Ultra-smooth LiNbO3 micro and nano structures for photonic applications

Abstract

International audienceWe report on two approaches to achieve ultra-smooth structures on lithium niobate (LiNbO3) substrates. The first method relies on ICP-RIE (inductively coupled-reactive ionic etching) or on RIE, and is exploited here for the fabrication of rods with smooth etched surfaces. A series of tests have been performed with fluorine gases. Nanometric rods with 200, 400 or 600 nm diameters, with a periodicity of 400, 800 and 1200 nm respectively and etched angles close to 68 for the RIE process and 75 for the ICP-RIE process have been fabricated. The second process is based on ''optical grade dicing'' and is dedicated to the fabrication of deep-etched ridge waveguides. First optical characterization results are reported. They show optical propagation losses value close to 0.1 dB/cm

Nanoscale pillar hypersonic surface phononic crystals

“…Much research effort has therefore been invested into developing techniques for etching LiNbO 3 . These include wet etching with hydrofluoric acid (HF) [41][42][43] as well as dry etching using masked ion milling and direct write focused ion beam (FIB) milling [44], reactive ion etching [45,46], and plasma enhanced etching [40]. The latter dry etching techniques, in particular, have been shown to be effective for producing submicron structures, although redeposition of LiF and NbF x on the sidewalls tends to prevent material removal [47], yielding imperfections [40,45].…”

“…Wet etching, on the other hand, can be effective [41,42], although effective masking to prevent undercutting can be problematic, particularly for long etches with small features [48]. Two-dimensional structures etched into lithium niobate have been reported [42,46], however, none have sufficient precision or aspect ratio to enable phononic crystal behavior. Conversely, larger micron-scale phononic crystals have been reported in LiNbO 3 [49], but these structures can only achieve phononic band-gap behavior at near-GHz frequencies, far below the multi-GHz hypersonic frequencies required for strong nanophotonic-phononic interactions.…”

Deep anisotropic LiNbO3 etching with SF6/Ar inductively coupled plasmas

“…Wet etching, combined with a variety of methods, including proton exchange, 7 ion implantation, 8,9 metal deposition, 10,11 and domain inversion 12 has been reported to fabricate ridge LiNbO 3 waveguides in recent decades. [18][19][20][21] In this study, we also use the proton exchange (PE) technique to reduce the concentration of Li ions in the LiNbO 3 surface, a) Author to whom correspondence should be addressed; electronic mail: adanner@nus.edu.sg leading to less redeposition of LiF and an improved etching rate. The poor anisotropic property of wet etching is also a drawback.…”

Lightwave Circuits in Lithium Niobate through Hybrid Waveguides with Silicon Photonics

“…Lithium Niobate (LN) was once considered the most promising of materials for integrated optics 1 , but despite a rich set of properties, the technology of LN integrated optics has not evolved as much as integrated optics in III-V semiconductors and silicon (Si) photonics 2 3 . Although high performance stand-alone LN devices have been shown 4 5 and a technique of ion-sliced thin-film LN has been developed 6 7 8 , the technology of LN integrated optics has continued to rely on traditional waveguide fabrication techniques based on ion-exchange 9 , diffusion and serial writing 10 or mechanical sawing 11 12 , all of which are very different from the modern lithographic techniques and foundry processing available in Si or III-V photonics.…”