We present theoretical and experimental results of a novel fiber-optic wavelength-division multiplexing (WDM) design employing a broadband (>150-nm) dichromated gelatin volume holographic grating operating in a reflective Littrow configuration with on-axis optics, a single lens, and one fiber array. This configuration can achieve better than -1.5-dB insertion loss and -40-dB cross talk for a 6-channel system and -2.5-dB insertion loss and -20-dB cross talk for a 12-channel system with 15-nm channel spacing. For an experimental 4-channel WDM unit we measured better than -1.5-dB insertion loss for all channels and less than -32-dB cross talk. This design can provide cost and performance benefits for local area network communication applications.

We have fabricated and experimentally tested low-cost and mass-producible multimode fiber-optic couplers and connectors based on nonimaging beam-expanding optics and Liouville's theorem. Analysis indicates that a pair coupling loss of -0.25 dB can be achieved. Experimentally, we measured insertion losses as low as -0.38 dB. The beam expanders can be mass produced owing to the use of plastic injection-molding fabrication techniques and packaged in standard connector housings. This design is compatible with the fiber geometry and can yield highly stable coupling owing to its high tolerance for misalignments.

Expanded beam fiber-optic couplers offer great convenience for fiber cable connection, which is very desirable for local area network and other short-haul applications. But because most short-haul fibers are usually multimode, the large core causes significant aberration losses in conventional designs such as aspherics and GRIN lenses. Based on Liouville's theorem applied to nonimaging optics, we have developed a class of high efficiency expanded beam multimode fiber-optic coupler.

In general, Liouville's theorem holds for any time-reversible Hamiltonian system including the geometrical optics (both imaging and nonimaging1,2) model of monochromatic rays, where, in Hamiltonian formulation,2 the z-coordinate is treated as a parameter equivalent to the time variable in statistical classical mechanics. Thus the so-called ideal nonimaging optical elements, well known in the IR/VIS/UV region,1,3 can also be introduced to the collimation and concentration of XUV electromagnetic radiation (1–100 nm). Contrary to the IR/VIS/UV region, where the nonimagng elements are based on either metallic reflection or dielectric total internal reflection, the XUV concentrators/collimators are based on grazing incidence total external reflection, since the refractive index of all optical materials is smaller than 1 in the XUV region.