INDUSTRY LASERS
impinges on the grating with an incidence angle that is off from perpendicular. If this angle is optimal, any back-reflection from the grating to the laser is eliminated.
With our InP-based, horizontal-cavity surface-emitting laser that features etched facets at an angle off from 45°, the laser beam emerges at an angle to the gratings on the silicon photonics chip (see Figure 2). Light is then directed to the narrow silicon photonics waveguide through the gratings and an adiabatic taper.
A cleaved facet laser, packaged with a ball lens and a reflector in a hermetic enclosure, is also capable of directing the laser emission at the right angle to ensure a high intensity of light in the narrow waveguide (see Figure 3). If this cleaved-facet laser package is mounted to the silicon photonics chip, a hermetic package is not required around the combined chip. Although this means that additional optical elements beyond the laser are required, on the plus side only a relatively small hermetic package is needed around the cleaved facet laser.
It is not yet clear whether a hermetic package is needed for a hybrid silicon laser that is employed to couple light into a narrow waveguide on the silicon photonics chip (see Figure 4). If it’s not needed, this approach that Intel introduced is attractive, given that it is also alignment-free when the InP wafers are bonded to the silicon wafer.
Another issue to consider is the significant difference in the dimensions of the different InP lasers being considered for silicon photonics. Cleaved and etched facet laser chips are relatively small, with typical lengths and widths of around 300 µm and 250 µm, respectively. This means that they use up just 0.075mm2 of InP real estate, which is several orders of magnitude less than that of the hybrid laser – it is expected to have similar dimensions to the silicon photonics chip, such as 5 mm by 6 mm. However, this issue may be alleviated with an InP die attach process that involves using glass glue to bond the InP gain chips, rather than the full InP wafer, to the silicon photonics wafer.
Our survey of the three different light sources for silicon photonics – cleaved lasers, hybrid lasers, and etched fact
One of BinOptics’ vacuum systems used in the production of etched facet lasers.
lasers – shows that they all have some pros and cons. The ideal approach will ultimately depend on the desired final function, and how these technologies progress as silicon photonics continues to gain popularity in the computing and datacom worlds. Whichever way you look at it, silicon photonics has a bright future, and it will be exciting to witness how this technology transforms the world as the digital age continues to unfold.
© 2014 Angel Business Communications. Permission required.
March 2014
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