Modulated Grating Y Laser

Research Area: III-V Semiconductor Photonic ICs

Main Researcher: Reinhard Laroy

Widely tunable laser diodes, with a tuning range of several tens of nm, will play an important part in future WDM networks. A multitude of tunable laser concepts have been researched and developed in the past years, but not one of these concepts has the same qualities as (non-tunable) DFB lasers (high output power and high side mode suppression) and is widely tunable, easily controllable and easily manufacturable.

As part of the IST project Newton, we hope to develop and investigate new widely tunable laser concepts that have the same qualities as DFB lasers. The Modulated Grating Y-Branch Laser Diode is one of these concepts.

In the Modulated Grating Y laser concept the different functions are separated into different sections (Figure). The gain section amplifies the light, the MMI splits the light into 2 equal beams, the bends increase the seperation between the waveguides and the reflectors filter out certain frequencies. A phase section is responsible for the alignment between the cavity mode and the reflected peaks.

The additive Vernier effect is used to select one lasing frequency. Both reflectors have a slightly different peak spacing so the frequency where both peaks overlap will reach the laser threshold first. By tuning one reflector, the reflection spectrum will move to lower wavelengths and the overlapping peaks will occur at a higher frequency. Taking a couple of design rules into account, we can obtain a higher side mode suppression than with the multiplicative Vernier effect (used with the SSG-DBR laser), because the neighboring peaks add partly out of phase.

The 2 reflectors are at the back of the laser so a high output power and a low power variation are obtained. The fabrication is very similar to that of a DBR laser and thus relatively simple.

The figure above shows maps of the output frequency and the side mode suppression (SMSR) in function of the reflector currents and measured at a gain current of 100mA and a common phase current of 0mA.

A high high SMSR is observed in the central diagonal band so reflection peaks of the same order are aligned. For the other supermodes a further adjustment of the reflector design is needed to obtain in-phase addition of the reflection peaks.

Even without these neighboring repeat modes a large continuous tuning range of more than 5THz (40nm) can be reached while the side mode suppression remains above 40dB.

Other people involved:

• Reinhard Laroy

Related Research Projects

• IST: NEWTON (NEw Widely Tunable lasers for Optical Networks)