Aharon Bornstein

Low-threshold phase conjugate mirrors based on position-insensitive tapered waveguides

The potential for substantial threshold reduction in stimulated Brillouin scatter phase conjugate mirrors (PCMs) was systematically studied using tapered hollow glass waveguides filled with carbon disulfide. Using a low-threshold PCM of 100 cm straight section length and 10 μm inner diameter, the threshold was reduced by a factor of 1000 compared to the bulk liquid threshold. Use of a tapered input alleviated alignment sensitivity normally encountered with small-input-diameter fibers, and allowed for the fabrication of wide-field-of-view PCMs (and Brillouin amplifiers) of a type useful in many applications. Performance of the low-threshold PCM was found to meet theoretical expectations.

Attenuated total reflection spectroscopy with chalcogenide bitapered fibers

It is shown that bi-tapering of a chalcogenide fiber results in a substantial increase in the number of reflections from the fiber boundary. Furthermore the average angle of incidence is closer to the critical angle. As a result the ATR absorption increases substantially when bi- tapered fibers, as compared to straight ones, are used. Hence higher sensing demands may be answered by bi-tapered fiber probes.

Directional multimode fiber couplers in the mid-infrared

Construction and characterization of the first multimode fiber couplers in the mid-IR region (2 to 10 μm) are reported. These couplers are made of step-index As 2 Se 3 chalcogenide glass fibers whose cores were brought to a contact along a certain distance. Far-field measurements using selective angular excitation indicated a typical coupling ratio of 15% (8.2 dB) from couplers made of 550-μm core diameter fibers with a 10-cm interaction length. The excess insertion loss was less than 0.2 dB. Strong mode mixing caused by the coupling mechanism is observed, resulting in a significant broadening of the radiation distribution.

Mode coupling coefficient in chalcogenide-glass multimode fibers in the midinfrared

The optical power distribution along step index As2Se3 chalcogenide-glass multimode fibers in the mid IR region was studied experimentally. The experimental set-up consists of an Ir source with collimating and focusing optics, and step index As2Se3 multimode fibers in different lengths. The far field radiation intensity of the fiber was obtained by moving an MCT detector with different band pass filters on an arc centered at the fiber exit.

Far-field measurements of nonimaging concentrators

The far-field patterns of two types of nonimaging concentrators were studied experimentally both in the visible and in the infrared. The input beam was a diffuse light generated by a black-body source, with a well-defined divergence angle. Several new features were observed, and were explained with a simple model based on geometrical optics.