We seek to advance the capabilities of photonic technologies in support of ground-based infrared astronomy. Currently, observers in this field suffer from an irreducible background generated by emission from OH (hydroxyl) molecules in the upper atmosphere. However, if narrow-band notch filters could be incorporated into the optical path of astronomical instruments prior to any optical elements that would spectrally broaden such emission lines, then this background could be effectively suppressed with very little accompanying loss of signal from the astronomical sources of interest. Micron-scale ring resonators are one technology that provides a promising method of generating such notch filters. Building on our previous efforts in astrophotonic technology development, our current goals are 1) to optimize the design of ring resonators so that the notch filters they create provide greatest suppression at the wavelengths of the most prominent OH lines, and 2) to optimize the coupling of the resonator-equipped silicon devices with the input fibers (from the sky) and output fibers (to the spectrograph and detector) such that the throughput losses do not completely eliminate the signal-to-noise improvement gained from the OH suppression. Theoretical estimates show that suppression (by 20-40dB) of the most prominent OH lines improves the signal to noise of near-IR observations by a factor of 5 or more - this is similar in effect to turning a telescope with a 1m aperture into a telescope with a 5m aperture!
Microcavity exciton-polaritons based on transition metal dichalcogenide monolayers (TMDs) are a promising platform for coherent valleytronics, exhibiting valley-dependent phenomena at room-temperature. Using polarization-dependent transient reflectance, we demonstrate the valley-exclusive nature of the optical Stark effect in WS2 exciton-polaritons. We observe a simultaneous shift of both polariton branches when pump and probe are co-polarized and no appreciable shift when they are cross-polarized, demonstrating a polarization-selective stark shift in exciton-polaritons. This work highlights how the unique features of TMD exciton-polaritons can give rise to new polaritonic phenomena.
Photonic ring resonator arrays used as notch filters are a promising novel solution to improve the signal-to-noise ratio of ground-based astronomical observations by suppressing OH emission lines in the near-infrared (NIR) wavelength range (0.9-2.5 μm). We aim to fabricate a series of ring resonators connected by a waveguide, each with its resonance wavelength and full-width-half-maximum (FWHM) matched with one of the OH emission lines.
Control over the interactions between light and matter underlies many classical and quantum applications. In recent years, 2D layered semiconductors have gained prominence for optoelectronics because of their strong excitonic effects and capacity for van der Waals assembly. One of the unique features of these monolayer materials, the valley pseudospin, can be manipulated by controlling the local properties of optical fields. Here, we discuss two manifestations of this optical control across different regimes of coupling. In a strongly coupled regime, we discuss the dynamics of valley-polarized hybrid light-matter states, or exciton-polaritons, in a monolayer MoS2 embedded in a microcavity. Different dynamics of valley-polarized exciton-polaritons can be accessed with microcavity engineering by tuning system parameters such as cavity decay rate and exciton-photon coupling strength. Comparison of predictions and measurements demonstrate the ability to intentionally modify exciton-polariton valley characteristics, illustrating the microcavity as a tool for manipulating and engineering valley dynamics in 2D materials. In the weak coupling regime optical selection rules give rise to the valley-selective optical Stark shift. We discuss recent advances in probing this effect with improved sensitivity. Both of these complementary approaches show how the valley structure of monolayer materials yield interesting light-matter phenomena that allow tuning of optical properties.
KEYWORDS: Resonators, Silicon, Waveguides, Semiconducting wafers, Astronomy, Near infrared, Space telescopes, Electron beams, Linear filtering, Polarization
Photonic ring resonators used as wavelength notch filters are a promising novel solution to enable astronomical instruments to remove the signal from atmospheric OH emission in the near-infrared wavelength range. We derive design requirements from theory and finite difference time domain simulations. We find rings with radii less than 10 microns provide an adequate free spectral range for silicon nitride abd less than 3 microns for silicon. One challenge for this application is the requirement for many rings in series to suppress particular wavelengths within 0.2nm. We report progress in fabricating both silicon and silicon nitride rings for OH suppression.
Integrated optics has the potential to play a transformative role in astronomical instrumentation. It has already made a significant impact in the field of optical interferometry, through the use of planar waveguide arrays for beam combination and phase-shifting. Additionally, the potential benefits of micro-spectrographs based on array waveguide gratings have also been demonstrated.
Here we examine a new application of integrated optics, using ring resonators as notch filters to remove the signal from atmospheric OH emission lines from astronomical spectra. We also briefly discuss their use as frequency combs for wavelength calibration and as drop filters for Doppler planet searches. We discuss the theoretical requirements for ring resonators for OH suppression. We find that small radius (< 10 μm), high index contrast (Si or Si3N4) rings are necessary to provide an adequate free spectral range. The suppression depth, resolving power, and throughput for efficient OH suppression can be realised with critically coupled rings with high self-coupling coefficients.
We report on preliminary laboratory tests of our Si and Si3N4 rings and give details of their fabrication. We demonstrate high self-coupling coefficients (> 0:9) and good control over the free spectral range and wavelength separation of multi-ring devices. Current devices have Q ≈ 4000 and ≈ 10 dB suppression, which should be improved through further optimisation of the coupling coefficients. The overall prospects for the use of ring resonators in astronomical instruments is promising, provided efficient fibre-chip coupling can be achieved.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.