SEMINAR ON OPTICAL FIBRE MEASUREMENTS


  OPTICAL FIBRE MEASUREMENTS.ppt (Size: 534 KB / Downloads: 4)

INTRODUCTION

Measurement on optical fibers which characterize the fiber.
Transmission characteristics
Geometrical and optical characteristics
Mechanical characteristics

Fiber Dispersion Measurements

Indication of distortion to optical signals.
Determination of bandwidth of the fiber.
Transmission characteristic of an optical fiber.
In multimode fibers, inter modal dispersion and in single mode, intra modal dispersion takes place .
Characterized by taking measurements of the impulse response of the fiber in time domain or base band frequency response in frequency domain.

TIME DOMAIN MEASUREMENT

Short optical pulses from a suitable source launched into fiber using pulsed driver.
These pulses are broadened due to the various dispersion mechanisms.
Measurement of an isolated dispersion is done by using laser with narrow spectral width.
Pulses are received by high speed photo detector and are displayed on sampling oscilloscope.
A beam splitter is utilized for tri gerring the oscilloscope and for input pulse measurement.
After initial measurement of output pulse width, the long fiber length cutback to shorter length.
To obtain the effective input pulse width, the measurement is repeated.
Fiber cutback to 1% of original length.
Fiber dispersion is obtained from the two pulse width measurements which are convenient fraction of their amplitude.
Dispersion measurements are normally made on pulses using the half maximum amplitude or 3dB points.

FREQUENCY DOMAIN MEASUREMENT

Preferred method for acquiring the bandwidth of multimode optical fibers.
Two frequency domain measurement techniques is generally used.
Pulses from sources are launced into fiber using pulsed driver.
Here spectrum analyzer is used instead of sampling oscilloscope
It takes fourier transform of the pulse in time domain and display its constituent frequency components
Comparison of the spectrum at the fiber output .