ABSTRACT
Thin-film lithium niobate (TFLN) is a promising electro-optic (EO) photonics platform with high modulation bandwidth, low drive voltage, and low optical loss. However, EO modulation in TFLN is known to relax on long timescales. Instead, thermo-optic heaters are often used for stable biasing, but heaters incur challenges with cross-talk, high power, and low bandwidth. Here, we characterize the low-frequency (1â mHz to 1â MHz) EO response of TFLN modulators, investigate the root cause of EO relaxation and demonstrate methods to improve bias stability. We show that relaxation-related effects can enhance EO modulation across a frequency band spanning 1kHz to 20kHz in our devices - a counter-intuitive result that can confound measurement of half-wave voltage (V π) in TFLN modulators. We also show that EO relaxation can be slowed by more than 104-fold through control of the LN-metal interface and annealing, offering progress toward lifetime-stable EO biasing. Such robust EO biasing would enable applications for TFLN devices where cross-talk, power, and bias bandwidth are critical, such as quantum devices, high-density integrated photonics, and communications.
ABSTRACT
Bridging the "terahertz gap" relies upon synthesizing arbitrary waveforms in the terahertz domain enabling applications that require both narrow band sources for sensing and few-cycle drives for classical and quantum objects. However, realization of custom-tailored waveforms needed for these applications is currently hindered due to limited flexibility for optical rectification of femtosecond pulses in bulk crystals. Here, we experimentally demonstrate that thin-film lithium niobate circuits provide a versatile solution for such waveform synthesis by combining the merits of complex integrated architectures, low-loss distribution of pump pulses on-chip, and an efficient optical rectification. Our distributed pulse phase-matching scheme grants shaping the temporal, spectral, phase, amplitude, and farfield characteristics of the emitted terahertz field through designer on-chip components. This strictly circumvents prior limitations caused by the phase-delay mismatch in conventional systems and relaxes the requirement for cumbersome spectral pre-engineering of the pumping light. We propose a toolbox of basic blocks that produce broadband emission up to 680 GHz and far-field amplitudes of a few V m-1 with adaptable phase and coherence properties by using near-infrared pump pulse energies below 100 pJ.