S.C. Saha

Bio: S.C. Saha is an academic researcher from Vidyasagar University. The author has contributed to research in topics: Graded-index fiber & Single-mode optical fiber. The author has an hindex of 4, co-authored 7 publications receiving 54 citations.

Laser Diode to Single Mode Circular Core Graded Index Fiber Excitation via Hemispherical Microlens on the Fiber Tip: Identification of Suitable Refractive Index Profile for Maximum Efficiency with Consideration for Allowable Aperture

Abstract: Abstract Based on the prescribed ABCD matrix for refraction by hemispherical lens under paraxial approximation, we formulate an analytical expression of coupling efficiency of a laser diode to a single mode circular core graded index fiber via a hemispherical lens on the tip of the fiber. The analysis involves Gaussian field distribution for both the source and the fiber and consideration of allowable aperture provided by the hemispherical lens. In order to find out the suitable refractive index profile for maximum coupling efficiency, we investigate the coupling optics for different profile exponents in graded index refractive index profile. In this context two different laser diodes emitting wavelengths 1.3 μm and 1.5 μm are employed for the concerned study. It is found that the graded index fiber having triangular refractive index profile is the most efficient one for the said two wavelengths of practical importance. Our formalism is simple and executable with little computation. The results found should be of tremendous importance to the designer of such coupling in the field of optimum launch optics.

Simple Method for Study of Single-mode Dispersion-shifted and Dispersion-flattened Fibers

Abstract: Employing the simple series expression based on Chebyshev technique, we predict the fundamental modal field inside the core as well as cladding in case of dispersion-shifted trapezoidal and dispersion-flattened graded and step W fibers. This formalism also estimates cladding decay parameters (W ) of the said fibers. The a nalysis involves use of a linear relationship of the ratio of first and zero order modified Bessel functions in the form 1 0 () () KW KW with 1/W over a wide and practical range of W values appropriate for guidance of only fundamental mode in such fibers. The present method prescribes ana- lytical expressions for the concerned propagation charac- teristics and these are executable with little computations. Our results are found to match excellently with the avail- able exact results.

Mismatch Consideration in Circular Core Mono-mode Graded Index Fiber of Triangular Refractive Index Profile Excitation via Hemispherical Microlens on the Fiber Tip

Abstract: Abstract We report what, as per our knowledge, is the first theoretical investigation of the excitation efficiency in presence of possible transverse and angular misalignments in case of single-mode circular core triangular refractive index profile fiber excitation by laser diode via hemispherical microlens on the fiber tip. The present analysis takes into consideration limited aperture allowable by the hemispherical lens. Using ABCD matrix for refraction of paraxial rays by a hemispherical microlens, we prescribe analytical expressions for the coupling efficiencies in presence of the said mismatches. The evaluation of the concerned efficiencies and associated losses will require little computations. The results found will be extremely useful in the field of optimum launch optics involving such coupler.

Prediction of First Higher Order Modal Field for Graded Index Fiber in Presence of Kerr Nonlinearity

Abstract: Abstract We report evaluation of first higher order modal field for dual mode optical fiber having step and parabolic index profiles. The study is carried out both in absence as well as in presence of Kerr nonlinearity. The analysis is based on a simple iterative method involving Chebyshev formalism. Taking some typical step- and parabolic-index fibers as examples, we show that our results agree excellently with the exact results which can be obtained by applying rigorous methods. Thus, our simple formalism stands the merit of being considered as an accurate alternative to the existing cumbersome methods. The prescribed formalism provides scope for accurate estimation of different propagation parameters associated with first higher order mode in such kinds of fibers in presence of Kerr nonlinearity. The execution of formalism being user friendly, it will be beneficial to the system engineers working in the field of optical technology.

Coupling of a laser diode to single mode circular core graded index fiber via parabolic microlens on the fiber tip and identification of the suitable refractive index profile with consideration for possible misalignments

Abstract: We present a theoretical investigation of coupling optics involving a laser diode and circular core graded index single mode fiber via a parabolic microlens on the fiber tip to predict the nature of suitable refractive index profile for the first time in connection with optimum coupling. The study is carried out in absence and presence of possible transverse and angular misalignments. By employing Gaussian field distributions for both the source and the fiber and also ABCD matrix for parabolic microlens under paraxial approximation, we formulate analytical expressions for the concerned coupling efficiencies. The investigations are performed for two different light-emitting wavelengths of 1.3 μm and 1.5 μm for such fibers with different refractive index profile exponents. Further, it is observed that out of the studied refractive index profiles, triangular index profile having the dispersion-shifted merit comes out to be the most suitable profile to couple laser diode to such abovementioned fiber for two wavelengths of practical interest. The analysis should find use in ongoing investigations for optimum launch optics for the design of parabolic microlens either directly on the circular core graded index single mode fiber tip or such fiber attached to single mode fiber to achieve long working distance.