Terahertz waveform synthesis in integrated thin-film lithium niobate platform

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.

Scalable and efficient grating couplers on low-index photonic platforms enabled by cryogenic deep silicon etching

“…Although SOI is still -and will likely remain -the favorite choice for the optical communication sector, its limited transparency range, presence of two-photon absorption, and absence of second-order nonlinearities have motivated the development of PICs also on different materials. In this context, photonic platforms characterized by a refractive index ≃2 at telecom wavelength, such as silicon nitride (SiN) or thin-lm lithium niobate (TFLN), have stood out as new leading alternatives for applications involving the generation and manipulation of quantum states of light [22][23][24][25][26][27] , microcomb generation [28][29][30] , and high-speed optical signal processing [31][32][33] . Despite the refractive index substantially smaller than the one of silicon (n≃3.5 at λ = 1550 nm), their index contrast is still su cient for realizing compact PICs with bending radii of only few tens of micron.…”

Nonlinear THz Generation through Optical Rectification Enhanced by Phonon–Polaritons in Lithium Niobate Thin Films

“…22 Hybrid gold THz antennas on TFLN circuits demonstrated promising results for integrated tailored THz sources in the lower THz frequency range (<1 THz). 23 The TFLN platform holds great promise also for the development of efficient nonlinear metasurfaces. 16 These may provide the ultimate flexibility in terms of spatiotemporal control of the generated THz signals, as recently demonstrated using plasmonic metasurfaces.…”

“…In recent years, the emergence of the integrated thin-film LN (TFLN) technology led to many new developments and applications . Hybrid gold THz antennas on TFLN circuits demonstrated promising results for integrated tailored THz sources in the lower THz frequency range (<1 THz) . The TFLN platform holds great promise also for the development of efficient nonlinear metasurfaces .…”

Design of MZI electro-optic modulator on lithium niobate heterogeneous integration platforms

“…The precise processing of lithium niobate materials still poses challenges, which limits the further development of lithium niobate electro-optic modulators. There are some demonstrations that use hybrid optical modes formed by bonding LN to planarized silicon photonic waveguide circuits [3,[10][11][12][13][14] . These devices achieve 3-dB bandwidth greater than 100 GHz at 1550 nm, and a typical VπL product of 2~3 V•cm [1] .…”