Phase-locked-loop-based delay-line-free picosecond electro-optic sampling system

Abstract

A delay-line-free, high-speed electro-optic sampling (EOS) system is proposed by employing a delay-time-controlled ultrafast laser diode as the optical probe. Versatile optoelectronic delay-time controllers (ODTCs) based on modified voltage-controlled phase-locked-loop phase-shifting technologies are designed for the laser. The integration of the ODTC circuit and the pulsed laser diode has replaced the traditional optomechanical delay-line module used in the conventional EOS system. This design essentially prevents sampling distortion from misalignment of the probe beam, and overcomes the difficulty in sampling free-running high-speed transients. The maximum tuning range, error, scanning speed, tuning responsivity, and resolution of the ODTC are 3.9π (700°), <5% deviation, 25–2405 ns/s, 0.557 ps/mV, and ∼1 ps, respectively. Free-running wave forms from the analog, digital, and pulsed microwave signals are sampled and compared with those measured by the commercial apparatus.