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HIGHLIGHTS
ECOC 2007
Two post-deadline papers from the III-V Lab were accepted at the European Conference on Optical Communication (ECOC) last September in Berlin :
A first one reported on the integration of a laser and electro-absorption modulator (EML) with a record bandwidth of 60 GHz. This result is a major step toward the next generation 100 Gb/s optical source for Very Short Reach (VSR) transmission. This achievement also demonstrates a potential low cost approach, as the EML is designed to operate over a large temperature range (up to 70°C, as reported in May, at the last Indium Phosphide & Related Materials Conference). (Work supported by IST project GIBON).
-3dB EO bandwidth measured at -2.5V EAM bias: 60.9 GHz for 35 W matching resistor. The three curves correspond to 30, 50 and 80mA laser drive (3dB & 5GHz/div)
SEM photograph of an EML cross section showing planarised regrowths; stripe height is 5 µm
A second paper discussed the characteristics of a mode-locked laser emitting pulses at 42 GHz with a record wavelength tunability range of 16 nm, keeping constant both the output power and the narrow pulse width of 2 picoseconds. These performances have been obtained owing to a new active layer made of Quantum Dots. Moreover, the optical pulses are Fourier-transform limited, which is quite suitable for propagation in the fibre: these features make such a laser very attractive for various applications including very high bit rate tunable optical transmission (Work supported by French ANR projects TONICS and ROTOR).
Flat optical spectrum of the Fabry-Perot mode-locked laser module over a large wavelength range of 19 nm
The time and phase profiles deduced from a linear spectrogram show a duration of about 2 ps over the whole wavelength range
InGaAs mid-infrared FPAs for coolerless cameras
Infrared imaging is developing for applications like night vision, target acquisition and many spectroscopy applications, and the demand for Focal Plane Arrays (FPAs) keeps growing.
Near-infrared (1.5 µm wavelength) is of particular interest, since semiconductor material with bandgap energy close to 0.75 eV can be used, characterized by a low dark current at room temperature. This allows fabrication of lighter cameras, without any cooling as required with longer wavelength FPAs. Moreover eye-safe illumination sources can be used.
III-V lab, at the leading edge for conventional QWIP arrays, managed to associate this expertise to the in-house know-how associated to telecom applications in low-current high-homogeneity InGaAs pin photodiodes.
Arrays of InGaAs photosensitive pixels, patterned on the InP substrate. Arrays of 320 x 256 pixels are used in a camera FPA, requesting a high homogeneity both during growth of the epitaxial structure and later junction processing
Dark current of the InGaAs photosensitive pixel is a very important feature of the FPA. This figure shows the reverse bias characteristics of pixels of various geometry and surface. The low dark current achieved at 300 K (3 x 10-8 A.cm-2 at -1 V) is key for operation of the camera at room temperature.
Picture taken with the 320 x 256 pixels InGaAs FPA without any cooling of the camera
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