Tunable vertical-cavity surface-emitting lasers as a light source for diffuse optical spectroscopy

Vixar presents a novel monolithic tunable vertical cavity surface emitting laser (VCSEL) design with a demonstrated tunable wavelength range of 41 nm in the near-infrared. This design combines a microelectromechanical system (MEMS) top mirror over a gallium arsenide based VCSEL cavity, and a monolithic construction which side steps any complex external cavity structures needed for tuning. We will present results which show the electro-thermally tunable mirror physically and reproducibly moving up to 400 nm, which corresponds to potential tuning range of over 50 nm in output wavelengths. These results also illustrate the use of this single mode, continuous wave, tunable VCSEL as a light source for biological tomographic imaging. Data taken in collaboration with Notre Dame presents the use of such tunable light sources for diffuse optical spectroscopic imaging (DOSI) of breast tumors and other anomalous tissue inclusions. Previous work confirms the viability of this design as an optical source for DOSI instruments and the work presented here shows improved results with even greater tuning capabilities and higher optical power. In conjunction with past work centered at 775 nm, current work at 940 nm, and future proposed VCSEL examples at 905 nm, Vixar expects to show that this design is capable of supporting tomographic imaging spanning 765 -782 nm, and 885 -955 nm in total. Above and beyond these immediate imaging goals, these results continue to enable future visions of many possible applications for which a monolithic tunable light source might be ideal.