Examples of apparatus and methods are provided for controlling a bias in an optical modulator. An exemplary apparatus may comprise an optical modulator operable to modulate an optical signal. The optical modulation apparatus may comprise a photodetector disposed to receive at least a portion of the modulated optical signal. The optical modulation apparatus may comprise a bias controller coupled to both the optical modulator and the photodetector. The bias controller may be configured to receive a dither signal and to produce a bias feedback signal for the optical modulator. The bias feedback signal may be based on a ratio between an odd order harmonic signal of the modulated optical signal and an even order harmonic signal of the modulated optical signal.