3-port optical device

A thee port polarization beam splitter is disclosed which utilizes only two GRIN lenses. Two beams are split by a bireferingent crystal into two orthogonally linear polarized parallel sub-beams. The two parallel beams are redirected to converge to a single same location at an end face of the GRIN lens by a roof prism and are coupled by the same lens to two optical fibers held in a fiber tube physically coupled to the GRIN lens.

DETAILED DESCRIPTION Turning now to FIG. 1, a prior art PBS is shown, being utilized as a polarization beam combiner. It should be understood that these devices can be used in one direction as beam combiners and in another reverse direction as polarization beam splitters. Linearly polarized light is launched into a port at an input/output end of 101 which consists of an optical fibre held in a sleeve directly coupled with a GRIN lens; the light is destined for port 104 . Similarly linear polarized light having a polarization that is orthogonal to the light launched into 101 is launched into 102 consisting of a second optical fibre held in a sleeve directly coupled with a GRIN lens. The light incident upon beam combiner/splitter 103 combines the two orthogonally polarized beams and the resulting elliptically polarized beam is directed to port 104 which consists of a GRIN lens coupled to an optical fibre held in a sleeve. The purpose of each GRIN lenses directly coupled with a fibre is to collimate light received from the fibre or focus light destined for the fibre. In this figure the centres of the cores of the optical fibres are each directly coupled with the optical axis of the lens they are directly coupled with. Hence in each instance the lens is coaxial with its respective optical fibre. FIG. 2 illustrates a similar circuit however only two GRIN lenses are required. In a beam combining mode of operation elliptically polarized light is launched into optical fibre and GRIN lens port 206 . The light is collimated by the lens and is directed to a birefringent crystal 205 , for example, rutile, calcite, or other material that will provide two parallel, orthogonally linear polarized sub-beams. The crystal 205 separates the light into two sub-beams that are parallel as the exit the crystal. A glass roof prism 204 receives the two beams and redirects these collimated sub-beams to a same location at an end face of the lens; the two sub-beams then cross each other at this location and are directed to the two optical fibres 203 held side-by-side in an optical fibre sleeve. Thus light propagating the lower half of the prism couples to fibre 201 and light propagating through the upper portion of the prism 204 is directed couple into fibre 202 . In the exemplary embodiment shown, it is required to have two parallel beams converge to a single location at the end face of the lens, and a symmetrical roof prism is used, however in other instances if the beams are not completely parallel the prism may be of other geometry and may not be symmetrical roof prism. By way of example, if the beams are not completely parallel, a prism of different geometry that will direct both beams to cross the optical axis at a same location about the end face may be useful in directing the beams to two optical fibres spaced differently from the optical axis of the lens. Notwithstanding, using a symmetrical roof prism to direct two parallel beams to two fibres spaced a same distance from the optical axis of a GRIN lens has many practical and useful applications, since, often two fibers may be disposed in a common sleeve. Turning now to FIG. 3 a mechanical structure is shown where the metal outside housing 307 forms a hermetic structure; Prism 308 crystal 309 are directly fixed in the housing; the collimator and the housing are connected using metal solder. The crystal 310 can be YVO 4 , rutile, or any birefringent crystal. 301 and 302 are polarization maintaining optical fibres; Protective rubber sleeves 303 and 313 are shown and a stainless steel housing 304 and 312 are provided; 305 and 311 are solder. Element 306 is a double fibre collimator which includes a fibre sleeve and a GRIN lens; The right angle prism 308 and birefringent crystal 309 are shown disposed within the cavity of the housing 307 ; A single fibre collimator 310 is shown having a single optical fibre 314 housed within a fibre sleeve. The mechanism through which light couples to two adjacent closely spaced cores of two optical fibres 202 and 201 is shown in more detail by viewing FIG. 4 . Instead of light propagating along the optical axis of the GRIN lens, light is coupled to ports, optical fibres 201 and 202 that are offset a same distance from the optical axis of the GRIN lens 403 b . The optical fibres 202 and 201 are offset from the optical axis within sleeve 403 a coupled to the GRIN lens 403 b. Of course numerous other embodiments may be envisaged, without departing from the spirit and scope of the invention.