Bharat Kumar Yadav

Experimental study of the phenomenon of 1 × N spectral switch due to diffraction of partially coherent light

Spectral properties of a class of partially coherent light with spectral profiles of varying bandwidths are studied on diffraction by a circular aperture in the far zone for different diffractive angles, i.e., for on-axis and off-axis points on the observation plane. It is found that the spectrum of the light in the far zone is different from that at the aperture plane. This change in the spectrum is termed spectral shift, which is found to be different at different diffractive angles. The spectral shift for a fixed diffactive angle shows a gradual change. However, for a critical value of the coherence at the aperture plane, the spectral shift shows a rapid transition, termed spectral switch. For different diffractive angles the coherence that causes the spectral switch also differs. Therefore the phenomenon of 1 x N spectral switch (consisting of one input port and N output ports) is studied experimentally.

Experimental observation of spectral changes of partially coherent light in Young's experiment

Experimental observations of a study conducted to investigate spectral shifting and spectral switching that take place in Youngs double-slit experiment with partially coherent light are reported. It is shown that for certain critical distances in the near zone of the double slit, the phenomenon of spectral switching is observed, while for other situations a spectral shift is observed. These results are consistent with a theoretical study by Pan and Lu (2001 IEEE J. Quantum Electron. 37 1377; 2002 J. Opt. A: Pure Appl. Opt. 4 349).

Spectral Anomalies of Polychromatic DHGB and Its Applications in FSO

This paper contains some interesting experimental results of the study carried out on anomalous spectral behavior due to coherence and polarization change on polychromatic focused dark hollow Gaussian beam (DHGB). On the basis of experimental and numerical analysis, the possibility and significance of DHGB based free-space optical (FSO) links for indoor and outdoor optical communications are explored.

Information exchange in free space using spectral switching of diffracted polychromatic light: possibilities and limitations

Spectral switching is now a well-known phenomenon. Several research groups have studied it theoretically and experimentally for different optical systems. Recently, its potential applications have been demonstrated for information encoding and transmission in free space. In this paper we report experimental observations in the far field for spectral switching of polychromatic light passing through an astigmatic aperture lens. An information encoding scheme, a free-space optical link, and related boundary conditions are studied in detail. In addition, on the basis of experimental and theoretical studies carried out so far for spectral switching, we explore possibilities of information transmission in free space and analyze experimental limitations of spectral-switching-based free-space optical communication.

Experimental observation of the effect of astigmatic aperture lens on the spectral switches of polychromatic Gaussian beam

Experimental results of a study, conducted to investigate the effect of an astigmatic aperture lens on the spectral switches observed with spatially coherent polychromatic light, are reported. It is found that the spectrum at the observation plane exhibits anomalous behavior after passing through the astigmatic aperture lens. It is shown that at a particular position of the aperture, the spectrum splits into two halves, while at other positions the spectrum either shifts towards lower frequencies (red shift) or shifts towards higher frequencies (blue shift). These spectral changes take place in the vicinity of the dark region of the diffraction pattern. Experimental observations show that the behavior of the spectral switch is affected by the astigmatism of the lens. It is found that the spectral minimum value and the transition height of the spectral switch change as the astigmatism of the lens changes. Moreover, the critical position of the aperture where spectral switch occurs also changes with the astigmatism of the lens. The results are consistent with the theoretical predictions [Pan, L.; Lü, B. Opt. Commun. 2004, 234, 13–22].

Effect of polarization on spectral anomalies of diffracted stochastic electromagnetic beams

Theoretical and experimental studies are reported on the effect of polarization on spectral anomalies of diffracted stochastic electromagnetic beams (SEB). To the best of our knowledge we are the first to report experimental results that show the effect of the degree of polarization on spectral anomalies in diffracted SEB. The study might be useful in understanding the spectral behavior of SEB near phase singularities. Moreover, it might provide a sophisticated control mechanism for spectral switching.

Multi-level information encoding through spectral switches and multiple FSO link formation in the phase singularity domain

Spectral switching is now a well-known phenomenon. Recently, its potential applications have been explored for information encoding and transmission in free space. In this paper, we demonstrate a novel type of scheme to encode and process information at multiple levels through spectral switching. A new technique is also proposed to establish multiple parallel free-space optical (FSO) links using a single critical direction in the phase singularity domain of diffracted polychromatic light. These are contrived ideas on the basis of theoretical and experimental studies carried out so far on spectral switching. The study might find potential application in the fields of FSO interconnects and FSO communication.

Experimental observation of the effect of generic singularities in polychromatic dark hollow beams

This Letter presents the essence of our recent experimental study on generic singularities carrying spatially partially coherent, polychromatic dark hollow beams (PDHBs). To the best of our knowledge, this is the first experimental demonstration of generic singularities-induced wavefront tearing in focused polychromatic beams.

Effect of coherence and polarization on the polychromatic partially coherent dark hollow beam generated from axicon-lens system

An experimental study is carried out to investigate the effect of coherence and polarization on the polychromatic partially coherent dark hollow beam (PCDHB). The experimental results show that the spatial coherence and source polarization affect the dark region of the generated hollow beam. The study shows that by varying the source degree of polarization (DOP), we get a tunable dark region. We find that the longer the spatial coherence length of the input beam, the larger the central dark size of the resultant PCDHB. Further, it is shown that polychromatic PCDHB with low spatial coherence travel a longer distance without being distorted than a beam with a high spatial coherence. These kinds of polychromatic beams may find potential application in the field of polychromatic light based free-space optical (FSO) communications.

Effect of coherence on the polychromatic partially coherent dark hollow beam

We experimentally demonstrate that polychromatic partially coherent dark hollow beam with low coherence travel longer distance without being distorted than the beam with high coherence. The effect of coherence on dark region is also studied.