G. Kranzelbinder

Refractive Index Changes in Polymers Induced by Deep UV Irradiation and Subsequent Gas Phase Modification

Poly(4-vinylbenzyl thiocyanate) (PVBT) and a copolymer of styrene and 4-vinylbenzyl thiocyanate (PST-co-VBT) were investigated with regard to changes of the refractive index under UV irradiation (λ = 254 nm). After irradiation, the refractive index n D of PVBT films increased from 1.629 to 1.660. In the case of the copolymer PST-co-VBT n D increased from 1.616 to 1.630. The change of the refractive index mainly resulted from the photoinduced isomerization of thiocyanate groups (SCN) to the corresponding isothiocyanates (NCS). The NCS groups formed in the irradiated zones were selectively modified with gaseous amines (ammonia, propylamnie, ethylenediamine, and hydrazine) to give thiourea derivatives vias an addition reaction. The gas phase modification induced further changes of the refractive index without any loss of the film quality (e.g. propylamine, Δn up to -0.026, an hydrazine, Δn up to +0.035). In addition, the thickness h of the polymer films increased by up to 21% as a result of the gas phase modification. In contrast, wet chemical treatment with bulky amines (1-methylnaphthyl-amine, 1-pyrenemthylamine) caused a considerable deterioration of the film quality. The variation of the refractive index in polymers such as PVBT and PST-co-VBT is of potential interest for holographic and the recordings and the setup of polymer based DFB lasers.

Polymer microring lasers with longitudinal optical pumping

We propose an optical pumping scheme for microring cavity lasers. The pump beam is end-fire coupled into the optical fiber that supports the microring cavity. When propagating along the fiber, the pump light is coupled into and excites the gain medium in the microring. We have demonstrated that this pumping geometry leads to an enhanced slope efficiency and significant reduction of the lasing threshold. In addition, as the excitation of the gain medium is uniform, certain effects that are prone to occur in the usual transversal pumping configuration because of nonuniform excitation can be avoided.

Progress in erasable and permanent polymer based DFB-structures with multicolour tunable laser emission

Highly luminescent organic solid state media including molecular dye doped guest-host systems and novel conjugated polymers currently attract a lot of interest for application in photonic technology. We demonstrate organic solid-state lasers with broadly and continuously tuneable mode emission (Δλ = 40nm, FWHM < 1nm). Feed-back onto polymeric DFB-structures results from dynamic and permanent photoinduced in-plane gratings. A write and read - technique for easy and low cost fabrication of single and multiple grating devices is presented. The combination and optimization of tuneable gratings with specific confinement features as from different waveguiding formats open-up new approaches in integrated optics.

Blue green stimulated emission of a high gain conjugated polymer

Abstract The stimulated emission properties associated with high optical gain is investigated in pure methyl-substituted poly-(paraphenylene) laddertype polymer (m-LPPP). Amplified spontaneous emission (ASE) in combination with waveguiding in the polymer film results in a highly directional linear polarised blue output at low pumping threshold of 3kW/cm 2 . Above a threshold value of 400 kW/cm 2 , additional narrow lines can be observed, that are assigned to amplified Stokes modes of stimulated Raman scattering (SRS). The output characteristics of different waveguides are investigated and explained by leaky wave propagation.

Organic solid state lasers based on novel polymers-optical recording of designed structures and device characterization

Summary from only given. We present two types of new polymeric materials for organic device applications. From a novel synthesis route employing polycondensation we obtain an improved quality of MEH-PPV and use this /spl pi/-conjugated polymer as the active laser medium in a first-order DFB-laser. We also show a novel-type deep-UV photo-polymer, poly(styrene-co-4-vinylbenzylthio-cyanate) (PST-co-VBT) compatible with UV-lithography.

Phase Gratings in Photoreactive Polymers: A Way to Optically Pumped Organic Lasers

Poly-(4-vinylbenzyl-thiocyanate) (PVBT) was investigated as a photoreactive polymer which changes its refractive index upon UV irradiation as is required for the production of phase gratings. After UV irradiation, the refractive index of PVBT films increased from n 20 D = 1.629 to n 20 D = 1.660 (Δn = +0.031). The change in the refractive index resulted mainly from the photoinduced isomerization of thiocyanate (SCN) to isothiocyanate (NCS) groups. It was possible to modify irradiated PVBT with 1-naphthylmethyl amine which lead to a further increase of the refractive index. Both the isomerization and the modification were followed with FTIR spectroscopy. This modification of the irradiated zones also yields an advantageous stabilization of phase gratings enscribed in PVBT The investigations were carried out in the realm of novel organic distributed feedback (DFB) lasers.

Reductive Photopatterning of Phenylene-Vinylene-Based Polymers

Photochemical methods were developed to obtain a variation of the refractive index in aromatic polymer surfaces and a change in the photoluminescence characteristics of phenylenevinylene-based polymers. Films of aromatic polymers, among them polystyrene (PS), poly(2-vinylnaphthalene) (PVN) and derivatives of poly( p -phenylene-vinylene) (PPV) were UV irradiated in the presence of gaseous hydrazine (N 2 H 4 ). The photoreaction led to a strong reduction of the refractive index of the polymers due to a hydrogenation of the aromatic units. In the case of PPV, we observed reductive photobleaching. This new technique was employed to produce photogenerated patterns in PPV. The results are compared to oxidative bleaching.

Formation of relief gratings in photoreactive polymers via gas phase modification

Optically pumped DFB lasers based on conjugated polymers have been demonstrated during the past years. Optical feedback can be introduced by a spatial periodical variation of the refractive index. We investigated the UV-induced formation of gratings in polymer films which act as a matrix for the active material. Irradiation of poly(4-vinylbenzyl thiocyanate) and poly(styrene-co-4-vinylbenzyl thiocyanate) caused an increase of the refractive index n D by +0.03. Irradiated and unirradiated zones showed different reactivity towards gaseous modification agents (amines) which caused additional changes of the refractive index and an increase of the film thickness in the irradiated zones. The formation of gratings in such films by patterned illumination and subsequent gas phase modification is shown.

Fabrication of refractive index and relief gratings in polymer films for DFB lasers

A styrene copolymer of 4-vinylbenzyl thiocyanate (PST- co -VBT) was employed as recording material for optical interference patterns with periods ∧ -2 , λ = 266 nm), refractive index gratings were produced in PST- co -VBT by an UV induced photoisomerization SCN - NCS. Subsequent modification of the patterns with gaseous amines yielded surface relief gratings via the formation of derivatives of thiourea. Laser irradiation with higher pulse energies (7 mJ cm -2 , λ = 266 nm) directly produced surface relief gratings (modulation depth 30 nm). These gratings were also reactive towards amine reagents and allowed a selective functionalization of the grooves of the relief (“reactive gratings”). Optically inscribed gratings in PST- co -VBT were employed as optical resonators for distributed feedback (DFB) lasing. With a laser dye (DCM) dissolved in PST- co -VBT, optically pumped DFB laser action was observed after inscribing index and relief gratings. The pumping threshold for lasing I th was 250 nJ cm -2 at λ = 532 nm.