In this paper we propose and demonstrate a novel technique to suppress pump in four-wave mixing experiments. The residual pump powers at the fiber output are reflected by fiber-Bragg gratings (FBGs), amplified by an EDFA to compensate for pump losses in feedback path, and fed back to the fiber. With the increase in total input power to the fiber, the ratio of signal and idler to pump increases. Additional optical filters can then be used for further pump suppression. In our experiments, two pump waves of wavelengths 1549.70nm and 1549.85nm are combined using a 3dB coupler and fed to a highly-nonlinear fiber (HNLF) of length 1km, nonlinear coefficient of 12.4/W-km, and zero dispersion wavelength (ZDW) of 1513nm. Without feedback, we obtained the signal and idler to pump ratios of -21dB and -20.6dB respectively. After filtering by FBGs of 95% reflectivity and unity gain feedback, the ratio becomes - 14.1dB and -12.2dB respectively. When the residual pumps are amplified and fed back to the HNLF, the ratio improves to -7.5dB and -8.6dB indicating the potential of our method.
We describe a frequency-coded scheme to implement the BB84 quantum key distribution protocol using spin
wave (SW)-optical interactions. The interaction of SWs with optical coherent states allows TE↔TM mode
conversion with simultaneous change of frequency and polarization while introducing a phase difference between
the two modes. To implement the BB84 protocol, key bits are encoded as relative phases between the TE and
TM modes. The proposed scheme offers a higher key rate, due to a modulation frequency as high as 25 GHz,
which also relaxes the specifications on the optical filter at the receiver. In addition, SW-optical interactions
yield the added security of truly single-sideband modulation.
We report an all-fibre interferometric autocorrelation measurement of femtosecond optical pulses in the C-band.
An all-fibre Mach-Zehnder interferometer with piezo-electric fiber stretcher in one arm provides the interference
signal. A highly nonlinear and dispersion shifted fibre with Kerr coefficient 10.5 /W-km generates an idler by the
process of degenerate four wave mixing of the pump and target pulse signals. The idler intensity is proportional
to the interferometric autocorrelation of target pulse. We have measured approximately 100 fs optical pulses at
1552.52nm from an actively mode locked erbium doped fibre laser operating at 280 MHz repetition rate.
The Indian Remote Sensing Satellites use indigenously developed high resolution cameras for generating data related to
vegetation, landform /geomorphic and geological boundaries. This data from this camera is used for working out maps at
1:12500 scale for national level policy development for town planning, vegetation etc. The LISS-4 Camera was launched
onboard Resourcesat-1 satellite by ISRO in 2003. LISS-4 is a high-resolution multi-spectral camera with three spectral
bands and having a resolution of 5.8m and swath of 23Km from 817 Km altitude. The panchromatic mode provides a
swath of 70Km and 5-day revisit. This paper briefly discusses the configuration of LISS-4 Camera of Resourcesat-1, its
onboard performance and also the changes in the Camera being developed for Resourcesat-2.
LISS-4 camera images the earth in push-broom mode. It is designed around a three mirror un-obscured telescope, three
linear 12-K CCDs and associated electronics for each band. Three spectral bands are realized by splitting the focal plane
in along track direction using an isosceles prism. High-speed Camera Electronics is designed for each detector with 12-
bit digitization and digital double sampling of video. Seven bit data selected from 10 MSBs data by Telecommand is
transmitted. The total dynamic range of the sensor covers up to 100% albedo. The camera structure has heritage of IRS-
1C/D. The optical elements are precisely glued to specially designed flexure mounts. The camera is assembled onto a
rotating deck on spacecraft to facilitate ± 26° steering in Pitch-Yaw plane. The camera is held on spacecraft in a stowed
condition before deployment. The excellent imageries from LISS-4 Camera onboard Resourcesat-1 are routinely used
worldwide. Such second Camera is being developed for Resourcesat-2 launch in 2007 with similar performance. The
Camera electronics is optimized and miniaturized. The size and weight are reduced to one third and the power to half of
the values in Resourcesat-1.
The Indian Remote Sensing (IRS) P5 spacecraft carried two identical optical payloads (Cartosat-1), each with a different view angle, for acquiring high resolution remote sensing data in stereo mode for the purpose of generation of topographic maps. Information on terrain height derived from these payloads is useful for applications in a number of forms including digital elevation model (DEM) creation, orthoimage, DEM plus thematic data and scientific visualization. Each optical payload features an unobscured, three-mirror anastigmat, design providing high contrast, and wide swath imagery. The mechanical design of the camera structure enabled accurate location of the mirrors while maintaining a very high degree of dimensional stability during launch and in-orbit environment. This paper presents the optical and mechanical design of the camera assembly as well as the alignment and performance optimization carried out in realizing the Cartosat -1 payload.
Conference Committee Involvement (1)
Lidar Remote Sensing for Environmental Monitoring VII