High efficiency diffractive grating structures to interface a single mode optical fiber and a nanophotonic integrated circuit fabricated on silicon-on-insulator are presented. The diffractive grating structures are designed to be inherently very directional by adding a silicon overlay before grating definition. 55% coupling efficiency at a wavelength of 1.53 m is experimentally demonstrated on devices fabricated using standard complementary metal-oxide semiconductor technology. By optimizing the grating parameters, we theoretically show that 80% grating coupling efficiency can be obtained for a uniform grating structure.High refractive index contrast optical waveguide structures hold promise for large scale integration of optical functions on a single substrate. This is due to the fact that the high refractive index contrast allows realizing wavelengthscale optical components ͑e.g., photonic crystal cavities, 1 ring resonators, 2 modulators, 3 etc.͒ which can be interconnected by nanophotonic integrated waveguides. Silicon-oninsulator ͑SOI͒ is emerging as the dominant platform for this integration because the refractive index contrast between the silicon waveguide layer ͑n Si = 3.45 at a wavelength of 1.55 m͒ and the underlying buried oxide layer ͑n SiO 2 = 1.45͒ is very high. Moreover, these nanophotonic structures can be defined using state-of-the-art complementary metaloxide semiconductor ͑CMOS͒ technology. 4 While the high omnidirectional refractive index contrast allows realizing wavelength-scale optical functions, the interfacing between a nanophotonic waveguide and a standard single mode fiber is far from trivial due to the large mismatch in dimensions between the 9 m diameter core of a single mode fiber and the cross section of an integrated high index contrast waveguide, which is typically 0.1 m 2 for a single mode waveguide at telecommunication wavelengths. In this paper, we present the use of a diffractive grating structure defined in the waveguide layer to efficiently interface with a single mode optical fiber. The operation principle of the device is based on the Bragg diffraction from the grating. The optical fiber is slightly tilted off vertically in order to avoid second order Bragg reflection into the waveguide. 4 While the optical coupling properties of one-dimensional grating structures are very polarization dependent, it was shown that a twodimensional grating coupling approach allows tackling the issue of the polarization dependent loss of high index contrast photonic integrated circuits by applying a polarization diversity configuration, 5 without the need of integrating a polarization splitter and rotator on the photonic integrated circuit. 6The fiber-to-waveguide coupling efficiency is determined by the directionality of the grating, being the ratio of the power that is diffracted upward ͑P up ͒ to the total diffracted power ͑P up + P do ͒, as shown in Fig.
A high speed and low loss silicon optical modulator based on carrier depletion has been made using an original structure consisting of a p-doped slit embedded in the intrinsic region of a lateral pin diode. This design allows a good overlap between the optical mode and carrier density variations. Insertion loss of 5 dB has been measured with a contrast ratio of 14 dB for a 3 dB bandwidth of 10 GHz.
Slot and sandwiched waveguides with silicon nanocrystals were fabricated by means of industrial microelectronic tools, including DUV lithography. Low loss of 4 dB/cm will pave the way to compact all-optical XOR logic gates.
IntroductionUsing silicon, oxides, nitrides and other Si-based materials as active means for photonic functionalities is of great interest since it would allow a potential monolithic integration of electrical and optical circuits in a fully compatible CMOS processing. For example, optical interconnects, optical amplifiers and switches integrated in CMOS photonic chips would make it possible to develop low cost and all-optical communication networks without bottlenecks induced by electrical/optical converters. Passive devices (filters, couplers, multiplexers...) that make use of silicon-based waveguides and materials exhibiting non-linear optical properties have already been demonstrated. Nevertheless they use Si thermo-optic effects or refractive index variation due to the free carrier concentration in Si, as bulk Si is a very poor material for non-linear optics. Notwithstanding, nanostructured Si, due to quantum confinement effects, and particularly silicon nanoclusters (Si-nc) embedded in SiO2 (Si-nc/SiO2) are considered very promising materials due to extraordinarily enhanced nonlinear properties in comparison to bulk Si, as its Kerr coefficient is reported in the range
A first experimental demonstration of a planar superprism in silicon microphotonics technology using silicon on insulator (SOI) substrates is presented. Experimental results for anomalous wavelengthdependent angular dispersion in SOI triangular lattice planar photonic crystals are reported. An angular swing of 14 degrees is measured for light propagating near the Gamma-K direction as the input wavelength is changed from 1295 nm to 1330 nm, which corresponds to an angular dispersion of 0.4 degrees /nm. For the Gamma-M direction, a negative wavelength dispersion has been recorded. An opposite sign angular deviation of 21 degrees is observed as the input wavelength is changed from 1316 nm to 1332 nm, i.e. a dispersion of 1.3 degrees /nm.
We report the successful fabrication of low-loss submicrometric silicon-on-insulator strip waveguides for on-chip links. Postlithography treatment and postetching hydrogen annealing have been used to smoothen the waveguide sidewalls, as roughness is the major source of transmission losses. An extremely low silicon line-edge roughness of 0.75 nm is obtained with the optimized process flow. As a result, record-low optical losses of less than 0.5 dB/cm are measured at 1310 nm for strip waveguide dimensions exceeding 500 nm. They range from 1.2 to 0.8 dB/cm for 300-400-nm-wide waveguides. Those results are to our knowledge the best ever published for a 1310-nm wavelength. These results are compared to modeling based on Payne and Lacey equations.
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