SU1283578A1 - Device for measuring transfer characteristic of fibre lightguide - Google Patents

Abstract

The invention relates to a measurement technique and makes it possible to increase the measurement accuracy by increasing the signal-to-noise ratio. The voltage drop of the high-resistance element 4 automatically changes the multiplication factor of the avalanche photodiode 3 so that its value is close to the optimum value for any attenuation of the fiber 2 under study, which ensures the minimum error of signal detection. Additional gain control with the help of a controlled attenuator 7 and peak detector 9 provides a constant signal level at the output of the strobe transducer 8 and a constant image size of the spectrum of the signal under investigation on the spectrum analyzer 11. 1 il. 1 O)

Description

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The invention relates to a measurement technique and is intended to determine the transfer characteristics of optical fibers.

The purpose of the invention is to improve the measurement accuracy by increasing the signal-to-noise ratio.

The drawing shows a functional diagram of the proposed device.

The device contains an optical pulse source 1, the optical output of which is located opposite the optical end of the optical fiber 2, the avalanche photodiode 3, whose optical input is located opposite the output end of the optical fiber 2, a high-resistance element 14, one output of which is connected to the electrical input of the photodiode 3 through integrating link 5, constant voltage source 6, output. which is connected to the second output element 4, controlled attenuator 7, the input of which is connected to the output of photodiode 3, stroboscopic converter 8, the input of which is connected to the output of the controlled attribute 7, peak detector 9, the output of which is connected to the control input of the attenuator 7, 10 low-pass filter, the input of which is connected to the output of the converter 8, and the output to the input of the detector 9, the analyzer 11. spectrum, the input of which is connected to the output of the filter 10, and the generator 12 of the delayed pulses, one output of which is connected to the input of source 1, and the other to the input of the synchronization of the converter 8.

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walking m light guide; E - the maximum length of the fiber being examined. Converter 8, operating in standby mode, provides a selection at its output in a transformed time scale of the probe pulse. The phase shift in oscillator 12 (adjustable from 2 to tt) provides the opportunity to study optical fibers of various lengths. The spectrum analyzer 1 1 allows you to analyze: the spectral composition of the signal envelope at the output of the low-pass filter 10, taking into account which it is easy to determine the transmission x: cancer of a fiber with a fiber waveguide. The voltage from the output of the peak detector 9 is fed to the control input of unit 7 and provides a change in the attenuation introduced by it so that the amplitude of the envelope at the output of the filter W is kept constant regardless of the change in attenuation of the optical fiber samples under study.

When an optical signal arrives at the input of the photodiode 3, the integrating link 5 is discharged to a certain voltage, which leads to a decrease in the multiplication factor of the photodiode 3. At the same time, when the signal current decreases, the signal-to-noise ratio at the output of the converter 8 is reduced, and at increase As the signal current increases, the multiplication factor decreases, remaining close to the optimal value at any level of the optical signal. Thus, the voltage drop across the high-resistance element 4 allows the multiplication factor of the photodiode 3 to change automatically so that its value is close to optimal at any attenuation, which ensures

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The device operates as follows.

The generator 12 generates two pulse sequences, often „or. t g / minimum recording error of that 20 kHz each. One of them (support.. - -

.1 / - signal. Additional adjustment

na) comes to source 1 (for example

measures in the form of a laser). The inputs of the converter 8 receive a signal from the photodiode 3 and the sequence of clock pulses from block 12 is phase-shifted relative to the reference one by the time determined by the propagation delay of the optical probe 50

amplification using attenuator 7 and detector 9 provides a constant signal level at the output of converter 8 and a constant image size of the spectrum ng :. analyzer screen 11.

Claims (1)

Invention Formula of the pulse of the optical fiber 2, the response delay of the photodiode 3, the delay in block 7, and the start delay of the converter 8 (adjustable from T to t – t, is the delay of the optical signal during 50 amplification using attenuator 7 and detector 9 provides a constant signal level at the output of converter 8 and a constant image size of the spectrum ng :. analyzer screen 11. Invention Formula A device for measuring the transmission xapaK of the fiber optic characteristics, containing an optical pulse source, the optical output of which is located opposite the end optical fiber, avalanche photodiode, whose optical input is located opposite the other end of the optical fiber, connected by an electrical power input to the voltage source output and output through serially connected strobe converter, and low frequency filter - to the input of the spectrum analyzer, as well as delayed pulse generator, connected by one output to the input of the source of optical pulses, and the other input - to the control input of the stroboscopic converter. featured 835784 It means that, in order to improve the measurement accuracy by increasing the signal-to-noise ratio, a peak detector was inserted into it, an attenuator controlled between an avalanche photodiode output and a stroboscopic converter input and connected by a control input to the low-pass filter output via a jack a detector, and a series-connected high-resistance element and an integrating element, is included. - between the output of the voltage source and the electrical  5 inputs for avalanche power supply.