JPH0568152U - Optical signal receiver - Google Patents

Abstract

(57) [Abstract] [Purpose] It is possible to monitor without cutting the optical fiber that is transmitting the optical signal. [Structure] Optical fiber 61 transmitting modulated optical signal
The optical fiber is bent by the first optical fiber pressing plate 67 and the second pressing plate, and the leaked light 63 during transmission emitted from the bending point 66 is received by the plurality of light receiving means 1.
Here, each of the O / E converted electric signals is input to the delay means 2 to adjust the timing. The electric signals whose timings have been adjusted are input to the signal synthesizing means 3, where the respective electric signals are synthesized, and the signal reproducing means 4 restores the modulated signals. Furthermore, waveform evaluation is performed using the output of the signal synthesizing means 3.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an optical signal receiving device for receiving an optical signal transmitted through an optical fiber without cutting the optical fiber at any position other than an optical signal transmitting end and a receiving end of the optical fiber. More specifically, an optical pulse tester (OTDR) is used for measuring the transmission characteristics of the optical fiber and searching for the position of the break point. When a PCM signal is transmitted through the optical fiber, waveform distortion may occur due to the wavelength dispersion phenomenon of light. There is a demand to know where in the optical fiber the distortion of the waveform occurs, but the above-mentioned OTDR does not meet the demand. Therefore, the present invention relates to a technique for efficiently receiving a part of an optical signal being transmitted via an optical fiber and monitoring the transmission state of the optical fiber.

[0002]

[Prior Art]

 (In the case of a fiber-contrast sensor) A so-called fiber-contrast sensor is known as a method of measuring the power of an optical signal propagating through an optical fiber without cutting the optical fiber. In the case of a germanium photodiode (hereinafter referred to as PD) used for a core wire contrast sensor, a light receiving diameter φ of 1 mm to 2 mm is used to receive light leaking from a bent portion of an optical fiber. The electrical characteristics of such PDs are large corresponding to the light-receiving area, so a high-speed response of 1MHz or more is not possible, and an optical signal modulated at a high frequency such as PCM modulation is converted into an electrical signal. It was impossible to do.

The technology of the core wire contrast sensor is disclosed, for example, in Japanese Utility Model Application Laid-Open No. 40906/1982. The technical summary will be described with reference to FIG. The optical signal A incident from the one end 62 of the optical fiber 61 propagates in the optical fiber at an angle equal to or less than the critical angle for total reflection. When the optical fiber is bent (66) beyond the critical angle for total reflection, the optical signal A appears as leakage light 63 to the outside of the optical fiber. If the light receiving surface of the photodetector 64 is placed on the extension line of the leaked light, the leaked light can be detected.

(In case of communication using optical fiber) FIG. 5 is a diagram showing a basic concept of a communication system using an optical fiber. At the transmitting end 20, a signal to be transmitted is converted into an optical signal by an electric-to-optical converter (E / O converter) 21 and emitted to the optical fiber 21. On the receiving end side 30, the optical signal propagating through the optical fiber is demodulated into an electrical signal by an optical-to-electrical converter (O / E converter) 31. Communication using optical fibers enables high-speed, large-capacity, low-loss transmission. In particular, if the optical fiber is laid on a substantially straight line, the optical signal does not leak out of the optical fiber, so that low loss, that is, long distance transmission can be realized. The fact that the optical signal does not leak out means that the optical signal cannot be received in the middle of the optical fiber. That is, if an optical branching means is provided in the middle of the optical transmission system, the optical signal can be received in the middle of the optical transmission system. However, in other methods, the optical signal is received unless the optical fiber is cut. Can not do it. For example, the same applies when a code error rate measuring device, an optical power measuring device, or the like is used to monitor the change in the transmission state due to the deformation of the optical fiber.

[0005]

[Problems to be solved by the device]

 However, the conventional technique using the cord contrast sensor has the following drawbacks. As shown in FIG. 4, the leaked light 63 has a spread. In order to efficiently receive the leaked light, the area of the light receiving surface of the photodetector 64 must be increased (generally, the light receiving diameter is 1 mm to 2 mm). Increasing the area of the light receiving surface has a drawback that the frequency response speed of the photodetector 64 becomes slow. For example, the response frequency of a light receiving element having a light receiving surface with a diameter of 1 mm is limited to 1 MHz. When detecting the average value of the leaked light that appears at the bending point of the optical fiber, as in the case of a fiber-contrast sensor, a photodetector with a large light-receiving surface area can achieve the initial purpose sufficiently. it can. However, for example, in the case of PCM transmission that handles high-speed signals such as several gigabits per second, a conventional light receiving element with a large light receiving surface area cannot reproduce the modulated signal waveform because the frequency response speed is slow. There are drawbacks. Further, in the conventional technique, the optical signal incident on the one end 62 of the optical fiber 61 is detected by the leak light 63 because the photodetector 64 is provided on the extension line in the traveling direction at the bending point 66. However, on the contrary, there is a drawback that the leak light 63a of the optical signal B incident from the other end 65 of the optical fiber cannot be detected by the photodetector 64.

The object of the present invention is: (1) An optical signal modulated at high frequency without cutting the optical fiber at an arbitrary position between a transmitting end and a receiving end performing PCM communication using the optical fiber. (2) The optical signal received without cutting the optical fiber is input to a code error rate measuring device, an optical power measuring device, etc. to monitor the abnormality of the optical fiber.

[0007]

[Means for Solving the Problems]

 In order to solve the above-mentioned drawbacks, the optical signal receiving device of the present invention uses an optical signal emitted from a bending point of an optical fiber and modulated at a high frequency, for example, a signal such as PCM transmission that handles a high-speed signal. As a means for efficiently receiving the leaked light, the optical fiber that is propagating the optical signal is bent at a plurality of points so that the leaked light beam is covered on the extension line of the leaked light 63 emitted from the bending point 66. A plurality of light receiving means 1 arranged to convert the optical signal of the leaked light into an electric signal, a delay means 2 for adjusting the timing of each electric signal output from the plurality of light receiving means, and a delay means. Signal synthesizing means 3 for synthesizing a plurality of electrical signals whose timings have been adjusted.

Further, a signal reproducing means 4 for receiving the electric signal output from the signal synthesizing means and restoring the electric signal to a modulated signal is added, and the output signal is received to evaluate an optical fiber communication evaluation device, for example, It is provided with a waveform evaluation means 8 for inputting to a code error rate measuring device, an optical power measuring device and the like and for monitoring abnormality such as breakage or deformation of the optical fiber.

[0009]

[Action]

 In order to detect the leaked light of the optical signal modulated at a high frequency emitted from the bending point of the bent optical fiber, a light receiving element with a fast frequency response speed and a small light receiving area is used. Also, it is necessary to receive a small amount of leaked light so as not to affect the optical communication during transmission. Therefore, in order to improve the light receiving sensitivity, a plurality of light receiving elements having a small light receiving area are used. The received signal is used to monitor for abnormalities such as breakage and deformation of the optical fiber.

[0010]

【Example】

 (First Embodiment) FIG. 1 shows a configuration of a first embodiment of the present invention. In the following description, the case where the optical fiber 61 is used for PCM communication is taken as an example. The first optical fiber pressing means 67 and the second optical fiber pressing means 68 are in the shape of irregularities facing each other, and when the optical fiber 61 is placed between them to narrow the gap, the optical fibers follow the irregularities. Is bent and a bending point 66 is generated. The optical signal A incident on the optical fiber end 62 of the optical fiber 61 has leaked light 63 emitted from the bending point 66 in the traveling direction. The amount of this leaked light is determined by the radius of the bend. Normally, weak leaked light is emitted so as not to hinder the transmission system. In order to efficiently receive the leaked light, a plurality of light receiving means 1 are arranged so as to cover the outgoing beam width. When the passing optical signal is modulated at a high frequency such as in PCM communication, the light receiving means 1 uses a photo diode (not shown) having a small light receiving area in order to increase the frequency response speed. As an example of the frequency response speed of the germanium photo diode used here, the maximum response frequency is about 10 MHz (rise time is 0.5 μs) when the light receiving diameter φ = 0.1 mm. Although three light receiving means 1 are used in this embodiment, the number of light receiving means may be increased or decreased depending on the beam width of the leaked light and the intensity of the leaked light.

The signal detected by the light receiving means 1 is input to the delay means 2. The timing of the signal input to each delay means 2 varies depending on the detection position of the photo diode incorporated in each light receiving means 1 even if it is the same pulse signal. Therefore, the delay means 2 is for outputting the same delay time between the photodiodes from the leak point of the optical fiber.

The signal synthesizing means 3 is for adding the input signals. The signals with the same timing output from the respective delay means 2 are input to the signal synthesizing means 3 and added. The output of the signal synthesizing means 3 is input to the signal reproducing means 4 in the next stage. The signal reproducing means 4 is for amplifying and waveform-shaping the pulse signal output from the signal synthesizing means 3 to restore it to a modulated signal. The restored signal is input to the optical fiber communication waveform evaluation means at the next stage, for example, a code error rate measuring device to measure the transmission characteristics to monitor the deformation of the optical fiber, or to the optical power measuring device to input the optical signal. It is possible to monitor the increase in transmission loss and disconnection of optical fiber by measuring the fluctuation of power.

(Second Embodiment) FIG. 2 shows the configuration of the second embodiment of the present invention when signals A and B are incident from both directions of an optical fiber. In FIG. 2, the leaked light at the bending point 66 of the fiber 61 is detected by the light receiving means 1 in the optical signal A incident on the one end 62 as in the first embodiment. The signal B incident on the other end 65 is detected by the light receiving means 1a provided on the extension of the traveling direction thereof. Each of the detected signals is processed by the delay means 2, 2a, the signal synthesizing means 3, 3a and the signal reproducing means 4, 4a as in the first embodiment. The subsequent processing by the evaluation means is the same as in the first embodiment.

Third Embodiment This embodiment also shows a case where it is used for PCM communication similarly to the above embodiment. As shown in FIG. 3, in order to bend the optical fiber 61 to generate the leaked light 66, a plate-shaped first optical fiber holding means 5, a second optical fiber holding means 6 and a plurality of optical fiber bending means 7 are used. It is configured. An optical fiber 61 is placed between first and second optical fiber holding means, for example, a flat plate, and bending means 7, for example, a cylindrical rod is attached to the optical fiber, and first and second optical fiber holding means are provided. The first and second optical fiber pressing means are arranged alternately on the side to reduce the distance between them. At this time, the number, the outer diameter, and the interval of the bending means 7 may be selected so that the leaked light does not affect the transmission system.

In the method of detecting the leaked light 63 emitted from each bending point 66, the light receiving means 1 similar to that of the first embodiment is provided corresponding to each bending point. Since the respective delays of the same signal by the plurality of light receiving means 1 differ depending on the detection position, the delay means 2 is provided to cope with the signal processing in the subsequent stage as in the above embodiment. The signal processing after the delay means 2 is the same as that in the above embodiment. In this embodiment, if the beam width of each leaked light 63 is narrow, the number of light receiving means (photodiode) may be one, and the number can be increased / decreased according to the beam width. Further, as in the second embodiment, the light receiving means 2a or later may be provided on the emission line of the bidirectional leakage light.

[0016]

[Effect of the device]

 As explained above, in order to detect leaked light by bending the optical fiber that is transmitting the optical signal to be modulated at a high frequency, we have dealt with this problem by providing multiple light-receiving elements with a fast light-receiving area and a fast frequency response speed. It has the following effects. (1) A high-speed optical signal during transmission such as PCM communication can be received without cutting the optical fiber. (2) Since the reception efficiency can be improved, the optical signal in the optical fiber can be received without affecting the signal transmission between the transmitter and the receiver. (3) Since the light receiving means is provided on the emission line of the leaked light, the optical signal in the optical fiber can be received regardless of the transmission direction of the optical signal. (4) In addition to the above effects, it is possible to monitor the light transmission state in the optical fiber by using the received signal.

[0017]

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of an optical signal receiving device according to the present invention.

FIG. 2 is a block diagram showing a second embodiment of the optical signal receiving device according to the present invention.

FIG. 3 is a block diagram showing a third embodiment of the optical signal receiving device according to the present invention.

FIG. 4 Conventional optical signal receiving circuit

FIG. 5 is a configuration diagram of a communication system using an optical fiber.

[Explanation of symbols]

 1, 1a Light receiving means 2, 2a Delay means 3, 3a Signal combining means 4, 4a Signal reproducing means 5 First optical fiber holding means 6 of the third embodiment 6 Second optical fiber holding means 7 of the third embodiment 7th Optical fiber bending means of three examples 8 Waveform evaluation means 20 PCM communication transmission side 21 E / O converter 30 PCM communication reception side 31 O / E converter 61 Optical fiber 62 Optical fiber input end 63 Leaked light 64 Conventional Example light receiving means 65 The other input end of the optical fiber 66 Bending point 67 First optical fiber pressing plate 68 Second optical fiber pressing plate

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location 8426-5K H04B 9/00 U

Claims (2)

[Scope of utility model registration request] 1. A bending point (6) of an optical fiber during transmission of an optical signal.
6) a plurality of light receiving means (1) arranged on the extension line of the leaked light (63) and converting the optical signal of the leaked light into an electric signal; Delay means for adjusting the timing of electric signals (2)
And an optical signal receiving device including a signal synthesizing unit (3) for synthesizing a plurality of electric signals whose timings are adjusted by the delay unit. 2. A bending point (6) of an optical fiber during transmission of an optical signal.
6) a plurality of light receiving means (1) arranged on the extension line of the leaked light (63) and converting the optical signal of the leaked light into an electric signal; A plurality of delaying means (2) for adjusting the timing of the electric signal, a signal synthesizing means (3) for synthesizing the plurality of electric signals whose timings are adjusted by the delaying means, and an electric signal output from the signal synthesizing means Signal recovery means (4) for receiving the electric signal and restoring it to the original signal, and waveform evaluation for constantly monitoring the transmission state of the optical fiber based on the signal output from the signal reproduction means (4) Means (8)
And an optical signal receiving device characterized by being capable of restoring a signal and monitoring a light transmission state in an optical fiber.