JPH07325011A - Extinction ratio measuring apparatus - Google Patents

Abstract

PURPOSE:To provide an extinction ratio measuring apparatus which can obtain a dynamic extriction ratio with high precision and display light waveform in the time axial direction. CONSTITUTION:A light source 1 sends continuous light rays to an optical switch 20 whose quenching ratio is unknown, the optical switch 20 is pulse-modulated by a driving circuit 2, a photodetector 3 detects pulse-modulated light rays of the optical switch 20, an amplifier 4 amplifies the output of the photodetetor 3 and at the same time changes the sensitivity, a limitter circuit 5 limits the output amplitude of the amplifier 4 and sends the output to an A/D converter 6, and there A/D conversion is done. A signal processing part 7 adds and averages the data of the A/D converter 6 and carries out logarithmic transformation, and a display part 8 displays the results. A CPU 9 sends out a signal 9A to control the timing of switching of the optical switch 20, a signal 9B to control the sensitivity of the amplifier 4, a signal 9C to control the timing of the A/D conversion, and a signal 9D to control the signal processing part 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an extinction ratio measuring device for measuring an extinction ratio of an optical switch used for optical communication, an optical pulse tester or the like.

[0002]

2. Description of the Related Art Next, FIG. 10 shows the structure of an extinction ratio measuring device for an optical switch according to the prior art. In FIG. 10, 21 is a light source, 22 is an optical switch, 23 is an optical power meter, and 24 is a switching circuit of the optical switch 22. In FIG. 10, the light source 21
Outputs a continuous light. The switching circuit 24 is the optical switch 22.
To be transparent. The optical power meter 23 is the optical switch 2
The power of the light transmitted through 2 is measured. Next, the switching circuit 24 sets the optical switch 22 to the cutoff state. The optical power meter 23 again measures the power of the leaked light of the optical switch 22. Here, the extinction ratio of the optical switch 22 is obtained by calculating the ratio of the optical power when the optical switch 22 is in the transmission state and the optical power when it is in the cutoff state.

In addition to the configuration shown in FIG. 10, there is a method in which the optical switch 22 is actually incorporated in an optical pulse tester and the quality of the extinction ratio of the optical switch 22 is determined from the measured waveform. Figure 1
Reference numeral 1 denotes a measurement waveform of the optical pulse tester, FIG. 11A shows a reference measurement waveform, and FIG. 11A shows a measurement waveform when the optical switch 22 having a poor extinction ratio is used. Figure 1
Comparing 1 a and 1 a, it can be determined that the measured waveform in FIG. 11 a is distorted and an optical switch with a poor extinction ratio is used.

FIG. 12 is a waveform chart in which the vertical axis represents the average optical power and the horizontal axis represents the mark ratio. In FIG. 12, the mark ratio is changed several times, and the average optical power at that time is measured. The measurement points are connected by a straight line on a logarithmic axis, and the extinction ratio is defined as the ratio of the average optical power P ₁ when the mark rate is ₁ and the average optical power P ₀ when the mark rate is 0.

[0005]

The extinction ratio measured in FIG. 10 is the extinction ratio in static characteristics, but when actually using an optical switch, it is often used in a high-speed switching state, and the extinction ratio is different. There is. In FIG. 11, since the optical switch is actually used for the optical pulse tester, the quality of the optical switch can be judged from the output waveform, but the extinction ratio cannot be measured. In FIG. 12, the extinction ratio in a state close to the actual use condition is indirectly obtained, but there is a problem in accuracy. This invention
An object of the present invention is to provide an extinction ratio measuring device that obtains a dynamic extinction ratio with high accuracy and displays an optical waveform in the time axis direction.

[0006]

In order to achieve this object, the present invention comprises a light source 1 for outputting continuous light to an optical switch 20 having an unknown extinction ratio, and a drive circuit 2 for pulse-modulating the optical switch 20. , A photodetector 3 for detecting the pulse-modulated light of the optical switch 20, an amplifier 4 for amplifying the output of the photodetector 3 and switching the gain, a limiter circuit 5 for limiting the output amplitude of the amplifier 4, and a limiter circuit. A / D converter 6 for A / D converting the output of 5 and A / D
A signal processing unit 7 that adds and averages the data from the D converter 6 and performs logarithmic conversion, and a display unit 8 that displays the result of the signal processing unit 7.
And a signal 9A for controlling the switching timing of the optical switch 20 and a signal 9B and A for controlling the gain of the amplifier 4.
A CPU 9 that outputs a signal 9C that controls the timing of the / D conversion and a signal 9D that controls the signal processing unit 7 is provided.

[0007]

The structure of the extinction ratio measuring device according to the present invention is shown in FIG. 1, 1 is a light source, 2 is a drive circuit, 3 is a photodetector, 4 is an amplifier, 6 is a limiter circuit, 6 is an A / D converter, 7 is a signal processing unit, 8 is a display unit, 9 is a CPU, Reference numeral 20 is an optical switch to be measured.

In FIG. 1, the light source 1 outputs continuous light. C
The PU 9 outputs a periodic signal 9A and gives the drive circuit 2 a trigger for driving the optical switch 20. The drive circuit 2 drives the optical switch 20 by the signal 9A. Optical switch 2
Reference numeral 0 is a signal from the drive circuit 2, and pulse-modulates continuous light from the light source 1.

FIG. 6 shows a waveform of light input to the photodetector 3. The photodetector 3 detects the output light of the optical switch 20 shown in FIG. 6 and converts it into an electric signal. The amplifier 4 is the photodetector 3
Is amplified with a gain according to the signal 9B from the CPU 9. The limiter circuit 5 is a configuration required when measuring a high extinction ratio. The case where the extinction ratio is low may not be described here.

The A / D converter 6 receives the signal 9C from the CPU 9
To perform analog / digital conversion. FIG. 7 shows an input voltage waveform to the A / D converter 6. In Fig. 7, each point is a CPU
A / D of the A / D converter 6 given by the signal 9C of 9
It shows the timing of conversion. In order to improve the time resolution, the timing may be slightly shifted and repeated measurement may be performed.

The signal processing unit 7 receives the repetitive waveform of FIG. 7 from the A / D converter 6, and every arbitrary integral multiple (double in FIG. 7) of the cycle of the signal 9A input to the drive circuit 2. The data from the A / D converter 6 to the signal 9D of the CPU 9
To improve the signal-to-noise ratio by averaging,
After the averaging, the circled part in FIG. 7, that is, the time average at a signal voltage close to 0 is calculated to obtain the reference voltage. Further, the extinction ratio is obtained by calculating the time average of the part of Δ and dividing by the reference voltage. The extinction ratio may be obtained by performing logarithmic conversion of the data using the reference voltage and then subtracting the data. The display unit 8 displays the extinction ratio and the measured waveform obtained by the signal processing unit 7.

Next, the operation of the limiter circuit 5 will be described.
The limiter circuit 5 has a configuration necessary when the extinction ratio of the optical switch 20 is higher than the measurement limit of the extinction ratio limited by the A / D converter 6.

FIG. 8 shows the waveform of the input voltage to the A / D converter 6 when the gain of the amplifier 4 is reduced by the signal 9B of the CPU 9. The signal processor 7 performs the operation described with reference to FIG.
After the processing of the signal processing unit 7 is completed, the CPU 9 outputs the signal 9B.
Increase the gain of amplifier 4.

FIG. 9 shows the waveform of the input voltage of the A / D converter 6 when the gain is high. The limiter circuit 5 cuts over the limiter voltage shown in FIG. 9 to prevent an excessive input to the A / D converter 6. The signal processing unit 7 again performs the operation described in FIG.
The previously measured data when the gain is low is multiplied by the changed gain and combined. The optical switch 20 having a high extinction ratio can be measured by sequentially switching the gain of the amplifier 4 and repeating this operation in the signal processing unit 7.

As the light source 1, various laser light sources such as a semiconductor laser can be used. As the optical switch 20 to be measured, various optical switches such as a waveguide type optical switch and an A / O switch can be used. The photodetector 3 generally uses a photodiode, a photomultiplier tube, or the like.

[0016]

[Embodiment] Next, the configuration of an embodiment according to the second invention is shown in FIG.
Shown in. Reference numeral 10 in FIG. 2 is a variable wavelength light source, and other components are the same as those in FIG. That is, FIG. 2 shows a CPU instead of the light source 1.
Variable wavelength light source 10 for changing the oscillation wavelength by the signal 9E of 9
It is equipped with. As a result, the wavelength characteristic of the extinction ratio of the optical switch 2 is measured. The variable wavelength light source 10 may be a semiconductor laser alone, a semiconductor laser with an external resonator or a diffraction grating, or a solid-state laser such as a YAG laser.

Next, the configuration of the embodiment according to the third invention is shown in FIG.
Shown in. Reference numeral 11 in FIG. 3 is a polarization controller, and other components are the same as those in FIG. That is, FIG. 3 shows a polarization controller 11 which converts the light from the light source 1 into an arbitrary polarized light by the signal 9F from the CPU 9 between the light source 1 and the optical switch 20 and outputs the polarized light.
It is equipped with. Thereby, the extinction ratio of the optical switch corresponding only to the TE mode which is often found in the waveguide type optical switch can be measured. For the polarization controller 11, a fiber coil type, a combination of λ / 2 and λ / 4, a type in which a lateral pressure is applied to the fiber, a waveguide type, or the like is used. FIG. 4 is a configuration diagram when the variable wavelength light source 10 and the polarization controller 11 are combined.

Next, FIG. 5 shows a concrete configuration diagram of the embodiment shown in FIG. Reference numeral 10 in FIG. 5 denotes a variable wavelength light source, which includes a diffraction grating 10A, a rotary stage 10B, and a semiconductor laser 10C, and rotates the rotary stage 10B by a signal 9E from the CPU 9 to change the wavelength.

Reference numeral 11 denotes a polarization controller which is a combination of a λ / 2 wavelength plate and a λ / 4 wavelength plate, and which is a signal 9F of the CPU 9
, The λ / 2 plate and the λ / 4 plate are rotated to obtain an arbitrary polarized wave. Reference numeral 20 is an A / O switch to be measured.

Reference numeral 2 is a drive circuit assembled by TTL, and 2A
Is a monostable and 2B is a Schmitt trigger type buffer. Monostable 2A is signal 9 from CPU 9.
At the rising edge of A, for example, a pulse of 1 μs is output. The buffer 2B shapes the output pulse of the monostable 2A and outputs it to the A / O switch 20. The photodetector 3 uses the PIN-PD 3A, and the transimpedance amplifier 3B performs current-voltage conversion.

Reference numeral 4 is an amplifier, 4A is a Zener diode, 4B is an adder, 4C and 4D are relays, 4E is a relay drive circuit, and 4F is an amplifier having a gain of 40 dB. For switching the gain of the amplifier 4, relays 4C and 4D are used.
Then, the switching of the gain is further done. The Zener diode 4A and the adder 4B are for adding a white noise to the signal to obtain a dither effect in the A / D converter 6. A Darlington transistor is used for the relay drive circuit 4E, for example. The limiter circuit 5 uses a diode bridge and has a limiter voltage of ± 1.4 V here.

The A / D converter 6 is 8 bits and the input voltage is 0.
From + 2V was used. A boxcar integrator is used as the averaging unit of the signal processing unit 7, and other calculation processing and display unit 8 are used.
A personal computer was used for this.

To briefly explain the operation, the pulse signal detected by the photodetector 3 first passes through the adder 4B side of the amplifier 4 and is input to the limiter circuit 5 as a peak voltage of about 1V. Since the limiter voltage of the limiter circuit 5 is 1.4V, the pulse signal passes through the limiter circuit 5 here. After A / D conversion is performed by the A / D converter 6, the boxcar integrator of the signal processing unit 7 adds and averages.

In the circuit of FIG. 5, HI is calculated from the result of arithmetic mean.
Average some GH level data over time,
The average of the peak values of the pulses was calculated to obtain 0.93V. Then, the signal 9B is used to set the signal path of the amplifier 4 to the amplifier 4F side to increase the gain by 40 dB. By the limiter circuit 5, 1.
The voltage of 4V or more is cut off, and only the low level signal is A
Input to the / D converter 6. 12m by taking the time average of some LOW level data after arithmetic averaging
V is obtained.

When the average value of the HIGH level previously averaged using this average value as a reference voltage is logarithmically converted, it is 37.8d.
B is obtained. A gain of 40 dB in the amplifier 4 is added to the result of logarithmic conversion to obtain 37.8 + 40 = 77.8 dB. Since the optical power of the photodiode is proportional to the current, the extinction ratio of the A / O switch 20 is 77.8 / 2 =
It becomes 38.9 dB. The display 8 displays this data,
Check the waveform. Furthermore, by converting the data logarithmically and displaying it as waveform data, it is possible to observe waveform distortion at a minute level.

[0026]

According to the present invention, the optical switch is operated cyclically, the arithmetic mean is taken as an integral multiple of the cycle, and the logarithmic conversion is performed, so that the dynamic extinction ratio can be obtained accurately. It is possible to provide an extinction ratio measuring device that displays an optical waveform in the time axis direction. In addition, the wavelength characteristic of the extinction ratio of the optical switch 20 can be measured by using a variable wavelength light source as the light source that enters the optical switch. Further, by inserting a polarization controller 11 that converts the input light into an arbitrary polarization by the signal 9F of the CPU 9 between the light source 1 and the optical switch 20, only the TE mode often found in the waveguide type optical switch is supported. The extinction ratio of the optical switch can also be measured.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an extinction ratio measuring device according to a first invention.

FIG. 2 is a configuration diagram of an extinction ratio measuring device according to a second invention.

FIG. 3 is a configuration diagram of an extinction ratio measuring device according to a third invention.

FIG. 4 is a configuration diagram in which a variable wavelength light source 10 and a polarization controller 11 are combined.

5 is a configuration diagram of the embodiment of FIG.

6 is an output optical waveform diagram of the optical switch 20 of FIG.

7 is an input voltage waveform diagram of the A / D converter 6 of FIG.

8 is an input voltage waveform diagram of the A / D converter 6 when the gain of the amplifier 4 of FIG. 1 is low.

9 is an input voltage waveform diagram of the A / D converter 6 when the amplifier 4 of FIG. 1 has a high gain.

FIG. 10 is a configuration diagram of an extinction ratio measuring device according to a conventional technique.

FIG. 11 is a measurement waveform diagram of the optical pulse tester.

FIG. 12 is a waveform chart of average optical power and mark rate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 light source 2 drive circuit 3 photodetector 4 amplifier 5 limiter circuit 6 A / D converter 7 signal processing unit 8 display unit 9 CPU 10 variable wavelength light source 11 polarization controller 20 optical switch 21 light source 22 optical switch 23 optical power meter 24 Switching circuit

Claims (3)

[Claims] 1. A light source (1) for outputting continuous light to an optical switch (20) whose extinction ratio is unknown, a drive circuit (2) for pulse-modulating the optical switch (20), and an optical switch (20). Photodetector for detecting pulse-modulated light (3)
The amplifier (4) that amplifies the output of the photodetector (3) and switches the gain, the limiter circuit (5) that limits the output amplitude of the amplifier (4), and the output of the limiter circuit (5) are input. And A / D convert A
A / D converter (6) and a signal processing unit (7) that adds and averages the data from the A / D converter (6) and performs logarithmic conversion, and a display unit that displays the results of the signal processing unit (7) ( 8), a signal (9A) for controlling the switching timing of the optical switch (20), and a signal (9B) for controlling the gain of the amplifier (4) and A /
Signal (9C) for controlling D conversion timing and signal processing unit
An extinction ratio measuring device comprising a CPU (9) which outputs a signal (9D) for controlling (7). 2. The extinction ratio measuring device according to claim 1, further comprising a wavelength tunable light source (10) which tunes a wavelength by a signal (9E) from a CPU (9). 3. An optical switch according to a signal (9F) from a CPU (9)
Polarization controller that controls the input light of (20) to arbitrary polarization
The extinction ratio measuring device according to claim 1, further comprising (11).