Solving self-mixing equations for arbitrary feedback levels: a concise algorithm.

Self-mixing laser sensors show promise for a wide range of sensing applications, including displacement, velocimetry, and fluid flow measurements. Several techniques have been developed to simulate self-mixing signals; however, a complete and succinct process for synthesizing self-mixing signals has so far been absent in the open literature. This article provides a systematic numerical approach for the analysis of self-mixing sensors using the steady-state solution to the Lang and Kobayashi model. Examples are given to show how this method can be used to synthesize self-mixing signals for arbitrary feedback levels and for displacement, distance, and velocity measurement. We examine these applications with a deterministic stimulus and discuss the velocity measurement of a rough surface, which necessitates the inclusion of a random stimulus.

Advances in bio-tactile sensors for minimally invasive surgery using the fibre Bragg grating force sensor technique: a survey.

The large interest in utilising fibre Bragg grating (FBG) strain sensors for minimally invasive surgery (MIS) applications to replace conventional electrical tactile sensors has grown in the past few years. FBG strain sensors offer the advantages of optical fibre sensors, such as high sensitivity, immunity to electromagnetic noise, electrical passivity and chemical inertness, but are not limited by phase discontinuity or intensity fluctuations. FBG sensors feature a wavelength-encoding sensing signal that enables distributed sensing that utilises fewer connections. In addition, their flexibility and lightness allow easy insertion into needles and catheters, thus enabling localised measurements inside tissues and blood. Two types of FBG tactile sensors have been emphasised in the literature: single-point and array FBG tactile sensors. This paper describes the current design, development and research of the optical fibre tactile techniques that are based on FBGs to enhance the performance of MIS procedures in general. Providing MIS or microsurgery surgeons with accurate and precise measurements and control of the contact forces during tissues manipulation will benefit both surgeons and patients.

On the feasibility of self-mixing interferometer sensing for detection of the surface electrocardiographic signal using a customized electro-optic phase modulator.

Optical sensing offers an attractive option for detection of surface biopotentials in human subjects where electromagnetically noisy environments exist or safety requirements dictate a high degree of galvanic isolation. Such circumstances may be found in modern magnetic resonance imaging systems for example. The low signal amplitude and high source impedance of typical biopotentials have made optical transduction an uncommon sensing approach. We propose a solution consisting of an electro-optic phase modulator as a transducer, coupled to a vertical-cavity surface-emitting laser and the self-mixing signal detected via a photodiode. This configuration is physically evaluated with respect to synthesized surface electrocardiographic (EKG) signals of varying amplitudes and using differing optical feedback regimes. Optically detected EKG signals using strong optical feedback show the feasibility of this approach and indicate directions for optimization of the electro-optic transducer for improved signal-to-noise ratios. This may provide a new means of biopotential detection suited for environments characterized by harsh electromagnetic interference.