Microoptical research in Shanghai Institute of Optics and Fine Mechanics

This paper summarized the recent research results of Changhe Zhou's group of Information Optics Lab in Shanghai Institute of Optics and Fine Mechanics (SIOM). The first is about the Talbot self-imaging research. We have found the symmetry rule, the regular-rearranged neighboring phase difference rule and the prime-number decamping rule, which is briefly summarized in a recent educational publication of Optics and Photonics News, pp.46-50, November 2004. The second is about four novel microoptical gratings designed and fabricated in SIOM. The third is about the design and fabrication of novel supperresolution phase plates for beam shaping and possible use in optical storage. The fourth is to develop novel femtosecond laser information processing techniques by incorporating microoptical elements, for example, use of a pair of reflective Dammann gratings for splitting the femtosecond laser pulses. The most attractive feature of this approach is that the conventional beam splitter is avoided. The conventional beam splitter would introduce the unequal dispersion due to the broadband spectrum of ultrashort laser pulses, which will affect the splitting result. We implemented the Dammann splitting apparatus by using two-layered reflective Dammann gratings, which generates the almost same array without angular dispersion. We believe that our device is highly interesting for splitting femtosecond laser pulses.

Coma measurement of projection optics in lithographic tools based on relative image displacements at multiple illumination settings

In this paper, we propose a novel method for measuring the coma aberrations of lithographic projection optics based on relative image displacements at multiple illumination settings. The measurement accuracy of coma can be improved because the phase-shifting gratings are more sensitive to the aberrations than the binary gratings used in the TAMIS technique, and the impact of distortion on displacements of aerial image can be eliminated when the relative image displacements are measured. The PROLITH simulation results show that, the measurement accuracy of coma increases by more than 25% under conventional illumination, and the measurement accuracy of primary coma increases by more than 20% under annular illumination, compared with the TAMIS technique. (c) 2007 Optical Society of America.

Fetntosecond pulse shaping with space-to-time conversion based on planar optics

We propose a novel structure of planar optical configuration for implementation of the space-to-time conversion for femtosecond pulse shaping. The previous apparatuses of femtosecond pulse shaping are 4f Fourier-transforming type system that is usually large, expensive, difficult to align. The planar integration of free-space optical systems on solid substrates is an optical module with the attractive advantages of compact, reliable and robust. This apparatus is analyzed in details and the design of the particular lens for femtosecond pulse shaping based on planar optics is presented. (c) 2006 Elsevier GmbH. All rights reserved.

Optical generaton of millimeter-wave pulses using a fiber Bragg grating in a fiber-optics system

A scheme is proposed to transform an optical pulse into a millimeter-wave frequency modulation pulse by using a weak fiber Bragg grating (FBG) in a fiber-optics system. The Fourier transformation method is used to obtain the required spectrum response function of the FBG for the Gaussian pulse, soliton pulse, and Lorenz shape pulse. On the condition of the first-order Born approximation of the weak fiber grating, the relation of the refractive index distribution and the spectrum response function of the FBG satisfies the Fourier transformation, and the corresponding refractive index distribution forms are obtained for single-frequency modulation and linear-frequency modulation millimeter-wave pulse generation. The performances of the designed fiber gratings are also studied by a numerical simulation method for a supershort pulse transmission. (c) 2007 Optical Society of America.

Multi-channel 2-D pattern transfer model based on imaging optics for submarine laser uplink communication

An optical communication scheme of 2-D pattern transfer based on imaging optics for submarine laser uplink communication (SLUC) is suggested. Unlike the methods aiming at avoiding neighboring crosstalk used in traditional multi-channel optical beam transferring, we make full use of the overlapping of each spreading beam other than controlling divergence effect of each beam to avoid interference noise. The apparent parameters have been introduced to simplify theoretical analysis of optical pattern transfer problem involving underwater condition, with the help of which the complex beam propagation inside two kinds of mediums can be easily reduced to brief beam transfer only inside air medium. In this paper, optical transmission path and receiver terminal optics geometry have been described in detail. The link range equation and system uplink performance analysis have also been given. At last, results of a proof-of-concept experiment indicate good feasibility of the proposed SLUC model. © 2007 Elsevier GmbH. All rights reserved.

Self-adaptive optical systems for long-distance flying optics

The focusing characteristics of long-distance flying optics were studied systemically for TEMmn Gaussian beams. The results show that the ABCD law of parameter q can be extended to Gaussian modes of any order when waist radius w in the imaginary part of parameter q is replaced by Rayleigh range Z(R) of a certain resonator in the equation. The difference between the real focal length and the geometric focal length, defined as Delta f, was calculated for laser applications. A novel self-adaptive optical system was demonstrated for precisely controlling the focusing characteristics of long-distance flying optics, Theoretical analyses and experimental results were consistent. (c) 2006 Optical Society of America.

High quantum efficiency and high concentration erbium-doped silica glasses fabricated by sintering nanoporous glasses

A new method was used to prepare erbium-doped high silica (SiO2% > 96%) glasses by sintering nanoporous glasses. The concentration of erbium ions in high silica glasses can be considerably more than that in silica glasses prepared by using conventional methods. The fluorescence of 1532 nm has an FWHM (Full Wave at Half Maximum) of 50 nm, wider than 35 nm of EDSFA (erbium-doped silica fiber amplifer), and hence the glass possesses potential application in broadband fiber amplifiers. The Judd-Ofelt theoretical analysis reflects that the quantum efficiency of this erbium-doped glass is about 0.78, although the erbium concentration in this glass (6 x 103) is about twenty times higher than that in silica glass. These excellent characteristics of Er-doped high silica glass will be conducive to its usage in optical amplifiers and microchip lasers.

High quantum fluorescence yield of Er3+ at 1.5 mu m in an Yb3+, Ce3+-codoped CaF2 crystal

For the first time, a quaternary doping system of Er3+, Yb3+, Ce3+, Na+:CaF2 single crystal was demonstrated to have high fluorescence yield in the eye-safe 1.5 mu m region under 980 nm laser diode pumping, with relatively broad and flat gain curves. A simplified model was established to illustrate the effect of Ce3+ on the branching ratio for the Er3+4I11/2 -> I-4(13/2) transition. With 0.2-at.% Er3+ and 2.0-at.% Ce3+ in the quaternary-doped CaF2 crystal, the branching ratio was estimated to be improved more than 40 times by the deactivating effect of Ce3+ on the Er3+ 4I11/2 level. The quaternary-doped CaF2, system shows great potential to achieve high laser performance in the 1.5 mu m region. (c) 2006 Elsevier B.V. All rights reserved.