Sweep frequency transfer function measurement applied to optical fiber

Up to now, most of the experimental work on propagation through optical fibers was done using pulse measurements techniques. Short-light-pulse sources almost monochromatic and easy to drive to high-peak-power pulses are available on the optoelectronic components market; this is one of the main reasons why fiber manufacturers characterize their fibers by the broadening of the transmitted light pulse. This parameter does not provide enough information on the fiber behavior to the digital transmission system experts, unless one assumes a very-stable pulse shape at the fiber input and uses fast Fourier transform computation on time-domain signals. This paper presents the more classical technique which is being used on transmission cables and devices. The central unit is the network analyzer which can simultaneously provide attenuation versus frequency and phase rotation versus frequency of any optoelectronic device coupled between the reference and the test inputs. Various light sources have been selected for their sinusoidal modulation facilities; most of our measurements were made with fast-light-emitting diodes (GaAlAs 0.82 μm) and some of them with a CW injection laser (GaAlAs 0.82 μm).