In this paper, we demonstrate near-C-band semiconductor optical amplifiers (SOAs) integrated on silicon photonic chips using photonic wire bonds (PWBs). PWBs are three-dimensional, nano-printed, freeform, polymer waveguides which provide efficient coupling between optical components. The SOAs used in this work were 975μm long and 400μm wide, with a 1.54μm wide, 1.9μm thick active region. Measurements on a connectorized SOA are presented, showing a peak on-chip gain of 10.6dB at 1510nm when applying a 150mA bias current to it (here we have not calibrated out the coupling losses at the two SOI-waveguide/PWB interfaces nor have we calibrated out the losses at the two PWB/SOA interfaces, indicating that the gain of the SOA is significantly higher than the measured 10.6dB). The PWB connectorized SOA has a wavelength-dependent gain which was measured from 1480nm to 1555nm, the peak gain being obtained at 1510nm. In addition, the gain depends on the bias current applied, increasing with higher bias currents but saturating when the bias current exceeds 150mA. The PWB-connectorized SOA is also sensitive to the power of the input signal, the gain was larger for lower input powers (i.e., for powers below about -4.9dBm). Varying the polarization state of the input to our PWB-connectorized SOA changed the measured gain by 5.85dB.
The goal of SiEPICfab is to conduct research in the fabrication of silicon photonic devices and photonic integrated circuits, and to make leading-edge silicon photonic manufacturing accessible to Canadian and international academics and industry. SiEPICfab builds on the success of the Silicon Electronic Photonic Integrated Circuits (SiEPIC) program, which has been offering research training workshops since 2008, by adding a fabrication facility “fab”. We have developed a rapid prototyping facility to support a complete ecosystem of companies involved in silicon photonics product development, including modelling, design, library development, fabrication, test, and packaging of silicon photonics. SiEPICfab allows designers to rapidly complete design-fabricate-test cycles, with technologies such as sub-wavelength sensors, PN junction ring modulators, silicon defect-based detectors, single photon detectors, single photon sources, and photonic wire bond integration of lasers and optical fibres.
In this work, we experimentally demonstrate a FSR-free, MRR-based, coupling modulator that integrates a bent, grating-based contra-directional-coupler (contra-DC) into a microring cavity to achieve an FSR-free response at its through port. Our modulator suppresses the amplitude response at all but one resonance, operating mode (hence, has an FSR-free response). In our modulator, coupling modulation is used and is achieved by modulating a relatively short, 210 μm long, p-n junction phase-shifter in a two-point coupler (which forms the drop-port coupler of the MRR). We demonstrate open eyes at 2.5 Gbps and discuss how the effects of DUV lithography on the contra-DC limited the electro-optic bandwidth of the fabricated modulator to 2.6 GHz. In these proceedings, we also cover details of the device design and the small and large signal characterization of the device, including an analysis of the effect of lithography on the “as-fabricated" device performance. We also discuss how to significantly improve the electro-optic bandwidth in future implementations by accounting for these lithographic effects in the device design flow and layout.
Vernier effect, series-coupled microring resonators (MRRs) are used to extend the free-spectral-range (FSR) of MRRs. In this work we demonstrate integrating two MRRs in a compact Vernier configuration (compact as compared to previously demonstrated Vernier effect devices). our design was realized by using two waveguide crossings to form a major, outer ring that was coupled to a minor ring nested within the major ring. The ratio of the path length of the major ring to the path length of minor ring was 5:2. The spectral response of the device had an FSR of 27.94 nm, a drop port 3 dB bandwidth of 0.87 nm, a minimum extinction ratio of 16.1 dB, a minimum interstitial peak suppression of 10.6 dB, and a footprint of only 540 μm2 .
JGKB Photonics Inc. and the University of British Columbia present recent results for an alternative type of electro- optic modulator, the integrated-optic mode-converter [1]. The integrated-optic mode-converter has the potential to bring the drive-voltage of electro-optic modulators down to the 3 to 4 V range while preserving the benefits typically associated with LiNbO3-based integrated-optic Mach-Zehnders, e.g., low insertion loss and low chirp, and while being fabricated in compound semiconductors such as GaAs or possibly InP (i.e., these devices are based on mature, stable semiconductor technologies). Such devices are shown to operate at ultrahigh-speed, having electro- optic bandwidths in excess of 40 GHz.
We present a theoretical sensitivity analysis of silicon-on-insulator quadruple Vernier racetrack resonators based on varying, one at a time, various fabrication-dependent parameters. These parameters include the waveguide widths, heights, and propagation losses. We show that it should be possible to design a device that meets typical commercial specifications while being tolerant to changes in these parameters.
Large-area silicon-on-insulator (SOI) ring resonators, to be used as optical gyroscopes, have been designed and fabricated using an e-beam process. To characterize the devices, an automated turntable stage with an embedded high resolution gyroscope has been built. Its large payload capacity allows for safe rotation of a temperature-controlled opto-mechanical setup. A field programmable gate array interface has been implemented for mechanical actuation and signal acquisition. Various rotation schemes have been implemented to characterize the apparatus and devices. The turntable exhibits a bandwidth of 0.54 Hz, and minimum and maximum repeatable angular rates of 27 and 74.3 degrees per second (dps), with a maximum associated angular rate noise level of 2 dps.
Vernier racetrack resonators offer advantages over single racetrack resonators such as extending the free spectral range (FSR).1-3 Here, we have presented a theoretical sensitivity analysis on quadruple Vernier racetrack resonators based on varying, one at a time, various fabrication dependent parameters. These parameters include the waveguide widths, heights, and propagation losses. We have shown that it should be possible to design a device that meets typical commercial specifications while being tolerant to changes in these parameters.
We discuss recent progress and challenges in realizing Bragg-grating devices on the submicron silicon-on-insulator platform for next-generation optical communications applications, such as on-chip optical interconnects and signal processing. In particular, we focus on grating-assisted, wavelength-selective couplers, known as contra-directional couplers (contra-DCs). In contrast to conventional two-port Bragg gratings operating in the reection mode, contra-DCs are four-port devices with very weak backreections and, therefore, can be easily integrated with other photonic components on a chip. In order to provide a reliable on-chip wavelength-division multiplexing (WDM) solution for high-speed optical interconnects, we have developed high-performance add-drop filters and, furthermore, wavelength multiplexers/demultiplexers with combined advantages of at-top responses, low insertion loss (< 1 dB), and low crosstalk (< -23 dB). These WDM devices are ultra-compact and highly tolerant to temperature uctuations (up to ±50 °C), showing great potential for large-scale integration and low-power consumption. We further discuss a novel four-port Bragg photonic resonator for high-speed, low-power optical switching. Using a coupler-chirped design with uniform Bragg gratings, we have recently achieved an on-chip, continuously tunable photonic delay line with low insertion loss. These system-orientated devices indicate great potential for large-scale integration of Bragg-grating-defined functions using CMOS-compatible silicon photonics technology.
We demonstrated 2×2 broadband adiabatic 3-dB couplers based on silicon rib waveguides. Functioning as
50/50 optical power splitters, these devices can be used in optoelectronic applications. Fabricated using siliconon-insulator technology, we demonstrated the performance of the adiabatic 3-dB couplers by integrating two couplers into an unbalanced Mach-Zehnder Interferometer (MZI). Measurements of the MZI were made over a 100 nm wavelength range. Extinction ratios in excess of 33.4 dB were obtained over the wavelength range from 1520 nm to 1600 nm, for light injected into Input Port1 and measured at Output Port2, i.e., the cross port response.
A fully-etched grating coupler with improved back re ection and bandwidth is demonstrated in this paper. It can also be made in compact patterns with much smaller footprints than conventional, fully-etched grating couplers with long adiabatic tapers. Sub-wavelength gratings were employed to form the e ective index areas between the major gratings. Our grating has a measured 3-dB bandwidth of 64.37 nm with a back re ection of -14 dB.
We review the development of a unique, electro-optic, polarization modulator fabricated on epitaxial layers of aluminum gallium arsenide, grown on a gallium arsenide (GaAs) substrate. The device has a single waveguide structure combined with travelling-wave, slow-wave electrodes. This design allows for high-speed modulation of the polarization state of light with low differential group delay and low optical loss at frequencies in excess of 50 GHz. The devices are TE↔TM mode convertors that modulate the state of light from one linear polarization state to an orthogonal linear state passing through elliptical and circular polarization states. These devices can also be configured to modulate the phase or intensity of an optical signal by appropriate alignment of the polarization axis of the input light or by placing a polarizer at the output. Key characteristics and important performance advantages of such devices are discussed. Applications that use these devices for enhancing digital and analog communication links, analog-to-digital signal conversion, and sending keys for encryption are reviewed to illustrate the diverse nature of the systems being developed and provide an overview of the versatility of the ways in which the GaAs polarization modulator may be used.
A silicon racetrack resonator modulator, based on phase-match control, is proposed. The device is comprised of a straight
waveguide evanescently coupled to a ring resonator in the shape of a racetrack. A PN junction, formed in the straight
waveguide, is used to control the degree of phase-match in the coupler. Consequently, the coupling, and hence the power
transmission, is controlled by the voltage across the PN junction. The predicted free spectral range and switching voltage are,
respectively, 0.4 nm and 7.5 Volt, while the device dimensions are approximately 0.7 mm by 0.15 mm. The device behavior
is analyzed using two different analytic approaches for the coupling, the results of which are compared to numerical
simulations.
This paper presents a dumbbell shape micro-ring resonator designed for use as a reflective notch filter. Function-ring as a wavelength-selective notch reflector, the device can be used in optoelectronic applications. The device is designed and analyzed using the transfer-matrix method. Fabricated using silicon-on-insulator technology, the dumbbell micro-ring reflector shows a reflective response with a quality factor of ~11,000 and an extinction ratio of 20 dB.
Development of large-scale photonic integrated circuits requires an accurate, simple, and space-efficient method for characterizing the optical losses of integrated optical components. Here we present a ring-resonator-based technique for transmission-loss measurement of integrated optical components. Y-branch splitters are used to demonstrate the concept. This measurement techique is based on characterizing the spectral response of a waveguide ring resonator with a number of Y-branches inserted inside the cavity. The measurement accuracy is intrinsically limited by the optical loss of the ring waveguide and is independent of fiber-to-waveguide coupling losses. The devices were fabricated using a CMOS-compatible silicon-on-insulator technology. Our results show that the proposed technique is promising for high-accuracy, high-efficiency characterization of optical losses. Limitations of and potential improvements to the technique are also discussed.
Silicon photonic resonators, implemented using silicon-on-insulator substrates, are promising for numerous applications.
The most commonly studied resonators are ring/racetrack resonators. We have fabricated these and other resonators including
disk resonators, waveguide-grating resonators, ring resonator reflectors, contra-directional grating-coupler ring
resonators, and racetrack-based multiplexer/demultiplexers.
While numerous resonators have been demonstrated for sensing purposes, it remains unclear as to which structures
provide the highest sensitivity and best limit of detection; for example, disc resonators and slot-waveguide-based ring
resonators have been conjectured to provide an improved limit of detection. Here, we compare various resonators in
terms of sensor metrics for label-free bio-sensing in a micro-fluidic environment. We have integrated resonator arrays with
PDMS micro-fluidics for real-time detection of biomolecules in experiments such as antigen-antibody binding reaction
experiments using Human Factor IX proteins. Numerous resonators are fabricated on the same wafer and experimentally
compared. We identify that, while evanescent-field sensors all operate on the principle that the analyte's refractive index
shifts the resonant frequency, there are important differences between implementations that lie in the relationship between
the optical field overlap with the analyte and the relative contributions of the various loss mechanisms.
The chips were fabricated in the context of the CMC-UBC Silicon Nanophotonics Fabrication course and workshop.
This yearlong, design-based, graduate training program is offered to students from across Canada and, over the last four
years, has attracted participants from nearly every Canadian university involved in photonics research. The course takes
students through a full design cycle of a photonic circuit, including theory, modelling, design, and experimentation.
This paper presents a new type of broadband impedance transformer loaded with capacitive fins (ITF) suitable for use in
the frequency range 10 GHz to 70 GHz. Compared with conventional, unloaded, tapered impedance transformers, these
ITF structures extend the impedance matching range and the operating bandwidth for the same amount of on-chip real-estate.
We have designed ITFs capable of impedance matching resistive loads from ~ 10 Ω to ~ 229 Ω, on a 650 μm
thick GaAs substrate over about a 60 GHz bandwidth. Design examples are used to demonstrate the flexibility of these
ITF structures.
An electrooptic modulator containing a single SiGe/Si quantum-well has been designed for operation at λO= 1.55 μm.
This single quantum-well modulator has a lower VπLπ than the 3 quantum-well modulator recently designed and optimized
by Maine et al. for operation at λO = 1.31 μm, for which the VπLπ product was 1.8 V · cm. This single quantum-well
modulator contains a Si0.8Ge0.2 quantum-well with Non-Intentionally Doped (NID) and P+ highly doped layers on either
side. With no field applied, holes from the P+ layers are captured by and confined in the quantum-well and when a reverse
bias is applied holes are released from the quantum well and drift to the P+ contact layer. Variations of the hole distribution
lead to changes in the free-carrier absorption and the refractive index of each layer and subsequently to phase modulation
of guided TE modes. The VπLπ product of the single quantum-well modulator is estimated 1.09 V · cm for low voltage
linear modulation and 1.208 V · cm for 0 to 1.6 V digital modulation, whereas the 3 quantum-well modulator gives a
VπLπ of 2.039 V · cm for 0 to 6 V digital modulation for operation at λO = 1.55 μm. Also, the optical loss in the single
quantum-well (5.36 dB/cm at V = 0 V ) is lower than that of the 3 quantum-well structure (5.75 dB/cm at V = 0 V ).
This single quantum-well modulator should also offer higher frequency operation than the 3 quantum-well modulator.
Silica based fibre-optic refractive index sensors are gaining acceptance over conventional refractometers and finding
applications in chemical/biological sensing due to many of their desirable properties. Here we present an optical fibre-based
refractive index sensor that uses the power transmission through etched D-shaped fibres. The sensor's operating
point and resolution can be tailored for a specific application by selecting the correct combination of the operating
wavelength and the cladding thickness of the etched fibre. The sensor's power transmission depends on the surrounding
refractive index in which the sensor head is immersed. The sensor presented has a maximum resolution on the order of
10-6 in its "high resolution" region and on the order of 10-4 in its "low resolution" region. The refractive index at which
the maximum resolution occurs in the high resolution region can be shifted by ~0.012 and by ~0.027 in the low
resolution region. To date, such high resolutions have been reported over narrow ranges and/or for fibre Bragg grating
based sensors, which require optical spectral analysis which typically, is costly.
A liquid level sensor based on etched D-shaped silica optical fibers is presented. The optical transmission of the sensor depends on the liquid level. The sensor can be realized as a continuous level sensor with a high resolution and requires only one fiber and one optical source and detector. We have demonstrated a sensor with a resolution of ~1 mm. The sensor works for liquids with refractive indices greater than ~1.45. We show that the sensor response is the same for increasing and decreasing liquid levels.
Cladding-reduced fibers with elliptical cores can be used in the fabrication of fiber-optic sensors. Here we analyze the power transmission ratio in cladding reduced D-shaped optical fibers for the purpose of determining the cladding thickness, in a non-destructive manner, when the fibers have been etched to reduce their cladding thicknesses to allow interaction of the optical evanescent field with an external medium having a refractive index greater than the mode effective index of the fiber. Parameters needed to determine the cladding thickness are determined empirically using the measured power transmission ratio of a few calibration fibers. We show that one can estimate the cladding thickness by fitting the measured transmission ratio curves for the fiber of interest to the curves generated for the calibration fibers.
Optical electric field sensors have been used for the measurement of high-voltages found in power substations. Typical
sensors are based on electro-optic crystals and hence require the coupling of light into and out of the crystals from optical
fibers. This coupling is difficult and costly. The objective of the work presented here is the design and implementation of
an optical electric field sensor that uses an entirely fiber-based sensor-head. The sensor-head is comprised of a D-shaped
optical fiber with its flat side coated with liquid crystals. D-fibers allow easy access to the evanescent optical field and
replacement of part of the cladding with an external medium allows for modulation of this optical field. We are
investigating the use of chiral Smectic A liquid crystals, which respond linearly to electric fields through the electroclinic
effect. The propagation characteristics of the D-fiber for various distances between the fiber core edge and flat and for
various refractive indices of the external medium are theoretically investigated and experimentally verified. Preliminary
experimental results for a prototype electric field sensor are presented. The sensor responds in a linear fashion to an
applied electric field.
The spur-free dynamic range (SFDR) of a novel microwave-photonic link, using a polarization mode-converter electro-optic modulator in a balanced output configuration, is characterized in this work. Common-mode intensity noise and optical-amplifier-induced beat noise are suppressed using a polarization-selective balanced optical receiver. In addition, third-order predistortion is used to reduce 2-tone intermodulation distortion by up to 20 dB, further increasing the SFDR. Unlike the conventional approach using a dual-output Mach-Zehnder modulator, the complementary output signals are combined naturally as orthogonal polarizations into one transmission fiber.
A novel ultrahigh-speed electro-optic polarization modulator is introduced. The modulator uses a mode converter and a static polarization controller to change the output polarization state in a circular path, following a great circle, around the Poincaré sphere. Any two states on the Poincaré sphere can be connected. The mode converter is constructed using an AlGaAs ridge waveguide combined with slow-wave travelling wave electrodes. The travelling wave electrodes are designed to match the velocity of the electrical modulating signal, the data signal, to the optical carrier signal over a broad frequency range. This modulator demonstrates a 3 dB bandwidth in excess of 40 GHz. The polarization modulator exhibits extremely low differential group delay, on the order of a few 10s of femto-seconds, and low drive voltage, on the order of 5 V.
This paper describes a novel voltage transducer. Its design is based on a mathematical procedure that enables a small number
of strategically positioned electric field sensors to accurately measure the voltage. The voltage transducer takes advantage of
existing compact, non-intrusive optical electric field sensor technology, specifically, the integrated-optic Pockels cell (IOPC),
but is not limited to optical technology. The key advantage of this voltage transducer over other existing optics-based voltage
transducer technologies is that it does not require any customized electrode structures and/or special insulation. A highvoltage
integrated-optic voltage transducer has been used to obtain measurements with metering class accuracies.
Preliminary results are reported for a novel hybrid electro-optic/inductive current sensor for high-voltage, power system
applications. The sensor combines inductive current to voltage conversion with an optical modulator to provide isolated
signal transmission from a high-voltage conductor to ground. The components of the sensor to be located in the high-voltage
environment are passive, resulting in increased robustness over optical hybrid current sensor designs that require active
electronics in the high-voltage environment. A further advantage of the passive design is that a power supply is not required
in the high-voltage environment. The current sensor presented here is targeted at both revenue metering and protective
relaying applications. Tests conducted in a high-current laboratory show the relative accuracy of the sensor to be stable to
within from 200 A to 10 kA with phase stability within minutes of arc. Accuracy is presently limited by the
temperature stability of the optical modulator which varies by about over the range from -40 to +60°C. Methods to
improve the temperature stability are being investigated.
Integrated-optic devices for use in high-voltage substations are reviewed. Specifically, two types of integrated-optic Mach-Zehnder and the integrated-optic Pockels cell are described and compared. A system for monitoring the condition of fluid-and-paper insulation systems, such as are used in many current transformers and power transformer bushings, is also described. This condition monitoring system measures the dissipation factor of an insulation system being monitored. It uses an integrated-optic Pockels cell to measure the phase of the voltage on the high-voltage transmission line to which the insulation system is connected. Preliminary results, showing that the system is capable of measuring the dissipation factor to an accuracy of 0.5%, are presented.
The results of measurements of the intrinsic phase-differences of titanium- indiffused lithium niobate waveguides, for use in integrated optics Pockels cell high-voltage sensors, are presented. The dependencies of the intrinsic phase-differences of these waveguides on their lengths and widths are investigated; a change of between 4.9 and 5.9 degree(s)/micrometers /mm was obtained. Also, the change in the intrinsic phase-difference as a function of both temperature and time was investigated; a typical change of 0.02 degree(s)/ degree(s)C/mm was measured and, following a small initial change, the bias was found not to drift with time. Some suggestions for possible post-processing of the output signals, of the integrated optics Pockels cell high-voltage sensors, to increase the dynamic range and to compensate for small changes in the bias, are presented.
A novel microstrip resonator structure for use with integrated Y-branch optical modulators fabricated in Ti:LiNbO3 is proposed. The legs of the structure are intended to act as the electrodes of the modulator, with light being directed into each of the output waveguides of the Y-branch on alternate half-cycles of the standing wave excited in the resonator; forming an optical commutator switch. Such resonators having Al2O3 substrates were designed, fabricated, and tested. Measurements on one such resonator, operating at 7.12 GHz and having an unloaded quality factor of 123, indicating that 50 V should develop across the ends of its legs for 35 mW dissipated power; the corresponding values, from the model used to design the resonator, were 179, 50 V,and 24 mW, respectively. Using the model it is shown that a similar resonator fabricated on LiNbO3 should be able to develop about 50 V for 100 mW dissipated power at 15 GHz.
Coplanar slow-wave electrode structures capable of matching the velocities of microwaves to those of optical waves in compound semiconductor based electro-optic modulators are described. In such an electrode microwaves are slowed by periodically adding pairs of capacitive loading fins to the electrode to increase its capacitance per unit length, without obtaining a corresponding decrease in its inductance per unit length. Electro-optic modulators having wide bandwidths and requiring small amounts of modulating power may be realized by using slow-wave electrodes to achieve the velocity-match condition. The theory of operation of, and the results of some measurements on, electrodes of this type are presented.
A new optical commutator switch, capable of very high speed pulse generation and pulse multiplexing/demultiplexing, is proposed. It consists of an integrated optical Y-branch modulator and a `cul-de-sac' microstrip resonator. A possible compound digital optical modulator, using these optical commutators, is described. The results of measurements made on a cul-de-sac resonator, fabricated on an alumina substrate, and on optical Y-branch modulators, fabricated on z-cut lithium niobate substrates, are presented. For the resonator the unloaded quality factor was measured. For the optical Y-branch modulators the on/off ratios and percent guided powers were measured as functions of the applied voltage for several branch angles. The results indicate that optical commutators, of the type proposed, could be made.
To characterize z-cut Ti:LiNb03 Y-branch optical modulators, numerical simulations were performed showing that high on/off ratios are attainable without special Y-junction asymmetries or long electrodes. The effective index and 2-D finite difference beam propagation methods were used for the simulations. A modulator with a 2° Y-branch was fabricated. The measured on/off ratios were 5:1 at 25 V, 12:1 at 50 V, and 60:1 at 75 V, corresponding to 4:1, 12:1, and 62:1 for the simulations for y= 632.8 nm.
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