W. Thulke

Tunable twin‐guide laser: A novel laser diode with improved tuning performance

A new wavelength tunable laser diode with a basically continuous tuning behavior is presented. This essential progress is achieved by transversely tuning the effective index of a distributed feedback laser using a twin waveguide. Due to the built‐in synchronization of the Bragg wavelength and the optical cavity length, the wavelength is controlled by only a single current. The device technology and preliminary experimental results demonstrating the transverse tuning mechanism are presented.

Current confinement and leakage currents in planar buried-ridge-structure laser diodes on n-substrate

An electrical device model for the planar buried-ridge-structure laser on n-type substrate is discussed. It takes into account the finite p-type contact resistivity, the two-dimensional current spreading, and the electron leakage current by drift and diffusion. Using this model, the influence of the relevant device parameters on the leakage current in InGaAsP/InP devices emitting at 1.3 mu m is investigated. It is shown that leakage currents are negligible at room temperature if the contact stripe width does not exceed the sum of the active region width and the p-type confinement layer thickness, but they increase markedly with broader contact stripes and with contact resistivities above 10/sup -5/ Omega -cm/sup 2/. The most important parameter influencing the leakage currents is the doping level of the P-InP confinement layer. With a p-type doping level of 1*10/sup 18/ cm/sup -3/, a p-type contact resistivity below 10/sup -5/ Omega -cm/sup 2/ and a contact stripe width of 6 mu m, the model calculations predict a maximum operation temperature exceeding 100 degrees C. This agrees fairly well with experimental data proving that the rather simple planar buried-ridge-structure laser performs as well as more sophisticated devices incorporating current-blocking layers. >

Tuning range and threshold current of the tunable twin-guide (TTG) laser

The tuning range and threshold current of the tunable twin-guide (TTG) laser are calculated as a function of the relevant device parameters. It is shown that a maximum continuous tuning range up to 6-7 nm and low threshold currents around 25 mA can be expected with adequately designed 2 mu m wide and 400 mu m long 1.56 mu m TTG lasers. A comparison of the calculations to published experimental results shows fair agreement.<<ETX>>

Continuously tunable laser diodes: longitudinal versus transverse tuning scheme

The operating principles and performances of the two most powerful approaches to monolithic tunable laser diodes-the longitudinally integrated three-section (3S) distributed Bragg reflector (DBR) laser and the transversely integrated tunable twin-guide (TTG) distributed feedback (DFB) laser-are described and compared. Both laser configurations are capable of being continuously tuned over several nanometers. The practically useful tuning range strongly depends on structure geometry parameters and is limited by either the required amplification or the tuning densities. It is shown that, with comparable parameters, the useful continuous tuning range of the TTG-DFB laser is 30% larger than that of the 3S-DBR laser. Wide-range continuous tuning of the TTG-DFB laser requires only a single control current, which is particularly advantageous for the manufacture and design of the wavelength control circuitry. >

Surface emitting InGaAsP/InP distributed feedback laser diode at 1.53 mu m with monolithic integrated microlens

Monolithic integration of a distributed feedback (DFB) surface-emitting laser diode with a microlens is demonstrated. The transverse and longitudinal cross-sectional views of the laser diode are illustrated. The microlens and a DFB laser structure are located on opposite sides of an n-InP substrate. 11 mA minimum continuous wave (CW) threshold current and 5 mW CW emission perpendicular to the InP substrate are achieved at room temperature using a chemically etched 45 degrees mirror. Single mode emission at 1.53 mu m is obtained. The integrated microlens, etched by ion beam and coated with aluminum oxide, provides optical beam collimation and an ultralow laser mode reflectivity of <10/sup -4/.<<ETX>>

Tunable twin-guide lasers with improved performance fabricated by metal-organic vapor phase epitaxy

Tunable twin-guide (TTG) laser diodes have been fabricated using metal-organic vapor phase epitaxy (MOVPE) exclusively for all epitaxy stages. A significant performance improvement over previous experiments has been achieved with an effective current confinement in a considerably simpler laser structure. As a consequence, continuous wavelength tuning over 4.7 nm is obtained while maintaining a light output power per facet of 3 mW.<<ETX>>

Wavelength tuning efficiency and spectral linewidth broadening in tunable twin-guide dfb laser diodes

Continuously wavelength tunable laser diodes with integrated tuning regions, such as 3-section DBR lasers or tunable twin-guide (TTG) DFB lasers, often show a steep increase of the spectral linewidth while being tuned /1,2/. It exceeds the normal broadening due to spontaneous emission within the amplifying region and is part ly attributed t o injection-recombination shot noise within the tuning region /3/. The excess l inewidth broadening depends on the tuning current and strongly on the tuning efficiency. The latter is controlled b y the device geometry, the composition and doping level of the tuning region, and other factors, e.g. detuning of the Bragg wavelength from the gain maximum. In this paper w e report on experimental evidence of the expected interdependence be tween tuning eff iciency and linewidth broadening obtained with differently designed TTG-DFB lasers. A detailed description of the TTG-DFB laser (Fig. 1) and its fabrication has been given in /4 / . The relevant parameters of the t w o different structures investigated here are summarized in Tab. 1. The type A structure was designed to yield a large tuning efficiency, whereas the type B structure was designed for smaller l inewidth and larger output power. As compared to type B, type A has a larger optical confinement factor r within the tuning region, negligible detuning, and a tuning layer wi th larger thickness d, larger bandgap wavelength Xg, and lower doping level n. Over 7 nm continuous tuning has been obtained experimentally wi th this design /5/. The measured dependences of the wavelength shifts (Fig. 2). output powers (Fig. 31, and spectral linewidths (Fig.4) of the different devices on the tuning current show the strong influence of the parameters varied. Obviously, the larger tuning eff iciency ( t ype A) is correlated with the larger l inewidth broadening. The type A measurements of Figs.2 and 3 have been used to calculate the l inewidth broadening caused by spontaneous emission (Fig.5, dashed) and by both spontaneous emission and shot noise (Fig.5, solid). The calculated solid curve shows indeed that the shot noise contributes largely t o the l inewidth broadening. However, a difference between calculation and measurements still remains which needs more work for clarification. In conclusion, w e have shown that tunable laser diodes can be designed t o have small linewidths. This aim, however, can only be reached at the expense of the tuning efficiency.

Comparison of silica- and alumina-based spin-on sources for P-contact diffusion of zinc into InGaAs

Alumina- and silica- based spin-on sources for p+-doping of InGaAs contact layers are compared. Shallow diffusion profiles with hole concentrations up to 2×1020/cm3 were obtained. Higher doping levels and improved long-term stability of the spin-on solution were achieved with the alumina-based source.

Can liquid-phase epitaxy still be useful for optoelectronic devices?

Abstract Optoelectronic devices in the alloy systems AlGaAsGaAs and InGaAsPInP have been produced by liquid-phase epitaxy (LPE) for a long time. The most important role of LPE at present is to fabricate laser diodes in the quaternary system. The trend in the development of laser diodes is directed towards structures incorporating distributed feedback or distributed Bragg reflector gratings and quantum well layers and towards monolithically integrated devices. The requirements of these devices cannot completely be met by LPE. Therefore, the trend in optoelectronics is directed towards other epitaxy methods. However, LPE is still used in manufacture and will remain useful in research as an efficient supplementary tool.

Integratable tunable twin-guide laser on semi-insulating substrate

The continuously tunable twin-guide (TTG) distributed feedback (DFB) laser has been fabricated on semi-insulating substrate for the first time. A new contacting scheme is applied with all three contacts on top of the laser chip. The fabrication requires only four metalorganic vapour phase epitaxy (MOVPE) stages, i.e. only as many as that of simple TTG-DFB lasers on p-type substrate. An electronic tuning range of 1.2 nm has been achieved despite a high series resistance, which will be considerably reduced by optimising the structure. The fabrication on semi-insulating substrates makes the TTG-DFB laser suitable for integration in a heterodyne receiver chip.