Fiber optics links photo-detectors characterization and measurement techniques

In this paper, we have focused on photodetector structures, often complex junctions designed and optimized to perform the following functions:

• detection of low-value energy flows at the output of digital and analog transmission links ;

• emission control detection, at the head of a transmission link or opposite an optical pumping laser emitter in a fiber amplifier or local oscillator in a heterodyne detection stage.

Wavelengths in the spectral range under consideration range from λ _0min = 0.8 µm to λ _0max = 2 µm. Three types of structures stand out, with very different geometries and, consequently, very different production technologies, physical characteristics and areas of use:

• planar structures illuminated by the output wave of a multimode fiber, circular sensitive surfaces with a large diameter relative to the central wavelength of the incident spectrum;

• planar structures illuminated by the wave exiting a single-mode fiber, small-diameter circular sensitive surfaces;

• structures designed and built on dielectric guide models, optimized for very high-speed transmission applications at the output of single-mode fiber links.

The first part of this article reviews photoconduction and the modes of operation of PIN structures and photodiodes in the avalanche regime.

The second part describes the basic principles of measurement techniques for fundamental parameters and essential characteristics. Some experimental results are presented.