A variable optical attenuator is a key component for wavelength division multiplexing (WDM) transmission node power equalization, optical amplifier gain flattening, multiplexing point channel balancing, and receiving node power management in fiber optic communication. A fiber optic type variable optical attenuator has the advantages of simple structure, low insertion loss, low cost, and easy to interface with other optical fibers and waveguide structure, and is widely used. The adjustment accuracy and attenuation range are very important parameters of the variable optical attenuator, and there are few products with high adjustment accuracy and large attenuation range. In this paper, based on the traditional dislocation-type optical fiber variable optical attenuator with large dynamic range, the fluid pressure/pressure regulation is transformed into optical fiber micro-displacement control, which is easy to realize the micro-displacement precision control of optical fiber products to replace the high cost precision mechanical adjustment instrument of such products. In addition, the device meets the requirements of optical networks for attenuators, can work in a wide range of attenuation, and has low insertion loss and low wavelength-dependent loss, as well as compact structure,low cost, and high accuracy. According to the VOA optical power adjustment curve, film thickness can be selected to achieve configurable VOA optical attenuation accuracy.

The designed variable optical attenuator device is fabricated by ultra-precision processing technology. It contains components such as the polydimethylsiloxane (PDMS) elastic film, optical fiber carrying platform, and constant pressure pump. The adjustment of fluid pressure is transformed into micro-displacement control of the optical fiber by driving the ejection of the film through the fluid constant pressure pump, thus realizing the lateral dislocation of the docking fiber, and the optical attenuation is realized based on the dislocation of the ejected film driven by the fluid constant pressure pump and the docking fiber, while the adjustable accuracy of the optical intensity coupling efficiency is achieved by selecting the appropriate film thickness. We use the COMSOL Multiphysics software and three-dimensional finite difference time domain (FDTD) method to simulate and calculate the driving kinetic behavior and optical coupling efficiency of VOA, respectively. And in the experimental measurement stage, by replacing the film thickness of the device and adjusting the input pressure of the constant pressure pump, the trace mechanical dislocation and optical attenuation data are measured and the coupling efficiency is calculated, and then the relationship among the movement of the fiber-bearing platform, optical attenuation, and pressure control, and relationship between the wavelength-dependent loss and the optical attenuation of VOA with different film thickness and control pressure are derived. Finally, the relationship between the configuration of the film thickness and the precision of the variable optical attenuator is fitted numerically.

The experimental results show that the variable attenuation range of this attenuator is greater than 60 dB (Fig. 3) with an insertion loss of 1.24 dB (Fig. 5) and a wavelength-dependent loss less than 1 dB (Fig. 6) under appropriate film thickness conditions. The variable optical attenuator is used for repeatability experiments at the wavelength of 1550 nm with satisfied performance. The response time of the device is less than 50 ms. In order to study the influence of film thicknesses on the regulation accuracy of the configured VOA, the film thicknesses are set to 0.3 mm, 0.4 mm, and 0.5 mm, and the pressure interval is 12.2 Pa. The accuracy of the VOA is measured, and the worst regulation accuracy of the VOA with film thicknesses of 0.3 mm, 0.4 mm, and 0.5 mm can be obtained when the dynamic range of the VOA is 10 dB. When the dynamic range of VOA is set equal to or greater than 40 dB, there is an inflection point for the change of the slope of the curve, and the worst adjustment accuracy of VOA can be taken as 0.16 dB, 0.15 dB, and 0.11 dB respectively near the inflection point. When the dynamic optical attenuation range of the variable optical attenuator is set to 10 dB and 40 dB, the adjustment accuracy is better than 0.04 dB and 0.11 dB for a film thickness of 0.5 mm, respectively (Fig. 7). The tuning accuracy will be higher when the film thickness increases.

A variable optical attenuator with configurable adjustment accuracy is proposed to achieve transverse dislocation and optical attenuation of docked optical fibers by driving the film to pop up the fiber for lateral displacement. Both the numerical analysis and experimental measurement results show that the variable optical attenuator has an insertion loss of 1.24 dB, a return loss of -54 dB, a wavelength dependent loss of less than 1 dB, and a dynamic range of 60 dB. The thickness of the film of the device can affect the adjustment accuracy, and the relationship between the adjustment accuracy and the film thickness can be obtained by fitting the optical attenuation curve. This device can transform the adjustment of fluid pressure/pressure into precise control of transverse micro-displacement of fiber, which provides a new idea for the development of fiber optic products.