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1.
3 :Ti:Fe waveguides are thermally fixed during hologram recording at elevated temperatures. Different guides are fabricated
by titanium indiffusion using iron-doped and nominally pure y-cutLiNbO3 substrates and characterization is performed by dark-mode spectroscopy. The refractive index modulation of gratings written
and simultaneously fixed at 180 °C is investigated as a function of propagation depth, titanium and iron concentration. The
experimental results are compared with those obtained for unfixed holograms recorded at room temperature.
Received: 21. July 1997/Revised version: 13 October 1997 相似文献
2.
L. Tsonev I. Savatinova P. Simova 《Applied Physics A: Materials Science & Processing》1981,24(3):205-209
Various experiments on Ti diffused optical waveguides in LiNbO3 have been carried out in order to determine precisely the character of the diffusion process. The required guide parameters
and the effective mode indices could be controlled by adjusting only the diffusion time under fixed temperature and film thickness.
Therefore the dependence of the guide characteristics on the diffusion time has been investigated in detail. On the basis
of the data obtained, a two-stage diffusion model is proposed. In the first stage, the Ti diffusant profile is described by
a erfc-function, and the second stage is characterized by a modified Gaussian form. 相似文献
3.
I. Baumann R. Brinkmann M. Dinand W. Sohler L. Beckers C. Buchal M. Fleuster H. Holzbrecher H. Paulus K.-H. Müller T. Gog G. Materlik O. Witte H. Stolz W. von der Osten 《Applied Physics A: Materials Science & Processing》1996,64(1):33-44
The erbium incorporation into LiNbO3 by diffusion doping is investigated in detail by means of Secondary Ion Mass Spectrometry, Secondary Neutral Mass Spectrometry,
Rutherford Backscattering, Atomic Force Microscopy, X-ray Standing Wave technique and optical site-selective spectroscopy.
The diffusion of erbium in LiNbO3 can be described by Fick’s laws of diffusion with a concentration-independent diffusion coefficient. The diffusion constants
and activation energies for Z-cut (X-cut) LiNbO3 are 4.8×10-5 cm2/s (12.0×10-5 cm2/s) and 2.28 eV (2.44 eV), respectively. A limited solubility of erbium in LiNbO3 has to be taken into account increasing exponentially with rising temperature. During the first step of diffusion an Er
x
Nb
y
-oxide layer is formed at the surface of the sample acting as diffusion reservoir. Erbium is incorporated into LiNbO3 on vacant Li-sites slightly shifted from the original Li-position along the (-c)-direction. Site-selective spectroscopy found
four distinguishable energetically different erbium centres at this lattice site resulting from locally different symmetries
of the crystal field.
Received: 21 March 1996 / Accepted: 12 August 1996 相似文献
4.
V. Dierolf A.B. Kutsenko A. Ostendorf W. von der Osten W. Sohler H. Suche 《Applied physics. B, Lasers and optics》2001,72(7):803-810
Starting from previous investigations in LiNbO3 bulk crystals, we studied the optical properties of Er3+ ions in Ti:LiNbO3 channel waveguides and investigated the waveguide-specific lattice environment of the Er3+ ions (“sites”) caused by the doping method used and the presence of a large number of Ti4+ ions. For that purpose the method of combined excitation–emission spectroscopy was applied for the first time to waveguides
at low temperatures. Comparing the spectroscopic results obtained for the green, red, and near-IR luminescence (λ≈550, ≈650
and ≈980 nm) under direct (450 nm), 2-step (980 nm), and 3-step (1.5 μm) laser excitation, we found several distinguishable
Er3+ sites which in terms of energy levels and relative numbers are similar to those in bulk material, but exhibit significantly
different up-conversion efficiencies and strongly inhomogeneously broadened transitions. Moreover, we were able to distinguish
isolated and cluster Er3+ sites by their characteristic excitation and emission transition energies and studied the respective excitation/relaxation
channels. The cluster sites are most efficient in the up-conversion process, especially under 3-step excitation. Using accepted
microscopic models for Er3+ and Ti4+ incorporation into the LiNbO3 crystal lattice, the site distribution and up-conversion mechanisms are elucidated and their consequences for laser applications
in different spectral regions are discussed.
Received: 16 November 2000 / Published online: 21 March 2001 相似文献
5.
Comparison of the electro-optic coefficient r33 in well-defined phases of proton exchanged LiNbO3 waveguides 总被引:1,自引:0,他引:1
A. Méndez G. de la Paliza A. García-Cabañes J.M. Cabrera 《Applied physics. B, Lasers and optics》2001,73(5-6):485-488
The electro-optic coefficient, r33, of proton exchanged LiNbO3 waveguides has been measured in well-defined phases of the exchanged layer. Namely, in two low index-jump α-phases, i.e.
unannealed soft-exchanged (SPE) and annealed (APE) guides, and in two high index-jump phases, i.e. β1 guides and, for comparison, ordinary proton exchanged (PE) guides (having a mixture of phases). The following values have
been obtained (in pm/V): 22.1±0.6 for SPE; 20.9±0.7 for APE; 0.33±0.01 for β1; and 0.76±0.04 for PE. Differences between these values are discussed in terms of the structure of the phase involved.
Received: 18 May 2001 / Revised version: 22 August 2001 / Published online: 30 October 2001 相似文献
6.
V. Dierolf A.B. Kutsenko A. Ostendorf Chr. Sandmann 《Applied physics. B, Lasers and optics》2001,73(5-6):443-448
In order to elucidate the interaction effects among the various defects present in a LiNbO3-based integrated optical device, we investigated the change of the optical properties of Er3+ ions under the application of an external electric field and hydrostatic pressure. We obtained for stoichiometric bulk material
a complete picture of the field-induced spectral shifts as a function of transition and site. As a first important application
of these results we were able to clarify the mechanism of spectral broadening of the Er3+ transitions in Ti:Er:LiNbO3 channel waveguides. By selecting different waveguide modes for excitation and using highly selective double-resonance excitation
with two lasers, we found that the [Ti4+] concentration gradient caused by the indiffusion results in an internal E-field gradient. This translates, due to the averaging
within the guided mode, into mode-dependent spectral line broadening.
Received: 24 May 2001 / Published online: 23 October 2001 相似文献
7.
I. Savova I. Savatinova P. Kircheva E. Liarokapis 《Applied physics. B, Lasers and optics》2001,73(5-6):565-568
In this work we present polarized Raman measurements of z-cut multimode H:LiNbO3 waveguides in the κi- and βi-phase states. A spectrum with unexpected form and behaviour, originating from the layer at the very surface, was observed
in samples with various degrees of Li–H substitution. Possible reasons for the presence of this strange spectrum are considered.
Received: 16 May 2001 / Revised version: 7 August 2001 / Published online: 23 October 2001 相似文献
8.
We report on the fabrication and properties of He-implanted waveguides in lithium niobate, which are additionally doped with
copper by using an ion-exchange process. We show that the photorefractive sensitivity in the waveguides is increased by a
factor of 3000.
Received: 23 November 1998 / Revised version: 15 February 1999 / Published online: 12 April 1999 相似文献
9.
Permanent refractive-index gratings are generated by thermal fixing of holograms in photorefractive lithium niobate channel
waveguides. The guides are fabricated by successive indiffusion of titanium stripes and thin layers of copper. After high-temperature
recording with green light, refractive-index modulations exceeding Δn=8×10-5 for light of the telecommunication wavelength 1550 nm appear without the need of any development process of the written holograms.
The gratings are stable in the dark and no compensation mechanism via dark conductivity is observed. Thus this method may
be well suited for long-time applications in holography and integrated optics.
Received: 2 October 2000 / Revised version: 25 January 2001 / Published online: 22 March 2001 相似文献
10.
V. Dierolf A.B. Kutsenko C. Sandmann F. Tallian W. von der Osten 《Applied physics. B, Lasers and optics》1999,68(5):767-775
Detailed excited state absorption measurements under pumping at 980 nm and 1.5 μm together with conventional absorption and
emission spectroscopy is employed to investigate optical transitions of Er3+ in Ti:LiNbO3 channel-waveguides. The experimental data were evaluated using the Judd–Ofelt method giving parameters close to those in
the bulk. The good agreement between theoretical prediction and measurements allows us to calculate cross section, lifetimes,
and branching ratios. Based on these results we developed and tested a model which is able to predict the conditions for which
laser operation at 550 nm and 2.7 μm will be possible under 980 nm pumping.
Received: 9 December 1998 / Revised version: 8 January 1999 / Published online: 24 March 1999 相似文献
11.
3 crystal – was grown in our Laboratory. The absorption and fluorescence spectra were measured and show some differences from
the results of common Nd:MgO:LiNbO3 with monodomain structure. Third-order quasi-phase-matched violet second-harmonic generation in the sample was demonstrated
to characterize the quality of the crystal. The properties indicate that the periodically poled optical superlattice Nd:MgO:LiNbO3 has great potential for constructing a blue or green light source through self-frequency-doubling operation using the maximum
nonlinear optical coefficient d33 of LiNbO3 and the high-gain π polarization at the same time.
Received: 22 August 1997/Revised version: 10 January 1998 相似文献
12.
Dynamics of the Yb3+ to Er3+ energy transfer in LiNbO3 总被引:1,自引:0,他引:1
The energy transfer dynamics between Yb3+ and Er3+ ions in lithium niobate is investigated after ytterbium-pulsed excitation at 920 nm. The sensitisation of the LiNbO3:Er3+ system with Yb3+ ions does not modify the lifetime of the 4I13/2 erbium level (1.5-μm emission), whereas it induces a marked, concentration-dependent change in the lifetime of the 2F5/2 (Yb3+) and 4S3/2 (Er3+) multiplets (1060-nm and 550-nm emissions, respectively). The results are analysed by using the rate-equation formalism and
cross-relaxation model for the energy transfer.
Received: 15 October 1998 / Revised version: 24 November 1998 / Published online: 24 February 1999 相似文献
13.
G. Schreiber H. Suche Y.L. Lee W. Grundkötter V. Quiring R. Ricken W. Sohler 《Applied physics. B, Lasers and optics》2001,73(5-6):501-504
Using an FM-mode-locked Ti:Er:LiNbO3 waveguide laser as the fundamental source, wavelength conversion by cascaded χ(2):χ(2)-difference frequency generation with a conversion efficiency of up to +3(-4.6) dB was demonstrated at a pulse repetition
rate of about 2 (10) GHz. In addition, multi-channel conversion was demonstrated with a fully packaged wavelength converter
using a continuous fundamental source.
Received: 29 May 2001 / Revised version: 10 August 2001 / Published online: 2 November 2001 相似文献
14.
V.M. Petrov C. Denz A.V. Chamray M.P. Petrov T. Tschudi 《Applied physics. B, Lasers and optics》2001,72(6):701-705
Experimental and theoretical studies of the photovoltaic shift in the position of the diffraction efficiency maximum of holograms
recorded in LiNbO3 for the case of optimal electric field multiplexing are described. The experimental data are explained using a model in which
the bulk photovoltaic field is excited in a crystal that is electrically connected with a low loading resistance. We suggest
that the surface conductivity of the crystal can play an important role in the formation of this effective loading resistance.
Received: 29 November 2000 / Revised version: 9 February 2001 / Published online: 27 April 2001 相似文献
15.
The first observation of optical hexagons in a medium with dominating photovoltaic charge transport – in LiNbO3:Fe – is reported. The optimum conditions for hexagon observation are revealed and discussed. The dynamics of hexagon formation
are also studied.
Received: 9 February 2000 / Published online: 8 March 2000 相似文献
16.
3 crystal have been measured using Z-scan technique with picosecond pulses at 532 nm. The nonlinear absorption coefficient
and nonlinear refractive index are determined to be 2.5×10-10 cm/W and 5.3×10-15 cm2/W, respectively. Both sign and magnitude of the measured refractive nonlinearity are considerably different from the reported
Z-scan results in LiNbO3 obtained with cw laser beam at 514 nm. The nonlinearities in LiNbO3 induced by 532 nm picosecond pulses are believed to be mainly due to two-photon absorption and bound electronic Kerr effect
associated with the two-photon absorption.
Received: 4 July 1996 相似文献
17.
T. Volk B. Maximov T. Chernaya N. Rubinina M. Wöhlecke V. Simonov 《Applied physics. B, Lasers and optics》2001,72(6):647-652
LiNbO3:Zn single crystals and powders were studied by precise X-ray diffraction methods. Structural refinement yielded new models
of the intrinsic defect structure valid for different Zn concentration ranges. For concentrations up to 7 at. % in the crystal,
Zn ions incorporate onto Li sites; at higher concentrations Zn ions are found on both Li and Nb sites. Photorefractive properties
of LiNbO3:Zn are discussed in the context of the deduced defect models. A smooth increase in the photoconductivity up to 7 at. % Zn
is accounted for by a decrease of Nb antisites. Steeper growth of the photoconductivity at higher Zn concentrations is related
to vanishing Li vacancies.
Received: 17 November 2000 / Revised version: 23 January 2001 / Published online: 20 April 2001 相似文献
18.
E. Cantelar R.E. Di Paolo J.A. Sanz-García P.L. Pernas R. Nevado G. Lifante F. Cussó 《Applied physics. B, Lasers and optics》2001,73(5-6):515-517
In this work second-harmonic generation by quasi-phase matching (QPM) in Zn-diffused periodically poled lithium niobate channel
waveguides is presented. A stable TM?TE conversion by QPM has been found. The results are in good accordance with theoretical
estimations obtained by the phase-matching condition, either for the polarisation character of the second-harmonic wave as
well as for the spectral range, taking into account the periodicity of the domains.
Received: 16 May 2001 / Revised version: 7 September 2001 / Published online: 30 October 2001 相似文献
19.
Optical holographic memory using angular-rotationally phase-coded multiplexing in a LiNbO3:Fe crystal 总被引:2,自引:0,他引:2
We propose a new holographic memory scheme based on random-phase-coded multiplexing in a photorefractive LiNbO3:Fe crystal. Experimental results show that rotating a diffuser placed as a random-phase modulator in the path of the reference
beam provides a simple yet effective method of increasing the holographic storage capabilities of the crystal. Combining this
rotational multiplexing with angular multiplexing offers further data-storage possibilities. The advantage of using post-image
versus pre-image phase modulation of the object beam is demonstrated.
Received: 15 August 2000 / Published online: 10 January 2001 相似文献
20.
D. Zhang X. Chen Y. Jin X. Cao D. Zhu Y. Wang G. Ding Y. Cui C. Chen Z. Wu G. Lan 《Applied Physics A: Materials Science & Processing》2001,72(1):95-102
Raman spectra of Er:LiNbO3 crystal and Ti-diffusedEr:LiNbO3 strip waveguide, in which the Li/Nb ratio was altered using a vapor-phase equilibration (VPE) technique, were measured at
room temperature in the wave-number range 50–3500 cm-1. Both 488 and 514.5 nm radiations were used to excite Raman scattering, A1(TO) and E(TO) modes were recorded at backward scattering geometry. The results indicated that the lattice vibrational spectra
of the as-grown Er:LiNbO3 are almost the same as those of pure LiNbO3 except for the little shift of the peak position and the change of relative intensity of some peaks. In comparison with the
spectra of as-grown Er:LiNbO3 crystal the vapor-phase equilibrated Er:LiNbO3 and Er:Ti:LiNbO3 crystals in the lattice vibrational region exhibit the following features: firstly, Raman peaks become narrow, indicating
that the VPE process has brought Er:LiNbO3 and Er:Ti:LiNbO3 crystals closer to a stoichiometric composition; secondly, relative intensity of some peaks varies with the VPE time; and
finally, slight blue shifting in peak position was observed. Some of these features were correlated with the NbO6 octahedra and with the site distribution of the doped Er ions. In addition, green fluorescence peaks and/or bands associated
with the electron transitions 2
H
11/2?4
I
15/2 and 4
S
3/2?4
I
15/2 of the doped Er3+ were also observed. For 488 nm excitation they appear in the wavenumber range of 1200–3000 cm-1 and are well separated from lattice vibrational region; for 514.5 nm excitation, however, these fluorescence peaks shift
towards the low wavenumber region and overlap partially with the lattice vibrational spectra.
Received: 24 May 2000 / Accepted: 29 May 2000 / Published online: 13 September 2000 相似文献