VERTICAL: Vertical cavity laser technology for interconnection and access links

• Research unit: EU RFP
• Project number: 95.0714

Key words (English)

Wafer fusion; vertical cavity surface emitting laser; 1.55µm

Alternative project number (English)

EU project number: AC024

Research programs (English)

EU-programme: 4. Frame Research Programme - 1.2 Communications technologies

Short description (English)

See abstract

Abstract (English)

The main purpose of this project was the realization of vertical cavity lasers (VCSELs) emitting at 1.55µm wavelength. One of the successful approaches in VERTICAL was based on a novel fusion technique developed at EPFL and resulted in the first 1.52µm European VCSELs operating continuously at room temperature.
Our VCSELs are based on three main components: n- and p-type AlGaAs/GaAs distributed Bragg reflectors (DBRs) and InGaAsP/InP active cavity material. These three components are combined together to form a VCSEL structure by two wafer fusion processes. One of these processes is done in such a way that it provides lateral electrical and optical confinement in VCSEL structures. This novel technique is called localized wafer fusion. Its development involved the design and assembly of an original set-up, the detailed investigation of the cristallographic defects at and near the fused GaAs/InP interfaces and the control of its electrical conductance using locally grown anodic oxide layers.
Beside an effective fabrication process, VCSEL performances depend very much on the electrical and optical properties of n- and p- DBRs and active cavity material. Hence we developped advanced characterisation methods such as high accuracy reflectivity and absorption measurements (the z- and the fused cavity techniques). The results obtained were used as a feedback for the epitaxial growth of high quality DBRs and cavity materials. Chemical Beam Epitaxy was used for InAsP/InGaAsP cavities while Metalorganic Vapor Phase Epitaxy was prefered for GaAs/AlGaAs DBRs.
Our VCSELs operate in a continuous wave up to 30°C. Single mode lasing with a linewidth in the order of 0.1 A is obtained. Best VCSELs operate at voltage values below 3 V with a threshold current of 2-3 mA. Hence, these lasers are good candidates for applications in local area optical fiber networks.
The concept of polarisation and transverse mode control was demonstrated by incorporating sub-wavelength patterns obtained by electron beam or holographic lithography. In bottom emitting VCSELs (.. = 940 nm), the electrode covering the device was replaced by a 200nm pitch Au/Cr linear grating, resulting in a completely polarised laser emission with the electric field parallel to the grating lines, whatever the grating orientation.
The results of our work were reported in 10 fully refereed papers and 11 presentations in international conferences (including 1 invited).

References in databases (English)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 95.0714