Optical filters are crucial elements in optical communications. The influence of cascaded filters in the optical signal will
affect the communications quality seriously. In this paper we will study and simulate the optical signal impairment
caused by different kinds of filters which include Butterworth, Bessel, Fiber Bragg Grating (FBG) and Fabry-Perot (FP).
Optical signal impairment is analyzed from an Eye Opening Penalty (EOP) and optical spectrum point of view. The
simulation results show that when the center frequency of all filters aligns with the laser’s frequency, the Butterworth
has the smallest influence to the signal while the F-P has the biggest. With a -1dB EOP, the amount of cascaded
Butterworth optical filters with a bandwidth of 50 GHz is 18 in 40 Gbps NRZ-DQPSK systems and 12 in 100 Gbps PMNRZ-
DQPSK systems. The value is reduced to 9 and 6 respectively for Febry-Perot optical filters. In the situation of
frequency misalignment, the impairment caused by filters is more serious. Our research shows that with a frequency
deviation of 5 GHz, only 12 and 9 Butterworth optical filters can be cascaded in 40 Gbps NRZ-DQPSK and 100 Gbps
PM-NRZ-DQPSK systems respectively. We also study the signal impairment caused by different orders of the
Butterworth filter model. Our study shows that although the higher-order has a smaller clipping effect in the
transmission spectrum, it will introduce a more serious phase ripple which seriously affects the signal. Simulation result
shows that the 2nd order Butterworth filter has the best performance.
A two-dimensional self-consistent laser model has been used for the simulation of the facet heating of red emitting
AlGaInP lasers. It solves in the steady-state the complete semiconductor optoelectronic and thermal equations in the
epitaxial and longitudinal directions and takes into account the population of different conduction band valleys. The
model considers the possibility of two independent mechanisms contributing to the facet heating: recombination at
surface traps and optical absorption at the facet. The simulation parameters have been calibrated by comparison with
measurements of the temperature dependence of the threshold current and slope efficiency of broad-area lasers. Facet
temperature has been measured by micro-Raman spectrometry in devices with standard and non absorbing mirrors
evidencing an effective decrease of the facet heating due to the non absorbing mirrors. A good agreement between
experimental values and calculations is obtained for both devices when a certain amount of surface traps and optical
absorption is assumed. A simulation analysis of the effect of non absorbing mirrors in the reduction of facet heating in
terms of temperature, carrier density, material gain and Shockly-Read-Hall recombination rate profiles is provided.
Tapered semiconductor lasers have demonstrated both high power and good beam quality, and are of primary interest for
those applications demanding high brightness optical sources. The complex non-linear interaction between the optical
field and the active material requires accurate numerical simulations to improve the device design and to understand the
underlying physics. In this work we present results on the design and simulation of tapered lasers by means of a Quasi-
3D steady-state single-frequency model. The results are compared with experiments on Al-free active region devices
emitting at 1060 nm. The performance of devices based on symmetric and asymmetric epitaxial designs is compared and
the influence of the design on the beam properties is analyzed. The role of thermal effects on the beam properties is
experimentally characterized and analyzed by means of the numerical simulations. Tapered lasers with separate electrical
contacts in the straight and tapered sections, based on symmetrical and asymmetrical epitaxial designs are also presented
Quantum dot structures with tailored geometries were developed for different high power laser applications by
molecular beam epitaxy based self-assembly techniques. 920 nm quantum dot laser material with new record values of
0.08 nm/K in temperature dependent wavelength shift could be obtained, which is a factor of 4 lower than for quantum
well lasers. Tapered distributed Bragg reflector laser devices were processed, which exhibit single mode output powers
of more than 1 W in cw with an M<sup>2</sup> value of 2. For display applications based on frequency doubling, 1060 nm quantum
dot laser material is developed with and without tunnel injection quantum well active zones. With this new type of laser
material an output power of 4.5 W could be obtained on 100 μm broad area lasers. An overview is given on this recent
work performed within the frame of the EU project "WWW_BRIGHTER_EU".
This paper describes the theory and experimental results of a dynamic holographic wavelength filtering for use in optical telecommunication Coarse and Dense Wavelength Division Multiplexing (CWDM/DWDM) applications. The enabling component is a ferroelectric liquid crystal (FLC) spatial light modulator (SLM) where dynamic holograms are implemented in real time; as a consequence, tuning of the filter is possible according to the light modulation. The great advantage of this FLC device is a polarization insensitivity operation, allowing low crosstalk and potential low loss in optical communications.
Other applications, such as demultiplexers and wavelength routers, have been studied and practical values have been obtained according to central wavelengths recommended in ITU G. 694.1 and G. 694.2. Lab experiments have demonstrated the capability of a phase FLC-SLM to diffract the incident light, according its wavelengths and the hologram patterns, for the use in the former applications.