Mach-Zehnder (MZ) modulators in Silicon-on-Insulator (SOI) are key components for integrated silicon photonic devices. Reducing their energy dissipation is a crucial step for applications of silicon photonics, especially in large data centers. In this work, we combine band-edge slow light structures consisting of silicon waveguide gratings with a periodic (interleaved) p-n junction. The slow-light structures consist of a waveguide grating with wide/narrow sections realized in a 300-nm thick silicon layer, on top of an unetched silicon layer of 50 to 150 nm thickness, fully embedded in SiO2. The grating gives rise to a photonic stop band and to a slow-light region close to the lowest band edge. The profile of the p-n junction varies periodically along the waveguide with interleaved n and p regions. This structure maximizes the spatial overlap between the optical mode and the depletion regions, yielding a further improvement of modulator efficiency beyond the slow-light effect.
Under an applied reverse bias, the silicon refractive index is modified by the plasma dispersion effect, thus the waveguide grating acts as a phase shifter. The modulator efficiency VpiLpi is strongly improved in comparison with modulators without slow light or with a lateral p-n junction. Thanks to the optimized overlap between electric field and depletion regions, this improvement takes place over a spectral interval that is much larger than the slow-light bandwidth. Insertion losses due to free carriers are also lower than in conventional modulators. The advantage of combining slow-light grating waveguides with an interleaved p-n junction is especially pronounced at low driving voltage (of the order of 1V), where the dissipated energy can be as low as 0.4 pJ/bit over an optical bandwidth of several 10 nm. Thus, the present modulator structure is promising in view of realizing integrated MZ modulators with low power dissipation.
We present the characterization of Silicon-on-insulator (SOI) photonic-crystal based 2D grating-couplers (2D-GCs) fabricated by CEA-Leti in the frame of the FP7 Fabulous project, which is dedicated to the realization of devices and systems for low-cost and high-performance passives-optical-networks. On the analyzed samples different test structures are present, including 2D-GC connected to another 2D-GC by different waveguides (in a Mach-Zehnder like configuration), and 2D-GC connected to two separate 2D-GCs, so as to allow a complete assessment of different parameters. Measurements were carried out using a tunable laser source operating in the extended telecom bandwidth and a fiber-based polarization controlling system at the input of device-under-test. The measured data yielded an overall fiber-to-fiber loss of 7.5 dB for the structure composed by an input 2D-GC connected to two identical 2D-GCs. This value was obtained at the peak wavelength of the grating, and the 3-dB bandwidth of the 2D-GC was assessed to be 43 nm. Assuming that the waveguide losses are negligible, so as to make a worst-case analysis, the coupling efficiency of the single 2D-GC results to be equal to -3.75 dB, constituting, to the best of our knowledge, the lowest value ever reported for a fully CMOS compatible 2D-GC. It is worth noting that both the obtained values are in good agreement with those expected by the numerical simulations performed using full 3D analysis by Lumerical FDTD-solutions.
Four-wave mixing can be stimulated or occur spontaneously: the latter effect, also known as parametric fluorescence,
can be explained only in the framework of a quantum theory of light, and it is at the basis of many
protocols to generate nonclassical states of the electromagnetic field. In this work we report on our experimental
study of spontaneous four wave mixing in microring resonators and photonic crystal molecules integrated on a
silicon on insulator platform. We find that both structures are able to generate signal and idler beams in the
telecom band, at rates of millions of photons per second, under sub-mW pumping. By comparing the experiments
on the two structures we find that the photonic molecule is an order of magnitude more efficient than the
ring resonator, due to the reduced mode volume of the individual resonators.
We demonstrate electrically pumped silicon nano-light source at room temperature,
having very narrow emission line (<0.5nm) at 1500nm wavelength, by enhancing the
electroluminescence (EL) via combination of hydrogen plasma treatment and Purcell
effect. The measured output power spectral density is 0.8mW/nm/cm2, which is
highest ever reported value from any silicon light emitter.
Here we discuss the experimental characterization of the spatial far-field profiles for the confined modes in a
photonic crystal cavity of the L3 type, finding a good agreement with FDTD simulations. We then link the
far-field profiles to relevant features of the cavity mode near-fields, using a simple Fabry-Perot resonator model.
Finally, we describe a technique for independent all-electrical control of the wavelength of quantum dots in
separated L3 cavities, coupled by a waveguide, by electrical isolation via proton implantation
Photonic modes in 1-D and 2-D silicon-on-insulator photonic
crystal waveguides periodic or containing line-defects, are fully
explored by means of angle- and polarization-resolved
micro-reflectance measurements. Both quasi-guided and truly guided
photonic modes are probed with a frequency-wave vector range that
is greatly expanded under attenuated total reflectance
configuration. It is shown that the presence of a supercell
repetition in the direction perpendicular to a line defect leads
to the simultaneous excitation of defect and bulk modes folded in
a reduced Brillouin zone. Consequently, the group-velocity
dispersion of the defect modes corresponding to different
polarizations of light can be fully determined. We show also that
the measured dispersion is in good agreement with full 3D
calculations based on expansion in the waveguide modes.