Electro-optic Detection Research Articles

80 to 10 Gbit/s clock recovery using phase detectionwith Mach–Zehnder modulator

A Mach–Zehnder modulator, driven by a harmonic of a local oscillator, is used as an electro-optic phase detector to lock the oscillator to the 10 GHz base rate of an 80 Gbit/s time-division multiplexed data stream with a timing jitter of 341 fs. Clock recovery is robust and may be scaled to higher data rates.

Environmental biosensors for organochlorines, cyanobacterial toxins and endocrine disrupting chemicals

Environmental biosensors and related techniques for monitoring organochlorines, endocrine disrupting chemicals and cyanobacterial toxins are described. The practical requirements for an ideal environmental biosensor are analyzed. Specific case studies for environmental applications are reported for triazines chlorinated phenols, PCBs, microcystins, and endocrine disrupting chemicals. A new promising approach is reported for microcystins and alkylphenols that utilize electrooptical detection.

Electro-optical detection of charged particles

We have made the first observation of a charged particle beam by means of its electro-optical effect on the polarization of laser light in a LiNbO 3 crystal. The modulation of the laser light during the passage of a pulsed electron beam was observed using a fast photodiode and a digital oscilloscope. The fastest rise time measured, 120 ps, was obtained in the single shot mode and was limited by the bandwidth of the oscilloscope and the associated electronics. This technology holds good for detectors of greatly improved spatial and temporal resolution for single relativistic charged particles as well as particle beams.

Millimeter-wave imaging using an electrooptic detector as a harmonic mixer

We have developed a new millimeter-wave (MMW) imaging system that uses an electrooptic (EO) detector. The EO detector functions as a harmonic mixer for the down-conversion of continuous wave (CW) MMWs. Both amplitude and phase images were simultaneously obtained with this method. Sensitivity, spatial resolution, and imaging of several objects were experimentally shown with MMWs of 60-GHz and 100-GHz frequencies.

Femtosecond high-field transport in compound semiconductors

A study of nonequilibrium transport of carriers in GaAs and InP at electric fields up to 130 kV/cm and with a temporal resolution of 20 fs is presented. All measurements are carried out at room temperature. The THz radiation originating from the ultrafast current change in a photoexcited semiconductor device is measured by ultrabroadband electro-optic detection. We probe the influences of two important lattice scattering processes on electron acceleration. Distinct differences are seen between GaAs and InP and interpreted in terms of the different band structures and coupling strengths of these important materials. The maximum velocities and carrier displacements achieved under nonequilibrium conditions are measured directly. Peak velocities of $6\ifmmode\times\else\texttimes\fi{}{10}^{7}$ and $8\ifmmode\times\else\texttimes\fi{}{10}^{7}\mathrm{c}\mathrm{m}/\mathrm{s}$ are obtained in GaAs and InP, respectively. The distances achieved during the overshoot regime are found to depend strongly on electric field and material. A displacement as large as 120 nm builds up in less than 200 fs at a field of 60 kV/cm in InP. These findings are important for the design of modern high-speed devices. Coherent excitation of the polar crystal lattice is observed and demonstrated to result from the coupling between free carrier displacement and material polarization via the linear dielectric function. Our experiment is sensitive to collective displacements of the lattice ions with an amplitude as small as ${10}^{\ensuremath{-}16}\mathrm{m}.$

Midbandgap electro-optic detection of Bloch oscillations

Bloch oscillations excited in a biased ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ superlattice are investigated in a time-resolved two-color electro-optic detection scheme. The detection of resonantly excited Bloch oscillations is based on the Pockels effect probed at a wavelength in the center of the band gap. The observed birefringence is induced by the macroscopic polarization of the electronic wave packets relative to the localized holes. The off-resonant detection away from optical transitions directly monitors the spatial dynamics of the electrons in amplitude and phase. The dependence of the amplitudes of the Bloch oscillating electrons on the applied electric fields are in good agreement with the electron-hole dipole lengths calculated by a quantum-mechanical model.

Free-space electro-optic detection of continuous-wave terahertz radiation

We present a scheme for the coherent detection of freely propagating continuous-wave terahertz radiation using electro-optic detection. The terahertz radiation is generated by photomixing two single-mode laser diodes in an antenna fabricated on low-temperature-grown GaAs. This radiation is detected using the electro-optic effect in 〈110〉 ZnTe. In contrast to typical terahertz detection techniques, this is a frequency-domain measurement that relies on coherent up-conversion of the terahertz field combined with optical homodyning to suppress background noise.

Electro-optic detection of terahertz radiation

We present a complete frequency-domain description of electro-optic (EO) detection of terahertz (THz) electromagnetic radiation, including a description of the ellipsometry technique employed. These frequency-domain results show the effect of EO detection of a pulse of THz radiation as the product of three spectral filters acting on the complex amplitude spectrum of the THz pulse that is entering the EO crystal. For the usual experimental situation in which the optical bandwidth of the interrogating light pulse is small compared with the optical carrier frequency, we obtain an important simplification of our general result for the detected EO signal. When this simplified result is rewritten in the time domain, a more general description of the previous time-domain picture of EO detection is obtained.

In-plane electro-optic anisotropy of (1−x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 thin films grown on (100)-cut LaAlO3

Strong electro-optical (EO) anisotropy has been measured in (1−x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 [(1−x)PMN–xPT] single crystalline films epitaxially grown on (100)-cut LaAlO3 substrate, through using an improved dynamic alternating-current ellipsometric null EO detection technique with high accuracy. Large quadratic EO coefficients, which can be as large as 1.38×10−16 (m/V)2 in 0.67PMN–0.33PT film, were obtained in all the used compositions when electric field was applied along {110} directions. The strong EO anisotropy has been explained according to the structural relationship between ferroelectric polarization, input light polarization, and the applied electric field.

Measurements of the THz absorption and dispersion of ZnTe and their relevance to the electro-optic detection of THz radiation

Via THz time-domain spectroscopy, we have measured the absorption and index of refraction of single-crystal 〈110〉 ZnTe from 0.3 to 4.5 THz. We find that the absorption is dominated by two lower-frequency phonon lines at 1.6 and 3.7 THz and not by the transverse-optical (TO) -phonon line at 5.3 THz as previously assumed. However, the index of refraction is determined mainly by the TO-phonon line. Using these data, we discuss a frequency-domain picture of electro-optic detection of THz radiation below the TO-phonon resonance and compare with the photoconductive THz receiver over the same frequency range.

An external electrooptic sampling technique based on the Fabry-Perot effect

Electrooptic sampling has proved itself as the best technique for the measurement of high-speed electronic signals. This is due to its high bandwidth and noninvasiveness. Standard sampling geometries rely on a rotation of polarization within an electrooptic material and subsequent polarization sensitive detection. In this paper, we present results using a simple technique which relies on Fabry-Perot resonances inside the electrooptic material to produce an amplitude modulation. This simplifies the experiment considerably.

Single-shot spatiotemporal terahertz field imaging

Using an optically chirped pulse in an electro-optic detection system, we image the spatiotemporal distribution of a terahertz (THz) pulse. We demonstrate single-shot THz field imaging of photoconductive emitters.

Distortion of terahertz pulses in electro-optic sampling

We present a detailed study of the characteristics of electro-optic sampling of ultrashort terahertz (THz) pulses including frequency-dependent phase matching, reflection, dispersive propagation, and absorption. In particular, we investigated the origin of the oscillatory tail that is often observed in electro-optic sampling traces and found that this tail results from the dispersive propagation of the THz pulse through the electro-optic crystal. For extremely broadband THz pulses, the THz pulse is additionally distorted by reflection and absorption in both the generation and the electro-optic detection crystal. The modeling of the distorted electro-optic sampling trace permits a detailed reconstruction of the initial THz pulse.

Electro-optic detection of THz radiation in LiTaO3, LiNbO3 and ZnTe

Freely propagating THz pulses are detected in electro-optic (eo) crystals by monitoring the phase retardation (PR) of an infrared femtosecond probe pulse. This technique permits the determination of the temporal shape of the THz pulse in the subpicosecond time domain. We present measurements in LiTaO3, LiNbO3, and ZnTe and compare their signal performance as eo crystals with theoretical calculations for the PR signal. ZnTe shows the best performance for eo detection.

Broadband detection capability of ZnTe electro-optic field detectors

We present our measurements of the broadband detection capability of copropagating electro-optic ZnTe field detectors for the characterization of free-space pulsed electromagnetic radiation. To demonstrate ultrawide detection bandwidth, radiation from both gigahertz and terahertz bandwidth pulsed microwave sources has been characterized. The high frequency limitation of the sensor is the first TO phonon resonance (5.31 THz). The ultrashort temporal resolution is demonstrated by the detection of a 177 fs (full width at half-maximum) pulse generated via THz optical rectification in 〈111〉 GaAs.

Dephasing and selection rules of interband and intraband polarizations in superlattices

We study the coherent dynamics of interband and intraband polarizations of Bloch oscillations in a GaAs/Al0.7Ga0.3 As semiconductor superlattice. Time-resolved measurements of both polarizations are simultaneously performed by combination of four-wave mixing and an electro-optic detection scheme in one experimental setup. This combination allows us to gain a much more comprehensive picture of the dynamics of a multilevel system. Distinctive differences in the oscillation frequencies and the dephasing of both polarizations are found. They arise from the fact that excitonic quantum beats are observed in four-wave mixing, whereas a quantum interference of electrons in continuum states is detected in the electro-optic signal. As a consequence, the polarizations are governed by different selection rules that explain the pronounced differences in the oscillation frequencies found for specific experimental conditions.

Reshaping of freely propagating terahertz pulses by diffraction

We discuss the application of diffraction theory to the reshaping of freely propagating terahertz pulses by narrow apertures. This is accomplished by using two separate electrooptic sampling detectors. The first contains a narrow electrode geometry that does not modify the frequency content of the incident terahertz field, while the second contains a narrow gap between two large electrodes. The latter detector transforms the incident bipolar terahertz waveform into a unipolar waveform. We find that diffraction theory properly accounts for this reshaping process. We discuss the applicability of alternate electrode geometries for terahertz pulse shaping.

Electro-optic detection of Bloch oscillations.

The coherent motion of electronic wave packets in the Wannier-Stark regime of extemally biased GaAs/AIxGal _xAs superlattices is investigated by a time-resolved electro-optic technique. As predicted by the semiclassical theory, electronic wave packets undergo Bloch oscillations. They are observed via anisotropie changes in the refractive index associated with a intraband polarization, which is set up by the coherent spatial motion of electronic wave packets relative to localized holes. The oscillation amplitude depends strongly on the initial excitation conditions. Frequency, amplitude, and dephasing of Bloch oscillations are investigated over a wide range of electric fields. Complementary results to four-wave mixing and THz emission experiments are obtained.

A noninvasive method for the measurement of flow-induced surface displacement of a compliant surface

A noninvasive optical method is described which allows the measurement of the vertical component of the instantaneous displacement of a surface at one or more points. The method has been used to study the motion of a passive compliant layer responding to the random forcing of a fully developed turbulent boundary layer. However, in principle, the measurement technique described here can be used equally well with any surface capable of scattering light and to which optical access can be gained. The technique relies on the use of electro-optic position-sensitive detectors; this type of transducer produces changes in current which are linearly proportional to the displacement of a spot of light imaged onto the active area of the detector. The system can resolve displacements as small as 2 μm for a point 1.8 mm in diameter; the final output signal of the system is found to be linear for displacements up to 200 μm, and the overall frequency response is from DC to greater than 1 kHz. As an example of the use of the system, results detailing measurements obtained at both one and two points simultaneously are presented.

Apparatus for three dimensional tomography utilizing an electro-optic X-ray detector: 42522 Flannery, B.P.; Deckman, H.W.; Eisenberger, P.M.; Roberge, W.G. U.S. Patent No. 4,833,698 (23 May 1989)

Apparatus for three dimensional tomography utilizing an electro-optic X-ray detector: 42522 Flannery, B.P.; Deckman, H.W.; Eisenberger, P.M.; Roberge, W.G. U.S. Patent No. 4,833,698 (23 May 1989)