JPH03233337A - Optical pulse testing device - Google Patents

Abstract

PURPOSE:To find the return loss of an optical fiber with high accuracy only by measuring the height of the reflected pulse of an image displayed on a CRT by providing a processor which calculates the return loss at a reflecting point based on level difference between the reflected light of an optical pulse in a reflection waveform and back scattered light just before the reflected light. CONSTITUTION:A light emitting part (LD) 2 is driven by a trigger pulse from a timing generator 1, and the optical pulse with prescribed pulse width and cycle period is generated. The optical pulse from the LD 2 passes a directional coupler 3, and is made incident on the optical fiber 4 of a subject to be measured. Return light such as the back scattered light and the reflected light, etc., from the optical fiber 4 passes the directional coupler 3 again, and is made incident on a receiver 5, and is displayed on the CRT 6 after arithmetic processing being applied with a CPU 9. The CPU 9 calculates the return loss based on the level difference between the power level of the back scattered light just before the reflecting point obtained at the receiver and that of reflected light by using a prescribed expression, and displays it on the screen of the CRT 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an optical pulse testing device, and more particularly to an optical pulse testing device for observing a reflected light waveform of an optical fiber.

[Conventional technology]

The configuration of a conventional optical pulse testing device is shown in FIG. The timing generator 1 applies a trigger pulse to the light emitting unit (LD).
2 to generate a light pulse with a predetermined pulse width and repetition period. This light pulse passes through the directional coupler 3 and enters the optical fiber 4 to be measured. The 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 and enters the light receiver 5 where it is converted into an electrical signal, which is processed by a processor (CUP) 12 and the result is displayed on a display unit (CRT) 6.

An example of a display image shown on the CRT 6 in this conventional optical pulse testing device is shown in FIG. 6. In FIG. 6, the horizontal axis represents the optical fiber length, the vertical axis represents the amount of optical attenuation, and Fl is the F2 corresponds to the reflection at the input part of the measuring fiber 4, F2 corresponds to the reflection at the connection part, and F3 corresponds to the reflection at the far end. Connection loss can be measured from the step at F2.

[Problem to be solved by the invention]

Although this conventional optical pulse testing device can measure the amount of optical attenuation using a displayed image, there is a problem in that it cannot measure the amount of return attenuation at a reflection point.

[Means to solve the problem]

The optical pulse testing device of the present invention is an optical pulse testing device that displays an image of a reflected waveform obtained by inputting an optical pulse into an optical fiber and detecting its backscattered light and reflected light with a photodetector. The apparatus includes a processor that calculates the amount of return loss at the reflection point from the level difference between the reflected light of the optical pulse and the backscattered light immediately before the reflected light.

〔Example〕

Embodiments of the present invention will be described using the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention. A trigger pulse from the timing generator 1 drives the light emitting unit (LD>2, and generates a light pulse with a predetermined pulse width and repetition period.The light pulse from the LD2 passes through the directional coupler 3 and reaches the target to be measured. The light enters the optical fiber 4 of the object.Return light such as backscattered light and reflected light from the optical fiber 4 passes through the directional coupler 3 again and enters the light receiver 5, and is input to the processor (CP).
U) After the arithmetic processing by 9 is performed, 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 equation <3> described later. and display it on the screen of CRT6.

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

R= ((ZVWS/2)/(Pbs/Pr)=ll
) Here, α is the loss of the optical fiber 4, ■ is the optical pulse propagation speed in the optical fiber 4, W is the pulse width of the optical pulse, S is the backscattering coefficient of the optical fiber 4, and Pbs is the backscattering just before the reflection point. The optical power and Pr are the reflected optical power. If we take the common logarithm of both sides of equation (1), we get the return loss Lr at the reflection point.
(dB) calculation formula % formula % ) (2) (2> The second term on the right side of the formula is the difference between the reflected pulse light level (peak value) displayed on the CRT 6 and the backscattered light level immediately before the reflected pulse, That is, it is twice the height Hr (dB) of the reflected pulse in FIG.

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

Lr=-10fflog <(ZVWS/2)-28r
... Kuu) Here, α, V, and S can be specified according to the type of optical fiber 4, and Hr can be read from the display image of CRT 6, so (
3) The right side of the equation can be obtained by calculation. Therefore,
The return loss Lr at the reflection point can be calculated using equation 3).

Note that the movement of the cursor indicating the measurement point on the screen of the CRT 6 during measurement is performed automatically by an instruction from the CPU 9, but it can also be performed manually. Also, the return loss L
The parameters necessary to calculate r are presettable.

Using the apparatus of this embodiment, the far end of the optical fiber 4 is immersed in various refractive index adjusting liquids 8 as shown in FIG. 3, and the return loss Lr at the far end is measured. It is shown in Table 1. The parameters of the single mode optical fiber used at that time were α = 8.06X10-5 (NP/m) and S =
1.15X10~3, V=2.05X108 (m/S
). For reference, measured values using an existing return loss measuring device are also listed. As can be seen in Table 1, the measured values in this example are in good agreement with the actual values measured by the actual return loss measuring device within 40 dB. As shown in FIG. 2, an optical attenuator 10 may be inserted at the input end of the optical fiber 4 to prevent the light receiver 5 from being saturated by reflected light and causing measurement errors.

[Effects of the Invention] As explained above, according to the present invention, the return attenuation of an optical fiber can be determined with high precision simply by measuring the height of the reflected pulse of a CRT display image, and the return attenuation can be easily determined in the field. This provides the effect of being able to measure quantities.

[Brief explanation of drawings]

Figures 1, 3, and 4 are block diagrams of an embodiment of the present invention, Figure 2 is a measurement waveform diagram of the embodiment of the present invention, and Figures 5 and 6 are conventional optical pulse test equipment. FIG. 2 is a block diagram and a measured waveform diagram. 1... Timing generator, 2... Light emitting section (LD),
3... Directional coupler, 4... Optical fiber, 5...
・Photoreceiver, 6...Display part (CR, T), 8...Refractive index adjustment liquid, 9.12...Processor (CPUI, 10
...Optical attenuator.

Claims (1)

[Claims] 1. In an optical pulse testing device that displays an image of a reflected waveform obtained by inputting a light pulse into an optical fiber and detecting its backscattered light and reflected light with a photodetector, An optical pulse testing device comprising: a processor that calculates a return loss at a reflection point from a level difference between the reflected light of the optical pulse and the backscattered light immediately before the reflected light. 2. The optical pulse testing device according to claim 1, wherein the return loss calculated by the processor is displayed as an image together with the reflected waveform.