Fig. 1. Fundamental concept behind the single (transverse) supermode lasing. (a) A single laser supports multiple longitudinal cavity modes (vertical black lines) separated by free spectral range. When N such rings are coupled, N closely spaced transverse supermodes emerge with equal threshold (middle panel). In the presence of gain, a suitable pump can induce simultaneous lasing of all the supermodes. The global mode coupling with a dissipative superpartner in a SUSY laser array, schematically shown in (b), can increase the threshold of undesired modes (shown in vertical purple lines in the bottom panel), enforcing a lasing of a single supermode that lacks a superpartner counterpart. (c) Second-order SUSY transformation for the superpartner design.

Fig. 2. SUSY laser array linear mode analysis. (a) Design parameter of a SUSY microring laser array containing nine coupled lasers. (b), (c) Linear eigen spectrum and corresponding modal intensities (only the cross-sectional view is shown), respectively. The spectrum shows that the fundamental mode of the SUSY array has the least threshold. All other modes of the conventional laser array split into symmetric and anti-symmetric pairs Ω±. Here ω˜=0, γ0=0.005k, γ=k/6, and k=1 are considered.

Fig. 3. Device and spectrum. (a) Scanning electron microscope images of the fabricated SUSY microring laser array. The image was taken before the transfer of the sample into a silica substrate. (b) Evolution of the photon emission spectrum from photoluminescence to amplified spontaneous emission and then to supermode lasing at the wavelengths of about 1544 nm and 1568 nm, when pumping is increased. The two lasing peaks, separated by 24 nm, belong to two longitudinal modes in a single microring laser [see Fig. 4(a)].

Fig. 4. Comparison of measured spectra. (a) Output spectra for a single laser, a conventional laser array, and the SUSY laser array when 2.46  GW/m2 pump intensity is considered. The conventional array is seen to be highly multimoded (as evident from the magnified spectrum shown in the inset). The spectra of a single laser and the SUSY laser array are almost indistinguishable. The enhancement of lasing output peak intensity is seen in the SUSY laser array. The nearfield images of lasing emissions are also shown. (b) Light–light curve showing the lowering of the threshold and enhancement of lasing output in a SUSY laser array compared to a single microring laser.