| 摘要 |
Polarization-dependent losses (PDL) are balanced in an optical system through the use of a weak polarizer placed in an optical path so as to compensate for the static PDL of the rest of the system. The weak polarizer comprises an interface or a layer of material having a different refractive index in the operating wavelength band, placed in the optical path at an angle to provide a desired level of PDL compensation. The geometry and indices of the two material are deliberately chosen to compensate for PDL elsewhere in the system. One implementation of the invention involves the use glass and air as the two materials, either in the form of a prism or a glass plate. The invention may alternatively take the form of a weak polarizer adhered to, or sandwiched between, a block of optical material such as glass. Preferably, a material having an index close to that of glass would be used in such a case, such as a polymer. The invention is applicable to many different optical configurations, including spectrum analysis, optical telecommunication networks and multiplexing devices. A Raman/fluorescence detection system is disclosed including a grating which diffracts and spectrally disperses light at characteristic wavelengths. In this embodiment, the PDL compensator is preferably placed in the optical path upstream of the grating (whether reflective or transmissive), with a trap being used to collect energy of the unwanted polarization.
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