Compact thin film lithium niobate folded intensity modulator using a waveguide crossing

Abstract

A small footprint, low voltage and wide bandwidth electro-optic modulator is critical for applications ranging from optical communications to analog photonic links, and the integration of thin-film lithium niobate with photonic integrated circuit (PIC) compatible materials remains paramount. Here, a hybrid silicon nitride and lithium niobate folded electro-optic Mach Zehnder modulator (MZM) which incorporates a waveguide crossing and 3 dB multimode interference (MMI) couplers for splitting and combining light is reported. This modulator has an effective interaction region length of 10 mm and shows a DC half wave voltage of roughly 4.0 V, or a modulation efficiency (Vπ ·L) of roughly 4 V·cm. Furthermore, the device demonstrates a power extinction ratio of roughly 23 dB and shows .08 dB/GHz optical sideband power roll-off with index matching fluid up to 110 GHz, with a 3-dB bandwidth of 37.5 GHz.

Integrated Lithium Niobate Intensity Modulator on a Silicon Handle With Slow-Wave Electrodes

“…G LOBAL networking traffic continues to grow past the capabilities of current infrastructure while existing systems become slow, inefficient and unreliable [1]. As coaxial transmission lines are upgraded to support the next communication standard and cellular towers reinforced to support their weight, a band-aid is applied to a deeper issue: existing hardware that supports these systems has reached the limit of its capabilities and must be replaced not only to maintain stable operation, but to raise the technological "ceiling" and pave the way for the faster, more reliable and more secure networks of the future.…”

“…material, while electro-optic modulation takes advantage of the non-linear optical properties of a crystal to modulate a beam of light within an applied electric field [3], [4]. EO modulators show increased bandwidth, lower voltage operation, increased extinction ratio (ER), higher spurious-free dynamic range, zero chirping and increased power handing capability over their free-carrier dispersion counterparts [1]- [6]. Thin-film lithium niobate (LiNbO 3 ) on insulator (TFLNOI) is chosen as the electro-optic medium for it's high second-order non-linearity (χ (2) ), low third-order non-linearity (χ (3) ), low optical absorption, and exceptional environmental stability [1], [3], [4].…”

“…EO modulators show increased bandwidth, lower voltage operation, increased extinction ratio (ER), higher spurious-free dynamic range, zero chirping and increased power handing capability over their free-carrier dispersion counterparts [1]- [6]. Thin-film lithium niobate (LiNbO 3 ) on insulator (TFLNOI) is chosen as the electro-optic medium for it's high second-order non-linearity (χ (2) ), low third-order non-linearity (χ (3) ), low optical absorption, and exceptional environmental stability [1], [3], [4]. TFLNOI offers tighter mode confinement leading to a smaller footprint, and improved voltage-bandwidth performance over bulk LiNbO 3 devices [3], [6], [7].…”

“…TFLNOI offers tighter mode confinement leading to a smaller footprint, and improved voltage-bandwidth performance over bulk LiNbO 3 devices [3], [6], [7]. To guide a tightly-confined optical mode and support the use of an on-chip fiber-coupler at the end facets of the device, silicon nitride (SiN x ) is chosen as the ideal candidate to form a low-loss strip-loaded waveguide on the TFLNOI [1], [5].…”

“…In previous work, co-planar waveguide (CPW) electrodes have been used to apply the RF modulating signal [1], [5], [6]. To closely match the RF phase and optical group index (n RF and n og ), an index matching epoxy (Masterbond™ UV15) is applied to the interaction region between the signal and ground electrodes [1], [5]. However, the presence of the epoxy nearly doubles the RF loss (α RF ) over 100 GHz compared to a standard, unmatched CPW [1].…”