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We present a novel, to the best of our knowledge, remote gas detection and identification technique based on correlation spectroscopy with a piezoelectric tunable fiber-optic Fabry–Perot filter. We show that the spectral correlation amplitude between the filter transmission window and gas absorption features is related to the gas absorption optical depth, and that different gases can be distinguished from one another using their correlation signal phase. Using a previously captured telluric-corrected high-resolution near-infrared spectrum of Venus, we show that the radial velocity of Venus can be extracted from the phase of higher order harmonic lock-in signals. This correlation spectroscopy technique has applications in the detection and radial velocity determination of weak spectral features in astronomy and remote sensing. We experimentally demonstrate a remote C O 2 detection system using a lock-in amplifier, fiber-optic Fabry–Perot filter, and single channel avalanche photodiode.

The absorption spectra of distant targets can be used for remote gas detection. However, the detection of very faint absorption features is difficult since noise can dominate the molecular signal in the acquired spectrum. Rather than using typical dispersive spectroscopy, high sensitivity remote gas sensing is possible by correlation spectroscopy using a spectral matching filter. In this work, we use a thermo-optically tunable nanophotonic silicon waveguide ring resonator as an integrated spectral filter to obtain a correlation signal proportional to the absorption spectrum of a specific gas. We demonstrate the ability to resolve very small absorption depth changes using integrated photonics at the level required for the characterization of exoplanet atmospheres during transits of their host stars., 2021 Photonics North (PN), May 31 - June 2, 2021, Toronto, ON, Canada

We present fully apodized and perfectly vertical surface grating couplers in 300 nm silicon waveguides. We achieve ultrahigh coupling efficiency of -0.35 dB at 1550 nm for an optical fiber with 10.4 µm mode-fiber-diameter. To this end, we followed a two stage process in which, we first optimized a pool of periodic grating couplers using machine learning techniques, and then apodized them over 100 parameters using the gradient based adjoint- method. Using a simple fabrication tolerance analysis, we also show that segment variations mostly causes a wavelength shift for the maximum coupling efficiency of the apodized grating couplers, similar to those typically observed for periodic grating couplers., Integrated Optics: Devices, Materials, and Technologies XXV, March 6-12, 2021, Online Only, United States, Series: Proceedings of SPIE

Absorption spectroscopy is widely used in sensing and astronomy to understand molecular compositions on microscopic to cosmological scales. However, typical dispersive spectroscopic techniques require multichannel detection, fundamentally limiting the ability to detect extremely weak signals when compared to direct photometric methods. We report the realization of direct spectral molecular detection using a silicon nanophotonic waveguide resonator, obviating dispersive spectral acquisition. We use a thermally tunable silicon ring resonator with a transmission spectrum matched and cross-correlated to the quasi-periodic vibronic absorption lines of hydrogen cyanide. We show that the correlation peak amplitude is proportional to the number of overlapping ring resonances and gas lines, and that molecular specificity is obtained from the phase of the correlation signal in a single detection channel. Our results demonstrate on-chip correlation spectroscopy that is less restricted by the signal-to-noise penalty of other spectroscopic approaches, enabling the detection of faint spectral signatures.

We present an integrated photonic correlation filter for the detection of remote HCN gas. We demonstrate sensing of absorption due to HCN using thermo-optic tuning of the drop port transmission spectrum in a silicon waveguide ring resonator., 2020 IEEE Photonics Conference (IPC), September 28 - October 1, 2020, Vancouver, BC, Canada

We study the fabrication tolerance of two types of grating antennas featuring U-shape and L-shape structures. The L-shape design is found to be more fabrication tolerant, showing performance degradation of less than 2% assuming common fabrication imperfections, making it promising for optical phased array applications., 2020 IEEE Photonics Conference (IPC), September 28 - October 1, 2020, Vancouver, BC, Canada

We report a novel and simple fabrication process to realize vertically tapered spot size converters (SSC) on InP photonic integrated circuits. The vertical tapering was achieved via a linewidth controlled local optical dose variation, leading to a grey tone photoresist profile. The fabricated SSCs are compact, polarization insensitive and demonstrate a very high mode conversion efficiency of 95%. Integrated SSCs improved the overall loss by 5 dB giving a coupling loss as low as 1.3 dB/facet, for a lensed fibre with a mode field diameter of 3.0 µm. A good agreement was found between the fibre-to-fibre optical loss measurements and those predicted from simulations.

Subwavelength metamaterial structures in silicon waveguides open new degrees of freedom to control on-chip light propagation. They have been applied to many silicon photonic devices such as fiber-chip couplers, waveguide crossings, microspectrometers, ultra-fast optical switches, athermal waveguides, evanescent field sensors, polarization rotators and colorless interference couplers [1]. Here we report a demonstration of a metamaterial coupler and an InAs-on-InP quantum dash buried heterostructure laser optimized for mutual integration by direct facet-to-facet coupling with -1.2 dB coupling efficiency, coupled laser relative intensity noise (RIN) of -150 dB/Hz and 152 kHz linewidth. We further demonstrate the design of multi-line spectral notch filters based on narrow linewidth metamaterial Bragg filters synthesized using the layer-peeling method., 2020 Photonics North (PN), May 26-28, 2020, Niagara Falls, ON, Canada

Absorption spectroscopy is a powerful technique for characterizing remote gas composition where direct interaction with a target it not possible. While dispersive spectroscopy is typically used to acquire a spectrum with which the gas presence is determined, correlation spectroscopy can directly detect such spectral features in a single detection channel. Here we present a novel integrated photonics correlation technique on an integrated photonic platform which uses real-time spectral processing to generate a multiline gas specific detection signal., 2020 Photonics North (PN), May 26-28, 2020, Niagara Falls, ON, Canada

In recent years photonic thermometers - temperature sensors based on optical frequency measurement which exploit the thermo-optic effect to translate thermal changes into frequency shifts - are gaining popularity as a possible alternative to their electrical counterparts: platinum resistance thermometers and thermocouples. In this work, we report our results of testing photonic thermometers based on silica fiber-Bragg-grating technology supplied by a commercial company, as well as preliminary testing results of a silicon ring-resonator thermometer developed at the National Research Council of Canada. The main purpose of showing these two examples is to highlight some of the challenges that need to be addressed if photonic thermometers are to replace thermocouples or platinum resistance thermometers in metrology laboratories and other environments where high accuracy and stability are required, namely the influence of packaging on the sensor's performance and the need for rigorous testing to be done in a temperature metrology lab.

We design perfectly vertical grating couplers with minimum feature sizes above 100 nm, high coupling efficiencies up to 75%, and low back reflection of -20 dB over 100 nm bandwidth, using a machine learning method., Integrated Photonics Research, Silicon and Nanophotonics 2020 , July 13-16, 2020, Washington, DC

An InAs-on-InP quantum dash buried heterostructure laser and silicon chip optimized for mutual integration by direct facet-to-facet coupling have achieved -1.2 dB coupling efficiency, with coupled laser RIN of -150 dB/Hz and 152 kHz linewidth., 2020 22nd International Conference on Transparent Optical Networks (ICTON), July 19-23, 2020, Bari, Italy

We present the design of a 3.6-µm-long silicon antenna with vertical emission. Across the optical communication C band, diffraction efficiency is above of 0.9, back-reflection below -18 dB, and the emission angle shifts by only 4.3 ◦ .

An accurate model for the silicon refractive index including its temperature and wavelength dependence is critically important for many disciplines of science and technology. Currently, such a model for temperatures above 22°C in the optical communication bands is not available. The temperature dependence in the spectral response of integrated echelle grating filters made in silicon-on-insulator is solely determined by the optical properties of the slab waveguide, making it largely immune to dimensional uncertainties. This feature renders the echelle filters a reliable tool to evaluate the thermo-optic properties of silicon. Here we investigate the temperature dependence of silicon echelle filters for the wavelength range of both O and C bands, measured between 22°C to 80°C. We show that if a constant thermo-optic coefficient of silicon is assumed for each band, as is common in the literature, the predictions show an underestimate of up to 10% in the temperature-induced channel wavelength shift. We propose and assess a model of silicon refractive index that encompasses both the wavelength and temperature dependence of its thermo-optic coefficients. We start from literature data for bulk silicon and further refine the model using the echelle filter measurement results. This model is validated through accurate predictions of device channel wavelengths and their temperature dependence, including the quadratic term, over a wide wavelength and temperature range. This work also demonstrates a new high-precision method for characterizing the optical properties of a variety of materials.

Astronomical instrumentation is traditionally costly, large, and alignment-sensitive owing to the use of bulk optics. The use of integrated photonic devices in astronomical instrumentation can mitigate such drawbacks in certain applications where high light throughput and spectral bandwidth are less crucial. In this work, we present an ultra-compact carbon dioxide detection scheme using a single silicon waveguide ring resonator. The comb-like absorption line spectrum of CO2 around 1580 nm wavelength can closely match the comb spectrum of an appropriately designed ring resonator. By actively correlating such a ring spectrum with the CO2 absorption lines, a specific detection signal can be generated. We design the free spectral range of a ring resonator to match the absorption line spacing of carbon dioxide lines in the range from 1575 to 1585 nm. Using thermo-optic modulation, the ring resonator drop or through port transmission spectrum can be shifted back and forth across the incoming CO2 light spectrum, resulting in a modulated signal with an amplitude proportional to the CO2 absorption line strength. Furthermore, high frequency modulation and lock-in detection can result in a significant improvement in the signal to noise ratio. We demonstrate that such a device can provide real-time carbon dioxide detection for applications in ground- and satellite-based astronomy, as well as remote atmospheric sensing, in a compact package. In future work, such a sensor can be adapted to a range of gases and used to determine radial velocities and compositional maps of astronomical objects.

We report on the design of an ultra-compact integrated wavelength demultiplexer in echelle configuration for the optical O-band realized on silicon-on-insulator technology. The device has four channels with channel spacing of 800 GHz and a small footprint of 260 &times, 83 &mu, m2. Channel crosstalk lower than &minus, 28 dB across the four channels is experimentally demonstrated along with insertion losses of &minus, 1.5 dB.

We present the design and experimental results for a silicon photonic thermometer module for secondary and working thermometry standards. The chip is mechanically robust and insensitive to contamination. Using surface coupling gratings the chip temperature can be monitored remotely using free space beams, thereby eliminating temperature hysteresis effects arising from conventional optical assembly methods and materials., 2019 Photonics North (PN), May 21-23, 2019, Quebec City, QC, Canada

We present a correlation spectrometer using a silicon waveguide ring resonator for the identification of molecules in stellar and planetary atmospheres. We tailor the free spectral range of a ring resonator to the vibronic overtones of carbon dioxide in the near infrared. The ring resonator spectrum is modulated via the thermo-optic effect and produces a detection signal unique to carbon dioxide. This spectrometer can be used for real-time remote gas detection and radial velocities of exoplanets in a narrow spectral band., 2019 Photonics North (PN), May 21-23, 2019, Quebec City, QC, Canada

Temperature sensitivity is an issue that severely affects many integrated silicon photonic devices. Proper circuit functionality is normally ensured by active thermal control at the expense of energy consumption. In some cases, athermal behavior can be achieved exploiting cladding materials with a negative thermo-optic coefficient to counterbalance the positive coefficients of silicon and silica. On the other hand, in echelle grating filters this method is not effective because in the slab free-propagation region the modal overlap with the cladding is small, especially for TEpolarized light. Moreover the need to add non-standard materials to the established silicon-on-insulator (SOI) fabrication process could make these solutions impractical. Here we present the design of a temperature-insensitive echelle grating demultiplexer with four channels operating in the TE polarization that does not use any materials with negative thermooptic coefficient and relies exclusively on standard processes for SOI photonics. The design exploits a temperaturesynchronized Mach-Zehnder interferometer as input to the echelle to compensate the shift of the imaged field with temperature. The device achieves a significant reduction in the temperature dependence of the overall transmission with a residual channel wavelength fluctuation smaller than 45 pm over a temperature range of 20 K, compared to a 1.6-nm shift for the same grating with a conventional waveguide input. The excess loss due to the use of the Mach-Zehnder input is no more than 0.7 dB for all four channels. Furthermore, the proposed design shows a very good tolerance to fabrication uncertainty, with minimum degradation of the performance for waveguide width variations of 10 nm., Silicon Photonics XIV, February 2-7, 2019, San Francisco, United States, Series: Proceedings of SPIE

Optical antennas are key components in optical phased arrays for light detection and ranging technology requiring long sensing range and high scanning resolution. To achieve a narrow beam width in the far-field region, antenna lengths of several millimeters or more are required. To date, such long antennas have been impossible to achieve in silicon waveguides because currently demonstrated technologies do not allow accurate control of grating strength. Here, we report on a new type of surface-emitting silicon waveguide with a dramatically increased antenna length of L = 3.65 m m . This is achieved by using a subwavelength metamaterial waveguide core evanescently coupled with radiative segments laterally separated from the core. This results in a far-field diffracted beam width of 0.025°, which is a record small beam divergence for a silicon photonics surface-emitting device. We also demonstrate that by using a design with L -shaped surface-emitting segments, the radiation efficiency of the antenna can be substantially increased compared to a conventional design, with an efficiency of 72% at the wavelength of 1550 nm.

We present perfectly vertical grating couplers for the 220 nm silicon-on-insulator platform incorporating subwavelength metamaterials to increase the minimum feature sizes and achieve broadband low back-reflection. Our study reveals that devices with high coupling efficiencies are distributed over a wide region of the design space with varied back-reflections, while still maintaining minimum feature sizes larger than 100 nm and even 130 nm. Using 3D-finite-difference time-domain simulations, we demonstrate devices with broadband low back-reflection of less than − 20 d B over more than 100 nm bandwidth centered around the C-band. Coupling efficiencies of 72% and 67% are achieved for minimum feature sizes of 106 nm and 130 nm, respectively. These gratings are also more fabrication tolerant compared to similar designs not using metamaterials.

Athermal design of integrated photonic devices can reduce the need for active temperature stabilization and consequently the energy required to operate photonic integrated circuits. For silicon photonic filters such as AWGs which employ wire or ridge waveguides, temperature insensitivity can be achieved using cladding materials with negative thermo-optic coefficients. On the other hand, in echelle grating filters the inteference takes place in the slab free-propagation region, and therefore the modal overlap with the cladding is small, rendering this method ineffective. In this work we present an approach to design an athermal echelle grating filter exploiting a temperature-synchronized Mach-Zehnder interferometer as input. This reduces the spectral shift over a temperature range of 20 K to less than ±45 pm compared to the 1.6 nm shift for the same echelle grating with a conventional waveguide input. Furthermore, the proposed design relies exclusively on a standard fabrication process for silicon-on-insulator photonic devices and exhibits a good tolerance to fabrication uncertainties.

Subwavelength grating (metamaterial) waveguide devices are becoming established as key building blocks for advanced integrated photonic circuits. In this talk we will present an overview of our recent advances in this surging field.

As data demand rises endlessly in the world, continuing exponential growth of data generation, transfer, collection, analysis, and storage is driving and shaping optical communication networks in different ways. The two most notable advances have been wavelength division multiplexing (WDM) and coherent communications, which again continue to evolve and are being combined to create even more advanced networks such as super-channel and flex-grid architectures. Semiconductor diode lasers, as light sources of these systems, must meet an ever more demanding and diverse set of technical specifications. For example, some of the new transmission schemes also require that the wavelength channels are mutually coherent, or locked together in phase.

We have developed an InAs/InP quantum dot (QD) C-band coherent comb laser (CCL) module with actively stabilized absolute wavelength and power, and channel spacing of 34.462 GHz with ± 100 ppm accuracy. The total output power is up to 46 mW. The integrated average relative intensity noise (RIN) values of the lasing spectrum and a filtered single channel at 1540.19 nm were −165.6 dB/Hz and −130.3 dB/Hz respectively in the frequency range from 10 MHz to 10 GHz. The optical linewidth of the 45 filtered individual channels between 1531.77 nm to 1543.77 nm ranged from 850 kHz to 2.16 MHz. We have also analyzed the noise behaviors of each individual channel.

4 pags., 5 figs., We present two techniques for mitigating the effects of temperature drifts in waveguide spatial heterodyne Fourier-transform on-chip spectrometers. In high-resolution devices, large optical path length differences result in an increased sensitivity to temperature variations and impose stringent requirements on the thermal stabilization system. In order to overcome this limitation, here we experimentally demonstrate two new temperature mitigation techniques based on a temperature-sensitive calibration and phase error correction. The spectrometer chip under analysis comprises an array of 32 Mach¿Zehnder interferometers fabricated on a silicon-on-insulator platform. The optical path delays are implemented as microphotonic spirals of linearly increasing length up to 3.779 cm, yielding a spectral resolution of 17 pm. We demonstrate that the degradation in retrieved spectra caused by temperature drift is effectively eliminated by temperature-sensitive calibration and phase error correction., Ministerio de Economía y Competitividad (MINECO) (FJCI-2014-22836, TEC2015-71127-C2-1-R, TEC2015-71127-C2-2-R); Comunidad de Madrid (S2013/ MIT-2790); EURAMET (H2020-MSCA-RISE-2016: SENSIBLE); EMPIR Programme (JRP-i22 14IND13- PhotInd); National Research Council Canada (NRC); Horizon 2020 Framework Programme (H2020) (734331).

Current communication networks needs to keep up with the exponential growth of today’s internet traffic, and telecommunications industry is looking for radically new integrated photonics components for new generation optical networks. We at National Research Council (NRC) Canada have successfully developed nanostructure InAs/InP quantum dot (QD) coherence comb lasers (CCLs) around 1.55 m. Unlike uniform semiconductor layers in most telecommunication lasers, in these QD CCLs light is emitted and amplified by millions of semiconductor QDs less than 60 nm in diameter. Each QD acts like an isolated light source acting independently of its neighbours, and each QD emits light at its own unique wavelength. The end result is a QD CCL is more stable and has ultra-low timing jitter. But most importantly, a single QD CCL can simultaneously produce 50 or more separate laser beams at distinct wavelengths over the telecommunications C-band. Utilizing those unique properties we have put considerable effort well to design, grow and fabricate InAs/InP QD gain materials. After our integrated packaging and using electrical feedback-loop control systems, we have successfully demonstrated ultra-low intensity and phase noise, frequency-stabilized integrated QD CCLs with the repetition rates from 10 GHz to 100 GHz and the total output power up to 60 mW at room temperature. We have investigated their relative intensity noises, phase noises, RF beating signals and other performance of both filtered individual channel and the whole CCLs. Those highly phase-coherence comb lasers are the promising candidates for flexible bandwidth terabit coherent optical networks and signal processing applications.

We propose a robust polarization rotator based on the mode-evolution mechanism. The polarization rotation in a silicon wire waveguide is achieved by forming an amorphous silicon (a-Si) overlayer and an SiO2 spacer on top of the waveguide. A strip pattern of a constant width is designed to be etched through the overlayer at a specific angle with respect to the Si waveguide. The asymmetry in the a-Si overlayer affects the waveguide mode by rotating the modal axis. This polarization rotator design is amenable to comparatively simple fabrication compatible with standard silicon photonic processing for integration. The length of the rotation section is 17 μm, and the broadband operation is achieved with a rotation efficiency higher than 90% for a wavelength range exceeding 135 nm. A maximum polarization rotation efficiency of 99.5% is predicted by calculation.

Bragg gratings are fundamental building blocks for integrated photonic circuits. In the high-index contrast silicon-on-insulator material platform, it is challenging to accurately control the grating strength and achieve narrow spectral bandwidths. Here we demonstrate a novel Bragg grating geometry utilizing a silicon subwavelength grating (SWG) waveguide with evanescently coupled periodic Bragg loading segments placed outside the SWG core. We report experimental 3 dB filter bandwidths in a range from 8 nm to 150 pm by adjusting the distance of the Bragg loading segments from the core and the relative phase shift of the segments on the two sides of the waveguide, with a structure that has a minimum feature size of 100 nm.

A planar waveguide Fourier-transform spectrometer with densely arrayed Mach-Zehnder interferometers is demonstrated. Subwavelength gratings are used to produce an optical path difference without waveguide bends. The fabricated device comprises of an array of 32 Mach-Zehnder interferometers, which produce a spatial interferogram without any moving parts, yielding a spectral resolution of 50 pm and a free-spectral range of 0.78 nm. As a result of similar propagation losses in subwavelength grating waveguides and conventional strip waveguides, loss imbalance is minimized and high interferometic extinction ratio of -25 to -30 dB is obtained. Furthermore, phase and amplitude errors arising from normal fabrication variation are compensated by the spectral retrieval process using calibration measurements.

This tutorial will cover the principles, design, fabrication and applications of subwavelength metamaterial structures in integrated optics, including a comprehensive overview of recent advances in implementations of these structures in silicon photonics.

We report our advances in development of subwavelength engineered structures for integrated photonics, specifically high-efficiency fiber-chip couplers, broadband surface grating couplers and ultra-broadband nanophotonic beam splitters.

Multimode interference couplers (MMIs) are fundamental building blocks in photonic integrated circuits. Here it is experimentally demonstrated, for the first time, a two-fold length reduction in an MMI coupler without any penalty on device performance. The design is based on a slotted 2 × 2 MMI fabricated on a commercial silicon-on-insulator (SOI) substrate. The slot is implemented with a subwavelength grating (SWG) comprising holes fully etched down to the oxide cladding, thereby allowing single etch step fabrication. The device has been designed using an in-house tool based on the Fourier Eigenmode Expansion Method. It has a footprint of only 3.5 μm x 23 μm and it exhibits a measured extinction ratio better than 15 dB within the full C-band (1530 nm‒1570 nm). SWG engineered slots thus offer excellent perspectives for the practical realization of MMIs couplers with substantially reduced footprint yet with outstanding performance.

Subwavelength engineering in silicon photonic integrated circuits is a powerful design tool that allows one to synthesize an effective photonic medium with adjustable refractive index. This creates a new degree of freedom in photonic circuit design. We present an overview of the fundamental concept and its application to address several important practical challenges in the implementation of silicon photonics as a next generation photonics platform for telecom, datacom and sensing. In particular, we report our results in developing highly efficient and broadband fiber-chip couplers for silicon photonic wire waveguides using subwavelength engineered edge coupling structures. We experimentally demonstrate a coupling efficiency of -0.4 dB and polarization independent operation for a broad spectral range exceeding 100 nm for optical fiber with a core diameter of 3.2 μm. For coupling to standard SMF-28 fiber with 10.4 μm mode field diameter we numerically demonstrate a subwavelength engineered overlayer structure composed of SiO2 and Si3N4 which exhibits an overall coupling efficiency exceeding 90%. We have also used our subwavelength structure for coupling experiments with a conventional InGaAsP/InP buried heterostructure laser at λ = 1.3 μm with a measured near field mode size of 2.1 μm×2.8 μm. Peak coupling efficiency is 1.5 dB with 1-dB alignment tolerance of approximately ±1.2 μm horizontally and ±0.8 μm vertically. We further present subwavelength engineered grating couplers fabricated in a single-etch step for the telecom (1.55 μm) and datacom (1.3 μm) wavelengths with efficiencies exceeding -0.5 dB. Further applications that will be discussed include waveguide crossings, microspectrometers, ultra-fast optical switches, athermal waveguides, evanescent field sensors, polarization rotators and colorless interference couplers., 2016 Progress in Electromagnetic Research Symposium (PIERS), August 8-11, 2016, Shanghai, China

We report our advances in development of subwavelength engineered structures for integrated photonics. This unique technology allows synthesis of an effective photonic medium with an unprecedented control of material properties, constituting a powerful tool for a designer of photonic integrated circuits. By locally engineering the refractive index of silicon by forming a pattern of holes at the subwavelength scale it is possible to manipulate the flow of light in silicon photonic waveguides. We have demonstrated a number of subwavelength engineered devices operating at telecom wavelengths, including fiber-chip couplers, waveguide crossings, WDM multiplexers, ultra-fast optical switches, athermal waveguides, evanescent field sensors, polarization rotators, transceiver hybrids and colorless interference couplers. The subwavelength metamaterial concept has been adopted by industry (IBM) for fiber-chip coupling and subwavelength engineered structures are likely to become key building blocks for the next generation of integrated photonic circuits. We present an overview of different implementations of these structures in silicon photonic integrated circuits, such as high-efficiency fiber-chip couplers, wavelength multiplexers, microspectrometers, waveguide crossovers, ultra-broadband splitters and mid-infrared waveguide components, to name a few., 2016 Progress in Electromagnetic Research Symposium (PIERS), August 8-11, 2016, Shanghai, China

We report our recent advances in development of subwavelength engineered dielectric metamaterial structures for integrated photonics., 18th International Conference on Transparent Optical Networks (ICTON), July 10 -14, 2016, Trento, Italy

In this review, we summarize and discuss our recent studies of subwavelength grating (SWG) structures for engineering the refractive index of silicon microphotonic waveguides. The SWG effect allows control of the effective refractive index of a waveguide core over a range spanning the values of the cladding material and silicon by lithographic patterning. We demonstrate this effect with the example of segmented photonic wire waveguides, which are shown to exhibit low propagation loss, and can be used to make highly efficient waveguide crossings and in-plane fiber-chip coupling structures. Other applications of SWG structures in silicon photonic waveguide devices include surface grating couplers with enhanced performance and simplified fabrication requirements, as well as a novel curved waveguide sidewall grating micro-spectrometer, in which an SWG structure fulfills a dual purpose by acting as an effective slab waveguide for diffracted light and as a lateral cladding for a channel waveguide.

Single mode silicon-on-insulator rib waveguides offer a weak lateral confinement, which makes it difficult to design high-performance multimode interference couplers (MMIs) based on these waveguides. Here, a complete design procedure for single etch step MMIs with tapered rib access waveguides is presented, which yields low excess loss (0.1 dB) and good imbalance (0.02 dB). Furthermore, polarization dependence is low, and high fabrication tolerances are achieved, especially with respect to etch depth.

First implementations of subwavelength gratings (SWGs) in silicon-on-insulator (SOI) waveguides are discussed and demonstrated by experiment and simulations. The subwavelength effect is exploited for making antireflective and highly reflective waveguide facets as well as efficient fiber-chip coupling structures. We demonstrate experimentally that by etching triangular SWGs into SOI waveguide facets, the facet power reflectivity can be reduced from 31% to 94% facet reflectivity can be achieved with square SWGs for 5 μm thick SOI waveguides. Finally, SWG fiber-chip couplers for SOI photonic wire waveguides are introduced, including design, simulation, and first experimental results.

We review the use of the oxide cladding stress-induced photoelastic effect to modify the polarization dependent properties in silicon-on-insulator (SOI) waveguide components, and highlight characteristics particular to this high index contrast (HIC) systems. The birefringence in SOI waveguides has its origin in the electromagnetic boundary conditions at the waveguide boundaries, and can be further modified by the presence of stress in the waveguiding materials. With typical stress levels in SiO2 films, which are often used as the upper cladding, the waveguide effective index can be altered anisotropically up to the order of 10−3 for ridges with heights ranging from 1 μm to 5 μm. This effect can be used effectively to counter the waveguide geometrical birefringence, allowing the waveguide cross-section profiles to be optimized for design criteria other than null geometrical birefringence. Design strategies are developed for using stress engineering to achieve a variety of functions. Polarization insensitive arrayed waveguide gratings (AWGs), polarization insensitive ring resonators, and polarization splitters and filters are demonstrated using these design principles.

International audience; We report, for the first time, on the design and experimental demonstration of fiber-chip surface grating couplers based on subwavelength grating engineered nanostructure operating in the low fiber chromatic dispersion window (around 1.3 μm wavelengths), which is of great interest for short-reach data communication applications. Our coupler designs meet the minimum feature size requirements of large-volume deep-ultraviolet stepper lithography processes. The fiber-chip couplers are implemented in a standard 220-nm-thick silicon-on-insulator (SOI) platform and are fabricated by using a single etch process. Several types of couplers are presented, specifically the uniform, the apodized, and the focusing designs. The measured peak coupling efficiency is −2.5 dB (56%) near the central wavelength of 1.3 μm. In addition, by utilizing the technique of the backside substrate metallization underneath the grating couplers, the coupling efficiency of up to −0.5 dB (89%) is predicted by Finite Difference Time Domain (FDTD) calculations.

We experimentally demonstrate a subwavelength refractive index engineered nanostructure for edge coupling, enabling a coupling efficiency of -0.4 dB and polarization independent operation for a broad spectral range exceeding 100 nm., Optical Fiber Communication Conference, March 20-24, 2016, Anaheim, CA USA

37th PIERS, Progress In Electromagnetics Research Symposium, PIERS 2016 in Shanghai, China, 8 August - 11 September, 2016 ; http://piers.org/piers2016Shanghai/, We present some of the latest developments in silicon-based Fourier-transform microspectrometers for the near and mid-infrared. The devices comprise waveguide arrays of Mach-Zehnder interferometers with linearly increasing optical path differences, enabling scan-less spectral retrieval with large radiant throughput. Resolutions down to 40pm are experimentally demonstrated. Spatial heterodyne Fourier-transform (SHFT) spectrometry is an interferometric technique which circumvents the need of moving elements and provides an increased έtendue. The SHFT scheme can be implemented with a waveguide array of Mach-Zehnder interferometers (MZI) with linearly increasing optical path differences. The high refractive index contrast of the SOI platform and the waveguide bend radius of ~ 5 μm readily allow achieving high resolutions in a reduced footprint. We report three alternative implementations of the SHFT principle in SOI waveguides. Firstly, a SHFT chip with Si-wire microphotonic spirals, reaching a resolution of 40 pm at a central wavelength near 1.5 μm. Secondly, a SHFT micro-spectrometer with subwavelength gratings for refractive index engineering of the optical delay lines. Finally, an extension of the SHFT scheme to the mid-infrared, addressing specific challenges of this spectral region such as efficient coupling and power splitting structures, and robust performance over a substantially broader free spectral range. SHFT spectrometers are promising for a wide range of applications, including chemical and biological sensing, astronomy, communications, hand-held spectroscopy, and sensing from satellites or planetary rowers. Furthermore, the resolution of these devices can be readily scaled up to very long optical delays, opening a new pathway toward possibly overcoming current resolution limits of state-of-the-art spectroscopic instruments.

The applications of cladding stress in SOI waveguide components to enhance de- vice functionality and improve fabrication tolerance are reviewed. Assisted by FEM design tools, characteristics of stress-induced efiects are studied in depth. Design strategies are developed for using stress engineering to achieve a variety of functions. Polarization insensitive arrayed waveg- uide gratings (AWGs) and ring resonators, and polarization splitters and fllters are demonstrated using these design principles.

Polarization controllers are key elements in many fields of optics, including coherent communications, optical imaging, and quantum applications. Here we present a technology-independent polarization controller scheme based on electrically tunable phase shifters and polarization rotators with largely relaxed fabrication tolerances. Using this scheme, we experimentally demonstrate a fully integrated polarization controller in the silicon-on-insulator platform that is tunable over the complete C-band and achieves a polarization extinction range of 40 dB (±20 dB ). These results constitute, to the best of our knowledge, the highest polarization extinction range achieved in a fully integrated device, and overcome the existing limitation in the trade-off between integration and performance in polarization management circuits.

We present the first experimental demonstration of a new fiber-chip grating coupler concept that exploits the blazing effect by interleaving the standard full (220 nm) and shallow etch (70 nm) trenches in a 220 nm thick silicon layer. The high directionality is obtained by controlling the separation between the deep and shallow trenches to achieve constructive interference in the upward direction and destructive interference toward the silicon substrate. Utilizing this concept, the grating directionality can be maximized independent of the bottom oxide thickness. The coupler also includes a subwavelength-engineered index-matching region, designed to reduce the reflectivity at the interface between the injection waveguide and the grating. We report a measured fiber-chip coupling efficiency of −1.3 dB , the highest coupling efficiency achieved to date for a surface grating coupler in a 220 nm silicon-on-insulator platform fabricated in a conventional dual-etch process without high-index overlays or bottom mirrors.

Surface grating couplers are fundamental components in chip-based photonic devices to couple light between photonic integrated circuits and optical fibers. In this work, we report on a grating coupler with sub-decibel experimental coupling efficiency using a single etch process in a standard 220-nm silicon-on-insulator (SOI) platform. We specifically demonstrate a subwavelength metamaterial refractive index engineered nanostructure with backside metal reflector, with the measured peak fiber-chip coupling efficiency of -0.69 dB (85.3%) and 3 dB bandwidth of 60 nm. This is the highest coupling efficiency hitherto experimentally achieved for a surface grating coupler implemented in 220-nm SOI platform.

Coupling of light to and from integrated optical circuits has been recognized as a major practical challenge since the early years of photonics. The coupling is particularly difficult for high index contrast waveguides such as silicon-on-insulator, since the cross-sectional area of silicon wire waveguides is more than two orders of magnitude smaller than that of a standard single-mode fiber. Here, we experimentally demonstrate unprecedented control over the light coupling between the optical fiber and silicon chip by constructing the nanophotonic coupler with ultra-high coupling efficiency simultaneously for both transverse electric and transverse magnetic polarizations. We specifically demonstrate a subwavelength refractive index engineered nanostructure to mitigate loss and wavelength resonances by suppressing diffraction effects, enabling a coupling efficiency over 92% (0.32 dB) and polarization independent operation for a broad spectral range exceeding 100 nm.

We present the first experimental demonstration of a new fiber-chip grating coupler concept that exploits the blazing effect by interleaving deep and shallow etch trenches to maximize directionality. The grating couplers were fabricated using both 193 nm deep-ultraviolet lithography and electron beam lithography. The measured peak fiber-chip coupling efficiency is -1.8 dB at a wavelength of 1550 nm, with a 3 dB bandwidth of 52 nm., 2015 IEEE 12th International Conference on Group IV Photonics (GFP), 2015-8-26 - 28, Vancouver, BC, Canada

We report our advances in development of subwavelength engineered waveguide structures. This unique NRC patented technology [1,2] allows synthesis of a metamaterial with an unprecedented control of material properties, constituting a powerful tool for a designer of photonic integrated circuits. We have demonstrated a number of subwavelength engineered devices operating at telecom wavelengths [3-7], for example fibre-chip couplers, waveguide crossings, WDM multiplexers, ultra-fast optical switches, athermal waveguides, evanescent field sensors, polarization rotators, transceiver hybrids and ultra-broadband interference couplers. The subwavelength metamaterial concept has been adopted by industry (IBM) for fibre-chip coupling and subwavelength structures are likely to become key building blocks for the next generation of integrated photonic circuits. Here we present an overview of recent examples of our subwavelength engineered structures, with an emphasis on couplers for optical interconnects and evanescent field sensors. We demonstrate an unprecedented control over the light coupling between optical fibers and silicon chips by constructing metamaterial couplers operating at telecom (1.55 μm) and datacom (1.3 μm) wavelengths. We also show that by subwavelength patterning of silicon-wire waveguides the field delocalization can be engineered to increase the sensitivity of evanescent field waveguide sensors [8]. Finally, we discuss some emerging applications of subwavelength engineered structures in mid-infrared photonics., 2015 17th International Conference on Transparent Optical Networks (ICTON), July 5-9, 2015, Budapest