High-reliability, miniature liquid crystal variable optical attenuator

Author: J.J. Pan, Haiming Wu, Paul Huang, Xiangdong Qiu, Feng Qing Zhou Publication: Printed in NFOEC2002, Sept.15-19, Dalas, Texas, pp1197-1203

Abstract: Variable Optical Attenuators (VOA) play a key role in today's Dense WDM optical networks. Evolving from simple point-to-point single wavelength links, today's multi-wavelength Dense WDM optical networks are dynamic in nature: optical signals are dynamically added to and dropped from existing traffic, while the existing optical traffic is re-routed through the optical switch. As a result, optical power levels within such networks change dynamically over time. Since these power variations can cause significant degradation in network performance, components such as variable optical attenuators are needed to manage and control the optical power so that the system can be maintained in optimum condition.

Although VOAs have been developed using several different technologies, such as mechanical, Micro-Electro-Mechanical-System (MEMS), magneto-optical, thermal-optical and liquid crystal, not all of these technologies can meet the stringent requirements of today's Dense WDM network applications. As the typical optical channel count of DWDM systems continues to grow, so too is the number of VOAs required by these systems growing. For this reason, VOAs not only need to meet traditional performance requirements such as low insertion loss, low polarization dependent loss (PDL), and low wavelength dependent loss (WDL), but they also need to be compact, low cost and electrically efficient (low power consumption) to be suitable for use in high channel count systems.

Liquid crystal materials have drawn considerable interest in the construction of telecom devices due to their excellent optical performance, environmental stability and long-term reliability demonstrated through decades of use in the display industry [1-2]. More importantly, since an LC cell can manipulate an optical signal through electrical voltage control, the power consumption of a VOA based on such technology can be very low.

In this paper, we report on a newly developed variable optical attenuator based on Liquid Crystal (LC) technology. As the results presented in this paper shows, this LC VOA is very compact in size, provides excellent optical performance and is extremely stable under external stress.