Roshan Thapliya

Electrooptic characteristics of thin-film PLZT waveguide using ridge-type Mach-Zehnder modulator

The design, characterization, and drift due to electrical bias (DC drift) of thin-film lanthanum-doped lead zirconate titanate (PLZT) waveguide is reported using a Mach-Zehnder modulator. The mechanism of the electrooptic responses based on hysteresis of the applied field is proposed to understand the behavior of the device. It is shown that the thin film exhibits a Kerr effect having a coefficient value of 5/spl times/10/sup -18/ (m/V)/sup 2/. It is reported that by utilizing hydrogen-deficient dry etching, the DC drift is improved by a factor of 3.5. In addition, the verification of the operation of a PLZT-based device for more than 1400 h at 70/spl deg/C is reported, for the first time.

Tunable power splitter based on an electro-optic multimode interference device

Power splitters based on multimode interference (MMI) devices that offer the possibility of dynamically tuning the power-splitting ratio using electro-optic (EO) polymers are presented. The so-called 1 x 2 electro-optic MMI (EO-MMI) is demonstrated to provide a tuning range of 6 dB at approximately 54 V as theoretically predicted. Also a method is discussed to reduce the driving voltage by generating multiple beats, which provide 15 V for a tunable range of 10 dB for r(33)=15 pm/V at wavelength 1.55 microm.

Electro-optic multimode interference device using organic materials

We present experimental results verifying the optical robustness of a 1 x 1 multimode interference (MMI) device that is directly butt coupled with optical fibers at 70 degrees C for 1050 h and discuss the gradual increase of polarization dependent loss. Based on this structure, an electro-optic (EO) MMI waveguide device that can control the output optical power by using an electrode structure located directly on top of the multimode is presented. As a proof of principle, we demonstrate the switching operation of the EO-MMI device using commercially available chromophore as the active EO material.

High Speed Electro-Optic Polymeric Waveguide Devices With Low Switching Voltages and Thermal Drift

Experimental investigation of the feasibility of electro-optic (EO) polymeric devices is reported. A 2 × 2 latch-type EO multimode interference switch is shown to operate at 3.8 V with cross-talk 15 dB and switching time 6 ns. By introducing a macrocyclic polyether in the core for ion-trapping, thermal phase-drift of less than 1 radian for both 25°C and 70°C, after 500 hours of continuous operation, is achieved. This level of phase-drift suggests that EO polymers are attractive material platforms for practical photonic devices.

Investigation of drift in electro-optic polymer waveguides

The mechanism of the phase drift in electro-optic polymer waveguide devices is presented based on buildup of free ion charge at the electrode-clad interfaces. The difference of the electrode-clad interfaces at the top and bottom electrodes is shown to be important in reducing the drift and that doping of the core with macrocyclic polyethers can suppress this phenomenon. Arrhenius curves of long-term phase drifts using Mach–Zehnder modulators show the activation energies for symmetric electrode interfaces, asymmetric electrode interfaces, and macrocyclic polyether doped cores to be 0.30, 0.28, and 0.15 eV, respectively.

AdapComm: a bandwidth allocation methodology for multimedia applications in wireless networks

In this article, we propose AdaptMetric Communication (AdapComm), an end-to-end bandwidth estimation and allocation methodology putting emphasis on Quality of Experience at the user side. AdapComm dynamically samples the connection by sending dummy probing-TCP packets and derives the bandwidth online. This information is then sent to the server to adaptively change the data transmission to maintain user experience even in highly fluctuating networks, such as wireless connections. In future office-works, the usage of multimedia in mobile environments will be the norm, thus, we demonstrate the implementation of smooth, stall-free video streaming based on this scheme for enhanced user experience.

Encoded Semantic Tree for Automatic User Profiling Applied to Personalized Video Summarization

We propose an innovative method of automatic video summary generation with personal adaptations. User interests are mined from their personal image collections. To reduce the semantic gap, we propose to extract visual representations based on a novel semantic tree (SeTree). A SeTree is a hierarchy that captures the conceptual relationships between the visual scenes in a codebook. This idea builds upon the observation that such semantic connections among the elements have been overlooked in the previous work. To construct the SeTree, we adopt a normalized graph cut clustering algorithm by conjunctively exploiting visual features, textual information, and social user-image connections. Using this technique, we obtain an 8.1% improvement of normalized discounted cumulative gain in personalized video segments ranking compared with existing methods. Furthermore, to promote the interesting parts of a video, we extract a space–time saliency map and estimate the attractiveness of segments by kernel fitting and matching. A linear function is utilized to combine the two factors, based on which the playback rate of a video is adapted to generate the summary. We play the less important segments in a fast-forward mode to keep users updated with the context. Subjective experiments were conducted which showed that our proposed video summarization approach outperformed the state-of-the-art techniques by 6.2%.

Multiple-Beat Electrooptic Multimode Interference Devices

The reduction of the driving voltage for 1×1 electrooptic multimode interference devices (EO-MMIs) was investigated using 850 nm vertical-cavity surface-emitting laser (VCSEL) by increasing the beat number, Nb, defined as the number of single self-images generated inside the multimode section. The driving voltages of EO-MMIs were measured to be 71, 39, and 24 V for Nb=1, 2, and 3, respectively, using commercially available EO polymers, suggesting an overall reduction of 1/2–2/3 compared with an EO-MMI with Nb=1.

Electrooptic Multimode Interference Device Based on Nonlinear Organic Materials

Experimental verification of switching and stability of our novel electrooptic multimode interference device using organic materials is presented. Relaxation of the initial driving voltage 35.5 V is shown to be <20% for 180 hours at 70degC