Fundamental Sensitivity Limits Research Articles

An improved analysis for optically preamplified pulse‐position modulation receivers in optical‐fiber systems

AbstractUsing a recently developed moment‐generating function (MGF) we apply a Chernoff bound to the bit‐error probability of an optically preamplified pulse‐position modulation (PPM) receiver. Sensitivity results for PPM coding levels are presented for operation at the STM‐4 bit rate. It is shown that this receiver configuration can outperform an equivalent on‐off‐keyed nonreturn‐to‐zero (OOK NRZ) system by 7.1 dB. We further demonstrate the impressive potential of such an optically preamplified PPM receiver by giving results that improve on the fundamental sensitivity limit of an optically preamplified OOK NRZ receiver and approach the sensitivity of coherent detection. A Gaussian approximation is also developed and we compare it with results obtained from the Chernoff bound. © 1995 John Wiley & Sons, Inc.

An improved gaussian approximation for optically preamplified PPM systems including the effect of timing jitter

AbstractThe effect of timing jitter is evaluated using an improved Gaussian approximation for an optically preamplified PPM receiver. For the parameters considered a potential sensitivity of 23.6 photons/bit is demonstrated in the unjittered case with the jittered optimum at worst only 1 dB less sensitive. Both these results surpass the fundamental sensitivity limit of an OOK NRZ system. The analysis predicts that wrong‐slot and jitter errors first become dominant at a coding level higher than that suggested by an earlier model. © 1995 John Wiley & Sons, Inc.

Sensitivity of intracavity absorption measurements with Ti: sapphire laser

Broadband emission of a Ti: sapphire laser is achieved by reduction of the spectral loss modulation resulting from the birefringence of the laser crystal. The laser emission in a 4 nm wide spectral band has been recorded at 200 μs delay after the onset of laser oscillations. The spectrum of the atmospheric absorption in the cavity of this multimode laser has been measured in the spectral range 790–830 nm. The absorption coefficients of atmospheric lines as well as the sensitivity of the measurements are estimated by dynamically recording the spectra of the laser emission. The sensitivity limit, 1.7 × 10 -8 cm -1, is the lowest obtained so far with a Ti: sapphire laser. However, it still exceeds the fundamental sensitivity limit, 10 -12 cm -1, expected for this laser.

Mechanically modulated microwave cavity for detection of low-frequency gravitational radiation.

Consideration of the estimated strengths and rates of occurrence of various classes of gravitational-radiation sources points to the desirability of developing detectors with sensitivity that is sufficient for seeing predicted events at frequencies below 1 kHz. This paper discusses the sensitivity limitations of a laboratory-scale detector consisting of a microwave cavity with ends that are free to move in response to a gravitational wave. Fundamental sensitivity limits due to readout amplifier noise as well as limitations due to thermal, seismic, and oscillator noise sources are considered. Between roughly 10 and 200 Hz it appears feasible to operate a detector at the linear amplifier sensitivity limit with a dimensionless strain noise spectral density of 10/sup -21//Hz/sup 1/2/ at 100 Hz. This sensitivity is sufficient for detecting 100 M/sub c//sub i//sub r//sub d//sub o//sub t/ black-hole coalescence events to a distance of 50 Mpc with an amplitude signal-to-noise ratio greater than 10.