[11p-N404-1~9] 4.6 Terahertz Photonics

▲ [11p-N404-3] Terahertz Emission from Titanium-diffused Magnesium Oxide-doped Lithium Niobate Optical Waveguides

〇(P)Joselito Echavez Muldera¹, Jessica Pauline Castillo Afalla², Takashi Furuya¹, Hideaki Kitahara¹, Elmer Surat Estacio³, Katsuhiko Saito⁴, Qixin Guo⁴, Masahiko Tani¹ (1.Fukui University, 2.Tsukuba University, 3.UP Diliman, 4.Saga University)

Keywords:terahertz emitters, optical waveguides, nonlinear optical crystals

Titanium-diffused lithium niobate waveguides are well known for their use in integrated optical circuits but find little use in terahertz applications. In this work, we show that Ti-diffused MgO-doped lithium niobate (Ti:MgLN) strip waveguides can also be terahertz emitters and amend this oversight. Titanium-diffusion was done on an X-cut magnesium oxide-doped lithium niobate plate with dimensions 10 mm x 10 mm and thickness = 0.5 mm. Titanium was deposited along the Y-direction by electron beam deposition using a 40-µm wide opening in a lithographic mask to create a stripe pattern with a length of 10 mm and a thickness of 100 nm. This was then annealed at a temperature of 1050°C for 10 h in Ar gas to diffuse the Ti. To generate the terahertz pulses, the strip waveguide was excited with a 1.55-µm wavelength ultrafast pulsed laser source with an average power of 21 mW. A lens of focal length f = 30 mm was used to focus the beam onto the waveguide facet. The prism-coupled Cherenkov-phase matching configuration in a terahertz time-domain spectroscopy system was used to extract the generated terahertz waves, with a silicon prism as the outcoupler and a photoconductive antenna as the detector. A near-single cycle terahertz time-domain pulse was observed. To assess the waveguiding, the contrast between emissions from the waveguide and bulk of the sample while moving vertically along the facet was measured; an enhancement of ~18% in the time-domain signal was seen. This is due to the pump being confined in smaller space and resulting in a more efficient conversion from optical to terahertz frequencies. The insertion loss of the waveguide using the output power from the transmitted central maxima against the pump power was 10.6 dB, indicative of the small difference in the THz signals. The result proves the feasibility of titanium-in-diffusion for strong terahertz waves from Ti:MgLN waveguides and it can be an option for other emitters available in the market.