Low-loss integrated photonics for the blue and ultraviolet regime

Abstract

We present a low-loss integrated photonics platform in the visible and near ultraviolet regime. Fully-etched waveguides based on atomic layer deposition (ALD) of aluminum oxide operate in a single transverse mode with <3 dB/cm propagation loss at a wavelength of 371 nm. Ring resonators with intrinsic quality factors exceeding 470,000 are demonstrated at 405 nm, and the thermo optic coefficient of ALD aluminum oxide is estimated to be 2.75 × 10 −5 [RIU/ • C]. Absorption loss is sufficiently low to allow on-resonance operation with intracavity powers up to at least 12.5 mW, limited by available laser power. Experimental and simulated data indicates the propagation loss is dominated by sidewall roughness, suggesting lower loss in the blue and UV is achievable. I. INTRODUCTIONThe success of silicon photonics in telecommunications has lead to the application of nano-scale photonics in a variety of fields including computing, nonlinear optics, quantum information processing, and biochemical sensing 1-5 . Compact device footprints and an ability to leverage the same manufacturing techniques employed in the semiconductor industry are strong incentives both for systems designers and in applications where low cost is necessary. Label-free biosensors, optical interconnects for computers and datacenters, integrated lasers with III-V gain media, and phased arrays consisting of thousands of elements have all been demonstrated using the same basic silicon photonic technology 1,5-8 . However, with a bandgap at 1.1 um, silicon is unsuitable for applications which require visible or ultraviolet light, such as optogenetics 9,10 , protein sensing 11,12 , and atom-based sensing, time-keeping, and information processing [13][14][15][16] . A straightforward way of bypassing this limitation is to use silicon nitride, commonly integrated alongside silicon, which has transparency into the visible. Waveguide platforms based on silicon nitride are quite mature, particularly for red and near infrared (NIR) wavelengths. Less progress has been made for devices operating in the blue and near ultraviolet (UV, NUV). This is predominantly due to the high material absorption (>20 dB/cm) that begins in the low 400 nm wavelength range 17 .The most common alternative to silicon nitride for ultraviolet photonics are the III-V nitride materials, particularly aluminum nitride (AlN) and aluminum-gallium nitride alloys (AlGaN) 18 . AlN has a bandgap corresponding to λ ∼ 200 nm and exhibits second-order nonlinearities, making it attractive for integrated nonlinear optics and electrical tuning of reso-2 nant structures. Early demonstrations of ultraviolet waveguides in AlN suffered extremely high loss (389 dB/cm at a wavelength λ = 450 nm) due to a combination of bulk (polycrystalline) material loss and high sidewall roughness 19 . More recent work using nanocrystalline AlN has brought the loss coefficient down by an order of magnitude (∼50 dB/cm at λ = 405 nm) but in a regime where device size is restricted to sub-centimeter or sub-millimeter lengths when s...

Multilayer ion trap technology for scalable quantum computing and quantum simulation

“…These same techniques could be applied to realize so-called analog quantum simulators in ion trap arrays [32][33][34], possibly with integrated control [35]. Moreover, such an approach may enable the embedding of complex integrated components such as trench capacitors [36,37], low-loss integrated waveguides [38]; or the realization of more elaborate devices including reliable iontransport junctions [39,40], increased optical access [17] or manipulation of scalable arrays of two-dimensional trapped ion systems [33,34].…”

Visible-light silicon nitride waveguide devices and implantable neurophotonic probes on thinned 200 mm silicon wafers

“…This may be due to the higher refractive index of the LPCVD SiN causing increased sidewall scattering. This may also be due to the absorption mechanism noted in [9] at wavelengths close to and below 400 nm. However, since the exact roughness of each wafer was not quantified, variations in roughness between the wafers may also contribute to this observation.…”

“…In [5] on 200 mm wafers, single-mode SiN waveguides formed by plasma enhanced chemical vapour deposition (PECVD) exhibited a loss of about 1 dB/cm at a wavelength of 532 nm. In [8,9], SiN waveguide losses ≤ 20.7 dB/cm and Al 2 O 3 waveguide losses ≤ 1.6 dB/cm were observed at 4 discrete wavelengths between 405 nm and 458 nm; losses as low as 4.8 and 0.6 dB/cm were observed at 458 nm for the SiN and Al 2 O 3 waveguides, respectively. Although SiN generally exhibited higher losses than Al 2 O 3 in that demonstration, the CMOS compatibility and fabrication maturity of SiN makes it a promising material for further development for visible light integrated photonics platforms.…”

“…To date, single-mode visible light waveguides have been demonstrated using SiN [5][6][7] and alumina (Al 2 O 3 ) [8,9] on 200 mm or 300 mm Si wafers, and using aluminum nitride (AlN) with chip-scale fabrication [10]. However, in all of these demonstrations, waveguide losses were only reported at discrete wavelengths, and complete, continuous waveguide loss spectra were not obtained.…”

Al2O3:Yb3+ integrated microdisk laser label-free biosensor

“…Aluminum oxide (Al 2 O 3 ) is an emerging photonic material that exhibits a large transparency window covering the visible and near-infrared wavelength ranges [14]. When doped with rare-Earth ions, it provides optical gain that has been used to demonstrate on-chip amplifiers [15] and lasers [16,17].…”