Progressing The Photonic-crystal Surface-emitting Lasers
Thanks to a number of advances, photonic-crystal surface-emitting lasers (PCSELs) now combine a high output power with great beam quality, polarization, beam-pattern control and on-chip two-dimensional beam scanning. BY SUSUMU NODA FROM KYOTO UNIVERSITY
Semiconductor lasers continue to make important contributions to our society. They are deployed for many tasks and have made significant and lasting contributions to communication networks and optical storage. In these settings, much effort has been devoted to expanding the utility of this source by widening its range of emission wavelengths and increasing its modulation speed.
There are also opportunities for lasers in Smart Mobility and Smart Manufacturing. However, conventional lasers that are designed for these tasks produce a very broad spectral emission and struggle to meet the high output powers and high beam qualities that are required (see Figure 1 left ).
Figure 1. Comparison of conventional broad-area semiconductor laser and a PCSEL.
Like many other classes of laser, those made from semiconductors have additional areas for improvement. Today's chips are incapable of providing an on-chip beam pattern, polarization and direction control. Failing to offer these functionalities is a significant weakness - these omissions have to be addressed with external elements, and this forfeits the advantage of compactness, for which semiconductor lasers are renowned.
Fortunately, this paradigm can change, thanks to the development of the PCSEL, an acronym for the photonic-crystal surface-emitting laser (see Figure 1 right). This device is currently attracting much attention, because it can realise simultaneously a high output power and a high beam quality, and offer functionalities that are not easily achievable with other types of laser, such as polarization and beam-pattern control, as well as on-chip beam-direction control, which eliminates the need for bulky external optics.
The remainder of this feature offers a brief overview of the history of the PCSEL, along with an account of recent progress, including success associated with newly developed photonic crystals.