Modulation Of Optical Radiation Research Articles

Photothermal excitation and self-excitation of silicon microresonators

Abstract Fiber optic sensors with a silicon microresonator acting as a sensitive element have been proposed for measurement of many physical parameters. The basic principle is that the measured value changes the resonance frequency of the microresonator. The flexural vibrations of the microresonator are excited photothermally under the action of modulated optical radiation. The interferometric optical feedback may cause self-oscillation of the microresonator even without light modulation. This is a theoretical paper devoted to consideration of the effects of photothermal excitation and self-excitation of silicon microresonators. For the first time the mechanism of parametric excitation of microresonators is investigated. The temperature compensation techniques are analyzed.

Low-frequency modulation of optical radiation in chalcogenide glass fibers

Low-frequency modulation of radiation was found to be feasible in the spectral range 0.7–1.15 μm when arsenic sulfide fibers were used. The relative modulation of the radiation depended on the modulated radiation wavelength when the fiber was subjected to additional radiation of photon energy 1.96 eV and 10−2–1 W/cm2 power density.

Perturbations of the surface of a liquid interacting with modulated optical radiation

An analysis is made of the excitation of waves on the surface of a viscous liquid which absorbs modulated optical radiation. These waves are excited because of thermal expansion, a surface tension gradient, and ponderomotive forces. Surface vibrations in a cylindrical resonator are investigated. It is shown that the surface tension gradient predominates at moderate intensities.

Low-noise receivers for fiber-optic microwave signal transmission

The problem of low-noise reception of high-frequency narrowband modulated optical radiation is discussed. Relatively simple p-i-n diode/FET based optical receiver structures which achieve good narrowband optical sensitivity are proposed. These receivers achieve good gain and noise performance due to a lossless parallel resonance circuit which shunts the input to the detector and FET. Design characteristics are presented for S-band receivers constructed using low-capacitance photodetectors, and GaAs MESFETs. Experimental realizations of these receiver designs, which achieve conversion efficiencies on the order of 250 V/W and optical noise equivalent power of less than 10 pW/ square root Hz for 0.8- mu m radiation, are reported. Scaling rules which should be of use in optimizing the performance of more advanced designs are stated and other types of receiver structures which can be expected to yield high narrowband optical sensitivity are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optically stimulated sound from gas bubbles in water: A novel optoacoustic mechanism

We detected high‐frequency sound radiated by individual gas bubbles in response to modulated green light from an argon‐ion laser. The bubbles were in clear water and were attached to a needle. Their radii were typically less than 100 μm. The sound radiated in response to single light pulses, of duration ≃10 μs and power ≃2 W, exhibits the ringing of the bubble's monopole resonance. The resonance frequency fR was found by Fourier transforming this signature; typical values were 30 kHz. Bubbles were subsequently illuminated by bursts of pulses with a frequency f≃fR. The resulting sound was characterized by an initial buildup of its amplitude. The mechanism for driving the monopole oscillations appears to be the modulated optical radiation pressure on the bubble's surface rather than thermal expansion. Related experiments on the optical levitation of bubbles in water and the emission of sound from dyed drops in water will be discussed. [Work supported by ONR.]

Statistics of photocounts of modulated radiation and coherence of field in optical waveguides

A brief review is given of the statistical theory of detection of modulated optical radiation and of the theory of propagation of partly coherent waves in optical waveguides.

Coherent approach to analysis of modulated optical radiation

A method is proposed for determining the modulation parameters of optical radiation that does not require wide-band photodetectors for modulation at high and microwave frequencies. The method is based on measurement of the time coherence of optical radiation containing a modulation signal.

Use of modulated optical radiation to obtain narrow resonances in gas spectroscopy

Use of modulated optical radiation to obtain narrow resonances in gas spectroscopy

Diffraction modulation of optical radiation by layered structures. II

On the basis of the theory of diffraction modulation of optical radiation by layered structures, formulated earlier, the properties of structures made of electrooptical plates are investigated. It is shown that in such modulators a gain in the controlling voltage can be obtained compared to the widely used amplitude-polarization modulator. The results of an experimental investigation are presented.

Modulation of optical radiation of λ = 10.6 μ

An investigation was made of the suitability of GaAs, CdSe, CdS, and CdTe crystals for the modulation of lasers whose active media were gaseous mixtures of CO2, He, and N2. The modulation efficiencies of these crystals were compared on the basis of the results obtained. Calculation formulas were derived and prototype modulators were constructed.