Tailoring inhomogeneous PT -symmetric fiber-Bragg-grating spectra

High Speed, Localized Multi-Point Strain Measurements on a Containment Vessel at 1.7 MHz Using Swept-Wavelength Laser-Interrogated Fiber Bragg Gratings

“…FBGs are sensitive to strain and temperature and have been used for many years [ 1 , 2 , 3 ]. The process for manufacturing the gauge is to write a periodic index change into a single mode fiber which can be done uniformly or non-uniformly [ 20 ]. The index change periodicity determines the reflected wavelength, λ, through the relation λ = 2nΛ, where Λ is the periodicity, and n is the refractive index of the fiber.…”

$N$-channel comb filtering and lasing in $\mathcal{PT}$-symmetric superstructures

“…Recently, discrete comb lasing modes were demonstrated in a topological PT -symmetric structure [1]. It should be noted that the broken PT -symmetric spectrum of any PTFBG feature a lasing behavior as reported by many authors [42,46,47,51,52]. The natural question arises from these investigations is that whether it is possible to realize discrete and identical lasing modes with the aid of a SFBG operating in the broken PTsymmetric regime.…”

“…This is possible because of the fact that the TMM approach allows computation of the output field of a short section of the grating in a single iteration [53]. In the subsequent iterations, the resulting matrix that represents the output fields from the previous section is taken as the input matrix for a given section and this process is repeated for n-number of cycles until the whole FBG is computed [46]. Another important reason to choose TMM over other methods (for modeling SFBG) is that the direct analytical solutions are tedious to calculate if the number of samples is large [33,53].…”

“…It is well-known that the real and imaginary parts of the RI profile, respectively, need to be even and odd functions of propagation distance (z) for a PT -symmetric FBG (PTFBG) [39,41,42]. Prior to this work, linear spectrum of homogeneous [39,41,44] and inhomogeneous PT -symmetric gratings [42,[45][46][47] were investigated and the literature seems to lack any comprehensive investigation on the linear spectrum based on sampled PTFBG. Nevertheless, the demonstration of frequency comb in a supersymmetric (SUSY) DFB structure by Longhi [48] could be translated into the context of PTFBGs.…”

Low-power optical bistability in $\mathcal{PT}$-symmetric chirped Bragg gratings with four-wave mixing

“…This notion would have remained as an unrealistic subject in real physical settings forever if not for the fact that the fundamental postulates of P T -symmetry can be translated from quantum mechanics to optics [26,37,38]. As far as FBGs are concerned, P T -symmetric structures reveal some atypical light propagation characteristics such as direction-dependent (linear) [29,[39][40][41][42][43][44], nonreciprocal (nonlinear) [45][46][47], and unidirectional [39] wave transport provided that the mathematical condition n(z) = n * (−z) for the refractive index is fulfilled by the structure via a precise equilibrium between gain and loss regions. Also, it is proven that different kinds of nonlinearity including Kerr modulation could essentially suppress the instability in certain P T -symmetric systems with equal amount of gain and loss [48,49].…”