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.
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.
In this Letter, we propose and demonstrate an integrated mode-size converter (MSC) with a compact footprint, low losses, and a broad bandwidth. By exploiting a parabolic mirror, the divergent light from a narrow waveguide (450 nm) is collimated to match the mode size of a wide waveguide (10 µm). The measured insertion loss (IL) is ≈ 0.15 dB over a 100-nm bandwidth. The mode-size conversion is achieved with a footprint as small as ≈ 20 × 32 µm2, which is much shorter than the linear taper length required to attain the same level of losses.
We propose and demonstrate a silicon photonic integrated circuit (PIC) for exciting different spatial modes launched into a multimode-fiber (MMF) speckle imaging system. The PIC consists of a 45-channel optical phased array (OPA) and an array of nanoantennas to bridge the PIC and MMF. The nanoantenna array can excite a wide range of spatial modes in the MMF, with a mode-group dependent loss of less than 3 dB. A high spatial resolution, which approaches the theoretical limit determined by the number of modes in the MMF, is realized by using the proposed PIC. An equivalent resolution of 1.75 μm is experimentally attained across a field of view of 105 μm. Two different algorithms for image reconstruction are compared. The algorithm based on truncated singular value decomposition is computationally efficient and suitable for real-time image reconstruction, whereas the algorithm based on total-variation regularization produces higher imaging quality. The number of resolvable points is derived to be ~3000, which is more than the square of the number of phase shifters. These results represent the highest spatial resolution yet demonstrated in a PIC-based MMF imaging system.
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.