Single integrated device for optical CDMA code processing in dual-code environment.

We report on the design, fabrication and performance of a matching integrated optical CDMA encoder-decoder pair based on holographic Bragg reflector technology. Simultaneous encoding/decoding operation of two multiple wavelength-hopping time-spreading codes was successfully demonstrated and shown to support two error-free OCDMA links at OC-24. A double-pass scheme was employed in the devices to enable the use of longer code length.

Optical add-drop multiplexers based on the antisymmetric waveguide Bragg grating.

A novel optical add-drop multiplexer (OADM) based on a null coupler with an antisymmetric grating was designed and experimentally demonstrated. The antisymmetric grating exclusively produces a reflection with mode conversion in a two-mode waveguide. This improves the performance compared with previous demonstrations that used tilted Bragg gratings. Our design minimizes noise and cross talk produced by reflection without mode conversion. In addition, operational bandwidth and, versatility are improved while the compactness and simplicity of the null coupler OADM are maintained.

Diffraction-limited performance of flat-substrate reflective imaging gratings patterned by DUV photolithography.

We report on the first demonstration of flat substrate imaging gratings fabricated by deep ultraviolet (DUV) photoreduction lithography, which uniquely offers sub-100-nm resolution and spatial coherence over centimeter scales. Reflective focusing gratings, designed according to holographic principle, were fabricated on 300-mm silicon wafers by immersion DUV lithography. Spatial coherence of the fabrication process is evident in measured diffraction-limited imaging function. Flat-substrate gratings, with lines of arbitrary spacing and curvature, offer both dispersion and general spatial wavefront transformation combining the function of multiple optical elements. Fabrication at the sub-100-nm resolution level allows high-line-count, low-order efficient gratings even into the deep ultraviolet region. Nanoreplication of gratings at the wafer level provides a pathway to devices of ultimate low cost.

Low-loss silica-on-silicon two-dimensional Fabry-Perot cavity based on holographic Bragg reflectors.

We report on the demonstration of an integrated slab-waveguide-based concentric Fabry-Perot resonator that employs holographic Bragg reflectors as cavity mirrors. The cavity, produced in a low-loss silica-on-silicon slab waveguide by high-fidelity deep-ultraviolet photolithographic fabrication, exhibits a reflectivity-limited Q factor of approximately 10(5). Increasing the mirror's reflectivity will provide Q values similar to those of silica-based ring resonators, whereas the folded Fabry-Perot resonator design allows access to a substantially larger free spectral range by cavity shortening.

Demonstration of mode conversion using anti-symmetric waveguide Bragg gratings.

We experimentally demonstrate a novel grating which only produces reflection with mode conversion in a two-mode waveguide. That characteristic can improve the performance of optical devices that currently use tilted Bragg gratings to provide the mode conversion. Tilted Bragg gratings produce also reflections without mode conversion which increases noise and crosstalk of the optical device.

Wavelength division multiplexing based on apodized planar holographic Bragg reflectors.

We report wavelength division multiplexing based on lithographically fabricated slab-waveguide-contained planar holographic Bragg reflectors (HBRs). Partial HBR diffractive contour writing and contour displacement are successfully demonstrated to enable precise bandpass engineering of multiplexer transfer functions and make possible compact-footprint devices based on hologram overlay. Four- and eight-channel multiplexers with channel spacings of approximately 50 and approximately 100 GHz, improved sidelobe suppression, and flattop passbands are demonstrated. When a second-order apodization effect, comprising effective waveguide refractive-index variation with written contour fraction, and the effect of hologram overlap on the hologram reflective amplitude are included in the simulation, excellent agreement between predicted and observed spectral passband profiles is obtained. With demonstrated simulation capability, the ability to fabricate general desired passband profiles becomes tractable.