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Optics Letters Jul 2024Photonic stepped-frequency radars based on optical frequency-shifting modulation have shown attractive properties such as wide bandwidth, centimeter range resolution,...
Photonic stepped-frequency radars based on optical frequency-shifting modulation have shown attractive properties such as wide bandwidth, centimeter range resolution, inherent frequency-time linearity with low spectrum spurs, and reduced system complexity. However, existing approaches typically exhibit meter- or centimeter-level radar range ambiguity, inversely proportional to the frequency step, due to the large frequency shift determined by acousto-optic or electro-optic (EO) modulators. Here, we overcome this limitation by injecting a narrowband, stepped-frequency signal into an optical frequency-shifting fiber cavity to achieve, for the first time, to our knowledge, a broadband photonic stepped-frequency radar with 150-m unambiguous detection and centimeter range resolution, surpassing the reported photonic- and electronic-based counterparts. The demonstrated approach effectively resolves the trade-off between ambiguity range and shifting frequency while maintaining the signal quality and bandwidth, bringing its practicality into reach for outdoor applications.
PubMed: 38950275
DOI: 10.1364/OL.530772 -
Optics Letters Jul 2024Open-top light-sheet (OTLS) microscopy offers rapid 3D imaging of large optically cleared specimens. This enables nondestructive 3D pathology, which provides key...
Open-top light-sheet (OTLS) microscopy offers rapid 3D imaging of large optically cleared specimens. This enables nondestructive 3D pathology, which provides key advantages over conventional slide-based histology including comprehensive sampling without tissue sectioning/destruction and visualization of diagnostically important 3D structures. With 3D pathology, clinical specimens are often labeled with small-molecule stains that broadly target nucleic acids and proteins, mimicking conventional hematoxylin and eosin (H&E) dyes. Tight optical sectioning helps to minimize out-of-focus fluorescence for high-contrast imaging in these densely labeled tissues but has been challenging to achieve in OTLS systems due to trade-offs between optical sectioning and field of view. Here we present an OTLS microscope with voice-coil-based axial sweeping to circumvent this trade-off, achieving 2 µm axial resolution over a 750 × 375 µm field of view. We implement our design in a non-orthogonal dual-objective (NODO) architecture, which enables a 10-mm working distance with minimal sensitivity to refractive index mismatches, for high-contrast 3D imaging of clinical specimens.
Topics: Imaging, Three-Dimensional; Humans; Microscopy; Staining and Labeling; Light
PubMed: 38950270
DOI: 10.1364/OL.521591 -
Optics Letters Jul 2024Photonics in the ultraviolet provides an avenue for key advances in biosensing, pharmaceutical research, and environmental sensing. However, despite recent progress in...
Photonics in the ultraviolet provides an avenue for key advances in biosensing, pharmaceutical research, and environmental sensing. However, despite recent progress in photonic integration, a technological solution to fabricate photonic integrated circuits (PICs) operating in the UV-C wavelength range, namely, between 200 and 280 nm, remains elusive. Filling this gap will open opportunities for new applications, particularly in healthcare. A major challenge has been to identify materials with low optical absorption loss in this wavelength range that are at the same time compatible with waveguide design and large-scale fabrication. In this work, we unveil that thermal silicon oxide (TOX) on a silicon substrate is a potential candidate for integrated photonics in the UV-C, by removing the silicon substrate under selected regions to form single-side suspended ridge waveguides. We provide design guidelines for low-loss waveguide geometries, avoiding wrinkling due to residual intrinsic stress, and experimentally demonstrate waveguides that exhibit optical propagation losses below 3 and 4 dB/cm at a wavelength of 266 nm with claddings of air and water, respectively. This result paves the way for on-chip UV-C biological sensing and imaging.
PubMed: 38950267
DOI: 10.1364/OL.530364 -
Optics Letters Jul 2024We propose a scheme for realizing nonreciprocal microwave photon routing with two cascaded magnon-cavity coupled systems, which work around the exceptional points of a...
We propose a scheme for realizing nonreciprocal microwave photon routing with two cascaded magnon-cavity coupled systems, which work around the exceptional points of a parity-time (PT)-symmetric Hamiltonian. An almost perfect nonreciprocal transmission can be achieved with a broad bandwidth, where the transmission for a forward-propagating photon can be flexibly controlled with the backpropagating photon being isolated. The transmission or isolated direction can be reversed via simply controlling the magnetic field direction applied to the magnons. The isolation bandwidth is improved by almost three times in comparison with the device based on a single PT-symmetric system. Moreover, the effect of intrinsic cavity loss and added thermal noises is considered, confirming the experimental feasibility of the nonreciprocal device and potential applications in quantum information processing.
PubMed: 38950266
DOI: 10.1364/OL.528451 -
Optics Letters Jul 2024Ultrashort ultraviolet (UV) pulses are pivotal for resolving ultrafast electron dynamics. However, their efficient generation is strongly impeded by material dispersion...
Ultrashort ultraviolet (UV) pulses are pivotal for resolving ultrafast electron dynamics. However, their efficient generation is strongly impeded by material dispersion and two-photon absorption, in particular, if pulse durations around a few tens of femtoseconds or below are targeted. Here, we present a new (to our knowledge) approach to ultrashort UV pulse generation: using the fourth-harmonic generation output of a commercial ytterbium laser system delivering 220 fs UV pulses, we implement a multi-pass cell (MPC) providing 5.6 µJ pulses at 256 nm, compressed to 30.5 fs. Our results set a short-wavelength record for MPC post-compression while offering attractive options to navigate the trade-off between upconversion efficiency and acceptance bandwidth for UV pulse production.
PubMed: 38950263
DOI: 10.1364/OL.527988 -
Optics Letters Jul 2024We experimentally investigate the coherently controllable generation and annihilation of a pseudospin-induced optical vortex in an optically induced honeycomb photonic...
We experimentally investigate the coherently controllable generation and annihilation of a pseudospin-induced optical vortex in an optically induced honeycomb photonic lattice in a Λ-type Rb atomic vapor cell. Three Gaussian coupling beams are coupled into the atomic gases to form a hexagonal interference pattern, which can induce a honeycomb photonic lattice under electromagnetically induced transparency. Then, two probe beams interfere with each other to form periodical fringes and cover one set of sublattice in the honeycomb lattice, corresponding to excite the K or K' valleys in momentum space. By properly adjusting the experimental parameters, the generation and annihilation of the induced optical vortex can be effectively controlled. The theoretical simulations based on the Dirac and Schrödinger equations are performed to explore the underlying mechanisms, which will support the observations. The demonstrated properties of such controllable optical vortex may lay the foundation for the design of vortex-based optical devices with multidimensional tunability.
PubMed: 38950259
DOI: 10.1364/OL.527186 -
Optics Letters Jul 2024An approach for continuous tuning of on-chip optical delay with a microring resonator is proposed and demonstrated. By introducing an electro-optically tunable waveguide...
An approach for continuous tuning of on-chip optical delay with a microring resonator is proposed and demonstrated. By introducing an electro-optically tunable waveguide coupler, the bus waveguide to the resonance coupling can be effectively tuned from the under-coupling regime to the over-coupling regime. The optical delay is experimentally characterized by measuring the relative phase shift between lasers and shows a large dynamic range of delay from -600 to 600 ps and an efficient tuning of delay from -430 to -180 ps and from 40 to 240 ps by only a 5 V voltage.
PubMed: 38950255
DOI: 10.1364/OL.519479 -
Optics Letters Jul 2024A material platform that excels in both optical second- and third-order nonlinearities at a telecom wavelength is theoretically and experimentally demonstrated. In this...
A material platform that excels in both optical second- and third-order nonlinearities at a telecom wavelength is theoretically and experimentally demonstrated. In this TiN-based coupled metallic quantum well structure, electronic subbands are engineered to support doubly resonant inter-subband transitions for an exceptionally high second-order nonlinearity and provide single-photon transitions for a remarkable third-order nonlinearity within the 1400-1600 nm bandwidth. The second-order susceptibility χ reaches 2840 pm/V at 1440 nm, while the Kerr coefficient n arrives at 2.8 × 10cm/W at 1460 nm. The achievement of simultaneous strong second- and third-order nonlinearities in one material at a telecom wavelength creates opportunities for multi-functional advanced applications in the field of nonlinear optics.
PubMed: 38950252
DOI: 10.1364/OL.528340 -
Optics Letters Jul 2024A stable photonic delay line with large and tunable delay is essential for large-distance simulation, beamforming, and diverse photonic signal processing applications....
A stable photonic delay line with large and tunable delay is essential for large-distance simulation, beamforming, and diverse photonic signal processing applications. Here, we demonstrate a fiber-based tunable photonic delay line (TPDL) with a maximum delay of 905 µs. Its environmental-related delay jitter is compensated for by a homodyne phase-locked loop (PLL). Precise delay tuning is realized by changing the phase of the reference with a minimum tuning step of 0.5 ps without breaking its locking state. The demonstrated delay line shows exceptional stability, as indicated by an overlapping Allan deviation (ADEV) of 2.06 × 10 at the averaging time of 1000 s and the delay jitter below 20 fs. Its high stability, wide delay range, wideband characteristics, and precise tunability make the TPDL an ideal photonic delay line for the above-mentioned applications.
PubMed: 38950244
DOI: 10.1364/OL.529187 -
Optics Letters Jul 2024This study explores the manipulation of photonic nanojets (PNJs) via axial illumination of cylindrical dielectric particles with cylindrical vector beams (CVBs). The...
This study explores the manipulation of photonic nanojets (PNJs) via axial illumination of cylindrical dielectric particles with cylindrical vector beams (CVBs). The edge diffraction effect of cylindrical particles is harnessed to achieve the near-field focusing of CVBs, minimizing the spherical aberration's impact on the quality of the PNJ. By discussing how beam width, refractive index, and particle length affect PNJs under radially polarized incidence, a simple and effective approach is demonstrated to generate rod-like PNJs with uniform transmission distances and super-diffraction-limited PNJs with pure longitudinal polarization. Azimuthal polarization, on the other hand, generates tube-like PNJs. These PNJs maintain their performance across scale. Combining edge diffraction with CVBs offers innovative PNJ modulation schemes, paving the way for potential applications in particle trapping, super-resolution imaging, photo-lithography, and advancing mesotronics and related fields.
PubMed: 38950241
DOI: 10.1364/OL.528111