Anna Pyajt

All-Dielectric Electrooptic Sensor Based on a Polymer Microresonator Coupled Side-Polished Optical Fiber

A novel electrooptic (EO) electric field (E-field) sensor based on side-polished fiber coupled with an EO polymer microring resonator is proposed and demonstrated. An EO polymer waveguide with a ring shape is fabricated on the polished flat of an optical fiber. Light in the fiber evanescently couples into the resonator and forms resonant modes for certain wavelengths and produces notches in the output intensity of the fiber. External electric fields change the index of refraction of the ring waveguide and therefore dither its resonant wavelengths. For light of wavelength on the slope of a resonance notch, a change in the output intensity can be detected. The sensor is all dielectric without metal layers to distort the measured E-field. The resonant structure allows the sensor to potentially have much higher sensitivity than other electrooptic sensors based on Mach-Zehnder or polarization modulation. Since electrooptic polymers have higher electrooptic coefficients, lower dielectric constants and faster electrooptic responses than inorganic crystals, higher sensitivity, lower invasiveness, and higher bandwidth of E-field sensing can be expected. This sensor eliminates unreliable fiber-to-waveguide butt coupling as well as the high propagation loss encountered in the long straight EO polymer waveguides of sensors based on Mach-Zehnder structures. By using the fiber itself as the supporting substrate of the ring waveguide, the sensor can have small size and low disturbance to the measured electric field. The concept is demonstrated using AJLS103 EO polymer. A sensitivity of 100 mV/m has been achieved at frequencies up to 550 MHz (limited by the measurement system)

Broadband electric field sensor with electro-optic polymer micro-ring resonator on side-polished optical fiber

A novel broadband E-field sensor based on electro-optic polymer micro-ring resonator directly coupled to the core of optical fiber is proposed and demonstrated. A flat is made on the side of the optical fiber by polishing and an electro-optic polymer waveguide in the shape of a ring is placed on the polished flat. One side of the ring is directly above the core of the fiber and light is evanescently coupled between the fiber and the micro-ring. External electric fields change the index of refraction of the ring resonator and therefore its resonant wavelengths. The sensor is all dielectric without metal layers to distort the measured E-field. The resonance structure allows the sensor to potentially have much higher sensitivity than other electro-optic sensors based on interferometry or polarization modulation. Since electro-optic polymers have higher electro-optic coefficients, lower dielectric constants and faster electro-optic responses than inorganic crystals, higher sensitivity, lower invasiveness and higher bandwidth of E-field sensing can be expected. The sensor with EO polymer micro-ring directly coupled to side-polished fiber eliminates unreliable and possibly lossy fiber to waveguide butt coupling as well as the high propagation loss which comes from the long straight EO polymer waveguides. Unlike devices based on waveguide technology, a supporting substrate is not necessary in this device. This leads to sensors of small size and low disturbance to the measured electric field. In the proof-of-concept experiment, a sensitivity of 100 mV/m has been achieved at frequencies up to 550 MHz (limited by the measurement system) using AJLS103 electro-optic polymer.

Novel wavelength selective switch based on electro-optic polymer microrings

A novel wavelength selective 2x2 switch based on two microring resonators is proposed. The device consists of two intersecting channel waveguides with each of the two rings coupled to both waveguides. Depending on the control voltage the light of selected wavelength either can propagate through the straight waveguide or can be coupled to one of the rings and from the ring couple to the perpendicular output. Therefore every ring can independently switch one wavelength from any input to the perpendicular output. This wavelength selective switching adds to the traditional switch functionality. Theoretical calculations were carried out to determine optimum parameters of the switch and soft-lithography was used for implementation. Being fabricated from the latest electro-optical polymers this device can provide very high switching speed and low operation voltage.

Feasibility study of integration of electro-optic polymer waveguide device with MOSFET circuitry on silicon

Systematic development of electro-optic (EO) polymers is leading to optical and material properties such that they present an increasingly viable alternative to crystalline-based technologies for integrated optics. EO polymers demonstrate an inherent velocity match between radio-frequency and optical waves, making them excellent candidates for applications in high-speed telecommunication switching and optical interconnects for VLSI circuitry. In addition, EO polymer devices are relatively simple to fabricate at conditions compatible with microelectronics industry processes, making same-substrate integration of optical and electronic circuitry possible. In this paper, we describe two vertical integration schemes whereby a polymer-based electro-optic modulator may be controlled by metal-oxide semiconductor field effect transistor (MOSFET) circuitry. One scheme described is an insitu integration on the same silicon (Si) substrate. The second scheme is the integration of a modulator built on a flexible substrate with a MOSFET circuit on a second Si substrate. Both schemes have potential applications for integrated electro-optics.

A biased push-pull technique to achieve fractional volt half-wave voltage of Mach-Zehnder modulators

In this paper, we report a novel technique that combines push-pull Mach-Zehnder modulator structure with dc bias to achieve fractional volt half-wave voltage in intensity modulation. The technique is accomplished by simultaneously applying a common mode operation voltage and a differential dc bias voltage on the two arms of a Mach-Zehnder modulator. The modulators are tested for half-wave voltage at different temperatures while applying different push-pull biases. The results are compared with a push-pull EO polymer modulator that has identical dimensions and the same materials, and which is fabricated and poled with conventional method. It is found that our new approach reduces the half-wave voltage by a factor of more than five.

Organic electro-optic glasses for WDM applications

This communication primarily deals with utilizing organic electro-optic (OEO) materials for the fabrication of active wavelength division multiplexing (WDM) transmitter/receiver systems and reconfigurable optical add/drop multiplexers (ROADMs), including the fabrication of hybrid OEO/silicon photonic devices. Fabrication is carried out by a variety of techniques including soft and nanoimprint lithography. The production of conformal and flexible ring microresonator devices is also discussed. The fabrication of passive devices is also briefly reviewed. Critical to the realization of improved performance for devices fabricated from OEO materials has been the improvement of electro-optic activity to values of 300 pm/V (or greater) at telecommunication wavelengths. This improvement in materials has been realized exploiting a theoretically-inspired (quantum and statistical mechanics) paradigm for the design of chromophores with dramatically improved molecular first hyperpolarizability and that exhibit intermolecular electrostatic interactions that promote self-assembly, under the influence of an electric poling field, into noncentrosymmetric macroscopic lattices. New design paradigms have also been developed for improving the glass transition of these materials, which is critical for thermal and photochemical stability and for optimizing processing protocols such as nanoimprint lithography. Ring microresonator devices discussed in this communication were initially fabricated using chromophore guest/polymer host materials characterized by electro-optic coefficients on the order of 50 pm/V (at telecommunication wavelengths). Voltage-controlled optical tuning of the pass band of these ring microresonators was experimental determined to lie in the range 1-10 GHz/V or all-organic and for OEO/silicon photonic devices. With new materials, values approaching 50 GHz/V should be possible. Values as high as 300 GHz/V may ultimately be achievable.

Dynamic hologram recording and relaxation in C60 solutions

We performed numerical experiments on dynamic hologram (grating) recording and relaxation in fullerene C60 solutions and carried out the comparison with experiment on self-diffraction (intensity up to 50 MW/cm2, pulse duration 10nm, wavelength 532 nm, angle between pump beams 0.16 rad). The grating recording was numerically simulated by the differential equations: (1) balanced equations system describing population in six-level system, (2) time-space equation for absorption from different levels, (3) equation for the hologram thermal relaxation. Using this method the time-space dependence of medium refraction index due to thermal absorption was determined. Based on phase grating recording the estimation of diffraction efficiency in different diffraction orders was determined. It was shown that during the recording the shape of phase thermal grating becomes nearly rectangular due to absorption on exited singlet and triplet sublevels. The long time of life of triplet sublevels of C60 influences phase grating relaxation. The calculated values of diffraction efficiency in 1-5 levels are almost equal to the values form the experiment. According to our results of numerical analysis we can make a conclusion that the model successfully describes recording and relaxation of thermal phase hologram in fullerene solution. Results of phase grating relaxation can be used for investigation of fullerene properties and life-times of triplet sublevels. Our model can be used for numerical simulation of phase and amplitude grating recording and relaxation in fullerene solution and fullerite with pumping by nano-pico and femtosecond pulses and CW radiation.

Dynamic holograms recording in fullerene-containing solid state media by 300-ps and 20-ns laser pulses

The results of experimental investigation of dynamic holograms recording by 20 ns and 300 ps laser pulses in fullerene-containing solid-state matrices are presented in this paper. The spectral analysis in range 300 - 700 nm shows correlation between efficiency of dynamic holograms recording and presence of absorption band at nearly 330 nm. We use two types of solid-state matrices: porous glass and polymethylmethacrylate hosts, which were filled with fullerene C60. From the dynamic holograms recording experiments and from the spectral analysis we obtained data on sensitivity and stability of the media, which can be used later in practical applications like all-optical switching.

Dynamic hologram recording in fullerene-containing nano-size porous glasses

We report the theoretical and experimental results of dynamic holograms recording in nano-size porous glasses containing fullerine C60 and its use for optical limiting. To record a grating with spatial frequency 20 mm-1 we used laser pulses with 18 ns duration and 532 nm wavelength. Initial transmittance of the samples varied from 30% to 70%. We found that high diffraction orders appeared out of the medium during the experiment and investigated dependence self-diffraction on initial transmittance of the samples and in case when the samples were filled by toluene. It was found that the most effective self-diffraction is in situation when we use toluene and initial transmittance of the sample is nearly 70%. For explanation of our experimental results we made a numerical model of dynamic hologram in fullerene-containing media taking into consideration amplitude and phase grating forming during the pulse length. Our model showed good agreement with experimental results.

Amplitude-phase dynamic holograms recording in C60 fullerene solutions

The theoretical model of dynamic hologram recording in fullerene solutions based on the system of balanced equation and equation for absorption is constructed. The profiles and diffraction efficiencies of the amplitude and phase gratings are numerically calculated depending on input intensity. Due to nonlinear absorption the profile of amplitude grating for high energies becomes significantly non-sinusoidal and the amplitude of phase grating increases. Computation shows appearance of high diffraction orders and their number and intensity increase with increasing of input intensity. The comparison of theoretical results with results of experiment1 shows good adequacy of the model.