Ultralow Loss High Delta Silica Germania Planar Waveguides

Abstract

A plasma enhanced chemical vapor deposition process was developed to deposit SiO 2 -GeO 2 films suitable for high index contrast planar waveguides. These films were deposited in a standard parallel plate reactor from silane, germane, nitrous oxide, and a nitrogen carrier. The germania content of the film was equal to the mole fraction germane of the hydride precursors in the gas stream, and the refractive index of the film varied linearly with the mole fraction of germania. Low loss guides ranging from 1.5-4.0% ⌬ were fabricated. With standard photolithographic patterning, a 0.05 dB/cm propagation loss and minimum bend radius of 1.5 mm were measured for 2.0% ⌬. Improvements to the photolithographic patterning to reduce sidewall roughness were required to achieve low propagation loss at higher ⌬. This reduced the propagation loss for 3.5% ⌬ cores to 0.086 dB/cm. An average minimum bend radius of 570 m was measured for 3.5% ⌬, but modeling suggests the bend radius could be reduced below 500 m with offsets to reduce transition loss. Ring resonator, fabricated from 3.5% ⌬ waveguides, exhibited a free spectral range as large as 62.7 GHz and a very low round trip insertion loss of 0.06 dB.

High index contrast polysiloxane waveguides fabricated by dry etching

“…From the raw data we see that the best fit propagation losses at 1550 nm are 0.76 and 0.79 dB/ cm, respectively, for the 4 and 3 m waveguides, while it is clear that the 2 m waveguides have suffered significant bending loss as predicted by Bellman et al 7 The 4 m wide waveguides measured 0.36 dB/ cm at 1310 nm.…”

“…[2][3][4] The modest index contrasts used to date preclude bend radii below 1 cm, 7 and are relatively insensitive to roughness on the waveguide surfaces due to both the low contrast and large size. 7 This represents an increase in the index contrast of over three times that of all previously demonstrated polysiloxane waveguides. Minimum usable bend radius is a strong function of index contrast, and for waveguides with indices around those of typical polymers, it is necessary to reach an index contrast of ϳ2% to obtain around 1 mm bend radii.…”

Fabrication of microchannel arrays in borophosphosilicate glass

“…18,19 Controlled formation of voids was achieved by depositing and annealing layers of borophosphosilicate glass over templates etched into undoped or germanium-doped silica layers. 18,19 Controlled formation of voids was achieved by depositing and annealing layers of borophosphosilicate glass over templates etched into undoped or germanium-doped silica layers.…”

Nanophotonic Devices Based on Silicon-On-Insulator Nanowire Waveguides

“…Recently also ultra high Ge rich material have been PECVD fabricated giving, together with thermal silica cladding, refractive index contrast up to 4% [4]. This allows shrinking the bending radius to 0.4 mm and core size to 2.6 × 2.2 µm, but increases propagation and coupling losses additionally.…”