Visible to mid-infrared giant in-plane optical anisotropy in ternary van der Waals crystals

Abstract

Birefringence is at the heart of photonic applications. Layered van der Waals materials inherently support considerable out-of-plane birefringence. However, funnelling light into their small nanoscale area parallel to its out-of-plane optical axis remains challenging. Thus far, the lack of large in-plane birefringence has been a major roadblock hindering their applications. Here, we introduce the presence of broadband, low-loss, giant birefringence in a biaxial van der Waals materials Ta2NiS5, spanning an ultrawide-band from visible to mid-infrared wavelengths of 0.3–16 μm. The in-plane birefringence Δn ≈ 2 and 0.5 in the visible and mid-infrared ranges is one of the highest among van der Waals materials known to date. Meanwhile, the real-space propagating waveguide modes in Ta2NiS5 show strong in-plane anisotropy with a long propagation length (>20 μm) in the mid-infrared range. Our work may promote next-generation broadband and ultracompact integrated photonics based on van der Waals materials.

Symmetry-Engineering-Induced In-Plane Polarization Enhancement in Ta2NiS5/CrOCl van der Waals Heterostructure

“…We used polarization Raman spectroscopy to determine the lattice orientation of the material (Figures S2 and S3). Simultaneously, we combined the literature findings to confirm that the long-axis of Ta 2 NiS 5 was the a-axis, while the long-axis of CrOCl was referred to as the a-axis [22,25]. In order to enhance the interlayer coupling of the heterostructure and remove the residual adhesive on the heterostructure surface, we annealed the heterostructure at 325 • C for 1 h. Six pairs of electrodes with Cr/Au (10/70 nm) were fabricated using electron-beam lithography (Raith, Pittsburgh, Germany) and PVD75 e-beam evaporation (Kurt J. Lesker, Pittsburgh, Jefferson Hills, UT, USA).…”

Ultrastrong Coupling between Polar Distortion and Optical Properties in Ferroelectric MoBr2O2

“…The lines between the Γ and Y 2 as well as that between the Γ and V 2 have the largest DTM 2 values. Remarkably, the Cc phase of MoBr 2 O 2 exhibits a larger birefringence than several other compounds documented in the literature, such as Tl 3 AsSe 3 , GaSe, and α-MoO 3 , owing to its layered structure. This is important for enhancing the phase match and, in turn, the efficiency of nonlinear optics .…”

“…As shown in Figure 2c,d 71 such as Tl 3 AsSe 3 , 72 GaSe, 73 and α-MoO 3 , 74 owing to its layered structure. This is important for enhancing the phase match and, in turn, the efficiency of nonlinear optics.…”

Dispersion Engineering of In‐Plane Anisotropic Phonon Polaritons in hBN/Te van der Waals Heterostructures

“…For example, the very recently reported ternary biaxial crystal Ta 2 NiS 5 , with a large in-plane optical birefringence (∆n ≈ 2 in the mid-infrared region), holds promise for achieving an even stronger in-plane anisotropy of PhPs in the hBN van der Waals heterostructure. [47]…”