The Development Of Tunable Filter

With the development of dense wavelength division multiplexing (DWDM)technology, channel density in fiber is higher and higher, the transmission rate isfaster and faster, optical fiber network is become more agile and flexible. As a kind ofcomponent that can separate certain wavelength from multiple wavelength, tunableoptical filter is one of indispensable components in flexible optical network, therefore,the tunable optical filter performance requirements is high. In addition to being able toachieve high bandwidth, high isolation, low insertion loss requirements, it alsorequires lower cost, long time reliability assurance. At present, the realization of thetunable filter mainly include liquid crystal display(LCD) based filter, acousto-opticmodulation based filter, grating based filter, etc., and these technologies are relativelydifficult to achieve all requirements at the same time when working in50GHzchannel spacing DWDM network. The bandwidth of the pass band isn’t enough whenkeep sufficient isolation. And temperature performance is difficult to meet therequirement. Because the multi-cavity thin film optical filter has the advantages ofgood temperature stability, wide tunable range, lower price, it has been widely used.But due to its polarization sensitive, in some applications, we need avoid to use itbecause of the polarization sensitivity.This article took the whole tunable optical filter(TOF) module as the researchobject, introduced the principle of the thin film optical filter. Through studied oncharacteristics of the filter, as well as its auxiliary light path, the electric circuit, thethin film tunable filter can be under effective control and can meet the requirement ofpractical optical network. At the same time, by researching on the theoretical of thefilter and the control method, we designed a tunable optical filter module. Accordingto the test results, the tunable filter can adapt to complex applications demand onDWDM network. This article also Analyzed the relationship between the incidenceAngle and the transmission wavelength, According to the sensitivity of therelationship between Angle and wavelength, designed a set of mechanical Anglecontrol system, used for high precision Angle adjustment. In view of the high demandfor tunable filter of absolute Angle, specially designed a method to get the absoluteangle position with two cheap optical-couplers, this absolute positioning system canreach to0.0025degrees repeatability. According to the design, we made a tunablefilter module for50GHz interval DWDM system. The performance such as pass bandbandwidth, isolation, tuning time and so on can meet the requirement of practicalapplication.