Zero-energy topological states, which are protected by chiral symmetry against certain perturbations topologically, localize at interfaces between trivial and non-trivial phases in the Su–Schrieffer–Heeger (SSH) chain model. Here, we propose and demonstrate a method to manipulate chiral symmetry itself to improve the localized interfaces and enlarge the mode volume of topological states in the SSH model, thus optimizing the lasing performance of localized interfaces. As multiple defects corresponding to off-diagonal perturbations in an eigenmatrix are introduced, the topological state expands and extends to extra defects at the topological interface without breaking chiral symmetry. We apply the proposed method in electrical pumping semiconductor laser arrays to verify our theoretical prediction and optimize the output characteristics of the devices. The measured results of the proposed multi-defect SSH laser array show that the output power has been increased by 27%, and the series resistance and far-field divergence have been reduced by half compared to the traditional SSH laser array, establishing a high-performance light source for integrated silicon photonics, infrared light detection and ranging, and so on. Our work demonstrates that the proposed method is capable of improving topological localized interfaces and redistributing zero-energy topological states. Furthermore, our method can be applied to other platforms and inspire optimizations of more devices in broader areas.

Optical resonators with high quality (Q) factors are paramount for the enhancement of light–matter interactions in engineered photonic structures, but their performance always suffers from the scattering loss caused by fabrication imperfections. Merging bound states in the continuum (BICs) provide us with a nontrivial physical mechanism to overcome this challenge, as they can significantly improve the Q factors of quasi-BICs. However, most of the reported merging BICs are found at Γ point (the center of the Brillouin zone), which intensively limits many potential applications based on angular selectivity. To date, studies on manipulating merging BICs at off-Γ point are always accompanied by the breaking of structural symmetry that inevitably increases process difficulty and structural defects to a certain extent. Here, we propose a scheme to construct merging BICs at almost an arbitrary point in momentum space without breaking symmetry. Enabled by the topological features of BICs, we merge four accidental BICs with one symmetry-protected BIC at the Γ point and merge two accidental BICs with opposite topological charges at the off-Γ point only by changing the periodic constant of a photonic crystal slab. Furthermore, the position of off-Γ merging BICs can be flexibly tuned by the periodic constant and height of the structure simultaneously. Interestingly, it is observed that the movement of BICs occurs in a quasi-flatband with ultra-narrow bandwidth. Therefore, merging BICs in a tiny band provide a mechanism to realize more robust ultrahigh-Q resonances that further improve the optical performance, which is limited by wide-angle illuminations. Finally, as an example of application, effective angle-insensitive second-harmonic generation assisted by different quasi-BICs is numerically demonstrated. Our findings demonstrate momentum-steerable merging BICs in a quasi-flatband, which may expand the application of BICs to the enhancement of frequency-sensitive light–matter interaction with angular selectivity.

We first study the effect of cavity modes propagating in the lateral dimension on high-power semiconductor lasers with a large stripe width. A sidewall microstructure was fabricated to prevent optical feedback of lateral resonant modes. Theoretically, we demonstrate the existence of lateral resonant modes in the Fabry–Perot cavity with a large stripe width. Experimentally, we design the corresponding devices and compare them with conventional broad-area diode lasers. About a 15% reduction in threshold current and a 27% increase in maximum electro-optical conversion efficiency are achieved. The amplified spontaneous emission spectrum is narrowed, which proves that lateral microstructures suppress optical feedback of lateral resonant modes. Under a large continuous-wave operation, the maximum output power of laser device is 43.03 W, about 1 W higher than that of the standard broad-area laser at 48 A.

Recently, the concepts of parity–time (PT) symmetry and band topology have inspired many novel ideas for light manipulation in their respective directions. Here we propose and demonstrate a perfect light absorber with a PT phase transition via coupled topological interface states (TISs), which combines the two concepts in a one-dimensional photonic crystal heterostructure. By fine tuning the coupling between TISs, the PT phase transition is revealed by the evolution of absorption spectra in both ideal and non-ideal PT symmetry cases. Especially, in the ideal case, a perfect light absorber at an exceptional point with unidirectional invisibility is numerically obtained. In the non-ideal case, a perfect light absorber in a broken phase is experimentally realized, which verifies the possibility of tailoring non-Hermiticity by engineering the coupling. Our work paves the way for novel effects and functional devices from the exceptional point of coupled TISs, such as a unidirectional light absorber and exceptional-point sensor.

In this paper, high-uniformity 2×64 silicon avalanche photodiode (APD) arrays are reported. Silicon multiple epitaxy technology was used, and the high performance APD arrays based on double-layer epiwafers are achieved for the first time, to the best of our knowledge. A high-uniformity breakdown voltage with a fluctuation of smaller than 3.5 V is obtained for the fabricated APD arrays. The dark currents are below 90 pA for all 128 pixels at unity gain voltage. The pixels in the APD arrays show a gain factor of larger than 300 and a peak responsivity of 0.53A/W@M = 1 at 850 nm (corresponding to maximum external quantum efficiency of 81%) at room temperature. Quick optical pulse response time was measured, and a corresponding cutoff frequency up to 100 MHz was obtained.

A high peak power density and low mechanical stress photonic-band-crystal (PBC) diode laser array based on non-soldered packaging technology is demonstrated. The array consists of the PBC diode laser bars with small fast axis divergence angles. Meanwhile, we design the non-soldered array structure that realizes mechanical stacking of 10 bars in the vertical direction. In the experiment, the peak power density of the PBC array is about 1.75 times that of the conventional array when the same total power is obtained. The peak power of the non-soldered array is 292.2 W, and the “smile” effect is improved by adjusting the mechanical fixing force of the array.

We studied the spectral beam combining (SBC) of a large optical cavity (LOC) laser array to achieve high-power and high-brightness laser output. We discussed the characteristics of the external cavity feedback efficiency and the focal length of the transform lens for lasers with different waveguide thicknesses. We have found that using LOC laser diodes can increase the proportion of external cavity feedback, thereby improving the SBC efficiency. At a current of 90 A, the CW output power of the SBC system is 59.2 W, and the SBC efficiency reaches up to 102.8%. All emitters of the laser array have achieved spectral locking with a spectral width of 11.67 nm, and the beam parameter product is 4.38 mm·mrad.

We experimentally demonstrate for the first time to our knowledge electrically injected vertical-cavity surface-emitting lasers (VCSELs) with post-supported high-contrast gratings (HCGs) at 940 nm. The HCG-VCSELs have two posts to support the air-suspended HCGs, which are realized by simple fabrication without critical point drying. The HCG-VCSEL achieves a threshold current of about 0.65 mA and a side-mode suppression ratio of 43.6 dB under continuous-wave operation at 25°C. Theoretically the HCG-VCSEL with a λ/2-cavity for the transverse magnetic polarization has a smaller effective mode length of 1.38·(λ/n). Thus, the relaxation resonance frequency can be increased by 16% compared with that of the conventional VCSEL. The modulation speed of 100 Gbit/s for the HCG-VCSEL is expected in the on–off keying modulation format. Our easy design of HCG-VCSELs has great potential for applications in optical interconnects, sensing, illumination, and so on.

We design a 645 nm laser diode (LD) with a narrow vertical beam divergence angle based on the mode expansion layer. The vertical beam divergence of 10.94° at full width at half-maximum is realized under 1.5 A continuous-wave operation, which is the smallest vertical beam divergence for such an LD based on the mode expansion layer, to the best of our knowledge. The threshold current and output power are 1.07 A and 0.94 W, limited by the thermal rollover for the 100 µm wide and 1500 µm long broad area laser, and the slope efficiency is 0.71 W/A. The low coherence device is fabricated with the speckle contrast of 3.6% and good directional emission. Such 645 nm LDs have promising applications in laser display.