Chongxi Zhou

Holographic video at 40 frames per second for 4-million object points.

We propose a fast method for generating digital Fresnel holograms based on an interpolated wavefront-recording plane (IWRP) approach. Our method can be divided into two stages. First, a small, virtual IWRP is derived in a computational-free manner. Second, the IWRP is expanded into a Fresnel hologram with a pair of fast Fourier transform processes, which are realized with the graphic processing unit (GPU). We demonstrate state-of-the-art experimental results, capable of generating a 2048 x 2048 Fresnel hologram of around 4 × 10(6) object points at a rate of over 40 frames per second.

Structured lens formed by a 2D square hole array in a metallic film

A method is proposed to modulate phase using variant square holes in a metallic film based on a fundamental mode approximation model. Phase retardation through square holes in a subwavelength scale in a thin metal film has been analyzed and calculated. Based on the model, a structured lens with a numerical aperture of 0.583 and a focal length of 240 microm formed by a 2D square hole array in a metallic film is designed. Numerical simulation using the finite-difference time-domain method is carried out, and the results agree with the theoretical analysis. A focal spot close to the diffraction limit can be obtained.

Imaging by a sub-wavelength metallic lens with large field of view.

The characteristics of the phase retardations and the invariability against the incident angles are investigated when light enters the rectangular holes with different sizes perforated on metallic film. A kind of metallic structure with a great potential in imaging is brought forward. The finite difference time domain (FDTD) method and the Rayleigh-Sommerfeld diffraction integrals are used to testify the imaging ability at different incident angles by examining the electric field on focal plane. The calculation results indicate that a quite large view of field lens can be achieved by increasing the number of the holes per unit area with the mentioned structure. A metallic structured lens with a 280 microm aperture and 240 microm focal length is designed and the view angle range of +/-15 degrees can be achieved.

Profile control technology for high-performance microlens array

A profile formation and control approach has been developed for manufacturing micro-optical elements with continuous profile and deep relief depth. Based on Dills exposure model, an effective expression for determining the exposure dose function is established by using a supposition of equivalent exposure threshold inside a resist layer. An analytical simplified formula is further deduced by taking absorbance as constant B, and the approximate condition is discussed. For evaluating the simplified formula, the profile error was calculated and analyzed by simulation. With the exposure dose function, the binary mask for manipulating the light distribution by means of a moving-mask lithographic method can be designed. Experimental results are given and show the comparative performance to the required profile and relief depth. A series of refractive microlens arrays with aspherical profiles, a wide range of numerical apertures (0.005 to 0.6), and high fill factors were accomplished in the lab and may be applied to many systems

Experimental study of a multiwavelength photon sieve designed by random-area-divided approach

In this paper, a design method for a multiwavelength photon sieve is described based on a random-area-divided approach, where the whole aperture of a multiwavelength imaging photon sieve is divided into multiple discrete spaces corresponding to the number of the selected working wavelengths. The micropinhole distribution in each discrete space can be calculated for the defined wavelength with one fixed focal length in terms of the normal design for photon sieve. A three-wavelength photon sieve was designed and fabricated in the lab, and its imaging properties are analyzed in the experimental optical system with satisfactory results.

Real-time photolithographic technique for fabrication of arbitrarily shaped microstructures

Sichuan UniversityInformation Optics InstituteChengdu 610064, ChinaE-mail: pengqinjun@263.netChongxi ZhouChinese Academy of SciencesState Key Laboratory of Optical Technologyon MicrofabricationChengdu 610209, ChinaZheng CuiRutherford Appleton LaboratoryChilton, DidcotOxon OX11 0QXUnited KingdomAbstract. A new photolithographic technique that combines the advan-tages of a programmable digital liquid crystal display (LCD) system andprojection photolithography system to fabricate arbitrarily shaped micro-structures using LCD panels as real-time masks is reported. Its principleand design method are explained. Based on a partial coherent imagingtheory, the process to fabricate microaxicon arrays and zigzag gratings issimulated. The experiment has been set up using a color LCD as areal-time mask. Microaxicon arrays and zigzag gratings have been fab-ricated by a real-time photolithographic technique. The 3-D surface reliefstructures are made on panchromatic silver-halide sensitized gelatin(Kodak-131) with trypsinase etching. The pitch size of the zigzag gratingis 46.26 mm, and the etching depth is 0.802 mm. The caliber of theaxicon is 118.7 mm, and the etching depth is 1.332 mm.

Micrograting-array beam-shaping technique for asymmetrical laser beams

A beam-shaping technique is presented for asymmetrical laser beams with different beam waists and divergences in both vertical and horizontal directions. We utilize a pair of two-dimensional micrograting arrays to equalize the beam parameter products of an asymmetrical beam in orthogonal directions by deflecting the appointed parts of the beam on the longer side of the beam and by recombining the parts on the shorter side. When combined with divergent transformation by means of collimating optical components, the beam-shaping system can produce a symmetrical beam in orthogonal directions with optimized beam waists and divergences. A beam-equalization system is designed and demonstrated for a typical asymmetrical beam of a laser diode bar. In the experiment an emission beam with dimensions of 1 microm x 10 mm and half-divergences of 148 mrad x 576 mrad in the far field is transformed into an almost-square distribution with dimensions of -12 mm x 12 mm and half-divergences of -2 mrad x 2 mrad, which confirm the effectiveness of the proposed technique.

Laser diode stack beam shaping by reflective two-wedge-angle prism arrays

An innovative beam-shaping method for laser diode stacking is presented by employing a pair of reflective two-wedge-angle prism arrays. Each subprism with two variable wedge angles is designed for deflecting the partial emission from different bars to the dead spaces of the stack, according to the configuration of the real laser diode (LD) stack and the requirement of the system. The formula to determine the parameters of each subprism is deduced by way of geometrical analysis. A beam-shaping system for stack laser diodes with three bars is designed and simulated, and the results show that the stack laser beam is well transformed into a required distribution efficiently. (c) 2005 Society of Photo-Optical Instrumentation Engineers.

Dispersive element based on grating and tunable Fabry–Perot filter in miniature spectrometer

We present a new design for the integration of a tunable Fabry-Perot (FP) filter and the grating etched on top of the cavity (IGFP) in the miniature spectrometer. It is based on the predispersion of the grating with the capacity of spatial separation of the spectral component and filter effect of the tunable FP filter. The free spectral range (FSR) of the IGFP is determined by the FSR of the grating, and its resolution depends on the filtering capacity of the FP filter. In the experiment, the high-resolution and wavelength scanning process of the IGFP were demonstrated with a narrowband and broadband light source, respectively. The results of the sub-nanometer resolution agree well with those from a commercial optical spectrum analyzer. Further, the IGFP provides an effective approach to solve the problem of the decrease of spectral resolution in the miniaturization process.

Microlens array for stacked laser diode beam collimation

To collimate effectively the beam emitted from the stacked laser diode in which the lasing surfaces of the diode bars are not located in a plane, a new type of fast-axis collimator, refractive cylindrical microlens array with tunable focal lengths, is presented in this paper. Each lens of the array has the same diameter of 300μm but different focal lengths, ranged from 430μm to 540μm. By means of the mask moving lithography and replication technology, the microlens array was successfully fabricated. The measured fast-axis divergence of the stacked laser diode beam after the collimator was 25mrad, about half of the one (40mrad) for the microlens array with common focal lengths of 400μm.