Planar waveguides in calcium barium niobate fabricated by MeV He ion implantation

A planar optical waveguide was formed in calcium barium niobate (CBN) crystal by 2.8-MeV He-ion implantation with a dose of 1.0×10¹⁶ ions/cm² at room temperature. The prism-coupling method was used to take dark mode measurements at both 633 nm and 1539 nm. The refractive-index profile (n_o and n_e) of the He-implanted CBN waveguide was analyzed with the reflectivity calculation method. The results show that the MeV He implantation results in a decrease in refractive index in barriers for both n_o (4.1%) and n_e (3.1%), but for n_e there is an increase in the waveguide region. The intensity profile of the guide mode and waveguide loss were obtained by end-fire coupling. PACS 42.79.Gn; 61.80.Jh     

LiNbO3 channel and ridge waveguides based on helium ion implantation combined with lithography and precise diamond dicing

Lithium niobate(LiNbO₃, LN) channel and ridge waveguides have been successfully fabricated by He ion implantation, which has energy of 500 keV and fluence of 1.5 × 10¹⁶ ions/cm² and is combined with lithography and the precise diamond dicing technique. The refractive index profile of the annealed LN planar waveguide was reconstructed. The propagation loss of the channel waveguide with a width of 10 μm and that of the ridge waveguides with widths of 25 μm and 15 μ...     

Fabrication of waveguides in Yb:YCOB crystal by MeV oxygen ion implantation

Oxygen ions with energies of 6.0 or 3.0 MeV were implanted into y-cut Yb:YCOB crystals at fluences ranging from 5.0 × 10¹³ to 2.0 × 10¹⁵ ions/cm² at room temperature, forming optical planar waveguide structures. Dark-mode line spectroscopy was applied at two wavelengths, 633 and 1539 nm, in various excitation configurations, showing strong enhancement of one of the indices (n_x) in the implanted near surface. The n_x refractive index profile is reconstructed by a reflectivity calculation method and compared to the ion energy losses profiles deduced from SRIM-code simulation. Moreover, the near-field patterns were imaged by an end-fire coupling arrangement.     

Low-loss ridge waveguides on lithium niobate fabricated by local diffusion doping with titanium

The development of a novel self-aligned photolithographic process is reported enabling selective Ti-deposition on the surface of wet etched ridges on lithium niobate. Thus local diffusion doping of the ridges becomes possible to fabricate optical waveguides. They have surprisingly low propagation losses down to 0.05 dB/cm for TE-polarization (at ～1.55 μm wavelength). The fabrication procedure of locally doped ridge guides in LN and their optical properties are presented in detail.     

Annealing effect on planar waveguides in LiNbO3 produced by oxygen ion implantation

We reported on planar waveguides in stoichiometric lithium niobate fabricated by 4.5 MeV oxygen ion implantation with a dose of 6 × 10¹⁴ ions/cm² at room temperature. After ion implantation, these samples were annealed at 240 °C, 260 °C, and 300 °C for 30 min. We investigated annealing effect on the guiding modes and near-field images in the waveguides by prism-coupling method and end-face coupling method respectively. We found that for the extraordinary refractive index a positive alternation occurred in the near-surface region while a negative alternation happened at the end of ion track. Moreover, we measured the transmission spectra for the pure sample and implanted samples before and after annealed at different temperatures, and we observed an absorption peak at ∼480 nm (2.6 eV) in all of these SLN samples.     

Reconstruction of extraordinary refractive index profiles of optical planar waveguides with single or double modes fabricated by O ion implantation into lithium niobate

A method named intensity calculation method (ICM), which is based on beam propagation method (BPM) and image processing, was carried out to reconstruct the extraordinary refractive index profile (RIP) of single-mode planar waveguide in lithium niobate (LiNbO₃), which was fabricated by multi-energy megaelectron-volt (MeV) O²⁺ ion implantation. In addition, it has been proved reasonable that the alternation of extraordinary refractive index induced by ion implantation into LiNbO₃ is mainly due to the degradation of polarization and reduction of material physical density. As a result, the possible extraordinary RIP of the double-mode planar waveguide could be reconstructed using BPM according to such a hypothesis and the calculated guiding mode values. The end-fire coupling and m-line arrangements were carried out to obtain the near-field modal patterns and dark-mode spectra of waveguides, respectively.     

Second harmonic generation from precise diamond blade diced ridge waveguides

Carbon ion irradiation and precise diamond blade dicing are applied to fabricate Nd:GdCOB ridge waveguides. The propagation properties of the fabricated Nd:GdCOB waveguides are investigated through experiments and theoretical analysis. Micro-Raman analysis reveals that the Nd:GdCOB crystal lattice expands during the irradiation process. Micro-second harmonic spectroscopic analysis suggests that the original nonlinear properties of the Nd:GdCOB crystal are greatly enhanced within the waveguide volume. Under pulsed 1064 nm laser pumping, second harmonic generation (SHG) at 532 nm has been achieved in the fabricated waveguides. The maximum SHG conversion efficiencies are determined to be ～ 8.32 %·W^-1 and ～ 22.36 %·W^-1 for planar and ridge waveguides, respectively.     

Optical waveguides in LiNbO3 formed by ion implantation

Abstract

Ion implantation in LiNbO₃ can be used to modify the refractive index. The change in indices, n ₀ n _e results from the damage formed by energy deposited by the (dE/dx)_nuclear collisions between the ions and the lattice and is independent of the ion species. A saturation change in index of some ?7% occurs after a deposition of 10²³ keV cm^?3 at 300K, greater changes of ?9 % occur with implants at 77K. Annealing studies indicate the optical absorption formed during irradiation is removed below 200°C whereas the index changes exist up to 400°C. For optical waveguide production a negative change in the index is not ideal as the damaged layer cannot directly act as the region of optical confinement. However the (dE/dx)_electronic term is unimportant and so we have been able to form optical waveguides by ion implantation with light energetic ions (e.g. MeV He⁺ ions) because the damaged layer is then formed beneath an unchanged high index surface layer. This retains the desirable electrooptic properties of the single crystal LiNbO₃. The experimentally observed waveguide modes are in accord with our theoretical predictions of the refractive index profiles.     

Optical properties of He+-implanted and diamond blade-diced terbium gallium garnet crystal planar and ridge waveguides

Terbium gallium garnet (Tb₃Ga₅O₁₂, TGG) crystal can be used to fabricate various magneto-optical devices due to its optimal Faraday effect. In this work, 400-keV He⁺ ions with a fluence of 6.0×10¹⁶ ions/cm² are irradiated into the TGG crystal for the planar waveguide formation. The precise diamond blade dicing with a rotation speed of 2×10⁴ rpm and a cutting velocity of 0.1 mm/s is performed on the He⁺-implanted TGG planar waveguide for the ridge structure. The dark-mode spectrum of the He⁺-implanted TGG planar waveguide is measured by the prism-coupling method, thereby obtaining the relationship between the reflected light intensity and the effective refractive index. The refractive index profile of the planar waveguide is reconstructed by the reflectivity calculation method. The near-field light intensity distribution of the planar waveguide and the ridge waveguide are recorded by the end-face coupling method. The He⁺-implanted and diamond blade-diced TGG crystal planar and ridge waveguides are promising candidates for integrated magneto-optical devices.     

Fabrication of ridge waveguides in zinc-substituted lithium niobate by means of ion-beam enhanced etching

We present results on the fabrication and characterization of ridge waveguides in zinc-substituted lithium niobate. High-quality waveguides were fabricated by a combination of liquid-phase epitaxy and multiple applications of ion-beam enhanced etching. The two major demands on ridge waveguides, a very low side-wall roughness and a rectangle shape with side-wall angles close to 90 degrees , were realized simultaneously by using this technique. Single-mode waveguiding at a wavelength of 1064 nm was demonstrated with attenuation values of 0.9 dB/cm.     

Direct fabrication and IV characterization of sub-surface conductive channels in diamond with MeV ion implantation

In the present work we report about the investigation of the conduction mechanism of sp² carbon micro-channels in single crystal diamond. The structures are fabricated with a technique which employs a MeV focused ion-beam to damage diamond in conjunction with variable thickness masks. This process changes significantly the structural properties of the target material, because the ion nuclear energy loss induces carbon conversion from sp³ to sp² state mainly at the end of range of the ions (few micrometers). Furthermore, placing a mask with increasing thickness on the sample it is possible to modulate the channels depth at their endpoints, allowing their electrical connection with the surface. A single-crystal HPHT diamond sample was implanted with 1.8 MeV He⁺ ions at room temperature, the implantation fluence was set in the range 2.1×10¹⁶-6.3×10¹⁷ ions cm^-2, determining the formation of micro-channels with a graded level of damage extending down to a depth of about 3 μm. After deposition of metallic contacts at the channels’ endpoints, the electrical characterization was performed measuring the I-V curves at variable temperatures in the 80-690 K range. The Variable Range Hopping model was used to fit the experimental data in the ohmic regime, allowing the estimation of characteristic parameters such as the density of localized states at the Fermi level. A value of 5.5×10¹⁷ states cm^-3 eV^-1 was obtained, in satisfactory agreement with values previously reported in literature. The power-law dependence between current and voltage is consistent with the space charge limited mechanism at moderate electric fields.     

Optical planar waveguides in yb3＋-doped phosphate glasses produced by He＋ ion implantation

Optical planar waveguides in Yb 3+-doped phosphate glasses are fabricated by implanting triple-energy helium ions. The guiding modes and the near-field intensity distribution are measured by using the prism-coupling method and the end-face coupling setup with a He-Ne laser at 633 nm The intensity calculation method (ICM) is used to reconstruct the refractive index profile of the waveguide. The absorption and the fluorescence investigations reveal that the glass bulk features are well preserved in the active volumes of the waveguides, suggesting the fabricated structures for possible applications as waveguide lasers.     

Optical channel waveguides with trapezoidal-shaped cross sections in KTiOPO4 crystal fabricated by ion implantation

Optical channel waveguides were fabricated in KTiOPO₄ crystal by He⁺-ion implantation using photoresist masks with wedged-shaped cross sections. Semi-closed barrier walls with reduced refractive indices inside the crystal constructed the enclosed regions to be channel waveguides with trapezoidal-shaped cross sections. The m-line as well as end-fire coupling arrangements were performed to characterize the waveguides with light at wavelength of 632.8 nm. The propagation loss of the channel waveguides was determined to be as low as ∼2 dB/cm after simple post-irradiation thermal annealing treatment in air.     

Thermally induced self-focusing and optical beam interactions in planar strontium barium niobate waveguides

We present an experimental study of thermally induced self-focusing effects and interactions of incoherent light beams in strontium barium niobate waveguides. Depending on the input power, a single parallel beam is strongly focused inside the sample up to diameters of several micrometers. For higher input power we observe the splitting of the beam in a sequence of several spots. We demonstrate that these thermally induced refractive-index patterns can be used to focus and deflect an incoherent guided probe beam in the waveguide with time constants below 1 ms.     

Comparison between MeV Ni and He ion-implanted planar optical waveguides in quartz

Optically polished crystalline quartz samples were implanted at room temperature by 2.6 MeV Ni⁺ ions with a dose of 9×10¹⁴ ions/cm² and 2.0 MeV He⁺ ions with a dose of 1.5×10¹⁶ ions/cm², respectively. A comparison of the MeV Ni⁺ ion-implanted planar waveguide formation was made with the MeV He⁺ ion-implanted one. The prism-coupling method was carried out to measure the dark modes in the quartz waveguides by using model 2010 prism coupler. Five modes were observed in the Ni⁺ implanted waveguide while 15 modes were found in the He⁺ ion-implanted one. Reflectivity calculation method was applied to fitting the refractive index profile. TRIM’98 (transport of ions in matter) code was used to simulate the damage profile in quartz by MeV Ni⁺ and He⁺ ions implantation, respectively. It is found that the refractive index profile in MeV Ni⁺ ions implanted waveguide is somewhat different in shape from that in MeV He⁺ ions implanted waveguide.     

Channel waveguides in Ca4GdO(BO3)3 fabricated by He+ implantation for blue-light generation

Blue light at 405 nm is generated by frequency doubling of a Ti:sapphire tunable laser in He(+)-implanted channel waveguides in gadolinium calcium oxoborate crystal. A conversion efficiency of approximately 2% W(-1) cm(-2) is achieved between TM00 fundamental and TE01 harmonic modes.     

Amorphization of diamond by low temperature133Xe ion implantation

The structure of the amorphous layer in¹³³Xe implanted diamond is investigated by Mössbauer spectroscopy. Very different Debye Waller factors are measured after room temperature and liquid nitrogen temperature implantation.     

Enhanced refractive index well-confined planar and channel waveguides in KTiOPO<Subscript>4</Subscript> produced by MeV C<Superscript>3+</Superscript> ion implantation with low dose

We report on the fabrication and characterization of planar and channel waveguides in KTiOPO₄ crystals by 6.0 MeV C³⁺ ion implantation with the dose of 1×10¹⁴ ions/cm². The dark mode spectroscopy of the planar waveguide was measured using a prism coupling arrangement. An increase of the both n _x and n _y refractive indices induced by the annealing after implantation is believed to be responsible for waveguide formation. The bright near-field intensity distribution of the transverse-electric and transverse-magnetic modes in the annealed channel waveguide was collected and studied by end-coupling method.