Currently, near-IR selleck chemical distributed feedback (DFB) laser diodes developed for telecommunications are used for gas sensing because they satisfy all these requirements. However, there is a strong need to develop mid-IR laser sources because the absorption intensities of most gases are well larger in the mid-IR than near-IR by a factor 100�C10,000. As shown in [3], a large number of very important gases for industrial, environmental and safety needs, such as HCl, CH4, C2H6, CO2, NH3, N2O, SO2, H2O, can be detected using lasers operating in the mid-IR wavelength range 2�C10 ��m. Thus, the use of mid-IR lasers is expected to greatly increase the sensitivity of gas sensing and reduce the optical path length and system sizes.

Recently, mid-IR laser sources based on difference frequency generation in quasi-phase-matched (QPM) LiNbO3 have been studied as promising candidates for these applications because they can provide continuous wave (CW) mid-IR light in the wavelength range 2�C5 ��m at room temperature. However, Inhibitors,Modulators,Libraries in Inhibitors,Modulators,Libraries spite of their excellent sensitivity, the low conversion efficiency of the conventional QPM-LiNbO3 devices has limited their use because large, expansive, high power lasers must be also used to achieve a reasonable amount of mid-IR optical output [3]. Moreover, different structures of 3.5 ��m small wavelength distributed feedback quantum cascade lasers have actually been developing to achieve low threshold mid-IR sources for gas sensing [5]. A recent work proposed in [6] has shown the possibility to use an interband Inhibitors,Modulators,Libraries cascade laser as light source to detect gases in the range �� = 3.

6 �� 4.3 ��m.Another approach recently proposed to realise mid-IR light sources is based on Stimulated Raman Scattering (SRS) effect. In fact, one of Inhibitors,Modulators,Libraries the major advantages of Raman lasers is their ability to generate coherent light in wavelength regions that are not easily accessible with other types of lasers [7]. To this aim, silicon is a particularly suitable material for Raman lasers operating in the near and mid-IR regions because it can guarantee a very good trade-off between low cost and high performance. As well described in [8,9], silicon represents the ideal platform for Integrated Optics and Optoelectronics because the quality of commercial GSK-3 silicon wafers driven by Microelectronics industry continues to improve while the cost continues to decrease.

Moreover, the compatibility with silicon integrated circuits manufacturing and silicon Micro-Electro-Mechanical Systems most (MEMS) technology is another important reason for this interest in Silicon Photonics. As a transmission medium, silicon has much higher nonlinear effects than the commonly used silicon dioxide, in particular the Raman effect. In fact, Raman gain has been successfully exploited in fiber amplifiers and lasers, but usually several kilometres of fibre are required to create a useful device.