Optical arbitrary waveforms are complex ultrashort laser pulses used for a variety of experiments in chemistry and telecommunications. Although such waveforms are typically produced using Fourier transform pulse-shaping techniques in which 1) the spectral components of a comb source are independently modulated and 2) the phase and amplitude components are updated at the repetition rate of the source, these conditions are difficult to satisfy at the same time using existing techniques. But engineers at the College of Optics and Photonics at the University of Central Florida (CREOL; Orlando, FL) have demonstrated line-by-line pulse shaping at update rates of up to half the repetition rate of the comb source using vertical cavity surface-emitting lasers (VCSELs) as modulators.
First, comb lines from an optical frequency-comb source are demultiplexed into four separate optical fiber channels. The 6.25 GHz frequency separation of the comb lines matches the channel spacing of the demux-mux pair. Then, the comb line in each channel is independently modulated by an optically injection-locked VCSEL, whose current is modulated using an RF source at frequencies up to 3.125 GHz. The modulated comb lines are then multiplexed into a single output fiber, generating 1.28 ns period complex waveforms (with a shape dependent on the VCSEL modulation) due to the coherent combination of the modulated light. Contact Peter Delfyett at [email protected].
