PIN photodiode tunes across the C-band

July 7, 2004 London -- An international collaboration has developed a tunable and wavelength-selective PIN photodiode with a full-width half-maximum of less than 0.2 nm and a free spectral range of 44 nm, reports Tami Freeman, deputy editor of FibreSystems Europe in association with Lightwave Europe.

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July 7, 2004 London -- An international collaboration has developed a tunable and wavelength-selective PIN photodiode with a full-width half-maximum of less than 0.2 nm and a free spectral range of 44 nm. The researchers, from the Darmstadt University of Technology and the University of Kassel in Germany, the Central Electronics Engineering Research Institute in India, and the Laboratoire de Photonique et de Nanostructures in France, used a simple bulk-machined two-chip structure to create the tunable receiver.

The device combines a deflectable dielectric Bragg mirror membrane chip and a PIN photodiode chip. The membrane is tuned by electrothermal heating of a metallic layer on top of its suspension beams and exhibits a linear relation between the electrical power dissipated in the membrane and the wavelength of the photodiode's responsivity peak.

"Micromechanical tuning offers the advantage of high selectivity combined with a broad tuning range," explains Hubert Halbritter from the Darmstadt University of Technology. "Current research by other groups shows only limited tuning range with low selectivity. Moreover," he says, "the fabrication of our device is simpler than rival, more complex structures."

The PIN photodiode has a 2 -Hz bandwidth, suitable for use in 2.5-Gbit/sec communications systems; an optical insertion loss of around 6 dB; and a tuning range that covers the entire C-band. The device is targeted for use as a flexible monitoring device in DWDM systems, replacing multiple fixed-wavelength receivers.

Halbritter says the researchers now plan to improve the photodiode's characteristics, especially its parasitic resonance, so that it exhibits ripple-free operation. The two-chip micromechanical technique can also be applied to create tunable VCSELs. "We have created a spin-off firm, Two-Chip Photonics, which currently holds the tuning record for electrically pumped VCSELs," he says.


Tami Freeman is deputy editor, FibreSystems Europe in association with LIGHTWAVE Europe.

• This article originally appeared in FibreSystems Europe in association with LIGHTWAVE Europe, May 2004, p7.Th 152838

Shown here is the PIN photodiode's circular mesa structure, air bridge, and contact metallization (concentric circle).
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