Improving the Raman amplifier bandwidth and gain using multi-micro ring photonic crystal structures
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Improving the Raman amplifier bandwidth and gain using multi‑micro ring photonic crystal structures Amire Seyedfaraji1 Received: 4 April 2020 / Accepted: 16 October 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract In this paper, first the improvement in the Raman amplification bandwidth through the selfphase modulation (SPM) effect in the straight photonic crystal structures was compared to the single-ring and 2-ring photonic crystal structures. The resonance effect in micro ring structures, enhances the effective pump power and thus can achieve the same level of Raman gain at a much lower input pump power, but an increase in the amplification bandwidth in a ring structure is limited by the filtering effect of the micro ring. Then, in order to increase the Raman amplification bandwidth and gain, a 10-ring new structure was introduced. The design of this new structure is based on the use of optofluidic materials. To model Raman amplification in these structures, Maxwell equations are solved using finite difference time domain method considering optical nonlinear parameters like two photon absorption, free carrier absorption, Kerr effect and self-phase modulation effect. This multi-ring Raman amplifier yields a large Raman gain (26.79 dB) and a considerable Raman amplification bandwidth (10.33 mm) despite its extremely short amplification length (160 μm) and an extremely low input pump power (0.5 W). Keywords Raman amplification · Bandwidth · SPM · Photonic crystal · Optofluidic materials
1 Introduction It is extremely important to make the optical amplifiers, optical sources, fast modulators, and optical detectors out of silicon (Si). Si-based photonics has many applications in various areas such as medicine, military, optical telecommunications. Moreover, the optical amplification and lasing in silicon using stimulated Raman scattering have captured considerable attention in the past years (Rong et al. 2007). In the spontaneous Raman scattering, the lattice thermal vibrations cause sinusoidal modulation in the optical susceptibility at the ωυ frequency, which is about 15.6 THz in silicon. Moreover, as a result of the collision of the input pump field (at the ωl frequency) vibrations with the optical susceptibility vibrations, polarizations occur at the sum (ωl + ωυ) * Amire Seyedfaraji [email protected] 1
Faculty of Engineering and Technology, Alzahra University, Tehran, Iran
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and difference (ωl − ωυ) frequencies. The radiations from these two polarization components are known as the anti-stokes and stokes waves, respectively. In the stimulated Raman scattering process, the atomic vibrations can be stimulated through the concurrent propagation of the pump and stokes fields with a frequency difference equal to the frequency of the atomic vibrations in the Raman medium. The result of this stimulation is an increase in the stokes field amplitude (Jalali et al. 2006). In recent years, Raman gain in the Si waveguide
