Increase In Numerical Aperture Research Articles

Variable numerical-aperture temporal-coherence measurement of resonant-cavity LEDs

The first interferometric measurements of temporal-coherence length variation with numerical aperture (NA) are described for 650 nm, resonant-cavity light-emitting diodes (LEDs) agreeing with spectrally derived results. The interferometrically measured coherence length (22 /spl mu/m to 32 /spl mu/m) reduced by 37% for a 0.42 increase in NA. For a larger range of NA (0-1), this would give coherence lengths (10 /spl mu/m-40 /spl mu/m) lying in the gap between that of conventional LEDs (/spl sim/5 /spl mu/m) and superluminescent diodes (/spl sim/60 /spl mu/m).

Phase-shifting apodizer for next-generation digital versatile disk

The next generation digital versatile disk (DVD) using blue lasers will have a capacity of 13 to 15 Gbytes. Compared with current DVD, the wavelength will be shorter and the numerical aperture (NA) will be higher. But with the increase of NA and decrease of wave length, the depth of focus (DOF) decrease rapidly, which makes it hard for the servo-system to track. We propose an optimized three-portion phase-shifting apodizer to increase the depth of focus and at the same time minimize the spot size, which makes the DOF of next generation DVD comparable to current DVD. The simulation result shows that an optical system with this apodizer also has a good defocus characteristic. (C) 2001 Society of Photo-Optical Instrumentation Engineers.

Study on elliptical polarization illumination effects for microlithography

The vector image code (VIC) consisting of the vector transmission cross coefficient (TCC) and Fourier transform of the mask function is widely applied to simulate the effects of polarization in microlithography. Until now studies were restricted to the effects of linear polarization. This linear polarization illumination predicts a larger contrast gap between TE polarization and TM polarization as the numerical aperture increases or the critical dimension decreases. In this article, we have studied the effects of elliptical polarization illumination (EPI) as a new method in order to decrease these contrast gaps. We improved VIC by adopting EPI including circular polarization. As a result of using the improved VIC, EPI shows that the contrast and the contrast gap can be tuned by adjusting the angle of polarization and the ratio of the ellipticity. The simulation result also shows that the higher the ratio of ellipticity the lower the contrast gap but at the expense of lowering the contrast somewhat. If this new EPI is adopted into microlithography, the contrast gap can be decreased while the contrast to a specified direction of the mask pattern can be kept high.

Extending scalar aerial image calculations to higher numerical apertures

The usual formula for the scalar aerial image of an isolated object due to a projection lens system has been generalized beyond the paraxial approximation in an attempt to extend scalar diffraction theory to include numerical aperture (NA) values up to about 0.6. Beyond this regime, or certainly beyond NA=0.7, polarization effects need to be included, thereby demanding a full vector treatment and invalidating the present scalar formulation. A key point to the present scalar result without the paraxial approximation is the predicted functional dependence of the aerial image on magnification as NA increases. A second key point is that the usual scaling of λ/NA for the object dimensions and λ/NA2 for defocus become invalid for high NA systems. Numerical results of illustrative test cases are shown.

Selfoc microlens with a spherical surface

This paper presents the light-focusing properties of a gradient-index rod lens with a spherical end surface which aims at increasing numerical aperture and decreasing lens aberration. Optimum refractive-index profiles for obtaining a smaller focused spot are derived, and the increase of numerical aperture is clarified. Experimental results are described; the Selfoc microlens with a spherical end surface realizes a focused spot below 2 microm in diameter.