Optical measurements are necessary to verify the operational characteristics of the optical fiber communication link. Various measurement techniques and special-purpose test equipments are employed for determining key performance parameters of the constituent components and devices including the optical fiber. It is quite obvious that optical measurements are needed at different levels of research and design, manufacturing and production of optical components and devices, installation and commissioning of optical fiber communication systems in the field. There is wide variety of optical measurement and test equipments used. These include optical power meter, optical oscilloscope and spectrum analyzer, optical time-domain reflectometer (OTDR), optical waveform analyzer, connector inspection microscope, dispersion analyzer, live fiber detector, talk-set, optical test set (combined source and power meter), etc. All these measurements are wavelength specific. Fiber attenuation and occurrence of faults in the optical fiber link is the main concern in ensuring the desired performance. There are several challenges involved with optical measurements like multiple wavelengths/channels, high optical power levels, need to carry tests remotely along with a high degree of automation.
Optical power and insertion loss measurements are among the easiest yet the most important optical measurements in optical fiber communications. An OTDR has several uses such as loss measurements as well as fault detection. Live fiber detectors and talk-sets are useful portable test equipment for the purpose of installation, maintenance and repair. Software prediction of an OTDR trace is a recent development in optical measurements. This chapter focuses on optical measurements of transmission properties of major constituents of optical fiber communication system such as optical source power output, optical amplifier noise characteristics, modulation response, insertion loss, fiber attenuation, dispersion parameters, and link fault detection.
Requirements of Optical Fiber Measurements
Optical fiber communication systems are evolving with innovations and numerous applications. Existing copper cables are being replaced with optical fibers everywhere in all accessible areas.