JPS637329B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical signal input device in an optical signal observation device.

In optical communication and optical measurement using optical signals, there are methods that measure the intensity of light by converting a weak optical signal with intensity modulation of optical power into an electrical signal using a photodetector, and methods that measure the intensity of light by converting the optical signal into heat. A common method is to measure the intensity of light by electrically measuring this temperature. In this case, a PIN photodiode, a phototransistor, an avalanche photodiode (APD), or the like is used as a light receiving element that converts an optical signal into an electrical signal. Further, a thermal disk, a thermopile, etc. are used as a light receiving element that converts an optical signal into heat. However, the characteristics of these light-receiving elements change depending on temperature and electrical conditions of use, which deteriorates measurement accuracy. In particular, changes in dark current are a big problem. In addition, when converting into electricity with these light receiving elements, the output is obtained as a detected and rectified waveform or a predetermined time average value of the light intensity, so the modulation degree of the optical signal itself, the level of the light intensity, It was difficult to accurately observe the optical modulation waveform.

Here, an optical signal observation device in which the present invention is implemented will be explained with reference to FIGS. 1A, B, and C. FIG. 1A is a block diagram of an optical signal observation device, FIG. 1B is a signal waveform diagram of a main part of the optical signal observation device, and FIG. 1C is an example of waveforms displayed on a cathode ray tube.

In the optical signal observation device shown in FIG. 1A, an optical signal 1 input through an optical fiber or the like is chopped by a chopper of an optical signal input device 2 and converted into an electric signal 15 by a light receiving element. This electric signal 15 is amplified by an amplification device 3 to obtain an output signal 11 as shown in FIG. 1B. When this output signal 11 is displayed on the cathode ray tube 10 through the Y-axis deflection circuit 7, the waveform shown in FIG. 1C is obtained. Here, 52 is a change waveform of the optical signal intensity when the optical signal is transmitted by the chopper.
53 is a waveform in which the optical signal intensity is at zero level when the optical signal is cut off by the chopper. Therefore, it is possible to measure the level of an optical signal and the degree of modulation. Reference numeral 4 in FIG. 1A is a photosensitivity calibrator, which is composed of a light emitting element, an optical fiber, an optical connector, an optical modulator, etc., and has the function of a normal oscilloscope calibrator. The time axis circuit 6 generates a trigger signal at a predetermined level 50 shown in FIG. 1B, performs a sweep operation, and generates a slope signal shown in FIG. 1B (b). This is the output signal 17 of the time axis circuit 6.
becomes. This output signal 17 is applied to the cathode ray tube 10 through the X-axis deflection circuit 8. Further, the output 16 of the waveform shown in FIG. 1B from the time axis circuit 6 is Z
It is applied to the axis circuit 9. Here, a bright line appears at the H level of the output 16, and no bright line appears at the L level. On the other hand, the control circuit 5 detects the chopper synchronization signal 14 as shown in FIG. Also,
The control circuit 5 creates the waveform shown in FIG. This becomes the time axis control signal 13 in FIG. 1A. Furthermore, the control circuit 5 generates the signals shown in FIG. Figure 1B
1A is the waveform display control signal 19 of FIG. 1A, which enables the display of the waveform 52 of FIG. 1C when it is at L level, and FIG. Yes, when this is L level, the first
In addition to displaying the waveform 53 in FIG. 1C, it is also used to compensate for the drift of a broadband amplifier used in the optical signal input device 2 and amplifier 3 in FIG. 1A. It should be noted that drift compensation when only the waveform 52 is displayed is always performed or is performed during a period when no display is performed on the cathode ray tube. Further, an operation mode switching signal 18 is supplied from the control circuit 5 to the optical signal input device 2 to switch the operation mode.

As described above, the optical signal observation device makes it possible to observe the intensity level of the optical signal by chopping the optical signal, and also makes it possible to compensate for the drift of the amplification device, including the drift of the photodetector. . Therefore, a device that stably and reliably chops an optical signal and an optical-to-electrical converter that efficiently inputs the optical signal to a light receiving element are important. Generally known tuning fork type choppers have a small beam diameter of less than 1 mm, which makes them susceptible to vibrations, and if the optical intermittent frequency (hereinafter referred to as chopper frequency) is not stabilized, the Q of the oscillator will decrease and the operation will be impaired. The drawback is that it tends to become unstable. In addition, optical modulators using optical crystals, liquid crystals, etc. have excellent chopper frequency stability, but it is still difficult to achieve highly efficient modulation, making it difficult to achieve reliable intermittent light.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical signal input device for an optical signal observation device that has high photoelectric conversion efficiency and has flat frequency characteristics with respect to optical signal input.
Furthermore, another object of the present invention is to provide an optical signal input device for an optical signal observation device that is easy to control and allows stability of the chopper frequency to be easily obtained. Still another object of the present invention is to provide an optical signal input device for an optical signal observation device that allows easy observation of optical signals from various types of optical fibers.

Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 2 is a block diagram of an optical signal input device according to an embodiment of the present invention, in which an optical signal input from an optical fiber 201 is condensed by a converging lens 202 and a condensing lens 203 of an optical input connector section 209. This focused optical signal beam 204 is transmitted to a motor 211,
For example, the light receiving element 21 passes through the light transmission section 207 of the rotating disk 205 driven by a DC motor.
0, such as a PIN photodiode. The light receiving element 210 is biased by a power supply 290 through a filter composed of a resistor 231 and a capacitor 232, and connected to a 50Ω coaxial cable 220.
Broadband amplifier 21 with input impedance 50Ω at A
8 is input. Incidentally, the rotating disk 205 is driven by a motor 211 equipped with a gear head 212 for reduction. Here, the gear head 212 is the rotating disk 2
It has the function of increasing the rotational stability of 05 and facilitating control when the motor is stopped. This is because if the motor 211 has a relatively high rotational speed and is decelerated when the rotational torque is large, the influence of the motor's inertia can be reduced when the optical signal observation device is switched from DC mode to AC mode. There is an advantage that fluctuations in the stopping position of the rotating disk 205 can be minimized as much as possible. Here, the DC mode is a mode in which an optical signal is chopped and the waveform shown in FIG. 1C is displayed. In other words, the zero level 53 of the optical signal intensity and the optical signal waveform 52 can be displayed simultaneously. Further, the AC mode is a mode in which only the optical signal waveform 52 (waveform of change in optical signal intensity) is displayed. this
In the AC mode, the rotating disk 205 of the chopper is controlled by the motor control circuit 213 so as to always stop at the position of the light transmitting section 207. The chopper frequency of this chopper may be a low frequency that does not cause the display waveform displayed on the cathode ray tube to flicker. Furthermore, when the time axis sweep speed of the optical signal observation device is slowed down, the AC mode is automatically set, and the motor control circuit 213 controls the rotating disk 205 to stop at a position where the optical signal is always transmitted. be done.
Such switching of the operating mode is performed by inputting the operating mode switching signal 18 from the control circuit 5 of FIG. 1A to the input terminal 223 of the motor control circuit 213.

FIG. 3 is an example of a rotating disk used in a chopper of an optical signal input device. Here, 207 is the second
A transmission section 208 for transmitting the optical signal beam 204 shown in the figure is a transmission section used to control the rotational speed of the motor 211 and the stop position of the rotating disk 205. On the other hand, 206 is a base that blocks light, and is preferably a color that does not reflect light. Transparent part 2
07 needs to be large enough to completely transmit the optical signal beam 204. Note that although four rotating disks are shown in each transmitting section here, this may be changed as necessary. It goes without saying that the shape of the transparent portion can also be changed in the same way. By the way, as shown in FIG. 2, light detecting sections 215A and 215B made of, for example, photointerrupters are provided in a positional relationship opposite to the transmitting sections 207 and 208 of the rotating disk 205, so that the light detecting sections 215A and 215B, which are composed of, for example, photointerrupters, are provided to oppose the transmitting sections 207 and 208 of the rotating disk 205. Section 207, 208
Pick up the intermittent signal. Photodetector 215
The output of A is waveform-shaped by a waveform shaping circuit 217A and outputted to a synchronization signal terminal 222 as a chopper synchronization signal (14 in FIG. 1A). This synchronization signal passes through the control circuit 5 shown in FIG. 1A and is output as a drift compensation control signal (12 in FIG. 1A) to the terminal 2 in FIG.
24 and activates a drift compensation circuit 219 attached to a broadband amplifier 218. This makes it possible to eliminate the drift caused by the dark current of the light receiving element 210 and the drift caused by fluctuations in the offset voltage of the broadband amplifier 218 itself. Further, the output of the photodetector 215B is waveform-shaped by a waveform shaping circuit 217B and fed back to the motor control circuit 213 as a rotation synchronizing pulse for the rotating disk 205 to control the rotation speed of the motor 211.

Now, the optical signal photoelectrically converted by the photodetector 210 is amplified by a drift-compensated broadband amplifier 218, and the output signal is transmitted to a 50Ω coaxial cable 222.
B, connected by a coaxial connector 221, and supplied to the amplifying device 3 of FIG. 1A. Note that the broadband amplifier 218 is made to have an output impedance of 50Ω for matching with the coaxial cable 220B. Furthermore, since the output of the broadband amplifier 218 is drift-compensated, it hardly fluctuates even when the optical signal is blocked by the chopper. Furthermore, this broadband amplifier 218 is connected to the light receiving element 2.
Since the frequency characteristics of 10 are also compensated for, the signal output to the coaxial connector 221 has flat frequency characteristics with respect to the optical signal input. Therefore,
Since the amplification device 3 in FIG. 1A only needs to have flat frequency characteristics, if the optical signal input device 2 in FIG. 1A related to the optical signal input device of the present invention is removed and used, it can be used as an optical signal observation device. It also has the advantage of being able to be used as a regular oscilloscope with an input impedance of 50Ω.

FIG. 4 is a detailed configuration diagram of the optical input connector section of the optical signal input device. Components that are the same as in FIG. 2 are designated by the same numbers.

Here, 243 is an optical connector receptacle in which the condensing lens 203 is incorporated, and the light receiving element 21
0 are mutually arranged on the optical axis of the condenser lens 203 of the optical connector receptacle 243. Also,
The optical connector adapter 241 is screwed into the optical connector receptacle 243. This optical connector adapter 241 has a converging lens 202 as shown in the figure.
A is fixed by a sleeve 200A, and the optical axes of the condenser lens 203 and the convergent lens 202A are aligned by the sleeve 200A. The dotted line 202 of the optical connector receptacle 243 indicates the convergent lens 20 when the optical connector adapter 241 is screwed in.
This shows the position of 2A. Furthermore, optical fiber 2
The optical connector plug 240 of 01 is screwed into the optical connector adapter 241, and the optical connector plug 240 is screwed into the optical connector adapter 241.
The protrusion 244 of the optical fiber 200A is fitted into the sleeve 200A of the optical connector adapter 241, and the end 201A of the optical fiber is butted against the right end surface of the converging lens 202A. By coupling the optical connector plug 240 and the optical connector receptacle 243 with the optical connector adapter 241 in this manner, even an optical fiber having a wide aperture angle can be coupled with reduced optical power loss. That is, the optical signal beam output from the optical fiber 201 is converted into a substantially parallel beam by the converging lens 202A, and further condensed by the condensing lens 203 to form the optical signal beam 2.
04 to the light receiving element 210. At this time, since the rotating disk 205 is inserted between the light receiving element 210 and the optical connector receptacle 243, the focal length of the condenser lens 203 is, for example, about 10 to 25 mm. By the way, due to the difference in refraction of light depending on the wavelength of light, the optical signal beam transmitted through the converging lens 202A is not necessarily parallel, but some deviation occurs, but the focal length of the condensing lens 203 is the optical signal beam diameter of the incident light. Since the beam is large compared to , the focused optical signal beam can enter the light receiving surface of the light receiving element 210 almost perpendicularly. Therefore, the light receiving element 210
It has the advantage of being able to operate near the maximum photoelectric conversion efficiency.

Furthermore, for optical fibers that do not have optical connector adapters attached, the optical fibers can be easily connected by using the optical connector adapter 242 shown in FIG. 4. That is, the optical fiber 201 is inserted into the tapered portion of the optical connector adapter 242, and the optical fiber end face 201A is butted against the converging lens 202B. Sleeve 202B supports converging lens 202B and aligns the optical axis as in the previous example. Here, a convex lens or a plano-convex lens can be used for the condensing lens 203, and a commercially available rod lens (trade name: Cellhook Lens) can be used for the converging lenses 202A and 202B.

By configuring the optical input connector section 209 in this manner, the number of lenses can be reduced, and the attenuation of the intensity of the optical signal due to the transmittance of the lenses can be suppressed as much as possible. Moreover, in order to use a rotating disk as a chipper, it is necessary to secure a space in which the focused optical signal beam can be emitted over a certain distance. For this purpose, a lens with a long focal length is used as the condenser lens 203, so that the necessary space can be secured. Moreover, since it is possible to obtain a focused optical signal beam, the beam can be incident almost perpendicularly to the light receiving element 210 and can be received at a position close to the maximum photoelectric conversion efficiency, which has the advantage of minimizing changes in light receiving sensitivity due to the wavelength of the optical signal. . When inputting the optical signal output from the photosensitivity calibrator 4 in FIG. 1A, it is also possible to reduce measurement variations by using the same optical connector adapter as in actual use by using this optical connector adapter.

Note that the same effect can be obtained even if the condensing lens 203 is disposed between the light receiving element 210 and the rotating disk 205 to collect the optical signal output from the optical input connector and inputting it to the light receiving element 210. Needless to say.

As is clear from the above explanation, according to the present invention, since the optical signal input has a flat frequency characteristic, the amplifying device of the optical signal observation device can also have a flat frequency characteristic, so it is possible to achieve a wider band. In addition, since stability of the chopper frequency can be easily obtained, switching from DC mode to AC mode can be easily controlled.
Furthermore, the use of an optical input connector improves photoelectric conversion efficiency, and it is now possible to connect various optical fibers by simply replacing the optical connector adapter, further improving its practicality as an optical signal observation device.

[Brief explanation of the drawing]

Figure 1A is a block diagram of the optical signal observation device.
Figure B is a signal waveform diagram of the main part of the optical signal observation device, Figure 1C is an example of the waveform displayed on a cathode ray tube, and Figure 2 is a block diagram of the optical signal input device in the optical signal observation device according to an embodiment of the present invention. FIG. 3 is an example of a rotating disk used in a chopper of an optical signal input device, and FIG. 4 is a configuration diagram of an optical input connector section of the optical signal input device. 201... Optical fiber, 202... Focusing lens,
203... Condensing lens, 209... Optical input connector section, 204... Optical signal beam, 210... Light receiving element,
218... Broadband amplifier, 219... Drift correction circuit, 205... Rotating disk, 212... Gear head, 2
11...Motor, 213...Motor control circuit, 215
A, B...Photodetector, 217A, B...Waveform shaping circuit.

Claims (1)

[Scope of Claims] 1. An optical signal observation device having a DC mode in which an optical signal to be measured is chopped and an optical signal waveform including a zero level is displayed, and an AC mode in which only the optical signal waveform is displayed, An optical connector adapter is connected to an optical fiber through which a measurement optical signal is passed, and has a converging lens that converts the optical signal to be measured outputted from the optical fiber into a parallel beam; and the optical connector adapter is coupled to convert the parallel beam into a parallel beam. an optical connector receptacle having a condensing lens for condensing light; a light receiving means for detecting the measured optical signal condensed by the condensing lens; a rotating body having a first transmitting part that chops the transmitted optical signal to be measured; and a second transmitting part provided corresponding to the transmitting part and narrower than a transmitting area of the transmitting part; a synchronization signal generating means for generating a rotation synchronization signal using a transparent section; a rotary body control section for generating a rotation control signal using the second transmission section to control rotation and stop of the rotary body; An optical signal observation device comprising: amplifying means that includes a drift compensation circuit controlled by the output from the signal generating means and amplifies the output of the light receiving means and inputs it to the optical signal observation device. optical signal input device.