Polarization state frequency multiplexing

A method for measuring optical properties of an optical device, comprising the steps of:

• (a) providing a light beam of varying frequency from a frequency-tunable light source,
• (b) splitting the light beam into a first light beam and a reference light beam,
• (c) splitting the first light beam into at least four sub-beams,
• (d) imparting a different time delay to each of the sub-beams,
• (e) imparting a different polarization state to each of the sub-beams,
• (f) recombining the sub-beams into a single combined light beam containing the supersposition of the polarization states,
• (g) passing the single combined light beam through a device under test to produce a transmitted light beam,
• (h) imparting a path length difference between the single combined light beam and the reference light beam,
• (i) combining the transmitted light beam and the reference light beam to cause interference therebetween and to produce an output beam containing modulations at beat frequencies associated with the different polarization states, and
• (j) determining and displaying a measure of at least one of polarization dependent loss (PDL) and polarization mode dispersion (PMD) by analyzing signal levels of the beat frequencies of the output beam.

An apparatus for measuring optical properties of an optical device, the apparatus comprising

• a frequency-tunable light source,
• a beam splitter coupled to receive a light beam from the source and to split the light beam into a signal beam and a reference beam,
• an interferometer having at least a first and a second optical paths having different path length, coupled to pass the signal beam through the first path and the reference beam through the second path,
• a second beam splitter disposed in the first path to split the signal beam into at least four sub-beams;
• means for imparting a different time delay to each of the sub-beams,
• means for imparting a distinctly different polarization state to each of the sub-beams,
• means for recombining the sub-beams with different polarization states into one recombined optical beam to be passed through the optical device and to be interfered with the reference beam in the interferometer to form an interfered beam containing modulations at beat frequencies associated with the different polarization states, and
• means for analyzing the interfered beam in the frequency domain to obtain signal levels of the beat frequencies at the different polarization states from which polarization mode dispersion (PMD) or polarization dependent loss (PDL) is calculated

A device for determining optical properties of a device under test comprising:

• a tunable light source for providing a light beam, the beam having a wavelength that varies periodically through a range of wavelengths at a sweep frequency rate;
• a first beam splitter for splitting the light beam into a signal beam and a reference beam,
• a second beam splitter having one input and at least four outputs for splitting the signal beam into at least four sub-beams;
• at least four polarizing optics for imparting a distinctly different polarization state to each of the sub-beams in order to associate each of the sub-beams with a different polarization state;
• a beam combiner having at least four inputs and one output for combining the sub-beams into a single optical beam for input to the device under test;
• an interferometer for interfering the single optical beam with the reference beam to obtain
• an output light signal, having an amplitude which varies in time;
• and
• a detector for detecting the output light signal and resolving the output light signal into frequency components thereof, and for calculating polarization mode dispersion (PMD) or polarization dependent loss (PDL) of the device under test based on amplitudes of the frequency components associated with the different polarization states;
• wherein the time delay for each the sub-beams is selected such that a unique frequency component of the output light signal is associated with each one of the different polarization states.