Passive optical network (PON) is considered as the most appealing access network architecture in terms of cost-effectiveness,
bandwidth management flexibility, scalability and durability. And to further reduce the cost per
subscriber, a Fabry-Perot (FP) laser diode is preferred as the transmitter at the optical network units (ONUs) because of
its lower cost compared to distributed feedback (DFB) laser diode. However, the mode partition noise (MPN) associated
with the multi-longitudinal-mode FP laser diode becomes the limiting factor in the network. This paper studies the MPN
characteristics of the FP laser diode using the time-domain simulation of noise-driven multi-mode laser rate equation.
The probability density functions are calculated for each longitudinal mode. The paper focuses on the investigation of
the k-factor, which is a simple yet important measure of the noise power, but is usually taken as a fitted or assumed
value in the penalty calculations. In this paper, the sources of the k-factor are studied with simulation, including the
intrinsic source of the laser Langevin noise, and the extrinsic source of the bit pattern. The photon waveforms are shown
under four simulation conditions for regular or random bit pattern, and with or without Langevin noise. The k-factors
contributed by those sources are studied with a variety of bias current and modulation current. Simulation results are
illustrated in figures, and show that the contribution of Langevin noise to the k-factor is larger than that of the random bit
pattern, and is more dominant at lower bias current or higher modulation current.
Radiation coupling plays a key role in the bending waveguide structure with very small bending radius. Insights of radiation coupling and energy transfer by way of high order bending modes have been discussed. Modes in bending waveguide structures with small bending radii are investigated.
The edge-emitting distributed Bragg reflector (DBR) laser with a metal nano-strip grating is proposed. It achieves a high reflectivity with a much shorter grating length of 200μm due to the high refractive index contrast of the metal and the semiconductor. Moreover, the modal coupling (κL) of the grating can be tuned in a wide range by simply changing the design parameters of the metal nano-structure. In this work, the metal grating is investigated by the coupled-wave theory (CWT) and the complex mode matching method (CMMM). Results from these two methods are compared and the effects of changing the grating parameters, such as the spacing of the grating and the core region, the thickness of nano-strips and the duty cycle, are discussed regarding the peak reflectivity and the full-width half-maximum (FWHM) of the reflection spectrum. Further simulation of the laser output with the multi-mode rate equation model demonstrates the single-mode operation for a broad range of the metal grating’s design parameters, thus the design freedom is provided. For various applications of the DBR laser, the requirements such as a shorter cavity length, a lower threshold current, or a very high SMSR can be satisfied by properly setting the design parameters.
Resonant coupling to radiation field in optical waveguides is simulated accurately and efficiently by complex coupled
mode theory. Salient features of complex mode theory are demonstrated by investigation of transmission spectra in
short/long period gratings.
In this paper both statistic and dynamic behaviors of the multimode fiber Bragg grating external cavity lasers
(MMFBG_ECL) have been studied experimentally, and simulated numerically by time domain traveling wave (TDTW)
rate equations. Experimentally, multiple wavelength selection has been realized by offsetting the coupling between the
laser diode (LD) and the MMFBG. Small signal modulation responses at these wavelengths have been measured and
over 8 GHz modulation bandwidths have been demonstrated at several wavelengths. Numerically, the TDTW model has
been employed to simulate the multiple wavelength lasing selection and L-I curves. Comparison between single mode
fiber Bragg grating external cavity lasers (SMFBG-ECL) and MMFBG-ECL have been addressed. In addition, steady
experiments and numerical simulated are made to verify our numerical model.
A long range surface plasmon polaritons Bragg grating is investigated by a complex mode matching method. A high
order finite difference method is employed to find the complex eigenmodes. Benefited from the cascading and doubling
algorithm, the computation effort is significantly saved for Bragg gratings with large number of periods. Numerical
results are verified by previous reported experiments.
For realization of highly integrated optical circuits, various metallic nanostructures supporting the propagation of surface
plasmon polaritons have been extensively studied experimentally and theoretically in recent years. This paper reports on
the development of a numerically stable and accurate finite-difference-based bidirectional beam propagation method
(FD-BiBPM) for analyzing piecewise z-invariant plasmonic structures. Our method is developed based on the scattering
operators. The adoption of complex coefficient rational approximations to the square root operator allows to correctly
model the propagation of evanescent modes excited at discontinuity interfaces. In view of the large index contrast at
metal-dielectric interfaces, a fourth-order accurate finite difference formulation for discretization is incorporated to the
present method and its fine treatment of these interfaces guarantees accuracy. By using the present method, the reflection
and transmission spectra of the Bragg gratings consisting of a thin metal film embedded in dielectric medium and an
array of equidistant metal ridges on each side of the film are calculated. The good agreement of our results with the
previously reported simulations illustrates the potential of the newly developed FD-BiBPM for the analysis of longrange
surface plasmon polariton (LRSPP) waves guided along the described Bragg gratings.