Ian M. Barton

Design and fabrication of diffractive optical elements

An introduction to the design and fabrication of diffractive optical elements is presented. Design techniques for diffractive optic in the two theoretical design areas, the scalar and resonance domains, and the dominant methods of fabrications are described. Theoretical and experimental examples are given in each section.

Dual-wavelength operation diffractive phase elements for pattern formation

We report on the design and fabrication of novel diffractive phase elements that reconstruct distinct intensity patterns in the far-field on illumination with two specific wavelengths. The elements contain deep surface-relief structures that represent phase-delays of greater than 2p radians. The design process incorporates a modified version of the iterative Fourier transform algorithm. A 16 phase-level element for dual wavelength (blue and red) operation, with high diffraction efficiency, is demonstrated experimentally.

Application of optimization algorithms to the design of diffractive optical elements for custom laser resonators

We report what we believe to be the first applications of numerical optimization algorithms to the design of diffractive elements that customize the fundamental mode profile of a laser system. Standard design techniques treat these elements as specific phase-conjugation devices, which leads to performance loss when they are quantized to permit fabrication. Numerical optimization can account for quantization of the element to increase the effective performance. Also, it is shown that allowing a slight increase in the intrinsic loss of the cavity can substantially increase the fidelity of the fundamental mode of the customized cavity. The good discrimination qualities of the mode-selection elements are shown to be unaffected by this process.

Diffractive phase elements for pattern formation: phase-encoding geometry considerations

Space-invariant, multilevel, diffractive phase elements are designed for large-scale pattern-formation tasks. The importance of the design algorithm and the phase-encoding geometry of the diffractive element is discussed with regard to the performance of both on- and off-axis reconstruction, notably for pixelated gratings. A new phase-encoding scheme is presented that results in an increase of the diffraction efficiency for the off-axis case.

Beam-shaping diffractive optical elements for high-power solid-state laser systems

Diffractive optical elements to modify laser beam spatial intensity distributions are described. The elements have been applied to free-space Gaussian to flat-top beam conversion and customization of the modes of a laser resonator. The single pass free space elements demonstrate a high efficiency but result in to much high frequency noise on the beam. The intra-cavity elements significantly altered the TEM00 profile but practical limitations with the positioning of the element within the cavity prevented operation in the design mode.

Diffractive optics development for application on high-power solid state lasers

This paper reports on the development of several diffractive optical elements (DOE) to fulfill applications on high power Nd glass laser systems. The measured performance for those components realized is discussed. These are focusing beam samplers, beam shapers, and harmonic separation filters (HSF). Designs of more demanding components operating in the resonance domain are also presented. These are linear polarizing elements and beam deflectors.

High-fidelity optical interconnections using ternary phase-amplitude filtering

We propose to use dynamic ternary phase-amplitude modulation for free-space reconfigurable optical interconnections, and demonstrate its significant advantages over the widely- adopted binary-phase scheme.

Design and fabrication of diffractive optical elements for use in solid state laser systems

Scalar and resonance domain diffractive optical elements are proposed for use within high power laser systems. Resonance domain elements are described for beam deflection and polarization selection. Scalar domain elements for harmonic separation filtering and beam shaping in the near- and far- fields are also described. Experimental results are presented for far-field beam shaping and harmonic separation filtering elements.

Synthetic multilevel diffractive optical elements for beam shaping and harmonic separation applications in high power laser systems

put. This enabled us to glue-join a silica fibre to the fluoride fibre with losses of only 0.4 dB by butt-joining two flat cleaved ends together and gluing. Figure 2 shows the amplified signal power at the end of the fluoride fibre as a function of the pump power launched into the fluoride fibre. The three curves correspond to launched signal power values of 0 dBm, -10 dBm, and -20dBm. For a signal power as low as -20 dBm, saturation effects are still evident. This is shown in Fig. 3, which shows the variation of amplified signal power with respect to signal power launched into the fluoride fibre for launched pump powers of 7.5 mW, 15 mW and 30 mW. As can be seen from Figs. 2 and 3, efficient amplification can be achieved with a modest amount of diode pump power launched into the fluoride fibre. The system gain from telecoms fibre to telecoms fibre for a signal power of -10 dBm was 14 dB. This performance could be improved by removal of the output WDM coupler, and refinement of the system. *BT Laboratories, Martlesham Heath, Ipswich, 1P5 7RE, U.K. 1. R. G. Smart, A. C. Tropper, D. C. Hanna, J. N. Carter, S. T. Davey, S. E Carter, D. Szebesta, ”High efficiency, low threshold amplification and lasing at 0.8 pm in monomode Tm3+-doped fluorozirconate fibre,” Electron. Letts. 28(1), 58-59 (1992). top produced by such an element when illuminated by the intensity distribution of Fig. l(a). The fidelity of the flat-top reRooms & gion can be seen to be around +21%, which is somewhat larger that the design value of 57%. Future experiments will concentrate on tightening the fabrication tolerances required to produce this element, which are the main source of error. The diffraction efficiency of this element was measured to be 90.5%, including a 1400 CMN