Deep reactive ion etched anti-reflection coatings for sub-millimeter silicon optics

Gallardo, Patricio A.; Koopman, Brian J.; Cothard, Nicholas F.; Bruno, Sarah Marie; Cortes-Medellin, German; Marchetti, Galen J.; Miller, Kevin H.; Mockler, Brenna; Niemack, Michael D.; Stacey, G. J.; Wollack, Edward J.

doi:10.1364/ao.56.002796

Cited by 16 publications

(14 citation statements)

References 31 publications

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“…For holes, a simple linear model (n eff − 1) = f Si (n Si − 1) provides a reasonable design guide, although it slightly underpredicts the index when the fill factor is small, f Si < 30%. An effective capacitor model [14,20,34] systematically underestimates the effective index for f Si > 30%. For posts, an effective capacitor model [34] provides a general guide but systematically underestimates the effective index, possibly because this static theory does not include high-frequency effects.…”

Section: B Effective Index Of Microstructured Siliconmentioning

confidence: 98%

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16:1 bandwidth two-layer antireflection structure for silicon matched to the 190–310 GHz atmospheric window

et al. 2018

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Although high-resistivity, low-loss silicon is an excellent material for THz transmission optics, its high refractive index necessitates antireflection treatment. We fabricated a wide-bandwidth, two-layer antireflection treatment by cutting subwavelength structures into the silicon surface using multi-depth deep reactive ion etching (DRIE). A wafer with this treatment on both sides has <−20 dB (<1%) reflectance over 187-317 GHz at 15°angle of incidence in TE polarization. We also demonstrated that bonding wafers introduces no reflection features above the −20 dB level (also in TE at 15°), reproducing previous work. Together these developments immediately enable construction of wide-bandwidth silicon vacuum windows and represent two important steps toward gradient-index silicon optics with integral broadband antireflection treatment.

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Section: B Effective Index Of Microstructured Siliconmentioning

confidence: 98%

“…DRIE is a mature micromachining technique that can create arbitrary patterns of deep features with aspect ratios up to 30:1. DRIE has been used in a few demonstrations of flat one-layer structures at THz frequencies [14][15][16][17][18][19]. Multi-layer structures have also been designed and fabricated at THz frequencies using DRIE.…”

Section: A Previous Workmentioning

confidence: 99%

16:1 bandwidth two-layer antireflection structure for silicon matched to the 190–310 GHz atmospheric window

et al. 2018

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“…Due to the high index of refraction of silicon (n ∼ 3.4), the other side of the mirror must be patterned with an ARC. Deep reactive ion etching (DRIE), a plasma etching process, is used to create a two-layer metamaterial ARC [12,14]. A two-layer ARC is necessary in order to provide adequate suppression of parasitic reflections across the wide bandwidth of the instrument.…”

Section: Fabry-perot Interferometermentioning

confidence: 99%

The Design of the CCAT-prime Epoch of Reionization Spectrometer Instrument

Cothard¹,

Choi²,

Duell³

et al. 2020

J Low Temp Phys

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The Epoch of Reionization Spectrometer (EoR-Spec) is an instrument module for the Prime-Cam receiver of the 6 m aperture CCAT-prime Telescope at 5600 m in Chile. EoR-Spec will perform 158 µm [CII] line intensity mapping of star-forming regions at redshifts between 3.5 and 8 (420 -210 GHz), tracing the evolution of structure during early galaxy formation. At lower redshifts, EoR-Spec will observe galaxies near the period of peak star formation -when most stars in today's universe were formed. At higher redshifts, EoR-Spec will trace the late stages of reionization, the early stages of galaxy assembly, and the formation of large-scale, three-dimensional clustering of star-forming galaxies. To achieve its science goals, EoR-Spec will utilize CCAT-prime's exceptionally low water vapor site, large field of view (∼ 5 degrees at 210 GHz), and narrow beam widths (∼ 1 arcminute at 210 GHz). EoR-Spec will be outfitted with a cryogenic, metamaterial, silicon substrate-based Fabry-Perot Interferometer operating at a resolving power (λ /∆ λ ) of 100. Monolithic dichroic arrays of cryogenic, feedhorn-coupled transition edge sensor bolometers provide approximately 6000 detectors, which are read out using a frequency division multiplexing system based on microwave SQUIDs. The novel design allows the measurement of the [CII] line at two redshifts simultaneously using dichroic pixels and two orders of the Fabry-Perot. Here we present the design and science goals of EoR-Spec, with emphasis on the spectrometer, detector array, and readout designs.

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“…Stacking multiple quarter wavelength layers provides wider bandwidth ARCs. 8 This paper discusses the development of silicon-substrate based metal mesh mirrors for use in scanning FPIs in upcoming ground (e.g. CCAT-prime 9, 10 ), air (e.g.…”

Section: Introductionmentioning

confidence: 99%

Optimizing the efficiency of Fabry-Perot interferometers with silicon-substrate mirrors

Cothard

Abe

Nikola

et al. 2018

Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation III

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We present the novel design of microfabricated, silicon-substrate based mirrors for use in cryogenic Fabry-Perot Interferometers (FPIs) for the mid-IR to sub-mm/mm wavelength regime. One side of the silicon substrate will have a double-layer metamaterial anti-reflection coating (ARC) anisotropically etched into it and the other side will be metalized with a reflective mesh pattern. The double-layer ARC ensures a reflectance of less than 1% at the surface substrate over the FPI bandwidth. This low reflectance is required to achieve broadband capability and to mitigate contaminating resonances from the silicon surface. Two silicon substrates with their metalized surfaces facing each other and held parallel with an adjustable separation will compose the FPI. To create an FPI with nearly uniform finesse over the FPI bandwidth, we use a combination of inductive and capacitive gold meshes evaporated onto the silicon substrate. We also consider the use of niobium as a superconducting reflective mesh for long wavelengths to eliminate ohmic losses at each reflection in the resonating cavity of the FPI and thereby increase overall transmission. We develop these silicon-substrate based FPIs for use in ground (e.g. CCAT-prime), air (e.g. HIRMES), and future space-based telescopes (e.g. the Origins Space Telescope concept). Such FPIs are well suited for spectroscopic imaging with the upcoming large IR/sub-mm/mm TES bolometer detector arrays. Here we present the fabrication and performance of multi-layer, plasma-etched, silicon metamaterial ARC, as well as models of the mirrors and FPIs.

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Deep reactive ion etched anti-reflection coatings for sub-millimeter silicon optics

Cited by 16 publications

References 31 publications

16:1 bandwidth two-layer antireflection structure for silicon matched to the 190–310 GHz atmospheric window

16:1 bandwidth two-layer antireflection structure for silicon matched to the 190–310 GHz atmospheric window

The Design of the CCAT-prime Epoch of Reionization Spectrometer Instrument

Optimizing the efficiency of Fabry-Perot interferometers with silicon-substrate mirrors

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