Heterodyne Detection Scheme Research Articles

Contactless measurements of the photocarrier lifetime in amorphous silicon by a heterodyne experiment

We describe a heterodyne detection scheme for an optical measurement of the photocarrier lifetime in semiconductors. The setup utilizes the Doppler shift of a laser beam that is diffracted from a periodic modulation of the optical constants of a sample, when it is illuminated with a moving interference grating. The advantage of heterodyne detection is its high sensitivity and the extraction of phase information of the diffracted beam. We present measurements on amorphous hydrogenated silicon.

A generalized suboptimum unequally spaced channel allocation technique. II. In coherent WDM systems

For pt.I see ibid., vol.46, no.8, p.1027-37 (1998). Four-wave mixing (FWM) in dispersion-shifted optical fiber is a major problem associated with low optical input power levels in optical wavelength-division multiplexed (WDM) systems. To reduce the crosstalk caused by FWM, a generalized suboptimum unequally spaced channel allocation (S-BISCA) technique has been proposed. While the S-USCA technique reduces the PWM power substantially, it also reduces the minimum channel spacing compared to conventional equal channel spacing (ECS) systems when the same number of carrier channels are accommodated in a fixed optical bandwidth. This results in more interchannel interference (ICI) when employing the S-USCA scheme. The power penalty of the ECS and the S-USCA systems caused by crosstalk and frequency drift are investigated and compared in this paper. The superior system performance region, where S-USCA systems out perform ECS systems, is also quantified. For 20-channel systems using an amplitude-shift keying (ASK) heterodyne detection scheme, for instance, results show that the S-USCA technique pays less power penalty up to bit rates of 5.5, 7.5, and 9.5 Gb/s, when all channels have identical states of polarization and the launched input power per channel P/sub in/, equals to -6, -3, and 0 dBm, respectively.

Interferometric system for precise submicrometer particle sizing

Following a recently exploited line of thought, we present an interferometric system for particle sizing in the submicrometer region. The phase of the field that results from the interference between the incident and the scattered waves is measured through a heterodyne detection scheme in a Mach-Zehnder-type interferometer. We explored the possibility of extending previous work on this subject to the case of larger particles, i.e., particles larger than 0.5 mum. Experimental results obtained with polystyrene spheres in the range of diameters 0.16-0.71 mum are reported and compared with theoretical predictions. We show that in this range univocal detection of the particle size is not successful because the phase versus particle-size plot exhibits a maximum in correspondence to diameters close to 0.5 mum.

Light scattering by surface waves on a vertical layer of liquid toluene

It is demonstrated that light scattering from surface waves on a vertical liquid layer can be used for the determination of surface tension and kinematic viscosity of the liquid under investigation. In contrast to usual approaches of surface light scattering, a setup is described that enables measurements with the same setup as that with experiments for the determination of other thermophysical properties by light scattering from bulk fluids and without an imposed grating or seed particles. The experiments rely on a heterodyne detection scheme and a signal analysis by photon correlation spectroscopy. First results are presented for toluene over a temperature range from 323 to 483 K at saturation conditions.

Time resolved four-wave mixing technique to measure the ultrafast coherent dynamics in semiconductor optical amplifiers

A femtosecond four-wave mixing technique is used to measure the ultrafast coherent dynamics of the optical polarization in semiconductor optical amplifiers. A heterodyne detection scheme enables us to measure a background-free quasi-degenerate four-wave mixing signal even without spatial separation of the pump and probe beam. First results indicate that the polarization dephasing time close to the transparency point is on the order of 100 fs.

Quantum trajectories and quantum measurement theory

Beyond their use as numerical tools, quantum trajectories can be ascribed a degree of reality in terms of quantum measurement theory. In fact, they arise naturally from considering continuous observation of a damped quantum system. A particularly useful form of quantum trajectories is as linear (but non-unitary) stochastic Schrödinger equations. In the limit where a strong local oscillator is used in the detection, and where the system is not driven, these quantum trajectories can be solved. This gives an alternative derivation of the probability distributions for completed homodyne and heterodyne detection schemes. It also allows the previously intractable problem of real-time adaptive measurements to be treated. The results for an analytically soluble example of adaptive phase measurements are presented, and future developments discussed.

Vibration Suppression in a Flexible Structure Based on Fiber Optics Michelson Interferometric Sensor

A two-wavelength fiber optics Michelson interferometric sensor has been employed to detect the vibration signal in a flexible beam. The synthetic wavelength and synthetic heterodyne detection schemes have been adopted for signal processing on optical phase detection. The active control technique was also developed and implemented to suppress the vibration signal that was generated from the piezoelectric transducer. A 38 dB suppression has been obtained.

Two-mode quantum systems: Invariant classification of squeezing transformations and squeezed states.

A general analysis of squeezing transformations for two mode systems is given based on the four dimensional real symplectic group $Sp(4,\Re)\/$. Within the framework of the unitary metaplectic representation of this group, a distinction between compact photon number conserving and noncompact photon number nonconserving squeezing transformations is made. We exploit the $Sp(4,\Re)-SO(3,2)\/$ local isomorphism and the $U(2)\/$ invariant squeezing criterion to divide the set of all squeezing transformations into a two parameter family of distinct equivalence classes with representative elements chosen for each class. Familiar two mode squeezing transformations in the literature are recognized in our framework and seen to form a set of measure zero. Examples of squeezed coherent and thermal states are worked out. The need to extend the heterodyne detection scheme to encompass all of $U(2)\/$ is emphasized, and known experimental situations where all $U(2)\/$ elements can be reproduced are briefly described.

Electron-spin-echo spectroscopy at 604 GHz using FIR lasers

We demonstrate that electron-spin-echo spectroscopy is possible at 604 GHz, corresponding to a magnetic field of 21.6 T for a g-factor of two. The problems concerning suitable microwave equipment for EPR at very high frequencies are circumvented by the use of optical techniques. For the generation of the high frequency radiation, two pulsed, optically pumped FIR lasers are used. The detector consists of a Schottky-diode in a heterodyne detection scheme with a cw FIR laser as local oscillator. A sensitivity of 10 12 spins per gauss is achieved.

Rotation angle, phases of oscillators with definite circular polarizations, and the composite ideal phase operator.

The exposition of the formalisms of the quantum optical phase has been provided commencing from the quantum mechanics of a massive particle. The clockwise and counterclockwise components of the planar motion are shown to correspond to the signal and idler modes in the heterodyne detection scheme. The appropriate ideal phase proposal has been embodied in this scheme.

Presumable solutions of quantum phase problem and their flaws

A combination of less frequent criticism with positive investigations has resulted in the substitution of group theoretic considerations by a simpler quantum mechanical model, has taken into account homodyne and heterodyne detection schemes, and proceeded by an analysis of phase data processing. Limiting procedures in s-phase formalisms have been provided concentrating on the Wigner function for number and ideal phase. The Wigner function for number and realistic phase has been expressed by closed formulae along with the antinormal phase distributions.

Sensitivity improvement of a 1-um ladar system incorporating an opticalfiber preamplifier [also Erratum 33(12)4108(Dec1994)

In an effort to increase the SNR of a continuous wave, 1-μm all solid state ladar system, a rare-earth-doped optical fiber amplifier is investigated as a preamplifier for ladar return signals. The experimental system is detailed and a theoretical analysis of the fiber amplifier's effect on both heterodyne and direct detection schemes is provided. Beginning with the optical powers incident on the detector, the signal and noises are analyzed, through the detector electronics, to predict the SNR. The SNR is then plotted as a function of the return signal power, and a SNR threshold is defined to determine a minimum detectable signal power. The return signals required to attain the SNR threshold are then compared for four cases: direct detection with and without the fiber amplifier and heterodyne detection with and without the fiber amplifier. For the direct detection scheme considered, our results predict a sensitivity increase of 20.6 dB with the addition of the fiber amplifier, yet for heterodyne detection the predicted sensitivity increase is only 3.1 dB.

Synthetic heterodyne detection in a fiber-optic ring-laser gyro

A synthetic heterodyne detection scheme for ring-laser gyros to sense both rotation rate and direction is presented. This scheme is compatible with the sinusoidal push-pull phase-modulation technique for suppressing frequency locking. The good experimental results achieved in a fiber-optic Brillouin ring-laser gyro show the potential of this detection scheme in applications.

TFTR microwave reflectometer (abstract)

A microwave reflectometer is in operation on TFTR for the measurement of density fluctuations. The system operates in the X mode and comprises three channels with fixed frequencies of 140, 132, and 125 GHz, and one with stepped frequency of 111–123 GHz. All channels use solid state Gunn oscillators and a heterodyne detection scheme. The system is located outside of the TFTR test cell with the power conveyed to the tokamak vessel by low-loss corrugated waveguides and remotely controlled parabolic mirrors. Preliminary results indicate that the level of density fluctuations with k⊥ <1 cm−1 is very small in the central region of Ohmic plasmas (ñ/n<10−3), and that it increases monotonically with minor radius to values of ≊10−2 at r/a=0.9. This work supported by U.S. Department of Energy Contract No. DE-AC02-76-CHO-3073.

Direct measurement of the amplitude and the phase of photorefractive fields in KNbO_3:Ta and BaTiO_3

Real-time direct measurement of the amplitude and the phase of photorefractive fields is performed for all stages of photorefractive grating formation including saturation. The photorefractive processes in tantalum-doped potassium niobate and nominally pure barium titanate crystals are investigated as a function of the grating spacing. The diffusion and photovoltaic transport lengths, the Debye screening length, and the net trap concentration are determined. Independent direct measurement of the photorefractive phase permits a more accurate and reliable comparison between experimental results and existing models. The measurement technique involves the diffraction of an amplitude-modulated laser beam by an acousto-optic Bragg cell operating with the same laser modulation frequency. The photorefractive gratings are formed by the interference of the transmitted and diffracted components of the beam. This nondestructive measurement technique produces excellent sensitivity and signal-to-noise ratio. The heterodyne detection scheme results in a dynamic range of 50-dB and a phase measurement accuracy of 2°.

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

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

Optical FSK heterodyne detection using image rejection mixer

A new optical FSK heterodyne detection scheme is proposed and demonstrated. This scheme uses an optical image rejection mixer. The intermediate frequency bandwidth is the same as ASK heterodyne detection while equalling dual filter FSK detection receiver sensitivity.

Heterodyne detection of small angle scattered far‐infrared laser radiation

AbstractA heterodyne detection scheme for far‐infrared small angle scattered laser radiation is reported and demonstrated by measuring the known scattering from a thin wire scatterer. Frequency shifts were on the order of 10 Hz. A Golay cell was used as a detector. The results were compared with theoretical predictions and direct detection data. The method should be useful for scattering measurements of density waves in plasmas.

Polarization insensitive coherent detection using orthogonally polarized optical fields

AbstractRecently reported polarization insensitive heterodyne detection schemes that use the properties of polarized light are all shown to be related to the basic concept of simultaneously using two different frequency, orthogonally polarized optical fields. The various system design options associated with this concept are compared in terms of receiver complexity.

Theory for optical heterodyne DPSK receivers with post-detection filtering

We present a general theoretical model for optical heterodyne DPSK receivers for optical communications systems where transmitter and local oscillator lasers have significant linewidths. Quantum phase noise in the lasers is treated as such, but in contrast with previous models for DPSK, receiver noise and local oscillator shot noise are treated as additive noise on the receiver output voltage, as this allows a straightforward description of the effects of post-detection filtering. As a consequence of the detection scheme, a key issue is to account for the non-Gaussian statistics of the output voltage, and this is done using a Chernov bound formulation. Detailed numerical results for a typical 140 Mbit/s p-i-n-FET front end are presented. It is found that heterodyne DPSK gives improved receiver sensitivity compared to other heterodyne detection schemes for IF linewidths below 0.7 percent of the data rate.