JPH0634894A - Excessive light cutting-off device - Google Patents

Abstract

PURPOSE:To prevent excessive light whose intensity exceeds a prescribed level from reaching optical circuit components of an optical measuring instrument, an optical communication device, etc. CONSTITUTION:This excessive light cutting-off device is equipped with an optical branching means 2 which takes part of light propagated on a main transmission line 1 as monitor light by a constant intensity rate, an optical delay means 3 which delays the propagation of the light on the main transmission line passed through the optical branching means 3, an optical switch 4 which cuts off the propagation of the light on the main transmission line passed through the optical delay means 3, a photodetecting means 6 which generates an electric signal corresponding to the intensity of the monitor light taken out by the optical branching means 2, a comparing means 8 which discriminates the level of the output of the photodetecting means 6, and a driving means 9 which turns OFF the optical switch 4 when the comparing means 8 detects the output of the photodetecting means 6 exceeding the set level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an excessive light blocking device for preventing excessive light having an intensity of a specified level or more from reaching an optical circuit component such as an optical measuring device or an optical communication device.

[0002]

2. Description of the Related Art With the progress of optical circuit technology, the intensity of a laser light source used for optical communication is gradually increasing, and when the optical amplifier abnormally oscillates, the intensity of the light exceeds the specified level. May not propagate and may damage optical components such as optical isolators and light receiving elements. Therefore, it becomes necessary to protect the optical circuit component from such excessive light, but there has been no suitable light blocking device that meets this purpose.

[0003]

There is an optical attenuator as a device for adjusting the intensity of light propagating on an optical circuit. By inserting this optical attenuator in the optical circuit, there is an effect to prevent excessive light from propagating to the subsequent stage to some extent, but this is an attenuating action even for normal level light under normal conditions. Therefore, it is essentially different from a circuit breaker that operates only for an excessive input, such as an overcurrent circuit breaker or an overvoltage circuit breaker in an electric circuit.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to operate when the intensity of light propagating on an optical transmission line exceeds a prescribed level to interrupt the optical propagation, An object of the present invention is to provide an excessive light blocking device in which light is not attenuated as much as possible.

[0005]

SUMMARY OF THE INVENTION An excessive light cutoff device according to the present invention comprises an optical branching means for extracting a part of light propagating through a main transmission line as a monitor light at a constant intensity ratio, and a main transmission via this optical branching means. Corresponding to the optical delay means for delaying the propagation of the light on the path, the optical switch for blocking the propagation of the light on the main transmission path via the optical delay means, and the intensity of the monitor light extracted by the optical branching means. Light detection means for generating an electric signal, comparison means for discriminating the output of the light detection means, and the optical switch when the comparison means detects that the output of the light detection means exceeds a set level. And a drive means for turning off the switch.

[0006]

Strictly speaking, the optical branching means and the optical delay means are inserted in the main transmission line to give a slight loss to the main transmission line, but this transmission loss is sufficiently small to be negligible. can do. The intensity of the light propagating through the main transmission line is constantly monitored by the light detection means and the comparison means, and when the light intensity exceeding the set level is detected, the drive circuit shuts off the optical switch. Be put in a state. There is some delay time from the time when the excessive light propagates to the time when the optical switch shuts off, but the optical delay means inserted between the optical branch handoff and the optical switch absorbs the response delay.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a schematic structure of an excessive light blocking device according to an embodiment of the present invention. The optical branching device 2, the delaying optical fiber 3 and the optical switch 4 which constitute the excessive light blocking device of the present invention are provided between the input side optical fiber 1 and the output side optical fiber 5 which form the main transmission line. They are inserted in order.

The optical branching device 2 is for branching out the monitor light for measuring the intensity of the light propagating through the main transmission line from the main transmission line, and the input light intensity is constant regardless of the polarization state of the input light. It is configured such that a proportion of light is branched and output as monitor light. It is preferable that the intensity ratio of the branched light is as small as possible, for example, about 0.5% is preferable. The optical branching device 2 of the illustrated embodiment has a birefringent plate 23 between the fiber collimator 21 of the input side optical fiber 1 and the fiber collimator 22 of the delay optical fiber 3 and an inclination with respect to the main optical axis. The glass plate 24 with the dielectric thin film is disposed. The ray axis of the birefringent plate is inclined by 45 ° with respect to the incident surface of the light on the glass plate with the dielectric thin film. The invention is not limited to such a polarization beam splitter type optical splitter 2, and a well-known optical fiber coupler can be used as an optical splitter having the same function as described above.

99% of the light propagating through the input side optical fiber 1
The above is transmitted to the delay optical fiber 3 via the optical branching device 2. The delay optical fiber 3 is inserted in order to obtain a propagation time as described below, and its length is determined according to the required delay time.

The optical switch 4 normally transmits the input light to the output side optical fiber 5 without loss, enters a cutoff mode in response to a signal from a drive circuit described later, and the input light is transmitted to the output side optical fiber 5. Shut off completely. The optical switch 4 of this embodiment includes a fiber collimator 41 on the delay optical fiber 3 side and a fiber collimator 4 on the output side optical fiber 5.
Between the birefringent plate 43 and the Faraday effect element plate 4
4, a half-wave plate 47, and a birefringent plate 45 are arranged, and as is well known, a Faraday effect element plate 44 is provided.
The optical switch 4 is turned on / off by a signal applied to the coil of the exciter 46 attached to the. Besides this, optical switches of various types and configurations can be used.
That is, for example, there are those that use an electro-optical element such as PLZT in place of the Faraday effect element plate and the half-wave plate, and those that mechanically displace the shutter and the reflector by an actuator. Any of these can be applied to the present invention.

The monitor light branched by the optical branching device 2 is received by the photodetector 6, and the optical fiber 1 is emitted from the detector 6.
An electric signal corresponding to the intensity of the input light from is output.
As the photodetector 6, basically any device may be used as long as the required sensitivity and accuracy with respect to the light of the used wavelength can be obtained. The wavelength band of laser light currently generally used for optical communication is 1.31 or 1.55 micrometers,
In this case, a semiconductor sensor such as a photodiode or a photoconductive element is suitable.

The output signal of the photodetector 6 is preprocessed by the preamplifier 7 and input to the comparator 8 which is a comparison means, and is compared with the reference level signal Vs set appropriately. The drive circuit 9 receives the level discrimination output of the comparator 8 and drives the optical switch 4. That is, when the detection level by the photodetector 6 is equal to or lower than the reference level, the optical switch 4 is kept on and the input light propagates to the output side optical fiber 5. on the other hand,
When the detection level of the input light exceeds the reference level, the output of the comparator 8 is inverted, the optical switch 4 is turned off at this time, and the light propagation to the output side optical fiber 5 is blocked.

Although there is a certain amount of response delay until the optical switch 4 is turned off after the intensity of the input light becomes excessive, the delay time (length of the optical fiber) of the delaying optical fiber 3 is the above-mentioned response. Set a little larger than the time. Then, excessive input light will not be transmitted to the output side optical fiber 5. If the response time is 0.5 to 20 microseconds, the length of the delay optical fiber 3 is 100 to 400.
It will be 0 meters.

[0014]

As described in detail above, according to the excessive light blocking device of the present invention, if the intensity of light propagating through the main transmission line is within the normal level range, almost no transmission loss occurs in the main transmission line. If the intensity of light propagating through the main transmission line increases and exceeds a specified level for some reason, the optical switch turns off in response to the excessive light, and excessive light is transmitted to the optical circuit in the subsequent stage. Can be reliably prevented.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an excessive light blocking device according to an embodiment of the present invention.

[Explanation of symbols]

 1 input side optical fiber (main transmission line) 2 optical branching device (optical branching means) 3 delay optical fiber (optical delaying means) 4 optical switch 5 output side optical fiber 6 photodetector (light detecting means) 8 comparator (comparison) Means) 9 Driving circuit (driving means)

Claims (1)

[Claims] 1. An optical branching unit for extracting a part of light propagating through the main transmission line as a monitor light by a constant intensity ratio, and an optical delay unit for delaying propagation of light on the main transmission line through the optical branching unit. An optical switch for blocking the propagation of light on the main transmission line passing through the optical delaying means, a light detecting means for generating an electric signal corresponding to the intensity of the monitor light taken out by the optical branching means, and this light detection A comparing means for discriminating the level of the output of the means; and a driving means for turning off the optical switch when the comparing means detects that the output of the light detecting means exceeds a set level. Characteristic over-light blocking device.