Advancing large-scale thin-film PPLN nonlinear photonics with segmented tunable micro-heaters

Thin-film periodically poled lithium niobate(TF-PPLN)devices have recently gained prominence for efficient wavelength conversion processes in both classical and quantum applications.However,the patterning and poling of TF-PPLN devices today are mostly performed at chip scales,presenting a significant bottleneck for future largescale nonlinear photonic systems that require the integration of multiple nonlinear components with consistent performance and low cost.Here,we take a pivotal step towards this goal by developing a wafer-scale TF-PPLN nonlinear photonic platform,leveraging ultraviolet stepper lithography and an automated poling process.To address the inhomogeneous broadening of the quasi-phase matching(QPM)spectrum induced by film thickness variations across the wafer,we propose and demonstrate segmented thermal optic tuning modules that can precisely adjust and align the QPM peak wavelengths in each section.Using the segmented micro-heaters,we show the successful realignment of inhomogeneously broadened multi-peak QPM spectra with up to 57%enhancement of conversion efficiency.We achieve a high normalized conversion efficiency of 3802%W-1cm-2in a 6 mm long PPLN waveguide,recovering 84%of the theoretically predicted efficiency in this device.The advanced fabrication techniques and segmented tuning architectures presented herein pave the way for wafer-scale integration of complex functional nonlinear photonic circuits with applications in quantum information processing,precision sensing and metrology,and low-noise-figure optical signal amplification.

Broadband adiabatic polarization rotator-splitter based on a lithium niobate on insulator platform

Polarization rotator-splitters(PRSs)are crucial components for controlling the polarization states of light in classical and quantum communication systems.We design and experimentally demonstrate a broadband PRS based on the lithium niobate on insulator(LNOI)platform.Both the rotator and splitter sections are based on adiabatically tapered waveguide structures,and the whole device only requires a single etching step.We show efficient PRS operation over an experimentally measured bandwidth of 130 nm at telecom wavelengths,potentially as wide as 500 nm according to simulation prediction,with relatively low polarization crosstalks of~-10 d B.Our PRS is highly compatible with the design constraints and fabrication processes of common LNOI photonic devices,and it could become an important element in future LNOI photonic integrated circuits.

Systematic investigation of millimeter-wave optic modulation performance in thin-film lithium niobate

Millimeter-wave(mmWave)band(30–300 GHz)is an emerging spectrum range for wireless communication,short-range radar,and sensor applications.mmWave-optic modulators that could efficiently convert mmWave signals into the optical domain are crucial components for long-haul transmission of mmWave signals through optical networks.At these ultrahigh frequencies,however,the modulation performances are highly sensitive to the transmission line loss as well as the velocity-and impedance-matching conditions,while precise measurements and modeling of these parameters are often non-trivial.Here we present a systematic investigation of the mmWave-optic modulation performances of thin-film lithium niobate modulators through theoretical modeling,electrical verifications,and electro-optic measurements at frequencies up to 325 GHz.Based on our experimentally verified model,we demonstrate thin-film lithium niobate mmWave-optic modulators with a measured 3-dB electro-optic bandwidth of 170 GHz and a 6-dB bandwidth of 295 GHz.The device also shows a low RF half-wave voltage of 7.3 V measured at an ultrahigh modulation frequency of 250 GHz.This work provides a comprehensive guideline for the design and characterization of mmWave-optic modulators and paves the way toward future integrated mmWave photonic systems for beyond-5G communication and radar applications.

High-Q lithium niobate microring resonators using lift-off metallic masks [Invited]

High-Q lithium niobate(LN) optical micro-resonators are an excellent platform for future applications in optical communications, nonlinear optics, and quantum optics. To date, high-Q factors are typically achieved in LN using either dielectric masks or femtosecond laser ablation, while the more standard and commonly available lift-off metallic masks are often believed to lead to rough sidewalls and lowered Q factors. Here, we show that LN microring resonators with strong light confinement and intrinsic Q factors over 1 million can be fabricated using optimized lift-off metallic masks and dry etching processes, corresponding to a waveguide propagation loss of ~0.3 d B=cm. The entire process is fully compatible with wafer-scale production and could be transferred to other photonic materials.

Broadband adiabatic polarization rotator-splitter based on a lithium niobate on insulator platform: publisher's note

The second paragraph in Section 2 of this article was corrected as follows.In the polarization rotator (Step I), the LN rib waveguide adiabatically widens from a top width of 1.2 to 3.6μm via a linear taper, such that the effective index of the second-order TE (TE;) mode surpasses that of the fundamental TM (TM;)mode [Fig. 1(c)].