Design of a mode-hop-free tunable external cavity diode laser with a PLZT electro-optic ceramic deflector

Abstract

ABSTRACT A stable tunable external cavity diode laser (ECDL) which uses an intracavity electro- optic deflector incorporated into a Littrow-type external cavity as a wavelength tunable element is proposed. The deflector comprises an antireflection-coated rectangle Lead Lanthanum Zirconate Titanate (PLZT) electro-optic ceramic with a pair of parallel trapezoidal electrodes on the up and down surfaces, which can simultaneously change the cavity length and the beam-grating angle to achieve mode-hop-free tuning. The theory for mode-hop-free tuning will be presented in this paper, and the model calculations predict that the laser can be tuned continuously by as much as 110GHz. This new approach is simple in structure with no mechanical moving parts and has potential configuration of compact grating-stabilized ECDL. Keywords: Laser tuning, Mode-hop-free, Electro-optic defl ectors, External cavity diode laser, Ceramics 1. INTRODUCTION Due to the merits of single-mode, narrow-linewidth, fine tuna bility and large tunable range, external cavity diode lasers (ECDLs) have found more and more applications in high resolution spectroscopy, synthetic aperture laser radar, optical communication systems, and so on [1~3]. Usually, the wavelength of ECDLs is usually tuned by rotating a diffraction grating in the Littrow configuration [4] or a mirror in the Littman–Metcalf configuration [5] via a piezo-electrical actuator. Continuous single-mode scanning without mode hopping can be achieved by synchronous tuning of external cavity modes and grating selectivity [6]. However, the modulation frequency and reliability are restricted by the movement mechanical construction of the laser system. To avoid the drawbacks referred above, using a deflector as the tuning element without moving component in the extended cavity appears to be more attractive, among which the electro-optic crystal (EOC), acousto-optic modulator (AOM), and nematic liquid-crystal (NLC) deflectors have had a large development [7~10]. However, the mode-hop-free tuning range is limited to 10 GHz because of limitation of the high driving voltage, as reported in reference [7]. Although using two AOMs or NLC can achieve wider tuning rage (including mode hops), up to 225GHz for AOMs [9] and 12nm for NLC [10], these kinds of tuning have a drawback in application for high repetition rates.