Miniature spectrometer and beam splitter for an integrated optical coherence tomography system

Optical coherence tomography (OCT) is a widely used optical imaging technology [1]. Current OCT systems contain a variety of fiber and free-space optical components, which add to the instrument size and cost. By utilizing a suitable mass-fabrication technology and a monolithic design, integrated optics can provide miniaturized OCT systems that offer dramatic cost and size reduction as well as more stable interferometric detection [2,3]. In this paper we present an important step toward a cheap, compact, and quasi-maintenance-free spectral-domain OCT (SD-OCT) system by integrating its central components, the beam splitter and spectrometer, on a silicon chip as schematically shown in Fig. 1 A. An arrayed waveguide grating (AWG) [4] operating at a center wavelength of 1250 nm with a large free spectral range of 136 nm and a high wavelength resolution of 0.21 nm forms the integrated spectrometer, and a non-uniform adiabatic coupler [5] forms the beam splitter in our device. The coupler and AWG were fabricated in silicon oxynitride (SiON) [6]. Single-mode SiON channel waveguides with a 1.8-μm width, 1-μm height, 1.54 core refractive index, and 1.4485 cladding refractive index, enabling bending radii down to 0.5 mm, were fabricated.