Summary: Raman Spectroscopy and Optical Coherence Tomography on a Chip
N. Ismail, B.I. Akca, F. Sun, G. Sengo, K. Wörhoff, M. Pollnau, and R.M. de Ridder
Miniaturization of optical instruments for biomedical applications requires the development of
efficient means to deliver excitation light to and collect the resulting signals from biomedical
tissue by an optical microchip, as well as spectral analysis of the acquired information on the chip.
We have investigated light collection by integrated waveguides, invented a method for on-chip
confocal light delivery and collection, proposed new designs and developed high-resolution arrayed-
waveguide gratings (AWGs), and demonstrated Raman spectroscopy and spectral-domain optical
coherence tomography (OCT) on a chip.
1. Light collection by integrated waveguides
In a semi-analytical model  and Monte-Carlo simulations , the light collection efficiency of
integrated waveguide probes (Fig. 1, left) was compared to that of different types of fiber probes for
different thicknesses of weakly and highly scattering samples, respectively. The simulation results
show that integrated probes have a collection efficiency that is higher than that of small-core fiber
probes, and, in the particular case of thin samples, also exceeds the collection efficiency of large-
core, highly multimode fiber probes (Fig. 1, right). An integrated waveguide probe with one
excitation and eight collector waveguides (Fig. 1, left) was fabricated and applied to excite and
collect luminescence from a Ruby rod  and a highly scattering water suspension of latex
nanospheres . Experimental and calculated results are in good agreement with each other.
Fig. 1. (left) Top view of a multi-waveguide integrated probe for backscattered light collection. An expanded