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Infrared detectors: status and trends

Diffraction characteristics of general dielectric planar (slab) gratings and surface-relief (corrugated) gratings are reviewed. Applications to laser-beam deflection, guidance, modulation, coupling, filtering, wavefront reconstruction, and distributed feedback in the fields of acoustooptics, integrated optics, holography, and spectral analysis are discussed. An exact formulation of the grating diffraction problem without approximations (rigorous coupled-wave theory developed by the authors) is presented. The method of solution is in terms of state variables and this is presented in detail. Then, using a series of fundamental assumptions, this rigorous theory is shown to reduce to the various existing approximate theories in the appropriate limits. The effects of these fundamental assumptions in the approximate theories are quantified and discussed.

Analysis and applications of optical diffraction by gratings

Publisher Summary A refractive index can be increased by ion implantation by changes in density and structure, by the addition of high-polarizability impurity ions, by a reduction of the plasma effect that increases the index and that is most important in the wavelength region far from the energy gap, and by absorption changing in the index in the region of the gap, that is, via the Kramers–Kronig relation. This chapter discusses the optical properties of implanted semiconductors, electrooptic components formed by ion implantation, general principles that determine most luminescent systems, effects of implantation temperature, luminescence centers in LiF-Mg-Ti radiation dosimeters, and use of line spectra in defect studies. In the LiF system, the luminescence bands are broad, and if alternative versions of the same complex exist, they cannot be resolved from the spectra. The addition, by implantation, of ions with incomplete inner electron shells opens up new possibilities as the lattice distortions of the free-ion energy levels are strongly perturbed by the defects in the neighborhood of the ion.

Optical Effects of Ion Implantation

The current state of the art of optical fiber sensors is reviewed. The principles of operation are detailed and the various types of fiber sensors are outlined. Achievable performance and limitations are discussed and a description of technology used to fabricate the sensor is presented. The characteristics of acoustic, magnetic, gyro, laser diode, and other sensors are described. Trends in the development of this sensor technology and expected application areas are briefly outlined.

Optical fiber sensor technology

Infrared thermal imaging of the skin has been used for several decades to monitor the temperature distribution of human skin. Abnormalities such as malignancies, inflammation, and infection cause localized increases in temperature which show as hot spots or as asymmetrical patterns in an infrared thermogram. Even though it is nonspecific, infrared thermology is a powerful detector of problems that affect a patient's physiology. While the use of infrared imaging is increasing in many industrial and security applications, it has declined in medicine probably because of the continued reliance on first generation cameras. The transfer of military technology for medical use has prompted this reappraisal of infrared thermology in medicine. Digital infrared cameras have much improved spatial and thermal resolutions, and libraries of image processing routines are available to analyze images captured both statically and dynamically. If thermographs are captured under controlled conditions, they may be interpreted readily to diagnose certain conditions and to monitor the reaction of a patient's physiology to thermal and other stresses. Some of the major areas where infrared thermography is being used successfully are neurology, vascular disorders, rheumatic diseases, tissue viability, oncology (especially breast cancer), dermatological disorders, neonatal, ophthalmology, and surgery.

A reappraisal of the use of infrared thermal image analysis in medicine

A practical fiber-optic measurement instrument for temperature was constructed consisting of a small sensor responding to optical absorption change in a semiconductor, and a unique signal processing system with two different-wavelength light emitting diodes (LED's). The fiber-optic sensor with a semiconductor chip is quite small, very sensitive, highly reliable, and easy to manufacture at low cost. The most outstanding feature of this system is that it is free from optical-stray-loss. The accuracy of about \pm1\deg and the response time of about 2 s were obtained in the temperature range from -10°C to 300°C.

Fiber-optic instrument for temperature measurement

A practical laser Doppler velocimeter with optical fibers in the whole system was developed. The novel optical probe designed for this LDV is constructed of a graded-index rod lens attached to the end of an optical fiber. Since the laser beam from the probe is well collimated, the velocity accuracy and sensitivity are significantly improved. Mechanical vibration measurements were also carried out with this LDV; vibration amplitude down to 1.0 μm p-p can be measured at a frequency of 120 Hz with high accuracy.

Laser Doppler velocimeter with a novel optical fiber probe

By using Faraday and Pockels' effects of a Bi 12 GeO 20 (BGO) single crystal, two kinds of fiber-optic sensors for electric current and voltage were tentatively fabricated. The optimum design of these sensors and their performances were investigated. It was verified that the BGO crystal is very available for either of the current and voltage sensors with regard to their sensitivity and stability. As for the experimental results, the minimum detectable magnetic field of 10-2Oe and the temperature dependence within ±2 percent in the temperature range of -25 to 85°C was obtained for the current sensor, while for the voltage sensor the sensitivity of 10-3V and the temperature dependence within ± 0.5 percent was in the same temperature range.

Fiber-optic current and voltage sensors using a Bi 12 GeO 20 single crystal

The investigations were carried out on optical waveguides obtained by thermal diffusion of Ti into LiNbO3 single crystals. In the Ti-diffused LiNbO3 slab waveguides, the relationships of the refractive index profile (index change at the surface, diffusion depth) to various diffusion conditions were examined. Conditions were found to fabricate the waveguides of the required number of modes (TE modes) and effective indices for the wavelength of a He–Ne laser (0.6328 μm) and a GaAs–GaAIAs double heterostructure laser (DH laser) (0.8730 μm). The slab waveguides of the required number of modes and effective indices could be obtained by adjusting only the thickness of evaporated Ti film.

Mode control of Ti-diffused LiNbO 3 slab optical waveguide

A practical fiber optic measuring system for heavy electric current was developed by using the magnetooptic (Faraday) material. In order to obtain better SNR and smaller temperature dependence, the most suitable combination of the light source and Faraday material was experimentally and theoretically determined. Consequently, it was emphasized that an LED and diamagnetic SF-6 flint glass gave the superiority of overall system capability over LD's and para- or ferromagnetics. A novel type of fiber optic current sensor was constructed of the Faraday rotator of SF-6 flint glass with two thin-film polarizers. By using this sensor and a high radiance LED, high accuracy within ±0.5 percent was obtained for magnetic field between 20 and 500 Oe, and at temperatures from -25°C up to 80°C.

Masahiro Nunoshita

Papers

Fiber-optic instrument for temperature measurement

Laser Doppler velocimeter with a novel optical fiber probe

Fiber-optic current and voltage sensors using a Bi 12 GeO 20 single crystal

Mode control of Ti-diffused LiNbO 3 slab optical waveguide

Fiber optic measuring system for electric current by using a magnetooptic sensor