Optical Heterodyne Technique Research Articles

Ultra-high-speed PLL-type clock recovery circuit based on all-optical gain modulation in traveling-wave laser diode amplifier

A new phase lock loop (PLL) is developed for very-high-speed optical timing extraction using traveling-wave laser-diode amplifier (TW-LDA) as a phase detector. The all-optical gain modulation of the TW-LDA is utilized to detect the relative phase difference between an optical signal and an optical clock The frequency response of the optical gain modulation measured with the optical heterodyne technique agrees with the theoretical results based on a rate equation model. With the developed PLL, 10-GHz optical timing clock is successfully extracted from randomly modulated optical signal pulses and the measured bit-error-rate performance shows no power penalty. Influence of the received optical noise on the phase variance of the PLL is also evaluated and it is concluded that 100 GHz operation is possible by increasing the input optical power to 10 mW.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optical heterodyne detection of pulsed ultrasonic pressures

An optical heterodyne interferometer was used for measuring short ultrasonic pulses in fluids. The optical phase shift of the probe beam, proportional to the acoustic pressure integrated along the light path, was demodulated quantitatively by electronic processing. The detection sensitivities of 10(-3) (Pa/ radicalHz) in water and 10(-4 ) (Pa/ radicalHz) in air were deduced. The experimental results obtained in water as well as in air show that this optical heterodyne technique offers a very sensitive way of measuring ultrasonic pressures in the low megahertz range even for very low pressures.

Optical heterodyne measurement of pulsed lasers: Toward high-precision pulsed spectroscopy

In this paper we explore theoretically and experimentally the effect of fluctuations in the instantaneous frequency of a pulsed laser on the shape and position of two-photon transition spectra. The usual procedure of characterizing a pulsed laser by its frequency energy spectrum is insufficient for precision measurements. The nonlinear nature of the two-photon transition produces a systematic shift of the atomic spectrum with respect to the laser frequency spectrum that is dependent on the phase evolution of the laser pulse. In fact, any nonlinear process (e.g., second-harmonic generation) may result in displaced or distorted spectra. We also find that Fabry-P\'erot filtering a laser pulse can result in large frequency chirps. We use an optical heterodyne technique to measure the instantaneous frequency of our excimer-pumped dye-laser system to an uncertainty of 1.3 MHz and determine the effect of the inherent frequency chirps of this system on a two-photon transition. We conclude that with this technique, precision nonlinear spectroscopy to the level of 1 MHz may be achieved with pulsed lasers.

Comparison of fast photodetector response measurements by optical heterodyne and pulse response techniques

Characterization of high-speed photodetectors by optical heterodyne and pulse response techniques is reported, and the results are compared. Scalar deconvolution was used to obtain photodetector response from the pulse response measurements with effects of the measurement apparatus removed. Linearity of the detector response is verified, validating comparison in the frequency domain using a Fourier transform of the pulse response data. The comparison is limited to the magnitude of the transfer function in the frequency domain, since the optical heterodyne technique does not give phase information. Both sets of results are corrected for the effects of their respective measurement systems. After these corrections, close agreement between results obtained by using the two techniques was found. >

Coherent Detection Imaging Method Using Lasers. Achievement of Laser CT(Computed Tomography) for Biomedical Applications.

In this paper, we report and discuss the achievment of laser absorption computed tomography of actual in vivo/in vitro biological objects using the Coherent Detection Imaging (CDI) method. This CDI scheme offers the feasible and reliable means for the computer-assisted optical tomographic imaging based on the optical heterodyne technique that has excellent directionality and very high sensitivity. We have experimentally demonstrated the fulfillment of fundamental conditions for the establishment of laser absorption tomography by our novel CDI method in highly scattering and absorptive media such as actual biological tissues and objects. Thus we have realized the tomographic image reconstruction of several biological objects including plant stems, chicken tissue, whole egg, struma specimen and new-born mouse brain employing the projection slice theorem.

Recent High-Precision Measurements of Physical Quantity Using Laser Interferometer.

This paper describes recent trends of high-precision optical measurements. First, interferometric length-measuring methods are reviewed, wich inclnde fringe-counting methods, optical heterodyning techniques, synthetic-wavelength methods and two-color methods for an air refractive index. Secondly, the outline of measuring methods are presented of dimensions, length, gravity, water-density, fluxoid quantum, Avogardro's number, and earth strain in physics.

Laser Spectroscopic Coputed Topography Using Coherent Detection Imaging Method of Biomedical Applications

In this paper, we reprot the feasible and realible method for the laser absorption computer-assisted tomographic imaging based on the optical heterodyne technique that has very high sensitivity and excellent directivity to distinguish one direction from another. This new method is named the Coherent Detection Imaging (CDI). We have demonstrated experimentally the fulfillment of three fundamental conditions for the establishment of laser absorption computed tomography by means of the optical heterodyne method in biological tissues exhibiting severe multiple light scattering. Thus the first successful imaging by laser absorption computed tomography of In vivo/in vitro biological objects has been achieved utilizing our CDI method and the projection slice theorem.

Real time interferometric ellipsometry with optical heterodyne and phase lock-in techniques

In this paper, we have combined a Mach-Zehnder interferometer and an optical heterodyne using an AO modulator to set up an interferometric ellipsometer for measuring the optical properties of metal surfaces. Because there is no moving mechanism, e.g., compensators and quarterwave plates, we can eliminate the errors caused by these elements. By using a phase lock-in technique and computer processing, we can measure parameters Psi and Delta in real time and with great accuracy (where Psi is the amplitude ratio of the P- and S-waves, and Delta is the phase difference in the P- and S-waves).

A Chromatic Aberration-Free Heterodyne Alignment for Optical Lithography

This paper describes the principle of a new alignment method (SMART) and alignment optics using an optical-heterodyne technique. This SMART dose not need to correct chromatic aberration. Therefore, it dose not require any mechanism, such as mirrors, a prism or a lens system to correct chromatic aberration for the projection lens. A pair of one-dimensional gratings for the mask mark and a checker grating for the wafer mark were used in SMART optics. The relation displacement between the mask and the wafer can be directly detected by measuring the phase difference of the heterodyne beat signals. The experimental result for the phase difference was similar to the calculation result. An alignment signal variation of less than 10 nm was obtained.

Identification of liquid mixtures for ultrasonic applications

Liquid mixtures and solutions are sought that exhibit improved properties for ultrasonic applications such as acoustic microscopy and stimulated Brillouin scattering. Both these applications require liquid media with low acoustic velocity and attenuation. A thermodynamic theory is used to predict the acoustic velocity of a mixture from the heat of mixing; consulting a table of heats of mixing then provides a way of identifying candidate liquid mixtures. Acoustic attenuation is not predicted and must be found experimentally. The method works well for liquid solutes, but is shown to be ineffective for solid solutes since the lattice energy of the solute dominates the heat of mixing. An optical heterodyne technique was used to measure the acoustic properties of candidate mixtures in the frequency range 0.2–1.2 GHz. New acoustic data are reported for these mixtures: aqueous cetyl pyridinium chloride (a detergent solid), aqueous ethylene carbonate, and ethyl acetate in carbon disulphide. No mixtures were found with superior properties for ultrasonic applications.

High-speed optical modulator for application in instrumentation

The design and characterization of the first integrated optic modulator for a commercial instrument application are described. Alternative forms of modulation, including direct laser current modulation and optical heterodyne techniques, are reviewed for the application, which requires modulation to 20 GHz. The advantages of an integrated optic modulator fabricated using titanium in-diffused lithium niobate are discussed. Performance tradeoffs between x-cut and z-cut LiNbO/sub 3/ including bandwidth, modulation efficiency, bias point stability, and acoustic resonances are detailed. The x-cut device is found to give the best overall performance for this instrument application. Device reliability and testing, including temperature cycling, humidity, electrostatic discharge, mechanical shock, and vibration are described for complete packaged and pigtailed devices. >

Optical heterodyne investigation of the ultrasonic properties of aqueous biomolecules, dimethyl sulfoxide, and 1,4-butanediol

An optical heterodyne technique has been used to make new measurements of the ultrasonic properties of aqueous solutions of biomolecules, dimethyl sulfoxide, and 1,4-butanediol. A LiNbO3 transducer provided acoustic excitation from 0.2 to 1.5 GHz. Acoustic velocity and attenuation were measured using angularly resolved detection of Bragg-scattered light from the liquid sample. A thermodynamic theory based on the heat of mixing was used to explain the concentration dependence of the liquid mixture properties. This paper contributes new data at high frequencies, a calculation of measurement sensitivity for this technique, and a complete treatment of a little known thermodynamic theory that describes these results.

新しいレーザー生体計測法としての光ヘテロダイン方式CT法の研究開発

This paper reports, we believe for the first time, the basic principle and experimental demonstration of differential absorption computed tomography of Coherent Detection Imaging(CDI) method. Although the CDI scheme offers the feasible and reliable means for optical computed tomographic imaging of in vitro/in vivo biological objects based on the optical heterodyne technique incorporating laser beams, the single laser beam method is difficult to distinguish or to eliminate apparently detected absorption due to multiple scattering from actual absorption distributed inside the object. In order to solve this problem, the differential absorption technique employing the two different-wavelength beams is practically usefull. We performed the experiment using glass phantoms along with red and green beams simultaneously genarated from a He-Cd laser.

Broadband microwave absorption spectrometer for liquid media

A broadband, continuous-sweep microwave spectrometer has been constructed for measurements of the absorption coefficient of aqueous solutions and other liquid media. The spectrometer makes use of the phase fluctuation optical heterodyne technique, which provides a direct measure of the microwave power deposited in the sample. Consequently, in contrast to the standard dielectrometric techniques that indirectly determine the absorption coefficient via separate measurements of the real and imaginary parts of the dielectric constant, this spectrometer directly measures the microwave absorption coefficient. Broadband spectra are obtained using a transmission line to couple microwave power into the liquid sample. The absorption spectrum for deionized water in the range 3–20 GHz is presented as an example and shows excellent agreement with calculated values of the absorption coefficient based on previously published dielectric data.

Optical heterodyne measurement of the phase retardation of a quarter-wave plate

We propose and discuss an optical heterodyne technique to measure the phase retardation of a wave plate. The accuracy of this measurement technique in determining the optical path difference of a quarter-wave plate is of the order of 0.1 nm, thus exceeding the accuracy of other measurement techniques.

Measuring phase retardation of wave plates: A NOVEL TECHNIQUE

AbstractThis paper proposes and discusses an optical heterodyne technique to measure the phase retardation of a wave plate. The accuracy of this measurement technique in determining the optical path difference of a quarter wave plate is smaller than the wavelength of light source divided by 6000, exceeding the accuracies of other measurement techniques.

Raman heterodyne Ramsey spectroscopy in a Samarium atomic beam

A novel optical heterodyne technique for Raman Ramsey spectroscopy of atomic radio-frequency resonances in an atomic beam is reported. The method relies on coherent resonance Raman transitions to optically excite and probe sublevel coherence in atomic ground states using two separated atom-field interaction regions. First experimental results obtained with the use of Zeeman sublevels in the Samarium λ=570.68 nm (J=1)–(J′=0) transition are discussed.

Planar embedded InP/GaInAs p-i-n photodiode for very high-speed operation

Planar embedded InP/GaInAs p-i-n photodiodes have been fabricated by using preferential ion-beam etching for planarizing and embedding the p-i-n photodiode structure in a semi-insulating InP substrate. The stray capacitances caused by a bonding pad and an interconnection have been markedly reduced, which resulted in extremely low capacitance of less than 0.08 pF for a diameter of 20 μm of photosensitive area. It has been demonstrated by an optical heterodyne technique that the photodiode exhibits a maximum cutoff frequency of 14 GHz. This result was analyzed taking the depletion layer thickness into account and has been found to be dominated by the carrier transit time. The demonstrated low capacitance and high-speed response result indicates the suitability of the p-i-n photodiodes not only for a discrete p-i-n photodiode but also for optoelectronic integration.

The application of coherent optical techniques to wide-band networks

The successful demonstration of optical heterodyne and homodyne techniques for point to point transmission links has led to an examination of their use in the context of wide-band systems. The high receiver sensitivity and frequency tuning ability potentially provide a means for accessing a significant part of the 50 000-GHz bandwidth provided by single-mode fiber. The possibilities for new network structures based on combinations of space, wavelength, and time switching are presented here, together with the concept of transparent networks which are not dependent on a particular modulation format or information rate.

Quantum limited frequency modulation laser spectroscopy

Frequency modulation spectroscopy (FMS) is an optical heterodyne technique which allows high-resolution, high-sensitivity measurements of absorptions or dispersions associated with narrow spectral features. With new methods, the sensitivity limitations of FMS (caused by residual amplitude modulation) can be overcome, and quantum-limited performance can be readily achieved.