All-optical control of light on a silicon chip
ABSTRACT Photonic circuits, in which beams of light redirect the flow of other beams of light, are a long-standing goal for developing highly integrated optical communication components. Furthermore, it is highly desirable to use silicon--the dominant material in the microelectronic industry--as the platform for such circuits. Photonic structures that bend, split, couple and filter light have recently been demonstrated in silicon, but the flow of light in these structures is predetermined and cannot be readily modulated during operation. All-optical switches and modulators have been demonstrated with III-V compound semiconductors, but achieving the same in silicon is challenging owing to its relatively weak nonlinear optical properties. Indeed, all-optical switching in silicon has only been achieved by using extremely high powers in large or non-planar structures, where the modulated light is propagating out-of-plane. Such high powers, large dimensions and non-planar geometries are inappropriate for effective on-chip integration. Here we present the experimental demonstration of fast all-optical switching on silicon using highly light-confining structures to enhance the sensitivity of light to small changes in refractive index. The transmission of the structure can be modulated by up to 94% in less than 500 ps using light pulses with energies as low as 25 pJ. These results confirm the recent theoretical prediction of efficient optical switching in silicon using resonant structures.
- SourceAvailable from: Zhuan Zhu
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- "Silicon is a natural choice of material for EPIC because of its mature technology, but silicon is an indirect bandgap semiconductor which makes it difficult to fabricate optoelectronic devices. In the socalled silicon photonics, much effort has been made to transform silicon to an active optical material for light generation and detection, especially in the sub-bandgap wavelength range so that silicon itself can be used as optical waveguide    . There are also hybrid approaches to implementing board-level EPIC, for instance, by creating a Raman laser using optical pumping, or by integration with III-V devices  . "
ABSTRACT: The monolithic integration of electronics and photonics has attracted enormous attention due to its potential applications. However, the realization of such hybrid circuits has remained a challenge because it requires optical communication at nanometer scales. A major challenge to this integration is the identification of a suitable material. After discussing the material aspect of the challenge, we identified atomically thin transition metal dichalcogenides (TMDs) as a perfect material platform to implement the circuit. The selection of TMDs is based on their very distinct property: monolayer TMDs are able to emit and absorb light at the same wavelength determined by direct exciton transitions. To prove the concept, we fabricated simple devices consisting of silver nanowires as plasmonic waveguides and monolayer TMDs as active optoelectronic media. Using photoexcitation, direct optical imaging and spectral analysis, we demonstrated generation and detection of surface plasmon polaritons by monolayer TMDs. Regarded as novel materials for electronics and photonics, transition metal dichalcogenides are expected to find new applications in next generation integrated circuits.
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- "The filter doesn't introduce any relevant impairment in the downstream signal, as the optical power reaching the ONU, at the resonant wavelength, is generally so small that nonlinear effects can be generally neglected. Nevertheless, if the upstream signal, that generally has a much higher power, has to pass through the same resonator can undergo nonlinear effects like two-photon absorption (TPA), free-carriers absorption (FCA), and free-carrier dispersion (FCD) . In this abstract we show the results of an experimental analysis we carried out in order to investigate the impact of optical nonlinear effects in WDM integrated micro-filters exploiting different designs (double-and triple-resonators structures, racetracks, rings, curved coupling regions, etc…) and exhibiting significantly different waveguide cross-sections (from 500 × 220 nm to 825 × 100 nm). "
ABSTRACT: Integrated optical chips enabling the realization of low-cost optical network units (ONU) is of great interest both for data centre solutions and for passive optical networks. In particular, in the frame of passive optical networks an interesting possibility is constituted by the presence, in the ONU of a Wavelength Division Multiplexing (WDM) filter  One of the most popular solution is based on a micro-ring resonators. The filter doesn't introduce any relevant impairment in the downstream signal, as the optical power reaching the ONU, at the resonant wavelength, is generally so small that nonlinear effects can be generally neglected. Nevertheless, if the upstream signal, that generally has a much higher power, has to pass through the same resonator can undergo nonlinear effects like two-photon absorption (TPA), free-carriers absorption (FCA), and free-carrier dispersion (FCD) . In this abstract we show the results of an experimental analysis we carried out in order to investigate the impact of optical nonlinear effects in WDM integrated micro-filters exploiting different designs (double-and triple-resonators structures, racetracks, rings, curved coupling regions, etc…) and exhibiting significantly different waveguide cross-sections (from 500 × 220 nm to 825 × 100 nm). The nonlinear behaviour evaluation has been carried out by performing two different sets of experiments. In the first one the amplified spontaneous emission emitted by an Er-doped fiber amplifier was filtered (by using a tunable filter with 5 nm band-width) and then amplified and then input by grating-assisted coupling to the filtering structures. Changes of filter transfer function were observed as a function of the input power. Conversely, in the second setup a narrowband CW-laser was used, and the behaviour of output power as a function of the input power was recorded. Fig. 1 Left: Optical fundamental-mode intensity distribution in the three waveguides used to realize the integrated filters. Center: example of transfer function deterioration (loss increase and band broadening) caused by optical nonlinear effects. Right: curves of output power as a function of input power for filters exploiting the three different waveguides (500 × 220, 525 × 100 and 825 × 100 nm, in green, red and blue respectively) The obtained results clearly highlight that even when moderate optical power (e.g. 0-3 dBm) is present on the chip, the resonating filter performance can be severely degraded by the two-photon absorption and by the accumulation of free carriers in the waveguide structure. Interestingly, the use of waveguides with a reduced-height, which have been extensively reported in the literature to allow a significant reduction of propagation losses, also show an increased saturation-power with respect to the standard (500 × 220 nm) waveguide cross-section. We believe that this behavior can be related to the reduced height of the waveguide: as recombination centers are mainly located on the waveguide surfaces, the use of a reduced-height structure allows for a faster free-carrier recombination. Indeed free-carriers travel for less than half of the length required in standard waveguides before reaching the surface. Further measurements on additional structures, including both measurements with modulated signals (to evaluate also the impact of self-phase modulation) and measurements of free-carriers recombination time are currently ongoing .Cleo Europe 2015; 06/2015
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- "Several methods is used to improve the efficiency of Electro-optical filter as expanding the active area and increasing the sensitivity in passive section of photonic device, resonators based on silicon photonics enhance Controllability at the Passive photonic devices     . Resonant wavelength in Electro-optical filter is adjusted by applying an electrical voltage to the silicon cavity and changes in the optical properties of the cavity and leads to shift in the output wavelength of Electro-optical filter. "
ABSTRACT: In this paper, a high tunable Electro-optical filter is designed and simulated with low electric power consumption. A Silicon nanobeam resonator based on one-dimensional photonic crystal in the form of Fabry–Perot structure, silicon-on-insulator waveguide, is proposed with a PIN junction. In designing nanobeam resonator, "deterministic design method" is used to achieve the high quality factor and high-transmission rate. Tuning of the resonant wavelength in the output channel of the filter is achieved by manipulating the refractive index of the active area by using the free-carrier dispersion effect. The output wavelengths of designed device can be tuned for the telecom-friendly 1.55 μm range. The device shows a wavelength shift higher than 3 nm for a power consumption of only 0.9 mw. Finally, the simulation results show that the provided device can be considered as a narrowband and tunable Electro-optical filter that is suitable for DWDM communication system.Physica E Low-dimensional Systems and Nanostructures 02/2015; · 2.00 Impact Factor