JP2718234B2 - Optical pulse test equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pulse test apparatus, and more particularly to an optical pulse test apparatus for observing a reflected light waveform of an optical fiber.

[Prior Art] FIG. 5 shows the configuration of a conventional optical pulse test apparatus. Light emitting part (LD) by giving trigger pulse from timing generator 1
2 to generate an optical pulse having a predetermined pulse width and a repetition period. This light pulse passes through the directional coupler 3 and enters the optical fiber 4 to be measured. Backscattered light and reflected light returning from the optical fiber 4 to the directional coupler 3 are:
The light passes through the directional coupler 3 again, enters the light receiver 5 and is converted into an electric signal.

FIG. 6 shows an example of a display image displayed on the CRT 6 in this conventional optical pulse test apparatus. In FIG. 6, the horizontal axis represents the optical fiber length, and the vertical axis represents the optical attenuation, where F1 is at the entrance of the fiber 4 to be measured, F2 is at the connection, and F3 is at the far end. Of light reflected. For example, the loss of the optical fiber can be measured from the optical fiber length and the level difference between F1 and F2, and the connection loss can be measured from the step at F2.

[Problems to be solved by the invention]

In this conventional optical pulse test apparatus, although the amount of light attenuation can be measured by a display image, there is a problem that the amount of return loss at a reflection point cannot be measured.

[Means for solving the problem]

The optical pulse test apparatus of the present invention is an optical pulse test apparatus that displays an image of a reflected waveform obtained by detecting a backscattered light and a reflected light with a photodetector by injecting an optical pulse into an optical fiber. A processor for calculating a return loss at a reflection point from a level difference between the reflected light of the light pulse and the backscattered light immediately before the light pulse.

〔Example〕

 An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention. The light emitting unit (LD) 2 is driven by a trigger pulse from the timing generator 1 to generate an optical pulse having a predetermined pulse width and a repetition period. The light pulse from the LD 2 passes through the directional coupler 3 and enters the optical fiber 4 of the device under test. Optical fiber 4
Return light, such as backscattered light and reflected light from the light source, again passes through the directional coupler 3 and is incident on the light receiver 5 to be processed by a processor (CPU).
After being subjected to the arithmetic processing by 9, it is displayed on the display unit (CRT) 6.

The CPU 9 of this embodiment calculates the return loss Lr from the difference between the backscattered light power level immediately before the reflection point obtained by the light receiver 5 and the reflected light power level, using the following equation (3). And display it on the CRT6 screen.

The reflectance R at the reflection point of the optical fiber 4 is represented by the following equation (1).

R = (αVWS / 2) / (Pbs / Pr) (1) where α is the loss of the optical fiber 4, V is the light pulse propagation speed in the optical fiber 4, W is the pulse width of the light pulse, and S is the pulse width of the light pulse. The backscattering coefficient of the optical fiber 4, Pbs is the backscattered light power immediately before the reflection point, and Pr is the reflected light power. By taking the common logarithm of both sides of the equation (1), the equation (2) for calculating the return loss Lr (dB) at the reflection point is obtained.

Lr = −10log (αVWS / 2) −10og (Pr / Pbs) (2) The second term on the right side of the equation (2) is the reflected pulse light level (peak value) displayed on the CRT 6 and the backward position immediately before the reflected pulse. The difference from the scattered light level, that is, the height Hr of the reflected pulse in FIG.
(DB).

 Therefore, equation (2) can be rewritten as equation (3).

Lr = −10log (αVWS / 2) −2Hr (3) Here, α, V, and S may be specified according to the type of the optical fiber 4, and Hr can be read by the display image on the CRT 6 (3). The right side of the equation can be obtained by calculation. Therefore, the return loss Lr at the reflection point can be obtained by the calculation of the expression (3).

The movement of the cursor indicating the measurement point on the screen of the CRT 6 at the time of measurement is automatically performed according to a command from the CPU 9, but can also be performed manually. Further, parameters necessary for calculating the return loss Lr can be preset.

Using the apparatus of the present embodiment, as shown in FIG. 3, the far end of the optical fiber 4 was immersed in various refractive index adjusting liquids 8, and the result of measuring the return loss Lr at the far end was shown in FIG. The results are shown in Table 1. The parameters of the single mode optical fiber used at that time are based on general single mode fiber data.
Α = 8.06 × 10 ^-5 (NP / m), S = 1.15 × 10 ^-3 ,
V was set to 2.05 × 10 ⁸ (m / S). For reference, the values measured by the existing return loss measuring device are also shown. As can be seen from Table 1, the measured values in the present embodiment are in good agreement with the measured values by the measured return loss measuring device at 40 dB or less.

When the reflectivity at the reflection point is high, an optical attenuator 10 is inserted at the incident end of the optical fiber 4 as shown in FIG. Should be prevented.

〔The invention's effect〕

As described above, according to the present invention, the return loss of the optical fiber can be determined with high accuracy only by measuring the height of the reflected pulse of the CRT display image, and the return loss can be easily measured in the field. The effect is obtained.

[Brief description of the drawings]

FIGS. 1, 3, and 4 are block diagrams of an embodiment of the present invention, FIG. 2 is a measurement waveform diagram in the embodiment of the present invention, and FIGS. 5 and 6 are conventional optical pulse test apparatuses. 3 is a block diagram and a measured waveform diagram of FIG. 1 ... timing generator, 2 ... light emitting unit (LD), 3 ...
Directional coupler, 4 ... optical fiber, 5 ... receiver, 6
... Display unit (CRT), 8 ... refractive index adjusting liquid, 9, 12 ... processor (CPU), 10 ... optical attenuator.

Claims (1)

(57) [Claims] 1. An optical pulse test apparatus for injecting an optical pulse into an optical fiber and displaying an image of a reflected waveform obtained by detecting backscattered light and reflected light thereof with a photodetector, wherein the optical pulse in the reflected waveform is displayed. A processor that calculates the return loss at the reflection point from the level difference between the reflected light and the immediately preceding backscattered light, and displaying the return loss calculated by the processor together with the reflection waveform as an image. Characteristic light pulse test equipment.