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Using photonic devices, we developed a new approach to traditional spectroscopy where the spectral cross-correlation with a template spectrum can be done entirely on-device. By creating photonic devices with a carefully designed, modulated transmission spectrum, the cross-correlation can be carried out optically without requiring any dispersion, vastly simplifying the instrument and reducing its cost. The measured correlation lag can be used for detecting atomic/molecular species within and determining the radial velocity of a particular astrophysical object. We present an overview of two design approaches that are currently being developed that use different photonic platforms: silicon and fibre-based photonics. The silicon photonic approach utilizes ring resonators that can be thermo-optically modulated to carry out the cross-correlation. The fibre approach uses customized fibre Bragg gratings (FBGs) with transmission spectra that can be strain-modulated. Both approaches have been able to detect molecular gas in a lab setting, and we are now in the process of on-sky testing. Lastly, we discuss the future for these types of devices as their simplicity opens up the possibility of developing low-cost, purpose-built multi-object or integral field spectroscopic instruments that could make significant contributions to scientific programs requiring stellar RV measurements and exoplanet detections., Comment: SPIE Proceedings, Astronomical Telescopes and Instrumentation, July 2022, 10 pages, 7 figures

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.

We show how existing iterative methods can be used to efficiently and accurately calculate Bloch periodic solutions of Maxwell’s equations in arbitrary geometries. This is carried out in the complex-wavevector domain using a commercial frequency-domain finite-element solver that is available to the general user. The method is capable of dealing with leaky Bloch mode solutions, and is extremely efficient even for 3D geometries with non-trivial material distributions. We perform independent finite-difference time-domain simulations of Maxwell’s equations to confirm our results. This comparison demonstrates that the iterative mode finder is more accurate, since it provides the true solutions in the complex-wavevector domain and removes the need for additional signal processing and fitting. Due to its efficiency, generality and reliability, this technique is well suited for complex and novel design tasks in integrated photonics, and also for a wider range of photonics problems.

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

Vision impairment caused by degenerative retinal pathologies such as age-related macular degeneration can be treated using retinal implants. Such devices receive power and data using cables passing through a permanent surgical incision in the eye wall (sclera), which increases the risk to patients and surgical costs. A recently developed retinal implant design eliminates the necessity of the implant cable using a photonic power converter (PPC), which receives optical power and data through the pupil and is directed by an ellipsoidal reflector and micro-electromechanical mirror. We present a misalignment compensation algorithm model that accounts for rigid-body motions of the reflector relative to the eye and applies the correction to the mirror coordinates in the presence of angular misalignment of the reflector. We demonstrate that up to 85% of the nominal optical power can be delivered to the implant with axial reflector misalignments up to 30 deg using the compensation algorithm.

Modern design of photonic devices is quickly and steadily departing from classical geometries to focus more and more on non-trivial structures and metamaterials. These devices are governed by a multitude of parameters and the optimal design requires to simultaneously consider different figure of merits. In this invited talk we will present our recent work on the application of machine learning tools to the multi-objective optimization of multi-parameter photonic devices. In particular, we will demonstrate the potentiality of dimensionality reduction for the analysis of the complex design space of subwavelength metamaterials devices.

Exoplanetary biosignatures, molecular compounds which indicate a likelihood of extraterrestrial life, can be detected by highly sensitive spectroscopy of starlight which passes through the atmospheres of exoplanets towards the Earth. Such sensitive measurements can only be accomplished with the next generation of telescopes, leading to a corresponding increase in cost and complexity spectrometers. Integrated astrophotonic instruments are well-suited to address these challenges through their low-cost fabrication and compact geometries. We propose and characterize an integrated photonic gas sensor which detects the correlation between the near-infrared quasi-periodic vibronic absorption line spectrum of a gas and a silicon waveguide ring resonator transmittance comb. This technique enables lock-in amplification detection for real-time detection of faint biosignatures for reduced observation timescales and rapid exoplanetary atmosphere surveys using highly compact instrumentation.

We present a comparative experimental study of three silicon photonic echelle grating demultiplexers that are integrated with a Mach-Zehnder interferometer (MZI) launch structure. By appropriate choice of the MZI configuration, the temperature induced shift of the demultiplexer channel wavelengths can be suppressed (athermal) or enhanced (super-thermal) or be controlled by an on-chip micro-heater. The latter two configurations allow the channel wavelengths to be actively tuned using lower power than possible by temperature tuning a conventional echelle demultiplexer. In the athermal configuration, the measured channel spectral shift is reduced to less than 10 pm/°C, compared to the 83 pm/°C shift for an unmodified echelle device. In super-thermal operation an enhanced channel temperature tuning rate of 170 pm/°C is achieved. Finally, by modulating the MZI phase with an on-chip heater, the demultiplexer channels can be actively tuned to correct for ambient temperature fluctuations up to 20 °C, using a drive current of less than 20 mA.

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

Subwavelength engineered metamaterial waveguides and devices are considered as fundamental building blocks for the next generation of integrated photonic circuits. Here we present an overview of recent advances in this surging field.

The optimization of complex high-dimensional photonic structures is often limited by computational resources. Current techniques based on global optimization algorithms or shape/topology inverse design treat design variables as entirely independent. However, there is often correlation between the input variables and patterns in the design outcomes. We review our strategy of using machine learning pattern recognition for building the performance map of a high-dimensional design space, thereby quickly guiding the search to a small region of interest and significantly improving the computational efficiency. This strategy is found beneficial in both forward and inverse design process flow., 2020 Photonics North (PN), May 26-28, 2020, Niagara Falls, Ontario, Series: Photonics North

We present the design of integrated astrophotonic instruments for high background atmospheric gas detection. Such instruments can be fibre-coupled to long focal length space telescopes as compact, flexure-free, instruments., Conference on Lasers and Electro-Optics/Pacific Rim 2020, August 3-5, 2020, Sydney Australia

Compact and efficient optical antennas are fundamental components for many applications, including high-density fiber-chip coupling and optical phased arrays. Here we present the design of grating-based micro-antennas with perfectly vertical emission in the 300-nm silicon-on-insulator platform. We leverage a methodology combining adjoint optimization and machine learning dimensionality reduction to efficiently map the multiparameter design space of the antennas, analyse a large number of relevant performance metrics, carry out the required multi-objective optimization, and discover high performance designs. Using a one-step apodized grating we achieve a vertical upward diffraction efficiency of almost 92% with a 3.6 $\mu {}$ m-long antenna. When coupled with an ultra-high numerical aperture fiber, the antenna exhibits a coupling efficiency of more than 81% (−0.9 dB) and a 1-dB bandwidth of almost 158 nm. The reflection generated by the perfectly vertical antenna is smaller than −20 dB on a 200-nm bandwidth centered at $\lambda$ = 1550 nm.

Spectral pattern recognition is used to measure temperature and generate calibrated wavelength/frequency combs using a single silicon waveguide ring resonator. The ring generates two incommensurate interleaving TE and TM spectral combs that shift independently with temperature to create a spectral pattern that is unique at every temperature. Following an initial calibration, the ring temperature can be determined by recognizing the spectral resonance pattern, and as a consequence the wavelength of every resonance is also known. Two methods of pattern based temperature retrieval are presented. In the first method, the ring is locked to a previously determined temperature set-point defined by the coincidence of only two specific TE and TM cavity modes. Based on a prior calibration at the set-point, the ring temperature and hence all resonance wavelengths are then known and the resulting comb can be used as a wavelength calibration reference. In this configuration, all reference comb wavelengths have been reproduced within a 5 pm accuracy across an 80 nm range by using an on-chip micro-heater to tune the ring. For more general photonic thermometry, a spectral correlation algorithm is developed to recognize a resonance pattern across a 30 nm wide spectral window and thereby determine ring temperature continuously to 50 mK accuracy. The correlation method is extended to simultaneously determine temperature and to identify and correct for wavelength calibration errors in the interrogating light source. The temperature and comb wavelength accuracy is limited primarily by the linewidth of the ring resonances, with accuracy and resolution scaling with the ring quality factor., Comment: 15 pages, 11 figures

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

Enabled by technological improvements, photonic devices and circuits are becoming increasingly more complex. Non-trivial geometries are designed to reduce device footprint, improve performance, and introduce novel functionalities. However, the number of design variables required to properly represent these geometries quickly grows, limiting the effectiveness of classical design approaches. Moreover, parameters are often strongly interdependent, restricting the use of sequential optimizations or independent parameter sweeps. Although several optimization techniques can be effective for multi-parameter design, they commonly allow to optimize for a single or a handful designs and the optimization process needs to be repeated if new performance criteria are introduced. In contrast to classical design approaches, the influences of the design parameters remain hidden as well as the general behavior of the design space. In this paper we present an extension of our recent work on the application of machine learning pattern recognition to the design of multi-parameter photonic devices. In particular, we propose using a combination of local optimization based on the adjoint method and the use of dimensionality reduction. Adjoint optimization is used multiple times to generate a small set of different designs with high performance. Dimensionality reduction is applied to analyze the relationship between these degenerate designs and identify a lower-dimensional design sub-space that includes all alternative good designs. This sub-space can be mapped for any performance criteria thus enabling informed decisions based on the relative priorities of all relevant performance specifications. As a proof of concept, we demonstrate a ten-parameter design of an integrated photonic power splitter using silicon-on-insulator technology. We identify a region of possible high performance design solutions and select two design candidates either maximizing the splitter efficiency or minimizing back-reflection., Integrated Photonics Platforms: Fundamental Research, Manufacturing and Applications, April 6-10, 2020, Online Only, France, Series: Proceedings of SPIE

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

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 ◦ .

Metamaterial engineered waveguide structures are emerging as fundamental building blocks for integrated photonics. Here we present an overview of our recent advances in this field, including fiber-chip couplers, ultra-broadband beam splitters, nanophotonic waveguides with engineered anisotropy and integrated Bragg filters., 2019 IEEE Photonics Conference (IPC), September 29 - October 3, 2019, San Antonio, TX, USA

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.

A laser-based power and data delivery scheme is described for completely wireless operation of a epiretinal prostheses. Laser steering is achieved using a single, two-axis microelectromechanical system mirror and a custom curved reflection optic are used to enable beam trajectories at different angular coordinates of the pupil. Real-time pupil detection and laser steering operation are characterized on a 3D printed robotic eye platform and optimized for maximum optical power delivery., 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

Due to Silicon (Si) material abundance and lower cost, integration of high efficiency III-V solar cells on Si substrates is of major importance for future solar energy harvesting devices. In this paper, we report on the growth optimization with a detailed characterization of epitaxial growth of crystalline GaAs on porous silicon layers (PSL), and demonstration of single-junction GaAs solar cell on PSL performances. GaAs deposition is performed on engineered porous Si surfaces with different growth temperatures. One and two-steps growth (TSG) were also investigated. X-ray diffraction demonstrated almost one order of magnitude lower threading dislocation density (TDD) of 2× 108 cm-2 for TSG process of GaAs on PSL compared to the one-step growth. Atomic Force Microscopy and Scanning Electron Microscopy showed that a reduction of growth temperature leads to surface morphology improvement. A single junction GaAs solar cell heterostructure grown by TSG and fabricated atop the porous layer, demonstrated higher open-circuit voltage (Voc) and fill factor (FF) when compared to an identical structure grown on crystalline Si (c-Si).

The design and benchtop operation of a wireless miniature epiretinal stimulator implant is reported. The implant is optically powered and controlled using safe illumination at near-infrared wavelengths. An application-specific integrated circuit (ASIC) hosting a digital control unit is used to control the implant's electrodes. The ASIC is powered using an advanced photovoltaic (PV) cell and programmed using a single photodiode. Diamond packaging technology is utilized to achieve high-density integration of the implant optoelectronic circuitry, as well as individual connections between a stimulator chip and 256 electrodes, within a 4.6 mm × 3.7 mm × 0.9 mm implant package. An ultrahigh efficiency PV cell with a monochromatic power conversion efficiency of 55% is used to power the implant. On-board photodetection circuity with a bandwidth of 3.7 MHz is used for forward data telemetry of stimulation parameters. In comparison to implants which utilize inductively coupled coils, laser power delivery enables a high degree of miniaturization and lower surgical complexity. The device presented combines the benefits of implant miniaturization and a flexible stimulation strategy provided by a dedicated stimulator chip. This development provides a route to fully wireless miniaturized minimally invasive implants with sophisticated functionalities.

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.

We present the growth of InGaN/GaN quantum dots in nanowire as solar cells on silicon (111) along with optical, electrical and morphological characterization of fabricated solar cells. Morphology of the nanowires is assessed using scanning electron microscopy. Diffuse and specular reflectivity of the nanowires are measured over the range of the solar spectrum for bare nanowires and fabricated nanowire solar cells. Quantum efficiency is measured as a function of wavelength and attributed to both band-to-band and sub-bandgap current generation. Micro-electroluminescence imaging suggests that much higher performance can be realized through improved nanowire uniformity.

The InGaAsN(Sb) material system is an attractive candidate for use in lattice-matched four-junction (4J) solar cells based on germanium substrates. Design optimizations for an InGaAsN(Sb) subcell are proposed for optimal power conversion efficiency within a 4J solar cell under a highly concentrated AM1.5D solar spectrum. The performance of the subcell is modeled using drift-diffusion simulations using Crosslight Apsys. An InGaAsN(Sb) test subcell was fabricated to obtain realistic materials parameters for the optimization of subcell performance. A thin InGaAsN(Sb) subcell is suggested for operation at 1000 Sun illumination intensities at low carrier lifetimes and mobilities.

Optoelectronic devices based on single, self-assembled semiconductor quantum dots are attractive for applications in secure optical communications, quantum computation and sensing. In this paper we show how it is possible to dictate the nucleation site of individual InAs/InP quantum dots using a directed self-assembly process, to control the electronic structure of the nucleated dots and also how to control their coupling to the optical field by locating them within the high field region of a photonic crystal nanocavity. For application within fiber networks, these quantum dots are targeted to emit in the spectral region around 1550 nm., Quantum Sensing and Nanophotonic Devices VII, January 24, 2010, San Francisco, California, USA

We present a medium-dependent quantum optics approach to describe the influence of electron-acoustic phonon coupling on the emission spectra of a strongly coupled quantum-dot cavity system. Using a canonical Hamiltonian for light quantization and a photon Green function formalism, phonons are included to all orders through the dot polarizability function obtained within the independent Boson model. We derive simple user-friendly analytical expressions for the linear quantum light spectrum, including the influence from both exciton and cavity-emission decay channels. In the regime of semiconductor cavity-QED, we study cavity emission for various exciton-cavity detunings and demonstrate rich spectral asymmetries as well as cavity-mode suppression and enhancement effects. Our technique is nonperturbative, and non-Markovian, and can be applied to study photon emission from a wide range of semiconductor quantum dot structures, including waveguides and coupled cavity arrays. We compare our theory directly to recent and apparently puzzling experimental data for a single site-controlled quantum dot in a photonic crystal cavity and show good agreement as a function of cavity-dot detuning and as a function of temperature., Comment: Regular Paper, Submitted to PRB, Dec, 2010

In this paper, we present experimental results from site-selected single quantum dots that have undergone a number of intermixing process steps via rapid thermal annealing. We show that the intermixing process blueshifts the dot's emission spectrum without affecting the linewidth as well as decreasing its biexciton binding energy and s-p shell spacing. The anisotropic exchange splitting is shown to have undergone a sign inversion implying that the splitting had gone through zero. Intermixing provides another nanoengineering tool for the design of scalable solid-state photon and entangled photon pair sources. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE)., Quantum Dots and Nanostructures: Synthesis, Characterization, and Modeling VIII, January 25-26, 2011, San Francisco, CA, USA, Series: Proceedings of SPIE; no. 7947

Self-assembled semiconductor quantum dots show great potential as efficient semiconductor-based non-classical light sources. However, due to the very nature of the self-assembled growth process, the characteristics of individual dots can vary widely and their spatial location is generally uncontrolled. Using a directed self-assembly process, the nucleation site of single quantum dots are designed through lithography. The site-control is used to facilitate the spatial alignment of single quantum dots to high finesse optical microcavities. The single dot-cavity device is a unique system to study the dot-cavity coupling where the presence of background emitters can be unambiguously ruled out. © 2011 IEEE., 2011 ICO International Conference on Information Photonics, IP 2011, 18 May 2011 through 20 May 2011, Ottawa, ON

We present a theory of valence holes as Luttinger spinor based qubits in $p$-doped self-assembled quantum dots within the four-band $k\ensuremath{\cdot}p$ formalism. The two-qubit levels are identified with the two chiralities of the doubly degenerate ground state. We show that single-qubit operations can be implemented with static magnetic field applied along the $z$ axis (growth direction) for ${\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{\ensuremath{\sigma}}}_{z}$ operation and with magnetic field in the quantum dot plane, $x$ direction, for ${\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{\ensuremath{\sigma}}}_{x}$ operation. The coupling of two dots and hence the double-qubit operations are shown to be sensitive to the orientation of the two quantum dots. For vertical qubit arrays, there exists an optimal qubit separation suitable for the voltage control of qubit-qubit interactions.

Site-selective epitaxy is used to deterministically control the nucleation site of a single quantum dot. A photonic crystal cavity is fabricated at the dot site for a true single quantum dot-cavity system which, by design, contains no background emitters. Cavity tuning at fixed temperature is used to measure the dot-cavity coupling over a large $(g15\text{ }\text{meV})$ detuning range using nonresonant excitation. The low-excitation spectra are modeled using a master equation model based on incoherent excitation. We find that pure phonon dephasing alone does not account for the observed nonresonant cavity emission and an additional cavity feeding mechanism, consistent with phonon-assisted dot-cavity coupling, must be included to reproduce the experimental spectra.