On June24th, the latest research result of a research team led by Prof. Chen Xianfeng, School of Physics and Astronomy of Shanghai Jiao Tong University has been published on the scientific journal the Physical Review Applied, a sub-journal of the Physical Review Journal, titled "White beam lasing from a hybrid micro-cavity with slab–capillary mode coupling". Their study demonstrated the first time to realize a microlaser which can emission white lasing beam, and the lasing beam can keep straight line transmission in one direction. Meanwhile, collimating and color tunable lasing beam be excited on a micro waveguide chip by using waveguide modes coupling technology.This study provides a powerful platform for further studies on biophotonics and physical medicine fields.

Multi-colour and multi-wavelength lasers with a wavelength span using a single micro-chip has been a subject of great interest in recent years, with the realization of white lasers as the ultimate goal. So far, producing emission covering all visible wavelengths in a single structure requires the growth of potentially very dissimilar semiconductors into single structure with high crystal quality, resulted in this method of achieving wavelength variability is severely limited in the existing methods of growing planar epitaxial heterostructure of semiconductor thin films on a crystalline substrate. Therefore seeking a perfect monolithic structure to achieve white-colour and full-colour lasing, it is a key of technical question in microlaser research field.

Figure 1. The pump beam illuminates the upper surface of the triple hybridmicrocavity chip. The threecapillaries are placed side by side. S-420, C-540, and R-610 dye solutions are injected into the capillaries.

We present a hybrid multi-channel metal-cladded slab-capillary micro-cavity composed of a sub-millimeter symmetrical metal-cladding slab waveguide (SMSW) and hollow-core capillary. Multiple capillaries have been integrated on slab, which formed low-background noise metal-cladding slab-capillaries multi-channel microcavity to simultaneously achieve width line of ~1nm multi-wavelength lasing beams. Moreover, the metal-cladding capillary can couple the modes into inner coming from SMSW transmission modes and trap the modes into the hollow-core of metal-cladding capillary. Therefore, an energy oscillating field with high density has been formed in hollow-core of capillary. That’s because the design makes the most of UOMs of SMSW to resonate the capillary eigenmodes with enhanced mode spacing. Through numerical simulation, the incident light has been coupled into waveguide layer, when the incident angle reaches the coupling angle by mode eigenvalue equation of SMSW. This design supports more than 1000 modes with small incident angle or minimum effective index difference ( minΔneff ) between adjacent modes over the whole waveband, indicating fully lifted eigenmodes channels for SMSW transmission.

Figure 2. Fitted light-in–light-out curves with multimode lasing: (a)–(c) for the 423, 530, and 636 nm lasing peaks. Inset: plots of thecurves at threshold. (d) RGB lasing peaks are excited with pumping on the triple slab-capillary microcavity chip.

Our experiment will spark a lot of interest in the in many applications such as laser lighting, full-colour laser imaging and display, biological and chemical sensing. The results demonstrate that the apparently contradictory terms ‘white’ and ‘lasing’ can both be realized in a single waveguide structure. It is greatly simplifies that the process of creating monolithic laser structures with dynamically colour-controllable emissions, and is an important first step towards the realization of electrically driven white-colour and full-colour microlaser from a single monolithic structure.

Dr. Dai Hailang is first author and Pro. Chen Xianfeng is corresponding author. This work was supported by the National KeyR&D Program of China (Grant No. 2018YFA0306301, 2017YFA0303701); National Natural Science Foundationof China (NSFC) (Grant No. 11734011); The Foundationfor Development of Science and Technology of Shanghai (Grant No. 17JC1400400).

Acticle：Hailang Dai, Cheng Yin, Zhiyuan Xiao, Zhuangqi Cao, and Xianfeng Chen, White beam lasing from a hybrid micro-cavity with slab–capillary mode coupling, Physical Review Applied, 11, 064055 (2019). 10.1103/PhysRevApplied.11.064055.