Broadband Optical Communication Systems Research Articles

Surface plasmon induced broadband single-polarization filter based on high birefringence photonic crystal fiber

A broadband and single-polarization filter based on high birefringence photonic crystal fiber (HB-PCF) with selectively infiltrated gold wires and liquid crystal is proposed, and its filtering characteristics are studied by the full-vector finite element method (FV-FEM). Two gold wires are selectively filled on both sides of the liquid crystal core to act as two defect cores. The results show that the confinement loss of x-polarized core mode is much larger than that of y-polarized core mode in the wavelength range of 0.85–1.75 μm. The confinement losses of x- and y-polarized core modes are 99.87 dB/cm and 0.001 dB/cm at 0.88 um, 726.50 dB/cm and 0.004 dB/cm at 1.02 um, and 474.60 dB/cm and 0.046 dB/cm at 1.30 um, respectively. The bandwidth with extinction ratio less than 20 dB is 900 nm. Moreover, compared with the traditional structures, we find that our structure has higher birefringence. High birefringence helps to separate the resonant wavelengths of x- and y-polarized core modes. Therefore, the excellent properties of the proposed filter can make it widely used in sensing systems and broadband optical communication systems.

Luminescent Properties and Optical Amplification of Erbium‐Doped Nano‐Engineered Scandium‐Phospho‐Yttria‐Alumina‐Silica Glass Based Optical Fiber

In this work, a new erbium (Er) doped nano‐engineered scandium‐phospho‐yttria‐alumina‐silica (SPYAS) glass‐based optical fiber is reported, fabricated through the MCVD process, and solution doping technique, followed by a suitable thermal annealing of pristine preform. The fabrication process comprises the incorporation of erbium doped phase‐separated scandium‐yttria rich crystalline nanoparticles into the core region through in situ process based on phase‐separation and crystal growth phenomena. The material characterization results, obtained from transmission electron microscopy, electron diffraction pattern, energy dispersive X‐ray, electron probe micro analysis, and X‐ray fluorescence, confirm the formation of Er2O3 doped crystalline phase‐separated scandium‐yttria rich nanoparticles in the core region. The formation of scandium‐ultra rich nano‐crystalline environment, possessing low photon energy around the erbium ions, enhanced the fluorescence intensity. Such kind of nano‐engineered glass reduces the noise figure around 4.35 dB, and provides broadband optical flat gain with an average value of 38.675 dB, varied by less than ±0. 7 dB spanning over a broad wavelength region of 1530–1590 nm compared to the pristine and Sc free Er‐doped fibers. Such kind of nano‐engineered glass based Er doped fiber will be useful for making highly efficient optical amplifiers, suitable for present broadband optical communication systems.

Optimal design of single resonant and ultrabroadband long-period fiber grating filters

We propose a spectral flat-top, single resonant, and ultrabroadband-more than 180 nm in a −20-dB bandwidth-long-period fiber grating (LPG) filter. The ultrabroadband LPG is based on a thin cladding layer LPG synthesized by the Lagrange multiplier optimization (LMO) algorithm. As the bandwidth and resonant spectra cover a very wide band, both material dispersion and waveguide dispersion were included in the calculations of the LMO method. To the best of our knowledge, the bandwidth of the designed flat-top LPG filter in the −20-dB coupling is the broadest currently existing in the literature. Such designed LPG devices can be very useful for a variety of applications in broadband optical communication systems.

Clock and data recovery IC for 40-Gb/s fiber-optic receiver

The integrated clock and data recovery (CDR) circuit is a key element for broad-band optical communication systems at 40 Gb/s. We report a 40-Gb/s CDR fabricated in indium-phosphide heterojunction bipolar transistor (InP HBT) technology using a robust architecture of a phase-locked loop (PLL) with a digital early-late phase detector. The faster InP HBT technology allows the digital phase detector to operate at the full data rate of 40 Gb/s. This, in turn, reduces the circuit complexity (transistor count) and the voltage-controlled oscillator (VCO) requirements. The IC includes an on-chip LC VCO, on-chip clock dividers to drive an external demultiplexer, and low-frequency PLL control loop and on-chip limiting amplifier buffers for the data and clock I/O. To our knowledge, this is the first demonstration of a mixed-signal IC operating at the clock rate of 40 GHz. We also describe the chip architecture and measurement results.

Volterra series analysis of semiconductor laser diode

Theoretical models for laser nonlinearities are analyzed. Volterra transfer function G/sub n/ are calculated from the laser rate equations using an output-to-input approach. Nonlinear models for second-harmonic, third-harmonic, and two-tone third-order intermodulation distortions are calculated from G/sub n/. The transfer function-based models are simplified and a new equation for intermodulation distortion is developed. Comparisons with previous results are presented. It is suggested that this analytical technique offers a valuable tool for the performance analysis of future broadband optical communication systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>