For Very Long Baseline Interferometry high-resolution imaging of exoplanets, an astrophotonic-based aperture synthesis concept is proposed for high-resolution direct imaging of exoplanets. A silicon photonic chip incorporates microheaters and optical phase shifters for precise control of delays and phase synchronization from widely separated receivers. A satellite laser guide star with a modulated optical signal serves as a global phase reference, enabling high-speed, high-stroke phase compensation and combining. The chip's design addresses challenges such as atmospheric turbulence and phase stability in optical frequencies. The study outlines the current proof-of-concept instrument status, measured performance, chip fabrication, and routes towards photonics-enabled exoplanet imaging.
Many modern astronomical instruments rely on the optimal coupling of starlight into single-mode fibers (SMFs). For ground-based telescopes, this coupling is limited by atmospheric turbulence. We propose an integrated wavefront corrector based on silicon-on-insulator (SOI) photonics, which samples the aberrated wavefront via a microlens array (MLA). The MLA focuses the sampled wavefront onto an array of grating couplers that inject the beamlets into the single-mode waveguides of the corrector. The beams in each waveguide are then shifted in phase using thermo-optic phase shifters before combining the co-phased beams into one single-mode waveguide. In this work, we analyze the external factors that we anticipate will impact the performance of the corrector. Specifically, we study the effects of the telescope pupil function with obscuration, determine whether the corrector requires tip/tilt pre-correction, and analyze the impact of scintillation on the correction quality.
In ground-based astronomy, the ability to couple the light into single-mode fibers (SMFs) is limited by atmospheric turbulence, which prohibits the use of many astrophotonic instruments. We propose a silicon-on-insulator photonic chip capable of coherently coupling the out-of-phase beamlets from the subapertures of a telescope pupil into an SMF. The PIC consists of an array of grating couplers used to inject the light from free space into single-mode waveguides on a chip. Metalic heaters modulate the refractive index of a coiled section of the waveguides, facilitating the co-phasing of the propagating modes. The beamlets can then be coherently combined to efficiently deliver the light to an output SMF. In an adaptive optics system, the phase corrector would act as a deformable mirror commanded by a controller that takes phase measurements from a wavefront sensor. We present experimental results for the PIC tested on an AO testbed and compare the performance to simulations.
In this paper, we evaluate the viability of Cubesats as an attractive platform for lightweight instrumentation by describing a proof of concept CubeSat that houses an astrophotonic chip for transit spectroscopy-based exoplanet atmosphere gas sensing. The Twin Earth SEnsoR Astrophotonic CubesaT (TESERACT) was designed to house a correlation spectroscopy chip along with an electrical and optical system for operation. We investigate design challenges and considerations in incorporating astrophotonic instrumentation such as component integration, thermal management and optical alignment. This work aims to be a pathfinder for demonstrating that astrophotonic-based CubeSat missions can perform leading edge, targeted science in lower-cost CubeSat platforms.
Integrated photonics can be used for stable, cost-effective and precision instruments in astronomy. We present our development and testing of a silicon ring resonator as a tunable correlation filter, facilitating real-time gas contrast for specific molecules with low cross-sensitivity. Ring resonators for various gases in H-band, polarization-selective filters, and fiber-coupled prototypes are described. We present the first on-sky demonstration of silicon-on-insulator astrophotonics, and telluric CO2 absorption feature detection as a proof-of-concept using the 1.2m DAO telescope and REVOLT adaptive optics instrument. Comparisons with traditional spectrographs inform discussions on improving performance and extensions towards an observatory-class instrument for exoplanet biosignature detection.
Silicon Ring Resonators (RR) are currently being assessed by several national metrology organizations as thermometers for use in calibration laboratories and in high-accuracy commercial applications. In this paper, we summarize the results of one such assessment carried out at the National Research Council of Canada (NRC). The prototype of silicon RR thermometer (developed at NRC) was evaluated in the stirred liquid bath between 23 °C and 80 °C over the period of several years in order to get the full uncertainty budget. The combined 10-mK standard uncertainty for our RR thermometer is not only identical to the repeatability reported previously for an unpackaged RR but it also includes a contribution due to long-term drift of RR thermometer estimated over two consecutive 11-month periods. We also report the results of our on-going efforts to reduce the long-term drift by using the controlled gas atmosphere inside RR thermometer and discuss the ultimate accuracy achievable with our current setup.
Over the past 15 years since their first demonstration, subwavelength grating metamaterials in silicon photonic devices have become widely used and attracted rapidly growing research interest while also breaking into commercial applications. We will discuss recent advances in this research field, with a focus on novel components and circuits for beam steering applications, on-chip filtering and quantum optics. On-chip optical waveguides comprised of Mie resonant particle chains have only recently been demonstrated and promise to be the foundation of a new and exciting branch of integrated metamaterials research. We will review the early work in this area.
KEYWORDS: Free space optics, Modulation, Data modeling, Data transmission, Telecommunications, Atmospheric modeling, Signal attenuation, Systems modeling, Optical transmission, Fiber optic gyroscopes
The emerging technology of power-by-light enables power and data delivery over a single Free Space Optical (FSO) link for electrically isolated, interference-free remote operation. Telecom wavelength bands (λ ≈ 1550 nm) are well known for applications in data communication over optical fiber and overlap atmospheric transparency windows, extending the reach of FSO power and data systems through the air. This creates the opportunity to directionally deliver significant power (above 1mW) and high speed data wirelessly over long distances. FSO channels can experience turbulence and weather conditions that affect data and power transmission. Hence, they should be modeled and verified against measurements under varied atmospheric conditions. This will help improve model precision and robustness in predicting FSO channel performance. Accurate modeling of data transmission in FSO channels is urgently required to support the design of wireless optical communication systems for remote areas to which fiber deployment is difficult or uneconomic and instead long-range data communications between ground stations and High-Altitude Platform Systems (HAPS) may be employed. We have modelled an FSO channel transmitting data and power at 1550 and 1520 nm respectively under various meteorological conditions. The system model was developed in the commercially available OptiSystem software for modeling signals transmission. Different weather conditions translate directly to different FSO channel signal attenuations, impacting both data and power transmission. We also explore the impact of different modulation schemes such as Quadratic Amplitude Modulation (QAM), Pulse Amplitude Modulation (PAM), and Quadratic Phase Shift Keying (QPSK) on the bit error rate of the transmitted data thereby achieving the optimal required hardware design parameters. We found that QPSK is predicted to have the longest viable FSO range across all weather conditions and that power cannot be transmitted past 1 km in foggy weather.
We report on simulations carried out for an integrated phase corrector that can efficiently couple the light distorted by atmospheric turbulence into a single-mode fiber (SMF). The photonic integrated circuit (PIC) consists of a square array of surface grating couplers used to deflect the off-plane wave vector of the free-space beamlets into the plane of a single-mode waveguide in the chip. Resistive elements acting as heaters are subsequently used to stretch a coiled section of the individual waveguides and, in doing so, shift the phase of the propagating modes. With the correct phase shifts applied to the channels — each corresponding to a subaperture on a telescope pupil — the channels can be coherently combined, and the collected light can be delivered to one output SMF. In an adaptive optics (AO) system, the phase corrector would act as a deformable mirror (DM) commanded by a controller that takes phase measurements from a wavefront sensor (WFS).
For high contrast imaging, atmospheric turbulence may be sensed and corrected at very high band-width without Wavefront Sensors (WFS) or deformable mirrors using phase correcting integrated photonics devices and advanced signal processing. The overall system employs radio astronomy techniques developed for clock distribution, to sense and correct phase, and radio interferometry procedures to produce high resolution images. One of the tallest poles in high-contrast AO is the frame rate. Our simulation models estimate correction band-width can be 1-2 orders of magnitude faster than current high contrast Adaptive Optics (AO). The method employs a satellite loitering near a science object to send a coded reference laser to the telescope. We have designed and measured a 32 channel astrophotonics phase sensing and correcting device, which is low-cost and compact due to its telecommunications heritage. We are developing a prototype AO system to test the concept, first on a bench and then using a telescope pointed at sources on a tower. This paper also describes how the scheme may be extended to arrays of optical telescopes to give unprecedented micro-arcsecond resolution in the near infrared to obtain image and spectral data cubes of extrasolar planets. The method is also useful for satellite communications, and we have applied for a patent for both astronomy and communications.
Bulk optical astronomical instruments face significant cost, complexity, flexure and alignment challenges with increasing next generation telescope sizes. Astrophotonics can mitigate these issues by using compact optical fiber or chip-based instruments. Here we present the design and development of a single-mode fiber coupled optical telescope system (ARTEMIS) designed for the demonstration of novel integrated astrophotonic instrumentation. Using a 4 cm fiber collimator as a telescope, we show on-sky measurements from an integrated astrophotonic chip. We have demonstrated the ability to detect <0.002% absorption depth changes of telluric CO2 lines using a sub-centimeter scale astrophotonic correlation spectroscopy chip with the sun as a background light source. These results provide a route towards demonstrating astrophotonic instrumentation on the larger 35 cm ARTEMIS telescope for the atmospheric characterization of smaller, fainter targets such as planets.
High sensitivity spectroscopy of astronomical targets is used for determining stellar radial velocities, exoplanet detection, and even exoplanet atmosphere sensing. However, high resolution spectrographs are bulky, highly complex and expensive instruments. While this bulk optical approach is versatile, fiber optic photonic instruments can be lower cost, more compact, and simpler to parallelize for multiple targets. Here we present a low-cost fiber-based correlation spectroscopy technique which can be used for simultaneously measuring radial velocity and molecular/atomic composition of astronomical targets. The correlation is achieved using a commercial, piezoelectrically tunable fiber Fabry-Pérot (FFP) filter that can be tuned from 1520 to 1620 nm. The output of the filter is measured using a single channel photodetector and processed using a lock-in amplifier. By adjusting the bias and modulation amplitude of the transmission spectrum of the FFP filter, the device can be optimized for maximum sensitivity to a certain absorption/emission line. We perform an on-sky demonstration using a 4.25 cm telescope to detect telluric CO2 with the sun as a background light source.
Long baseline optical interferometry and aperture synthesis using ground-based telescopes can enable unprecedented angular resolution astronomy in the optical domain. However, atmospheric turbulence leads to large, dynamic phase errors between participating apertures that limit fringe visibility using telescopes arrays or subaperture configurations in a single large telescope. Diffraction limited optics or adaptive optics can be used to ensure coherence at each aperture, but correlating the phase between apertures requires high speed, high stroke phase correction and recombination that is extremely challenging and costly. As a solution, we show an alternative phase correction and beam combination method using a centimeter-scale silicon astrophotonic chip optimized for H-band operation. The 4.7x10mm silicon photonic chip is fabricated using electron beam lithography with devices with 2 up to 32 independent channels. Light is coupled into the chip using single mode fiber ribbons. An array of microheaters is used to individually tune the effective index of each spiral delay waveguides. Narrowband spectral splitters at each spatial channel divert a modulated digital reference signal from an artificial guide star off-chip for phase measurement. Science light from other wavelengths is coherently combined using on-chip beam combiners and outputted to a single waveguide. We described the role, design, fabrication and characterization of the photonic chip. This photonic phase control scheme can be applied in astronomical interferometry or optical satellite communications.
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.
Design of novel integrated photonic components often benefits from periodic geometries (either fully periodic or apodized) along the direction of light propagation, offering a wide range of capabilities including mode matching and optical rerouting. Here, we show how existing iterative methods that were originally developed for resonant nanophotonic systems in the frequency domain can be reliably used for calculation of optical Bloch modes in periodic systems in the complex wavevector domain. This method can be used for arbitrary shaped geometries and even when open boundary conditions are applied, therefore heavily impacting the fast-paced design of integrated photonic devices.
Determining the radial velocity and atmospheric composition of exoplanets is typically performed using dispersive spectroscopy. However, while this approach is versatile, spectrometers for such applications are complex, expensive and are bulky instruments. In contrast, tunable fiber-based filters are commercially available and can be used for low cost, passive remote gas sensing. In this work, we experimentally demonstrate Fabry-Pérot based correlation spectroscopy in a simple, low-cost, compact, and stable instrument package for astrophotonic gas sensing. We also show via simulation that exoplanet radial velocities can be determined simultaneously.
Photonic crystals can exhibit interesting optical properties such as peculiar dispersion, small group velocity, negative refraction and diffraction. Group velocity engineering in a certain wavelength range allows for enhanced nonlinear optical interactions, while higher light confinement achievable in photonic crystal waveguides leads to a reduced footprint for integrated photonic components. Silicon-based photonic crystals are relatively well studied,1–3 however, they are not suitable for a monolithic integration with active devices. III-V semiconductors exhibit light-emitting properties, large Kerr nonlinearity and negligible two-photon absorption in the telecommunication regime, and therefore are more suitable for frequency conversion, all-optical signal processing, laser absorption spectroscopy and microcomb generation for correlation spectroscopy applications. In this work, we theoretically investigate the design and fabrication of photonic crystal waveguides based on an airbridge Al0.18Ga0.82 slab for frequency conversion using FWM. We demonstrate a suspended Al0.18Ga0.82 layer fabricated by HF-controlled wet etching of an AlGaAs heterostructure, which selectively etched top and bottom claddings of higher aluminum concentration AlGaAs leaving behind the core suspended in air. We show, by simulations, that the group-index values of 25 over a bandwidth of 22 nm around 1590 nm in a dispersion-engineered W1 photonic crystal defect waveguide are possible enabling this device to operate in the slow-light regime where we also demonstrate a phase mismatch of nearly zero. Future designs can be optimized for longer wavelengths in the mid-infrared (MIR) as a promising platform to realize compact, slow-light enhanced integrated photonic components for sensing and wavelength conversion, thanks to the low propagation loss of AlGaAs in the MIR regime.
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.
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 in uences 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.
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.
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.
Dan Dalacu, Khaled Mnaymneh, Vera Sazonova, Philip Poole, Geof Aers, Ross Cheriton, Mike Reimer, Jean Lapointe, Pawel Hawrylak, Marek Korkusiński, Eugene Kadantsev, Robin Williams
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.
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