Investigation Of Planar And Channel Optical Waveguides Fabricated By Ion Implantation And Ion Beam Etching

A waveguide is characterized by a region of high refractive index bounded by regions of lower index. It can confine the optical energy in small space and improve the optical energy density. Optical waveguide is the basic structure of integrated optics and the holo-optical network. It also plays an important roll in the fabrication of various optical devices because of its excellent characteristics, possibility in integration and rather low cost in manufacturing. Because of its importance in practical application, scientists and engineers are trying to find various ways to fabricate "high-quality" optical waveguide. Ion implantation, as an outstanding method to modify the surface property of materials, is confirmed to be an effective method for fabricating various waveguide structures. Up to now, many waveguide structures have been formed by ion implantation in most optical materials such as optical crystals, glass, semiconductors and polymers etc.In all the implanted waveguides, MeV H and He ions are most frequently used, which build up an optical barrier at the end of the track due to the damage induced by nuclear energy loss. Such an optical barrier confines the light in an "optical well" between itself and the surface. More recently, waveguides fabricated by heavier-ion implantation have been extensively investigated. The indices in surface layer have been found to be raised when heavier ions are implanted into some optical materials, such as LiNbO₃, Nd:YVO₄, BBO and KTA etc, then a waveguide can be formed by a region of high refractive index bounded by regions of lower index (air and substrate). This "increase" could help to form better waveguide structures and also reduce the implanted ion dose (1-3 order lower than that of light-ion implantation). Therefore, the investigation on heavier-ion-implanted waveguides is important not only for the theoretical study but also for the potential application as well.Most optoelectronics devices such as optical coupler, modulator, optical switch and waveguide laser are based on channel waveguide structure. The attempt of fabrication of such waveguide structure is necessary for both optoelectronics technology itself and the combination between nuclear technology and optoelectronics.The present work is focused on three aspects: (1) The planar optical waveguides are fabricated in RTP, Yb:GdCOB, Yb:YCOB, Nd:YCOB, Er:Yb:YCOB and CSBN crystals by ion implantation. Based on experimental results from measurement, analysis of waveguide mode and annealing behavior of ion-implanted waveguide, the parameters of implantation can be optimized. The mechanism of the refractive index change due to ion implantation has been discussed. (2) Optical channel waveguide in KTA crystal is produced by photographic masking and following direct O⁺ ion implantation at 3.0MeV. One dimensional channel waveguide array is fabricated in photorefractive Ce-doped potassium sodium strontium barium niobate crystal by photographic masking and following direct multiple energy He⁺ ion implantation. (3) Optical diffraction gratings in fused quartz and lithium niobate are fabricated by standard photolithography technique and the following etching of argon ion beam. And optical ridge waveguides are fabricated by combination of ion implantaiton and ion beam etching. The structural, optical and guiding properties of the samples are analyzed. The main results are given as follows:Calcium yttrium oxoborate [Ca₄YO(BO₃)₃, YCOB] is a new efficient nonlinear optical crystal belonging to the monoclinic biaxial crystal family of rare-earth (Re) calcium oxyborates (ReCOB, Re=Y, Gd, Nd, Er, La, Sm). The Y³⁺ ion in YCOB crystal can be easily substituted by other rare earth ions with similar ion radii such as Nd³⁺ or Yb³⁺. Recent research shows that Yb:YCOB and Nd:YCOB have exhibited promising performance on laser activities and nonlinear optical frequency doubling for its good chemical and physical properties, such as non-hygroscopicity, wide transparent range, high damage threshold and large effective non-linear coefficient along phase-matching direction. The output laser at 1550nm has been demonstrated pumped by laser diode (LD) at 976.4nm for Er:Yb:YCOB. In the present work, we report the fabrication of planar waveguides in Yb:YCOB, Nd:YCOB and Er:Yb:YCOB crystals by MeV O⁺ implantation at different doses. The dependence of refractive indices changes versus implanted doses were investigated. Annealing treatment was performed. The behavior of annealing on guiding mode and propagation loss were studied.The Yb doped crystals display some advantages: Yb-doped medias generally have long radiative lifetimes (there is no concentration quenching effect for high Yb doping concentration) and high quantum efficiency. The doped Yb³⁺ ions possess no up-conversion effect or excited state absorption, which will greatly reduce thermal effects in the crystal. Ytterbium-doped gadolinium calcium oxoborate (Yb:GdCOB) crystal is a new type of oxide crystal based on the nonlinear optical crystal GdCOB. It has very attractive nonlinear and laser properties, which make it more interesting than the pure GdCOB. It is very promising for selffrequency doubling. Thus the formation of a waveguide in this crystal should be useful for exploration of its integrated optical properties. In the present work, we report the fabrication of planar waveguides in Yb:GdCOB crystal by MeV O, C, Si ion implantation at the doses from 5×10¹³ to 2×10¹⁵ ions/cm². Positive changes of n_x refractive index happened in the waveguide region. The relationship between doses and refractive index changes is also presented. The refractive index profiles of waveguides are reconstructed by an effective refractive index method. By using end-fire coupling method, the optical intensity distribution of the light traversed the waveguide was obtained.Rubidium titanyl phosphate, RbTiOPO₄ (RTP), is an orthorhombic crystal, isostructural with the well known potassium titanyl phosohate, KTiOPO₄ (KTP), non-linear optical crystal. RTP has high non-linear optical and electrooptical coefficients, that could drive to important applications in non-linear optics and electrooptics. In this work, we have formed the planar waveguides in RTP crystal by MeV O, C ion implantation. Dark modes are measured by prism coupling method at 632.8nm as well as telecommunication wavelength of 1539nm. We use RCM method to simulate the refractive index profile of the waveguide. Annealing treatments of the samples are performed to improve the waveguide stability and to reduce losses. After 200℃ for 60 minutes, the dark modes index increase a little, this means that the refractive index of waveguide recovered to some extent.Calcium strontium barium niobate (CSBN), like Calium barium niobate (CBN) and Strontium barium niobate (SBN), belongs to the materials family of partially filled tetragonal tungsten bronzes, which show relaxor-type ferroelectric phase transition and large electro-optic effects. It has been found that CBN is similar to SBN except for the transition temperatures and the birefringence. The detected phase transition temperature at about 280℃ is nearly 200℃ higher than that of SBN, which makes CBN potentially attractive for applications at higher temperatures. We have formed what is believed to be the first planar optical waveguide in CSBN crystals by MeV C ion implantation. The properties of the waveguides were investigated by prism coupling as well as end-face coupling methods. Extraordinary refractive index (n_e) has a positive change. The program code SRIM'03 (stopping and ranges of ions in matter) is used to simulate the implantation process of carbon ions into the CSBN crystal. It provides the original information on the fabrication of waveguides formed by ion implantation based on CSBN crystals.Biaxial crystal potassium titanyl arsenate (KTiOAsO₄ or KTA) is an excellent nonlinear optical crystal developed recently for non-linear optical and electro-optical device applications. Compared to KTiOPO₄ (KTP), KTA has electro-optic coefficients and a nonlinear figure of merit larger than KTP by 30% and 60%, respectively. In particular, KTA has lower absorption in the 3-5 μm spectral region compared to KTP, which is important for mid-IR optical parametric oscillation (OPO) application, and it is reported to have a higher damage threshold than KTP. Since waveguide devices can increase the efficiency of nonlinear interactions by two orders of magnitude for its confinement of the interacting waves, the remarkable nonlinear optical properties of KTA make it a great interest for developing optical waveguide devices in it. In 2006, Dr. Jiang reported the fabrication of planar waveguides in KTA crystal with positive changes of both n_x and n_y refractive indices by 3.0MeV O⁺ implantation at lower doses from 5×10¹² to 1×10¹⁴ ions/cm². In the present work, we report on optical channel waveguide in KTA crystal produced by photographic masking and following direct O⁺ ion implantation at 3.0MeV with dose of 5×10¹³ions/cm². Quasi-TM and TE guided modes are both observed by end-face coupling method. Positive changes of n_x and n_y refractive indices induced by the implantation are believed to be responsible for the waveguide formation.Photorefractive photonic devices exhibit attractive applications in many areas, such as holographic storage, optical amplification, and optical communications.Potassium sodium strontium barium niobate ((K_0.5Na_0.59)_0.2(Sr_0.75Ba_0.25)_0.9Nb₂O₆ or KNSBN) has relatively large electro-optic coefficients, large transparent range, and high threshold energy for optical damage. Ce- or Cu-doped KNSBN crystals possess controllable and intriguing photorefractive and ferroelectric properties, which have been used for self-pumped phase conjugations and holographic recording, we report on the fabrication of channel waveguide array in Ce:KNSBN crystal by multienergy He ion implantation combined with lithographic photoresist masking.As one of the most favorite dielectric crystals, lithium niobate (LiNbO₃) is widely used in a variety of photonic devices due to its high electro-optical, acousto-optic, piezoelectric, and nonlinear optical coefficients. Fused quartz is widely used in the manufacture of optoelectronics devices because of its low thermal conductaivity, high electircal receptivety and excellent properties in thermal, optics and mechanics. The refractive index value of fused quartz is so close to that of fiber, which makes the coupling between fused quartz-based device and fiber much easier, therefore the fused quartz has been frequently employed as substrate for many integrated optical devices. In the present work, we report optical diffraction gratings in fused quartz and lithium niobate fabricated by standard photolithography technique and the following etching of argon ion beam. Diffraction patterns of the gratings are observed by a He-Ne laser beam. Moreover optical ridge waveguides are fabricated by combination of ion implantaiton and ion beam etching. Using end-fire coupling method, the optical intensity distribution of the light traversed the ridge waveguides are obtained. The etch depth is measured by a profilometer. A scanning electron microscope is used for visual inspection of the structures produced.