Multiwavelength laser on SOI

Research Area: Integrated lasers and LEDs

Main Researcher: Liu Liu

Optical interconnection has been considered as the most promising approach for Tbps intra- or inter-chip communication in future generation integrated circuits. To stay with silicon, the major difficulty here is to realize a laser source on it. Recently we have presented a electrically injected InP-microdisk laser, with dimension of 1um thick and 7.5um in diameter, bonded on a sub-micron SOI waveguide. Continuous operation with threshold of 0.5mA and output power 10uW has been measured.
To fully exploit the bandwidth capacity of the SOI photonic integrated circuit, compact multiwavelength laser (MWL) sources are needed. The easiest way to integrate several microdisk lasers is by cascading them on one bus SOI waveguide as the following figure. A MWL with four microdisks has been fabricated (see (b)).

Schematic and fabricated structure of the MWLs.

The measured laser spectra of this type of MWL are shown as follow for two different groups. The diameters of the disks in each group are designed such that the emitting wavelength is equally distributed in one free frequency range. The measurement results are nicely matched with the designs. However, we realized a large nonuniformity of the laser power. The microdisk laser that is closest to the receiving end generally has a higher output power level, i.e., there is ~2dB insertion loss for one microdisk laser in this integration scheme. Simulation shows that this is due to the leakage losses to high-order modes supported by the thick active layer.

Measured laser spectra of MWLs.

We are exploring approaches to eliminate this nonuniformity by, e.g., employing a ultrathin active layer of ~300nm, to ensure single mode in the thickness direction. Theoretically, this could reduce the insertion loss to ~0.1dB. Alternatively, we could use a multiplexer, e.g., an AWG, to combine each laser source. This could give a much better uniformity, but maybe even larger insertion loss.

Other people involved:

• Liu Liu
• Joris Van Campenhout

Publications

International Journals


1. G. Roelkens, L. Liu, D. Liang, R. Jones, A. Fang, B. Koch, J. Bowers, III-V/silicon photonics for on-chip and inter-chip optical interconnects, Laser & Photonics reviews (invited), p.DOI: 10.1002/lpor.200900033 doi:10.1002/lpor.200900033 (2010)  .
2. L. Liu, G. Roelkens, J. Van Campenhout, J. Brouckaert, D. Van Thourhout, R. Baets, III-V/silicon-on-insulator nanophotonic cavities for optical network-on-chip, Journal of Nanoscience and Nanotechnology (invited), 10, p.1461-1472 doi:10.1166/jnn.2010.2032 (2010)  .
3. J. Van Campenhout, L. Liu, P. Rojo Romeo, D. Van Thourhout, C. Seassal, P. Regreny, L. Di Cioccio, J.-M. Fedeli, R. Baets, A Compact SOI-Integrated Multiwavelength Laser Source Based on Cascaded InP Microdisks, IEEE PHOTONICS TECHNOLOGY LETTERS, 20(16), p.1345-1347 doi:10.1109/lpt.2008.926857 (2008)  .