Measurement of on-chip back-reflection; direct and interferometric methods compared.

AbstractThe design and characterisation of integrated circuits on SOI aimed at comparing two different measurement methods is proposed. A first set of designs will provide a direct comparison between the wavelength responses of two sample components with distinct levels of back-reflection. A selected pair of samples will then be used as partial mirrors in an on-chip Michelson interferometer arrangement and back-reflection levels versus wavelength will be extracted from SiEPIC automated measurement results. Sensitivities of the two measurement methods will be compared.

Introduction

For sensing applications measurement techniques based on interferometric arrangements typically provide higher sensitivity than direct measurement techniques. Can we demonstrate this on-chip, for the back-reflection measurement of various elements? Due to practical constrains the elements considered here are the ones readily available in SiEPIC Process Development Kit (beam dump, un-terminated waveguide or grating couplers). In a more realistic scenario, this experiment would measure the optical properties of bio-material or gas samples.
Designs placed on this fabrication run fall in two groups: design for direct measurements and designs using a Michelson type of interferometer. The direct measurement compares the back-reflection response over the 1500nm-1600nm wavelength range of two different components/samples from SiEPIC's library. Then, one pair of reference component is chosen and integrated to a Michelson interferometer arrangement. A second Michelson interferometer design allows a more direct comparison with the direct measurement.

Results will be compared to assess if one type of measurement leads to a better ability to resolve levels of back-reflection.



Theory

Same theory as for MZIs with double the Optical Path Length Difference and a phase shift of Pi at each reflection.