electrospray-deposition-uniform-thickness-ge23sb7s70-as40s60

Electrospray Deposition of Uniform Thickness Ge23Sb7S70 and As40S60 Chalcogenide Glass Films

Solution-based electrospray film deposition, which is compatible with continuous, roll-to-roll processing, is applied to chalcogenide glasses. Two ...

University of Central Florida

We demonstrate electrical tuning of phase mismatch in silicon wavelength converters. Active control of birefringence induced by a thin-film piezoelectric transducer integrated on top of the waveguides is used for dispersion engineering. The technology provides a solution for compensating the phase mismatch caused by fabrication errors in integrated waveguides. It also offers a mean to dynamically control the relative dispersion between interacting waves and hence, to introduce electronic control of optical parametric processes.

Electrical control of parametric processes in silicon waveguides.

An electro-optic silicon modulator with negative electrical power dissipation is proposed. The device performs optical modulation through electrical control of losses caused by two photon absorption. It further exploits the nonlinear photovoltaic effect to recover the optical power that is normally dissipated when the modulator is in the on state.

Energy harvesting in silicon optical modulators.

Nonlinear loss is the central problem in silicon devices that operate using nonlinear optical effects. Wavelength converters are one example of such devices, wherein high optical intensities required for nonlinear interactions cause two-photon absorption and severe free-carrier absorption. In this paper, we report the first demonstration of nonlinear photovoltaic effect in silicon wavelength converters. This useful phenomenon allows us to eliminate the nonlinear loss caused by free-carrier absorption, while harvesting the optical power that is normally consumed by two-photon absorption.

Energy harvesting in silicon wavelength converters.

Influence of the refractive index of the surrounding material on the performance of a C-shaped subwavelength aperture is investigated. The changes in the spectral response (0.6 microm to 6 microm wavelength range) and power throughput of the aperture in an optically opaque silver (Ag) film are described for two configurations: one where the film with the aperture is immersed in an infinite dielectric slab and the other where the metallic layer is immediately adjacent to a semi-infinite dielectric substrate. It is shown that, while the resonant wavelengths increase monotonically with refractive index for both cases, the rates of these increases, as well as the behavior of the power throughput, depend not only on the configuration, but also strongly on the transmission mode. These findings have important implications for the design of subwavelength aperture-enhanced devices.

Effects of the surrounding medium on the optical properties of a subwavelength aperture.

Electronically tunable optical true-time delay lines are proposed. The devices utilize the combination of apodised gratings and the free-carrier plasma effect to tune the enhanced delay of silicon waveguides at a fixed wavelength. Three variations of the proposed scheme are studied and compared. The compact and integrable devices can achieve tuning ranges as high as ~660 ps with a loss of < 2.2 dB when operated in the reflection mode of the gratings. A delay of ~40 ps with a loss of < 10 dB and an estimated operation bit rate of ~20 Gb/s can be achieved.

Electronically tunable silicon photonic delay lines.

A novel class of high-speed and tunable integrated photonic delay lines that compromise between loss and size is proposed. The devices consist of two cascaded apodized grating waveguides and with complementary (positively and negatively modulated) refractive index profiles for dispersion compensation. It is shown that the compact tunable delay lines are low-loss and offer long true-time delays and tuning ranges and high operation bit rates.

Complementary apodized grating waveguides for tunable optical delay lines.

Submicron tantalum pentoxide ridge and channel optical waveguides and microring resonators are demonstrated on silicon substrates by selective oxidation of the refractory metal, tantalum. The novel method eliminates the surface roughness problem normally introduced during dry etching of waveguide sidewalls and also simplifies fabrication of directional couplers. It is shown that the measured propagation loss is independent of the waveguide structure and thereby limited by the material loss of tantalum pentoxide in waveguides core regions. The achieved microring resonators have cross-sectional dimensions of ~600 nm × ~500 nm, diameters as small as 80 µm with a quality, Q, factor of 4.5 × 10(4), and a finesse of 120.

Submicron optical waveguides and microring resonators fabricated by selective oxidation of tantalum.

High-speed, tunable integrated silicon photonic delay lines are demonstrated by cascading complementary apodized silicon grating waveguides. The cascaded grating waveguides, with inward and outward super-Gaussian apodization profiles, compensate each other's dispersion and allow high-speed operation. Characterization of the compact delay lines shows that they have low loss, offer true time delays of 82 ps and a tuning range of 32 ps, and can potentially operate at bit rates as high as 107 Gb/s.

Demonstration of complementary apodized cascaded grating waveguides for tunable optical delay lines.

High-speed and tunable integrated optical delay lines are demonstrated based on silicon grating waveguides apodized by the super-Gaussian function. The submicron channel waveguides with inward-apodized gratings are fabricated by deep-ultraviolet optical lithography. Characterization of the compact delay lines shows that they offer true-time delays as long as 132 ps, tuning range of ~86 ps, and a minimum bit rate of ~13 Gb/s. For lower bit rates, delays as high as 220 ps and tuning range of 174 ps are feasible.

Demonstration of tunable optical delay lines based on apodized grating waveguides.

A platform for the realization of tightly-confined lithium niobate photonic devices and circuits on silicon substrates is reported based on wafer bonding and selective oxidation of refractory metals. The heterogeneous photonic platform is employed to demonstrate high-performance lithium niobate microring optical resonators and Mach-Zehnder optical modulators. A quality factor of ~7.2 × 10⁴ is measured in the microresonators, and a half-wave voltage-length product of 4 V.cm and an extinction ratio of 20 dB is measured in the modulators.

Heterogeneous lithium niobate photonics on silicon substrates.

Spatially-variant photonic crystals (SVPCs), in which the orientation of the unit cell changes as a function of position, are shown to be capable of abruptly controlling light beams using just low index materials and can be made to have high polarization selectivity. Multi-photon direct laser writing in the photo-polymer SU-8 was used to fabricate three-dimensional SVPCs that direct the flow of light around a 90 degree bend. The lattice spacing and fill factor were maintained nearly constant throughout the structure. The SVPCs were characterized at a wavelength of 2.94 μm by scanning the faces with optical fibers and the results were compared to electromagnetic simulations. The lattices were shown to direct infrared light of one polarization through sharp bends while the other polarization propagated straight through the SVPC. This work introduces a new scheme for controlling light that should be useful for integrated photonics.

Tight control of light beams in photonic crystals with spatially-variant lattice orientation.

Thin films of lithium niobate are wafer bonded onto silicon substrates and rib-loaded with a chalcogenide glass, Ge(23)Sb(7)S(70), to demonstrate strongly confined single-mode submicron waveguides, microring modulators, and Mach-Zehnder modulators in the telecom C band. The 200 μm radii microring modulators present 1.2 dB/cm waveguide propagation loss, 1.2 × 10(5) quality factor, 0.4 GHz/V tuning rate, and 13 dB extinction ratio. The 6 mm long Mach-Zehnder modulators have a half-wave voltage-length product of 3.8 V.cm and an extinction ratio of 15 dB. The demonstrated work is a key step towards enabling wafer scale dense on-chip integration of high performance lithium niobate electro-optical devices on silicon for short reach optical interconnects and higher order advanced modulation schemes.

Heterogeneous microring and Mach-Zehnder modulators based on lithium niobate and chalcogenide glasses on silicon.

The two-photon photovoltaic effect is demonstrated in gallium arsenide at 976 and 1550 nm wavelengths. A waveguide-photodiode biased in its fourth quadrant harvests electrical power from the optical energy lost to two-photon absorption. The experimental results are in good agreement with simulations based on nonlinear wave propagation in waveguides and the drift-diffusion model of carrier transport in semiconductors. Power efficiency of up to 8% is theoretically predicted in optimized devices.

Two-photon photovoltaic effect in gallium arsenide.

A platform for high index-contrast integrated photonics based on tantalum pentoxide submicrometer waveguides on silicon substrates is introduced. The platform allows demonstration of microring resonators with loaded quality factor, Q, of 67,000 and waveguides with a propagation loss of 4.9 dB/cm. Grating couplers, with an insertion loss of ~6 dB per coupler and 3 dB bandwidth of ~50 nm, are also demonstrated and integrated with microring resonators.

Article	Year
Electrical control of parametric processes in silicon waveguides. Optics express\| PubMed ID: 18575553	2008
Energy harvesting in silicon optical modulators. Optics express\| PubMed ID: 19529490	2006
Energy harvesting in silicon wavelength converters. Optics express\| PubMed ID: 19529661	2006
Effects of the surrounding medium on the optical properties of a subwavelength aperture. Optics express\| PubMed ID: 20052096	2009
Electronically tunable silicon photonic delay lines. Optics express\| PubMed ID: 21716410	2011
Complementary apodized grating waveguides for tunable optical delay lines. Optics express\| PubMed ID: 23037038	2012
Submicron optical waveguides and microring resonators fabricated by selective oxidation of tantalum. Optics express\| PubMed ID: 23546079	2013
Demonstration of complementary apodized cascaded grating waveguides for tunable optical delay lines. Optics letters\| PubMed ID: 24081087	2013
Demonstration of tunable optical delay lines based on apodized grating waveguides. Optics express\| PubMed ID: 24105501	2013
Heterogeneous lithium niobate photonics on silicon substrates. Optics express\| PubMed ID: 24150397	2013
Tight control of light beams in photonic crystals with spatially-variant lattice orientation. Optics express\| PubMed ID: 25401613	2014
Heterogeneous microring and Mach-Zehnder modulators based on lithium niobate and chalcogenide glasses on silicon. Optics express\| PubMed ID: 26368243	2015
Two-photon photovoltaic effect in gallium arsenide. Optics letters\| PubMed ID: 26466255	2014
Low-loss and high index-contrast tantalum pentoxide microring resonators and grating couplers on silicon substrates. Optics letters\| PubMed ID: 26466277	2014

Sasan Fathpour

Biography

JoVE Journal Publications

Other Publications