Potassium Sodium Strontium Barium Niobate Research Articles

Channel waveguide array in Ce-doped potassium sodium strontium barium niobate crystal fabricated by He+ ion implantation

The authors report on the fabrication of one dimensional channel waveguide array in photorefractive Ce-doped potassium sodium strontium barium niobate crystal by photographic masking and following direct multiple energy He+ ion implantation. The dark mode spectroscopy is investigated for determining the refractive index modulation of the waveguide. The Floquet-Bloch modes (band transmission spectra) of the light propagating in the array are observed. It is found that the induced optical barriers with reduced refractive indices form semiclosed wedged walls, which confine the enclosed region (together with air) to be channel waveguides. The propagation loss of the waveguide array is determined to be ∼1.6dB∕cm for ordinary polarized light at 632.8nm.

Double optical waveguide in Cu-doped KNSBN crystal formed by MeV boron ion implantation

We reported for what is to be believed the first time a double optical waveguide in a Cu-doped potassium sodium strontium barium niobate (KNSBN) crystal formed by double boron ion implantation. The energy and dose of B + and B 3+ ions were (3+6) MeV and (2+2)×10 14 ions/cm 2, respectively. The refractive index profile of the waveguide showed a double-barrier confined shape, which suggested the formation of a two-layer waveguide structure. The two waveguide layers were with thickness of 2.6 and 2 μm, respectively, which was in a good agreement with the parameters obtained from transport and range of ions in matter 98 (TRIM) code simulation. The nuclear energy loss distribution of the MeV B ions implanted into this crystal had a similar shape to that of the waveguide index profile, which means an inherent relationship between the waveguide formation and the energetic energy deposition.

Double signal phase conjugation with a Cat conjugator

The phase conjugate reflection of double signals, induced by the self-pumped phase conjugation, is demonstrated in a 16° cut Cu-doped potassium sodium strontium barium niobate (KNSBN) photorefractive crystal. The phase conjugate reflectivities of signals were measured versus the pump-signal beam ratio. A comparison was made between the signal's reflectivity with and without the presence of the other signal beam. The multi-region four-wave mixing model within the same crystal has been employed to explain the geometry performance and the experimental results.

Enhancement of two-wave coupling in a Ce:KNSBN crystal with optimum polarization of the writing beams

We have improved the two-wave coupling amplification and the signal-to-noise ratio of an amplified signal with photorefractive cerium-doped potassium sodium strontium barium niobate (Ce:KNSBN) by employing optimum polarization orientation of the pump beam while the signal beam retains extraordinary polarization. The optimum polarization angle of the pump beam was found experimentally to be 30 degrees with respect to the extraordinary polarization direction in a symmetrically incident system. Nearly 1.9-times enhancement of the gain and nearly 3-times enhancement of the signal-to-noise ratio were achieved at a signal-to-pump beam intensity ratio of 1:40. At a beam intensity ratio of 1:2000, a two-wave coupling gain of nearly 500 was obtained, which is much higher than the gain previously reported. Modified coupled-wave equations that involve beam fanning with certain assumptions concerning the fanning parameters were used. The numerical solution is in good agreement with the experimental data. The results are compared with those obtained with a 45 degrees -cut BaTiO(3) crystal.

Four-wave mixing and edge-enhanced optical correlation in a Ce:KNSBN crystal

In the case of degenerate four-wave mixing in a cerium-doped potassium sodium strontium barium niobate (Ce:KNSBN) crystal, it is found that the transmission grating is dominant when the incident beams are extraordinarily polarized, the crystal response is more rapid, and the conjugate beam is more intense. Furthermore, the variation of the conjugate beam intensity forms a loop as the fringe modulation of the transmission grating varies. Based on this observation, we have implemented edge enhancement of an image and edge-enhanced optical correlation via four-wave mixing in a Ce:KNSBN crystal without the requirement of reversal of the signal-pump-beam intensity ratio.

Real-time edge-enhanced optical correlation with a cerium-doped potassium sodium strontium barium niobate photorefractive crystal

The nonlinear diffraction property of a volume grating written by two-wave mixing in a cerium-doped potassium sodium strontium barium niobate crystal is applied in a coherent image processing system to obtain real-time image edge enhancement as well as edge-enhanced optical correlation. The theoretical analysis of the correlator is given, and the experimental results of optical correlation are presented, which are compared with the computer-simulated results.

Fabrication and Characterization of Sol-Gel Derived Potassium Sodium Strontium Barium Niobate

Potassium sodium strontium barium niobate (K0.2Na0.2Sr0.48Ba0.32Nb2O6, KNSBN) powder and thin films dip coated onto Si(100) substrates have been prepared by sol-gel route. The thermal evolution of these sol-gel derived KNSBN was studied by differential thermal analysis (DTA) and thermogravimetry (TG). Their structural changes at different annealing temperatures were examined by X-ray diffraction (XRD) and Raman spectroscopy. Our results suggest that the KNSBN tetragonal tungsten bronze (TTB) phase is formed via an intermediate orthorhombic phase. Pure TTB phase KNSBN was obtained at annealing temperatures of 1200°C and 600°C for powder and films respectively.

Diffraction properties of transmission photorefractive volume gratings in a cerium-doped potassium sodium strontium barium niobate crystal

The diffraction efficiency of volume gratings written by two-wave mixing in a cerium-doped potassium sodium strontium barium niobate (Ce:KNSBN) photorefractive crystal is studied. It is found that the diffraction efficiency strongly depends on the polarization of writing beams and exhibits loop behavior with respect to the fringe modulation. The fringe modulations before and behind the crystal are compared. Modified coupled-wave theory is used to fit the experimental data. This research presents data that are relevant to the application of Ce:KNSBN crystals to holographic recording and optical information processing.

Spectroscopic Study of Light-Induced Charge Transfer Processes in Pure KNSBN, KNSBN:Ce and KNSBN:Cu Crystals

Photorefractive potassium sodium strontium barium niobate (KNSBN) crystals show two light-induced absorption bands under illumination at low temperature. The first absorption lies in the NIR (around 0.72 eV) and can be assigned to Nb4+ polarons. The second light-induced absorption appears as a broad band in the VIS spectral region (around 2.0 eV). The temperature dependence and the decay kinetics of the two centers are investigated for pure KNSBN, KNSBN:Ce and KNSBN:Cu crystals. Pure KNSBN crystals show a photoluminescence emission band around 765 nm, whereas Ce or Cu doping quenches the luminescence of KNSBN crystals. Two thermoluminescence peaks are observed at 80 and 228 K, respectively, with the same spectral distribution in pure KNSBN, confirming the existence of two electron trapping centers induced by illumination. The related light-induced charge transfer processes and the roles of Ce and Cu in KNSBN crystals are discussed and compared with similar centers in SBN crystals.

Spectroscopic Study of Light-Induced Charge Transfer Processes in Pure KNSBN, KNSBN:Ce and KNSBN:Cu Crystals

Photorefractive potassium sodium strontium barium niobate (KNSBN) crystals show two light-induced absorption bands under illumination at low temperature. The first absorption lies in the NIR (around 0.72 eV) and can be assigned to Nb4+ polarons. The second light-induced absorption appears as a broad band in the VIS spectral region (around 2.0 eV). The temperature dependence and the decay kinetics of the two centers are investigated for pure KNSBN, KNSBN:Ce and KNSBN:Cu crystals. Pure KNSBN crystals show a photoluminescence emission band around 765 nm, whereas Ce or Cu doping quenches the luminescence of KNSBN crystals. Two thermoluminescence peaks are observed at 80 and 228 K, respectively, with the same spectral distribution in pure KNSBN, confirming the existence of two electron trapping centers induced by illumination. The related light-induced charge transfer processes and the roles of Ce and Cu in KNSBN crystals are discussed and compared with similar centers in SBN crystals.

Photorefractive Properties of Co-Doped Potassium Sodium Strontium Barium Niobate Crystals

The transmissivity and the results of two-beam coupling and self-pumped phase conjugation (SPPC) experiments on Co-doped potassium sodium strontium barium niobate (KNSBN) single crystals are reported. The Co ions doped into KNSBN can form a deep energy level near 2.25 eV. The two-beam coupling gain coefficients of the Co-doped KNSBN are nearly 20 cm-1 at 2 teta = 370 for the transmission photorefractive index grating and larger than 29.2 cm-1 for the reflecting photorefractive index grating. A striking single-beam asymmetric transmission was observed. The maximum SPPC reflectivity is larger than 70% at teta = 49.70 for an intensity W = 77 mW, which is the largest value measured in the family of KNSBN crystals.

Photorefractive beam coupling between orthogonally polarized light beams by linear dichroism in Cu-doped potassium sodium strontium barium niobate

Two-beam coupling between orthogonally polarized waves is demonstrated by use of linear dichroism in Cu-doped potassium sodium strontium barium niobate. A maximum coupling gain coefficient of approximately 4 cm-1 is obtained at a grating spacing of 1 µm and a wavelength of 514.5 nm, where linear dichroism is moderate. The experimental results are compared with a theoretical model that allows a photorefractive grating to have an arbitrary phase shift with respect to an intensity-interference pattern. Fitting results indicate that the grating is not 90°-phase-shifted under open-circuit conditions. The contribution of the bulk photovoltaic field to the photorefractive phase shift is discussed.

Polarization and dipole moments of Co-doped potassium sodium strontium barium niobate crystals

Single crystals of potassium sodium strontium barium niobate (KNSBN) and cobalt-modified KNSBN were prepared using the Czochralski technique. The ferroelectric hysteresis loops and the infrared reflectivity spectra were collected. Compared with the undoped KNSBN crystals, the cobalt-modified crystals have stable hysteresis loops, whose spontaneous polarization is about 0.17 C/m2 and coercive field strength is about 670 V/mm, but those of the undoped KNSBN crystals are about 0.04 C/m2 and 530 V/mm, respectively. The measured infrared reflectivities vary with the orientations of the dipole moments owing to the Co doping. The c axis becomes the most stable orientation of the dipole moments, and the polarization can be locked and does not recede when the cobalt-modified crystals are polarized into a single domain.

Incoherent light amplification and phase conjugation of four beams with a photorefractive crystal

A mutually pumped phase conjugator is realized using a bridge configuration with a novel crystal of copper-doped potassium sodium strontium barium niobate. Phase conjugation reflectivity reaches 218%. The buildup times of phase conjugation outputs are measured, and a curve fit of the times is made. A self-curving coupling channel is observed. We use the theory developed by Lyubomudrov and Shkunov to model the coupling channels. The curved beam trajectory depending on the incident position and the incident angle is also calculated. With the results we show that one, two, three, and more four-wave mixing interaction regions exist in photorefractive bridge mutually pumped phase conjugators. Additionally, the simultaneous phase conjugation outputs of four incident beams are also demonstrated experimentally with the crystal.

Double phase conjugation in copper-doped potassium sodium strontium barium niobate crystals

We show a double phase conjugator with novel crystals of copper-doped potassium sodium strontium barium niobate. The phase conjugation reflectivity can reach 278% and depends on relative input positions of both incident beams. The response time with the input beam power ratio is measured and modeled as a function of input beam power ratio. The formation of the arch coupling loop is analyzed with theoretical simulation results and a positive feedback process is proposed. The influence of a self-pumped phase conjugation process on double phase conjugation fidelity is also discussed. It is necessary to avoid generating self-pumped phase conjugation to prevent the reduction of double phase conjugation fidelity.

Sickle Mutually Pumped Phase-Conjugate Mirror: Theoretic and Experimental Demonstration

A new mutually pumped phase conjugator with a photorefractive copper-doped potassium sodium strontium barium niobate crystal is demonstrated, in which the beams travel along a geometric path similar to the outline of a sickle. The maximum reflectivity is as high as 168%. Phase-conjugate images are obtained. The two-interaction region theory, based on the coupled plane wave amplitude, is used to account for the main characteristics of the new phase conjugator. The threshold coupling strength which depends on the reflection loss and the incident beam ratio, is also investigated and calculated.

Studies on growth and photorefractive properties of manganese-doped potassium sodium strontium barium niobate crystal

The crystal growth and photorefractive properties of Mn-doped potassium sodium strontium barium niobate(KNSBN) was reported. The Mn ions doped in the crystals can take part in the photorefractive processes, acting as charge stimulation and combination centers. The two-wave coupling gain coefficient of KNSBN:Mn is increased to be two times greater than that of undoped KNSBN and the self-pumped phase conjugation reflectivity as high as 73%.

Polarization and Dipole Moments of Manganese-Modified Potassium Sodium Strontium Barium Niobate Crystals

The crystal growth, the ferroelectric hysteresis loops, and the infrared reflectivity spectra of manganese-modified potassium sodium strontium barium niobate (KNSBN) single crystals are reported. Compared with the undoped KNSBN crystals, the manganese-modified crystals have stable hysteresis loops, whose spontaneous polarization is about 0.18 C/m2 and coercive field strength is about 600 V/mm, but those of the undoped KNSBN crystals are about 0.04 C/m2 and 530 V/mm, respectivery. The experimental results of the infrared reflectivity spectra show that the infrared reflectivities vary as the orientations of the dipole moments. The c-axis becomes the stablest orientation of the dipole moments owing to the manganese doping, and the polarization will be locked and not recede if the manganese-modified crystals are polarized into mono-domain.

Superior real-time holographic storage properties in doped potassium sodium strontium barium niobate crystal

We demonstrate superior holographic storage performance in a cobalt doped potassium sodium strontium barium niobate (Co:KNSBN) crystal that possesses a fast response time of 1.4 ms, a large photorefractive sensitivity of 13 x 10(-3) cm(3) J(-1) under a total writing intensity of 1 W/cm(2) , and high spatial resolution of 45 line pairs/mm. Reconstructed images with high fidelity have been obtained in real-time holographic storage. The dynamic properties of the index grating, the dependence of response time on writing intensity, and the dark decay of diffraction signal with increased writing intensity indicate that two species and shallow traps exist in Co:KNSBN crystal.

Planar optical waveguide in Cu-doped potassium sodium strontium barium niobate crystal formed by mega-electron-volt He-ion implantation

The first planar optical waveguide to the authors' knowledge has been formed in Cu-doped potassium sodium strontium barium niobate crystal by mega-electron-volt He(+) implantation. Both TE and TM modes are observed. The profiles of the ordinary and the extraordinary refractive indices are deduced from dark-line mode spectroscopy. The results show that the mega-electron-volt He implantation results in a decrease in refractive index in barriers for both n(o) and n(e), but for n(e) there is an obvious increase in the waveguide region. From an experiment in photorefractive two-wave mixing, it is found that the erasure time for two-wave mixing is prolonged by ion implantation.