Proc. SPIE. 9891, Silicon Photonics and Photonic Integrated Circuits V
KEYWORDS: Semiconductors, Resonators, Luminescence, Silicon, Near field, Photonics, Silicon photonics, Silicon carbide, Single walled carbon nanotubes, Group III-V semiconductors, Microrings, Near field optics, Carbon nanotubes
Hybrid structures are needed to fully exploit the great advantages of Si photonics and several approaches have been addressed where Si devices are bonded to different materials and nanostructures. Here we study the use of semiconductor carbon nanotubes for emission in the 1300 nm wavelength range to functionalize Si photonic structures in view of optoelectronic applications. The Si micro-rings are fully characterized by near field forward resonant scattering with 100 nm resolution. We show that both TE and TM modes can be addressed on the top of the micro-rings in a vectorial imaging of the in-plane polarization components. We coupled the Si micro-resonators with selected carbon nanotubes for high photoluminescence emission. Coupling nanotubes with the evanescent tails in air of the electric field localized in the photonic modes of the micro-resonators is demonstrated by sharp resonances over imposed to the nanotube emission bands. By mapping the Si and the nanotube emission we demonstrate that strong enhancement of the nanotube photoluminescence can be achieved both in the photonic modes of micro-disks and slot micro-rings, whenever the spatial overlap between nano-emitters and photonic modes is fulfilled.
Silicon photonics, due to its compatibility with the CMOS platform and unprecedented integration capability, has become the preferred solution for the implementation of next generation optical interconnects. However, current Si photonics require on-chip integration of several materials, including III-V for lasing, doped silicon for modulation and Ge for detection. The very different requirements of these materials result in complex fabrication processes that offset the cost-effectiveness of the Si photonics approach. We are developing an alternative route towards the integration of optoelectronic devices in Si photonic, relying on the use of single wall carbon nanotubes (SWNTs). SWNTs can be considered as a Si compatible material able to emit, modulate and detect near-infrared light. Hence, they hold a unique potential to implement all active devices in the Si photonics platform. In addition, solution processed SWNTs can be integrated on Si using spin-coating techniques, obviating the need of complex epitaxial growth or chip bonding approaches. Here, we report on our recent progress in the coupling of SWNTs light emission into optical resonators implemented on the silicon-on-insulator (SOI) platform.
Semiconducting carbon nanotubes are an emerging material for photonics. We report on the enhancement of semiconducting carbon nanotubes photoluminescence with silicon microring resonators. Polyfluorene extracted semiconducting carbon nanotubes, deposited on such resonators, display sharp emission peaks superposed to nanotube emission, which is attributed to the interaction with the cavity modes of the microring resonators. Ring resonators with radii of 5 and 10 μm were used, to demonstrate the tuning of the spectral distance between two successive emission resonances. Quality factors ranged between 3000 and 4000 in emission. These are among the highest values reported so far for carbon nanotubes coupled with optical microcavity on the silicon platform, highlighting the bright perspectives for carbon nanotube photonics.
Semiconducting SWNT extraction was studied using an ultra-centrifugation method assisted by a conjugated polymer. It was demonstrated that the emission intensity can be highly improved and that in some conditions emission from one single nanotube chirality can be achieved. This optimized material was integrated on several photonic structures. The ability of nanotubes to emit light when drop-casted on a silicon waveguide was first demonstrated and its thermal stability was further investigated. We concluded over interesting integration ability on Silicon-On-Insulator (SOI) substrate, with coupling efficiency up to the order of 10%. The integration of SWNT on Bragg mirrors based cavity was also investigated. This is the first milestone towards a carbon nanotube based fully integrated LASER.
In this paper, we first review and compare the two main techniques allowing to purify and extract selectively semiconducting single-walled carbon nanotubes (s-SWNT)). These purification steps are essential to obtain an optical-quality material. Such material is then suitable for optical applications and photonic devices. We present two major advances in carbon nanotubes optics and photonics: on one hand, the demonstration of optical gain in s-swnt by two independent methods, with modal gain as high as 160 ±10 cm-1 at 1.3 μm and on the other hand, the integration of SWNT in silicon-on-insulator (SOI) platform as a potential material for integrated photonic devices. Overall coupling efficiency could be estimated up to 10-1.
Room temperature direct gap electroluminescence (EL) from a Ge/Si0.15Ge0.85 MQW waveguide was experimentally
studied. The dependence of the EL intensity on the injection current and temperature was measured. The direct gap EL
from Ge/SiGe MQWs was shown to be transverse-electric (TE) polarized, confirming that the EL originates from
recombination with a HH state.
Carbon nanotubes are more and more considered for future use in microelectronics. On the other hand, the use
of optics to overcome the limitation of metallic interconnects start to be considered as a viable solution. Carbon
nanotubes are promising candidate to bridge the gap between optics and microelectronics, thanks to their ability
to emit, modulate and detect light in the wavelength range of silicon transparency. In this proceeding, we
will rst underline the use of carbon nanotube for photonics. We will then show that thin lm doped with
semiconducting carbon nanotubes displays strong optical gain at a wavelength of 1.3 μm. Finally, we will report
the integration of carbon nanotube thin layer with silicon waveguide, and present the successfull coupling of their
absorption and emission properties. This leds to the demonstration of temperature independent emission from
carbon nanotubes in silicon at a wavelength of 1.3 μm.
Semiconducting single wall carbon nanotubes (s-SWNT) are unique monodimensional material of particular interest in
photonics for their direct band-gap, allowing tunable near-IR luminescence from electron-hole recombinaison.
However, the presence of metallic nanotubes and impurities in real carbon nanotubes samples creates several non
radiative relaxation mechanisms, leading to an effective quenching of s-SWNT photoluminescence and limiting their
usability in photonics devices. Recently, we have developed a process to selectively extract s-SWNT and embedded
them in polyfluorene (PFO) thin films. A removal of metallic nanotubes leads to an enhancement of the
photoluminescence properties, with a 6-fold increase of the photoluminescence intensity of (8,6) s-SWNT.
Development of nanotubes based photonics devices is also reported. The SWNT-based layer was inserted between two
Bragg mirrors to form a Fabry-Perot cavity, leading to a huge photoluminescence enhancement by a factor of 30 in
comparison with an identical film and by a factor of 180 in comparison with a non s-SWNT enriched film.
Nowadays, it seems evident that a unique nonlinear optical (NLO)material cannot offer simultaneously linear transparency,colour neutrality and broadband optical limiting efficiency at the performance levels required for sensor and eye protection against all laser threats.Several combinations of NLO materials were investigated last few years, including multicell or multilayer geometries.
The approach presented here combines multiphoton absorption with nonlinear scattering. For that purpose, singlewall carbon nanotubes are suspended in various solutions of multiphoton absorbing chromophores. Such combinations allow us to obtain optical limiters of high linear transmittance and excellent colour neutrality. Broadband optical limiting is expected from the association of these two broadband materials,and enhanced optical limiting efficiency is expected from cumulative effects in the nanosecond regime.
We report here on the optical limiting studies performed with nanosecond laser pulses on several families of multiphoton absorbers in chloroform,with carbon nanotubes suspended in the solutions. The performances of these samples are compared with those of simple multiphoton absorber solutions and carbon nanotube suspensions, and the differences observed are interpreted in terms of cumulative NLO effects and adverse aggregation phenomenon. Ways to optimise stability of the suspensions are also experimented and discussed.