The paper presents results of experimental investigations of spatial distribution of radiation emitted by quantum
cascade lasers. Measurements have been performed by means of a unique goniometric profilometer specially de-
signed for the large angle laser beams. The advantages and limitations of the set-up and the applied experimental
method are discussed. The obtained results have enabled the analysis of dependence of geometry of the beam
on the geometry of the laser structure and on the mount method of the laser chips. The angular divergence of
the beams has also been tested as a function of laser power supply.
Quantum cascade lasers (QCL’s) have proven their usefulness as light sources in many applications, like remote gas
sensing, molecular spectroscopy or free-space communication. In most cases the high-quality low-divergence beam is
desired. This work presents the theoretical analysis of QCL’s beam divergence. The electromagnetic field in the
resonator is calculated according to effective index method. Theoretical results are compared with measurements.
In the paper, the dynamics in the microsecond time-range of thermally induced wavelength shifts in emission spectra of
pulse operated semiconductor lasers is studied. The experimental technique of time-resolved laser spectra mapping,
developed to assess thermo-optical properties of pulse operating lasers is described. The presented technique enables
measurements of the laser mode spectral characteristics at an arbitrarily selected moment within the duration of driving
current pulse. The measured shift of the dominant mode wavelength in the spectrum envelope enables to find out
temperature change of the laser active region. The values of the temperature change have been compared with the ones
numerically calculated employing the finite element method.
In the paper, a technique termed time-resolved spectra mapping, developed to assess thermo-optical properties
of pulse operating lasers, is described. The technique enables measurement of the laser mode spectral characteristic at an
arbitrarily elected moment within the width of the driving current pulse. The measured shift of the central mode
wavelength in the spectrum envelope serves then to determine temperature change of the laser active region. The timeresolved
spectra mapping technique has been found useful in evaluation of the efficiency of heat removal from lasers
mounted in different packages.
External cavity lasers (ECLs) have been around for many years and are recognised as useful tunable narrow line light sources. In this communication we present space resolved spectral characteristics of the ECLs with a standard glass grating and ridge-waveguide broad-contact optical amplifiers (SOAs). The gain of the SOAs was centered in the range of 960 to 980 nm. The spectral characteristics have been measured with an optical spectrum analyzer. The results are compared with the ones obtained after the glass grating was substituted by a grating made from silicon. Application of such silicon gratings can be considered as a first step towards ECLs made fully in a MEMS configuration.
Deep insight into thermal effects in the broad-area lasers is the main condition of obtaining the improved devices. We present the analytical solution of the two-dimensional, stationary heat conduction equation yielding the temperature profile in the laser cross-section in plane parallel to the mirrors. Our approach allows for considering various heating mechanisms and assessing their contribution to the total temperature of the device.
Threshold current and differential quatnum efficiency of broad contact lasers with optically asymmetric mirrors is discussed with the purpose to reveal factors essential for optimization of the power efficiency of such lasers.
We have developed resonant-cavity light emitting diodes (RC LED) with very good emission characteristics. RC LEDs proved to be more tolerant to the epitaxial growth parameters and device fabrication procedures. As relatively robust devices they are less sensitive to typical for VCSEL manufacturing challenges and seem to have great potential for applications. Comparing to classical LED the spectrum of RC LED is concentrated into a narrow line with less than 2 nm halfwidth. The RC LED spectrum is determined mainly by the cavity resonance; its width decreases with the increase of the cavity finesse and the intensity increase reflect the on axis cavity enhancement. Additional, favorable RC LED property is its emission characteristic directionality which depends on the tuning between QW emission and cavity resonance. We have optimized the series resistance of diodes. The best results have been obtained for digital alloy graded distributed Bragg reflector (DRB) interfaces. The MBE grown structures were tested extensively prior to the device fabrication by reflectivity and photoluminescence. The assembled diodes were subjected to electrical and optical tests. Generally we have found very good correlation between the results of optical test (PL maps) on as grown wafers and probe tests on final devices.
To meet the requirements for the narrow emission line of ht laser diode pumping system exactly at 808 nm wavelength, an optimization of the laser (AlGa)As heterostructure because of the composition and thickness of the constituent layers is necessary. In the paper the design principles, the characteristics of the manufactured laser diodes based on this design and intrinsic limitations of the possibility of 'tuning' the lasers to desired wavelength in the MOVPE growth process are presented.
We provide results of the theoretical analysis of guided lateral mode in broad-area (BA) semiconductor lasers with modal reflectors formed by patterning the reflectivity of the front facet. The analysis has been performed by using a simple model based on the effective index method and the concept of the effective facet reflectivity. The numerical results include mode threshold conditions and far-field patterns of the lasing modes for various reflector configurations.
Continuous progress observed in performance of semiconductor lasers is to a great extent owed to implementation of quantum well heterostructures. Quantum confinement of carriers in such structures leads to lower threshold current density, higher quantum efficiency and output power, and to many more improvements of laser parameters. Most of them can be further developed when strained layer quantum well heterostructures are used. Application of quantum wires and dots are promising further advantages in the future.