Experiments of Multi-Level Read-Only Recording Using Readout Signal Wave-Shape Modulation

An innovative multilevel read-only recording method is proposed. In this method, a short pit/land is deliberately inserted to the original land/pit. This modifies the wave-shape of readout signM. Taking the wave-shape as the symbol of level detection, a signal wave-shape modulation （SWSM） multilevel method is realized. This method is carried out and validated on the DVD read-only manufacture and readout system. A capacity of 15 GB can be expected, and a bit error rate of 10-4 is achieved. The capacity can meet the demand of high definition movie publication. This method also provides a potential multi-level solution for other storage formats and systems.     

Numerical Analysis of Nano-Aperture Light Source for High-Density Optical Data Storage

Two unconventional nano-aperture light sources, an L-shaped nano-aperture source and a 3D nano-aperture source for high-density optical data storage, are numerically investigated. With incidence of a Gaussian beam, the spot size of the Poynting vector coupled into the recording medium is 130 × 175 nm^2 for the L-aperture and 120 × 135 nm^2 for the 3D nano-aperture. The quantitative analyses indicate that the unconventional nanoaperture sources can provide enough power density to record marks in the commercial recording medium. It is feasible to use a laser diode with a nano-aperture as an active nanometer light source for high-density optical data storage.     

Triple Encrypted Holographic Storage and Digital Holographic System

We propose a triple encrypted holographic memory containing a digital holographic system. The original image is encrypted using double random phase encryption and stored in a LiNbO3：Fe crystal with shift-multiplexing. Both the reference beams of the memory and the digital holographic system are random phase encoded. We theoretically and experimentally demonstrate the encryption and decryption of multiple images and the results show high quality and good fault tolerance. The total key length of this system is larger than 4.7×10^33.     

Approximated Vector Diffraction Theory for Readout Signal of Multi-Level Run-Length-Limited Discs

Multi-level run-length-limited read-only optical storage is a kind of high density storage method. The width and height of recording marks are varied with different levels, which is the key technology for the optical storage. Then the readout signal of these discs with complex recording marks is computed by vector analysis method, it is very hard and time-consuming. Approximated vector computation combines the convenience of scalar method and precision of vector method, which is effective for multi-level run-length-limited read-only optical storage.     

Multilevel phase Fresnel zone plate lens as a near-field optical element

We propose and develop a new solid immersion lens (SIL), which is called the multilevel phase Fresnel zone plate lens (FZPL) for the near-field (evanescent wave) microscopy. The simple analysis is presented by using the scalar diffraction theory. The outstanding advantages of this FZPL are that it both focuses incident waves and produces evanescent waves. A FZPL can effectively concentrate the high angle rays important for the high resolution in comparison with the conventional SILs. The optical system equipped with the FZPL is not only simple in the assembly but also effective in making an optical head unit.     

Zero-Chirp Return-to-Zero Pulses Generation with Two Single-Driver z-Cut Mach-Zehnder Modulators

A novel method is proposed to suppress the frequency chirp of single-driver z-cut Mach Zehnder modulators. Theoretical analysis shows that by multiplying the output pulses of a half clock frequency driving single-driver z-cut modulator with the one delayed odd multiple bit duration, the frequency chirp can be removed entirely, and return-to-zero （RZ） pulses with duty cycles of about 25% and 56% are obtained. An experimental scheme is proposed to validate the proposed method. The pulses can be obtained by using this scheme. experimental results show that perfect 40 GHz zero-chirp RZ     

Modulation of Splitting Beam Angle with Metal--Nonlinear Optical Material--Metal (M-NL-M) Array Structure

We demonstrate active manipulating plasmonic signals with metal--nonlinear optical material--metal (M-NL-M) arrays consisting of slits with variant widths. The parameters of the M-NL-M array structure are derived by theoretical analysis of dispersion relationship. The splitting angle can be modulated by the incident light intensity, and verified by a nonlinear two-dimensional finite difference time domain method. The physical principle of this phenomenon is analysed from the phase of surface plasmon polaritons and Fabry--Pérot (F-P) resonance in slits     

A Feasible Approach to Optical--Electrical Hybrid Data Storage Using Phase Change Material

We present our experimental results supporting optical-electrical hybrid data storage by optical recording and electrical reading using Ge2Sb2Te5as recording medium. The sheet resistance of laser-irradiated Ge2Sb2 Te5 films exhibits an abrupt change of four orders of magnitude （from 107 to 10^3 Ω/sq） with increasing laser power, current-voltage curves of the amorphous area and the laser-crystallized dots, measured by a conductive atomic force microscope （C-AFM）, show that their resistivities are 2. 725 and 3.375 × 10^-3 Ω, respectively, the surface current distribution in the films also shows high and low resistance states. All these results suggest that the laser-recorded bit can be read electrically by measuring the change of electrical resistivity, thus making opticalelectrical hybrid data storage possible.     

SiO2 Waveguide Resonator Used in an Integrated Optical Gyroscope

An integrated optical waveguide resonator based on a SiO2 waveguide is proposed, fabricated and tested. The method of designing the resonator is also presented. The optimal splitting ratio of the coupler is gained by simulating the relationship between the splitting ratio of the key coupler in the resonator and the resonator＇s finesse with resonance depth. The calculated fundamental detection limit of this integrated optical vcaveguide resonator is 1.6°/h. Finally, a micro-optical gyroscope system based on the integrated waveguide resonator is built, and the measured resonator＇s finesse F is close to 70 under fluctuating temperature. To the best of our knowledge, the present F is the best result to date. For the coupler splitting rate the experimental results have fixed errors with the simulation results caused by fabrication processes which can be easily eliminated, implying that the method of design is effective and applicable.     

Broadly Tunable SOA-Based Active Mode-Locked Fibre Ring aser by Forward Injection Optical Pulse

We present a broadly tunable active mode-locked fibre ring laser based on a semiconductor optical amplifier （SOA）, with forward injection optical pulses. The laser can generate pulse sequence with pulsewidth about 12ps and high output power up to 8.56 dBm at 2.5 GHz stably. Incorporated with a wavelength-tunable optical bandpass filter, the pulse laser can operate with a broad wavelength tunable span up to 37nm with almost constant pulsewidth. A detailed experimental analysis is also carried out to investigate the relationship between the power of the internal cavity and the pulsewidth of the output pulse sequence. The experimental configuration of the pulse laser is very simple and easy to setup with no polarization-sensitive components.     

Realization of Optical Phase Locked Loop at 9.2GHz between Two Independent Diode Lasers

The optical-phase-locked-loop (OPLL) at 9.2GHz between two independent narrow linewidth diode lasers is realized. Ultrabroad servo bandwidth at 4MHz is first achieved and it is guaranteed that the full spectral characteristics of the master laser can be transferred to the slave laser. The experimental results prove that the coherence between two lasers is about 99%. This offers a new method to study the interaction between lasers and atoms based on the ground hyperfine structure of caesium atoms.     

Optical Switching in Silicon Nanowaveguide Ring Resonators Based on Kerr Effect and TPA Effect

We analyze theoretically the 1 × 2 low-power all-optical switching in silicon nanowaveguide ring resonators （RR） based on the Kerr effect and two-photon absorption （TPA）, and give a comparison between both the all-optical switches. The calculation shows that the switching power of the TPA-RR switch is 3 orders smaller than that of the Kerr-RR switch. The switching time for both the switches is about 100ps.     

Mixing kinetics and write-once optical recording characteristics of Sb/Se bilayer films

Bilayer Sb/Se films are irradiated with 12 ns pulses from an ArF laser (extended areas) and from a focused Ar⁺ laser (micron-sized areas). Real-time reflectivity measurements are used to determine if the process occurs within the solid or liquid phase and the transformation time, in addition to measure the optical contrast and the medium sensitivity. Transmission electron microscopy is used to analyze the structure of the transformed areas and the medium resolution. The results show that mixing is initiated by preferential melting at the grain boundaries and an amorphous phase is produced upon irradiation at high energy densities. Finally, the characteristics of the mixing process in Sb/Se films as a write-once optical recording mechanism are discussed in terms of the sensitivity and resolution of the recorded spots and the time required for recording.     

Optical vortices generated by multi-level achromatic spiral phase plates for broadband beams

We analyze the characterizations of the optical vortices generated by a multi-level achromatic spiral phase plate. The effective topological charge of the multi-level fractional spiral phase plate is expanded into Fourier series and the analytical formula of the relative intensity of each component is obtained. It is shown that the fractional part of the topological charge sharply reduces the purity of vortices. Using the 36 levels achromatic spiral phase plate, we can obtain a vortex beam with purity larger than 95% across a bandwidth exceeding 140 nm in the visible region of the spectrum.     

Self-Q-switched and mode-locked 946 nm Cr,Nd:YAG laser

A simultaneous self-Q-switched and mode-locked diode-pumped 946 nm laser by using a Cr,Nd:YAG crystal as gain medium as well as saturable absorber is demonstrated for the first time as we know. The maximum average output power of 751 mW with a slope efficiency of 18.38% is obtained at an intra-cavity average peak power intensity of 4.83 × 10⁶ W/cm². Under this circumstance, the repetition rate of Q-switched envelopes is 9.63 kHz and the pulse width is about 460 ns. Almost 100% mode-locked modulation depth is obtained at all time in the experiment process whether the incident pump power is low or high. The repetition rate of mode-locked pulses within a Q-switched envelope is 135.13 MHz and the mode-locked pulse width is within 600 ps. The laser produces high-quality pulses in TEM₀₀-mode in the simultaneous self-Q-switched and mode-locked experiment.     

Self-Q-switched and mode-locked Nd,Cr:YAG laser with 6.52-W average output power

Simultaneous self-Q-switched and mode-locked have been demonstrated in a diode-pumped Nd,Cr:YAG laser. For the first time as we know, almost 100% modulation depth has been achieved at an intracavity intensity of 5.6 × 10⁵ W/cm². The maximum average output power of 6.52 W corresponding to a slope efficiency of 30% is obtained at 1064 nm. The laser produces high-quality pulses in a TEM₀₀-mode at the pump power of 16.5 W. The pulse duration of the mode-locked pulses is about 600 ps with 136 MHz repetition rate.     

Delayed transitions between fluid-like and solid-like granular states

Analysis of granular flows has been a significant theoretical challenge over the past several decades. These flows are difficult to analyze largely because they exhibit both solid-like and fluid-like behaviors side-by-side in single experiments. In this paper, we examine two experiments in which the co-existence between these states is especially marked and leads to unique patterns that may serve as signatures for underlying granular dynamics deserving of further scrutiny. In these experiments, we find that when fluidization of grains is prolonged — as can be expected to occur for example under reduced gravity environments or under conditions of strong kinetic forcing (e.g. during earthquakes) — grains can produce residual depositional patterns that are difficult to distinguish from fluvial deposits. This suggests that geological landforms under low gravity (for example on Mars) or influenced by strong forcing (for example during earthquakes) may behave in a fluid-like manner despite being entirely dry.     

LD end pumped, actively mode locked and passively Q-switched Nd:YAP laser at 1341 nm

An end pumped Nd:YAP laser at 1341 nm is actively mode locked and passively Q-switched. Pumping was done with a pulsed high power laser diode with maximum power 425 W. V³⁺:YAG with 61% initial transmission served as saturable absorber, and an acousto-optic modulator is used for active mode locking. The output pulse train with 69 ns duration has a total energy of 3.2 mJ with ±4% shot-to-shot fluctuation. The peak output energy of a single mode locked pulse is 0.25 mJ. The pulse duration of a single mode locked pulse is less than 800 ps. The output laser beam is nearly diffraction limited with 1.6 mm diameter, and beam propagation factor M² about 1.3.     

Design of Super-resolution Filters with a Gaussian Beam in Optical Data Storage Systems

Super-resolution filters based on a Gaussian beam are proposed to reduce the focusing spot in optical data storage systems. Both of amplitude filters and pure-phase filters are designed respectively to gain the desired intensity distributions. Their performances are analysed and compared with those based on plane wave in detail. The energy utilizations are presented. The simulation results show that our designed super-resolution filters are favourable for use in optical data storage systems in terms of performance and energy utilization.     

A Novel Micro-Displacement Measuring Method Based on Optical Path Modulation

According to the interference theory of double-grating interferometers, the feature of Moire fringe imaging in each region is investigated and a novel micro-displacement measuring method based on optical path modulation is proposed. The basic measurement principle is that the displacement is measured through Moire fringe shifting, which is caused by the whole phased object thickness variation, in the case of non-relative movement of gratings. The object displacement measured can be changed into the phased object variation inserted in region Ⅱ using a mechanical arrangement. The principle of the micro-displacement measurement is analyzed theoretically. The light intensity of the distributing image in each interference region is given no matter whether we insert the phased object or not. The effect on the Moire fringe of the whole thickness variation of the phased object is also discussed. It is confirmed that the Moire fringe shifts with phased object variation by calculation with MATLAB. The experimental result proves that the resolution of this method is 2.1093 μm, and the resolution of the system is 0.5273μm after a four-subdivision circuit.