculation using the waveform data selected by the waveform data selection means,
An optical signal measuring device characterized by comprising:   The desired statistical calculation includes at least one of an average wavelength, average power, maximum wavelength, minimum wavelength, maximum power, minimum power, wavelength standard deviation, and power standard deviation of the light to be measured. The optical signal measuring device according to claim 1.   3. The optical signal measuring apparatus according to claim 1, wherein the measured light is a multiplexed optical signal.   4. The waveform data selected by the waveform data selection means is a channel having a wavelength closest to the (m-1) th waveform data and the mth measurement result. The optical signal measuring device described.

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