Optics letters最新文献

We present a coaxial fiber probe that integrates optical coherence tomography ranging and fiber Bragg grating force sensing within a single-mode fiber, enabling synchronized distance-force feedback for minimally invasive interventions. A short no-core and graded-index fiber segment forms a weakly focused beam, extending the depth of focus while maintaining the probe's miniature and intrinsically aligned design. Proof-of-concept experiments first demonstrate endoscopic palpation, where the probe distinguishes stiff inclusions from surrounding tissue, and then subretinal injection, where contact and puncture are simultaneously detected as changes in distance and force. This compact coaxial architecture provides a scalable platform for integrated optical sensing in robotic microsurgery and other precision manipulation tasks.

Achieving multidimensional modulation and analysis of breathers in a local nonlinear medium is a highly significant research area. We present what we believe is the first investigation of space-time odd-symmetric Butterfly (STOSB) wave packets in a local nonlinear medium, focusing on their odd-symmetric focus and focal length control. Meanwhile, a completely new modulation method for breathers is proposed that can alter the intensity distribution of breathers in the X-Y plane while leaving the intensity distribution in the X-T and Y-T planes unchanged. Furthermore, both the unique self-healing capability of breathers in STOSB wave packets when obstructed by barriers and the variation trend of the waist diameter are discussed. Our work develops spatiotemporal wave packets with multidimensional modulation and self-healing functions and advances the basic research on breathers in fields such as optical communication.

An all-solid-state single-frequency 248 nm deep-ultraviolet (DUV) source with watt-level (~1.2 W) average power was realized by sum-frequency generation (SFG) between 355 nm and 827 nm lasers, which is nearly one order-of-magnitude higher than our previous result [Opt. Lett.50, 1881 (2025)10.1364/OL.553247]. For this advancement, pulsed pumping was employed to increase the pulse energy of the 1064-nm fundamental driver. Meanwhile, simulation-guided optimization on the length of the LBO crystal was performed to maximize the conversion efficiency of the 827-nm optical parametric oscillator (OPO). Benefiting from both, the conversion efficiency from 1064 nm to 248 nm source was improved from 1.41% to 3.93% at 4 kHz. The beam quality factors M² in the x and y directions were measured to be 1.61 and 1.10, respectively, and the linewidth was estimated to be ~270 MHz. To the best of our knowledge, this is the first watt-level output reported for all-solid-state single-frequency 248 nm source.

Nonreciprocal transport is indispensable for many modern optical devices. However, traditional nonreciprocal devices heavily depend on external bias. Achieving significant nonreciprocity in practice remains challenging. In this work, we propose a Kerr-nonlinearity-based design to achieve strong nonreciprocal transmission. By leveraging high-Q guided-mode resonances (GMRs) in a Si waveguide nanostructure decorated with periodic grooves, we demonstrate magnetic-free bidirectional nonreciprocal transmission and isolation. A large nonreciprocal intensity range (NRIR ≈ 3.7) is achieved through parameter tuning under the low pump intensity. Simultaneously, high-performance bidirectional isolation behaviors are realized including an isolation of 71.16 dB with 2.59 dB insertion loss for forward transmission and an isolation of 80.98 dB with 1.62 dB insertion loss for reverse transmission. This design offers a versatility for applications in optical communication, optical switches, and bidirectional nonreciprocal devices.

This study demonstrates, to the best of our knowledge, a record-breaking 6.8 W all-fiber laser operating at 3795 nm. The monolithic resonator integrates a 5-meter-long lightly doped Er^³+:ZrF₄ fiber (1 mol.%) and femtosecond laser direct-written fiber Bragg gratings (FBGs). A slit-assisted beam-shaping technique enabled the fabrication of ultra-low-loss FBG pairs (97% high-reflective, 60% low-reflective at 3795 nm, total insertion loss: 0.2 dB), reducing sensitivity to the laser power before slit modulation during inscription. Notably, we experimentally observed the coexistence of 3795 nm lasing and 2796 nm parasitic lasing and subsequently investigated the conditions enabling simultaneous dual-wavelength operation as well as effective suppression strategies for parasitic oscillations.

Holographic polymer-dispersed liquid crystal (HPDLC) gratings have great potential for applications in displays and data storage due to their exceptional optical modulation capabilities. Since their optical performance strongly depends on the phase separation between the polymer and liquid crystal (LC) induced by the photopolymerization, it is essential for improving the performance of HPDLC through the photokinetic aspect. In this work, we report (for the first time, to our knowledge) an enhanced HPDLC grating by using the reversible addition-fracture chain transfer (RAFT) agent. Experimental results show that a p-polarization diffraction efficiency (η) of 84% and a refractive index modulation (Δn) as high as 0.07 with the addition of RAFT are achieved in a 3-μm HPDLC grating. Significantly, comparing with the undoped grating, this corresponds to a near two-fold enhancement on η and an improvement of 62% on Δn. Moreover, we confirm that an increase in the size of LC-rich phase leads to a decreasing in the threshold voltage. We believe that the enhancement of HPDLC performance by RAFT provides an effective path to optimize the holographic photopolymer materials for uses of AR display and holographic data storage.

We demonstrate high harmonic generation beyond the water window using an intense infrared light source operating at 2000 nm in lithium niobate-based optical parametric chirped-pulse amplification by using an Yb:YAG thin-disk laser as a pump. The output pulses from the parametric amplifier (pulse energy: 1.68 mJ, wavelength: 1750-2500 nm, repetition rate: 5 kHz) are temporally compressed with an efficiency of 79% (1.32-mJ compressed pulse) down to 19.5 fs, which corresponds to the 2.9-cycle duration. The generated soft x-ray harmonics have been employed to measure x-ray absorption near-edge structure around the K edges of carbon, nitrogen, and oxygen, with acquisition times short enough to enable practical applications in time-resolved soft x-ray spectroscopy.

Unidirectional electromagnetic modes, as an extreme regime of wave propagation, enable extraordinary and counterintuitive optical effects. These modes are typically realized as tightly confined surface waves in photonic crystals or materials with topologically nontrivial bandgaps. Here, we show that a structure comprising a magnetized semiconductor layer sandwiched between electro- and magneto-opaque materials can support unidirectional bulk magnetoplasmons at terahertz frequencies, in which all field components maintain constant amplitudes within the core layer. These modes exhibit modal properties that are independent of the core thickness, allowing the modal spot to extend over several wavelengths. Numerical simulations further confirm their immunity to backscattering. By combining the tunability of modal spot with the robustness of unidirectional propagation, these unidirectional bulk modes offer more degrees of freedom for the manipulation of terahertz waves.

To address the challenges of weak signals and poor system stability in Raman spectroscopy for trace gas detection, an enhanced spectroscopy technique based on a circular confocal cavity is proposed. This technique is centered on a circular multi-pass cell comprising multiple independent spherical mirrors, whose unique confocal configuration affords the system exceptional stability and alignment tolerance. A double-cycle optical path, realized through an integrated retro-reflector, doubles the effective optical path length while simultaneously collecting both forward and backward scattered signals, thereby maximizing collection efficiency. Under ambient conditions, a limit of detection (LOD) of 19 ppm for carbon dioxide was achieved within a 20-s integration time. This apparatus paves the way for the development of portable, high-sensitivity Raman gas analyzers.

Refractive error is a global public health challenge, with astigmatism correction being one of the key issues. While spherocylindrical lenses compensate for static astigmatism, they fail to address optical axis shifts during eye movement. To address this problem, we propose a single vision lens design method with freeform surfaces based on differentiable ray tracing. Our method integrates the rotation model of the human eye into the optical design framework. Besides, it leverages the high design freedom of the freeform surface to realize effective correction of optical focus errors across different fields of view. To verify the effectiveness of the method, we develop spectacle lens designs to correct astigmatism in the human eye through systematic comparison of traditional spherocylindrical and aspheric lenses with various freeform designs, including deformed XY polynomials and both single- and double-Zernike surfaces. Results show that our method achieves superior off-axis aberration correction at equivalent optimization orders, demonstrating its technical advantage for vision correction.