Minimum Detectable Signal Power Research Articles

Detection and upconversion of three-dimensional MMW/THz images to the visible

We present an inexpensive technique to obtain a three-dimensional (3D) millimeter wave (MMW) and terahertz (THz) image using upconversion. In this work we describe and demonstrate a method for upconversion of MMW/THz radiation to the visual band using a very inexpensive miniature glow discharge detector (GDD) and a silicon photodetector. We present MMW/THz upconversion images based on measuring the visual light emitting from the GDD rather than its electrical current. The results show better response time and better sensitivity compared to the electronic detection performed previously. Furthermore, in this work we perform frequency modulation continuous wave (FMCW) radar detection based on this method using a GDD lamp, with a photodetector to measure GDD light emission. By using FMCW detection, the range in addition to the intensity at each pixel can be obtained, thus yielding the 3D image. The GDD acts as a heterodyne mixer not only electronically but also optically. The suggested 3D upconversion technique using the GDD is simple and inexpensive and has better performance compared to other MMW/THz imaging systems suggested in the literature. This method provides minimum detectable signal power that is about 6 orders of magnitude better than similar plasma systems due to the very large internal signal gain deriving from the much smaller electrode separation and resulting in much higher plasma electric field.

Noise Analysis for Simple Lidar Detecting Wake Profiles Based on Bubble Laser Backscattering at 180°

Simple lidar detecting wake profiles based on laser backscattering by wake bubbles at 180° is firstly introduced. Then the various noises of this simple lidar, including the background light, power frequency of 50Hz and its harmonics, radio frequency noise and inherent noise within the electronic system, are analyzed in detailed, and the relationship of the minimum detectable signal power and the echo signal power is discussed. Finally, under the condition of satisfying the noise level, the data processing method of wake profiles is given. For this method, the power spectral density estimation method is used to process the bubble laser scattering signal and cubic spline interpolation is used to obtain contour map of wake profile. The results show that the data processing method of wake profiles meets the noise level and the obtained contour map is reasonable.

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.

Noise limitations of Brillouin two-beam coupling: theory and experiment

A theoretical and experimental study of noise in Brillouin two-beam coupling is presented, which includes both the nondepleted and the depleted pump regimes. The signal-to-noise ratio (SNR) is shown to be proportional to the weak signal input power as well as to the pump intensity in the nondepleted regime. Pump depletion causes both the SNR and the gain to degrade significantly, leading to an optimum working point of gBIpL ≃ 20. The minimum detectable signal power per mode of noise, predicted and measured to be approximately 5 μW at λ = 1.06 μm, is dependent on frequency and temperature, while the peak gain is also dependent on the Brillouin coupling coefficient gB, interaction length, and cross-sectional area of the amplifier.

Properties of fiber Raman amplifiers and their applicability to digital optical communication systems

Bit error rate performances of fiber Raman amplifiers both as booster amplifiers and as detection preamplifiers are studied in intensity modulation/direct detection optical communication systems. It is theoretically shown that, in the booster amplifier application, receiver sensitivity degradation due to amplification can be made less than 0.2 dB for signal-to-noise power ratio larger than 20 dB, and thus an allowable transmission line loss can be increased approximately by the value of Raman gain. For detection preamplifier use, receiver sensitivities in the Raman preamplifier system are numerically calculated in terms of minimum detectable signal power at 100-Mbit/s and 2-Gbit/s bit rates. In both bit rates, it is shown that, for a Raman gain greater than 20 dB, minimum detectable signal power can be improved by more than 15 dB over the conventional detection level without Raman amplification. Preliminary experiments are carried out using a 1.32- mu m Nd:YAG laser and a 1.4- mu m laser diode as pump and signal light sources, respectively. The experimental results are in good agreement with theoretical estimations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

New monostatic balanced Doppler velocimeter using a high birefringence fiber

A novel fiber-optic Doppler velocimeter is presented. By suitably controlling the polarization state of the local oscillator, illuminating beam, and signal light, balanced mixing with a noise reduction of 30 dB as compared to unbalanced mixing can be realized. The remaining noise level is predominantly due to shot noise. Allowing for losses in the receiving optics and for nonperfect mixing efficiency, the minimum detectable signal power is estimated to be 10/sup -18/ W-Hz/sup -1/. The high sensitivity of the system is demonstrated by the detection of light scattered from a distant moving object.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Radiation Effects Analysis of a Coherent Laser Detection System

An analysis of the effects of Co60 gamma ray irradiation on the signal-to-noise ratio, noise equivalent power or minimum detectable signal power, and mean squared noise current of a coherent laser detection system has been performed. The detector used in this study was a wide bandwidth, HgCdTe photovoltaic detector operated at 80°K with peak response at 10.6 ?m wavelength. The analysis indicates that a threshold for system degradation of approximately 1010 to 1011 ?/cm2-s depending upon the magnitude of standard noise sources such as diode dark leakage current and preamp input resistance noise. Gamma flux thresholds as low as ~107 ?/cm2-s are possible for local oscillator, shot-noise limited performance. A comparison of these calculations with experimental tests produced agreement within approximately a factor of two. Based on the analysis, it was determined that the detector design requirements for reducing gamma noise are similar to those for passive detectors; namely, small detector thickness, low Z materials, low lifetime, low substrate resistivity, and suitable signal processing.