Abstract
Finite element method is a powerful technique for solving a wide range of engineering problems. However, the existence of the spurious solutions in full-vectorial finite element method has been a major problem for both acoustic and optic modal analyses. For emerging photonic devices exploiting light-sound interactions in high index contrast waveguides, this problem is a major limitation. A penalty function is introduced to remove these unwanted spurious modes in acoustic waveguides, which also identifies the acoustic modes more easily. Numerically simulated results also show considerably improved vector mode profiles. The proposed penalty method has been applied for the characterization of low index contrast single mode fiber and also for high index contrast silicon nanowire to demonstrate its effectiveness.
Highlights
Stimulated Brillouin Scattering (SBS) is an important nonlinear optical effect that occurs due to the interaction of optical and acoustic waves in a medium
For high power fiber lasers, which have excellent properties, such as high beam quality, high efficiency, very high output power capability and ease of thermal management, the SBS is often considered as one of the main limitations [3]. To overcome this limitation SBS threshold level is required to be increased, which may be achieved by using different techniques, such as the modification of the fiber geometry in order to push the acoustic modes into cladding [4], use a higher effective area multimode fibers [5, 6] or doping fiber with anti-acoustic material to suppress SBS [7]
In order to study the effect of penalty term, first we have considered a low-index contrast single mode optical fiber (SMF) with a core radius of 4.1 μm
Summary
Stimulated Brillouin Scattering (SBS) is an important nonlinear optical effect that occurs due to the interaction of optical and acoustic waves in a medium. It was identified that as the vector formulation considered only two curl equations but did not consider the divergence-free nature of the field, which allowed spurious modes to appear As these spurious solutions introduce difficulties to identify physical modes and deteriorate eigenvector quality, different techniques have been considered to eliminate them. We used a penalty approach to modify the node element based acoustic wave variational formulation and successfully applied to eliminate the spurious acoustic modes in both low and high index contrast acoustic waveguides. The proposed penalty approach is tested for both low and high index contrast acoustic waveguides, reported in following sections
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