Reliable and stable interferometric sensors will make use of highly birefringent fibers. Rugged and reasonably expensive systems must involve all-fibre components having prescribed polarization properties, one of which is a polarization maintaining fibre coupler.
Such component is consistently achievable by means of a polishing technique which preserves most of the polarization features of the fibre. An extinction ratio of 20 dB is routinely achieved.
A variable version has been developped in order to allow balancing and fine tuning of interferometric systems. It uses monolithic mechanical concepts which result in a very compact device with good temperature and mechanical stability.