Date of publication xxxx 00, 0000, date of current version xxxx 00, 0000.

No abstract

With the advent of technology and multimedia production, the world has witnessed a tremendous increase in digital media attacks, which duplicates, forges and tamper the data leading to the violation of copyright laws. In this paper, a robust and secure digital image watermarking is proposed, which exploits the chaotic behaviour of the nonlinear oscillators realized through Memristive diodes. The proposed scheme relies on a Human Visual System (HVS) model in order to mimic the real-life scenario. To improve the robustness of the proposed approach and to further increase the security of the digital watermarked media whilst still retaining compatibility with the real-time events, Histogram of Oriented Gradients (HOG) and extreme learning machine (ELM) is implemented. Secure key generation by means of scrambling through Arnold Transform and the coefficients of Memristive Chaotic Oscillator ensures extreme security. The watermark embedding followed the pixel transformation based on discrete cosine coefficient modification, and a semiblind watermarking extraction procedure was carried out through trained ELM models. A detailed analysis has been presented to evaluate the tradeoff between imperceptibility, security and robustness using performance metrics like PSNR, NC, SSIM, and BER. To establish a real-time implementation of the proposed architecture, the simulated results were verified using real-time chaotic signals generated from the chaotic oscillator, which dictates excellent performance against watermarking attacks and image processing tasks.

We propose the design of a nonvolatile, low-loss optical phase shifter based on optical phase change material (O-PCM). The optical phase change material Ge 2 Sb 2 Se 4 Te 1 (GSST), which exhibits low loss at telecommunication wavelength 1.55 µm as compared to other commonly used O-PCMs, is used in this work as the active material. Instead of direct interaction of the waveguide mode with the O-PCM, the design utilizes coupling between the primary SiN strip waveguide and a waveguide formed by O-PCM, in its amorphous state. The phase matching in the amorphous state inhibits the interaction of the waveguide mode with GSST in its highly lossy crystalline state resulting in low loss operation. Due to a high differential refractive index between the two states of GSST, the design requires a very small length of the phase shifter to accumulate the desired phase difference. The overall response of the Mach-Zehnder Interferometer (MZI) configuration using the designed phase shifter shows that the design can be used to obtain optical switching with a very small insertion loss and crosstalk over the entire C-band. Index Terms-Coupled mode analysis, Optical Switches, Phase change materials. I. INTRODUCTION hase shift for optical switching in silicon photonic devices is mainly achieved by free carrier injection [1-3] and thermo-optic effects [4]. These effects give rise to a small change in the refractive index, which results in large device length to obtain the required phase change. The alternative is to use the resonant structures to obtain devices with a small footprint, however, at the expense of low bandwidth and high sensitivity [5,6]. The compact hybrid plasmonic-photonic switches based on 3-waveguide directional couplers have also been reported, but the associated insertion loss is high [7,8]. In recent years, optical phase change materials (O-PCMs) have

We present an ultra-compact strip to slot waveguide mode converter to facilitate excellent fundamental mode coupling between the strip and slot waveguide over a broad wavelength range. The design utilizes tapered waveguide geometries for adiabatic mode conversion. The taper profiles are optimized using a fast quasi-adiabatic approach to achieve the adiabatic mode conversion within the smallest possible length. We numerically demonstrate a conversion efficiency of 99.4% at a wavelength 1.55 μm with a variation of <1.5% over a bandwidth of 100 nm and <5% over a bandwidth of 200 nm. In addition, the design is ultra-compact with a footprint of only 1.23×3.7 μm 2 and offers a high tolerance to the possible fabrication inaccuracies.