Molecular host-guest energy-transfer system with an ultralow amplified spontaneous emission threshold employing an ambipolar semiconducting host matrix.

We report on the characteristics of a host-guest lasing system obtained by coevaporation of an oligo(9,9-diarylfluorene) derivative named T3 with the red-emitter 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran dye (DCM). We demonstrate that the ambipolar semiconductor T3 can be implemented as an active matrix in the realization of a host-guest system in which an efficient energy transfer takes place from the T3 matrix to the lasing DCM molecules. We performed a detailed spectroscopic study on the system by systematically varying the DCM concentration in the T3 matrix. Measurements of steady-state photoluminescence (PL), PL quantum yield (PLQY), time-resolved picosecond PL, and amplified spontaneous emission (ASE) threshold are used to optimize the acceptor concentration at which the ASE from DCM molecules takes place with the lowest threshold. The sample with a DCM relative deposition ratio of 2% shows an ASE threshold as low as 0.6 kW/cm(2) and a net optical gain measured by femtosecond time-resolved pump-and-probe spectroscopy as high as 77 cm(-1). The reference model system Alq(3):DCM sample measured in exactly the same experimental conditions presents an one-order-of-magnitude higher ASE threshold. The ASE threshold of T3:DCM is the lowest reported to date for a molecular host-guest energy-transfer system, which makes the investigated blend an appealing system for use as an active layer in lasing devices. In particular, the ambipolar charge transport properties of the T3 matrix and its field-effect characteristics make the host-guest system presented here an ideal candidate for the realization of electrically pumped organic lasers.

Circular grating resonators as small mode-volume microcavities for switching.

We demonstrate the suitability of microcavities based on circular grating resonators (CGRs) as fast switches. This type of optical resonator is characterized by a high quality factor and very small mode volume. The waveguide-coupled CGRs are fabricated with silicon-on-insulator technology compatible with standard complementary metal-oxide semiconductor (CMOS) processing. The linear optical properties of the CGRs are investigated by transmission spectroscopy. From 3D finite-difference time-domain simulations of isolated CGRs, we identify the measured resonances. We probe the spatial distribution and the parasitic losses of a resonant optical mode with scanning near-field optical microscopy. We observe fast all-optical switching within a few picoseconds by optically generating free charge carriers within the cavity.

25ps all-optical switching in oxygen implanted silicon-on-insulator microring resonator.

We present all-optical switching in oxygen ion implanted silicon microring resonators. Time-dependent signal modulation is achieved by shifting resonance wavelengths of microrings through the plasma dispersion effect via femtosecond photogeneration of electron-hole pairs and subsequent trapping at implantation induced defect states. We observe a switching time of 25 ps at extinction ratio of 9 dB and free carrier lifetime of 15 ps for an implantation dose of 7 x 10(12) cm(-2). The influence of implantation dose on the switching speed and additional propagation losses of the silicon waveguide--the latter as a result of implantation induced amorphization--is carefully evaluated and in good agreement with theoretical predictions.

High-speed all-optical switching in ion-implanted silicon-on-insulator microring resonators.

We demonstrate high-speed all-optical switching via vertical excitation of an electron-hole plasma in an oxygen-ion implanted silicon-on-insulator microring resonator. Based on the plasma dispersion effect the spectral response of the device is rapidly modulated by photoinjection and subsequent recombination of charge carriers at artificially introduced fast recombination centers. At an implantation dose of 1 x 10(12) cm(-2) the carrier lifetime is reduced to 55 ps, which facilitates optical switching of signal light in the 1.55 mum wavelength range at modulation speeds larger than 5 Gbits/s.