Ke-Ming Wang

Monomode optical waveguide in lithium niobate formed by MeV Si+ ion implantation

The monomode enhanced-index LiNbO3 waveguide fabricated by low-dose ion implantation is reported. LiNbO3 crystals were implanted with 3 MeV Si+ ions to doses around 1014 ions/cm2. After annealing, the waveguides were formed by the extraordinary refractive index enhancement in the waveguide regions. The effective extraordinary refractive index of the waveguide increased with ion implantation dose. The loss was 0.64 dB/cm in the X-cut sample with an implantation dose of 3.3×1014 ions/cm2. The scattering loss in the Z-cut samples was even lower than that in the X-cut samples.The monomode enhanced-index LiNbO3 waveguide fabricated by low-dose ion implantation is reported. LiNbO3 crystals were implanted with 3 MeV Si+ ions to doses around 1014 ions/cm2. After annealing, the waveguides were formed by the extraordinary refractive index enhancement in the waveguide regions. The effective extraordinary refractive index of the waveguide increased with ion implantation dose. The loss was 0.64 dB/cm in the X-cut sample with an implantation dose of 3.3×1014 ions/cm2. The scattering loss in the Z-cut samples was even lower than that in the X-cut samples.

Optical waveguides formed in Nd:YVO4 by MeV Si+ implantation

The planar waveguide has been fabricated in a Nd:YVO4 crystal by 3.0 MeV Si+ ion implantation at a dose of 1×1015 ions/cm2 at room temperature. The waveguide was characterized by the prism-coupling method. The dark modes are measured before and after the annealing at 240 °C for 60 min in air. The refractive index profile is reconstructed using reflectivity calculation method. It is found that relatively large positive change of ordinary refractive index happens in the guiding region, which is quite different from most of the observed ion-implanted waveguides. The TRIM’98 code is carried out to simulate the energy loss during the implantation in order to obtain a better understanding for the waveguide formation.

Formation of c-axis oriented ZnO optical waveguides by radio-frequency magnetron sputtering

ZnO/Mg0.16Zn0.84O (ZnO/MgZnO) films are fabricated on x-cut and z-cut LiNbO3 (LN) substrates by radio-frequency magnetron sputtering. High transparencies are confirmed by a spectrophotometer. X-ray diffraction (XRD) spectra show that all the films are c-axis oriented. The waveguiding properties, as well as the refractive indices and thickness of the films are demonstrated and determined by prism coupling. Both transverse electric (TE) and transverse magnetic (TM) modes are measured at lambda=0.633 mum and 1.539 mum, respectively. The waveguide loss is measured at lambda=0.633 mum with a fiber probe technique. The experimental results show that high optical quality ZnO films can be obtained with MgZnO buffer layers.

Optical properties of stoichiometric LiNbO3 waveguides formed by low-dose oxygen ion implantation

The planar waveguides in z-cut stoichiometric LiNbO3 crystal have been fabricated by 3.0 MeV oxygen ion implantation with the dose of 6×1014ions∕cm2 at room temperature. The modes of the waveguides were measured by the prism-coupling method with the wavelength 633 and 1539 nm, respectively. The refractive index profiles of the waveguides were reconstructed using reflectivity calculation method. The Rutherford backscattering/channeling technique was used to investigate the damage produced by the ion implantation, the minimum yield of the spectra was 4.52%. The propagation loss of waveguide was 0.61 dB/cm obtained by fiber probe technique. It was found that positive changes of extraordinary refractive indices happened in the guiding regions, and such change increased after the annealing treatment at 260 °C for 60 min.

Waveguide laser film in erbium-doped KTiOPO4 by pulsed laser deposition

Erbium doping into potassium titanyl phosphate (KTiOPO4 or KTP) was performed by pulsed laser deposition. Waveguide laser film in Er-doped KTiOPO4 was formed using both KTiOPO4 and erbium as targets and optically polished KTiOPO4 as a substrate. Rutherford backscattering, photoluminescence spectrometry, x-ray diffraction, and prism coupling method are used to investigate the properties of Er-doped KTiOPO4. The results show that (1) Er-doped KTiOPO4 emits the characteristic photoluminescence of Er3+ around 1.54 μm corresponding to transition between the 4I13/2 and 4I15/2 manifolds of the Er3+ ions in KTiOPO4 host. (2) two bright modes in Er-doped KTiOPO4 were observed. This approach may be useful for direct fabrication of thin film waveguide laser for other optoelectrical materials.

Optical channel waveguides in Nd:YVO4 crystal produced by O+ ion implantation

In this letter, we report on optical channel waveguides in Nd:YVO4 crystals produced by photographic masking and following direct O+ ion implantation at 3.0MeV. Annealing treatments of the samples are performed to improve the waveguide stability and to reduce losses. An increase of the ordinary refractive index induced by the implantation is believed to be responsible for waveguide formation. Quasi-TM guided modes are observed, while no quasi-TE ones are detected. The optical damping coefficients are of 0.43, 0.63, and 0.54cm−1 for channel waveguides with widths of 4, 5, and 6μm, respectively. The result of modal analysis is in agreement with the experimental data.

Low-loss planar and stripe waveguides in Nd3+-doped silicate glass produced by oxygen-ion implantation

We report on the fabrication and characterization of low-loss planar and stripe waveguides in a Nd3+-doped glass by 6MeV oxygen-ion implantation at a dose of 1×1015ions∕cm2. The dark mode spectroscopy of the planar waveguide was measured using a prism coupling arrangement. The refractive index profile of the planar waveguide was reconstructed from a code based on the reflectivity calculation method. The results indicate that a refractive index enhanced region as well as an optical barrier have been created after the ion beam processing. The near-field mode profiles of the stripe waveguide were obtained by an end-fire coupling arrangement, by which three quasitransverse electric modes were observed. After annealing, the propagation losses of the planar and stripe waveguides were reduced to be ∼0.5 and ∼1.8dB∕cm, respectively.

Monomode optical waveguide excited at 1540 nm in LiNbO(3) formed by MeV carbon ion implantation at low doses.

The monomode enhanced-index LiNbO(3) waveguide excited at 1540 nm is reported. X-cut LiNbO(3) crystals were implanted at room temperature by 6.0 MeV C(3+) ions with a dose of 2.0x10(15) ions/cm(2). Low loss planar optical waveguides were obtained and characterized by the prism coupling technique. Four dark modes were observed for extraordinary light at 633 nm, while only one enhanced-index mode was observed at 1540 nm. The propagation loss of the waveguide is 1.01 dB/cm measured with the moving fiber method. Reflectivity calculation method (RCM) was applied to simulate the refractive index profiles in waveguide. The width of waveguide structure induced by carbon ion implantation is ~3.6 microm.

Planar optical waveguides in β-BaB2O4 produced by oxygen ion implantation at low doses

The planar waveguides have been fabricated in z-cut β-BaB2O4 crystal by 2.2MeV O+ ion implantation at doses ranging from 5×1012 to 5×1014ions∕cm2 at room temperature. The waveguides were characterized by the prism-coupling method. Monomode, nonleaky planar waveguides at λ=633nm in β-BBO single crystals were fabricated at doses from 5×1012 to 2×1013ions∕cm2, and two mode and three mode waveguides were fabricated at doses from 4×1013 to 5×1014ions∕cm2, respectively. The refractive index profiles of the waveguides are reconstructed using reflectivity calculation method. The propagation loss of the measured ion implanted waveguide was about 1.6dB∕cm. It was found that positive changes of extraordinary refractive indices happened in the guiding regions, and such changes increased with the doses, which were different from most of the observed ion-implanted waveguides.

High-efficiency second-harmonic generation in doubly-resonant χ (2) microring resonators

By directly simulating Maxwells equations via the finite-difference time-domain (FDTD) method, we numerically demonstrate the possibility of achieving high-efficiency second harmonic generation (SHG) in a structure consisting of a microscale doubly-resonant ring resonator side-coupled to two adjacent waveguides. We find that ≳ 94% conversion efficiency can be attained at telecom wavelengths, for incident powers in the milliwatts, and for reasonably large bandwidths (Q ∼ 1000s). We demonstrate that in this high efficiency regime, the system also exhibits limit-cycle or bistable behavior for light incident above a threshold power. Our numerical results agree to within a few percent with the predictions of a simple but rigorous coupled-mode theory framework.