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Research Review: PICs could benefit from square lasers

A team of researchers at the Chinese Academy of Sciences has built the first square microlasers featuring output ports on opposite corners.

These devices that are produced by planar processes could provide a key building block for the fabrication of photonic integrated circuits (PICs).

The shape of microdisk lasers governs the direction of their emission. Square lasers with output ports in the corners were investigated, because this design can realize highly confined modes while still producing directional emission.

Fabrication of the structures begins by using plasma enhanced CVD to deposit an 800 nm-thick SiO2 film onto the top of epitaxial laser structures grown on InP. Photolithography defines the profile of the laser, before plasma and wet etching techniques remove the oxide film. A second SiO2 layer is then deposited, with further photolithography and etching steps defining a window in the cavity. The addition of Ti/Au and Au/Ge/Ni contacts creates n and ptype electrodes.

A 1514 nm laser created by this process delivered 4.8 μW at a 72 mA injection current. “It’s only a concept device, and the threshold current and output power are not good enough for making photonic integrated circuits yet,” explains corresoponding author Yong-Zhen Huang.

He says that the team will now focus on reducing the threshold current and increasing the output power of its microlasers.

“We are now investigating coupled circular resonators, which can have over 99 percent coupling efficiency, according to finitedifference time-domain simulations,” says Huang. 

The two-port square microlaser has 20 μm sides and output waveguides on opposite corners. Credit: CAS.

K-J. Che et al Electron. Lett. 46 585 (2010)

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