Abstract: A tunable wavelength filter is independent of the polarization. The filter includes first and second liquid crystal layers. Each liquid crystal layer includes two opposing glass substrates on which transparent electrodes, dielectric mirrors and alignment layers are coated in this order, respectively, and a liquid crystal interposed between the opposing alignment layers. In the first liquid crystal layer, the molecule alignment of the liquid crystal is twisted by n.pi./2 radian to one twisting direction where n is a positive uneven number. In the second liquid crystal layer, the molecule alignment of the liquid crystal is twisted by -n.pi./2 radian to the twisting direction. The first and second crystal layers are laid to overlap each other so that an axis of liquid crystal molecules on the emission side of the first liquid layer is perpendicular to an axis of liquid crystal molecules on the incidence side of the second liquid crystal layer.