H. Burkhard

Chirp reduction of directly modulated semiconductor lasers at 10 Gb/s by strong CW light injection

The influence of strong light injection on the reduction of the dynamical linewidth broadening of directly current-modulated semiconductor lasers at high bit rates is theoretically investigated and experimentally verified for 10 Gb/s NRZ pseudorandom modulation with a large current swing of 40 mA pp. Significant chirp reduction and single-mode operation are observed for bulk DFB, quantum well DFB lasers at 10 Gb/s and a weakly coupled bulk DFB laser at 8 Gb/s, so that an improvement of the transmission performance using standard monomode fibers in the 1.55 /spl mu/m low-loss wavelength region can be achieved for all these laser types, where dispersion otherwise causes severe penalties for long-haul transmission. The properties of injection-locked bulk DFB and quantum well DFB lasers with respect to high bit rate modulation have been systematically studied by the use of the rate equation formalism. A dynamically stable locking range of more than 30 GHz under modulation has been found for both laser types with injection ratios higher than 0.5. >

Refractive indices of InAlAs and InGaAs/InP from 250 to 1900 nm determined by spectroscopic ellipsometry

Abstract 2 μm thick layers of MBE-grown In0.53Ga0.47As and In0.52Al0.48As on InP are measured with spectroscopic ellipsometry in the wavelength range from 245 to 845 nm and the fitted n,k dispersion curves given. From 450 to 845 nm the real and imaginary part of the refractive index of In0.52Al0.48As are about 0.1 higher than those of InP. The angle of incidence of two ellipsometers are controlled by measuring the same sample at different wavelengths and a correction for one ellipsometer is made. About 0.5 μm thick In0.53Ga0.47As and In0.52Al0.48As layers on InP are measured in the same manner and in addition from 410 to 1900 nm to determine the n,k values for this wavelength range. For the fitting procedure an interface layer between the substrate and the ternary layer is necessary. First results are given.

Variation of coupling coefficients by sampled gratings in complex coupled distributed-feedback lasers

We present an efficient method for an almost arbitrary variation of the complex coupling coefficient of distributed feedback lasers by using superstructure gratings, As shown by detailed transfer matrix model calculations the coupling coefficient can be reduced locally according to the duty cycle of a sampled grating. The additional supermodes caused by the superstructure can be strongly suppressed by choosing a small superperiod so that the supermodes are shifted apart from the gain curve. This novel approach for the realization of nonuniform coupling coefficients is applied to analyze experimentally the influence of the complex coupling strength on the performance of loss coupled InGaAs-InGaAlAs-InP-DFB lasers. >

Laser diodes with integrated spot-size transformer as low-cost optical transmitter elements for telecommunications

We have realized laser diodes with integrated spot-size transformer to achieve a high-coupling efficiency to a standard single-mode fiber (SMF) without microoptical elements. A coupling loss of about 1 dB has been achieved with tolerances of 12 /spl mu/m in both vertical and horizontal direction. We have fabricated both distributed-feedback (DFB) and Fabry-Perot (FP)-type lasers. In the case of the FP lasers the longitudinal single-mode emission was stabilized by means of an external fiber Bragg-grating which was directly butt-coupled to the laser. We have experimentally and theoretically investigated the optical and electrical properties of the devices using a transmission line model.

Spectroscopic ellipsometry: a useful tool to determine the refractive indices and interfaces of In0.52Al0.48As and In0.53AlxGa0.47−xAs layers on InP in the wavelength range 280–1900 nm

Abstract In0.52Al0.48As and In0.53AlxGa0.47−xAs layers on InP are promising quaternary materials for optoelectronic devices: lasers containing these materials have been realized and show excellent performance. The refractive indices of both In0.52Al0.458Ga0.022As and In0.53Al0.055Ga0.415As are measured for the first time with multiple angle spectroscopic ellipsometry in the wavelength range 280–1900 nm.

A tractable large-signal dynamic model-application to strongly coupled distributed feedback lasers

The modulation characteristics of DFB semiconductor lasers have been studied using a transfer matrix method combined with an appropriate rate equation analysis. The model takes into account longitudinal mode spatial hole burning, as well as the nonuniform current injection resulting from the axially varying Fermi voltage, and can be used for the efficient simulation of static, small-signal, and large-signal dynamic properties. The program is applied to the interpretation of experimental data from a strongly coupled InGaAsP/InP DFB laser. The experimental high-frequency properties of this device are well described by the simulations. >

Design and realization of InGaAs/GaAs strained layer DFB quantum well lasers

Optical waveguiding in an InGaAs/GaAs strained-layer distributed feedback (DFB) quantum well laser is investigated using the one-dimensional shooting method presented. The numerical approach is used to optimize the waveguide geometry and to calculate the corrugation period and the coupling factor for the integrated Bragg grating. The quantum well DFB structure designed according to the numerical calculations for an emission wavelength of 982 nm was realized for the first time entirely by molecular beam epitaxy (MBE) growth. Thus, side-mode suppression ratios of 49 dB, threshold currents of 7 mA and quantum efficiencies of 0.4 mW/mA were achieved. >

Determination of refractive indices of In0.53Al0.40Ga0.07As and In0.53Al0.11Ga0.36As on InP in the wavelength range from 280 to 1900 nm by spectroscopic ellipsometry

The refractive indices of In 0.53 Al 0.40 Ga 0.07 As and In 0.53 Al 0.11 Ga 0.36 As layers on InP are measured for the first time by spectroscopic ellipsometry in the wavelength range from 280 to 1900 nm. In previous papers we found out that between InP and MBE-grown In 0.52 Al 0.48 As and In 0.53 Ga 0.47 As layers an interface layer exists, due to the interaction of arsenic with InP in the preheat phase of the MBE growth. We investigated three layers of each composition with different thicknesses for the determination of the refractive indices and the exact values of the thicknesses

High-speed complex-coupled strain-compensated AlGaInAs/InP 1.5 /spl mu/m DFB laser diodes

The technology and characterization of high-speed partly loss-coupled distributed feedback (DFB) 1.55 /spl mu/m laser diodes realized on a strain-compensated AlGaInAs/InP MBE/MOVPE grown epitaxial structure is presented. We observe low thresholds, SMSRs of 50 dB, very high -3 dB intensity modulation (IM) bandwidths up to 23 GHz and good large signal behaviour.

Spectroscopic ellipsometry : a useful tool to determine the refractive indices and interfaces of In0.52Al0.48As and In0.53AlxGa0.47-xAs on InP in the wavelength range from 280 to 1900 nm

Abstract The refractive indices of layers of the quaternary materials In 0.53 Al 0.21 Ga 0.26 As and In 0.53 Al 0.31 Ga 0.16 As on InP are measured for the first time by spectroscopic ellipsometry in the wavelength range from 280 to 1900 nm. In previous papers we found out that between InP and molecular beam epitaxy (MBE) grown In 0.52 Al 0.48 As, In 0.53 Al 0.405 -Ga 0.065 As, In 0.53 Al 0.11 Ga 0.36 As, and In 0.53 Ga 0.47 As layers an interface layer exists, owing to the exchange of phosphorus and arsenic atoms during the As 4 -stabilized oxide desorption procedure before the MBE growth. We investigated two layers (with different thicknesses) of each composition for the determination of the refractive indices and the exact values of the thicknesses.