Maurice Ayache

Nonreciprocal light propagation in a silicon photonic circuit.

An engineered metallic-silicon waveguide allows for direction-dependent light propagation. Optical communications and computing require on-chip nonreciprocal light propagation to isolate and stabilize different chip-scale optical components. We have designed and fabricated a metallic-silicon waveguide system in which the optical potential is modulated along the length of the waveguide such that nonreciprocal light propagation is obtained on a silicon photonic chip. Nonreciprocal light transport and one-way photonic mode conversion are demonstrated at the wavelength of 1.55 micrometers in both simulations and experiments. Our system is compatible with conventional complementary metal-oxide-semiconductor processing, providing a way to chip-scale optical isolators for optical communications and computing.

Compact chip-scale filter based on curved waveguide Bragg gratings

We propose a method for miniaturization of filters based on curved waveguide Bragg gratings, so that long structures can be packed into a small area on a chip. This eliminates the stitching errors introduced in the fabrication process, which compromise the performance of long Bragg gratings. Our approach relies on cascading curved waveguide Bragg gratings with the same radius of curvature. An analytical model for the analysis of these devices was developed, and a filter based on this model was designed and fabricated in a silicon on insulator platform. The filter had a total length of 920μm, occupied an area of 190μm×114μm, and exhibited a stop band of 1.7nm at 1.55μm and an extinction ratio larger than 23dB.

Micro-resonator with metallic mirrors coupled to a bus waveguide

We demonstrate a micro-resonator based on a channel waveguide terminated with metallic mirrors side coupled to a bus waveguide. Transmission through such a resonant structure implemented in a silicon-on-insulator platform is investigated theoretically and demonstrated experimentally. The resonator is 13.4 μm long, exhibits an unloaded Q-factor of ~2100, and a free spectral range of 21 nm around the wavelength of 1.55 μm.

Near-field measurement of amplitude and phase in silicon waveguides with liquid cladding

In recent years Near-Field Scanning Optical Microscopy (NSOM) has emerged as an important characterization tool for guided-wave photonic devices. The NSOM uses a subwavelength aperture probe to couple evanescent waves to the far-field, allowing subdiffraction-limited imaging and measurement of local properties of photonic structures. By integrating the NSOM into one of the arms of a heterodyne interferometer, we may image near-field phase as well as amplitude. However, on-chip guided-wave devices are typically coated with a solid overcladding. Heterodyne NSOM (H-NSOM) characterization of these devices has typically been limited to similar devices without cladding since the probe cannot penetrate the solid cladding layer to access the evanescent fields contained within. Here we demonstrate a technique that allows optical near-field characterization of devices while preserving their optical properties. To do so, a liquid overcladding is introduced to emulate the actual overcladding of the final operational device while allowing the probe to sample the evanescent field at the core-cladding interface for analysis by the NSOM. This technique enables metrology on the actual rather than duplicate device and preserves the dispersion of the optical structures to replicate the designed structure. To our best knowledge this is the only H-NSOM technique allowing characterization of photonic circuits in their final form.

Independent manifold analysis for subpixel tracking of local features and face recognition in video sequences

Effortless and robust recognition of human faces in video sequences is a practically important, but technically very challenging problem, especially in the presence of pose and lighting variability. Here we study the statistical structure of one such sequence and observe that images of both facial features and the full head lie on low-dimensional manifolds that are embedded in very high-dimensional spaces. We apply IndependentManifold Analysis (IMA) to learn these manifolds and use them to track local features to sub-pixel accuracy. We utilize sub-pixel resampling, which allows a very smooth estimate of head pose. In the process, we learn a manifold model of the head and use it to partially compensate for pose. Finally, in experiments on the standard FERET database, we report that this pose compensation results in more than an order of magnitude reduction of the equal error rate.

Near-Field measurement of amplitude and phase in silicon waveguides with liquid cladding

In recent years Near-Field Scanning Optical Microscopy (NSOM) has emerged as an important characterization tool for guided-wave photonic devices. The NSOM uses a subwavelength aperture probe to couple evanescent waves to the far-field, allowing subdiffraction-limited imaging and measurement of local properties of photonic structures. By integrating the NSOM into one of the arms of a heterodyne interferometer, we may image near-field phase as well as amplitude. However, on-chip guided-wave devices are typically coated with a solid overcladding. Heterodyne NSOM (H-NSOM) characterization of these devices has typically been limited to similar devices without cladding since the probe cannot penetrate the solid cladding layer to access the evanescent fields contained within. Here we demonstrate a technique that allows optical near-field characterization of devices while preserving their optical properties. To do so, a liquid overcladding is introduced to emulate the actual overcladding of the final operational device while allowing the probe to sample the evanescent field at the core-cladding interface for analysis by the NSOM. This technique enables metrology on the actual rather than duplicate device and preserves the dispersion of the optical structures to replicate the designed structure. To our best knowledge this is the only H-NSOM technique allowing characterization of photonic circuits in their final form.

Nonreciprocal light propagation on an integrated silicon photonic chip

We have designed, fabricated, and tested a CMOS compatible silicon waveguide system that demonstrates nonreciprocal light propagation on-chip, by mimicking microscopic non-Hermitian optical potentials for guided light and thus spontaneously breaking parity-time symmetry. Experiments were performed at 1.55 µm wavelength for potential telecommunication applications.

Broadband heterodyne NSOM characterization of propagation loss in waveguide bends

We use a heterodyne NSOM with superluminescent diode illumination to measure the loss in an SOI waveguide around a bend. For a bend of radius 10 µm, we measure loss of .09 dB.