S. Illek

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.

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>>

Tunable laser diodes utilizing transverse tuning scheme

High-performance devices have been developed in the 1.5- mu m wavelength range by transversely integrating the lasing and tuning functions, enabling continuous wavelength tuning over a frequency range up to 900 GHz. The convenient wavelength tuning by a single control current in a tunable twin-guide (TTG) distributed-feedback (DFB) structure makes these lasers very attractive for application in coherent detection, and initial system demonstrators have already proved their suitability in practice. >

Design and realization of a buried-heterostructure tunable-twin-guide laser diode with electrical blocking regions

An InGaAsP-InP buried-heterostructure tunable-twin-guide (TTG) laser diode is presented, incorporating epitaxially regrown p-n-p-n current blocking regions to minimize current leakage around the active region in the ridge. The laser design is based on a theoretical model describing the mechanism of current leakage and the influence of electrical blocking regions by a two-dimensional computer simulation. The technological realization of the laser device reveals a way to achieve a self-aligned transverse blocking region and a lateral ridge contact in any desired depth by a two-stage epitaxial process. Completely processed TTG laser diodes with buried blocking regions exhibit very good high-temperature performance and a wavelength tuning range of around 4.5 nm under forward bias together with a maximum light output of as much as 25 mW at room temperature.

Linewidth broadening by 1/f noise in wavelength-tunable laser diodes

The excess linewidth broadening of continuously tunable InGaAsP/InP laser diodes at 1.5 μm wavelength is investigated. Terminal electrical and FM noise measurements indicate that the recombination processes in the forward biased tuning region produce significant 1/f carrier noise. Below 1 MHz the 1/f noise dominates yielding a noise enhancement of about 30 dB at 1 kHz. The discrepancy observed so far between theoretically expected and measured spectral linewidth can be well resolved by taking into account this additional noise source.

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>>

Distributed forward coupled (DFC) laser

The device structure and the operation principle of the distributed forward coupled (DPC) laser are presented. In this laser, periodic absorption losses induce the codirectional coupling of the two forward propagating modes in a twin-waveguide structure. Exploiting the strong dependence of the coupling wavelength on the effective index difference of the two modes enables the wide wavelength tuning of these devices by only one wavelength control current. In close analogy with the contradirectionally coupled DFB and DBR laser structures, the DFC laser corresponds to the DFB laser, while the previous types of codirectionally coupled tunable lasers more resemble the DBR type devices. Accordingly, the homogeneous distribution of the forward coupling along the entire cavity length yields optimum wavelength selectivity and side mode suppression, as compared with the previous approaches. Theoretically, well-designed 600-/spl mu/m long InGaAsP-InP DFC lasers, operating at 1.5-/spl mu/m wavelength, yield tuning ranges up to 100 nm and side mode suppression ratios up to 30 dB. >

Tuning range and spectral selectivity of the distributed forward coupled (DFC) laser

The tuning performance and spectral filtering mechanism in the distributed forward-coupled (DFC) laser diode are investigated. This widely tunable device is based on codirectional mode coupling along the entire laser length by a gain/loss grating perturbation. Due to the transverse integration, even rather short (L approximately=300-600 mu m) DFC lasers may achieve side-mode suppression superior to that of previous codirectionally coupled devices over similar tuning ranges. Model calculations yield a tuning range above 100 nm at 1.5- mu m wavelength with a side-mode suppression ratio around 30 dB.<<ETX>>

Leakage Current Reduction in Buried Heterostructure Tunable Twin-Guide Laser Diodes

An effective concept for leakage current reduction in tunable twin-guide (TTG) lasers is proposed. TTG lasers fabricated according to this modified design using a hybrid metalorganic vapour phase and liquid phase process achieve CW output power exceeding 25 mW and linewidth below 10 MHz within the tuning range of 2 nm.

Tunable twin guide laser diodes with high output efficiency fabricated by an improved reactive ion etching technique

An buried heterostructure (BH) tunable twin guide (TTG) laser diode with low threshold current, high output efficiency (over 0.25 W ) and a tuning range around 2.5 nm has been developed. Since BH laser diodes are highly sensitive to the waveguide quality we have improved the dry etching technique for the definition of the ridge in order to enhance the laser performance. Within the developed reactive ion etching (RIE) procedure a plasma with optimized composition has been used alternating with short plasma steps to remove remaining hydrocarbon polymer contamination deposited during the cycles. The first TTG laser diodes fabricated with this process exhibit up to 30% improved output efficiencies as compared to former devices, and show almost no degradation effects during high temperature lifetime stress.