Field-induced Refractive Index Change Research Articles

Temperature dependence of Kerr coefficient and quadratic polarized optical coefficient of a paraelectric Mn:Fe:KTN crystal

We measure temperature dependence on Kerr coefficient and quadratic polarized optical coefficient of a paraelectric Mn:Fe:KTN crystal simultaneously in this work, based on digital holographic interferometry (DHI). And the spatial distribution of the field-induced refractive index change can also be visualized and estimated by numerically retrieving sequential phase maps of Mn:Fe:KTN crystal from recording digital holograms in different states. The refractive indices decrease with increasing temperature and quadratic polarized optical coefficient is insensitive to temperature. The experimental results suggest that the DHI method presented here is highly applicable in both visualizing the temporal and spatial behavior of the internal electric field and accurately measuring electro-optic coefficient for electrooptical media.

A novel coupled quantum well with large negative electro-refractive index change and low absorption loss

In order to solve excessive insertion loss and low on/off ratio in quantum well reflection-type waveguide optical switches, a novel InGaAs/InAlAs coupled quantum well structure is proposed. In the case of low applied electric field (F=19 kV/cm) and low absorption loss (α ≈61.2 cm−1), a large negative field-induced refractive index change (Δn=−0.0134) is obtained in the novel coupled quantum well structure at the operating wavelength (λ=1550 nm). The value is larger by over one to two order of magnitude compared to that in a rectangular quantum well (RQW) on the above same work conditions.

A Quasi-Symmetric Coupled Quantum Well and ItsElectric-Optical Properties

We propose a novel coupled quantum well structure, i.e. aquasi-symmetric coupled quantum well (QSCQW). Based on the demands ofoptical switching devices for quantum well materials, the QSCQWconfiguration is further optimized. Consequently, in the case of lowapplied electric field 25 kV/cm and low absorption loss 100 cm−1,a large field-induced refractive index change (for TE mode, n = 0.0106;for TM mode, n = 0.0115) is obtained in the QSCQWstructure at the operation wavelength 1550 nm. The value is in one ortwo order of magnitude larger than that in a rectangular quantum welland about 50% larger than that of five-step asymmetric coupled quantumwell structure under the same working conditions. The refractive indexchange obtained with the optimized QSCQW under so low absorption lossand applied electric field is very attractive for semiconductor opticalswitching devices. This manifests that the QSCQW structure has a greatpotential for applications in ultra-fast and low-voltage opticalswitches and in travelling wave modulators.

A Novel Coupled Quantum Well Structure with Low-DrivingVoltage, Low Absorption Loss and Large Field-Induced Refractive IndexChange

Based on a two-energy-level system, we analyse the changingground eigenenergies of symmetric GaAs/AlxGa1−x As coupledquantum wells in the presence of an applied electric field. From thetheoretical analysis for symmetric coupled quantum well, we find theadvantages and disadvantages when it is applied to travelling wavemodulator. Hence the conception of quasi-symmetric coupled quantum wellsis put forward. Based on the demands of travelling wave modulator forquantum well materials, the configuration of quasi-symmetric coupledquantum well is further optimized. Consequently, in the case of lowapplied electric field (F = 20 kV/cm) and low absorption loss (α⩽100 cm−1), a large field-induced refractive change Δn(for TE mode, Δn = 0.021; for TM mode, Δn = 0.0121) isattained in the optimized coupled quantum well.

Action from tunable periodic structures. II. Experimental observation of electric field-induced diffraction peaks.

As previously predicted [Appl. Opt. 40, 5583 (2001)], we have now observed electric field-induced diffraction peaks in transmission and reflection experiments by use of a LiNbO3 sample with interdigital planar electrodes that serve as a diffraction grating. The magnitudes of the new peaks in the reflection experiments are ten times larger than those in the transmission experiments. We interpret these effects in terms of a field-induced refractive-index change produced by the linear electro-optic effect. The positive and negative changes in the refractive index produce two diffraction gratings that are period doubled with respect to the original grating and that have a phase difference between them. The superposition of the diffracted light from these gratings is shown to account for the new peaks. From the relative magnitude of the new peak to that of the central peak, we estimate the refractive-index change to be 0.004.

Variation of attenuated total reflection due to the birefringence of liquid crystals by excitation of surface plasmons

Attenuated total reflection (ATR) is a prominent effect in examining the excitation of surface plasmons. The Kretschmann–Raether and Otto configurations are implemented to generate surface plasmons and to examine the change of the refractive index of liquid crystals (LCs) by an applied field. A mixture of nematic and cholesteric liquid crystals is sandwiched between two glass substrates coated with conducting films. The minimum ATR angle changes by only 1° as the applied voltage increases to as much as 30 V (corresponding to 6×105 Vm-1), which does not agree with the calculation based on field-induced refractive-index change. This fact suggests that the orientation of LC molecules adjacent to an electrode surface is unaffected by the external field because of the strong-anchoring effect. A Jones-matrix simulation together with a multilayered structure of a LC clearly adduces this fact.

Anomalous Sharp Dip of Large Field-Induced Refractive Index Change in GaAs/AlGaAs Five-Layer Asymmetric Coupled Quantum Well

The five-layer asymmetric coupled quantum well (FACQW) is a new potential-tailored quantum well for ultrafast and low-voltage optical modulators and switches. Almost linear and large electrorefractive index change can be obtained in the transparency wavelength regions. In the GaAs/AlGaAs FACQW, an abrupt change in refractive index change Δn due to an applied electric field F occurs at a certain electric field range, which results in an anomalous sharp dip of Δn versus F. The physical origin and the elimination of the dip are discussed in detail. The abrupt change of refractive index is caused by significant changes of the wavefunction overlap integrals (and exciton binding energies) of transitions between the ground states for an electron (e1) and a heavy hole (hh1), and transitions between e1 and the first excited state for a heavy hole (hh2). The overlap changes are mainly due to shifts of the wavefunction distribution of hh1 and hh2, respectively. The dip can be eliminated by changing the position or Al content of the AlGaAs barrier layer in the FACQW. In addition, the larger negative index change in a modified FACQW structure is demonstrated.

Polarization-independent large field-induced refractive index change in a strained five-step GaAs–InAlGaAs asymmetric coupled quantum well

A tensile-strained five-step asymmetric coupled quantum well (FACQW) structure is proposed for large field-induced refractive index change without polarization dependence and redshift of the absorption edge. A strong exciton absorption peak is caused by electron-hole transitions between symmetric wave functions and antisymmetric wave functions with a small applied electric field. The field-induced refractive index change of strained the FACQW is larger by one order of magnitude compared to that of a rectangular quantum well and the difference in the refractive index change of TE and TM modes is under 2% when the operation wavelength is not at the absorption edge.

Large field-induced refractive index change without red shift of absorption edge in five-step asymmetric coupled quantum wells with modified potential

A structure composed of five-step asymmetric coupled quantum wells (FACQWs) is first proposed for large field-induced refractive index change without red shift of absorption edge. A strong exciton absorption peak is caused by e1hh2 and e2hh1 transitions with a small applied electric field. The field-induced refractive index change of FACQWs is larger by one order compared to that of rectangular quantum well when the operation wavelength is apart from absorption edge.

Field-induced refractive index variations in GaAs/AlGaAs multiple quantum well waveguide modulator

A quantum well electroabsorption waveguide modulator utilizing a field-induced refractive index change was designed and fabricated. The on/off ratios of the device were investigated as a function of wavelength over the spectral range of 850 nm to 910 nm for the various reverse biases. The field-induced refractive index variations associated with quantum-confined Stark effect was theoretically obtained based on the measured on/off ratios. The resulting maximum refractive index change( ${\DELTA}n) of ~7.5 {\times} 10^{-4}$ at -8 V was estimated.

Large field-induced refractive-index change on TM-polarized light in an InGaAlAs-InAlAs MQW waveguide structure

For optical modulation devices with low-loss and high efficiency, we have investigated field-induced refractive index change (/spl Delta/n) and absorption change (/spl Delta//spl alpha/) in the large detuning wavelength region where absorption is almost negligible using an InGaAlAs-InAlAs MQW waveguide structure. The result shows larger /spl Delta/n induced on TM-polarized light than that on TE-polarized light. Moreover, in induced on TM-polarized tight can become smaller than that on TE-polarized light. This suggests that TM-polarized light is more useful for low-loss and high-efficiency phase-modulation devices, especially large-scale matrix switches.

Electrooptic effects in an InGaAs/InAlAs multiquantum well structure

The field-induced refractive index change of an InGaAs/InAlAs MQW waveguide is examined for various wavelengths and TE/TM modes using a MZ modulator. The quadratic EO coefficients in the MQW waveguide for both TE and TM modes due to quantum confined Stark effect (QCSE) is on the order of 10/sup -18/ (m/sup 2//V/sup 2/), which is dominant compared with the linear EO effect. An effective linear EO effect, however, is significant because of the bias field arising from the built-in potential. This effect is more than one order greater than the conventional laser EO effect, which may suggest new device applications for QCSE. >