Lin Zhang

Nonreciprocal optical devices are key components of modern optical information processing. The on-chip integration of complete nonreciprocal devices is highly desirable for integrated photonic circuits but remains a longstanding challenge. Nonlinear nonreciprocal devices are inherently compatible with integrated photonic platforms and exclude external bias, facilitating fabrication and operation. To date, nonlinear nonreciprocal devices have relied on resonator-enhanced Kerr or photothermal nonlinearity or wave mixing relying on narrow-band phase matching, restricting the bandwidth to the subnanometer range and requiring watt-level laser power. By combining asymmetric inputs in opposite directions with saturable absorption in Er-doped optical waveguides, this work reports a non-magnetic, bias-free, broadband, integrable nonreciprocal device at telecommunication wavelengths with only milliwatt-level laser power. In the proof-of-principle experiment using an Er-doped optical fibre, we obtain a transmission contrast of 16.75 dB over a bandwidth of 11.8 nm. Further, an experiment using an on-chip Er-doped optical waveguide achieves a contrast of 4.70 dB over a 4-nm bandwidth, confirming the feasibility of integration. This loss-enabled, bias-free, and chip-integrable nonreciprocal transmission mechanism may be applied to integrated LiDAR when the round-trip time of flight of the reflected pulse is much larger than the relaxation time of the saturable absorber.

In order to overcome the capacity limits of long-haul communication systems in single-mode fibers, mode-division multiplexing based on few-mode fibers (FMFs) is expected to greatly increase the per-fiber capacity. However, the signal pulse spread, induced by differential mode delay (DMD), and mode-dependent loss (MDL) are limiting factors in long-haul transmission, especially for a high mode count. Here, we develop the guidelines for identifying superior mode permutation strategies (MPSs) among a huge number of MPSs; 25 MPSs are found by taking DMD distribution of the FMFs into account and verified in experiments to greatly mitigate the DMD and MDL. For the first time, to our knowledge, we demonstrate a 15-Gbaud PM-QPSK 10-mode transmission over 2320 km, with a reach extension by 1000 km and a three times larger system capacity-distance product than those of previously reported works.

Thin-film lithium niobate (LN) has emerged as a promising platform for building chip-scale optical functional devices due to its versatile advantageous properties. A polarizer with a high extinction ratio is essential to suppress polarization crosstalk and enhance signal-to-noise ratio. Here, we demonstrate an LN-based polarizer that effectively addresses the long-standing issue of polarization crosstalk while simultaneously achieving high extinction ratio and broad bandwidth. Leveraging the pronounced loss disparity between the modes with different polarizations enhanced by resonant cavities formed by metal strips, we obtain a greatly improved polarization extinction ratio (PER) up to 42 dB, while the potential crosstalk between adjacent waveguides can be effectively suppressed down to −38 dB over a 160-nm bandwidth, with a low insertion loss (IL) of 0.7 dB at the wavelength of 1550 nm. This work paves the way for developing high-performance polarization-dependent photonic devices such as optical modulators and gyroscopes.

The predecessor of China Optics was China Optics and Applied Optics Digest, which was founded in 1985. At that time, it was the only retrieval journal in the field of optics in China. At the end of 2008, China Optics and Applied Optics Digest was renamed 《中国光学》的前身是1985年创办的《中国光学与应用光学文摘》，当时是国内光学领域唯一的检索刊物。2008年底《中国光学与应用光学文摘》转型更名为《中国光学与应用光学》期刊，刊载内容突破了文摘的限制，正式成为学术刊物。

Waveguide displays are promising for augmented reality or mixed reality, but chromatic dispersion in conventional diffractive elements limits full-color display performance. Although promising, achromatic metagratings’ diffraction efficiency needs to be improved. We propose an inverse design method using a quantum genetic algorithm for achromatic slanted metagratings. Two designs with 20° and 40° fields of view exhibit diffraction efficiencies as high as $29\%\pm 1\%$ for RGB wavelengths at normal incidence and excellent angular and spectral uniformity. The proposed single-layer manufacturable structures offer a promising route to future full-color waveguide displays.

Kerr nonlinear effect extremely impacts both the spectral and the temporal evolutions of ultrashort pulses, although it is challenging to tailor over a broadened spectral region. In this work, we propose an on-chip Si₃N₄-organic hybrid waveguide with sophisticated non-monotonic nonlinear coefficient γ(ω). A chirp-free pulse can be broadened or compressed at different peak powers in the normal dispersion range. The impact of the second-order Kerr nonlinearity with respect to frequency can overbalance that of dispersion. This new method deepens the understanding of the high-order nonlinear effects and help exploit innovative nonlinearity-engineered on-chip platforms for pulse shaping in the immediate future.

We propose what we believe to be a novel low-loss, gap-filling, nested, anti-resonant nodeless fiber (GF-NANF) designed for ultraviolet (UV) applications. The GF-NANF achieves loss reduction by integrating nested tubes and gap-filling structures. Our results show that the GF-NANF reduces confinement loss by four orders of magnitude to 2.29 × 10⁻⁵dB/m, and propagation loss by two orders of magnitude to 1.64 × 10⁻²dB/m, at 355 nm, when compared to an ARF of the same design that lacks both gap-filling cladding tubes and nested cladding tubes. Additionally, the fiber shows simulated low bending losses of 1.01 × 10⁻⁴dB/m at a 10-cm bending radius and 1.40 × 10⁻³dB/m at 5 cm, representing a reduction by approximately three orders of magnitude compared to the NANF without gap-filling tubes. Notably, at a bending radius of 10 cm, the GF-NANF maintains quite low bending losses below 1.2 × 10⁻⁴dB/m across all bending orientations from 0° to 360°, significantly lower than that of structures without gap-filling tubes, exhibiting its suitability for UV optical systems requiring high efficiency and operation flexibility.

For the first time, to our knowledge, we demonstrate a six-mode transmission over a 960-km fiber link using in-line integrated amplification provided by a six-mode erbium-doped fiber amplifier (6M-EDFA) for a 28-GBaud dual-polarization QPSK signal. This transmission distance is five times longer than that of previously reported works. The integrated 6M-EDFA enabling this long-haul transmission exhibits modal gains of >17.6 dB, while the gains increase to 25 dB with an input power of −25 dBm. Importantly, a Gaussian-like erbium doping profile has been proposed to optimize the differential modal gain to 1.15 dB, ensuring a more uniform signal-to-noise ratio between spatial modes after long-haul transmission.

Driven by the increasing demand for efficient optical communication, on-chip amplifiers have become essential components in photonic integrated circuits for realizing cost-efficient and compact wavelength-division multiplexing (WDM) receivers. In this work, we investigate the WDM signal transmission performance of an on-chip erbium-doped aluminum-oxide waveguide amplifier, fabricated using atomic layer deposition. The waveguide amplifier demonstrates a net gain of >5.0 dB across the entire C-band, with a peak value of 11.1 ± 1.5 dB at 1531.6 nm, corresponding to an off-chip net gain of 7.1 ± 1.5 dB. A maximum on-chip output power of 4.1 ± 1.4 dBm at 1531.6 nm is achieved. Broadband performance is further confirmed by a 16-channel gain measurement. Finally, a 16-channel 56-Gbps WDM transmission is demonstrated, with the Q² values comparable to those of the back-to-back transmission, highlighting the potential of the amplifier for high-speed coherent data transmission.

Conventional ultraviolet microplasma sources typically lack a back-reflection structure, resulting in radiative power loss from the backside. To enhance the emission efficiency of ultraviolet microplasma devices around 220 nm, we propose a multilayer reflective coating composed of alternating high- and low-refractive-index layers of Al₂O₃ and SiO₂, within a V-shaped groove. Key structural parameters, including the number of alternating film layer pairs, groove width, and light source position, are investigated to show their effects on ultraviolet reflection characteristics. The results show that reducing the groove width greatly enhances light reflection. When the groove width is 6.5 μm, the device exhibits a reflection efficiency of 47.82% and power enhancement of 91.66%, representing improvements of 2.5-fold and 4.2-fold, respectively, compared to non-optimized cases. Device performance is also influenced by the offset of the light source, which is more sensitive along the horizontal direction. This study provides a practical solution for developing high-efficiency ultraviolet emission devices.