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We experimentally demonstrate a continuously-tunable quasi-THz RF-photonic phase shifter based on a dual-phase-shifted waveguide Bragg grating on silicon. Phase shifts up to ~90° are demonstrated over the 16-20 GHz band, constrained only by instrumentation limitations.

We demonstrate the first fiber grating coupler with focusing curved subwavelength structures. An ultra-wide 1-dB bandwidth of over 100 nm with -6.7 dB coupling efficiency at 1550 nm has been experimentally achieved.

High-performance, ultracompact lenses are needed in the quest to miniaturize optical systems. It now seems that carefully engineered subwavelength gratings can function as almost perfect mirrors with custom-designed focusing properties.

An n-p-n transistor vertical-cavity surface-emitting laser (TX-VCSEL) is described and numerically modeled by Crosslight PICS3D. For a given collector-emitter voltage V CE, the optical output power as a function of the base current IB has three regions: 1) below-threshold, 2) linear increase, and 3) saturation. Different from the saturation caused by thermal effect and gain compression, this new-observed optical saturation comes from the three-port operation of the TX-VCSEL. The saturation power is determined by V CE, with an approximately linear relationship. This enables new applications with voltage control of laser in future optoelectronic integrated circuits.

Continuous glucose monitoring has been shown to help diabetes mellitus patients stabilize their glucose levels, leading to improved patient health. One promising technique for monitoring blood glucose concentration is to use optical absorption spectroscopy. This letter proposes the use of thermally tunable 2.3-mum vertical-cavity surface-emitting lasers to obtain blood absorption spectra. The partial least squares technique is used to determine the glucose concentration from the spectra obtained in aqueous glucose solutions.

We propose and experimentally demonstrate a novel communication system scheme with an optical injection-locked vertical-cavity surface-emitting laser (OIL-VCSEL) acting both as a transmitter and as a receiver, under an identical forward-bias condition. We show that an OIL-VCSEL can function as a receiver with a small signal modulation bandwidth of ~20 GHz, and for large signal digital modulation with data rate as high as 12 Gb/s.

This letter describes a modified optical heterodyne down-conversion system for measuring the frequency response of wavelength-sensitive electrooptical devices at millimeter-wave frequencies. The new system is presented, and the frequency response of an injection-locked vertical-cavity surface-emitting laser is measured to up to 35 GHz

We report injection-locked vertical-cavity surface-emitting lasers simultaneously achieving high extinction ratios of 20 dB, enhanced resonance frequency >30 GHz, and radio-frequency signal amplification of >10 dB, for the first time.

High-speed directly modulated diode lasers are important for optical communications and optical interconnects. In this work, we demonstrate greatly enhanced resonance frequency for vertical-cavity surface-emitting lasers, from 7 to 50 GHz, under ultrahigh injection-locking conditions. In addition, a 20-dB gain is achieved for small signal modulation below resonance frequency.

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.

A universal design methodology for grating couplers based on the silicon-on-insultator platform is presented in this paper. Our design methodology accomodates various etch depths, silicon thickness (e.g., 220 nm, 300 nm), incident angles, and cladding materials (e.g., silicon oxide or air), and has been verified by simulations and measurement results. Further more, the design methodology presented can be applied to a wide range, from 1260 nm to 1675 nm, of wavelengths.

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.

We demonstrate an apodization technique using tapered coupler gaps in grating-assisted asymmetric couplers, which circumvents the need for tapered waveguide perturbations and enables a higher tolerance to fabrication errors. A high sidelobe suppression ratio of 30 dB has been obtained on the submicrometer silicon-on-insulator platform using a CMOS-compatible photonics process with 193 nm lithography.

We propose and experimentally demonstrate a novel, ultra-broadband and continuously tunable integrated microwave photonic processor that can operate both as a RF phase shifter (PS) and a true-time-delay (TTD) line. The device is implemented with a silicon phase-shifted waveguide Bragg grating (PS-WBG) realized with a CMOS compatible process. The grating features a sharp phase shift localized within the reflection band that can be exploited in conjunction with optical single sideband modulation with full carrier (OSSB+C) to generate either PS or TTD on the modulated RF signal, depending on the relative frequency position of the carrier and the sideband with respect to the phase shift. Proof-of-concept experiments show the generation of a delay up to 25.7 ps over an 8 GHz bandwidth, and a phase shift of approx. 90 degrees over the bandwidth 16-20 GHz is also demonstrated. The phase shifter demonstration is ultimately limited by the available measurement setup, as the device is capable of providing up to 300 degrees phase shift for RF frequencies above 16 GHz over a record bandwidth approaching 1 THz.

This work presents a study, with preliminary fabrication, of thin optical resonators for sensing applications. Using thin waveguides shows promise in enhancing sensitivity for bulk and surface sensing.

We propose and experimentally demonstrate the first THz-bandwidth on-chip fractional Hilbert transformer based on an integrated phase-shifted waveguide Bragg grating on silicon. Experimental results show an error of only 0.24 % at 940 GHz bandwidth.

We have designed, fabricated, and characterized cascaded ring resonator on silicon on insulator, SOI, chips. This resonator configuration allows for simultaneously gathering multi-parametric information on gaseous/fluidic solutions in contact with sensors, without requiring molecular labeling.

We demonstrate a multi-period Bragg grating device in a silicon-on-insulator rib waveguide. The sidewalls of the rib and the slab are corrugated using different periods, resulting in two Bragg wavelengths that are controlled separately.

The spectral responses of series-coupled racetrack resonators exhibiting the Vernier effect have many attractive features as compared to the spectral responses of identical series-coupled racetrack resonators, such as free spectral range (FSR) extension and enhanced wavelength tunability. Here we present experimental results of a thermally tunable quadruple series-coupled silicon racetrack resonator exhibiting the Vernier effect. We thermally tune two of the four racetrack resonators to enable discrete switching of the major peak by 15.54 nm. Also, our device has an interstitial peak suppression of 35.4 dB, a 3 dB bandwidth of 0.45 nm, and an extended FSR of 37.66 nm.

Silicon photonic biosensors are highly attractive for multiplexed Lab-on-Chip systems. Here, we characterize the sensing performance of 3 µm TE-mode and 10 µm dual TE/TM-mode silicon photonic micro-disk resonators and demonstrate their ability to detect the specific capture of biomolecules. Our experimental results show sensitivities of 26 nm/RIU and 142 nm/RIU, and quality factors of 3.3x10(4) and 1.6x10(4) for the TE and TM modes, respectively. Additionally, we show that the large disks contain both TE and TM modes with differing sensing characteristics. Finally, by serializing multiple disks on a single waveguide bus in a CMOS compatible process, we demonstrate a biosensor capable of multiplexed interrogation of biological samples.

Silicon photonics is poised to revolutionize biosensing applications, specifically in medical diagnostics. Optical sensors can be designed to improve clinically-relevant diagnostic assays and be functionalized to capture and detect target biomarkers of interest. There are various approaches to designing these sensors - improving the devices' performance, increasing the interaction of light with the analyte, and matching the characteristics of the biomolecules by using architectures that complement the biosensing application. Using e-beam lithography and standard foundry processes, we have investigated Transverse Magnetic (TM) and Transverse Electric (TE) disk and ring resonators. TM devices hold the potential for higher sensitivity and large-particle sensing capabilities due to the increased penetration distance of light into the analyte. In addition, devices such as slot waveg­guide Bragg grating sensors have shown high sensitivities and high quality factors and may present advantages for specific biosensing applications. These devices have been investigated for wavelengths around λ=1550 nm (conventional wavelength window in fiber-optic communication) and λ=1220 nm, where the water absorption is greatly decreased, offering improved limits of detection. Using reversibly bonded PDMS microfluidic flow cells, the performance and bio-detection capabilities of these devices were characterized. Comparing binding performance across these devices will help validate architectures suitable for biological applications. The most promising sensors for each application will then be identified for further study and development. This paper will discuss the sensors' comparative advantages for different applications in biosensing and provide an outlook for future work in this field.

We present a novel silicon photonic biosensor using phase-shifted Bragg gratings in a slot waveguide. The optical field is concentrated inside the slot region, leading to efficient light-matter interaction. The Bragg gratings are formed with sidewall corrugations on the outside of the waveguide, and a phase shift is introduced to create a sharp resonant peak within the stop band. We experimentally demonstrate a high sensitivity of 340 nm/RIU measured in salt solutions and a high quality factor of 1.5 × 104, enabling a low intrinsic limit of detection of 3 × 10–4 RIU. Furthermore, the silicon device was fabricated by a CMOS foundry, facilitating high-volume and low-cost production. Finally, we demonstrate the device's ability to interrogate specific biomolecular interactions, resulting in the first of its kind label-free biosensor. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We experimentally demonstrate ultra-compact (

We demonstrate a compact Bragg grating in a silicon-on-insulator spiral waveguide. A 3.12 mm long grating with a bandwidth of 0.27 nm has been experimentally realized within an area of 141 um × 146 um.

We study the temperature effects on injection-locked vertical-cavity surface-emitting lasers (VCSELs) for use in wavelength-division-multiplexed (WDM) transmitters. We show that injection locking can be used to lock an uncooled VCSEL to the WDM grid while improving its analog performance.

We demonstrate record performance of series-coupled silicon racetrack resonators exhibiting the Vernier effect. Our device has an interstitial peak suppression (IPS) of 25.5 dB, which is 14.5 dB larger than previously reported results. We also demonstrate the relationship between the inter-ring gap distance and the IPS as well as the 3 dB bandwidth (BW) both theoretically and experimentally. Namely, we show that as the inter-ring gap distance increases, the IPS increases and the 3 dB BW decreases.

Injection locking is demonstrated to improve the analog performance of long wavelength vertical-cavity surface-emitting lasers. The third-harmonic dynamic range was improved by /spl sim/20 dB/spl middot/Hz/sup 2/3/ to be /spl sim/94 dB/spl middot/Hz/sup 2/3/, and the modulation bandwidth was increased two fold. The locking conditions are studied and show that the improvement is present over a wide range of injection power and wavelength detuning.

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.

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.

We demonstrate wavelength-selective reflectors based on silicon microdisk resonators integrated with compact Y-branch splitters, using a CMOS-photonics technology. A high quality factor (Q) of ~ 88,000 was measured in the reflection spectrum for a 2.5-μm-radius device with a small footprint of 6 × 17 μm(2) and a wide free-spectral range (FSR) of over 41 nm. As the radius is reduced to 1.5 μm, corresponding to a device footprint of 4 × 15 μm(2), the spectrum shows an ultra-wide FSR of over 71 nm with the compromise of having a reduced Q of ~ 4000. The coupling between a microdisk and a waveguide is numerically investigated. We further propose a multichannel sensing system using cascaded microdisk reflectors.

We demonstrate a wide-bandwidth add-drop filter using silicon contra-directional couplers with a novel anti-reflection design. Single-band operation, with a bandwidth of 6.5nm and an extinction ratio of over 20dB, has been experimentally obtained.

We demonstrate an electrically tunable resonant filter with FSR-free operation using a silicon photonic quarter-wavelength phase-shifted, grating-assisted contra-directional coupler. The spectrum shows a stop-band of 7nm, an extinction of 24dB, and a Q of 7,000.

We demonstrate the design, fabrication and measurement of integrated Bragg gratings in a compact single-mode silicon-on-insulator ridge waveguide. The gratings are realized by corrugating the sidewalls of the waveguide, either on the ridge or on the slab. The coupling coefficient is varied by changing the corrugation width which allows precise control of the bandwidth and has a high fabrication tolerance. The grating devices are fabricated using a CMOS-compatible process with 193 nm deep ultraviolet lithography. Spectral measurements show bandwidths as narrow as 0.4 nm, which are promising for on-chip applications that require narrow bandwidths such as WDM channel filters. We also present the die-to-die nonuniformity for the grating devices on the wafer, and our analysis shows that the Bragg wavelength deviation is mainly caused by the wafer thickness variation.

Generation of continuous-wave (CW) terahertz (THz) radiation with a power of 2µW is demonstrated. Two CW laser beams of wavelengths around 800nm are photomixed in a large-area photomixer to generate a THz radiation of 1.2THz. The utilized photomixer has interdigitated contacts with desirable radiation characteristics in the far-field region. We show that the radiated THz beam is steerable by changing the incidence angles of the CW pump beams. In our experimental setup, the emission direction of the large-area photomixer can be steered by rotating the beam splitter used for beam combining. Using this setup, we are able to steer the THz beam in a range of −30 to +30 degrees.

Cell-based testing is a key step in drug screening for cancer treatments. A microfluidic platform can permit more precise control of the cell culture microenvironment, such as gradients in soluble factors. These small-scale devices also permit tracking of low cell numbers. As a new screening paradigm, a microscale system for integrated cell culture and drug screening promises to provide a simple, scalable tool to apply standardized protocols used in cellular response assays. With the ability to dynamically control the microenvironment, we can create temporally varying drug profiles to mimic physiologically measured profiles. In addition, low levels of oxygen in cancerous tumors have been linked with drug resistance and decreased likelihood of successful treatment and patient survival. Our work also integrates a thin-film oxygen sensor with a microfluidic oxygen gradient generator which will in future allow us to create spatial oxygen gradients and study effects of hypoxia on cell response to drug treatment. In future, this technology promises to improve cell-based validation in the drug discovery process, decreasing the cost and increasing the speed in screening large numbers of compounds. Copyright 2012 Society of Photo-Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.

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.

We demonstrate a novel silicon microring resonator using grating-assisted contradirecitonal couplers for wavelength-selective coupling control. A single resonant peak can be selected in a wide frequency window without impairing its quality factor.

We demonstrate an improvement in transmission performance when an L-band VCSEL, directly modulated at 2.5 Gb/s, is injection-locked by relatively low injected optical power from another VCSEL. The improvement is attributed to a reduction in chirp.

The authors demonstrate the viability of high-performance vertical cavity surface emitting lasers transmission with semiconductor optical amplifiers as a low-cost alternative to distributed-feedback erbium-doped fiber amplifier systems. They study the effect of the optical amplifier noise figure on metro networks.

A broad range tunable optical filter using a torsional micromechanical structure is presented. The device has a continuous tuning range over 100 nm, from 1500 to 1600 nm, and the structure eliminates the potential catastrophic discharge problem associated with electrostatic micromachines. Transmission of a 2.5-Gb/s directly modulated 1550-nm vertical-cavity surface-emitting laser through the tunable filter shows no power penalty.

We demonstrate contradirectional couplers in silicon-on-insulator rib waveguides using a CMOS compatible technology, in which a periodic dielectric perturbation is introduced in the coupling region between two different-sized rib waveguides. This structure enables high fabrication tolerances for narrow-bandwidth add-drop filters, using commercially available deep-ultraviolet lithography, that do not suffer from having a free spectral range. The simulation using coupled-mode theory and mode-profile calculations shows good agreement with experiment. A narrow bandwidth of 0.35 nm and a low loss of less than 1 dB have been achieved experimentally.

We present an integrated transmission filter using phase-shifted Bragg gratings in silicon-on-insulator waveguides fabricated by deep-ultraviolet lithography. The measured resonant transmission band has a narrow linewidth of ∼15 pm with a quality factor of ∼100,000.

We demonstrate wavelength tuning of silicon-on-insulator racetrack resonators, induced by the by the creation of defects via ion implantation. This presents a method to alter the resonant wavelength after fabrication, albeit with increased optical loss.

We present a study on the effects of inert ion implantation of Silicon-On-Insulator (SOI) racetrack resonators. Selective ion implantation was used to create deep-level defects within a portion of the resonator. The resonant wavelength and round-trip loss were deduced for a range of sequential post-implantation annealing temperatures from 100 to 300 °C. As the devices were annealed there was a concomitant change in the resonance wavelength, consistent with an increase in refractive index following implantation and recovery toward the pre-implanted value. A total shift in resonance wavelength of ~2.9 nm was achieved, equivalent to a 0.02 increase in refractive index. The excess loss upon implantation increased to 301 dB/cm and was reduced to 35 dB/cm following thermal annealing. In addition to providing valuable data for those incorporating defects within resonant structures, we suggest that these results present a method for permanent tuning (or trimming) of ring resonator characteristics.

Silicon-On-Insulator (SOI) photonic microring resonators have shown promising potential for real time detection of biomolecules because of the sensitivity towards surface binding events. Previous work shows the use of single ring resonators for sensing applications. Each ring requires an input and output coupler and can be addressed only one at a time. We propose a novel use of cascaded ring resonators (width w = 200 nm and bending Radius R = 30 µm) together with a PDMS microfluidic network fabricated by soft lithography to expose each ring individually with different solutions. The SOI substrate with the planar waveguides and the PDMS with the microchannels are reversibly bonded to each other. The use of cascaded ring resonators offers the possibility to measure transmission spectra of multiple rings in different channels simultaneously. We measured Q-factors of >30'000 in air and >10'000 when exposed to water. Using a water/glycerin solution with known refractive indices we determine the sensitivity to be ~40 nm/RIU. Copyright 2011 Society of Photo-Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.

We have demonstrated uniform and sampled Bragg gratings in silicon-on-insulator strip waveguides with symmetric sidewall corrugations. The fabrication is based on 193-nm deep ultraviolet lithography using a single mask. The measured reflection spectra of sampled gratings exhibit ten usable peaks spaced by 4.2 nm, and show good agreement with theoretical predictions.

We demonstrate the design and performance of Bragg gratings on silicon-on-insulator waveguides. Two structures for achieving the modulation of the effective index of refraction are described. The grating fabrication is based on deep ultra-violet lithography using a single mask. The thermal tunability of the devices is demonstrated.

The effect of capacitive current-current feedback on the small signal modulation response of the transistor laser in the common-emitter configuration is modelled. Gain-bandwidth equalization and suppression of the relaxation oscillation resonance peak have been shown.