Loss reduction for phased-array demultiplexers using a double etch technique

Wavelength Division Multiplexing (WDM) is an effective technique to exploit the huge bandwidth of optical fibres. Key components in such WDM-systems are demultiplexers which spatially separate the different wavelength channels. Phased-array demultiplexers combine ease of fabrication and low insertion losses. Silica-based phased-array demultiplexers are realised with low losses from 2-3 dB [1,2]. InP-based demultiplexers show slightly higher on-chip losses of 4-6 dB [3,4]. In addition they have considerably higher fibre coupling losses (several dB’s), but the advantage of InP-based demultiplexers is that they can be integrated with active components. Earlier we reported a low-loss demultiplexer with reduced fibre coupling loss by applying deeply etched InGaAsP waveguides with a relatively large core and a low index contrast, which had an almost circular mode profile [5]. The component had 4-5 dB on-chip loss and fibre coupling loss of about 1 dB to a tapered fibre. In this article we report a method to further reduce the on-chip losses.