Actively-monitored periodic-poling in thin-film lithium niobate photonic waveguides with ultrahigh nonlinear conversion efficiency of 4600 %W⁻¹cm⁻²

Rejuvenating a Versatile Photonic Material: Thin‐Film Lithium Niobate

“…One of the main advantages of this method is the ease of processing. Several materials have been pursued in this regard, such as tantalum pentoxide (Ta 2 O 5 ), [29] chalcogenide glass (ChG), [70] silicon nitride (SiN, Si 3 N 4 ), [41,71,72,81,85,100,101,124] and titanium dioxide (TiO 2 ), [40] with reported propagation loss values as low as ∼1 dB cm −1 for plasma-enhanced chemical-vapor deposition Figure 3a), [71] dry-etched ( Figure 3b), [75,78] and SOI-bonded ( Figure 3d) [76,77,80,84] methods, while for nonlinear devices, rib-loaded [100,101] and dry-etched [102,105] have been the most commonly employed platforms. In comparison to platforms (a)-(c), platform (d) requires additional bonding and TFLN substrate removal steps.…”

“…[120] As depicted in Figure 3b, dry-etched waveguides have been also utilized for TFLN EO modulators (EOMs) [73][74][75]78] and nonlinear devices. [100][101][102]105] For EOMs, in comparison with rib-loading, this approach provides higher optical confinement in LN, which can consequently result in smaller electrode gaps in MZ-based devices, hence reducing the EOM's V . However, in the presence of certain requirements due to ultrahigh-speed design, the ribloaded method is more advantageous due to the lower dielectric constant of the rib compared to that of LN.…”

“…It is noted that among the above mentioned structures, most of the recently-demonstrated high-performance TFLN EOMs have utilized rib-loaded, [71] dry-etched, [75,78] and SOI-bonded [76,80] methods integrated on Si substrate. For nonlinear LN devices, rib-loaded [100,101] and dry-etched [102,105] methods have been employed so far.…”

“…TFLN platform is an excellent alternative that avoids the limitations of the predecessor approaches and demonstrates more compact and more efficient nonlinear integrated devices. On this platform, by employing rib-loading (see Figure 3a), [100,101] or direct-etching (see Figure 3b) [102,105] methods, high index contrast, and hence tight optical mode confinement, efficient modal overlap integral, and ultrahigh nonlinear conversion efficiency can be achieved. A variety of efficient nonlinear integrated devices have been recently demonstrated on this platform by various research groups, as elaborated in this section.…”

“…converters, [100][101][102][103][104][105][106][107][108][109][110][111] and entangled-photon sources [112][113][114][115][116] with significantly superior performances than their conventional LN counterparts have been demonstrated. The overall efforts have rejuvenated LN for novel electro-, nonlinear-, and quantum-optic applications and the material is considered among the top candidates for heterogeneous integrated photonics, where multiple materials are monolithically integrated on a single chip, while each material is chosen for the functionalities that suits it best.…”