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Research

Optical Communications (Research Funded by Science Foundation Ireland under grant I5/IA/2854

Optical communications bring the world of the internet to us at the touch of a button. The data we require is carried by modulating lasers and transmitting the light over optical fiber to be received at the other end. The lasers used in communications are single mode laser that operate near 1.5 microns in the region of lowest loss in the fiber.

Research on these lasers has been carried out in the Donegan group in Trinity College Dublin for over a decade.

Microscope image of Slotted laser (Top left). Scanning electron microscope image of laser grating slot. (Top right) 3D model of slotted laser.

Our method of generating single mode operation is to form a grating in the ridge of the laser. We generally use a high order grating, around 37th order. Such a grating structure allows each of fabrication without the need for re-growth or high resolution lithography. Our lasers are fabricated in an external foundry, so again the ease of fabrication is a key issue to ensure that the lasers can be obtained with high yield. Due to the simple design of our lasers, we have shown the integration of a semiconductor optical amplifier (SOA) and an electro-absorption (EA) modulator.

3D model of slotted laser with integrated electro-absorption (EA) modulator.
DC extinction ratio of 10 dB at bias of 2.3 V.

Reference

Single mode lasers based on slots suitable for photonic integration Lu, Qiaoyin; Guo, Weihua; Nawrocka, Marta; Abdullaev, Azat; Daunt, Chris; O’Callaghan, James; Lynch, Michael; Weldon, Vincent; Peters, Frank; Donegan, John F. 2011 Optics Express 19(26) B140-B145