Paul E. Jessop

Silicon waveguide-integrated optical power monitor with enhanced sensitivity at 1550nm

We describe the fabrication and operation of an optical power monitor, monolithically integrated with a silicon-on-insulator rib waveguide. The device consists of a p+‐v‐n+ structure with a detection volume coincident with the single-mode supporting waveguide. Detection of optical signals at wavelengths around 1550nm is significantly enhanced by the introduction of midband-gap generation centers, which provide partial absorption of the infrared light. The most efficient device extracted 19% of optical power from the waveguide and showed a responsivity of 3mA∕W. These devices are fabricated using current standard processing technology and are fully compatible with silicon waveguide technology and integrated operational amplifier circuits.

Design rules for slanted-angle polarization rotators

A simple and general set of design rules for slanted-angle polarization-rotating waveguides is presented in this paper. These design rules are employed to construct single-mode SOI polarization rotators that offer significant advantages in conversion efficiency, optical loss, fabrication tolerance, spectral response and spatial dimensions relative to III-V components.

Silicon photonic resonator-enhanced defect-mediated photodiode for sub-bandgap detection

We describe, model and demonstrate a tunable micro-ring resonator integrated monolithically with a photodiode in a silicon waveguide device. The photodiode is made sensitive to wavelengths at and around 1550nm via the introduction of lattice damage through selective ion implantation. The ring resonator enhances detector responsivity in a 60 mum long waveguide photodiode such that it is 0.14 A/W at -10Vbias with less than 0.2 nA leakage current. The device is tunable such that resonance (and thus detection) can be achieved at any wavelength from 1510 - 1600 nm. We also demonstrate use of the device as a digital switch with integrated power monitoring, 20 dB extinction, and no optical power tapped from the output path to the photodiode. A theoretical description suggests that for a critically coupled resonator where the round trip loss is dominated by the excess defects used to mediate detection, the maximum responsivity is independent of device length. This leads to the possibility of extremely small detector geometries in silicon photonics with no requirement for the use of III-V materials or germanium.

Electron cyclotron resonance chemical vapor deposition of silicon oxynitrides using tris(dimethylamino)silane

A new compound, tris(dimethylamino)silane was used as an organosilicon source for the deposition of silicon oxynitride thin films. The depositions were carried out at low substrate temperatures (<150 °C) in an electron cyclotron resonance plasma enhanced chemical vapor deposition reactor. Films with compositions varying from Si3N4 to SiO2 were deposited on silicon substrates by varying the N2/O2 flow ratio to the plasma chamber. In situ ellipsometry measurements of the film optical index were well correlated with film composition. Auger electron spectroscopy showed that only low levels of carbon (<3 at. %) were present, while Fourier transform infrared spectroscopy showed low levels of bonded hydrogen. The deposition rate of high quality Si3N4 was as high as 220 A/min.A new compound, tris(dimethylamino)silane was used as an organosilicon source for the deposition of silicon oxynitride thin films. The depositions were carried out at low substrate temperatures (<150 °C) in an electron cyclotron resonance plasma enhanced chemical vapor deposition reactor. Films with compositions varying from Si3N4 to SiO2 were deposited on silicon substrates by varying the N2/O2 flow ratio to the plasma chamber. In situ ellipsometry measurements of the film optical index were well correlated with film composition. Auger electron spectroscopy showed that only low levels of carbon (<3 at. %) were present, while Fourier transform infrared spectroscopy showed low levels of bonded hydrogen. The deposition rate of high quality Si3N4 was as high as 220 A/min.

Silicon-on-insulator waveguide photodetector with self-ion-implantation-engineered-enhanced infrared response

We describe the fabrication and characterization of silicon-on-insulator, p+-i-n+ waveguide photodetectors with enhanced sensitivity to wavelengths around 1550nm. Increased sensitivity to sub-band-gap light results from the deliberate introduction of mid-band-gap defects via 1.5MeV silicon-ion implantation to a dose of 1×1012cm−2. For a waveguide of length of 6mm, an on-chip signal of 3.5dBm generates a photocurrent of 5μA while the defect-induced excess optical absorption is 8dB. Postimplantation annealing at a temperature of 300°C for 10min increases the photocurrent to 19μA, corresponding to a responsivity of 9mA∕W, while reducing the excess loss to 2dB. The devices described here are completely compatible with standard silicon processing and can be integrated easily with other photonic and electronic functionalities on the same silicon substrate.

Defect-Enhanced Silicon-on-Insulator Waveguide Resonant Photodetector With High Sensitivity at 1.55

We describe the fabrication and characterization of a silicon waveguide resonant photodetector compatible with the optical-to-electrical conversion of wavelengths at, or around, 1550 nm. Sub-band responsivity is provided through the introduction of defects via inert self-implantation and subsequent annealing. The detector is located within a 20- m radius silicon microring resonator. An 18-dB resonant enhancement in absorption coefficient and 12-dB enhancement in photocurrent were measured, leading to a resonant responsivity of approximately 39 mA/W at 20-V reverse bias.

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Recent attention has been attracted by photo-detectors integrated onto silicon-on-insulator (SOI) waveguides that exploit the enhanced sensitivity to subbandgap wavelengths resulting from absorption via point defects introduced by ion implantation. In this paper, we present the first model to describe the carrier generation process of such detectors, based upon modified Shockley-Read-Hall generation/recombination, and, thus, determine the influence of the device design on detection efficiency. We further describe how the model may be incorporated into commercial software, which then simulates the performance of previously reported devices by assuming a single midgap defect level (with properties commensurate with the single negatively charged divacancy). We describe the ability of the model to highlight the major limitations to responsivity, and thus suggest improvements which diminish the impact of such limitations.

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This paper presents theoretical and experimental results detailing the design and performance of arrayed waveguide grating (AWG) demultiplexers fabricated in silicon-on- insulator (SOI). The SOI waveguide is inherently multimode because of the high refractive index difference between Si and SiO2, although appropriate tailoring of the rib width to height ratio can be used to make single mode rib waveguides. This single mode condition cannot be met in the input and output combiner sections, which can therefore support many higher order modes. Modeling results demonstrate that coupling from a single mode ridge waveguide to the fundamental slab mode is typically two orders of magnitude larger than the coupling to higher modes. Hence the effect of multimode combiners on performance should be minimal. We also present calculations of bending losses which indicate that with a Si thickness of 1.5 micrometers , single mode rib waveguides can be made with radii of curvature as low as 200 micrometers . Such waveguides can also be made with zero birefringence. AWG devices were fabricated with 8 channels centered around (lambda) equals 1550 nm, and chip sizes less than 5 X 5 mm. The performance of these devices is compared with our modeling results.

Modeling Defect Enhanced Detection at 1550 nm in Integrated Silicon Waveguide Photodetectors

In this paper we report a novel fabrication technique for silicon photonic waveguides with sub-micron dimensions. The technique is based upon the Local Oxidation of Silicon (LOCOS) process widely utilised in the fabrication of microelectronics components. This approach enables waveguides to be fabricated with oxide sidewalls with minimal roughness at the silicon/SiO2 interface. It is also sufficiently flexible to enable the depth of the oxidised sidewall to be varied to control the polarisation performance of the waveguides. We will present preliminary results on submicron waveguide fabrication and loss characteristics (less than 1 dB/cm), as well as effects of varying waveguide width on modal properties of the waveguides. We consider the ease of fabrication, as well as the quality of the devices produced in preliminary experimental fabrication results, and compare the approach to the more conventional requirements of high resolution photolithographically produced waveguides. We also discuss preliminary optical results, as measured by conventional means. Issues such as the origins of loss are discussed in general terms, as are the fabrication characteristics such as waveguide wall roughness and waveguide profile. We will discuss further work that will help to establish the potential of the technique for future applications.

Arrayed waveguide grating demultiplexers in silicon-on-insulator

A numerical study of the throughput and crosstalk in intersecting semiconductor rib waveguides was carried out using the beam propagation method. The fraction of the optical power that couples out of one input waveguide and into the crossed waveguide falls to below two percent for crossing angles greater than four degrees. A simple modification to the waveguide shape at the X-crossing region was found to reduce the crosstalk for crossing angles between four and ten degrees. The crosstalk to throughput ratio is reduced by up to a factor of nine while the throughput is reduced by, at most, a few percent. In device structures that combine X-crossings with curved waveguide sections this permits greater design flexibility and improved overall loss and crosstalk performance.