Robert Bruce Charters

WDM based on multimode interference-coupler built in an organic-inorganic material

Abstract The WDM phasar, which is a key element in optical telecommunication systems, is shown here to be made with a very low cost and promising technology based on organic–inorganic material, and with a design based on MMI devices for the splitter and the combiner instead of star couplers or gratings. A realization of a first 4×4 MMI phasar, for use around 1.55 μm wavelength, demonstrates the application of these two specific aspects. Experimental measurements and theoretical results are compared.

New dense organic-inorganic optical circuits using multimode interference (MMI) effects

An organic-inorganic materials associated with a direct printing by UV exposure was used to make MMI couplers. A 1 X 32 splitter and a 4 X 4 splitter/combiner were designed and achieved for working at 1.55 micrometers wavelength. The 4 X 4 splitter/combiner was then used to design a 2 nm selective MMI-Phasar working around 1.55 micrometers .

Photosensitive ormosil system for integrated optics

A photosensitive organically modified silica (ormosil) material has been developed for integrated optics applications. In this material, prepared via a simple one- step sol-gel process, the silica backbone is substituted with methacrylate groups to confer photosensitivity, and with phenyl and/or methyl groups to adjust the refractive index from 1.47 to 1.52. Ormosil films are spin-coated onto silica-on-silicon substrates, and waveguides are defined in the films using a 325 nm HeCd laser direct write system. The unexposed regions are then dissolved with isopropanol to leave the desired pattern of ridge waveguides, before baking. The width of the waveguides increases with the UV dose and the concentrations of the methacrylate groups and the photo-initiator. Waveguides with widths >= 5 micrometers have been written with UV doses of around 0.4 J/cm2, and baked at up to 200 degree(s)C without cracking. In the 1310 and 1550 nm communications windows, the major sources of optical loss are vibration overtones of OH and CH groups. The intensities of these absorption bands have been measured with infrared spectroscopy and photothermal deflection spectroscopy, and the effects of some strategies to reduce the concentration of CH and/or OH groups, including fluorination and higher baking temperatures, are assessed.

Wavelength shifts in UV-exposed single-mode fused taper fiber couplers

Fused taper single-mode fiber couplers are readily fabricated with specific spectral properties, including 3 dB splitting in the 1310 and 1550 nm windows, and 1310/1550 nm wavelength division multiplexing (WDM) and demultiplexing. The specific functionality of the coupler is achieved through precise control over the heating and drawing processes. A possible alternative approach to obtaining the required functionality is to use UV- trimming or post-tuning. The spectral response of single-mode fused taper fiber couplers can be shifted by exposing the entire coupler to intense UV light. Furthermore this occurs without any prior hydrogenation, and there is also no discernible increase in excess loss in the exposed couplers. Results will be presented showing the effect of varying both the fluence and the wavelength of the UV-source on the spectral shift of these and other types of couplers. Wavelength shifts of over 100 nm are possible with the 1310/1550 nm WDM couplers, using sufficient fluence. A simple slab model of the complete tapered coupler confirms that the major contribution to the wavelength shift due to the change in the core index originates mainly in the down- and up-taper regions and, to a lesser extent, in the central waist region. This model explains the greater sensitivity of the spectral shift of the more-tapered WDM couplers to UV-irradiation compared to the shift in the 3 dB couplers.