A. E. Vasdekis

Diode pumped distributed Bragg reflector lasers based on a dye-to-polymer energy transfer blend

We report the demonstration of a compact, all-solid-state polymer laser system comprising of a Gallium Nitride (GaN) semiconductor diode laser as the pump source. The polymer laser was configured as a surface emitting, distributed Bragg reflector laser (DBR), based on a novel energy transfer blend of Coumarin 102 and the conjugated polymer poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene vinylene). In this configuration, diode pumping was possible both due to the improved quality of the resonators and the improved harvesting of the diode laser light.

Broadband solid state optical amplifier based on a semiconducting polymer

A compact, solid state optical amplifier based on the conjugated polymer poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylene vinylene] has been demonstrated. The amplifier was optically pumped. Gratings were used to couple the signal into and out of the film. The transmitted signal was amplified over 100 times in a 1mm long waveguide giving 21dB gain at 630nm. A gain of >13dB was observed at 615 and 650nm giving a gain bandwidth of >26THz. The gain dynamics at pump densities below 5μJ∕cm2 are described by an exciton-exciton annihilation model. At higher pump intensities, amplified spontaneous emission and photoinduced losses become significant.

Low threshold edge emitting polymer distributed feedback laser based on a square lattice

We report the demonstration of a low-threshold, edge-emitting polymer distributed feedback laser based on a square lattice. The lattice constant was 268 nm, which corresponds to a lattice line spacing in the ΓM symmetry direction of the Brillouin zone of 189 nm. The latter was employed to provide feedback at 630 nm via a first order diffraction process. The device operated on two longitudinal modes, which were situated on the band-edge near the M symmetry point. The two modes had thresholds of 0.66 nJ and 1.2 nJ—significantly lower than comparable surface-emitting DFB lasers. Angle dependent photoluminescence experiments were performed to investigate the effect of the square lattice on the laser operation and the origin of the low threshold.

Silicon based organic semiconductor laser

The authors demonstrate silicon based visible lasers as potential optical interconnects by combining silicon processed resonators and solution processed light-emitting polymers. The high refractive index and absorption coefficient of silicon at these wavelengths were addressed by developing distributed Bragg reflector resonators on a silicon-on-insulator substrate. The performance of the hybrid structure was characterized and analyzed in comparison to an all-silica counterpart and mechanisms for controlling the number of longitudinal modes and for tuning the emission wavelength were explored.

Picosecond gain switching of an organic semiconductor optical amplifier

All-optical switching of an individual pulse within a sequence of amplified pulses is demonstrated in a conjugated polymer optical amplifier. The switching was achieved using a control pulse resonant with the excited state absorption. An extinction ratio of ∼5.5dB was observed, while the intensities of the remaining pulses in the sequence, spaced at 50ps intervals, were unaffected. A pump-probe study was performed and showed full gain recovery within 2ps.

Amplification of optical pulse sequences at a high repetition rate in a polymer slab waveguide

Amplification of three short light pulses in a 140ps time window at 5kHz repetition rate has been demonstrated using a compact amplifier based on the conjugated polymer poly(9,9′-dioctylfluorene-co-benzothiadiazole). The amplifier was optically pumped and gratings were used to couple the signal into and out of the film. A gain of 22dB was observed for a signal pulse temporally aligned with the pump pulse in a 1mm waveguide. For a signal pulse delayed by 140ps, the maximum gain achieved was 14dB. The results are a step towards the use of polymer amplifiers in data communications.

Holographic recording of sub-micron period gratings and photonic crystals in the photoresist SU8

SU8 is a commercial negative photoresist, which is highly transparent in the visible and near-infrared and extremely resistant to many organic solvents. Here we show that sub-micron period diffraction gratings, and 2D photonic crystal structures, can be readily formed holographically over extended areas. By coating the SU8 layer with a suitable gain medium, such structures may be used as feedback and output-coupling gratings for organic waveguide lasers. Thin films of SU8, were initially deposited by spin casting onto glass substrates. These films were then mounted in one arm of a Lloyds mirror interferometer and exposed with the expanded beam of a HeCd laser, operating at 325 nm. Subsequent baking and developing steps lead to both volume gratings with index contrast of 0.014, and surface gratings with corrugation depths of up to 140 nm. By varying the incidence angle of the HeCd laser beam to the SU8 film we have tuned the microstructure period from 500 nm down to 200 nm. Using multiple exposures, both doubly-periodic diffraction gratings and square-lattice crystal structures have been produced.

Diode-pumped polymer lasers

In this paper we describe the design and performance of diode-pumped organic lasers based on the poly(paraphenylene-vinylene) derivative MEH-PPV. To achieve the very low oscillation thresholds required for direct diode pumping, we use a novel surface-emitting distributed Bragg reflector cavity. We describe the operating characteristics of such devices when operating below and above threshold, and show that they can combine low threshold operation with the favourable spectral and emission characteristics of DFB lasers. We also describe and characterize an energy transfer gain medium using coumarin 102 laser dye as the host, which has been optimized for efficient harvesting of the diode laser excitation.

An organic semiconductor laser on silicon

Silicon photonics is a rapidly progressing field, where silicon structures are developed for optical information generation, transmission and processing. Although substantial progress has been achieved in the fields of transmission and processing, significant challenges remain to be addressed in generating light on silicon. In this paper we show that by integrating a silicon resonator with organic semiconductors, light generation on silicon chips can be achieved in the visible spectral range. Unlike similar attempts in the telecommunication spectral region, the signal from our device can be directly measured by silicon photodetectors.

Microstructured polymer lasers: diode-pumped lasing and extending operation lifetimes

In this paper, we demonstrate a very compact, all-solid-state polymer laser system comprising of a GaN semiconductor diode laser as the pump source with a novel surface-emitting resonator structure and an innovative energy-transfer gain medium is demonstrated. We also report studies of operating lifetime of polymer photonic crystal lasers based on MEH-PPV, which were simply fabricated using solvent assisted micromoulding. We demonstrate that suitable encapsulation can have little effect on the optical properties of the polymer laser.