Temperature insensitive long period waveguide gratings in rib waveguide

Abstract

We propose long period waveguide gratings (LPWGs) in a rib structure in which the coupling takes place between the fundamental mode and the higher order modes (slab modes). Such an LPWG avoids the need of finite over cladding. The structure is inherently temperature insensitive as the involved modes have light confinement in the same material in contrast to the LPWGs, which use the over cladding of different material. Moreover, such a structure has an added advantage of less critical and easier fabrication process than the conventional LPWGs, in which the choice and deposition process of over cladding layer imposes several limitations. We demonstrate formation of such rib LPWGs in ion exchanged BK7 glass by laser ablation method and show their applications as wavelength filters and refractive index sensors. In particular we demonstrate temperature insensitive wavelength filter having the center wavelength of 1557.5 nm, an extinction ratio of ˜ 12 dB and 3-dB bandwidth of 3.8 nm. We also show a refractive index sensing characteristics of the structure with a sensitivity of 246 nm/RIU as an additional application.