Hartmut Hillmer

10-Gb/s standard fiber transmission using directly modulated 1.55-μm quantum-well DFB lasers

10-Gb/s long-haul transmission on standard single-mode fibers at 1.55 /spl mu/m with intensity modulated, low-chirp MQW DFB lasers is investigated. Successful transmission is achieved by operating the laser at increased bias. Thus, the laser chirp acts favorably on the propagation after an initial distance of 30 km in the fiber. A detailed system evaluation with an optical preamplified PIN-receiver, reveals a negligible dispersion power penalty for transmission distances between 35 and 70 km. The power penalty, mainly caused by a lower extinction ratio, must be accepted.<<ETX>>

Static and dynamic properties of InGaAsP-InP distributed feedback lasers-a detailed comparison between experiment and theory

We have investigated the static and dynamic characteristics of phase shifted InGaAsP-InP DFB lasers mainly focusing on a comprehensive comparison between experimental results and numerical simulations. Experimental data of InGaAsP-InP mushroom type DFB lasers have been recorded, such as optical spectra, variations of the mode wavelengths with continuous and pulsed injection current, side mode suppression ratio, relative intensity noise, small signal amplitude modulation, and the transient response to 10 and 15 Gb/s large signal modulation. The theoretical model calculations in this paper are based on the transfer matrix method in combination with a rate equation analysis and take into account longitudinal mode spatial hole burning which is modified by the inhomogeneous current injection resulting from the axially varying Fermi voltage in both the static and the dynamic case. A good agreement between the experimental data and the theoretical simulations has been obtained extracting a set of parameters which consistently describes the measurements of our devices. >

Continuously chirped DFB gratings by specially bent waveguides for tunable lasers

We have implemented and studied a new type of tunable multiple-section semiconductor distributed feedback (DFB) laser using tailored chirped DFB gratings. Arbitrarily and continuously chirped DFB gratings are defined by bent waveguides on homogeneous grating fields with ultrahigh spatial precision. The mathematical bending functions are optimized in this case to provide enlarged wavelength tuning ranges. We present the results of model calculations, the technological device realization and experimental results of the DFB laser characterization e.g. a tuning range of 5.5 nm without wavelength gaps and high side mode suppression ratio. >

Novel tunable semiconductor lasers using continuously chirped distributed feedback gratings with ultrahigh spatial precision

We present experimental and theoretical results obtained from a new type of tunable two‐ and three‐section semiconductor distributed feedback (DFB) laser using tailored chirped DFB gratings. The chirped gratings are defined by bent waveguides on homogeneous grating fields with ultrahigh spatial precision using bent waveguides. Arbitrary and continuous chirping functions can be obtained by appropriate mathematical bending functions. Our method is applied for tunable lasers with optimized bending shapes revealing a considerably enlarged wavelength tuning range of 5.5 nm without wavelength gaps.

Study of wavelength shift in InGaAs/InAlGaAs QW DFB lasers based on laser parameters from a comparison of experiment and theory

Experimental data of InGaAs/InAlGaAs quantum well distributed feedback (DFB) lasers such as spectra, under continuous and pulsed biasing, relative intensity noise and linewidth, are compared with the results of model calculations based on a transfer matrix method. Using experimental data of different lasers, a set of physical DFB laser parameters was determined. We succeeded in describing all the experimental data of different lasers by the same set. The determined parameter set was further applied to study the influence of facet properties on the wavelength shift of DFB lasers. We found a very strong dependence of the wavelength tunability on the end facet phases. The wavelength shift varies by a factor up to three between different end facet phases and coatings. This is crucial for the yield of, for example, tunable multisection DFB lasers with an envisaged large tuning range. >

Characterization of high-quality molecular beam epitaxial grown InxAlzGa1−x−zAs/InyAluGa1−u−yAs/InP heterostructures

We focus on molecular beam epitaxy (MBE) growth and characterization of InAlGaAs/InP heterostructure layers by photoluminescence (PL) and X-ray diffraction (XRD) measurement. The epitaxial quality is demonstrated by very narrow XRD linewidths just above the theoretical limits independent of various quaternary compositions. In contrast to the XRD linewidths showing no dependence on the aluminum content for a fixed layer thickness, we observe PL linewidths decreasing with increasing bandgap wavelength and decreasing aluminum content. This may be explained by an interplay of alloy disorder fluctuations and defect formation which both strongly vary with composition. Multiple quantum well structures were grown for all possible combinations of ternary and quaternary materials in the wells and the barriers. Measured and simulated rocking curves show excellent agreement and the PL studies reveal low linewidths

Realization of high coupling coefficients in 1.53 μm InGaAsP/InP first‐order quarter‐wave shifted distributed feedback lasers

Coupling coefficients as high as 300 cm−1 have been achieved and investigated in the performance of distributed feedback lasers. High coupling has several important advantages like lower feedback sensitivity, and lower influence on facet reflectivity, thus easy handling for coatings without any penalty in terms of mode hopping. We obtain a side‐mode suppression ratio as high as 51.2 dB. 8 Gb/s ‘‘nonreturn to zero’’ modulation is demonstrated.

Compositional influence on photoluminescence linewidth and Stokes shift in InxAlzGa1−x−zAs/InyAluGa1−u−yAs/InP heterostructures grown by molecular beam epitaxy

We have grown InxAlzGa1−x−zAs/InP heterostructure layers of different geometry and composition by molecular beam epitaxy showing very narrow photoluminescence linewidth, small Stokes shift, and high epitaxial quality. For rising z we observe experimental linewidths strongly increasing from 1.45 meV (InGaAs) to 13 meV (InAlAs). The Stokes shift is found to grow with rising z. Several contributions are discussed to explain the measured compositional variation of linewidth and Stokes shift. The possibility of arbitrarily combining different material compositions is demonstrated by the growth and characterization of multiple quantum well structures, including possible combinations of ternary and quaternary materials in the wells and barriers.

Effects of injected light and optical feedback on directly modulated MQW lasers and OTDM multigigabit-per-second system performance

Injection-locked directly current modulated semiconductor laser transmitters are theoretically investigated with respect to transmission performance. By large signal simulation of laser, standard single-mode fiber propagation and direct detection optically pre-amplified PIN receiver, transmission distances of 80-120 km at 10 Gb/s and 40-60 km at 15 Gb/s have been evaluated with a bit-error-rate < 10-9 with reasonable power penalty. Exploiting fiber nonlinearities with higher power launched into the fiber is demonstrated to increase the transmission distance by about 40%. Additionally the dynamics of the residual chirp of the laser is shown to act favorably on transmission performance. Guidelines for operation conditions of injection-locked lasers depending on detuning between laser and slave laser and injected power are given. Gain switching including optical feedback and the gain- levering effect have been investigated with respect to pulse production for optical time domain multiplexing. A new method for short pulse generation is presented. It is based on single frequency CW light injection into an unmodulated single mode laser under nonstable locking- conditions. Repetition frequencies larger than 150 GHz can be achieved. By soliton generation in a dispersion shifted fiber pulse widths of less than 3 ps FWHM with a squared hyperbolic cosecans shape can be generated.

Strain-balanced AlGaInAsInP heterostructures with up to 50 QWs by MBE

Using solid-source MBE, strain-balanced quaternary AlGaInAs/AlGaInAs multiple quantum well (MQW) strucures have been grown and studied by photoluminescence (PL) and X-ray diffraction (XRD) measurements, showing high epitaxial quality and excellent homogeneity in growth direction. The PL linewidths are low and almost independent of the number of QWs (1 ≤ N QW ≤ 50). With respect to photonic device applications at 1.55 μm, structures with quaternary QWs seem to be superior compared to structures with ternary QWs: structures with quaternary QWs enable more degrees of freedom in device design and reveal a five times larger lateral wafer area in which the PL wavelength is constant.