Tejaswi Indukuri

Self phase modulation induced spectral broadening in silicon waveguides

We have investigated spectral broadening as a mean to generate multiple wavelengths on a silicon chip. A 2/spl times/ broadening at 22 W//spl mu/m/sup 2/ of peak pulse power is demonstrated and a 7/spl times/ is predicted at 70 W/cm/sup 2/.

Monolithic 3-D silicon photonics

A monolithic CMOS compatible process has been developed to realize vertically integrated devices in silicon. The method involves the implantation of an oxygen into a patterned silicon substrate to form buried guiding structures. These buried devices are separated from a surface silicon layer by an intervening layer of silicon dioxide formed through the implantation process. Photolithography and etching is used to define devices on the surface silicon layer. The method has been utilized to realize the vertically coupled microdisk resonators and a variety of microresonator-based integrated optical elements. A new method for extraction of the unloaded Q of a cavity from its measured spectrum is also described.

Add-drop filters utilizing vertically coupled microdisk resonators in silicon

Add-drop filters, based on vertically coupled microdisk resonators, have been realized in silicon, using a modified separation by implantation of oxygen process. Buried rib waveguides in the bottom-layer silicon, of a two-layer structure, are coupled to microdisk resonators in the top-layer silicon through a silicon dioxide layer formed by oxygen implantation. The radii of the microdisk structures were varied suitably to obtain resonators with slightly shifted resonance wavelengths. The average adjacent channel crosstalk suppression of these filters exhibits an upper limit of 12.11dB and a lower limit of 6.2dB over the wavelength band under consideration.

Vertically-coupled micro-resonators realized usingthree-dimensional sculpting in silicon

A modified separation by implantation of oxygen process has been developed to sculpt vertically coupled microdisk resonators in silicon. The approach involves the implantation of oxygen ions into a silicon substrate, patterned with thermal oxide, to define waveguides on the bottom silicon layer, and photolithography and reactive ion etching to define the microdisk resonators on the top silicon layer. The top and the bottom silicon layers are separated by the oxide layer that was formed after the oxygen implantation. Fabricated microdisk resonators show resonances with a Q value of 10 300 and a free spectral range of 5.4nm.

Sculpting of three-dimensional nano-optical structures in silicon

Separation by IMplantation of OXygen (SIMOX) based process has been developed to sculpt three-dimensionally integrated nano-optical waveguiding structures in silicon. An approach, based on the implantation of oxygen ions into a silicon substrate, patterned with thermal oxide, has been adopted to synthesize low loss buried rib waveguides in a single implantation step of thickness 286 nm and widths varying from 2 μm to 12 μm. These waveguides show propagation losses in the range of 3–4 dB/cm. The capability of the process to sculpt three-dimensional (3-D) structures has also been demonstrated by defining rib waveguides on the top silicon layer.

Subterranean silicon photonics: Demonstration of buried waveguide-coupled microresonators

Laterally-coupled silicon microresonators are fabricated beneath the surface of a silicon-on-insulator substrate using a modified separation by implantation of an oxygen technique. Implantation of oxygen ions into a substrate with patterned thermal oxide mask was utilized to realize buried waveguiding structures. Microdisk resonators in the buried silicon layer show loaded quality factors of 2000, with extinction ratios in excess of 20dB. The process also results in the formation of a silicon layer on the surface of the wafer that is suitable for the fabrication of electronic devices, thereby paving the way for three-dimensional monolithic integration of electronics and photonics in silicon.

Three-dimensional integration of metal-oxide-semiconductor transistor with subterranean photonics in silicon

Monolithic integration of photonics and electronics has been achieved in silicon by three-dimensionally integrating metal-oxide-semiconductor field-effect transistors and waveguide-coupled microdisk resonators. Implantation of oxygen ions into a silicon-on-insulator substrate with a patterned thermal oxide mask followed by a high temperature anneal was utilized to realize the buried photonic structures. This results in the formation of vertically stacked silicon layers separated from each other by an intervening oxide layer. Transistors are fabricated on the surface silicon by conventional processing techniques. Optical and electronic functionalities are thus separated into two different layers of silicon, paving the way toward dense three-dimensional optoelectronic integration.

Monolithic vertical integration of metal-oxide-semiconductor transistor with subterranean photonics in silicon

Monolithic integration of photonics and electronics has been achieved in silicon by vertically integrating metal-oxide-semiconductor field-effect transistors and waveguide-coupled microdisk resonators in a double-layer silicon-on-insulator wafer, thus paving the way towards dense three-dimensional optoelectronic integration

3D integration of sub-surface photonics with CMOS

The integration of photonics and electronics on a single silicon substrate requires technologies that can add optical functionalities without significantly sacrificing valuable wafer area. To this end, we have developed an innovative fabrication process, called SIMOX 3-D Sculpting, that enables monolithic optoelectronic integration in a manner that does not compromise the economics of CMOS manufacturing. In this technique, photonic devices are realized in subsurface silicon layers that are separated from the surface silicon layer by an intervening SiO2 layer. The surface silicon layer may then be utilized for electronic circuitry. SIMOX 3-D sculpting involves (1) the implantation of oxygen ions into a patterned silicon substrate followed by (2) high temperature anneal to create buried waveguide-based photonic devices. This process has produced subterranean microresonators with unloaded quality factors of 8000 and extinction ratios >20dB. On the surface silicon layers, MOS transistor structures have been fabricated. The small cross-sectional area of the waveguides lends itself to the realization of nonlinear optical devices. We have previously demonstrated spectral broadening and continuum generation in silicon waveguides utilizing Kerr optical nonlinearity. This may be combined with microresonator filters for on-chip supercontiuum generation and spectral carving. The monolithic integration of CMOS circuits and optical modulators with such multi-wavelength sources represent an exciting avenue for silicon photonics.

3-D Integrated Vernier Filters in Silicon

Three-dimensionally integrated microdisk resonators have been employed to realize Vernier filters in Silicon. Cascaded configuration of vertically-coupled microdisk resonators with dissimilar radii increases the free spectral range of filters from 5.5 nm to 23 nm.