T. Maka

1.3 µm luminescence and gain from defect-free InGaAs-GaAs quantum dots grown by metal-organic chemical vapour deposition

Annealing of InGaAs quantum dots (QDs) fabricated by metal-organic chemical vapour deposition and covered with a very thin GaAs cap layer completely eliminates large dislocated InGaAs clusters and remarkably improves the optical properties of the structures. A modal gain of ~4 cm-1 is achieved in the 1.35 µm range. The elimination of defects allows the stacking of QDs emitting at 1.3 µm without deterioration of their optical and structural properties and reduces the QD density in the upper sheets.

PHOTONIC BAND-GAP EFFECTS UPON THE LIGHT EMISSION FROM A DYE-POLYMER-OPAL COMPOSITE

A polymeric photonic crystal formed by impregnating an opal with a Coumarin 6 dye containing polymer has been prepared and its emission properties studied by angular-resolved photoluminescence. A strong spectral redistribution of the luminescence intensity was observed in the dye-polymer-opal compared to that of the dye-polymer reference sample. The emission spectrum shows a marked distortion compared with the reference sample, which changes with the rotation of the crystal due to the angular dispersion of the stop band. Under increasing optical pumping power, a band of amplified spontaneous emission was observed at the stop-band edge. The angular dispersion of the stop band in the luminescence observed from the back surface exhibits in a strong directionality at the maximum of the dye emission band.

Emission in a SnS2 inverted opaline photonic crystal

The photoluminescence of a dye embedded in the three-dimensional SnS2 inverted opal has been studied. Changes of the emission spectrum compared with the free-space dye emission was observed in the stop-band frequency range in accord with reflectance/transmission spectra of this photonic crystal. The angular-dependent component, due to the Bragg stop band, and the angular-independent component, which is, possibly, related to the minimum in the density of photon states, have been distinguished in the dye emission spectrum.

THREE DIMENSIONAL PHOTONIC CRYSTALS IN THE VISIBLE REGIME

dimensional photonic bandgap structures working in the visible have been given increasing attention in recent years encouraged by the possibility to control, modify or confine electromagnetic waves in all three dimensions, since this could have considerable impact on novel passive and active optical devices and systems. Although substantial progress has been made in the fabrication of 3D Photonic crystals by means of nano-lithography and nanotechnol- ogy, it still remains a challenge to fabricate these crystals with feature sizes of the half of the wavelength in the visible. Self-assembling of colloidal particles is an alternative method to prepare 3-dimensional photonic crystals. The aim of this article is to show how to use col- loidal crystals as templates for photonic crystals and how to monitor the changes of their optical properties due course of the modification.

Suppression of spontaneous emission in incomplete opaline photonic crystal

Angular-resolved photoluminescence spectra have been obtained from polymer-made opaline photonic crystals impregnated with Coumarin dye. Spectral changes with optical excitation power and the direction of detection have been analyzed. The anisotropy in the suppression of the spontaneous emission is shown to be in accord with the Bragg stop-band dispersion.

Thin film photonic crystals

Abstract Large area thin film photonic crystals consisting either of closely packed PMMA balls or their SnS 2 replicas have been synthesized and tested. The photonic bandgap (PBG) of these structures demonstrates a tendency towards omnidirectionality and a subsequent increase of the refractive index contrast (RIC) in the inverted opal structure. In particular, the bandgap width in SnS 2 replica exceeds that of PMMA opal by a factor of three. Observations of the PBG-related dip in photoluminescence spectra and the self-focusing of the emission of the dye/PMMA opal have proven the merit of quasi-three-dimensional photonic films in the control of light emission.

Dye-Polymer–Opal Composites as Photonic Crystals

We have fabricated a polymeric photonic crystal by impregnating an opal with a Coumarin 6 dye-containing polymer which was subsequently polymerised inside the opal to form a dye-polymer–opal composite. A strong spectral redistribution of the luminescence properties of the composite has been found by angle resolved photoluminescence measurements. The emission spectrum shows a marked distortion compared with a dye-polymer reference sample, which changes with the rotation of the crystal due to the angular dispersion of the stop band. At the maximum of the dye-emission band a strong directionality of the photoluminescence recorded from the back surface was found.

Light emission from thin opaline photonic crystals of low and high dielectric contrast

Abstract Photoluminescence of dye molecules embedded in PMMA opaline photonic crystals and their SnS 2 replicas has been studied. The stop-band in the emission spectrum has been demonstrated. The role of a low dielectric contrast photonic crystal is to filter the emission from embedded light sources in accord with its transmission spectrum. In contrast, inverted opaline films of a higher dielectric contrast provide stronger radiation-to-emitter interaction, which feedback results in an amplification of a spontaneous emission of dye molecules at stop-band edges. The directionality diagram of the emission has been observed in both type photonic crystals. This, so-called, self-focusing effect has been tentatively assigned to the ultra-refraction of the emitted radiation at the sample boundary, which is dictated by the configuration of dispersion surfaces in the vicinity of the photonic band gap. The self-focusing has been found strongly dependent upon the frequency.

Thin Opaline Photonic Crystals

Among attractive features of the three-dimensional (3D) photonic crystal (PC) is its capability to cope with the emission of an arbitrary mode structure if the frequency of radiation matches the photonic band gap (PBG). To realise this effect one has to create a PC with omnidirectional PBG and to incorporate a light source of appropriate frequency without compromising the refractive index (RI) contrast. Numerous effects are anticipated in the case of strong coherent localisation of photons in the gain medium [1]. As far as visible light is concerned neither complete 3D PBGs nor a suitable technology for integrating the proper emitters have been reported so far.

Directionality of light emission in three-dimensional opal-based photonic crystals

Experimental and theoretical studies of the emission directionality diagrams of a perylene dye covering the inner surface of three-dimensional opal-based photonic crystals with incomplete photonic bandgap are reported. Directionality diagram of emission intensity is interpreted in terms of the spontaneous emission suppression by photonic band gap and the emission enhancement due to photon focusing phenomenon. A theoretical model is based on the classical analysis of an angular distribution of the radiated power of a point dipole.