Silicon Photonics: Fundamentals and Devices

9.1 Introduction

Light emitters in the form of light-emitting diodes (LEDs) and laser diodes using silicon and related materials have been discussed in Chapter 6. The present chapter describes yet another form of light emitter, the operation of which depends on stimulated Raman emission.

The Raman effect was discovered in 1928 by Raman and Krishnan 1 in some organic liquids. Subsequently, the effect was observed in crystalline solids. Basically the effect is the scattering of photons by vibrational modes in materials or by optical phonons in crystalline solids. As a consequence of scattering, the frequency of the incoming radiation is downshifted (Stokes line) or upshifted (anti-Stokes line). The effect has been employed as a powerful analytical tool in spectroscopy. Simulated Raman scattering, in which a strong pump power causes a growth of the Stokes radiation, has been the subject of intensive research in materials since the 1960s. The possibility of Raman amplification in optical fibers was investigated as early as 1973 2. Recent years have witnessed a spectacular growth of investigations and practical applications of Raman amplifiers, in particular in optical fiber communication. Fiber Raman amplifiers in conjunction with Er-doped fiber amplifiers (EDFAs) are essential components in long-haul communications networks 3.

The Raman effect in crystalline silicon received attention from workers as early as 1973 [4]. The possibilities of stimulated Raman scattering (SRS) and consequent ...