24 research outputs found
A New Design of Ultra-Flattened Near-zero Dispersion PCF Using Selectively Liquid Infiltration
The paper report new results of chromatic dispersion in Photonic Crystal
Fibers (PCFs) through appropriate designing of index-guiding triangular-lattice
structure devised, with a selective infiltration of only the first air-hole
ring with index-matching liquid. Our proposed structure can be implemented for
both ultra-low and ultra-flattened dispersion over a wide wavelength range. The
dependence of dispersion parameter of the PCF on infiltrating liquid indices,
hole-to-hole distance and air-hole diameter are investigated in details. The
result establishes the design to yield a dispersion of 0+-0.15ps/ (nm.km) in
the communication wavelength band. We propose designs pertaining to
infiltrating practical liquid for near-zero ultra-flat dispersion of
D=0+-0.48ps/ (nm.km) achievable over a bandwidth of 276-492nm in the wavelength
range of 1.26 {\mu}m to 1.80{\mu}m realization.Comment: 6 pages, 13 figures, 1 tabl
Near-elliptic core triangular-lattice and square-lattice PCFs: a comparison of birefringence, cut-off and GVD characteristics towards fiber device application
In this work, detailed numerical analysis of the near-elliptic core
index-guiding triangular-lattice and square-lattice photonic crystal fiber
(PCFs) are reported for birefringence, single mode, cut-off behavior, group
velocity dispersion and effective area properties. For the same relative values
of d/P, triangular-lattice PCFs show higher birefringence whereas the
square-lattice PCFs show a wider range of single-mode operation. Square-lattice
PCF was found to be endlessly single-mode for higher air-filling fraction
(d/P). Smaller lengths of triangular-lattice PCF are required for dispersion
compensation whereas PCFs with square-lattice with nearer relative dispersion
slope (RDS) can better compensate the broadband dispersion. Square-lattice PCFs
show ZDW red-shifted, making it preferable for mid-IR supercontinuum generation
(SCG) with highly non-linear chalcogenide material. Square-lattice PCFs show
higher dispersion slope that leads to compression of the broadband, thus
accumulating more power in the pulse. On the other hand, triangular-lattice PCF
with flat dispersion profile can generate broader SCG. Square-lattice PCF with
low Group Velocity Dispersion (GVD) at the anomalous dispersion corresponds to
higher dispersion length and higher degree of solitonic interaction. The
effective area of square-lattice PCF is always greater than its
triangular-lattice counterpart making it better suited for high power
applications. Smaller length of symmetric-core PCF for dispersion compensation,
while broadband dispersion compensation can be better performed with
asymmetric-core PCF. Mid-Infrared SCG can be better performed with
asymmetric-core PCF with compressed and high power pulse, while wider range of
SCG can be performed with symmetric core PCF. Thus, this study will be
extremely useful for realizing fiber towards a custom application around these
characteristics.Comment: 10 pages, 17 figure
Probing liquid surface waves, liquid properties and liquid films with light diffraction
Surface waves on liquids act as a dynamical phase grating for incident light.
In this article, we revisit the classical method of probing such waves
(wavelengths of the order of mm) as well as inherent properties of liquids and
liquid films on liquids, using optical diffraction. A combination of simulation
and experiment is proposed to trace out the surface wave profiles in various
situations (\emph{eg.} for one or more vertical, slightly immersed,
electrically driven exciters). Subsequently, the surface tension and the
spatial damping coefficient (related to viscosity) of a variety of liquids are
measured carefully in order to gauge the efficiency of measuring liquid
properties using this optical probe. The final set of results deal with liquid
films where dispersion relations, surface and interface modes, interfacial
tension and related issues are investigated in some detail, both theoretically
and experimentally. On the whole, our observations and analyses seem to support
the claim that this simple, low--cost apparatus is capable of providing a
wealth of information on liquids and liquid surface waves in a non--destructive
way.Comment: 25 pages, 12 figures, to appear in Measurement Science and Technology
(IOP
"The fruits of independence": Satyajit Ray, Indian nationhood and the spectre of empire
Challenging the longstanding consensus that Satyajit Ray's work is largely free of ideological concerns and notable only for its humanistic richness, this article shows with reference to representations of British colonialism and Indian nationhood that Ray's films and stories are marked deeply and consistently by a distinctively Bengali variety of liberalism. Drawn from an ongoing biographical project, it commences with an overview of the nationalist milieu in which Ray grew up and emphasizes the preoccupation with colonialism and nationalism that marked his earliest unfilmed scripts. It then shows with case studies of Kanchanjangha (1962), Charulata (1964), First Class Kamra (First-Class Compartment, 1981), Pratidwandi (The Adversary, 1970), Shatranj ke Khilari (The Chess Players, 1977), Agantuk (The Stranger, 1991) and Robertsoner Ruby (Robertson's Ruby, 1992) how Ray's mature work continued to combine a strongly anti-colonial viewpoint with a shifting perspective on Indian nationhood and an unequivocal commitment to cultural cosmopolitanism. Analysing how Ray articulated his ideological positions through the quintessentially liberal device of complexly staged debates that were apparently free, but in fact closed by the scenarist/director on ideologically specific notes, this article concludes that Ray's reputation as an all-forgiving, ‘everybody-has-his-reasons’ humanist is based on simplistic or even tendentious readings of his work