M. Fleuster

Modeling of refractive index profiles of He+ ion‐implanted KNbO3 waveguides based on the irradiation parameters

Planar optical waveguides were fabricated by He+ ion implantation in KNbO3 crystals with doses from 2.5×1014 to 1×1016 cm−2 and energies from 1 to 3.5 MeV, and the index profiles were analyzed. A comparison with theoretical radiation damage profiles calculated by the trim code indicates that the index change is mainly caused by nuclear collisions. However, at higher implantation doses the influence of the electronic excitation on the refractive index profiles cannot be neglected. A method is derived to predict the index profile of nb from the He+ implantation parameters energy and dose. The measured mode spectra of waveguides produced by single and dual energy implantation are in excellent agreement with the predicted spectra.

OPTICAL AND STRUCTURAL PROPERTIES OF MEV ERBIUM-IMPLANTED LINBO3

LiNbO3 single crystals have been implanted with 2.0 or 3.5 MeV Er ions with fluences between 2.0×1014 and 7.5×1015 cm−2 and annealed at temperatures between 500 and 1060 °C in a wet oxygen atmosphere. Photoluminescence spectroscopy, Rutherford backscattering spectroscopy, and secondary‐ion‐mass spectrometry have been used to study the influence of the annealing treatment on the optical activity of the Er ions, the crystal structure of the implanted LiNbO3 layer, and the depth distribution of the Er ions, respectively. The as‐implanted, amorphized LiNbO3 already emits the characteristic photoluminescence (PL) of Er3+ around 1.53 μm. Annealing for 1 min at 500 °C causes recrystallization of the amorphized layer by columnar solid‐phase epitaxial regrowth from the substrate. The PL intensity increases by more than one order of magnitude on annealing at 500 °C and the PL lifetime rises from 1.65 to 2.85 ms. In contrast, much longer annealing times and a much higher temperature are necessary to remove the colum...

Low‐loss optical channel waveguides in KNbO3 by multiple energy ion implantation

Permanent optical channel waveguides in single crystals of KNbO3 are formed with low‐dose MeV He ion irradiation. A single energy implantation forms a confinement barrier at the projected range of the ions whereas multiple energy implantations combined with a positive shielding mask form the side walls. Guiding modes are produced and propagation losses as low as 1.0 dB/cm are measured without the need for any annealing. The irradiation induced refractive index changes that define the boundaries of the waveguiding channels are made visible with cross‐polarized light microscopy.

Rapid thermal annealing of MeV erbium implanted LiNbO3 single crystals for optical doping

LiNbO3 single crystals (x cut) were implanted with 3.5‐MeV Er ions with fluences up to 3×1016 cm−2. Upon annealing the implantation‐amorphized surface layer regrows epitaxially, displaying either columnar or planar layer‐by‐layer growth, depending on the rate at which the samples are brought to the final temperature of 1060 °C. Low heating rates (≊10 °C/s) result in columnar regrowth, and 8‐h anneals are necessary for complete dissolution of the grain boundaries. In contrast, using a rapid warm‐up (100 °C/s), annealing for 1 min at 1060 °C is sufficient to restore a perfect crystal without grain boundaries. The advantage of the short anneal is that it leads to only minimal diffusion broadening of the Er profile. The maximum concentration of optically active Er ions is 0.18 at. %.

Low‐temperature annealing of ion‐implanted KNbO3 waveguides for second‐harmonic generation

Results on annealing experiments of He+ ion‐implanted KNbO3 planar and channel waveguides are reported. Annealing at 150 °C for several hours leads to a reduction of the waveguide attenuation constant by more than 5 dB cm−1 at a wavelength of 457 nm without significant change of the profile of the mode confining barrier. A minimum waveguide attenuation constant of 1.3 dB cm−1 in planar and 2.2 dB cm−1 in channel waveguides at 515 nm was achieved. Second‐harmonic generation measurements in the waveguides showed that the conversion efficiency can be improved by more than a factor of 2 by the annealing process.

The refractive index distribution nc(z) of ion implanted KNbO3 waveguides

Abstract We have analysed by means of dark and bright light spectroscopy the c-polarised mode spectra of KNbO 3 planar waveguides. These waveguides were fabricated by He + ion implantation with ion doses from 2.5 × 10 14 to 3 × 10 15 cm −2 and ion energies from 1 to 2.9 MeV. A quantitative model is derived to correlate the index profile of n c with the implantation parameters. The results are in excellent agreement with profiles observed by measuring the surface reflectivity of wedge polished samples. The test of the mode spectra after partial surface stripping by ion sputtering does not evidence irregular structures in the index profile.

Quantitative SIMS-analysis of erbium profiles in LiNbO3

Modern fiberoptic communication technology uses light of 1.5 μm wavelength and Er3+ is the laser active ion for this wavelength. Doping of crystalline LiNbO3 (an electrooptical material) with erbium ions permits the fabrication of signal-amplifying electrooptic devices. Novel results of three different approaches have been presented to dope the near surface area of LiNbO3 for its application in planar optoelectronics: erbium indiffusion from the surface, implantation of erbium into LiNbO3 and subsequent annealing schemes, and the homoepitaxial growth of Er-doped LiNbO3 on LiNbO3 single crystalline material by a laser deposition method. These experiments are not only useful for creating integrated optical devices with active amplifying functions, but they are also important examples for fabricating and studying novel thin ferroelectric films. Secondary ion mass spectrometry (SIMS) has been employed as the main analytical tool for quantitative determination of the erbium concentration profiles.

Epitaxy of Erbium Doped LiNbO3 Films Produced by Pulsed Laser Deposition

The growth of thin films of LiNbO 3 and Er:LiNbO 3 on LiNbO 3 single crystals produced by pulsed laser deposition (PLD) was studied. Samples were characterized by RBS/Channeling Spectrometry, X-ray diffraction measurements, Secondary Ion Mass Spectroscopy (SIMS) and photoluminescence (PL) measurements. Film preparation is performed in a two-step process including deposition and in-situ-annealing. Buried Er doped layers of approx. 800 nm thickness were grown.

Second harmonic generation and two-wave mixing in ion-implanted KNbO3 waveguides.

Abstract We report on nonlinear optical and photorefractive effects in KNbO3 waveguides produced by He+ ion implantation. Optical frequency doubling from the near infrared into the blue spectral range has been investigated in two configurations: (i) guided mode phase-matched and (ii) Cerenkov-type second harmonic generation where the second harmonic is radiated into the substrate. Up to 12 mW of blue light is generated with -200 mW of fundamental power in a channel waveguide of 1.1 cm length. Photorefractive two-wave mixing experiments have been performed in Fe-doped KNbO3 planar waveguides at visible and near infrared wavelengths. We measured two-wave mixing gain coefficients of up to 8 cm−1 at 514 nm and typical response times of about 40 μ at a power level of 10 mW.

Ion implanted optical waveguides in KNbO3 for efficient blue light second harmonic generation

Abstract Single crystals of KNbO3 have an excellent potential for nonlinear optical applications, especially for the conversion of near infrared to blue layer light. We have used He ions of 2 to 3 MeV to fabricate low loss permanent waveguides in KNbO3. We present results on the waveguide characterization and demonstrate efficient guided wave second harmonic generation of blue light at 434 nm in a planar waveguide as well as Cherenkov-type frequency doubling in a channel waveguide at 130 nm.