Silicon Photonics: Fundamentals and Devices

9.7 Further Developments

Further improvement of the performance of the laser may be made by (1) optimizing the cavity mirror and cavity length design, (2) reducing the threshold power by using a waveguide of smaller cross-sections and/or by introducing a larger cavity enhancement for the pump beam, (3) improving the fiber-to-waveguide coupling efficiency by adding a mode converter, (4) reducing the effective carrier lifetime below 1 ns by optimizing the p–i–n diode design, and (5) replacing the multilayer mirrors with waveguide Bragg reflectors, rings, or microdisk resonators.

It is to be mentioned that Raman lasing has since been observed by other groups and in other material systems. Attempts are continuously being made to improve its performance. However, inclusion of all these recent works is beyond the scope of the book. The reader is referred to some of the recent publications [17–20].

Problems

9.1 Consider the expression for the current–voltage characteristic of a p–n junction diode. Let two voltages V₁sin(ω₁t) and V₂sin(ω₂t) be applied to the diode. Prove that, due to nonlinearity in the first order, there will be signals of frequencies (ω₁± ω₂).

9.2 Show from the wave vector conservation condition for the Stokes wave that the phonon wavevector must be less than twice the wave vector of light. Consider the wavelength of light to be 1 µm and the lattice constant to be 0.5 nm. Prove that optical phonons involved in Raman scattering have wave vectors in the vicinity of the ...