Lossy mode resonances in photonic crystal fibers

Abstract

The interaction effect of the fundamental mode in a special photonic crystal fiber (PCF) with a thin-film absorbing coating deposited on a surface of a fiber cladding on the optical transmission of the PCF is theoretically studied. It is shown that the transmission has a multi-peak spectrum that is determined by the resonance capture of the fundamental PCF mode energy by the coating. In some cases, this capture is explained by a resonance coupling between the fundamental core mode and leaky modes of the coating, or between the fundamental PCF mode and cladding modes located between PCF air channels and the coating. Examples are presented of using this effect to develop fiber-optic sensors of refractive index or pressure, and to sense a nanoscale adsorption layer of ammonia molecules deposited on a coating surface contacting air.

Fourier analysis of modes of microstructured optical fibers

“…3, the closeness of the indicated values Re β is explained by the fact that the fields of fundamental MOF modes are well localized in the core of the fiber and weakly interact with the outer boundary of the fiber [5]. At the same time, this interaction leads to the formation of standing waves between the air channels and the boundary r = ρ 0 , which significantly affects the damping of the modes caused by radiation leak from the fiber core [10]. According to Table 3 this effect leads to increase in mode dichroism, which opens up the possibility of creating the single-mode single-polarization fibers for telecommunication and sensor applications.…”

“…According to Table 3 this effect leads to increase in mode dichroism, which opens up the possibility of creating the single-mode single-polarization fibers for telecommunication and sensor applications. The resonant nature of this effect [10] leads to nonmonotonic dependences Im β(λ), shown in Fig. 4 by dashed lines.…”

“…The derivatives ∂H z /∂n ′ and ∂ Ēz /∂n ′ entering into them differ from the analogous derivatives in (10) and (12) in that they are calculated striving to the interface of media from opposite sides. It follows from the continuity conditions for the tangential components of the electric and magnetic fields at these interfaces that…”

“…The values N = 18, ε s = 1.45 2 , ε j = 1 ( j = 1, N) and proportions ρ 0 / = 30.85, ab/ 2 = 0.06, typical for quartz single-mode MOFs [10,20] Calculations shown that in the case of MOFs the direct numerical solution of equation (59) runs into the problem of the computed values det M going beyond the computer word length. A similar defect, caused by the multiplication of the set of Hankel functions, was already noted in [5] in the study of MOF with circular inclusions.…”

“…Various ways to overcome these difficulties are discussed in [1][2][3][4]. As applied to MOFs, the corresponding results were obtained without taking into account the interaction of their modes with the outer boundary of fiber, which can significantly affect the attenuation of the modes [5,9,10]. This limitation can be overcome using the Green's function method [5].…”