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1 nm and inter-channel extinction ratio in excess of 15dB. A broadband coupler was used to extract 15% of the signal power from the ring to the multi-wavelength lascr output. The remaining 85% signal power was propagated through 9 kin of dispersion shifted fibre (DSF) which equalised the channel powers through four wave mixing (FWM). The WDM channels did not expcrience Raman gain from the 1455 nm pump in the DSF as residual pump power was attenuated by the FBG circulator. To determine CW operation of the laser each output channel was filtered in turn using two tunable, 3nm bandpass filters in series to give sidemode suppression > 30dB. The filtered channcls were analysed using a photodetector with loops rise time in conjunction with a 500 MHz bandwidth oscilloscope.

Intellectual Property (IP) protection is a critical element in multimedia transmission and delivery systems. Conventional IP protection on multimedia data can be categorized into encryption and watermarking. In this paper, a structure to perform layered access control on scalable media by combining encryption and robust watermarking is proposed, implemented, and verified. By taking advantages of the nature of both encryption and watermarking, copyrights of multimedia contents can be well protected and at the same time, multiple-grade services can be provided. In the summated examples, we assume a scalable transmission scheme over the broadcasting environment and use it to test the effectiveness of proposed method. When the embedded watermark is extracted with high confidence, the key to decrypt the next layer can be perfectly recovered. Then, the media contents are reconstructed and the copyrights are assured. The application examples also demonstrate the practicality of the proposed system.

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An optimized scheme for watermarking based on zerotrees is proposed in this paper. Digital watermarking is an effective means for protecting copyrights with three of the most fundamental requirements: watermark imperceptibility, watermark robustness, and watermark capacity. Conventional techniques in the literature mainly perform watermark embedding and extraction processes in the transform domain, including the discrete Fourier transform, discrete cosine transform, and discrete wavelet transform domains. The three watermarking requirements above are in conflict with each other; therefore, finding a way to obtain a trade-off among them is the major purpose of this paper. We first perform watermarking in the wavelet domain. Next, we properly select zerotrees in a wavelet transform with the genetic algorithm. Our simulation results not only demonstrate better performances of the watermarked images after optimization, but also reveal the robustness of the extracted watermarks under common attacks.