Silicon Photonics: Fundamentals and Devices

9.6 Continuous-Wave Raman Laser

We now present some experimental results related to continuous-wave Raman lasing. Several groups reported Raman lasing in SOI waveguides; however, the operation was in pulsed mode [7–13]. As may be inferred from discussions in this chapter, the main disadvantage in having proper gain is the absorption by free carriers generated by TPA. The detrimental role of TPA was pointed out by Liang and Tsang 14.

The CW operation of the Raman laser was first reported by the workers at Intel Corporation [15, 16]. They circumvented the problem by wiping out the electrons by using a p–i–n structure and properly biasing it. The present section describes essentially the device structure employed, and the results obtained by the group.

The structure of the CW silicon Raman laser is shown in Figure 9.7. Amplification takes place in the core of the low-loss SOI waveguide, whose facets are coated with multilayer dielectric films. The front mirror is dichoric, having 71% reflectivity for the Stokes wavelength of 1686 nm, and 24% for the pump wavelength of 1550 nm. The coating at the back facet has a reflectivity of 90% for both the pump and Stokes wavelengths.

Figure 9.7 Structure of the CW Raman laser reported. Reproduced with permission from [15]. Copyright (2005) Macmillan Publishers Ltd. The silicon waveguide laser cavity, optical coatings applied to facets, and a p–i–n structure along the waveguide are shown.

The waveguide, the schematic of which is shown in