Joseph F. Revelli

Distribution of radiation from organic light-emitting diode structures with wavelength-scale gratings as a function of azimuth and polar angles

The angular distribution of radiation emitted from organic electroluminescent diodes fabricated on substrates with wavelength-scale gratings was measured using an optical Fourier transform instrument. A simple geometrical model is derived that specifies the polar angle of the exiting photon as a function of the azimuth angle, the grating pitch, the wavelength of light, and the effective index of the refraction of the light emitted by the fluorescing excitons. The radiation pattern of the extracted light is shown to fit that predicted by the model if one assumes that it comes from surface plasmon polaritons and bound TE waveguide modes.

Excitation of waveguide modes in organic light-emitting diode structures by classical dipole oscillators

Analytical techniques known in the literature are used to (i) identify all the planar waveguide modes in four top-emitting organic light-emitting diode (OLED) structures over the visible spectrum, and (ii) compute both TM and TE power spectra for classically radiating dipoles in the emissive layers of these OLED structures. Peaks in the computed power spectra are identified with the waveguide modes in the OLED devices, and areas associated with these peaks are used to estimate the excitation probability of the waveguide modes. In cases where ambiguities arise because of overlapping peaks, it is shown that computed power spectra can be approximated as sums of Lorentzian line shapes. It is found that for all four structures, the dipoles couple almost 80% of their radiant energy into TM modes with only about 20% going into TE modes. Furthermore, except for a narrow spectral band, the excited TM modes are primarily short-range surface plasmon polaritons. Excitations in the narrow spectral band correspond to TM and TE Fabry-Perot microcavity modes. Finally, the analysis shows that, in the absence of grating couplers, only light in the microcavity modes escapes into the air cover.

1- to 100-channel waveguide beam splitter and TE to TM polarization converter

This paper describes a channel waveguide beam splitter (CWBS) in which a single laser beam can be split into many beams using glass stripe waveguides and localized surface relief gratings. The grating element situated on top of individual 90 degree(s) T-branches couples a fraction of the backbone light down a side channel and acts as a miniature mode converter. Single-mode TE light in the backbone is converted into single-mode TM light in the side channel. The laser wavelength used in these experiments was 830 nm. Each individual grating was only a few microns in length and so the grating acceptance exhibited a large bandwidth. The total excess loss coupling the input waveguide optical power partially into 100 waveguide branches was only 0.25 dB.

Use of Nematic Liquid Crystal Overlayer Cells to Form Planar Waveguide Mach-Zehnder Interferometer and Deflector

Attempts to take advantage of the large electro-optic effect in waveguides formed directly in liquid crystal (LC) films have met with limited success because of large propagation losses associated with thermal fluctuations of the long-range crystal ordering.1 Recently, optical waveguide modulators2 and switches3 have been formed using nematic LC overlayers on passive waveguides. In both cases, the use of LC overlayer cells on passive waveguides significantly reduced propagation losses due to scattering in the liquid crystal. The reduced propagation losses are a direct result of sampling the LC material only via the evanescent portion of the guided light.