The chip-scale integration of optical spectrometers may offer new opportunities for in situ bio-chemical analysis, remote sensing, and intelligent health care. The miniaturization of integrated spectrometers faces the challenge of an inherent trade-off between spectral resolutions and working bandwidths. Typically, a high resolution requires long optical paths, which in turn reduces the free-spectral range (FSR). In this paper, we propose and demonstrate a ground-breaking spectrometer design beyond the resolution-bandwidth limit. We tailor the dispersion of mode splitting in a photonic molecule to identify the spectral information at different FSRs. When tuning over a single FSR, each wavelength channel is encoded with a unique scanning trace, which enables the decorrelation over the whole bandwidth spanning multiple FSRs. Fourier analysis reveals that each left singular vector of the transmission matrix is mapped to a unique frequency component of the recorded output signal with a high sideband suppression ratio. Thus, unknown input spectra can be retrieved by solving a linear inverse problem with iterative optimizations. Experimental results demonstrate that this approach can resolve any arbitrary spectra with discrete, continuous, or hybrid features. An ultrahigh resolution of <40 pm is achieved throughout an ultrabroad bandwidth of >100 nm far exceeding the narrow FSR. An ultralarge wavelength-channel capacity of 2501 is supported by a single spatial channel within an ultrasmall footprint (≈60 × 60 μm2), which represents, to the best of our knowledge, the highest channel-to-footprint ratio (≈0.69 μm−2) and spectral-to-spatial ratio (>2501) ever demonstrated to date.
We experimentally study the generation of optical frequency combs (OFCs) in dual-pumped high-quality factor (>106) multimode silicon racetrack resonators and show that sub-milliwatt (0.3 mW) input pump powers were sufficient to produce six-order OFC generation with eleven peaks, even in waveguides with normal dispersion. The low pump power and enhanced efficiency of the OFC generation can be attributed to mode coupling between two mode families of the multimode resonator, which acts to change the effective magnitude and the sign of the local dispersion of the resonator. We experimentally observed that the OFC generation had 3.6 times more peaks and 12.1 dB higher conversion efficiency than that without any bias. We compared the efficiencies of the OFC generation at different pump wavelengths within and beyond the mode coupling region. At low pump powers circulating in the resonator, pump wavelengths in the mode coupling regime produced 1.3 times more peaks and 8 dB enhancement in conversion efficiency than pumping beyond the mode coupling regime. The experimental results were consistent with the theoretical simulations by solving the modified Lugiato–Lefever equation.
The chip-scale miniaturization of optical spectrometers may enable many potential applications, such as wearable health monitoring, field deployable biochemical sensing, dense hyperspectral imaging, and portable optical coherence tomography. However, the widespread use of integrated spectrometers is hampered by an inherent trade-off between resolutions and bandwidths. Here, a ground-breaking design strategy is proposed to overcome the bottleneck. The most noteworthy finding in this work is that, by simultaneously leveraging temporal and spatial decorrelations, a single micro-ring resonator (MRR) can serve as a spectrometer with an ultra-high-resolution across an ultrabroad bandwidth far exceeding the narrow free spectral range (FSR). The structure is based on a tunable MRR that supports TE 0 and TE 1 transverse modes. When tuning the MRR, the unknown spectrum is scanned by dual-mode resonances in a synchronized manner. The recorded signal is formed by "splicing" the responses of TE 0 and TE 1 . Due to the intermodal dispersion, all of the wavelength channels in the transmission matrix are sufficiently decorrelated beyond the FSR limit by cross-referring two matrix halves; thus, any arbitrary spectra can be retrieved by solving a linear inverse problem with preconditioned iterative optimizations. Experimental results demonstrate an ultrahigh resolution of <80 pm across an ultrabroad working bandwidth of >100 nm, which yields an ultralarge-wavelength channel capacity of 1250. The device footprint is also as compact as 20 × 35 μm 2 . These results represent the smallest-resolution-footprint product (≈0.056 pm•mm 2 ), the highest bandwidth-to-footprint ratio (≈0.14 nm μm −2 ), and the highest channel-to-footprint ratio (≈1.79 μm −2 ) ever demonstrated.
The polarization beam splitter (PBS) is a pivotal element in the polarization management of free‐space optical instruments and systems. Photonic integrated circuits for sensing, imaging, communications, and quantum‐information processing also have needs for monolithically integrated PBSs with an ultra‐broad optical bandwidth. In this paper, a novel silicon nanophotonic PBS inspired by the crystalline Glan–Thompson prism but implemented with silicon subwavelength‐grating (SWG) metamaterials is presented. Due to the tailored artificial anisotropy of SWGs, the meta‐prism functions like a thin‐film reflector or a waveguide crossing for different polarizations. Thus, the incident light can be steered with strong polarization selectivity and negligible wavelength dependence. Unlike conventional PBS designs, the routing of polarized light is enabled by the wavelength‐independent total internal reflection in anisotropy‐engineered effective media, thereby breaking the bandwidth limit. The device footprint is as small as ≈15 × 7 µm2. Low insertion losses of 0.6–1.7 dB and high extinction ratios of 20–30 dB are experimentally achieved spanning a record broad bandwidth of over 415 nm, ranging from 1.26 to 1.675 µm wavelength. These results represent, to the best of their knowledge, the most broadband integrated PBS ever demonstrated to date.
Here, the influence of pump powers for silicon microresonator-based Kerr comb generation (KCG) was investigated theoretically and experimentally in two types of dual-pumped KCG. One employs dual pumps at different free spectral range (FSR) spacings of the resonator for broadband comb spectrum and the other to produce comb lines at one FSR spacing for low pump powers. The KCG is modeled by including nonlinear absorption and mode interaction into the Lugiato–Lefever equation. Both the theoretical and the experimental results indicate that the KCG with pump powers inside the ring of tens of milliwatts would be limited by high nonlinear absorption even with a 25 V reverse bias to deplete free carriers. The most efficient comb spectrum occurs with recirculating pump power in the ring cavity of 13 mW (0.3 mW pump power in the bus waveguide) at 25 V reverse bias. Generally, for silicon KCG at the telecom wavelengths, the use of low pump powers and reverse bias is essential. At 25 V reverse bias, increasing the stored pump power in the ring to 160 mW would suppress the KCG and produce a similar number of comb lines as 1 mW recirculating pump power. This work advances our understandings of silicon KCG in the telecom band.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.