ABSTRACT
We present a compact platform for biochemosensing based on the combination of a vertical-cavity surface-emitting laser (VCSEL) light source, microelectromechanical systems (MEMS)-based microoptics, a specially designed nanoplasmonic sensing chip, and charge-coupled device (CCD) detector. The platform does not require any spectral analyzer for signal evaluation, showing good promise for facile integration, neither does it use any microscope setup for the signal collection or imaging. The analytical capabilities of the developed biochemosensing platform are demonstrated by evaluation of the protein-substrate (biotinylated bovine serum albumin-gold) and the protein-protein (biotin-NeutrAvidin) binding kinetics, which is further compared to detection based on conventional optical extinction spectroscopy. The instrument is able to detect low femtomoles of adsorbed proteins with the limit of detection comparable to the state-of-the-art research and commercial optical label-free biochemosensors.
Subject(s)
Biosensing Techniques/methods , Lasers , Nanotechnology , Optical Phenomena , Adsorption , Animals , Avidin/metabolism , Biosensing Techniques/instrumentation , Biotin/metabolism , Cattle , Gold/chemistry , Kinetics , Light , Serum Albumin, Bovine/chemistry , Staining and Labeling , Surface PropertiesABSTRACT
We experimentally demonstrate that a grating outcoupler used for complex beam shaping (spot-array generation) can produce unintentional optical feedback that severely disturbs the integrated in-plane laser that illuminates the coupler. Simulations show that these outcouplers, in contrast to conventional collimating or focusing outcouplers, tend to produce high levels of feedback in spite of the detuning used to suppress feedback. Further, this feedback is focused to high intensity in the laser gain medium. This focused light acts as a seed for the nonlinear self-focusing that causes wave-front distortion and filamentation, which degrades the beam quality.
ABSTRACT
We experimentally demonstrate the use of two different multifunctional grating couplers in surface-emitting lasers for improved beam quality and advanced beam profiles. The lasers used for the demonstration are grating-based unstable resonator lasers, each with a grating coupler for surface emission and beam shaping. The new design method, described in detail, allows for simultaneous optimization of arbitrary feedback and outcoupling characteristics of the grating coupler. The first coupler is designed to reduce feedback to the resonator that would otherwise disturb the operation of the laser and lower the beam quality and to produce an output beam focused to four spots. The second coupler is designed to provide the feedback needed to support the unstable resonator, eliminating one feedback grating, and simultaneously focus the output beam to a single spot. As far as we know, this is the first time such multifunctional couplers are used in grating-coupled surface-emitting lasers. The couplers provide near-diffraction-limited spots that are a considerable improvement compared with previous lasers with no feedback control in the couplers.