Power dependent coupling efficiency for a butt-joined configuration using nonlinear cladding is analyzed by the beam propagation method. This configuration is not so sensitive to the angular misalignment as well as the offset between coupled waveguides on condition that the input power is appropriate to assure the propagation of spatial soliton.

Turbo coding is widely known as one of effective error control coding techniques in various digital communication systems since this coding method has proposed by C. Berrou, etc in 1993. In digital magnetic recording, it has been cleared that the error correcting capability of turbo coding is superior to most of conventional recording codes as a matter of course. But, the performance of a partial response maximum-likelihood (PRML) system combined with any recording code is degraded by many undesirable factors or effects. To improve the performance of the PRML system in high areal density recording, it is useful to adopt a higher order PRML system or high rate code in a general case. In this paper, the rate 32/34 turbo code combined with an enhanced extended class-4 partial response (E2PR4) is proposed. We call this trellis coded partial response (TCPR) system the rate 32/34 turbo-coded E2PR4 (32/34 TC-E2PR4). Our proposed TCPR system can be expected to get large coding gain and improve the performance of PRML system. As a result, the proposed coding system provides a good performance compared with the conventional systems. In especial, our system can achieve a BER of 10-5 with SNR of approximately 1.5 dB less than the conventional 8/9 maximum transition run (MTR) coded E2PR4ML system at a normalized linear density of 3.

The long-term bit error rate (BER) performance of partial response maximum likelihood (PRML) system using an adaptive equalizer in a perpendicular magnetic recording (PMR) channel with thermal decay is studied. A thermal decay model based on the experimental data giving the amplitude change of reproducing waveforms with the elapsed time for CoPtCr-SiO2 PMR medium is obtained. The BER performance of PR1ML channel for the 16/17(0,6/6) run-length-limited (RLL) code is evaluated by computer simulation using the model. The relationship between the ratio RJ of the jitter-like media noise power to the total noise power at the reading point and the required SNR to achieve a BER of 10-4 is also obtained and the performance is compared with that of the conventional equalization. The results show that the significant improvement in SNR by utilizing the adaptive equalization is recognized over all RJ compared with the conventional equalization.

Simplification of the Viterbi algorithm and the error rate performance are presented for a partial response maximum-likelihood (PRML) system employing the PR(1, 1) system as a PR system for (1, 7) run-length limited (RLL) code. The minimum run-length of 1's or O's in the output sequence of the precoder for (1, 7) RLL code is limited to 2. Two kinds of simplified Viterbi algorithms using this run-length constraint are proposed. One algorithm requires the path memory length of only two in the Viterbi detector. The Viterbi detector based on the other algorithm is equivalent to the simple PR(1, 1) system followed by a threshold detector. The bit-error rates of PRML systems with Viterbi detectors based on these algorithms are obtained by computer simulation and their performance is compared with that of conventional PRML systems for (1, 7) RLL code. It is shown that the proposed PRML system exhibits better performance than conventional PRML systems at high recording density.

The performance improvement of the partial response maximum-likelihood (PRML) system for (1, 7) run-length limited (RLL) code is studied. As a new PRML system, PR (1, 1, 0, 1, 1) system called modified E2PR4 (ME2PR4 ) followed by Viterbi detector for (1, 7) RLL code is proposed. At first, a determination method of the tap weights in transversal filter to equalize to PR (1, 1, 0, 1, 1) characteristic taking account of a noise correlation is described. And the equalization characteristics of the transversal filter are evaluated. Then, a Viterbi detector for ME2PR4 utilizing the constraint of run-length of (1, 7) RLL code is presented. Finally, the bit-error rate is obtained by computer simulation and the performance is compared with that of the conventional PRML systems called PR4, EPR4 and E2PR4 systems with Viterbi detector. The results show that among these systems our system exhibits the best performance and the SNR improvement increases with the increase in the linear density.

Recently, it is widely known that the partial response maximum-likelihood (PRML) system has attracted much attention as one of indispensable signal processing technique for achieving high density digital magnetic recording. But, the performance of PRML system is degraded by many undesirable causes in recording channel. For improving the performance, it is desirable to use any high order PRML system or high rate code. Our proposed two-track recording method increases the coding rate over 1, and contributes to decrease these degradation effects. The recording code in our system adopts a turbo code which provides a substantial near-ML performance by the suboptimum iterative decoding algorithm. In this paper, the turbo coded class four partial response (PR4) systems using the rate 4/6, 8/10 and 16/18 codes for high density two track digital magnetic recording are proposed. The error rate performance of the proposed system is obtained by computer simulation taking account of the partial erasure, which is one of nonlinear distortions at high densities. The performance of our system is compared with that of the conventional NRZ coded PR4ML system. The result shows that the proposed system is hardly affected by partial erasure and keeps good performance in high density recording. In especial, the proposed system using the rate 16/18 turbo code can achieve a bit error rate of 10-4 with SNR of approximately 12.2 dB less than the conventional NRZ coded PR4ML systems at a normalized linear density of 3.

In general, the performance of partial response maximum-likelihood (PRML) system is degraded by nonlinear distortion and high frequency noise in high-density digital magnetic recording. Conventional PRML system for single-track recording improves the performance when high order PRML systems and high rate codes are adopted. But, in general it is difficult to realize LSI circuits for high order PRML system and high rate code. In this paper, a trellis coded class four partial response maximum-likelihood (TC-PR4ML) system for high density two-track digital magnetic recording is proposed. Our two-track recording method can increase the coding rate over 1, which contributes to a decrease in both degradation effects from partial erasure, one of nonlinear distortions, and high frequency noise in high density recording. The error rate performance of the proposed system is obtained by computer simulation taking account of the partial erasure and it is compared with that of a conventional NRZ coded class four partial response maximum-likelihood (NRZ-PR4ML) system. The results show that the proposed system is hardly affected by partial erasure and keeps good performance in high density recording.

In this paper, we propose a new method to estimate and effectively reduce the effect of thermal asperity (TA) in the perpendicular magnetic recording (PMR) channels with the state trellis. The TA is estimated from the state trellis, then its average is used to modify the equalized signal entering the Viterbi detector. For the partial response (PR) targets with DC component, the proposed method with a maximum-likelihood detector can improve the bit error rate performance by more than an order of magnitude when TA occurs and degrades when the giant magneto-resistive (GMR) nonlinearity and base line wander (BLW) effects are present. Unlike the previous studies, this method allows the use of PR targets with DC component under the presence of TA.

The neural network equalization for polytopic multiplexing holography is studied to reduce interpixel interference. The bit error rate performance of the bilinear or bicubic interpolator followed by a neural network as an equalizer is obtained by computer simulation. The results show that the neural network equalizer provides an SNR improvement of about 1.0 dB over conventional equalization.

The previously-proposed model of the writing process in TDMR is modified based on the Stoner-Wohlfarth reversal mechanism. The BER performance for a neuro-ITI canceller is obtained via computer simulation using the R/W channel model based on the writing process, and it is compared to those for well-known TDMR equalization techniques.

Bit-patterned medium (BPM) is one of the promising approaches for ultra-high density magnetic recording systems. However, BPM requires precise write synchronization, and exhibits write-errors due to insufficient write field gradient, medium switching field distribution (SFD), demagnetization field from adjacent islands, and island position variation. In this paper, an iterative decoding system using a non-binary low-density parity-check (LDPC) code is considered for a BPM R/W channel with write-errors at an areal recording density of 2Tbit/inch2 including the coding rate loss. The performance of the iterative decoding system using the non-binary LDPC code over the Galois field GF(28) is evaluated by computer simulation, and it is compared with the conventional iterative decoding system using a binary LDPC code. The results show that the non-binary LDPC system has a larger write margin than the binary LDPC system.

A novel coupling configuration consisting of a tapered slab waveguide with a wedge-shaped nonlinear cladding is proposed. Coupling characteristics for TE waves are analyzed by means of the beam propagation method. The proposed configuration is less sensitive to the offset between coupled waveguides than is the configuration with a homogeneous non-linear cladding.

In various digital wireless communication systems, it is known that turbo coding provides an error rate performance within a few tenths of a dB of the theoretical Shannon limit. The error correcting capability of turbo coding is attractive for a recording code in a digital magnetic recording system. The performance of a partial response maximum-likelihood (PRML) system with any recording code is degraded by many undesirable factors such as linear and nonlinear distortions. For improving the performance of the PRML system, it is useful to adopt a high-order PRML system or high rate code in general. In this paper, the two-track recording system using turbo coding which can increase the coding rate over 1 and improve the performance is proposed. Turbo-coding provides a near-ML performance by the suboptimum symbol-by-symbol maximum a posteriori probability (MAP) decoding algorithm. Our proposed turbo-coded class 4 partial response (PR4) systems use the rate 4/6, 8/10 and 16/18 turbo codes for high-density two-track digital magnetic recording. The error rate performance is obtained by computer simulation, taking account of the partial erasure which is a prominent nonlinear distortion in high-density recording. As a result, the proposed systems are hardly affected by partial erasure and maintains good performance compared with the conventional NRZ coded PR4ML system.

A punctured convolutional coded PR4ML system for digital magnetic recording, which applies a punctured coding method to the convolutional code and records the punctured code sequences on two tracks, is proposed. In this study, the bit error rate performance of the proposed system is obtained by computer simulation taking account of partial erasure, which is one of the nonlinear distortions at high densities, and it is compared with those of a conventional 8/9 coded PR4ML system and an I-NRZI coded PR4ML system. The results show that the proposed system is hardly affected by partial erasure and exhibits good performance in high-density recording. A bit error rate of 10-4 can be achieved with SNR's of approximately 13.2 dB and 9.1 dB less than those of the conventional 8/9 coded and I-NRZI coded PR4ML systems, respectively, at a normalized linear density of 3.

Hydrogenated germanium films were fabricated in the thickness range of 7-98 nm on SiO2 at 150 by an rf glow discharge decomposition of 0.25% GeH4 diluted with H2, and the nucleation and growth of Ge nanocrystallites were measured from topographic and current images simultaneously taken by a conductive AFM probe after Cr contact formation on films so prepared. We have demonstrated that current images show fine grains in comparison with topographic images and the lateral evolution of the Ge grains with progressive film growth. The contrast in current images can be interpreted in terms of the difference in electron concentration between nanocrystalline grains and their boundaries.