Abstract. The resonance excitation of an optical fiber actuated by a conductive wire is studied in this paper. A novel approach based on exciting the micro-cantilever fiber at a location close to its base is proposed for this purpose. Analytical modeling is conducted on the mechanical models of this system in order to predict its behavior. The continuous Euler-Bernoulli beam equation with the effect of surrounding fluid medium is formulated as a boundary value problem. The natural frequencies of the system and its harmonic response are expanded analytically, and results are verified using Finite Element analysis. The obtained analytical solutions are used to draw conclusions on the response of the system and suggestions to optimize its performance are presented. In order to verify the idea in practice, an experimental setup that can closely resemble the system under consideration is made in the laboratory and its response to a periodic input with different frequencies are recorded. Comparison between the results of analytical formulation and experimental observations highlights the effectiveness of suggested technique in resonance vibration of optical fibers.
Keywords: micro-electro-mechanical systems (MEMS), micro-cantilever beam, thermal excitation, harmonic response, resonance vibration.
Optical fibers are widely used in various applications in high-tech industries such as telecommunication. Scanning fiber endoscopy is one of the emerging areas for using fiber optics in advanced applications for bio-medical image acquisition purpose [1-3]. In this method, optical fiber is used as a micro-cantilever vibrating at relatively high frequencies. Currently, fibers are actuated using methods such as high voltage electro-static force [4, 5], magnetic actuation , and piezoelectric effects . Electro-static and magnetic actuations require multiple components to induce their corresponding field and isolate it from external noises. In addition, is usually requires high voltage to maintain the electric/electromagnetic field . On the other hand, using piezoelectric actuators restricts material choices to a handful of options and requires complicated and high cost methods for manufacturing such as depositing .
The main goal of this research is coming up with an alternative method for actuation of optical fibers in relatively high frequency to achieve large amplitude of deflection at the tip point. Amongst potential options, use of thermal actuation through a novel technique is explored. Advantages of thermal actuation include: (1) higher forces and displacement can be achieved by applying smaller voltage; (2) there is more flexibility in material selection: thermal actuators can be manufactured from most metals; (3) generally it relies on simple principles that reduces the complexity of the system substantially (for instance there is no need for coils to induce magnetic field, or directionality of crystals for PZT).
Although the thermal expansion/contraction cycles from actuator can provide the micro-cantilever with enough perturbation to induce vibrations, the amplitudes of these vibrations are relatively small keeping in mind the magnitude of thermal expansion coefficients in conventional materials, and the range of temperatures that are acceptable. Generally, operating under resonance frequency is a common technique for increasing the displacement amplitudes in vibration of MEMS devices . Resonance vibrations can...