Non-linear behavior of ring-down time in cavity ring-down spectroscopy with tapered fibers

The effect of surrounding refractive index (n2) on ring-down time (τ) is studied in conventional and amplified cavity ring-down spectroscopy with tapered fibers. Simulation and experimental results indicate that τ varies as rational function of n2

Simulations of an OSNR-limited all-optical wavelength conversion scheme

We present simulations of a scheme to perform wavelength conversion of signals that eliminates phase-noise transfer from the pump to the converted signal. Nondegenerate four-wave mixing in a semiconductor optical amplifier is used to convert the signal to a new wavelength; and if an optical comb generator is used as the multiple-pump source, then the signal can be converted without incurring any phase-noise transfer from the pumps. We highlight the capabilities of this scheme by simulating the conversion of 16-QAM signals at 10 Gbaud and showing that errors due to phase-noise accumulation are eliminated thus enabling conversion whose only impairment would be the total additive optical noise

Performance analysis of frequency shift estimation techniques in Brillouin distributed fiber sensors

The performance of post-processing techniques carried out on the Brillouin gain spectrum to estimate the Brillouin frequency shift (BFS) in standard Brillouin distributed sensors is evaluated. Curve fitting methods with standard functions such as polynomial and Lorentzian, as well as correlation techniques such as Lorentzian Cross-correlation and Cross Reference Plot Analysis (CRPA), are considered for the analysis. The fitting procedures and key parameters for each technique are optimized, and the performance in terms of BFS uncertainty, BFS offset error and processing time is compared by numerical simulations and through controlled experiments. Such a quantitative comparison is performed in varying conditions including signal-to-noise ratio (SNR), frequency measurement step, and BGS truncation. It is demonstrated that the Lorentzian cross-correlation technique results in the largest BFS offset error due to truncation, while exhibiting the smallest BFS uncertainty and the shortest processing time. A novel approach is proposed to compensate such a BFS offset error, which enables the Lorentzian cross-correlation technique to completely outperform other fitting methods

Sub-harmonic injection locking of quantum-dash lasers using spectral enrichment from semiconductor optical amplifiers

We report sub-harmonic injection locking of a 40 GHz passively mode-locked quantum-dash (Q-dash) laser through spectral enrichment in a nonlinear semiconductor optical amplifier. The proposed scheme is demonstrated for injection locking of the Q-dash passively mode-locked laser using data modulated with non-returnto-zero line-coding at 10 G symbols/s with both intensity and phase shift keying modulations

Optical heterodyne analog radio-over-fiber link for millimeter-wave wireless systems

Optical heterodyne analog radio-over-fiber (A-RoF) links provide an efficient solution for future millimeter wave (mm-wave) wireless systems. The phase noise of the photo-generated mm-wave carrier limits the performance of such links, especially, for the transmission of low subcarrier baud rate multi-carrier signals. In this work, we present three different techniques for the compensation of the laser frequency offset (FO) and phase noise (PN) in an optical heterodyne A-RoF system. The first approach advocates the use of an analog mm-wave receiver; the second approach uses standard digital signal processing (DSP) algorithms, while in the third approach, the use of a photonic integrated mode locked laser (MLL) with reduced DSP is advocated. The compensation of the FO and PN with these three approaches is demonstrated by successfully transmitting a 1.95 MHz subcarrier spaced orthogonal frequency division multiplexing (OFDM) signal over a 25 km 61 GHz mm-wave optical heterodyne A-RoF link. The advantages and limitations of these approaches are discussed in detail and with regard to recent 5G recommendations, highlighting their potential for deployment in next generation wireless systems