We have developed ultra-broadband Super-Luminescent Emitting Diodes (SLEDs) at 840 nm with a 3-dB bandwidth of
45-75 nm. The SLEDs show high robustness against back-reflections of up to 50% with little change in coherence
length, sidelobe suppression ratio and secondary peak suppression over a wide range of back-reflections. First long-term
measurements do not show any signs of device degradation. Hence, these SLEDs can be employed in OCT systems
without costly broadband optical isolators.
We have fabricated superluminescent light-emitting devices in the 840nm wavelength range with flat top spectral shape.
The novel design allows more than 50nm bandwidth and up to 34mW of optical power at the chip facet. Moreover, the
3dB bandwidth changes by less than 2nm within a driving current range between 120mA and 200mA. This corresponds
to a power level change between 17mW and 34mW, without considerable shape changes, which is one of the main
concerns for many applications. The stability of the spectral bandwidth is also reflected by the central wavelength that
changes by less than 1nm in the same range of currents. The device shows great stability of the optical far field with
respect to the driving current, allowing stable coupling of the emitted beam in optical fibers. We have also measured the
coherence function of this device using an interferometric spectrum analyzer. Results show good side-lobes suppression
ratio of more than 10dB, which remains almost unchanged over the whole range of driving currents.
In this contribution, substrate modes in edge-emitting lasers in the material system Gallium-Nitride are analyzed by
means of comprehensive measurements and simulations. The simulations are complex vectorial optical mode
calculations using a finite-element method. The simulation domain comprises the ridge waveguide and the full substrate
with open boundary conditions on the sides. Therefore, the coupling mechanisms of the waveguides formed by the ridge
and the substrate can be analyzed in a realistic setup. The characterization data include the optical loss spectrum obtained
from Hakki-Paoli measurements, optical near field, and farfield measurements. The devices used for characterization are
ridge waveguide quantum well lasers grown on GaN substrates. A comparison of the measurement data with the
simulations explains the characteristics of the substrate modes in a consistent way, and shows very good agreement for
the optical loss oscillations, farfield angle, and nearfield pattern. It is shown that material losses, material dispersion and
optical diffraction are key ingredients for the analysis of substrate modes.
In this contribution, microscopic simulation of optical gain in GaN-based short-wavelength lasers is presented. The model is used to perform a design study of different active regions, and to discuss the impact of inhomogeneous broadening, carrier-induced screening of the piezo charges, and well thickness on material gain and laser threshold current. As a reference, the model parameters are calibrated with temperature dependent Hakki-Paoli measurements of spectral gain. Excellent agreement between measurement and simulation is achieved, which gives the design studies a quantitative character.
A super-luminescent light emitting diode (SLED) operating around 1300nm is simulated. This edge-emitting device is grown on an InP substrate and comprises multiple quantum wells. For the simulation the focus is put on the amplified spontaneous emission (ASE) spectra for different input currents as well as on the output power vs. current curves (light vs. current---LI). Simulated ASE spectra agree very well with measurements over a large wavelength range (more than 80nm). Regarding the LI-characteristics good agreement between simulations and measurements is obtained for input currents from 10mA up to 150mA. The simulated electrical characteristics of the device are obtained by solving drift-diffusion equations, the optical problem is solved by decomposing the vectorial (3D) Helmholtz equation into a transverse and into a longitudinal part.