JP2000330144A - Pulse laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pulse laser that can reduce an interpulse leakage light in a pulse light source and can obtain a correct measurement result in an OTDR (optical time domain reflectormetry) measurement. SOLUTION: The pulse light emitted from a pulse light source 1 is introduced into an optical fiber 2a as an optical path to be introduced into an optical fiber 2b for being measured through the optical switch 3 made up of an acoustooptical elements and it is emitted from the fiber 2b. When the pulse light is to transmit the optical switch 3, the pulse light is made to pass as it is through the switch by raising the transmissivity of the switch 3 while inputting the gate signal 4 synchronized with the pulse light to the gate of the switch 3 from the light source 1 and the interpulse leakage light is made so as not transmit the switch by lowering the transmissivity of the switch 3 at the time other than that time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a pulse laser, and more particularly to a pulse laser suitable as a pulse light source for OTDR (Optical Time Domain Reflectometry) measurement.

[0002]

2. Description of the Related Art An optical pulse tester or OTDR (Opti
cal Time Domain Reflectometry) is widely used for searching for a fault point in an optical fiber transmission line and measuring a loss distribution.

In the OTDR, an optical pulse is incident on an optical fiber to be measured, and the position of the scattering point is determined from the time required until the light pulse is backscattered and returned at the scattering point, or the loss is determined. Specific backscattered light in this case includes backward Rayleigh scattered light, backward Raman scattered light, and backward Brillouin scattered light. Since the intensity of the backscattered light is extremely weak, a very clear light pulse emission (transmission) technique and a highly sensitive photodetection (reception) technique are required.

[0004]

However, the OTD
The optical pulse generated in the transmitter of the R measuring device is not an ideal discrete signal, but has a leak component between the pulses.

FIG. 5 shows an example of a light emission waveform in a conventional pulse laser. Pulse light 1 repeated at a specific cycle
In addition to 0, inter-pulse leakage light 11 has occurred. Optical fiber OTDR measured using this light by OTDR method
The distribution is shown in FIG. Due to the influence of the leaked light, the distribution is distorted with the bottom rising. For this reason, it is difficult to obtain an accurate measurement result in the OTDR measurement.

In the prior art, there is a problem that a correct measurement result cannot be obtained.

Accordingly, an object of the present invention is to solve the above-mentioned problems, reduce inter-pulse leakage light in a pulse light source, and achieve OT
An object of the present invention is to provide a pulse laser capable of obtaining accurate measurement results in DR measurement.

[0008]

In order to achieve the above object, a pulse laser according to the present invention is provided with an optical switch at an output section of a pulse light source, and when the pulsed light is not transmitted through the optical switch, the transmittance thereof is reduced. It is configured so as to be lowered (claim 1). More specifically, an optical switch is provided at the output unit of the pulse light source, and a gate signal synchronized with the output pulse light from the pulse light source is applied to the gate of the optical switch,
When the pulse light does not pass through the optical switch, the transmittance is reduced (claim 2).

As described above, by adopting a configuration in which an optical switch is added to the output section of the pulse light source, it is possible to reduce inter-pulse leak light in the pulse light source and obtain an accurate measurement result in OTDR measurement.

An acousto-optic device or an electro-optic device can be used as the optical switch.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on the illustrated embodiment.

FIG. 1 shows the configuration of a pulse laser according to the present invention. Pulse light 10 emitted from the pulse light source 1 (FIG. 2A)
Is guided to an optical fiber 2a as an optical path, and is guided to an optical fiber 2b to be measured as an optical path to be measured and emitted through an optical switch 3 composed of an acousto-optical element. Further, a gate signal 4 (FIG. 2B) synchronized with the output pulse light 10 from the pulse light source 1 is input to the gate of the optical switch 3.

FIG. 2 is a timing chart of the gate signal 4.
Shown in As described above, when the pulse light 10 passes through the optical switch 3, the transmittance of the optical switch 3 is increased to pass the pulse light 10, and otherwise, the transmittance of the optical switch 3 is decreased to generate the inter-pulse leak light 11. Avoid transmission.

With such a configuration, the light waveform emitted from the optical fiber 2b to be measured has a reduced inter-pulse leak light 11 as shown in FIG. 3, and as a result, a distortion as shown in FIG. And a correct OTDR measurement result is obtained.

Next, an embodiment in which the present invention is applied to an optical fiber OTDR will be described.

First, the pulse light 10 in the pulse light source 1 is
The light emission cycle was 600 μs, the pulse width was 50 ns, the pulse peak power was 200 W, and the average leakage light power was 0.2 W. When this pulsed light source 1 was used as in the prior art and OTDR measurement was performed on 30 km of GI 50/125 fiber as the optical fiber 2b to be measured, a distorted OTDR distribution as shown in FIG. 6 was obtained.

Therefore, an acousto-optic device was used as the optical switch 3, and the measurement was performed again using the pulse laser of the present invention having the above-described configuration. The transmissivity of the acousto-optic element used is -2 dB when transmitting, and -20 dB when not transmitting, and the gate signal 4 is longer than the pulse width 10 of the pulsed light 10.
When the leak light component was cut using 0 ns, an OTDR signal with little distortion as shown in FIG. 4 was obtained.

In the above-described embodiment, an embodiment suitable for searching for a fault point in an optical fiber transmission line has been described. However, measurement of physical quantities, for example, OTDR measurement of Raman scattered light in the optical fiber is performed to measure the temperature The present invention can be applied to measurement for obtaining a distribution.

[0019]

As described above, according to the present invention, an optical switch is provided at the output portion of the pulse light source, and the transmittance is reduced when the pulse light is not transmitted through the optical switch. It is possible to reduce inter-pulse light leakage in the pulse light source and obtain an accurate measurement result in OTDR measurement.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a pulse laser according to the present invention.

FIGS. 2A and 2B are timing charts of a gate signal in the pulse laser according to the present invention, wherein FIG. 2A is a diagram illustrating an output pulse light of a pulse light source, and FIG. 2B is a diagram illustrating a pulse of the gate signal. .

FIG. 3 is a diagram showing an optical pulse waveform output from a pulse laser according to the present invention.

FIG. 4 is a diagram illustrating an OTDR distribution measured using a pulse laser according to the present invention.

FIG. 5 is a diagram showing an optical pulse waveform output from a conventional pulse light source.

FIG. 6: OT measured using a prior art pulsed light source
It is the figure which showed DR distribution.

[Explanation of symbols]

 Reference Signs List 1 pulse light source 2a optical fiber 2b optical fiber to be measured 3 optical switch 10 pulsed light 11 inter-pulse leaked light

Claims (3)

[Claims] 1. A pulse laser, wherein an optical switch is provided to an output section of a pulse light source, and the transmittance is reduced when pulse light is not transmitted through the optical switch. 2. An optical switch is provided at an output section of the pulse light source,
A pulse laser characterized in that a gate signal synchronized with an output pulse light from a pulse light source is applied to a gate of the optical switch, and the transmittance is reduced when the pulse light is not transmitted through the optical switch. 3. The pulse laser according to claim 1, wherein an acousto-optic device or an electro-optic device is used for the optical switch.