Tunable optical filter

[Subject] Offer reliable compact and cheap aligned type part light filter method and equipment. [Solution means] An aligned type optical filter including the arrangement of the filter element which can align independently is offered. Each of these elements is arranged along a different optical way extended between an input and an output port. Moreover, the optical assembly object for accepting the incidence optical signal for offering the filtered optical signal is offered. Polarization independent spectrum filtering is performed in the one case of the operation. Furthermore, addition/drops multiplexer which can choose a wavelength and a demultiplexer, a dynamic gain equalizer and an attenuator, optical channel interception and a branch filter, a switch, and a modulator are offered. Furthermore, the filter concerning the present invention is constituted and the method for making it operate is offered.