Photonic devices based on polymer waveguides have potential use because they can be fabricated by high-volume manufacturing techniques. These integrated photonic devices can potentially be applied to communications and sensing as they can be produced in a short cycle and at low cost. In this report, we present foundry fabrication of polymer-based photonic integrated circuits. The inverted-rib waveguide components are about 2 μm wide and 0.570 μm deep. Spincoated SU-8 polymer onto SiO2 is used to compose the guiding layer. In our preliminary results, we highlight the design, manufacturing, and characterization of microracetrack resonator notch filters. Those components were fabricated using complementary metal-oxide-semiconductor (CMOS) foundry process. Full wafers were processed at the foundry’s 150 mm-facility. Compact micro racetrack resonators based on SU-8 polymer are demonstrated, presenting high coupling efficiency. Facet sidewall roughness was reduced in the chip dies using mechanical polishing processes. We believe these results are promising for applications ranging from telecommunication components to sensing applications at low cost.
We report on experimental observations of a phenomenon whereby optical coupling of a high-power laser to a photonic subsystem locks a silicon microring’s resonance if temperature of the photonic device is allowed to drift, causing the thermal tuning control to fail. This is the first report of such a failure mechanism, to our knowledge. We refer to this effect as “optical hijacking” of the resonator wavelength. We demonstrate this effect showing that a ring resonator whose resonance drifts due to an increase in chip temperature can be locked to a normally nonresonant wavelength by injecting high optical power to the system leading to this “optical hijacking” effect. Additionally, an analytical description of this effect is presented.
We propose a novel and cost-effective copper-gold planar nanostructure resulting in strong plasmonic enhancement of
the electromagnetic field with a peak at 615 nm and FWHM of 180 nm. The structure consists of aggregates of 20 nm in
diameter gold nanospheres on a thin continuous 50 nm thick copper film. We attribute the strong field enhancement to
the coupling of interparticle plasmon resonances from gold nanospheres to the surface plasmons induced in the copper
film. The high reflectivity of the copper layer increases the collection efficiency in a reflection mode of the scattered
light that would otherwise be transmitted. We achieved the homogeneity and planarity of the copper-gold structure
through the electrostatic attraction between the negative surface charge of gold nanospheres and a lattice of positive
copper ions of copper oxide, formed by ionic bonds during the exposure of copper to air.
Tunable silicon microring filters are used to demonstrate CMOS-compatible on-chip wavelength control of Er+ doped
fiber-lasers. The filter uses a 10 μm-diameter microring resonator based on single-mode silicon-on-insulator (SOI) strip
waveguides operating around the telecom range of 1.55 μm. A piece of Er+ doped fiber (EDF) serves as the gain media
which is pumped by a 980 nm laser diode. An on-chip Ni-Cr micro-heater consuming up to 38 mW is capable of tuning
the Si microring filter by 2.3 nm with a lasing linewidths narrower than 0.02 nm. This approach enables arbitrary
multiple wavelength generation on a silicon chip. Possible applications include on-chip and chip-to-chip densewavelength
division multiplexed communications, telecommunications and optical sensor interrogation.
Microring resonators (MRs) are important photonic devices for large-port-count photonic circuits owing to their micrometer-scale device sizes. We describe the implementation of a 4×4 wavelength-reconfigurable photonic switch consisting of eight tunable MRs fabricated on a less expensive material platform: silicon on insulator. Wavelength reconfiguration is achieved through independent thermo-optic tuning of MRs with localized Nichrome microheaters fabricated on the same silicon-on-insulator substrate. A free spectral range of 18 nm and a 3-dB linewidth of 0.1 nm were observed for the fabricated MRs with a diameter of approximately 10 µm. The switch device shows negligible channel crosstalk (<0.01 nm) and moderate switching response time (<1 ms). The switch can potentially be scaled up to benefit the development of large-scale integrated photonics.
Slot-waveguides have attracted considerable attention recently due to the high-intensity electric fields and power
densities that can be achieved in very small volumes of low-index materials. Latest applications of this concept have led
to new designs of photodetectors, modulators and CMOS-compatible light-emitting devices. However, the coupling of
light to and from fiber optics and slot-waveguides remains a challenge. In this paper we present the numerical analysis of
a slotted nanotaper for coupling between a fiber and the horizontal slot-waveguide. We used numerical simulations to
study the coupling process and found a minimum mismatch loss of 0.4 dB for a tip width of 105 nm. The mode
conversion from the tip of the coupler to the full width of the slot-waveguide was performed with a loss less than 0.2 dB
when the length was at least 80 microns. This inverse taper increases significantly the coupling efficiency, compared to
other approaches such as direct butt coupling and an improved rectangular silicon nanotaper.
We designed a compact optical resonator with two distributed Bragg reflectors (DBR) embedded on single mode
polymer ridge waveguide structure towards micro-scale polymer lasers. Single DBR is made up of alternating layers
with λ/4 thickness of air and polymer. Numerical simulation of the device was carried out with 3D FDTD. We
investigated the reflectance of single DBR as a function of order and number of periods and found a maximum of 97.8%,
achieved for a TE mode with air cladding in material with low refractive index 1.54. Focused ion beam (FIB)
lithography was used to open periodic air gaps on a 3 um wide ridge waveguide consisting of 1 um thick polymer layer
doped with disperse red 1 (n=1.54) structure. Single DBR with five periods are optically characterized by observing the
transmission through the device.
A platform that enables optical coupling from fiber-ribbon connectors to planar lightwave circuits (PLCs) is described. Flexible optical waveguides are used to form a variable length directional coupler that inserts and extracts light from a waveguide located arbitrarily inside the chip. The contact length can be adjusted for optimal coupling allowing manufacturing variation in materials, widths and cladding thicknesses present on a chip. This approach may be ideal for packaging WDM devices as the 3dB bandwidth of the coupling covers the whole 1300 -1700 nm fiber-optic telecommunication range. Coupling length control in the range of 0.05-0.2 μm leads to maximum coupling in excess of 80% for the range of conditions investigated. Simulations of the performance are discussed and initial fabrication and optical coupling results are presented.
Micro-ring resonators have been traditionally fabricated using expensive III-V materials such as InP or GaAs. Device
tuning is typically to utilize the electro-optic effect of the III-V materials that usually leads to complex device layer
structures. As another tuning approach, thermo-optic tuning of micro-ring resonators is commonly achieved by heating
up the whole chip. In general, it is more challenging to achieve highly localized heating on a common chip for
independent tuning of multiple micro-ring resonators residing on the same substrate. To address these issues, we
describe the development of wavelength reconfigurable photonic switching using thermally tuned micro-ring resonators
fabricated on a low-cost silicon-on-insulator substrate. Independent tuning of multiple micro-ring resonators, spaced at
250 µm, is realized with highly localized micro heaters (50×50 μm2 per heater area) fabricated on the same silicon
substrate. Owing to the large thermo-optic effect of silicon (Δn/ΔT=1.8×10-4 K-1), 8 mA heating current is sufficient to
tune a micro-ring resonator with a 3-dB spectral line width of 0.1 nm by 2.5 nm while creating a minor peak shift of less
than 0.04 nm for an adjacent resonator. The switching response time is about 1 ms. A 1×4 wavelength reconfigurable
photonic switch device has been demonstrated. With a resonator diameter of approximately 10 μm (greater than 18 nm
in free spectral range of each micro-ring resonator), larger port-count switch matrix with wavelength reconfiguration on
a small device foot print is feasible for the development of large-scale integrated photonics.
Microstructure manipulation is a fundamental process to further the study of biology and medicine, as well as to advance micro- and nano-system applications. The manipulation of micro and nanostructures has been achieved through various microgripper devices developed recently, which lead to advances in single cell manipulation and micromachine assembly. However, the physical, mechanical, optical and chemical information about the microstructure under study is usually extracted from macroscopic instrumentation, such as confocal microscopy and Raman spectroscopy. In this paper we describe the design, simulation, fabrication and characterization (mechanical and optical) of a novel Micro-Opto-Electro-Mechanical-System (MOEMS) optical microgripper. This is the first device of this kind, which enables the direct manipulation, mechanical characterization, and simultaneous optical characterization of microstructures. Optical fluorescence measurements or identification, as well as absorption spectroscopy are possible with this new device. The device is implemented in SU-8 due to its suitable optical and mechanical properties. The current generation of the device was designed to manipulate structures with dimensions lower than ~5 μm.
Photonic crystals enable a reduction in the size of current photonic devices by virtue of forbidden propagation, except along engineered lines of defects. Furthermore, propagation above the band-gap has unique characteristics such as the superprism effect. Polymer materials which typically suffer from low optical confinement can benefit from photonic crystal structures to increase integration and functionality. Due to its unique advantages, several authors have reported attempts at fabricating photonic crystal structures in polymer materials. However, a clear photonic bandgap (PBG) was not demonstrated. In this paper we describe our recent work in design, simulation and fabrication polymer photonics devices. We will discuss specific slab photonic crystal devices based on 2D hexagonally packed structures achieved in polymethyl-methacrylate films. Supercomputer simulations were used to target optimal geometries that consist of points in a three dimensional space of lattice parameter, hole diameter and slab thickness that enable a design of the photonic bandgap of the structure. Fabrication of the devices was achieved through use of high-resolution electron-beam lithography and etching. A robust air-clad polymer photonic crystal film was enabled by the additional support of a 40 nm-thin low-stress silicon nitride layer.
An investigation of the influence of the process parameters pressure and flow on the room-temperature deposition of electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) of silicon nitride has been performed. The suitability of these films for micromachining applications has been studied, in particular for the use with KOH:isopropyl:H2O etching solutions. The deposition rate and the effect of process parameters on the physical properties of the films, as-deposited and after KOH etching, were investigated. Buffered HF etch rate, refractive index, and the infrared absorption spectra, especially the Si-N peak absorption wavenumber, were studied. We have found that films that withstand KOH etching with little modification of their physical properties can be obtained at room-temperature for depositions with low flows and low process pressures.
We discuss the fabrication and optical characterization of strained-layer InGaAs-GaAs nanometer scale wire arrays grown by selective-area MOCVD on silicon dioxide patterned substrates. The wire patterns studied were obtained by high resolution electron beam lithography on PMMA using a silicon dioxide lift-off process. The dependence of the growth structure on the wire orientation is presented. Wire arrays aligned parallel to the [011] crystal direction are found to be the extremely useful for the growth of narrow quantum wire structures. Due to the faceted nature of the growth, a large non-linear enhancement of growth inside the wire region is observed. In addition, the results of gas phase diffusion growth simulations on the expected inhomogeneity of the fabricated quantum wires are presented. The degree of inhomogeneity of fabricated quantum wire arrays was studied by spatially resolved photoluminescence. Our results show that a suitable patterning technique, coupled with proper growth conditions, could allow control of the selective growth profile across the wire array. Finally, the growth of strained wires with a lateral dimension of less than 50 nm is displayed along with optical characterization of the quantum wires by low temperature photoluminescence.
The photo-excited carrier distribution and radiative recombination efficiency in dryetched quantum well dots (QWDs) with diameters down to 80 nm have been investigated by photoluminescence (PL) spectroscopy and cathodoluminescence (CL) imaging. The quantum well dots were fabricated from lattice-matched single or multiple quantum well heterostructures with InGaAs well thicknesses ranging from 2 to 15 nm. Low temperature CL imaging indicated dot-to-dot variation of emission intensity. The PL efficiency exhibits no significant reduction for dot sizes larger than 170 nm. But for dot diameters smaller than approximately equals 100 nm, the PL intensity is not detectable. Such diminution of PL intensity is attributed to side wall damage due to reactive ion etching. For dot diameters smaller than 300 nm, PL peak energies shift to higher values, reaching a blue shift of approximately equals 3 meV for 128 nm diameter GSMBE grown dots and approximately equals 10 meV for 130 nm diameter MOCVD grown dots.
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