We present an empirical thermal model for VCSELs based on extraction of temperature dependence of macroscopic VCSEL
parameters from CW measurements. We apply our model to two, oxide-confined, 850-nm VCSELs, fabricated with
a 9-μm inner-aperture diameter and optimized for high-speed operation. We demonstrate that for both these devices, the
power dissipation due to linear heat sources dominates the total self-heating. We further show that reducing photon lifetime
down to 2 ps drastically reduces absorption heating and improves device static performance by delaying the onset
of thermal rollover. The new thermal model can identify the mechanisms limiting the thermal performance and help in
formulating the design strategies to ameliorate them.
This paper presents a review of recent work on high speed tunable and fixed wavelength vertical cavity surface emitting
lasers (VCSELs) at Chalmers University of Technology. All VCSELs are GaAs-based, employ an oxide aperture for
current and/or optical confinement, and emit around 850 nm. With proper active region and cavity designs, and
techniques for reducing capacitance and thermal impedance, our fixed wavelength VCSELs have reached a modulation
bandwidth of 23 GHz, which has enabled error-free 40 Gbps back-to-back transmission and 35 Gbps transmission over
100 m of multimode fiber. A MEMS-technology for wafer scale integration of tunable high speed VCSELs has also been
developed. A tuning range of 24 nm and a modulation bandwidth of 6 GHz have been achieved, enabling error-free
back-to-back transmission at 5 Gbps.
This paper presents detailed numerical and experimental study of SPM in semiconductor optical amplifiers (SOAs) with
ultrafast gain-recovery times. These SOAs have a range of gain-recovery speed which is a function of drive current. At
increased drive current, the amount of internal ASE in the SOA increases, which causes the small signal gain to saturate
and reduces the gain-recovery time. Understanding pulse amplification in these SOAs is important for optimizing the
performance of SOA-based optical regenerators and wavelength converters. Our study addresses the full range of gain-recovery
times in commercial SOAs extending from less than 10 ps to >100 ps.
Dispersion compensating discrete Raman amplifier are known to open up new wavelength bands. However there is also the issue of wastage of Raman pump power. The length of dispersion compensating discrete Raman amplifier is decided to minimize the dispersion. Hence significant pump power is wasted. In this paper, a novel design of dispersion compensating Raman/ Two stage EDFA hybrid is reported which recycles the residual pump power from the dispersion compensating Raman and feeds this pump to the second stage of two stage EDFA. The first stage is remotely pumped from another laser source. Using this configuration, we have achieved an extremely large gain bandwidth of 117.5nm from 1582.5-1700nm with a 3dB ripple, has been achieved This amplifier topology while using minimum no of pump sources solves the twin problem of wastage of Raman pump power and providing amplification in U-band. We also performed the simulations of another topology in which a 5m long unpumped EDF was inserted between the first stage and second stage of the EDFA. The backward traveling Amplified Spontaneous Emission (ASE) from the second stage caused the pumping in the unpumped EDF thereby causing signal gain instead of loss. This topology further showed an enhancement in gain of 1-2 dB in the wavelength band of interest (1600-1700nm). The design issue in these topologies is the length of the EDF's. By suitably modeling these lengths, we can obtain appropriate gain profile.