GaAs-based upconverter is efficient for near-IR light
One way to image IR radiation in the 1.2 to 1.6 µm region with silicon CCD cameras, which are normally not sensitive to this wavelength range, is to upconvert the light to wavelengths below 1 µm, where silicon is sensitive.
One way to image IR radiation in the 1.2 to 1.6 µm region with silicon CCD cameras, which are normally not sensitive to this wavelength range, is to upconvert the light to wavelengths below 1 µm, where silicon is sensitive. Upconversion can be done by combining photodetectors directly with LEDs that emit at shorter wavelengths; arrays of these elements then produce an image that can be captured with an ordinary CCD camera. But such upconversion elements have not been efficient, or have been difficult to fabricate. Now, researchers at Shanghai Jiao Tong University (Shanghai, China), the National Research Council (Ottawa, Canada), and Nanyang Technological University (Singapore), have produced a near-IR upconverter based on gallium arsenide (GaAs), which is inexpensive, straightforward to work with, and efficient.
For their demonstration, they placed a custom gallium nitrogen arsenic antimony (GaNAsSb)/GaAs photodetector in series with a commercial GaAs-based LED. In their room-temperature test, they illuminated the upconverter with a 1.3-µm-emitting laser diode; the upconverter emitted 0.95 µm light with an estimated upconversion efficiency of 0.048 W/W for an incident light intensity of 12 mW/cm2 (the efficiency decreased to 0.011 W/W at 335 mW/cm2; however, this is a much higher intensity than would be expected for practical applications). The efficiency can be further increased by using resonant microcavities or custom LEDs. Contact Hui Chun Liu at email@example.com.