Optical phased array using phase-controlled optical frequency comb

Abstract

We developed an optical phased array using an optical frequency comb and demonstrated its proof-of-principle. Optical phased arrays have been actively developed in recent years as a technology that can control the wavefront of light without any mechanical devices like phased array radar. Conventional optical phased arrays have been implemented using optical integrated circuits, but it has been difficult to achieve broadband operation with simple control. This is because control and calibration of a large number of phase modulators are required for each wavelength, and the dispersion of the waveguide makes whole bandwidth phase control of ultrashort pulses difficult. In contrast, we have developed a novel optical phased array that realizes wavefront control of ultrashort pulses generated by mode-locked laser by phase control of the comb, using high controllability of the comb and an optical array antenna with free-space optics. This is achieved by simply controlling the ratio of the two radio frequencies of the comb to realize a broadband optical phased array while suppressing environmental fluctuations. Experiments demonstrated broadband optical dot scanning at an optical frequency by forming an optical dot pattern and suppressing the environmental fluctuation by controlling the comb frequency. This innovative optical technology enables direct control of wavefronts by optical frequencies, i.e. controlling transverse modes by longitudinal modes.