Tunable Optical Equalizer Using Diffraction Grating Filters

A tunable bandpass filter is constructed using patterned mirrors and a diffraction grating to serve as an optical equalizer. The frequency response of an intensity-modulated light source can be tailored by the passband profile of the equalizer to achieve a larger 3-dB bandwidth. We demonstrate that the 3-dB bandwidth of two LiNO
₃
modulators is increased from 10 and 25 GHz to 45 and >70 GHz, respectively, by applying the optical equalizer. We also show preliminary results on bandwidth enhancement of a direct-modulated vertical-cavity surface-emitting laser using the optical equalizer.