No abstract

An electron beam recorder (EBR) was developed for mastering optical disks with a recording density of 100 Gbit/in2 using a multilevel recording format. In this recording format, a nanometer-scale accuracy of relative pit edge position is required in both radial and tangential directions. To achieve the recording position accuracy, a rotation stage with a noncontact vacuum seal and a correction system for rotation errors were developed. In addition, an active magnetic shield system and a learning compensation for beam displacement were adopted to improve the stability of the beam position. As a result, the ability to record with high accuracy and high resolution was confirmed from experimental results. A fine pit pattern with a minimum pit length of 70 nm was formed precisely. The recording accuracy of the EBR was evaluated to be approximately 2 nm (standard deviation) in both radial and tangential directions. Furthermore, a carrier-to-noise ratio of 64 dB was also obtained by reproducing an etched silicon master with a 240 nm monotone pit pattern.

Multiple access analysis is presented for pulsed direct sequence (DS) and hybrid DS time hopping (DSffH) ultra-wideband (UWB) communications considering a SalehValenzuela type clustered frequency selective Nakagami fading channel. A general analytical framework is developed for modeling the multiple access interference (MAl) in low-duty systems that is substantially complicated than analysis of more commonly known DS-code division multiple access (CDMA). Using Rake receiver with maximal ratio combining (MRC), we are able to produce a simple error rate expression for general number of combined paths. The theoretical results are then used for performance evaluation and comparison of the two systems. Results show that in multiple access environment, a DSffH system may gain many fold performance improvement as compared to a DS system.