Linear Photodetector Research Articles

Light Statistics by Non-Calibrated Linear Photodetectors

We theoretically demonstrate that detectors endowed with internal gain and operated in regimes in which they do not necessarily behave as photon-counters, but still ensure linear input/output responses, can allow a self-consistent characterization of the statistics of th e number of detected photons without need of knowing their gain. We present experiments performed with a photo-emissive hybrid detector on a number of classical fields endowed with non-trivial statistics and sh ow that the method works for both microscopic and mesoscopic photon numbers. The obtained detected-photon probability distributions agree with those expected for the photon numbers, which are also reconstructed by an independent method.

Linear 288×4-format photodetector with a bidirectional time-delay-and-storage regime

Infrared n-p-photodiode photodetectors based on a hybrid assembly of photosensitive elements of format 288×4 with a 56×43-μm step, made from mercury-cadmium telluride heteroepitaxial structures obtained by molecular-beam epitaxy, have been developed, fabricated, and investigated for the 8–12-μm spectral range, along with silicon multiplexers with bidirectional scanning and internal time delay and storage of the signal. The 288×4-format linear photodetector has the following mean values of voltage sensitivity, detectivity, and NETD at the maximum sensitivity: (1–3)×108V∕W, (1.5–2.0)×1011cmHz1∕2W−1, and 9mK, respectively. There are no defective channels.

Unambiguous identification of coherent states. II. Multiple resources

We analyze unambiguous identification of coherent states of an electromagnetic field. In particular, we study possible generalizations of an optical setup proposed in Sedl\'ak et al. [Phys. Rev. A 76, 022326 (2007)]. We show how the unambiguous identification of coherent states can be performed in a general case when multiple copies of unknown and reference states are available. Under the condition that the experimental setup consists only of linear optical elements and photodetectors, we prove the optimality of the setup. We also investigate whether reference states after the measurement can be ``recovered'' and further used for subsequent unambiguous identification tasks. We show that in spite of the fact that the recovered reference states are disturbed by measurements, they can be repeatedly used for unambiguous identifications. We analyze the influence of particular type of noise in the preparation of the unknown and the reference coherent states on the performance of our unambiguous-identification setup.

Equidistant fringe phase shift measurement by use of a trough integration method

A data processing method that extracts phase information through the integration of the trough part of the equidistant fringes was used in a phase shift measurement system based on a Michelson interferometer and a linear photo detector. The advantage of this method is substantiated theoretically and experimentally. The thermal drift and nonthermal drift of the system were observed and discussed. After deducting the error caused by the drifts, a 0.12-nm standard deviation was achieved in the displacement measurement with a movement range of several tens of nanometers. The measurement results of an antiparallel-aligned nematic liquid crystal (LC) cell and a polymer-dispersed liquid crystal (PDLC) cell by use of this system are also presented.

Complementary metal-oxide-semiconductor imaging array with laser Doppler blood flow processing

A fully integrated complementary metal-oxide-semiconductor 16×1 linear photodetector array with on-chip signal processing for applications in laser Doppler blood flow imaging has been designed and tested. Analog circuitry is used to provide the transimpedance amplifier, amplification of the modulated (ac) component, and antialiasing filter at each pixel, and also multiplexing of the 16 pixels. Digital signal processing is used to implement the lowpass, bandpass, and frequency-weighted filters, along with the signal averaging conventionally implemented as discrete components in laser Doppler blood flow imaging. The sensor demonstrates good agreement with simulation at each design stage. The measured optical performance of the array is demonstrated using modulated light signals and a vibrating test structure. As the first iteration of the chip, this 16×1 linear array provides an opportunity to evaluate the feasibility of full-field laser Doppler blood flow imaging with on-chip processing, with a view to providing a design that is scalable to a larger linear array or 2-D imaging array.

Diamond-based photosensitive matrix elements for the UV range

The design principles and the production technology for diamond-based photosensitive matrix devices operating in the UV range are considered. The spectral and I–V characteristics and the dark and leakage currents of linear (2 × 64) and matrix (64 × 64) photodetectors are measured at various applied voltages. The possibility of creating such structures with a relatively high sensitivity is demonstrated for the first time. It is shown that the surface leakage currents play the dominant role in limiting the photosensitivity of the structures under study. A significant spread of the dark current and the photocurrent of matrix photodetectors based on natural diamond is revealed. Such a spread is related to the defect-structure heterogeneity.

Entanglement criteria via the uncertainty relations in su(2) and su(1,1) algebras: Detection of non-Gaussian entangled states

We derive a class of inequalities, from the uncertainty relations of the SU(1,1) and the SU(2) algebra in conjunction with partial transposition, that must be satisfied by any separable two-mode states. These inequalities are presented in terms of the su(2) operators J_x, J_y, and the total photon number N_a+N_b. They include as special cases the inequality derived by Hillery and Zubairy [Phys. Rev. Lett. 96, 050503 (2006)], and the one by Agarwal and Biswas [New J. Phys. 7, 211 (2005)]. In particular, optimization over the whole inequalities leads to the criterion obtained by Agarwal and Biswas. We show that this optimal criterion can detect entanglement for a broad class of non-Gaussian entangled states, i.e., the su(2) minimum-uncertainty states. Experimental schemes to test the optimal criterion are also discussed, especially the one using linear optical devices and photodetectors.

Comparison of measured backscatter factors with Monte Carlo simulations for low energy X-ray

Experimentally determined values of X-ray backscatter factors (BSFs) are presented and compared with Monte Carlo simulation results. Measurements were made using X-rays generated at voltages between 50 and 100 kVp and various phantoms that differed in shape and size. To study the influence of irradiation geometry on BSFs, measurements were performed for different photon beam field diameters at the phantom front face. The phantoms were placed on the irradiation bench of an X-ray unit at a fixed distance of 100 cm from the focal spot. In this paper, BSFs were determined experimentally by using a measuring technique that utilized an ionization chamber of volume 1 cm 3. The generalized particle transport program MCNPX code was used for Monte Carlo simulations. Measured results are analyzed and discussed in comparison with simulated values and we acquired phantom images using a 512 channel linear array photodetector.

Homodyne measurement of the average photon number

We describe a scheme for measurement of the mean photon flux at an arbitrary optical sideband frequency using homodyne detection. Experimental implementation of the technique requires an acousto-optic modulator in addition to the homodyne detector, and does not require phase locking. The technique exhibits polarization and frequency and spatial mode selectivity, as well as much improved speed, resolution, and dynamic range when compared to linear photodetectors and avalanche photodiodes, with potential application to quantum-state tomography and information encoding using an optical frequency basis. Experimental data also support a quantum-mechanical description of vacuum noise.

Projection measurement of the maximally entangledN-photon state for a demonstration of theN-photon de Broglie wavelength

We construct a projection measurement process for the maximally entangled N-photon state (the NOON-state) with only linear optical elements and photodetectors. This measurement process will give null result for any N-photon state that is orthogonal to the NOON state. We examine the projection process in more detail for N=4 by applying it to a four-photon state from type-II parametric down-conversion. This demonstrates an orthogonal projection measurement with a null result. This null result corresponds to a dip in a generalized Hong-Ou-Mandel interferometer for four photons. We find that the depth of the dip in this arrangement can be used to distinguish a genuine entangled four-photon state from two separate pairs of photons. We next apply the NOON state projection measurement to a four-photon superposition state from two perpendicularly oriented type-I parametric down-conversion processes. A successful NOON state projection is demonstrated with the appearance of the four-photon de Broglie wavelength in the interference fringe pattern.

Metrology for Fresnel measuring method

The metrological characterization of a Fresnel method for measuring the dimensions of objects is investigated. In this method, free space, as an optical element, transforms the input image of the inspected object into its Fresnel image with great accuracy. The major sources of systematic measurement error are estimated analytically including non-uniform illumination of the object, the interference effect of the edge images of the diffracting object, the integration properties of the linear multi-element photodetector, the influence of the extended size of a partially coherent light source and the volumetric properties of a 3D object. It is proposed that algorithms are used to account for any error components; effective algorithms for this are proposed.

Infrared photodetector modules based on variband layers of HgCdTe and on structures with GaAs/AlGaAs quantum wells

A process has been developed for producing linear and two-dimensional array-type photodetector modules (PDMs), including the fabrication of photodetector structures based on heteroepitaxial layers of CdxHg1−xTe and GaAs/AlGaAs grown by molecular-beam epitaxy, fabrication of two-dimensional and linear arrays of silicon multiplexers, and hybrid assembly of PDMs consisting of a photodetector structure and a multiplexer by means of indium microposts. The photoelectric parameters are given for two-dimensional and linear array-type PDMs based on photodiodes for the mid-IR (3-5.5 µm) and far-IR (8-12 µm) regions, operating at temperatures of 78-80 K and 200-220 K. © 2005 Optical Society of America

High-Resolution Pseudorandom Encoder with Parallel Code Reading

This paper considers pseudorandom encoder as a new type of absolute encoder with only one code track. It is provided using an especial code technique based on pseudorandom binary sequences. A method for parallel reading of pseudorandom code using linear photodetector array is proposed. The presented solution considerably decreases the basic problem, which is a substantial time needed for the execution of the position measuring. The process of determining the fine and rough position is being divided based on the recorded pseudorandom code, and now, all known pseudorandom/natural code conversion methods can be directly applied, which results in 10 times measurement time reduction in relation to the already known solutions and methods in this field. Ill. 4, bibl. 11 (in English; summaries in Lithuanian, English and Russian).

Compact spectral analyzer of heavy-metal impurities in air

This paper describes the fundamental layout of a compact device for rapid analysis of heavymetal vapors and aerosols in air. The device is based on an original source for exciting the luminescence spectra of air. The source is a stabilized dc arc with a thermochemical cathode in which the air is pumped through the interelectrode gap. The luminescence spectrum of air is recorded by a linear position-sensitive CCD photodetector. The spectrum is processed and digitized by a special controller. The device makes it possible to determine the concentration in air of heavy-metal vapors and aerosols in real time at a level of 0.5 of the maximum permissible concentration.

Quantum gates using linear optics and postselection

Recently it was realized that linear optics and photo-detectors with feedback can be used for theoretically efficient quantum information processing. The first of three steps toward efficient linear optics quantum computation (eLOQC) was to design a simple non-deterministic gate, which upon post-selection based on a measurement result implements a non-linear phase shift on one mode. Here a computational strategy is given for finding non-deterministic gates for bosonic qubits with helper photons. A more efficient conditional sign flip gate is obtained.

Unambiguous state discrimination of coherent states with linear optics: Application to quantum cryptography

We discuss several methods for unambiguous state discrimination of N symmetric coherent states using linear optics and photodetectors. One type of measurements is shown to be optimal in the limit of small photon numbers for any N. For the special case of N=4 this measurement can be fruitfully used by the receiving end (Bob) in an implementation of the BB84 quantum key distribution protocol using faint laser pulses. In particular, if Bob detects only a single photon the procedure is equivalent to the standard measurement that he would have to perform in a single-photon implementation of BB84, if he detects two photons Bob will unambiguously know the bit sent to him in 50% of the cases without having to exchange basis information, and if three photons are detected, Bob will know unambiguously which quantum state was sent.

Sensing an edge with a lateral photodetector

The electrical response of a linear lateral photodetector to three different light projections is examined. First, one section of the photodetector is illuminated and the rest of the detector is covered with a piece of black tape forming a bright/dark edge. Second, the whole photodetector is illuminated and then a wire is placed in front casting a shadow onto the detector. Third, one section of the photodetector is illuminated and the rest of the detector is covered with an optical filter forming a bright/dim edge. The response to each projection is expressed by a set of equations and verified by experiments. The tracking of the position of the bright/dark edge, wire, and bright/dim edge is described.

A linear photodetector with noiseless sensitivity adjustment

The sensitivity of linear charge-coupled devices can be adjusted by using controlling voltages on a constant aperture. It is shown that, in the case of devices of traditional design, this adjustment can be accompanied by generation of a correlated (geometric) noise, which essentially deteriorates the resolution capability. A device free of these drawbacks is described.

Parameter estimation in quantum optics

We address several estimation problems in quantum optics by means of the maximum-likelihood principle. We consider Gaussian state estimation and the determination of the coupling parameters of quadratic Hamiltonians. Moreover, we analyze different schemes of phase-shift estimation. Finally, the absolute estimation of the quantum efficiency of both linear and avalanche photodetectors is studied. In all the considered applications, the Gaussian bound on statistical errors is attained with a few thousand data.

Bell measurements for teleportation

In this paper we investigate the possibility of making complete Bell measurements on a product Hilbert space of two two-level bosonic systems. We restrict our tools to linear elements, such as beam splitters and phase shifters, delay lines and electronically switched linear elements, photodetectors, and auxiliary bosons. As a result we show that with these tools a never failing Bell measurement is impossible.