Nonlinear optical waveguides generated in lithium niobate by swift-ion irradiation at ultralow fluences

Abstract

A novel method to produce optical waveguides is demonstrated for lithium niobate ͑LiNbO 3 ͒. It is based on electronic excitation damage by swift ions, i.e., with energies at approximately 1 MeV/ amu or above. The new technique uses high-energy medium-mass ions, such as Cl, with electronic stopping powers above the threshold value for amorphization ͑5-6 keV/nm͒, reaching the maximum value a few micrometers inside the crystal. At the ultralow fluence regime ͑10 12 -10 13 cm −2 ͒ an effective nanostructured medium is obtained that behaves as an optical waveguide where light propagates transversally to the amorphous nanotracks created by every single impact. The method implies a reduction of 4 orders of magnitude with respect to He implantation. The optical waveguides present reasonable losses ͑ϳ10 dB/ cm͒ and significant secondharmonic generation (SHG) and electro-optic (EO) responses (Ͼ50% bulk) for the lowest fluences. © 2007 Optical Society of America OCIS codes: 130.3730, 130.4310, 160.3730, 190.4390. Ion implantation [1] of light ions (H, He) at energies of 1 -3 MeV is a well-known procedure to fabricate optical waveguides and integrated optics devices on dielectric crystals [2]. The physical basis is the disorder and partial or full amorphization of the crystal at the end of the ion range caused by nuclear collisions between the incoming ions and the atoms of the material. A main disadvantage is that the required ion fluence (and therefore irradiation time) to achieve amorphization is very high ͑10 16 -10 17 cm −2 ͒. This feature has hindered the routine commercial use of ion implantation, so cheaper and simpler methods such as metal in-diffusion [3,4] or proton-exchange [5,6] are mostly used for LiNbO 3 . This crystal has been used in the present work since it is still a reference material in photonics for electro-optic (EO) and nonlinear optical applications [7]. Recently, the use of heavier ions and higher energies to induce damage and amorphization via electronic excitations has started to be explored. A method to produce high index-jump optical waveguides producing thick buried amorphous layers by accumulation of (subthreshold) electronic damage with moderate fluences ͑ϳ10 14 cm −2 ͒ was demonstrated in LiNbO 3 [8] and KGW [9] and is an alternative to light ion implantation.The purpose of this Letter is to go a step further and report on a novel method to fabricate a nanostructured effective medium for LiNbO 3 that acts as an optical waveguide. It dramatically reduces the required ion fluences down to ϳ10 12 cm −2 , while essentially keeping the nonlinear optical performance. The physical basis is as follows: Irradiation with mediummass ions having sufficiently high energy so that their electronic stopping power ͑S e ͒ is above a certain threshold value (S th Ϸ 5 -6 keV/ nm for LiNbO 3 ) generates amorphous tracks with a nanometric diameter [10][11][12][13]. Each track is associated with a single ion impact and presents [12,13] an isotropic refractive index (n a = 2.10 at = 633 nm). It has been show...

Optical Waveguides Fabricated by Ion Implantation/Irradiation: A Review Optical Waveguides Fabricated by Ion Implantation/Irradiation: A Review

“…and Er 3+ -doped telluride glass (Berneschi et al, 2007b), achieving unprecedented control over the refractive index changes of the substrate. Moreover, irradiation with swift heavy ions have been also used to produce waveguides in a wide number of materials, like LiNbO 3 (Olivares et al, 2005b(Olivares et al, , 2007bChen, 2009b;Dong et al, 2011a), KGW (García-Navarro et al, 2006), KLTN (Ilan et al, 2006), BGO , Nd:YAG (Ren et al, 2010a(Ren et al, , 2011a, Nd:GdCOB (Ren et al, 2011b), a-SiO 2 (Manzano et al, 2010), c-SiO 2 (Manzano-Santamaría et al, 2012) and chalcogenide glasses , allowing a fast fabrication of high-quality waveguides. In this section we briefly review the fabrication and properties of ion implanted waveguides in various materials, emphasizing the most recent results.…”

“…Olivares et al (Olivares et al, 2007b) also demonstrated a novel method to produce optical waveguides on lithium niobate using irradiations with high-energy medium-mass ions (i.e., swift heavy ions) at ultralow fluences (10 12 -10 13 cm -2 ). In this regime amorphous nanotracks are created by every single impact leading to an effective nanostructured medium that behaves as an optical waveguide where light propagates transversally to the ion tracks.…”

Materials research at CMAM

“…Since the beginning of CMAM in 2003 photonics has been strongly developed focusing, from the fundamental point of view on the interaction with solids of high energy heavy ions, that generate material transformation by means of their high electronic excitation and therefore (electronic) damage [4,5]. From the application point of view, a novel method has been developed for the processing of optical materials based on the use of high energy ions and their electronic excitation.…”

Mechanical response to swift ion irradiation-induced nano-tracks in silica

“…On one hand, it leads to material modification, usually, with detrimental results (as in Nuclear fusion facilities [1]) and on the other hand, it can be used to optimize or tailor the physical properties, e.g., as in waveguide fabrication [2,3].…”