Low through channel loss wavelength multiplexer using multiple transmission volume Bragg gratings.

We describe a wavelength multiplexer design that employs multiple transmission volume Bragg gratings written in the same region of a photosensitive glass having a through channel loss of < 0.5 dB. A two-channel multiplexer for wavelengths of lambda = 1310 and 1550 nm is demonstrated to test our design methods and assumptions. Agreement between simulation and experiment is within 0.2 dB at the peak diffraction efficiency. Grating apodization is used to reduce the interchannel cross talk from (13.5 +/- 0.5) to (41.5 +/- 8.5) dB, with an experimental through channel loss of (0.6 +/- 0.2) dB. Effects of angular dispersion on diffraction efficiency and grating spectral shape due to the finite diameter of the incident reading beam are also analyzed.