Optical Waveguide Theory

This chapter is a starting point to look around and see where you’re going before you dig into details. The goal is to put fiber optics and communications into context and show how they go together. I start with a personal commentary about the turbulent times of the past several years, then explain the plan for this book. A brief history of fiber optics follows, which introduces some important concepts. Then a brief history of communications explains the need for bandwidth and how fiber optics filled that need, perhaps too well. Finally, I explain some of the terminology of the field to help you in your looking about.

An Introduction to Fiber Optics

With an aim to explore the suitable refractive index profile for maximum coupling, we present a theoretical investigation of coupling optics involving a laser diode and single mode circular core graded index fiber via a hyperbolic microlens on the fiber tip in absence and presence of any possible transverse and angular misalignments. By employing Gaussian field distributions for both the source and the fiber and also ABCD matrix for hyperbolic 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 and 1.5 μm for such fibers with different profile exponents in refractive index profile. Further, it is observed that out of the studied refractive index profiles, the triangular index profile having the dispersion-shifted merit comes out to be the most suitable profile to couple laser diode to single mode circular core graded index fiber for two wavelengths of practical interest. The analysis should find use in ongoing investigations for optimum launch optics for the design of hyperbolic microlens either directly on the graded index circular core single mode fiber tip or such fiber attached to single mode fiber to achieve a long working distance.

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

This paper represents a spiral photonic crystal fiber (S-PCF) based optical sensor which exhibits high relative sensitive as well as low confinement loss simultaneously. The proposed PCF contains ten arms as well as each arm consists of nine circular air holes that forms spiral shape and core is formatted with circular holes filled with ethanol. Various geometrical parameters including diameters and pitches of the suggested S-PCF are tuned with the most efficient structure applying the full vectorial finite element method (FEM). Overall outcomes satisfy O + E + S + C + L + U (range of 1.26–1.675 μm) electromagnetic (EM) bands. The relative sensitivities of about 72.95%, 74.55% and 75.14% with ultra-low confinement loss of 1.85 × 10−10 dB/m, 4.62 × 10−11 dB/m and 6.35 × 10−11 dB/m are gained at the 1.33 μm wavelength for water (n = 1.33), ethanol (n = 1.354) and benzene (n = 1.366) analytes respectively. In addition, effective area, non-linear coefficient and V-parameter are also examined. Finally, the inquiry procedure depicts that the proposed S-PCF is highly capable in not only sensing applications but also high data traffic transmission applications.

Single-mode spiral shape fiber based liquid sensor with ultra-high sensitivity and ultra-low loss: Design and analysis

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.

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

We have sought a suitable coaxial refractive index profile with dispersion-flattened and dispersion-shifted criteria in the context of a single-mode Raman gain amplifier. We present a novel comparative study based on the effective core area and Raman gain coefficient in relation to the effect of aspect ratios of trapezoidal index profiles in the inner core on the Raman gain.

Comparative study of the influence of the aspect ratio of trapezoidal index profiles on the performance of a fiber Raman amplifier

A comparative study on fiber Raman gain amplifier performance for coaxial fiber structure having trapezoidal index profile with dispersion shifted criteria in inner core is presented to search for the suitable refractive index profile where single pump wavelength is used. The upper base and lower base of the trapezoidal profile with their ratio, known as aspect ratio, are adjusted to obtain the same phase matching condition for different core radii. The gain performance is analyzed for various core radii. The entire analysis reported for the first time shows that depending upon the fiber parameters the step profiles in the inner core structure perform as the most suitable candidate with a high tolerance for near step profiles.

Step index profile coming out as the best choice for the inner core in fiber Raman gain amplifier under fixed phase matching condition

Accurate knowledge of spot size, an important criterion in single-mode fiber optics, is obtained by two different optimization techniques, the well-known variational method and Marcuse formulation. The later is more accurate but cannot predict fiber parameters from given spot sizes. In this study, it is shown for the first time to the best of our knowledge that using simultaneously Marcuse relations of fiber spot sizes for single-mode graded index fibers and also variational formulation, we can more accurately and easily determine the fiber parameters for a particular normalized frequency. Then it is shown with typical example of fractional power in the core that in the case of such fibers, this synthesis of these two useful approaches can also more accurately estimate propagation characteristics of practical interest. This equivalence provides an easy and useful connection between two fundamental but disjoint approaches and should find wide use.

A simple and elegant technique connecting Marcuse spot size relations to variational formulations in single-mode fiber characterization

Effect of dip in refractive index profile on fiber Raman gain amplifier performance

The propagation characteristics of doped fiber amplifier have, already, been analyzed using simple coupled-mode analysis (CMA), which steers the interests to apply this simple theory to study the amplification performance of fiber Raman gain amplifier (FRGA) But such study is yet to be done for FRGA In this paper, a premier report based on CMA is presented to analyze and predict the performance of FRGA for first time, as per our knowledge, using coaxial structure consisting of step-index profiles in both inner and outer cores in terms of effective area, Raman gain coefficient, and effective Raman gain coefficient In our investigation, we use single pump to compute and compare our results with the results obtained by involved matrix method and a fairly excellent match over a wide region of frequency shift is reported

Sanchita Pramanik

Papers

Comparative study of the influence of the aspect ratio of trapezoidal index profiles on the performance of a fiber Raman amplifier

Step index profile coming out as the best choice for the inner core in fiber Raman gain amplifier under fixed phase matching condition

A simple and elegant technique connecting Marcuse spot size relations to variational formulations in single-mode fiber characterization

Effect of dip in refractive index profile on fiber Raman gain amplifier performance

Fiber Raman gain amplifier performance study using simple coupled-mode analysis