An optical add/drop filter for wavelength division multiplexed systems and construction methods are disclosed. The add/drop filter includes a first ferrule having a first pre-formed opening for receiving a first optical fiber; an interference filter oriented to pass a first set of wavelengths along the first optical fiber and reflect a second set of wavelengths; and, a second ferrule having a second pre-formed opening for receiving the second optical fiber, and the reflected second set of wavelengths. A method for constructing the optical add/drop filter consists of the steps of forming a first set of openings in a first ferrule; inserting a first set of optical fibers into the first set of openings; forming a first set of guide pin openings in the first ferrule; dividing the first ferrule into a first ferrule portion and a second ferrule portion; forming an interference filter on the first ferrule portion; inserting guide pins through the first set of guide pin openings in the first ferrule portion and second ferrule portion to passively align the first set of optical fibers; removing material such that light reflected from the interference filter from the first set of optical fibers is accessible; forming a second set of openings in a second ferrule; inserting a second set of optical fibers into the second set of openings; and positioning the second ferrule with respect to the first ferrule such that the second set of optical fibers receive the light reflected from the interference filter.

Optical properties of photonic crystal (PC) structures have attracted great interest in research area and industry field because of its capability to guide and control light propagation in compact device with feature sizes comparable to light wavelength. Optical filters are essential components of photonic integrated circuits and Wavelength Division Multiplexer (WDM). In this thesis, a WDM is designed based on PC with a defect gap mode. We first describe the design and simulation of the photonic band gap (PBG) in a perfect triangular lattice of air holes in Si. Then based on Silicon-On-Insulator (SOI) slab model, we will introduce pass band in the photonic band gap by moving the two slabs of PBG structure apart some distance, which results in a photonic crystal Fabry-Perot filter in an SOI waveguide. A WDM architecture with 3 channels is designed based on this kind of PC filter last and selective wavelength add/drop function in 2 channel filters is simulated with no more than 1.55dB loss using Finite-Difference Time-Domain (FDTD). PC has strong effects on optical group velocity. In addition to filter response, the dispersion properties in time domain are studied with FDTD. The dispersion was found to be about 45ps/(mmi︡m) through the passband around 1.55i︡m, but due to the small length of the filter, it should have nominal effects for signal propagation up to the bit rate of 4000Gb/s.