S. Hansmann

All-optical signal Processing and applications within the esprit project DO/spl I.bar/ALL

This paper reviews the work performed under the European ESPRIT project DO/spl I.bar/ALL (Digital OpticAL Logic modules) spanning from advanced devices (semiconductor optical amplifiers) to all-optical modules (laser sources and gates) and from optical signal processing subsystems (packet clock recovery, optical write/store memory, and linear feedback shift register) to their integration in the application level for the demonstration of nontrivial logic functionality (all-optical bit-error-rate tester and a 2/spl times/2 exchange-bypass switch). The successful accomplishment of the projects goals has opened the road for the implementation of more complex ultra-high-speed all-optical signal processing circuits that are key elements for the realization of all-optical packet switching networks.

Tailored DFB laser properties by individually chirped gratings using bent waveguides

DFB lasers with continuously and arbitrarily chirped gratings of ultrahigh spatial precision are implemented by a method we proposed recently, using bent waveguides on homogeneous grating fields. Choosing individual bending functions we generate special chirping functions and obtain additional degrees of freedom to tailor and improve specific device performances. We present two applications for lasers showing several improved device properties and the effectiveness of our method. First, we implement continuously distributed phase-shifted lasers, revealing a considerably reduced photon pile-up, higher single-longitudinal mode stability, higher output power, lower linewidth, and higher yield than conventional abruptly phase-shifted lasers. Second, a novel tuning principle is applied in chirped multiple-section DFB lasers, showing 5.5-nm wavelength tuning, without any gaps, maintaining high side-mode suppression. >

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. >

Properties of loss-coupled distributed feedback laser arrays for wavelength division multiplexing systems

The characteristics of loss-coupled distributed feedback (DFB) semiconductor laser arrays are investigated both theoretically and experimentally. Using simulations based on a transfer matrix method, the strong influence of the residual facet reflectivity on the singlemode yield and the statistical fluctuation of the emission wavelength for as-cleaved and AR/HR coated loss-coupled DFB lasers is pointed out and compared to purely index-coupled /spl lambda//4 phase-shifted devices. Experimental results and the fabrication techniques are given for loss-coupled 1.55 /spl mu/m InGaAs/InGaAlAs/InP DFB laser arrays with four channels and integrated striped thin-film heaters, which were successfully used for fine tuning the channel spacings.

High‐resolution x‐ray analysis of compressively strained 1.55 μm GaInAs/AlGaInAs multiquantum well structures near the critical thickness

Compressively strained InP/GaInAs/AlGaInAs multiquantum well (MQW) laser structures with up to 15 QWs designed for 1.55 μm emission wavelength were grown by metalorganic chemical vapor deposition (MOCVD) on p‐type InP(001) substrates. Crystallographic and optical properties are studied using double crystal x‐ray diffraction and photoluminescence measurements. The rocking curves of the complicated MQW structure can be perfectly modeled using dynamical diffraction theory. The critical thickness observed for strain relaxation upon growth and laser processing is found to be in good agreement with that predicted by Matthews and Blakeslee [J. Cryst. Growth 27, 118 (1974)] taking into account the MQW structure and the cap layer.

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.

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. >