An active ultra-low frequency vertical vibration isolator is presented in this paper, which could isolate the vibration from the earth. It could create an inertial reference point for precision physics research and experiments such as high precision absolute gravity measurement. This system is based on a structure with two-stage vertical suspension springs. For the second-stage spring, the suspension point is forced to track the suspended mass through closed loop control, and the length of the spring is almost constant and the restoring force of the mass is closed to zero. Consequently, a system with an ultra-low frequency is realized. With precision mechanical design, high resolution photoelectric detection method, and analog circuit feedback control, a vertical vibration isolation system has been constructed with a period of up to about 40s. This vibration isolator meets the demand of high precision absolute gravity measurement and is promisingly applied to the homemade T-1 absolute gravimeter.
A new rate 8/12 4-level run-length limited (2, 9) code with spaced pits/lands constraint has been constructed.
The code efficiency is high of 94.0%, and the density ratio is 2.0 bits per minimum recorded mark. The encoder
has six states and the decoder window length is only two. This byte-oriented code is very suitable to be applied
in practical multi-level read-only optical disc systems.
KEYWORDS: Modulation, Digital video discs, Signal to noise ratio, Sensors, Optical recording, Signal detection, Device simulation, Optical discs, Optical storage, Binary data
Multi-level optical recording using run-length-limited (RLL) modulation is a novel method to significantly increase
the information recording density without changing optical or mechanical parameters. In this paper, the
experimental results of four-level RLL modulation on read-only digital versatile discs (DVD-ROM) are introduced.
A new DC-free 4-level RLL (2, 8) code with code rate of 8/10 (bits/symbol) is designed, and a partialresponse
maximum-likelihood (PRML) detector is adopted to evaluate the detection performance of multi-level
readout signals. By analyzing and comparing the simulation performances of different PRML schemes, we
conclude that PR(1, 2, 2, 2, 1) target is preferred to be applied in four-level RLL modulation DVD channels.
A new rate 8/12 4-level run-length limited (2, 9) code with spaced pits/lands constraint has been constructed.
The code effciency is high of 94.0%, and the density ratio is 2.0 bits per minimum recorded mark. The encoder
has six states and the decoder window length is only two. This byte-oriented code is very suitable to be applied
in practical multi-level read-only optical disc systems.
KEYWORDS: Modulation, Digital video discs, Signal detection, Sensors, Signal to noise ratio, Optical recording, Optical storage, Atomic force microscopy, Binary data, Amplitude modulation
Multi-level run-length-limited (ML-RLL) modulation on optical storage channels is a promising method to increase
the recording density effectively. In this paper, some experimental results of 4-level RLL modulation on
digital versatile disc (DVD) read-only discs are firstly presented. A new DC-free 4-ary RLL (2, 8) code with
code rate of 8/10 (bits/symbol) is designed, and partial-response maximum-likelihood (PRML) detection is used
to evaluate the bit error rate (BER) performance of multi-level readout signals. Experimental and simulation
results show the feasibility of 4-level RLL modulation on DVD channels.
A new high efficient DC-free 3-ary run-length limited (RLL) code for 3-level optical recording system is presented. Signal processing techniques, partial-response maximum-likelihood (PRML), which is used for recovery data from readout signal, is discussed.
4-Level Run-Length Limited (4L-RLL) optical storage based on photo-chromic materials is firstly investigated in this paper to our knowledge. Unlike binary recording, information in Multi-Level Run-Length Limited (ML-RLL) modulation system is carried in both the amplitude and length of the marks. ML-RLL optical storage can increase the recording density and data transfer rate with no changes to the optical/mechanical unit. For photo-chromic materials, different levels of input laser power amplitude give rise to different reflection levels. Using optimal write strategies, a 4 level linear playback signal was obtained and the sigma-to-dynamic range (SDR) of the 4-level signal was calculated. The results show that the SDR is low enough to provide low bits error rate (BER).
Multi-level optical storage is a promising approach to increase recording density and data transfer rate significantly without altering optical and mechanical parameters of current optical disc systems. Multi-level amplitude modulation and multi-level run-length limited modulation are two different important recording approaches. In this paper, we discuss and compare these two multi-level modulation principles and corresponding multi-level coding schemes. With advanced coding and signal detection, multi-level run-length limited modulation shows better performances in terms of higher recording density. We present a new 8-ary (1, 3) RLL code constructed by state splitting algorithm for photochromic storage channel. The proposed code has only two coding states and high coding density of 3.0 bits per minimum mark. The encoder/decoder is simple and easy for implementation, which can be applied in future high density multi-level optical storage systems.
KEYWORDS: Photochromic materials, Optical storage, Absorption, Optical recording, Signal detection, Modulation, Data storage, Prisms, Signal to noise ratio, Signal processing
Multi-wavelength and multi-level optical storage based on novel photochromic materials is a promising approach to increase recording density and transfer rates signicantly. In our research, three laser beams with dierent wavelength are simultaneously used to record information in one recording layer, which consists three kind of photochromic materials with spectrum sensitivity suitable for each used laser beam. On the other hand, the reectivity of photochromic materials varies nonlinearly with the exposure energy, which shows feasible for multilevel optical recording. The principle of the experimental system construction and a results are described in this paper. The proposed multi-wavelength and multi-level photochromic recording has the great potential to be applicable for future high density optical data storage.
In order to meet the requirement of focusing in the multi-wavelength mastering system, a pneumatic sensing system is designed. It detects the objective lens position signals and sends to the focus control system as the focus error signals instead of the feedback signals of light intensity used traditionally. So it can solve the auto-focus problem caused by introducing multi-wavelength lasers. The static and frequency response characteristics of the system are tested. It is proved by the experiment that the focus error is under ±0.1μm and can meet the needs of the three-wavelength system.
Multi-wavelength and multilevel (MWML) optical storage with photochromic media is a novel technology that can increase storage capacity and transfer rates significantly. Signal processing and coding methods for the MWML storage channel are introduced in this paper. Two-dimensional codes with parallel detection and equalization are studied to increase storage capacity and combat the crosstalk between different wavelength materials. Multilevel amplitude modulation and M-ary runlength-limited (RLL) codes are described and compared for achieving higher coding capacity. The novel MWML recording technology has the potential to be applicable for the next generation optical data storage.
An experiment on the character of photochromic recording material is introduced. Numerical method is used to describe the material character. Based on it, the multi-level experiment demonstrates the availability using photochromic material as recoding medium of 4-level storage system. Finally, a further analysis on optimizing the exposal parameters of different levels of multi-level disc is presented.
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