March 2, 2009--Voxtel Inc. (Beaverton, OR) says it has developed a new class of near?infrared (NIR) photodetectors: carrier multiplication devices (CMDs). The nanostructured indium gallium arsenide/indium aluminum arsenide (InGaAs/InAlAs) devices were designed to overcome the limitations of avalanche photodiodes (APDs) in the 0.9 to 1.6 micron spectral region, including the eye?safe range beyond 1.3 microns.
According to Voxtel, the new photodetectors exceed the capabilities of APDs in both gain and noise performance. With high gain and low noise, combined with high quantum efficiency, Voxtel says its CMDs are ideal for low?light?level detection, and other applications that call for industry-leading sensitivity in the near?infrared spectral band. Coupling the CMD to a low?noise amplifier produces a receiver with high gain, superior noise equivalent power, and better overall sensitivity, says Voxtel. The company adds that CMD operating bias has low temperature sensitivity compared to APDs, making it easier and more cost effective to integrate CMDs into systems and laboratory instrumentation.
In the past, APDs have been used by designers of LIDAR, telecommunications, and other active optical systems to boost the photo signal above downstream electronics noise. However, the benefits of APDs are restricted by their limited useful amplification--typically less than 15x--and the noise that the avalanche gain process adds to the signal. Voxtel's CMDs can be operated at high gain with low noise, allowing for active optical systems with better sensitivity, longer range, and lower laser power.
Featuring ultra?low?noise analog optical detection up to approximately 1 GHz, Voxtel's new Siletz series of CMDs have very low effective ionization coefficients (k ~ 0.02), and can be operated with low excess noise: F(M) ~ 2 up to gain M = 50. The maximum linear?mode gain of Siletz CMDs is typically above M = 100. By contrast, standard telecom NIR APDs are generally not useful above M = 15, and carry a much greater noise penalty (k = 0.4; F(M) > 7 at M = 15).
Other applications for the new near?infrared CMD include quantum cryptography, optical time domain reflectometry, near?infrared Raman spectroscopy, biomedical NIR spectroscopy, time?resolved emission detection for failure analysis, and singlet oxygen detection.
For further information, see Voxtel's website.
Posted by Barbara G. Goode, barbarag@pennwell.com, for Laser Focus World.
