OALib Journal期刊

ISSN: 2333-9721




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匹配条件: “Roy Partha” ,找到相关结果约5674条。
Nuclear Matter for compact stars and its properties
Partha Roy Chowdhury
Physics , 2011,
Abstract: A pure nucleonic equation of state (EoS) for beta equilibrated charge neutral neutron star (NS) matter is determined using density dependent effective NN interaction. This EoS is found to satisfy both the constraints from the observed mass-radius of neutron stars and flow data from heavy-ion collisions. Recent observations of the binary millisecond pulsar J1614-2230 by P. B. Demorest et al. [1] suggest that the masses lie within (1.97\pm 0.04) M_\odot (M_\odot, solar mass). Most EoS involving exotic matter, such as kaon condensates or hyperons, tend to predict maximum masses well below 2.0M_\odot and are therefore ruled out. We are able to reproduce the measured mass-radius relationship for rotating and static NS. We ensure that the star rotating not faster than the frequency limited by r-mode instability gives the maximum mass about 1.95M_\odot with radius about 10 kilometer.
A New Design for All-Normal Near Zero Dispersion Photonic Crystal Fiber with Selective Liquid Infiltration for Broadband Supercontinuum Generation at 1.55?μm
Partha Sona Maji,Partha Roy Chaudhuri
Journal of Photonics , 2014, DOI: 10.1155/2014/728592
Abstract: A new design of all-normal and near zero flattened dispersion based on all-silica photonic crystal fibers (PCFs) using selectively liquid infiltration technique has been proposed to realize smooth broadband supercontinuum generation (SCG). The investigation gives the details of the effect of different geometrical parameters along with the infiltrating liquids on the dispersion characteristics of the fiber. Numerical investigations establish a dispersion value of ?0.48?ps/nm/km around the wavelength of 1.55?μm. The optimized design has been found to be suitable for SCG around the C band of wavelength with flat broadband wavelength band (375?nm bandwidth) and smooth spectrum with only a meter long of the PCF. The proposed structure also demonstrates good tunable properties that can help correct possible fabrication mismatch towards a better optimization design for various optical communication systems. 1. Introduction Broadband smooth flattened supercontinuum generation (SCG) has been the target for the researchers for its enormous applications in the field of metrology, optical sensing, optical coherence tomography, wavelength conversion, and so forth [1]. Recent developments for mid-infrared (MIR) SC source have been investigated based on nonsilica fibers [2, 3]. Unconventional PCFs based on aperiodic structure have also been investigated [4]. However, achieving flat broadband smooth SC sources for IR applications remains challenging [1]. One of the foremost requirements of generating broadband flattened SCG is to achieve near zero flattened dispersion around a targeted wavelength. Photonic crystal fibers (PCFs) [5, 6], which enjoys some unique properties like wide band single mode operation, great controllability over dispersion properties, and higher nonlinearity, has been the target host for SCG for the last decades [1]. Researchers have worked on designing novel dispersion profiles with variable air-hole diameter in the cladding [7–13] and this design can be further manipulated for SC generation by pumping at the near zero wavelength [9, 14]. However, the realizing technology of complicated structures or PCF having air-holes of different diameters in microstructure cladding remains truly challenging. An alternative route of achieving similar performance is shown to be practicable by filling the air-holes with liquid crystals [15, 16] or by various liquids such as polymers [17], water [18], and ethanol [19]. Tunable photonic band gap (PBG) effect and long-period fiber grating have been successfully realized with liquid-filled PCFs [20]. Theoretical
Circular Photonic Crystal Fibers: Numerical Analysis of Chromatic Dispersion and Losses
Partha Sona Maji,Partha Roy Chaudhuri
ISRN Optics , 2013, DOI: 10.1155/2013/986924
Abstract: Detailed numerical analysis for dispersion properties and losses has been carried out for a new type of Photonic crystal fiber where the air-holes are arranged in a circular pattern with a silica matrix called as Circular Photonic Crystal Fiber (C-PCF). The dependence of different PCF geometrical parameters namely different circular spacings, air-hole diameter and numbers of air-hole rings are carried out in detail towards practical applications. Our numerical analysis establishes that total dispersion is strongly affected by the interplay between material dispersion and waveguide dispersion. For smaller air-filing fraction, adding extra air-hole rings does not change dispersion much whereas for higher air-filling fraction, the dispersion nature changes significantly. With proper adjustment of the parameters ultra-flattened dispersion could be achieved; though the application can be limited by higher losses. However, the ultra-flat dispersion fibers can be used for practical high power applications like supercontinuum generation (SCG) by reducing the loss at the pumping wavelength by increasing the no of air-hole rings. Broadband smooth SCG can also be achieved with low loss oscillating near-zero dispersion fiber with higher no of air-hole rings. The detail study shows that for realistic dispersion engineering we need to be careful for both loss and dispersion. 1. Introduction Photonic crystal fibers (PCFs) or microstructured optical fibers (MOFs) [1, 2] are special types of optical fiber where air holes are arranged in a periodic nature in the cladding. These types of fibers possess some novel guiding properties, related to the geometric characteristics of the air holes in their cross-section and have been successfully exploited in different applications [1, 2]. Most of the air holes in the PCFs cladding have been arranged either in a periodic triangular or periodic square orientation. The modal properties, in particular, and the dispersion properties of the above types of PCFs can be altered by varying the hole-to-hole spacing ( ) and the air hole diameter ( ) with air-filling fraction being [3, 4]. Both types of PCFs with a silica background can be successfully implemented to compensate the positive dispersion parameter and dispersion slope of the existing inline fibers [3, 4]. These fibers can be engineered for designing ultraflattened near-zero dispersion [5–7] or can be engineered to have ultranegative dispersion values near the communication wavelength [8–10]. Recently, there have been new types of cross-sectional geometry where air holes are
Designing an Ultra-Negative Dispersion Photonic Crystal Fiber with Square-Lattice Geometry
Partha Sona Maji,Partha Roy Chaudhuri
ISRN Optics , 2014, DOI: 10.1155/2014/545961
Abstract: We have theoretically investigated the dispersion characteristics of dual-core PCF, based on square-lattice geometry by varying different parameters. The fiber exhibits a very large negative dispersion because of rapid slope change of the refractive indices at the coupling wavelength between the inner core and outer core. The dependence of different geometrical parameters, namely, hole-to-hole spacing ( ) and different air-hole diameter ( ), was investigated in detail. By proper adjustment of the available parameters, a high negative dispersion value of 47,500?ps/nm/km has been achieved around the wavelength of 1550?nm. Our proposed fiber will be an excellent device for dispersion compensation in long-haul data transmission as being thousand times more than the available DCFs. 1. Introduction Photonic crystal fibers (PCFs) [1, 2] or Holey Optical Fibers offered a tremendous variety of possible geometries utilizing the shape, size, and positioning of air-holes in the microstructured cladding. The air-hole diameter ( ) and hole-to-hole spacing ( ) not only control the dispersion properties, but also the transmission and the nonlinear properties of the fiber as well. Achieving very high negative values of dispersion around the communication band has been the target for a long time [3–15]. The principle behind having a very large negative dispersion in these Dispersion Compensating Fibers (DCFs) being the coupling between two spatially separated asymmetric concentric cores which support two leaky modes: inner mode and outer mode. By proper design, mode matching can take place between these two modes at the desired wavelength. A few analyses have been performed to realize high negative dispersion with triangular lattice PCF [8–15]. In this work we have studied rigorously towards achieving high negative dispersion value with regular square lattice. Square-lattice-based PCF is superior to triangular-lattice PCF for certain properties [16, 17]. Square-lattice PCF shows wider range of single mode operation with the same / value compared to the triangular one [16]. The effective area of square-lattice PCF is higher than triangular one, making the former better for high power management [17]. Square-lattice PCF can better compensate the inline dispersion around the 1550?nm wavelength than the triangular-lattice PCF [17]. In recent times, a square-lattice PCF preform has been realized with a standard fabrication process, stack and draw, in order to study the localization and control of high frequency sound by introducing two solid defects in the periodic
Designing an ultra negative dispersion Photonic Crystal Fiber (PCFs) with square lattice geometry
Partha Sona Maji,Partha Roy Chaudhuri
Physics , 2014,
Abstract: In this article we have theoretically investigated the dispersion characteristics of dual-core PCF, based on square-lattice geometry by varying different parameters. The fiber exhibits a very large negative dispersion because of rapid slope change of the refractive indices at the coupling wavelength between the inner core and outer core. The dependence of different geometrical parameters namely hole-to-hole spacing (pitch) and different air-hole diameter (d) was investigated in detail. By proper adjustment of the available parameters, a high negative dispersion value of -47,500 ps/nm/km has been achieved around the wavelength of 1550nm. Our proposed fiber will be an excellent device for dispersion compensation in long-haul data transmission as being thousand times more than the available DCFs.
Geometrical parameters dependence towards ultra-flat dispersion square-lattice PCF with selective liquid infiltration
Partha Sona Maji,Partha Roy Chaudhuri
Physics , 2014,
Abstract: We have performed a numerical analysis of the structural dependence of the PCF parameters towards ultra-flat dispersion in the C-band of communication wavelength. The technique is based on regular square-lattice PCF with all the air-hole of same uniform diameter and the effective size of the air-holes are modified with a selective infiltration of the air-holes with liquids. The dependence of the PCF structural parameters namely air-hole diameter and hole-to-hole distance along with the infiltrating liquid has been investigated in details. It is shown that the infiltrating liquid has critical influence on both the slope and value of dispersion, while pitch only changes the dispersion value whereas air-hole diameter modifies the slope of the dispersion. Our numerical investigation establishes dispersion values as small as 0+-0.58ps/(nm-km) over a bandwidth of 622nm in the communication wavelength band (C-band). The proposed design study will be very helpful in high power applications like broadband smooth supercontinuum generation, ASE suppressed amplification etc.
A New Design of Ultra-Flattened Near-zero Dispersion PCF Using Selectively Liquid Infiltration
Partha Sona Maji,Partha Roy Chaudhuri
Physics , 2014,
Abstract: 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.
ASE suppression in Er3+ doped dual-core triangular lattice Photonic Crystal Fibers (PCFs) for communication wavelength
Partha Sona Maji,Partha Roy Chaudhuri
Physics , 2014,
Abstract: In this article, silica based triangular lattice PCF has been investigated towards both narrowband and broadband dispersion compensation for application in the communication wavelength. A dual core structure is obtained by introducing two different air-hole diameters in the cladding of the PCF. Dependence of individual structural parameters towards high negative dispersion (both narrowband and broadband) has been investigated in details with multipole mode based solver. The numerical investigation exhibits narrowband of very large negative dispersion of -37,300 ps/nm/km around the wavelength of 1550 nm. Present investigation also reports broadband dispersion values varying from -800 ps/nm/km to -2600 ps/nm/km over a 200 nm wavelength (1400 nm to 1600 nm) range, and kappa values near 300 nm, which matches well with standard single mode fiber. Using the principle of power transfer from the inner core to the outer core after the coupling wavelength, we have investigated possible design of ASE suppressed amplifier in which wavelengths after the coupling wavelength cannot be amplified as most of the power tunnel to the outer core, where doped ion does not exist.
Near-elliptic core triangular-lattice and square-lattice PCFs: a comparison of birefringence, cut-off and GVD characteristics towards fiber device application
Partha Sona Maji,Partha Roy Chaudhuri
Physics , 2014,
Abstract: 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.
Multi-Use Multi-Secret Sharing Scheme for General Access Structure
Partha Sarathi Roy,Avishek Adhikari
Computer Science , 2014,
Abstract: The main aim of this paper is to construct a multi-secret sharing scheme for general access structure in a trusted dealer model using suitable hash function and Lagrange's interpolation method. Even though, the proposed scheme is a multi-secret and multi-use one, each participant has to carry only one share. The suitable use of collision resistant one way hash function makes the scheme efficient and multi-use. Moreover, the scheme has a nice property that secrets, participants or qualified sets of participants may be added to or even may be made inactive dynamically by the dealer to get a new access structure without altering the shares of the existing participants in the old access structure. Finally, in the proposed scheme, both the combiner and the share holders can verify the correctness of the information that they are receiving from each other.

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