Biomedical subjects

Markku Kuittinen

Publications and source records attributed to Markku Kuittinen.

7 recordsLinked to original sources

PubMed2006

White LED light coupling into light guides with diffraction gratings.

Radial diffractive gratings are used to couple light of a white LED into a light guide. Theoretical coupling efficiencies are evaluated with rigorous diffraction theory in a pure conical mounting. It is shown that when the refractive index of the grating increases from 1.46 to 2.05 the incoupling efficiency increases from 42% to 63%. Also, with the increasing refractive index the incoupling efficiency is shown to become more nearly uniform over the visible spectrum. Experimental results for the incoupled efficiencies and the color coordinates of the incoupled spectra are introduced for refractive indices n=1.46 and n=1.56.

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PubMed2006

Producing illumination-independent additively mixed colors by diffractive optics.

We apply transmission gratings under Littrow incidence to produce polychromatic colors by additive color mixing. Parametric optimization of gratings is employed to produce high efficiency. In addition, we show that the system can yield the same color from a wide variety of spectra; i.e., the system can produce metameric colors.

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PubMed2006

Double-groove, two-depth grating coupler for light guides.

A double-groove, two-depth dielectric grating structure for high-efficiency light coupling into a light guide is introduced. We show computationally that the optimized gratings can couple a monochromatic TE- or TM-polarized light beam with nearly 100% efficiency. For an unpolarized light beam 90% efficiency can be reached. In all cases the highest achieved coupling efficiencies require that the refractive index of the grating material be greater than 1.7. The illumination and fabrication tolerances of the couplers are also analyzed.

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PubMed2004

Coupling of light from an LED into a thin light guide by diffractive gratings.

Ring-shaped and radial diffractive gratings are designed with rigorous diffraction theory to couple light of a nearly monochromatic LED into a thin planar light guide on the bottom side. The theoretical coupling efficiencies for ring-shaped and radial gratings are 41% and 66%, respectively. Optimized diffractive elements are manufactured with direct electron-beam lithography and reactive-ion-etching into SiO2 substrates. Good agreement between experimental and theoretical results for selected radial gratings is reached. Furthermore, the mass production tests using injection molding are carried out with good replicability.

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PubMed2003

Novel electromagnetic approach to photonic crystals with use of the C method.

We introduce a new method allowing rigorous electromagnetic analysis of scattering through photonic crystals comprising polygonal or round rods. For this purpose, we reformulate the C method with adaptive spatial resolution by utilizing the hybrid-spectrum connection method, permitting the use of nonidentical trapezoidal profiles. Considering polygonal rods as gratings consisting of different piecewise-differentiable surfaces, we are able to analyze the reflection and the transmittance of crystals by means of the C method. To enhance computational efficiency, we apply the recursive S-matrix approach with Redheffer's star product to solve the transfer matrix for structures of numerous successive layers of rods.

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PubMed2002

Tunable external-cavity diode laser at 650 nm based on a transmission diffraction grating.

A tunable external-cavity diode laser (ECDL) based on a transmission diffraction grating in a Littrow mount has been developed and characterized. A single-transverse-mode diode laser at 650 nm is used in an external-cavity configuration in which the transmission grating is used as a dispersive element to select the single longitudinal mode. The transmission diffraction grating is made with electron-beam lithography. A tunable true single-mode cw output power of >20 mW is obtained from the ECDL. The total wavelength tuning range is 12 nm, and the mode-hop-free continuous tunability is >20 GHz.

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PubMed2002

Step-transition perturbation approach for pixel-structured nonparaxial diffractive elements.

An extension of an approximate step-transition perturbation method is presented that permits numerically efficient diffraction analysis of pixel-structured surface profiles in the nonparaxial domain. Comparison with the rigorous diffraction theory of gratings shows that the method is reasonably accurate provided that the pixel size exceeds approximately two wavelengths even if the structure contains isolated pixels.

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