JP2000032066A - Detector for momentary interruption in optical fiber transmission - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the detector for momentary interruption in optical fiber transmission by which an output image of a receiver is not disturbed from the occurrence of momentary interruption of an optical signal till an output of a serial parallel converter is restored to a normal output. SOLUTION: An optical fiber transmission system that transmits an optical signal with a transmission signal format where a specific code used to take timing of serial parallel conversion for serial data is provided for each prescribed period, is provided with a reception data storage means (frame memory) 15 that stores received data obtained by receiving the optical signal, an optical signal fault detection means (a light receiving level detection means 13 and a byte synchronizing signal fault detection section 31) that detects a fault in the optical signal, and a substitute reception data output means (an output substitute control section 34) that stops an output of the received data after the detection when the optical signal fault detection means detects a fault in the optical signal and outputs the received data stored in advance in the received data storage means instead.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an instantaneous interruption detecting apparatus for optical fiber transmission, and more particularly to a method for preventing an output image of a receiving apparatus from being disturbed even when an instantaneous interruption occurs in a video camera system using an optical fiber. The present invention relates to an instantaneous interruption detection device for optical fiber transmission.

[0002]

2. Description of the Related Art A digital optical fiber transmission device using a data transmission format for a high-speed network such as a fiber channel has a low possibility of an instantaneous interruption of an optical signal because an optical fiber cable is originally fixedly installed. Responsiveness of the return operation to disconnection is not sufficient.

On the other hand, in a video camera system provided with a digital optical fiber transmission device (hereinafter, referred to as a camera system), a video camera (hereinafter, referred to as a camera) which can be freely held by a photographer in a hand. Due to the nature of the optical fiber cable, the optical fiber cable is strongly dragged around, and the optical signal is likely to be momentarily interrupted by the bending of the cable.

In the conventional camera system, if there is a momentary interruption of the optical signal, the camera is synchronized with an externally applied reference clock so that the PLL circuit for clock recovery of the serial / parallel converter of the receiver does not stick. After that, when an optical signal comes in, the process of synchronizing with the received data again, clock recovery, detecting the byte synchronization code included in the received data, taking the timing of serial-parallel conversion, and obtaining the correct parallel received data is performed. I was trying to follow.

[0005]

However, during the period from the instantaneous interruption of the optical signal to the time when correct parallel data is obtained, the output of the serial-parallel converter continues to output indefinite data, and the output image of the receiving apparatus is disturbed. I stayed. Therefore, an object of the present invention is to provide an instantaneous interruption detection device for optical fiber transmission that does not disturb the output image of the receiving device from the moment when the optical signal is instantaneously interrupted until the output of the serial-parallel converter returns to normal. It is to be.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an optical signal transmission system which uses a transmission signal format having a special code for taking a timing for serial-to-parallel conversion of serial data every fixed period. In a fiber transmission system, received data storage means for storing received data obtained by receiving an optical signal, optical signal abnormality detecting means for detecting an optical signal abnormality, and the optical signal abnormality detecting means detecting an optical signal abnormality In this case, there is provided an alternative reception data output unit that stops the output of the reception data for a predetermined period after detecting the reception data, and outputs the reception data stored in the reception data storage unit in place of the reception data. .

With this arrangement, when the optical signal abnormality detecting means detects an abnormality in the optical signal, the alternative received data output means outputs the received data previously stored in the received data storage means as alternative received data. Therefore, the output image of the receiving device is not disturbed.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on an embodiment shown in the drawings. FIG. 1 is a diagram showing a signal format of digital optical fiber transmission in a camera system applied to the present embodiment. FIG. 2 is a circuit diagram of a receiving side of a camera system having a digital optical fiber transmission device. It is a timing chart of a break detector. Originally, in a camera system, CC
In addition to the transmission of image and audio signals to the U (communication control device), there are also image and audio signals called return video from the CCU to the camera, which are bidirectionally transmitted by two optical fibers. In the following description, since the transmission is the same, only the transmission from the camera to the CCU will be described as an example.

As shown in FIG. 1, "ANSI X3T11 Fiber c
In a transmission signal format conforming to the “hannel” standard, a special code (0011) called K28.5 is used to set the timing of serial / parallel conversion of serial data received by the receiving device.
11110) must be inserted into the data string without fail, and in the present embodiment, the code (byte synchronization code) is inserted during the horizontal blanking period.

As shown in FIG. 2, an optical signal of m [bps] transmitted from the camera 1 via the optical fiber cable 2 in the transmission signal format is photoelectrically converted by the receiving unit 11 of the CCU 10 and fixed by the AGC 12. After being amplified to the level, it enters the serial-to-parallel converter 20. In the serial-to-parallel converter 20, the clock enters the PLL circuit 21 in order to reproduce the clock from the received data, the clock is reproduced, and the received data is input to the n-bit shift register 22 by the clock. At the same time, the byte synchronization detection unit 23, which is a "special code presence / absence detection means", detects the K28.5 byte synchronization code (ByteSync) from the received data,
, A timing signal for extracting parallel data is generated, thereby obtaining n [bit] parallel data.
The above is the operation when the received data is normal (see FIG. 3).

If the optical signal is momentarily interrupted, first, the absence of light is detected by the light receiving level detecting section 13 which is "optical signal abnormality detecting means, receiving level detecting means". Input to the PLL 21 via m
The received data of [bps] is switched to the reference clock of (m / 2 [Hz]) to prevent the PLL 21 from sticking. From this switching until the PLL 21 locks, t
It takes one second (see Figure 3).

Further, even if the instantaneous interruption does not occur, the received data including the noise which is greatly attenuated by the bending of the optical fiber cable 2 and contains noise is input to the serial / parallel converter 20 and the byte synchronization code is inputted.
When (Byte Sync) is detected as an abnormal number by the byte synchronization signal abnormality detector 31 which is the “optical signal abnormality detection means, reception level detection means”, the Lock Ref signal (from the reference clock switching pulse generator 32) Next explained), P
The input of LL21 switches from the received data to the reference clock. In these states, the output of the shift register 22 becomes invalid data because the byte synchronization code is not normally detected.

After that, when the optical signal returns, the PLL 21 again synchronizes with the received data and reproduces the clock. However, it takes t2 seconds until the clock is locked and the normal serial-parallel conversion is performed. Has an invalid data period for at least [t1 + t2] seconds (see FIG. 3). The period from the moment when this optical signal is momentarily interrupted until the normal serial-parallel conversion is performed is the byte synchronization code (Byt
e Sync) abnormality detection is suspended, then restarted, and when an abnormality is detected again, the input of the PLL 21 is switched to the reference clock.

That is, 1 is always required for each horizontal blanking period.
The minimum period from when the byte synchronization code that should have existed anomaly is detected until the normal serial-parallel conversion is performed can be identified as the period of the invalid data. This situation is shown in the timing chart of FIG. In FIG. 3, a signal for switching the input of the PLL 21 to the reference clock after detecting an abnormality in the byte synchronization code is referred to as Lock Ref, and an identification signal from when the abnormality in the byte synchronization code is detected until normal data is output is output. Byte Sync Error. Byte Sync Error
The signal is output from the invalid data period identification pulse generator 33. After the received data is demultiplexed into image data by the demultiplexer circuit 14, several frames are always stored in the frame memory 15 which is a "reception data storage means". And, in the case of momentary interruption detection, the Byte
"Alternative reception data output means" that received Sync Error signal
The output substitution control unit 34 fixes the output image of the CCU 10 to the normal image immediately before the instantaneous interruption is detected during the invalid period [(t1 + t2) seconds] of the received light data so that the output image is not disturbed. This is shown as “accumulated image, substitute image” in FIG.

If the instantaneous interruption detection is frequently performed, C
The output image of the CU 10 frequently freezes, which is a problem for the camera system. In a camera system, even if there is some noise, it is sometimes better than the image is frequently stopped, so when the instantaneous interruption detection detects an abnormality of the byte synchronization code continuously for the p horizontal blanking period. The present embodiment is also characterized in that the instantaneous interruption recovery operation is started and noise resistance is provided. In the case of the present embodiment, p = 2.

That is, in the upper left part of FIG. 3, the received data is normal in "D1" because the byte synchronization code is generated once, abnormal in "D2" since no byte synchronization code is generated, and "D3" in the reception data. Similarly, normal and "D4" are abnormal. Of these, the abnormality of "D2" is ignored because the horizontal blanking period in which an abnormality occurs is once, and the abnormality of "D4" is twice in the horizontal blanking period in which an abnormality occurs (p = 2).
Since it is continuous, noise immunity is provided by starting the instantaneous interruption recovery operation. This function is performed by a "special code non-detection ignoring means" (not shown).

The above description relates to the transmission from the camera 1 to the CCU 10. Similarly, the transmission of the return video from the CCU 10 to the camera 1 has the same instantaneous interruption detection device. Output image distortion can be prevented.

[0018]

As described above, according to the present invention, a camera system having a digital optical fiber transmission device,
When an optical signal is momentarily interrupted due to bending of an optical fiber cable, etc.
The output image of the receiving device can be reliably restored in a minimum necessary time without being disturbed. Therefore, the degree of freedom of the camera work which has been limited due to the fear of bending of the optical fiber cable is increased.

[Brief description of the drawings]

FIG. 1 shows a digital optical fiber transmission format in a camera system applied to an embodiment of the present invention.

FIG. 2 is a block diagram of the embodiment.

FIG. 3 is a timing chart of instantaneous interruption detection in the embodiment.

[Explanation of symbols]

1: video camera, 2: optical fiber cable, 10: C
CU, 13: light reception level detection unit (optical signal abnormality detection means), 15: frame memory (reception data storage means),
20: serial-parallel converter, 23: byte synchronization detector, 30 ...
Instantaneous interruption detector, 31: byte synchronization signal abnormality detection unit (optical signal abnormality detection unit), 33: invalid data period identification pulse generation unit, 34: output substitution control unit (substitution reception data output unit).

Claims (4)

[Claims] 1. An optical fiber transmission system for transmitting an optical signal using a transmission signal format having a special code at regular time intervals for serial data to serial-parallel conversion of serial data. Receiving signal storage means for storing an error in the optical signal; optical signal abnormality detecting means for detecting an abnormality in the optical signal; and when the optical signal abnormality detecting means detects the optical signal abnormality, a predetermined period after detecting the output of the reception data. An instantaneous interruption detection device for optical fiber transmission, comprising: an alternative reception data output unit that stops and substitutes and outputs reception data stored in advance in the reception data storage unit. 2. The optical signal abnormality detecting device according to claim 1, further comprising: a receiving level detecting unit for detecting a receiving level of the optical signal; and a special code presence detecting unit for detecting the presence or absence of a special code during the predetermined period. The optical fiber transmission instantaneous interruption detection device according to claim 1. 3. The optical device according to claim 2, wherein said optical signal abnormality detecting means includes a special code non-detection ignoring means for ignoring a state where there is no special code detected by said special code existence detecting means. Instantaneous interruption detection device for fiber transmission. 4. An apparatus for detecting an instantaneous interruption of optical fiber transmission,
4. An optical fiber transmission system comprising a video camera and a communication control device for transmitting and receiving signals to and from the video camera.
The instantaneous interruption detection device for optical fiber transmission according to any one of the above.