Multi-mode Mid-IR Silicon Raman Amplifiers
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Multi-Mode Mid-IR Silicon Raman Amplifiers Bahram Jalali1, Varun Raghunathan2, and Robert R Rice3 1 Electrical Engineering department, University of California Los Angeles, 68-109 E-IV, 420 Westwood Plaza, Los Angeles, CA, 90095-1594 2 Electrical Engineering department, University of California Los Angeles, 63-128 E-IV, 420 Westwood Plaza, Los Angeles, CA, 90095-1594 3 Northrop Grumman Space Technology, One Space Park, Redondo Beach, CA, 90278
ABSTRACT This paper discusses the prospects of silicon as a Mid-wave Infra-red Raman crystal. As a specific example of novel devices that can be realized, we introduce the concept of multi-mode silicon Raman amplifiers and their application in infrared image pre-amplification. The same technology also has application in incoherent beam combining. INTRODUCTION Mid-wave infrared (MWIR)/ long-wave infrared (LWIR) sources have been the topic of active research for over two decades. These sources operating in the 3 – 5 and 8 – 12 µm wavelength range have found applications in free space communications, bio-chemical detection and certain medical applications. Most organic chemicals and biological agents have unique signatures in the MWIR and can be detected using these lasers. The strong water absorption peak at 2.9µm and the resulting applications in medicine and dentistry creates a large demand for such lasers. Typical laser sources used in this wavelength range include diode pumped optical parametric oscillators [1], impurity-based solid state lasers [2] and solid state Raman sources [3]. However, these sources have not achieved wide spread use owing to the complexity and high cost of implementation. Silicon Photonics in the near infrared has attracted significant attention in recent years with the aim of realizing low cost, high speed optoelectronic components. The enormous infrastructure available for silicon device manufacturing and the economy of scales have been the motivating factors in this direction. In particular, Raman scattering has been successfully used to demonstrate Lasers [4,5] and amplifiers [6,7] on a pure silicon chip. Silicon Raman devices can be extended to the mid infrared wavelengths regions with the objective of creating low-cost and small foot print devices for the applications discussed above. Table I compares silicon with popular Raman crystals such as Ba(NO3)2, LiIO3, KGd(WO4)2 and CaWO4 [3]. Silicon is quiet competitive with these crystals owing to: (i) the unsurpassed quality of commercial silicon crystals, (ii) the low cost and wide availability of the material, (iii) extremely high optical damage threshold of 1-4 GW/cm2 (depending on the crystal resistivity), and (iv) excellent thermal conductivity, renders silicon a very attractive Raman crystal for mid-IR applications. The promise of silicon Raman devices is dampened by competing nonlinear absorption processes such as two-photon absorption (TPA) and the associated free carrier absorption (FCA) processes. Low duty cycle pulse pumping [4,6] and reverse-biased carrier sweep out [5,7] w
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