In this paper, semiconductor laser feedback interferometry is applied to the characterization of vibrating mass microsensors, such as gyroscopes and accelerometers. Complete characterization of such devices with this technique includes the identification of the vibration modes and the measurement of the resonance curves of the different axes, the determination of resonance frequency, quality factor and the actuation efficiency as functions of different parameters such as pressure. In the case of a gyroscope, tuning of the driving and of the sensing axes can be also performed, as well as the measurement of the Coriolis force. Thanks to its very simple optical implementation, feedback interferometry provides a viable alternative to the standard electrical measurements, and is especially useful for the characterization of prototypes, for which a dedicated electronics circuit is not yet available.
We have developed a fiberoptics setup which can be easily specialized with minor changes to implement different schemes of optical chaos generation and synchronization using semiconductor lasers. Long and short cavity, open and closed loop configurations have been compared, as well as various encoding/decoding methods for secure transmission based on chaotic carriers, such as CSK (Chaotic Shift Keying), ACM (Additive Chaotic Masking), CM (Chaos Modulation). Different transmission media, possibly including optical amplifiers, have been also tested.
In this paper, we report on feedback interferometric measurements on a micromachined gyroscope and on a micromachined linear accelerometer. Characterization has been performed for different values of pressure and of other parameters using a laser diode. Resonance frequencies and quality factors have been measured. Moreover, hysteresis and other nonlinear phenomena on specific samples have also been detected. The proposed method is based on optical injection and represents an efficient alternative to the standard electrical measurements, which actually shows some limitations for bare prototype testing.
We propose different schemes for secure data transmission based on synchronization of chaotic semiconductor lasers. The sources are driven to chaos by light injection either from another laser or from a mirror. Synchronization is obtained by implementing a master/slave configuration, i.e., by controlled injection of the emission of one chaotic system into the other. In a first basic scheme (masking) encryption consists in hiding a message by superposition of a chaotic waveform. An alternative and better scheme (Chaotic Shift Keying) consists in the digital modulation of a suitable parameter (such as the supply current) of the master laser, which is located at the transmission end. Because of the very complex chaotic pattern of the transmitted waveform, an eavesdropper cannot detect the incoming bit stream by conventional time or frequency domain methods (such as by using filters or correlators). On the other side, decryption can be performed by the authorized listener, which owns tuned copies of the chaotic system, by implementing a suitable synchronization scheme.
Transmission via diffused radiation is a technique which implements a mobile wireless link exploiting the ambient diffusion of light or infrared radiation it operates over short range distances and medium range bandwidth and is therefore attractive for a variety of in-vivo laboratory experiences involving stimulation and/or monitoring of different physiological parameters on freely-moving animals. In this paper the main features of the optoelectronic transmission are presented making a comparison with other approaches namely electric and fiberoptic cabling and RF links. The diffused channel is characterized in terms of attenuation bandwidth and S/N ratio showing that it is suitable for transmission of biological signals in a typical laboratory environment. A two-way transmission system is described that has been specifically designed for telemetry on small animals. The system consists of a pair of LED/photodiode transmitters and receivers. The mobile unit has been implemented in surface mount technology (SMT) to achieve adequate compactness. The link offers an accuracy of 0. 5in amplitude and a signal bandwidth from d. c. to 1KHz and operates for over 15 hours with two standard lithium batteries. This system is being routinary used for in-vivo polarographic determinations of brain neurotransmitters and their metabolites (DOPAC and 5-HIAA) on freely-moving rats. Moreover it is pointed out that the optoelectronic approach can eliminate the severe crosstalk interference which has so far prevented the concurrent pickup of low-level electrophysiological signals during polarographic determinations.