Laserati

In this paper, we examine the performance of two different phase modulation methods in coherent optical code-division multiple-access (OCDMA) systems. As optical spreading sequences, a recently introduced prime code family hereby referred to as double-padded modified prime code has been employed and analyzed. The OCDMA system operates under synchronous homodyne dual-balanced detection scheme. In this analysis, binary phase-shift keying format is deployed where the phase is modulated by either a Mach–Zehnder interferometer external phase-modulator or an injection-locking of distributed feedback laser diode's driving current. The performances of the two phase-modulation techniques in the presence of multiple-access interferences in a shot-noise limited regime are studied. Phase limitations and reasonable consequence associated with the limited phase excursion are also investigated.

All-optical signal regeneration is experimentally demonstrated using a polarization bistable vertical-cavity surface-emitting laser. The retiming operation of signal regeneration is performed by using an AND gate operation and a reset operation. An optical clock pulse and input data signal are used for the AND gate operation. The timing jitter of the regenerated signal is reduced by optimizing the injection power ratio of the clock pulse and the data signal. The retiming operation is analyzed using a simple model that includes random fluctuation of the polarization switching threshold and bandwidth limitation of the response to the injection light.

An approach is proposed in this paper to generate ultra-wideband (UWB) pulses based on cross-phase modulation (XPM) effects in nonlinear optical loop mirror (NOLM). The NOLM can be considered as an optical switch which is controlled by pump to generate positive and negative Gaussian pulses, which are then delayed by SMF and combined to generate both Gaussian monocycle and doublet pulses. These two pulse shapes can be switched at a high speed by controlling the on–off of one of the probe. In addition, the SMF acting as a chromatic dispersion media in generating the UWB pulses can also be used to distribute the UWB signals from the central station (CS) to remote access points (AP). Different distance between CS and remote APs has no effects on the generated UWB pulses by adopting a wavelength tunable laser as probe.

In normal injection-locked semiconductor lasers, the modulation signals are applied to the slave laser. In this paper, we show that modulating the master light before injection exhibits distinctive modulation dynamics and frequency response. We first present a detailed theoretical model and simulation results. Experimentally, we have successfully demonstrated both master amplitude and master phase modulation. The resulting 3-dB bandwidths have been enhanced by up to three times, exceeding 50 GHz. The resonance frequency of the combined lasers is greater than 100 GHz.

We describe the stabilization of the beatnote of an Er,Yb:glass dual-frequency laser at 1.5 $mu$ m with and without an external microwave reference. In the first case, a classical optical phase-locked loop (OPLL) is used, and absolute phase noise levels as low as ${-}117$ dBrad $^2$ /Hz at 10 kHz from the carrier are reported. In the second case one or two fiber-optic delay lines are used to lock the frequency of the beatnote. Absolute phase noise levels as low as ${-}107$ dBrad $^2$ /Hz at 10 kHz from the carrier are measured, fairly independant of the beatnote frequency varying from 2 to 6 GHz. An analysis of the phase noise level limitation is presented in the linear servo-loop theory framework. The expected phase noise level calculated from the measurement of the different noise sources fits well with the predictions.

A coupled optoelectronic oscillator (COEO) based on a laser with a high finesse intracavity etalon is presented. Unlike a conventional COEO, the incorporation of the etalon produces a 10.24-GHz spaced optical frequency comb by selecting a single optical supermode. The same etalon serves as a reference for active stabilization of the optical frequencies and the pulse repetition rate via the Pound-Drever-Hall stabilization method. This results in 160 to 190 comb lines with sub-1-MHz drift and sub-10-kHz linewidth, as well as subpicosecond pulses and 350-Hz maximum deviation of the pulse repetition rate over 10 min. The completely self-contained source allows the COEO utility to extend to a host of new coherent communication and signal processing applications.

A wideband ( $>!!10~$ GHz) beamformer, based on a photonic true-time-delay, with submicrosecond scan-angle switching is reported. The smooth microwave transmission (ripples $≪!!0.5~$ dB and $≪!!3^{circ}$ ) and superb uniformity among the elements ( $≪!!0.1~$ dB and $≪!!0.5^{circ}$ ) are then used for the processing of 1 GHz-wide linear frequency modulation (LFM) signals in both the C and X bands with excellent performance. This performance is also maintained under dynamic operation, where a fast tunable laser is employed to provide $≪!!300~$ ns wavelength-controlled angle scanning. Based on these characteristics, an optimized architecture, where a photonic beamformer feeds a series of classical subarrays, can offer high performance in both the time and spatial domains for large, wideband phased-array antennas, with wide scan angles.

Broadband access networks evolution towards 10-Gb/s user connectivity will foster the evolution of the photonic and wireless technologies needed to implement multi-Gb/s wireless links. In particular, provision of data rates in excess of 1 Gb/s using wireless technologies is limited by currently available electrical technologies due to the required bandwidths and frequencies of operation in the millimeter-wave (mm-wave) band. Microwave photonic techniques and technologies have shown a clear potential to overcome these limitations. In this paper, the detailed study of a photonic vector modulator (PVM) architecture and its performance limitations are presented. The PVM architecture is based on direct baseband modulation and dispersion induced quadrature condition. The limitation of this architecture is the presence of a local oscillator (LO) component in the generated mm-wave spectrum which limits the system dynamic range. To overcome this limitation, a third continuous-wave (CW) laser is used to remove the unwanted LO component by properly adjusting its wavelength and emitted power.

A multiple beam former using multichannel chirped fiber grating (MCFG) and tunable optical delay lines is investigated in this paper. The simulation results shown in this paper exhibited that it could form two beams, which could be operated squint-free and independently from each other at 6 GHz. The use of a MCFG along with tunable optical delay lines has greatly reduced the system complexity and components requirements. Moreover, our proposed beam-former is able to operate using fewer tunable laser sources than other similar approaches. Successfully addressing this problem in the components cost would make the implementation of the scheme far more feasible.