【摘要：谐振腔是构成激光器的三大要素之一. 最近一项微腔激光器研究揭示了正方形微腔回音壁模式之谜, 《中国科学: 物理学力学天文学》英文版2015年第11期报道了这一成果. 】

Totally internal confinedwhispering-gallery modes can have high Q factorsin wavelength scale optical microresonators, such as microspheres andtwo-dimensional microdisk resonators. Square optical resonators can alsosupport high Q whispering-gallerymodes, suitable to realize unidirectional microlasers.

Microsquare lasers have a larger overlap between the mode fieldpattern and injected carriers than microdisk lasers, which can result in betterhigh-speed modulation behaviors. In addition, microsquare lasers can have higherslope efficiency and output power than microdisk lasers, due to the more evenlydistributed mode field.

For a square opticalmicroresonator, the mode field patterns around the perimeter exhibits the longitudinaland transverse mode field distributions. So the mode Q factors are greatly influenced by connecting an output waveguideto the resonator. The fundamental transverse mode with field pattern in Fig.1(a) has a very small mode Q factor due to its strongly coupling to the outputwaveguide, and the first order transverse mode in Fig. 1(b) has a high Q factor.

Figure 1  Mode field patterns for a square resonatorwith a side length of 2.5 mm connectedwith a waveguide.

Mode selection in square resonatormicrolasers is demonstrated by adjusting the width of the output waveguidecoupled to the midpoint of one side. Through adjusting the width of the outputwaveguide, the mode interval of the high-Qmodes can reach four times of the longitudinal mode interval. Therefore,mode hopping can be efficiently avoided and the lasing wavelength can be tunedcontinuously by tuning the injection current. For a 17.8-mm-side-lengthsquare microlaser with a 1.4-mm-width output waveguide, mode-hopping-freesingle-mode operation is achieved with a continuous tuning range of 9.2 nm.

Furthermore, dual-transverse-modemicrosquare lasers with a tunable wavelength interval are designed andfabricated by using a square-ring patterned contact window. For the microsquarelaser with the side length of 30 μm, the wavelength interval increases from0.25 to 0.37 nm with the intensity ratio less than 2.5 dB as the injection currentincreases from 89 to 108 mA.

Figure 2  Square microlaser with a patterned electrodefor current injection.

See the article:

1. LongHeng, Huang YongZhen, Yang YueDe, Zou LingXiu, Xiao JinLong, and Xiao ZhiXiong, Mode and modulation characteristics formicrosquare lasers with a vertex output waveguide, Sci China-Phys Mech Astron, 2015, 58(11): 114205

2. HengLong, Yong-Zhen Huang, Xiu-Wen Ma, Yue-De Yang, Jin-Long Xiao, Ling-Xiu Zou andBo-Wen Liu, Dual-transverse-mode microsquare lasers with tunable wavelengthinterval, Opt. Lett., 2015, 40(15): 3548-3551

3. Ming-Ying Tang,Shao-Shuai Sui, Yue-De Yang, Jin-Long Xiao, Yun Du, and Yong-Zhen Huang, Mode selection in square resonatormicrolasers forwidely tunable single mode lasing, Opt. Exp., 2015, 23 (inpress)

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