Photonics related industries in Canada have enjoyed remarkable success in the last decade, particularly in the area of fiber optic telecommunications. There is, however, growing concern that a shortage of highly skilled photonics professionals will limit future growth and weaken Canada's competitive position. A recent paper by Nantel and Beda' presents a good summary of the state of photonics in Canada and the projected needs for highly qualified personnel. The recent economic downturn, which has been particularly severe in the photonics sector, has reduced the sense of urgency surrounding the projected shortages of highly qualified personnel. Many individuals who were recently recruited into the photonics industry are now seeking other employment. This should serve as a warning to university educators not to focus their programs too narrowly on specific short term requirements of industry, but to provide graduates with a broad skill set that leaves them positioned to react to changing circumstances. Nevertheless, the critical importance of photonics education and training and the long term prospects in this sector remain unchanged. To meet the future demands for skilled professionals, there is a need for more bachelor's level university programs that include advanced photonics concepts and exposure to state of the art technology.
We have fabricated silicon avalanche photodetectors integrated with silicon-on-insulator straight waveguides as well as
ring resonator structures. The photodetectors comprise a p-i-n junction, with photogeneration mediated by the presence
of deep-levels. For a 400 μm straight waveguide detector we measure a responsivity of 4.4 A/W at 40 V, and an
avalanche multiplication gain of 640. The detectors incorporated with a ring resonator, offer a high sensitivity,
wavelength selective detector option suitable for very low power applications, with a responsivity of 20 A/W at 30 V.
In this paper we will describe the fabrication and characterization of passive waveguides which exploit the phenomenon
of variable charge state mediation of deep-levels in silicon to vary optical absorption. Silicon waveguides are doped with
either thallium or indium and co-doped with phosphorus. Optical absorption is reduced s phosphorus doping is increased.
These results suggest a novel method of modulation via charge-state control of the deep-level.
In this paper we outline recent results which combine defect mediated Photo-Detectors (PDs) in a Ring Resonator (RR)
structure. By exploiting the multiple-pass of the optical signal through the detector, we are able to significantly decrease
the size of the detector structure while maintaining good responsivity (typically 0.1 A/W). In such a geometry the
detector bandwidth is not capacitance limited, while the leakage current is reduced toward 1 nA. We also show that these
PDs may be used in the drop port of a RR to monitor the propagating signal. These devices have applicability in
multiplexing and potential for integration with high speed modulation functionality.
We have devised and fabricated high-speed silicon-on-insulator resonant microring photodiodes. The detectors comprise a p-i-n junction across a silicon rib waveguide microring resonator. Light absorption at 1550 nm is enhanced by implanting the diode intrinsic region with boron ions at 350 keV with a dosage of 1 × 1013 cm−2. We have measured 3-dB bandwidths of 2.4 and 3.5 GHz at 5 and 15 V reverse bias, respectively, and observed an open-eye diagram at 5 gigabit/s with 5 V bias.
Silicon Photonics is a field that has seen rapid growth and dramatic changes in the past 5 years. According to the MIT
Communications Technology Roadmap , which aims to establish a common architecture platform across market
sectors with a potential $20B in annual revenue, silicon photonics is among the top ten emerging technologies. This has
in part been a consequence of the recent involvement of large semiconductor companies around the world, particularly in
the USA. Significant investment in the technology has also followed in Japan, Korea, and in the European Union. Low
cost is a key driver, so it is imperative to pursue technologies that are mass-producible.
Therefore, Silicon Photonics continues to progress at a rapid rate. This paper will describe some of the work of the
Silicon Photonics Group at the University of Surrey in the UK. The work is concerned with the sequential development
of a series of components for silicon photonic optical circuits, and some of the components are discussed here. In
particular the paper will present work on optical waveguides, optical filters, modulators, and lifetime modification of
carriers generated by two photon absorption, to improve the performance of Raman amplifiers in silicon.
A tunable ring resonator (RR) formed from Si/SiO2 waveguides with an electro-optic polymer cladding is proposed with emphasis on the trade-off between the tuning voltage and ring radius. The ring resonator circuit combines the advantages of Si/SiO2 and polymer technologies. The advantages of this hybrid ring design over previously proposed tunable silicon rings include an increased switching speed, from 5 GHz to 20 to 100 GHz, single-polarity instead of dual-polarity voltage tuning and a voltage-independent quality factor. The hybrid design also displays a greater free spectral range (1.85 nm instead of 0.1 nm) and a wider tuning range (0.925 nm instead of 0.05 nm) and is further compatible with silicon devices. Moreover, the device has a high quality factor of 3.4×104.
We design a high-speed tunable electro-optical (EO) polymer-clad silicon over insulator (SOI) racetrack resonator with a 80-µm length and 5-µm radius that exhibits a switching speed of 100 GHz, a tuning voltage of 6.81 V, and an extinction ratio of 109.55 dB. This work employs high electro-optical coefficient polymers (r33=1000 pm/V), which are currently under development, to implement very high speed switches.
We present vertically-integrated multimode interferometers that optically couple between waveguide layers of
a three-dimensional photonic circuit. Coupling between these layers can be restricted to certain regions by
selectively fabricating a silicon channel between them, resulting in an isolated multimode waveguide section.
Simulations reveal that complete coupling between two waveguides that are 2 μm square is achieved over a
length of 236 μm, when the separating silicon channel is 1 μm thick. Standard photolithography and etching
techniques are used to fabricate a proof-of-concept device consisting of one waveguide coupling into a silicon
waveguide that is vertically multimode.
It is now established that defects introduced via ion implantation may act as generating centers in silicon waveguide
structures and consequently enhance photosensitivity at wavelengths in the region of 1550 nm. Although several
integrated p-i-n waveguide photodiode structures have been presented which exploit this behavior, no attempt has been
made to model the generation process and thus optimize device design. We report a model that has been implemented
using SILVACO's ATLAS software, and reproduces the observed behavior in the aforementioned device structures. By
varying parameters such as the dimensions of the device and the implantation conditions, the responsivity can be
maximized. In particular, we have designed an integrated structure centered on a 3 µm wide waveguide created by the
LOCOS (Local Oxidation of Silicon) technique on lightly p-doped Silicon-on-Insulator. A self aligned n+ polysilicon
contact is placed above the ridge, causing the majority of the depletion to overlap with the optical mode. Symmetric p+
regions are placed on either side of the waveguide, separated by a distance selected to optimize responsivity without
causing excess loss. This presents a vast improvement over previous structures of its size, having a predicted
responsivity in excess of 50 mA/W at a 2V reverse bias.
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.
We report the realization of a Bragg grating optical filter at telecommunication wavelengths in silicon-on-insulator (SOI) through the use of ion implantation induced refractive index modulation. Silicon self-irradiation damage accumulation results in an increase of the refractive index to a saturated value, upon amorphization, of approximately 3.75. This makes it an interesting candidate for passive gratings as the silicon retains a planar surface, making it ideal for further processing. Monte Carlo simulations and coupled mode theory demonstrate the viability of the approach. Planar implanted SOI waveguides showed extinction ratios of -5 dB for TE and -2 dB for TM. An annealing study suggests complete amorphization was not achieved and future results should be improved dramatically.
We present preliminary experimental results for silicon-on-insulator polarization rotators with asymmetric external waveguiding layers. These devices consist of a waveguide with vertical and sloped sidewalls and are fabricated using a combination of plasma and chemical etching techniques. For a device length of 3256 µm, a TE-to-TM polarization conversion efficiency of 75% was measured.
The development of monolithic silicon photonic systems has been the subject of intense research over the last decade. In addition to passive waveguiding structures suitable for DWDM applications, integration of electrical and optical functionality has yielded devices with the ability to dynamically attenuate, switch and modulate optical signals. However, for silicon to dominate as the substrate of choice for the fabrication of photonic circuits, the development of a full range of monolithically integrated functionality is required including detectors capable of signal monitoring at a wavelength around 1550nm. Photodetectors integrated with silicon-on-insulator rib waveguides are here demonstrated. Significant response at infrared wavelengths is shown to be mediated via deliberately introduced deep band-gap levels. This paper describes in detail the device fabrication and the performance of the waveguide photodetectors with regard to photoresponse, bandwidth, polarization sensitivity and thermal stability. Currently typical devices tap between 10-20% of an optical signal from an SOI waveguide and generate a photocurrent of several micro-amps. The most efficient device extracted 19% of the optical signal while exhibiting a responsivity of 3mA/W. We also describe results from the operation of an integrated photonic circuit consisting of a variable optical attenuator (VOA) and a photodetector. The detector monitors the optical signal as it is modulated using the VOA, however there exists a small, systematic offset in response as compared to measurements made with an external detector.
In this paper we present a variable optical attenuator (VOA) that is based on microbending of a silicon-on-insulator (SOI) rib waveguide. Optical attenuation is achieved by etching away the underlying SiO2 layer in a section of the waveguide and using electrostatic deflection to introduce vertical bending. When a single-mode rib waveguide is bent, the light traveling through it will undergo mode conversion. The amount of energy transferred to lossy modes depends on the curvature of the bending section. This mechanism is studied with the help of beam propagation method (BPM) simulations. In order to achieve a substantial amount of attenuation by bending, voltages in excess of the pull-in threshold are used, bringing a portion of the waveguide into contact with the underlying silicon substrate. An electrostatic zipping action determines the bending radii and the length of the contact region. The equation for the relationship between the bending radius of the waveguide and the controlling voltage is established through the energy method, and is numerically solved. FEM modeling is also performed to validate the result from the energy model. The device is fabricated by conventional silicon processing steps, plus steps to solve the stiction problem. The test setup for the device consists of a home-made interference microscope to monitor the vertical movement of the waveguide under test and align the input fiber to the waveguide, and other instruments to monitor the output from the device and perform the attenuation measurement. The experimental data agree well with both the BPM simulations and the calculations for the zipping actuation. The tested devices show that we can achieve 14dB attenuation over a 1mm span of a bent waveguide.
We report simulation results for a directional coupler between silicon waveguides in different layers of a three-dimensional (3D) optical circuit. The coupling length is 1.4 mm. The device is manufacturable using standard CMOS technology provided individual waveguide layers can be vertically stacked. In simulations of coupling efficiency the design exhibits negligible loss with respect to translational and rotational misalignments of up to 0.5 μm. Efficiency degradation is less than 5% for etch depth and waveguide width variations of 0.4 μm, and less than 1 dB over the range of standard lithographic tolerances for variations from layer to layer in feature width, depth, and alignment.
The current trend towards integrating CMOS circuitry and photonic devices on silicon-on-insulator (SOI) wafers into monolithic optoelectronic circuits requires modification of the traditional rib waveguide to provide a planar surface. One possible modification involves creating a trench on either side of the rib and then filling this trench with a planarizing oxide. The resulting planar surface is much more compatible with the photolithographic systems required to print the small dimensions found in state-of-the-art CMOS. We report the fabrication of prototype trench-isolated waveguides, measurement of optical performance and comparison with simulation. 2.5 μm thick Si film was utilized with 0.5 μm deep trenches ranging from 1 to several microns in width. Rib widths ranged from 2 μm to 3 μm (the maximum value providing single mode propagation). Allowed modes were determined with FEMLAB, while beam propagation was studied using Optiwave BPM. Simulation indicated mode confinement would be lost for trench widths less than 1.5 μm. The narrowest trench width which could be fabricated was 2.0 μm, and qualitative optical testing shows good mode confinement to the central rib for a trench geometry greater than 3.0 μm.
After the introduction in 2001 of community college programs at the Photonics Technician/Technologist levels, the need to cover the photonics educational space at the undergraduate level was addressed. In the last year, three very different new undergraduate degrees in photonics have started to develop in Ontario. These programs are presented in this paper.
The Honours B.Sc. in Photonics at Wilfrid Laurier University (Waterloo) will develop a strong understanding of the theory and application of photonics, with practical hands-on exposure to optics, fibre optics, and lasers. This program benefits from the particularity that the department offering it combines both Physics and Computer Science.
At McMaster University, the Engineering Physics program will provide students with a broad background in basic Engineering, Mathematics, Electronics, and Semiconductors, as well as an opportunity to pursue Photonics in greater depth and to have that fact recognized in the program designation.
The Niagara and Algonquin College Bachelor of Applied Technology in Photonics program is co-op and joint between the two institutions. Emphasis is placed on the applied aspect of the field, with the more hands-on experimental learning taking precedence in the first years and the more advanced theoretical subjects following in the latter years.
In the last year, three very different new undergraduate degrees in photonics have started to develop in Ontario where none was available before. One is an Honours B.Sc. in Photonics, one is a Photonics Engineering degree and another is a Bachelor of Applied Technology in Photonics. This paper presents these programs.
An integrated optical strain sensor based on a silicon-on-insulator (SOI) optical waveguide Mach-Zehnder interferometer has been demonstrated. The common problem of cross sensitivity to temperature changes has been greatly reduced by designing the lengths of the two interferometer arms to be exactly equal, in the absence of strain, so that thermally induced changes in the optical path lengths cancel out in the interference signal. The waveguide path in both arms of the interferometer has a long straight section and is folded back by a 180 degree bend. The straight section in one arm is perpendicular to that in the other arm so that the symmetry in the optical path lengths is broken when the applied strain in these two orthogonal directions is different. The interferometer output is thus a measure of the difference in strain along these two directions.
For the initial device, the interferometer's size was approximately 15 x 15 mm, with the straight sections in each of the two arms being 12 mm long. For TM polarized light at a wavelength of 1.55 microns, the interferometer output intensity was observed to vary sinusoidally with applied uniaxial strain at a rate of 10 degrees per microstrain. This is in good agreement with the theoretical prediction. The strain sensitivity, as limited by system noise, was below one microstrain. SOI is an ideal material choice for this device. It is suitable for passive fiber alignment using V-groove techniques, and the ability to use small waveguide bending radii makes possible sensors that are more compact than has been demonstrated here.
In-line pairs of InGaAs quantum well waveguide photodiodes are used to function as sensitive wavelength monitors near the absorption band edge of the detector material. These devices displayed an average wavelength sensitivity of 3 pm over a useful operating range of 1535-1570 nm for optical input powers as low as 5 (mu) W. In this paper, we demonstrate the simultaneous monitoring of several wavelengths using an array of in-line detectors and a wavelength demultiplexer. Some methods to improve the performance of the device are examined. By tailoring the lengths of the waveguide sections or by the application of a reverse bias, the individual channels of the array can be optimized for a particular wavelength range. Using a fixed reference wavelength and the quantum confined Stark effect, an effective temperature compensation scheme is proposed. As a demonstration of the technique, a multiplexed Bragg gratin strain senor was constructed. The sensor contained four in- fiber Bragg gratings with a 6 nm center wavelength spacing. Using a broadband wavelength demultiplexer, the photodetector array is used to track the small wavelength shifts induced in the gratings that result from the application of strain. An average strain sensitivity of 6 (mu) (epsilon) was obtained for the four channels.
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.
The simulation and performance of dual-wavelength demultiplexers fabricated in SiGe are presented. The device design is a symmetric directional coupler optimized for 1.3/1.55 micrometer demultiplexing. Modeling results using the Beam Propagation Method are presented as a means of examining the fabrication tolerances and design considerations of the devices. Initially the duplexers were fabricated with a Si.97Ge.03 core using chemical etching, and displayed crosstalk of -19 dB and -15 dB in the 1.3 and 1.55 micrometer wavelength channels, respectively. This performance was enhanced by thermal tuning, resulting in isolation of -21 dB and -18 dB. The high degree of strain in pseudomorphic SiGe layers results in highly birefringent waveguides. This characteristic restricts effective duplexer operation to a single polarization, but suggests that the same devices can be modified to act as polarization splitters for a chosen wavelength. Modeling of the devices in this configuration is also presented. The simple device design used for demultiplexers and splitters was chosen to evaluate the potential for fabrication of SiGe-based optoelectronic devices using standard VLSI processing relying on the local oxidation of silicon (LOCOS). A second set of devices was successfully fabricated using LOCOS and effectively separated 1.15 and 1.3 micrometer wavelength signals. This performance is compared to similar devices that were wet-etched.
Quantum well waveguide photodetectors that contain two inline segments have been used as wavelength monitors with sensitivities in the picometer range. Multi-segment detectors can also be configured as wavelength demultiplexers to separate up to four optical communications channels. We review recent work in this area and report on the use of a wavelength monitor for the 1.55 micrometers region in a fiber optic strain sensor application.
The design of manufacturable Si/Si1-xGex waveguide WDM components involves several unique materials and fabrication issues which must be confronted and resolved. Accurate data for the refractive indices of the waveguide materials are essential. Furthermore, the waveguide design is tightly constrained by the requirement that Si/Si1-xGex layer thickness is within the pseudomorphic growth limit. By combining refractive indices determined from mode profile measurements of MBE and CVD grown waveguides, and epilayer thickness constraints set by the pseudomorphic growth limits, we have determined a set of design criteria for Si/Si1-xGex waveguides for WDM and optical signal routing applications. Optically smooth and vertical Si/Si1-xGex waveguide facets are critical in permitting highly efficient coupling between the fiber and the Si chip. Since Si has an equal probability of cleaving alone either the <110> or <111> planes, producing such high quality facets consistently is extremely challenging. We have demonstrated that high quality facets can be obtained consistently by cleaving, with and without a dielectric layer on Si substrates.
An optical processor for phased-array antenna beamforming has been demonstrated. It is capable of providing real-time control of both antenna beam steering and beam shaping in one or two dimensions, with an rms phase linearity of 5 bits. The functions of beam shaping and steering are combined through a magneto-optic spatial light modulator (SLM), which is fast, small, and simple to use.
The Pockels Effect has been demonstrated in thermally evaporated polycrystalline thin films of ZnS. The strongly till] oiented films were found to have an electro-optic constant of r413 rn/V for fields perpendicular to the  plane. 2 .
An optical processor for phased array antenna beam forming has been demonstrated. It is capable of providing real-time control of both antenna beam steering and beam shaping in one or two dimensions, with an RMS phase linearity of five bits. The functions of beam shaping and steering are combined through a magnetooptic spatial light modulator (SLM) which is fast, small, and simple to use.