In one example, an optical channel monitor includes a tunable filter, a deinterleaver, first and second optical receivers, and a control module. The tunable filter is configured to receive an optical signal having a plurality of channels spaced at a nominal channel spacing. The deinterleaver has an input with an input channel spacing Fi, an even output, and an odd output, the input being connected to an output of the tunable filter. The nominal channel spacing is between about one and two times the input channel spacing Fi. A −20 dB bandwidth of the tunable filter is between about two and four times the input channel spacing Fi. The first and second optical receivers are coupled to the deinterleaver even and odd outputs, respectively. The control module is coupled to the tunable filter and is configured to tune the tunable filter to a desired center frequency.