Showing papers by "Guofan Jin published in 2002"

Theories for the design of diffractive superresolution elements and limits of optical superresolution.

Abstract: We suggest using the theory of linear programming to design diffractive superresolution elements if the upper bound of the intensity distribution on the input plane is restricted, and using variation theory of functional or wide-sense eigenvalue theory of matrix if the upper bound of the radiation flux through the input plane is restricted. Globally optimal solutions can be obtained by each of these theories. Several rules of the structure and the superresolution performance of diffractive superresolution elements are provided, which verify the validity of these theories and set some limits of optical superresolution.

Suppression of the influence of a photovoltaic dc field on volume holograms in Fe:LiNbO3.

Abstract: A nonuniform photovoltaic field is created in Fe:LiNbO3 during hologram recording exposures. Experimental results and analysis show the degradation of the volume holograms in the presence of the photovoltaic field. A sodium chloride solution is used to short-circuit the crystal to improve the stored-image quality. Experimental results to demonstrate the effectiveness of the proposed method are presented.

Achromatic quarterwave-plate for visible spectrum region using the dispersion of form birefringence

Abstract: Sub-wavelength gratings could function as polarization components, such as wave-plates and polarized beam splitters. Furthermore, gratings in resonate regime could act as achromatic wave-plate. Here, an achromatic quarter-wave plate of a submicrometer grating with sinusoidal profile is designed based on diffractive optics. Rigorous coupled wave theory (RCWT) was used to analyze the subwavelength grating made on photo-resist in ambient air. Design of a broadband form-birefringent phase retarder for 400nm to 800nm visible region is discussed. A sinusoidal sub-wavelength grating with good properties was designed. Its phase retard maintains at about 90° and maximum deviation is about 15%, which approaches normal binary waveplate.

Very low-loss fiber-to-waveguide coupling using diffraction optical element mode converter

Abstract: Very low-loss coupling between standard single-mode fibers (SMF) and high refractive-index waveguides is achieved using diffraction optical element (DOE) as mode converter. The DOE is a beam-shaping element designed based on diffraction optics theory. DOE shapes the mode field of SMF to that of the waveguide, or vice versa. The mode mismatch between them is eliminated. DOE is a pure phase element, which phase distribution optimized by G-S algorithm. The most attractive point of this mode converter is that the DOE can be designed to achieve any mode field distribution of any waveguide structure. This advantage makes DOE a strong and flexible mode converter. Though being a phase element, DOE has certain wavelength tolerance covering a sufficiently wide band, which makes it applicable in multi-wavelength integrated planar lightwave circuits (PLCs). DOE can be approximated by binary optical element (BOE), so that it can be fabricated using existing PLC fabrication step

Automatic feature extraction of head MR image based on limited region growing and improved boundary tracking method

Abstract: In this paper, based on the analysis ofhead MR (Magnetic Resonance) image, an effective method is developed to automatically extract skull area and edges from MR image. Based on slip gray scale threshold and specifically qualifications, a region growing method is applied to automatically form the skull area candidates and confirm the true area. Then an improved boundary tracking method is applied to remove the pseudo-structures of the rough skull area. Limited tracking bug and some definite shape operations are applied to remove the redundant protuberances and dead zones, without any effect on the true skull area. The experimental result is provided and discussed.

Sinusoidally chirped fiber Bragg grating for DWDM applications

Abstract: Summary form only given. Recently, many new profiles and structures of fiber gratings are proposed and demonstrated for high bandwidth utilization of optical filters. Here, we propose a new fiber grating structure whose period is sinusoidally chirped. The fiber grating provides abrupt-edges and flat-top passband channel with high side lobe suppression (>30 dB). We show uniform multiple wavelength operation by sampling this proposed fiber grating.

Planar integrated optical disk pickup

Abstract: Though DVD becomes more and more popular, there are still millions of CD-R disk in using. The ability of reading both DVD and CD-R disk is necessary in compatible disk drive. Traditional optical pickup consists of different bulk components, which result in high cost, high difficulty in assembly and low reliability. Integration is a way to overcome these troubles. Based on planar optics, an integrated digital versatile disk (DVD)/compact disk recordable (CD-R) compatible optical pickup has been developed. In this device, the beams of two wavelengths follow different zigzag optical paths inside a few-mm thick glass substrate, which is used as a light guide. It is demonstrated that a beam combiner, a polarized beam splitter, a Fresnel prism, and a beam separator were integrated around a glass substrate, and such a planar optical pickup exhibited an excellent performance with high efficiency. It confirms that planar optics is an effective way to realize compatibility of DVD/CD-R.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Maximum and uniform diffraction efficiency of the multiple-volume holographic gratings in the spectrometer

Abstract: In the spectral dispersive device of this paper more than one volume hologram are superimposed into the common volume of photorefractive material Fe:LiNbO3, permitting acquisition of high diffraction efficiency, high spectral resolution, full spectral coverage, and simple structure. With the Bragg compensatory multiplexing recording technique, this device could be recorded with only one single wavelength laser. The dependence of diffraction efficiency on both material and exposure parameters is investigated in Fe:LiNbO3. A linear discrete-type device working at sixteen discrete wavelengths is designed fabricated. The high resolution and imaging properties ofthis device are also demonstrated in experiment.

Design of flat-field arrayed waveguide grating based on aberration theory

Abstract: A new type flat-field arrayed waveguide grating (AWG) has been designed. The focal points of all wavelengths of operation distribute on a straight line. With parallel output waveguides, iti¯s convenient to connect with fiber-array directly. Flat-field AWG could function as a spectrometer when the output waveguides are thrown off. The work based on the developed aberration theory of AWG. In this theory, the restrains imposing on the conventional Rowland-type AWG have been removed. Various restrains will generate new type structures. In the flat-field AWG design, the restrains come from the concurrent imaging theory. Three aberration-free points restrain three dominant geometry parameters of AWG, geometry of star couplers, phased array ports distribution, and length increment between adjacent paths. A 16-channel flat-field AWG is designed. As stigmatic points introduced, the aberration of the device is much lower than that of the conventional Rowland-type AWG.

Using speckle to reduce the influence of DPL modes on holographic storage system

Abstract: In normal angular multiplexed holographic storage system, to make the system compact, replacing the Ar + laser with the diode-pumped solid-state laser (DPL) is an important means, but the application of DPL will increase the cross-talk and reduce the storage density because of the multiple longitudinal modes in the output of the DPL. In this paper, a novel speckle holographic storage scheme is proposed, in which a random phase diffuser is added in the front of storage medium along the reference optical path of the 90° geometry. A theoretical model has been derived to describe the storage properties of this scheme based on the cross-correlation of dynamic speckle and the diffractive theory. The angular selectivity in the normal angular multiplexed system and in the speckle-coded angular multiplexed system have been theoretically compared and experimentally confirmed. The results indicate that this scheme allows an increase of storage density with a simple modification in the DPL system.

Analysis of cross-talk noise in fractal multiplexed volume holograms

Abstract: Based on the coupled wave theory, the cross-talk noise in fractal multiplexed volume hologram is analyzed. The simulation of the reconstruction of a single hologram under conditions of different deflecting angles and pitching angles of read-out reference beam is made, experiment result is presented, and a 2D figure of cross-talk noise distribution is given. The analysis and the experiment result confirm that the read-out of spectrum hologram under changed pitching angle will appear as a horizontal strip, and the strip will move vertically with the change of deflecting angle.

A novel photopolymer material for holographic data storage

Abstract: Most photopolymer materials consist of a photopolymerizable monomer, a photoinitiator and a sensitizer in a polymer binder. During optical exposure, a few photons can initiate a chain reaction of photopolymerizable monomer molecules, which cause a change of the refractive index, forming hologram. In tradition, the refractive index of the monomer is higher than that of the binder, and the magitude of the refractive index modualtion is dependent on the differnce in refractive indices between the binder and the monomer. A novel photopolymer material different from the tradition is presented in this paper, in which the monomer is MMA with the refractive index much lower than that of the binder synthesized from epoxy resin monomer and XDA, so that the material can be conveniently developed into samples with dimension stability and high optical quality and thickness of several millimeters or more. A holographic recoridng medium of 0.8 mm thickness has been fabricated, and the storage characterizations as well as its relative theoretical analysis of its are presented.

Influence factors of interchannel pulses four-wave mixing in high-speed DWDM systems

Abstract: We systemically investigate the influence of channel spacing, fiber length, incident pulse peak power and width on interchannel ultrashort pulse four-wave mixing (FWM) in high-speed DWDM systems with nonzero dispersion-shifted fiber (NZDSF).

Multi-mother adaptive wavelet transform and its application in feature extraction

Abstract: Adaptive wavelet transform, using an adaptive wavelet as a linear combination of different wavelets, has been applied in optical information processing successfully. Most of the adaptive wavelets are built by daughter wavelets from only one mother wavelet. In this paper, we construct a new adaptive wavelet for feature extraction under noise as prepossessing in face pattern recognition. To have the ability of de-noising, daughters for construction are generated by two different mother wavelets. We call this transform multi-mother adaptive wavelet transform. It is important that the new wavelet combines advantages of different mother wavelets. With artificial neural network, the parameters are adaptively computed. Simulation results show the wavelet is not only robust to noise, but also keep good recognition performance. In frequency domain, the spectrum of our wavelet is real and easy to be realized as an optical filter.