A demultiplexer for use in a wavelength-division multiplexed optical system including a first positive lens group, a negative lens group, and a second positive lens group in order from a dispersive element and a reflective element. In some embodiments the reflective element is a light modulator, such as an actuatable diffraction grating. In some embodiments the demultiplexer is a part of a dynamic channel equalizer. In embodiments having a light modulator, the modulation may occur during both a first pass and a second pass.