28 Oct 2004
A look at some of the innovations in optics that have been reported in journals this month.
In a move that could benefit chemical and biological sensing, researchers in the US have developed hollow optical waveguides that can guide liquids or gases. The team from the University of California Santa Cruz (UCSC) and Brigham Young University use a standard silicon microfabrication process to make the hollow light guides with a thickness of 3.5 µm and a width of 9 µm. "We can make many waveguides in parallel on a chip, so you can imagine probing 20 to 30 channels at one time," said UCSC scientist Holger Schmidt. "And because it is all silicon technology, we can integrate it with electrical contacts and even put a silicon photodetector right on the chip." (Appl. Phys. Lett. 85 3477)
A research group from Poland's Military University of Technology, Warsaw, has produced a Q-switched Er:YAG laser set-up that delivers pulses as short as 91.2 ns with an energy of 137 mJ (at 3 Hz repetition rate). In their paper the authors demonstrate, using a gelatine substrate, how their Q-switched high energy pulses help to minimize thermal damage to surrounding material. The apparatus, which uses a LiNbO3 crystal based Pockels cell as an active modulator, can also deliver 30 mJ pulses at 10 Hz. Because the 2.94 µm wavelength corresponds to a strong absorption peak in soft and hard biological tissue, Er:YAG lasers have attracted interest from the medical community. The researchers claim that their device generates a level of pulse energy sufficient to ablate most biological tissue and could be used in surgery. (Optics Express 12 5125)
PHOTONIC CRYSTAL FIBER
Scientists in the UK have developed an all-solid photonic crystal fiber (PCF) that acts as a high-performance bandgap filter. Unlike typical PCF, which consists of a central air core surrounded by a periodic array of air holes in silica, the University of Bath creation is fabricated using two thermally matched silicate glasses. "In the fiber being described here the interference between the core and the cladding is better matched than in previously reported hollow-core fibers," say the authors in their paper. "And we see no evidence of surface-confined guided modes." (Optics Letters 29 2369)
A team of researchers and engineers from the University of Strathclyde, UK, and HORIBA Jobin Yvon IBH has shown that a pulsed ultraviolet LED can act as a convenient source for exciting fluorescence from protein. Described by the authors as inexpensive and compact, their LED source delivers 600 ps pulses at around 280 nm. Significantly, this short wavelength emission means that the set-up can be used to study amino acid fluorescence of proteins which absorb below 300 nm. Researchers used IBH's NanoLED drive circuitry operated at 1 MHz to achieve LED pulsing and time-correlated single-photon counting synchronization. (Meas. Sci. Technol. 15 L19)
A full-color auto stereoscopic three-dimensional display, which can be viewed without glasses, has been developed by researchers in South Korea. The team based at Seoul National University use color-dispersion-compensated (CDC) synthetic phase holograms on a spatial light modulator (SLM) to generate 3D images and video. Each left or right stereo input image is separated into red, green and blue primary color components. Simulation results revealed a large signal-to-noise ratio, high diffraction efficiency and a low reconstruction error. The team put their concept to the test using a one phase-type SLM, three laser diode sources (lambda = 635, 532 and 472 nm) and a projection lens module. Despite some speckling from the use of high coherence laser diodes, the researchers were able to observe a real 3D image with a high depth effect. (Optics Express 12 5229)