Electro-optic Modulation Effects Research Articles

Polarization control investigation based on an integrated graphene-assisted microring cavity

In this paper, we propose and analyze an integrated polarization-selective structure of a graphene-assisted silica microring cavity to realize polarization control due to different optical distributions of whispering-gallery modes in the microring and polarization-dependent absorptions of graphene. A graphene stripe is partially side coupled with a silica microring to distinctly influence the propagations of a TE mode and TM mode in the microring. Especially, the appearance of the plasmonic mode in the groove between the graphene and the microring enhances light–matter interaction between the graphene and the TM-polarized mode, while without that for the case of TE mode propagation. By applying voltage on the graphene stripe along with its electro-optic modulation effect, the difference in the polarization extinction ratio of 20.6 dB is obtained between the cases of the polarized TM mode and TE mode in the microring. Furthermore, a second silica microring is added in this hybrid structure to couple the original microring along with a graphene stripe embedded in between finally realizing an electromagnetically induced transparency line shape because of the plasmonic coupling in both cavities with the condition of TM mode propagation, while without any line-shape change for the case of TE mode propagation. This compact hybrid structure offers a good integrated photonic platform to realize an excellent polarization-selective device.

High-order harmonic generation in uniformly distributed topological edge states

Second-harmonic generation and third-harmonic generation have been widely investigated in nonlinear topological photonics. However, due to the weak nonlinear effect and the strict phase matching condition, it is a challenge to observe the high-order harmonic generation in general bulky or periodic structures. In this work, through the design of a binary one-dimensional photonic crystal, we obtain the topological edge states (TESs) with equal frequency spacing based on the electro-optic modulation effect. The designed structure has generated the high-order harmonic waves with the nonlinear effect excited by intense femtosecond laser pulses. The uniformly distributed TESs satisfy the request of phase matching. The nonlinear sum-frequency effect combined with the unique TESs leads to high-order harmonic waves. The presented work provides a feasible scheme to generate the high-order harmonic waves from the simple 1D structure.

Nonvolatile Electrically Reconfigurable Integrated Photonic Switch Enabled by a Silicon PIN Diode Heater.

Reconfigurability of photonic integrated circuits (PICs) has become increasingly important due to the growing demands for electronic-photonic systems on a chip driven by emerging applications, including neuromorphic computing, quantum information, and microwave photonics. Success in these fields usually requires highly scalable photonic switching units as essential building blocks. Current photonic switches, however, mainly rely on materials with weak, volatile thermo-optic or electro-optic modulation effects, resulting in large footprints and high energy consumption. As a promising alternative, chalcogenide phase-change materials (PCMs) exhibit strong optical modulation in a static, self-holding fashion, but the scalability of present PCM-integrated photonic applications is still limited by the poor optical or electrical actuation approaches. Here, with phase transitions actuated by in situ silicon PIN diode heaters, scalable nonvolatile electrically reconfigurable photonic switches using PCM-clad silicon waveguides and microring resonators are demonstrated. As a result, intrinsically compact and energy-efficient switching units operated with low driving voltages, near-zero additional loss, and reversible switching with high endurance are obtained in a complementary metal-oxide-semiconductor (CMOS)-compatible process. This work can potentially enable very large-scale CMOS-integrated programmable electronic-photonic systems such as optical neural networks and general-purpose integrated photonic processors.

Tunable filter based on cavity electro-optic modulation for DWDM applications

In this paper the authors have demonstrated the feasibility and the realization of a wavelength tunable filter with an electro-optic modulation effect realized on diffused Ti:LiNbO3 waveguide. The two reflectors of the cavity consist in two Bragg׳s mirrors of identical period Λ=1.81μm and whose total number N=140. Both mirrors have been engraved using the Focused Ion Beam technique up to the depths l1=l2=2.7μm separated by a distance of lc=500μm. We obtained thanks to electro-optic modulation effect a tunable shift whose value is 0.67nm in a free spectral range FSR=1.59nm for a voltage variation up to 60V. This designed and realized probe will find many DWDM (Dense Wavelength Division Multiplexing) applications.

Electro-optically tunable photonic crystals

We report on electro-optical modulation with a sub-1-V sensitivity in a photonic crystal slab waveguide resonator which contains a nanostructured second-order nonlinear optical polymer. The electro-optical susceptibility in the core was induced by high electric-field poling. A square lattice of holes carrying a linear defect was transferred into the slab by electron-beam lithography and reactive ion etching, creating a photonic crystal slab-based resonator. Applying an external electric modulation voltage to electrodes leads to a linear electro-optical shift of the resonance spectrum and thus to a modulation of the transmission at a fixed wavelength based on the electronic displacement polarization in a noncentrosymmetric medium (Pockels effect). This effect is therefore inherently faster than other reported electro-optic modulation effects in nanophotonics.

Orientationally Enhanced Photocurrent and Electrooptic Modulation Effects in Bacteriorhodopsin/Polyvinyl Alcohol Thin Films

Polymeric films of bacteriorhodopsin, formed by embedding purple membrane fragments into a poly(vinyl alcohol) matrix without field poling, exhibit modulated photocurrent and electrooptic effects when an AC modulating rectangular voltage or a sinusoidal voltage is applied across the films. When the modulating frequencies are lower than 100 Hz, both effects are enhanced by the orientation of the purple membrane fragments and exhibit two different orientational time constants. The orientational enhancement at low frequencies (∼7.1 Hz) arises from the permanent dipole moments of membranes, and the enhancement at higher frequencies (∼74.8 Hz) is attributed to the induced dipole moments of the purple membrane molecules. For quantitative analyses of these processes, a theoretical model is proposed. From the combination of model calculations and fitted experimental results, we determine that the permanent dipole moment of the membrane material is ∼33 kD and the induced dipole moment is ∼10-13 cm3. We also demonstrate that when a poling field is applied across the films, the electrooptic coefficients are increased linearly with increasing field strength.

Large electro-optic modulation effect observed in ion-exchanged KTiOPO4 waveguides

We report the observation of an anomalously large electro-optic modulation effect in potassium titanyl phosphate (KTiOPO4) waveguides fabricated under various conditions. An interferometric method was used to measure the effective electro-optic coefficient in the waveguides by measuring the phase retardation of an optical mode when a voltage was applied across the substrate. We observed that at low modulation frequency the effective electro-optic coefficient in the waveguides can be higher than the bulk value by a factor up to about 100. A space charge model relating the mobile charge, space charge field, and observed enhancement in the electro-optic modulation is proposed to explain the mechanism of this effect. Calculation for dc steady state, small signal analysis, and large signal simulation is compared to the experimental observation. Possible device application and long term effects on system operation are also discussed.

Novel electro-optic modulation effect at 10μm wavelength in GaAs/AlGaAs quantum wells

A novel method of controlling the intersubband optical absorption of a quantum well system is reported. The absorption is tuned to 10 μm wavelength by choosing the appropriate well width and its intensity is modulated by using a Schottky gate to control the carrier density in the quantum wells.