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1. Experimental demonstration of a concave grating for spin waves in the Rowland arrangement

   https://doi.org/10.1038/s41598-021-93700-z  

   Papp, Ádám; Kiechle, Martina; Mendisch, Simon; Ahrens, Valentin; Sahin, Levent; Seitner, Lukas; Porod, Wolfgang; Csaba, Gyorgy; Becherer, Markus (July 2021, Scientific Reports)

   Abstract We experimentally demonstrate the operation of a Rowland-type concave grating for spin waves, with potential application as a microwave spectrometer. In this device geometry, spin waves are coherently excited on a diffraction grating and form an interference pattern that focuses spin waves to a point corresponding to their frequency. The diffraction grating was created by focused-ion-beam irradiation, which was found to locally eliminate the ferrimagnetic properties of YIG, without removing the material. We found that in our experiments spin waves were created by an indirect excitation mechanism, by exploiting nonlinear resonance between the grating and the coplanar waveguide. Although our demonstration does not include separation of multiple frequency components, since this is not possible if the nonlinear excitation mechanism is used, we believe that using linear excitation the same device geometry could be used as a spectrometer. Our work paves the way for complex spin-wave optic devices—chips that replicate the functionality of integrated optical devices on a chip-scale. 

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2. High-resolution and compact serpentine integrated grating spectrometer

   https://doi.org/10.1364/JOSAB.423968  

   Brand, Michael; Zhang, Bohan; Onural, Deniz; Al_Qubaisi, Kenaish; Popović, Miloš; Dostart, Nathan; Wagner, Kelvin (June 2021, Journal of the Optical Society of America B)

   Integrated astrophotonic spectrometers are integrated variants of conventional free-space spectrometers that offer significantly reduced size, weight, and cost and immunity to alignment errors, and can be readily integrated with other astrophotonic instruments such as nulling interferometers. Current integrated dispersive astrophotonic spectrometers are one-dimensional devices such as arrayed waveguide gratings or planar echelle gratings. These devices have been limited to ${10}^4$resolving powers and $<<\#comment/>1000$spectral bins due to having limited total optical delay paths and 1D detector array pixel densities. In this paper, we propose and demonstrate a high-resolution and compact astrophotonic serpentine integrated grating (SIG) spectrometer design based on a 2D dispersive serpentine optical phased array. The SIG device combines a 5.2 cm long folded delay line with grating couplers to create a large optical delay path along two dimensions in a compact integrated device footprint. Analogous to free-space crossed-dispersion high-resolution spectrometers, the SIG spectrometer maps spectral content to a 2D wavelength-beam-steered folded-raster emission pattern focused onto a 2D detector array. We demonstrate a SIG spectrometer with $\sim <\#comment/>100\mathrm{k}$resolving power and $\sim <\#comment/>6750$spectral bins, which are approximately an order of magnitude higher than previous integrated photonic designs that operate over a wide bandwidth, in a $0.4{\mathrm{m}\mathrm{m}}^2$footprint. We measure a Rayleigh resolution of $1.93\pm <\#comment/>0.07\mathrm{G}\mathrm{H}\mathrm{z}$and an operational bandwidth from 1540 nm to 1650 nm. Finally, we discuss refinements of the SIG spectrometer that improve its resolution, bandwidth, and throughput. These results show that SIG spectrometer technology provides a path towards miniaturized, high-resolution spectrometers for applications in astronomy and beyond. 

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3. CubeSat Format 3-Mirror Spectrometer Designed with Freeform Surfaces

   Lui, Y; Bauer, A; Rolland, J (May 2019, Optical Design and Fabrication 2019 (Freeform, OFT))

   CubeSats are a type of miniaturized satellites that consist of 10×10×10 cm cubic units (1U), which is established as a standard by Jordi Puig-Suari and Robert Twiggs in 1999 to push low-cost educational and industrial space experimentation [1]. In recent years the CubeSat format has gained popularity for research and industrial purposes including Earth imaging, communication and technology demonstration. High performing optical systems such as spectrometers and imagers that can be contained in CubeSat format are also desired in many space missions. In this paper, a design study is conducted for a 3-mirror spectrometer based on the reflective triplet design form that is fully contained in 1U space. As shown in Fig. 1, the spectrometer consists of three mirrors and a plane grating serving as the aperture stop. Light from a slit enters the system and travels through the three mirrors to the grating where it is dispersed and reflected. The light then travels back through the system in reverse to the detector near the slit which results in a 2D image (or spectrum). To show the freeform advantage, we compared two designs of this spectrometer - one designed with freeform surfaces and the other with off-axis aspheres. 

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4. Monolithic dual-wedge prism-based spectroscopic single-molecule localization microscopy

   https://doi.org/10.1515/nanoph-2021-0541  

   Song, Ki-Hee; Brenner, Benjamin; Yeo, Wei-Hong; Kweon, Junghun; Cai, Zhen; Zhang, Yang; Lee, Youngseop; Yang, Xusan; Sun, Cheng; Zhang, Hao F. (January 2022, Nanophotonics)

   By manipulating the spectral dispersion of detected photons, spectroscopic single-molecule localization microscopy (sSMLM) permits concurrent high-throughput single-molecular spectroscopic analysis and imaging. Despite its promising potential, using discrete optical components and managing the delicate balance between spectral dispersion and spatial localization compromise its performance, including non-uniform spectral dispersion, high transmission loss of grating, high optical alignment demands, and reduced precision. We designed a dual-wedge prism (DWP)-based monolithic imaging spectrometer to overcome these challenges. We optimized the DWP for spectrally dispersing focused beam without deviation and with minimal wavefront error. We integrated all components into a compact assembly, minimizing total transmission loss and significantly reducing optical alignment requirements. We show the feasibility of DWP using ray-tracing and numerical simulations. We validated our numerical simulations by experimentally imaging individual nanospheres and confirmed that DWP-sSMLM achieved much improved spatial and spectral precisions of grating-based sSMLM. We also demonstrated DWP-sSMLM in 3D multi-color imaging of cells. 

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5. Miniaturized integrated spectrometer using a silicon ring-grating design

   https://doi.org/10.1364/OE.424443  

   Alshamrani, Naif; Grieco, Andrew; Hong, Brandon; Fainman, Yeshaiahu (May 2021, Optics Express)

   We introduce and experimentally demonstrate a miniaturized integrated spectrometer operating over a broad bandwidth in the short-wavelength infrared (SWIR) spectrum that combines an add-drop ring resonator narrow band filter with a distributed Bragg reflector (DBR) based broadband filter realized in a silicon photonic platform. The contra-directional coupling DBR filter in this design consists of a pair of waveguide sidewall gratings that act as a broadband filter (i.e., 3.9 nm). The re-directed beam is then fed into the ring resonator which functions as a narrowband filter (i.e., 0.121 nm). In this scheme the free spectral range (FSR) limitation of the ring resonator is overcome by using the DBR as a filter to isolate a single ring resonance line. The overall design of the spectrometer is further simplified by simultaneously tuning both components through the thermo-optic effect. Moreover, several ring-grating spectrometer cells with different central wavelengths can be stacked in cascade in order to cover a broader spectrum bandwidth. This can be done by centering each unit cell on a different center wavelength such that the maximum range of one-unit cell corresponds to the minimum range of the next unit cell. This configuration enables high spectral resolution over a large spectral bandwidth and high extinction ratio (ER), making it suitable for a wide variety of applications. 

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