We propose and theoretically investigate a novel approach for generating terahertz (THz) radiation in a standard single-mode fiber. The optical fiber is mediated by an electrostatic field, which induces an effective second-order nonlinear susceptibility via the Kerr effect. The THz generation is based on difference frequency generation (DFG). A dispersive fiber Bragg grating (FBG) is utilized to phase match the two interacting optical carriers. A ring resonator is utilized to boost the optical intensities in the biased optical fiber. A mathematical model is developed which is supported by a numerical analysis and simulations. It is shown that a wide spectrum of a tunable THz radiation can be generated, providing a proper design of the FBG and the optical carriers. 1. Introduction Due to a lack of generation and detection instrumentation, the electromagnetic spectrum between infrared light and microwave radiation, traditionally known as the terahertz (THz) gap, has not been fully explored [1]. The application of THz radiation was traditionally limited to astronomy and analytical science. Recent advances in photonics have laid the groundwork for the realization of THz sources and detectors for applications in biomedical imaging [2] and ultra-fast communications [3]. As THz sources become more readily available, THz technology is being increasingly used in a variety of fields, including information and communications technology, biology and medical sciences, nondestructive evaluation, homeland security, quality control of food and agriculture, global environmental monitoring, and ultrafast computing, to mention a few examples [4]. The wide and crucial applications of THz waves are due to its unique way of interacting with materials. For example, in medical science, the ability of THz wave to probe intermolecular interactions enables it to provide both structural and functional information. Consequently, and considering its safe, accurate, and economical features, THz radiation promisesto alternate other scanning methods such as high frequency ultrasound, magnetic resonance imaging, and near-infrared imaging [4]. This promising technology has the potential to lead the way many diseases are diagnosed and ultimately cured. In the past few years, several techniques have been proposed to generate THz waves. Generation of CW and pulsed THz waves have been both investigated. Techniques to generate CW THz waves include quantum cascade laser (QCL) [5], directly multiplied source [6], backward wave oscillator (BWO) [7], germanium laser [8], and silicon impurity
References
[1]
G. P. Williams, “Filling the THz gap—high power sources and applications,” Reports on Progress in Physics, vol. 69, no. 2, pp. 301–326, 2006.
[2]
P. H. Siegel, “Terahertz technology in biology and medicine,” IEEE Transactions on Microwave Theory and Techniques, vol. 52, no. 10, pp. 2438–2447, 2004.
[3]
T. Nagatsuma, “Generating millimeter and terahertz waves,” IEEE Microwave Magazine, vol. 10, no. 4, pp. 64–74, 2009.
[4]
M. Tonouchi, “Cutting-edge terahertz technology,” Nature Photonics, vol. 1, no. 2, pp. 97–105, 2007.
[5]
B. S. Williams, “Terahertz quantum-cascade lasers,” Nature Photonics, vol. 1, no. 9, pp. 517–525, 2007.
[6]
A. Maestrini, J. S. Ward, J. J. Gill et al., “A frequency-multiplied source with more than 1 mW of power across the 840-900-GHz band,” IEEE Transactions on Microwave Theory and Techniques, vol. 58, no. 7, pp. 1925–1932, 2010.
[7]
A. Dobroiu, M. Yamashita, Y. N. Ohshima, Y. Morita, C. Otani, and K. Kawase, “Terahertz imaging system based on a backward-wave oscillator,” Applied Optics, vol. 43, no. 30, pp. 5637–5646, 2004.
[8]
D. R. Chamberlin, E. Brundermann, and E. E. Haller, “Narrow linewidthintervalence-band emission from germanium terahertz lasers,” Applied Physics Letters, vol. 83, no. 3, pp. 3–5, 2003.
[9]
P.-C. Lv, R. T. Troeger, S. Kim et al., “Terahertz emission from electrically pumped gallium doped silicon devices,” Applied Physics Letters, vol. 85, no. 17, pp. 3660–3662, 2004.
[10]
N. N. Zinov'ev, A. S. Nikoghosyan, R. A. Dudley, and J. M. Chamberlain, “Conversion of short optical pulses to terahertz radiation in a nonlinear medium: experiment and theory,” Physical Review B, vol. 76, no. 23, Article ID 235114, 2007.
[11]
L. Miao, D. Zuo, Z. Jiu, and Z. Cheng, “An efficient cavity for optically pumped terahertz lasers,” Optics Communications, vol. 283, no. 16, pp. 3171–3175, 2010.
[12]
B. A. Knyazev, G. N. Kulipanov, and N. A. Vinokurov, “Novosibirsk terahertz free electron laser: instrumentation development and experimental achievements,” Measurement Science and Technology, vol. 21, no. 5, Article ID 054017, 2010.
[13]
A. Rice, Y. Jin, X. F. Ma et al., “A Terahertz optical rectification from <110> zinc-blende crystals,” Applied Physics Letters, vol. 64, no. 11, pp. 1324–1326, 1994.
[14]
Y. Jiang, D. Li, Y. J. Ding, and I. B. Zotova, “Terahertz generation based on parametric conversion: from saturation of conversion efficiency to back conversion,” Optics Letters, vol. 36, no. 9, pp. 1608–1610, 2011.
[15]
D. Dietze, J. Darmo, S. Roither, A. Pugzlys, J. N. Heyman, and K. Unterrainer, “Polarization of terahertz radiation from laser generated plasma filaments,” Journal of the Optical Society of America B, vol. 26, no. 11, pp. 2016–2027, 2009.
[16]
K. Saito, T. Tanabe, Y. Oyama, K. Suto, and J.-I. Nishizawa, “Terahertz-wave generation by GaP rib waveguides via collinear phase-matched difference-frequency mixing of near-infrared lasers,” Journal of Applied Physics, vol. 105, no. 6, Article ID 063102, 2009.
[17]
Y. Sasaki, A. Yuri, K. Kawase, and H. Ito, “Terahertz-wave surface-emitted difference frequency generation in slant-stripe-type periodically poled LiNbO3 crystal,” Applied Physics Letters, vol. 81, no. 18, pp. 3323–3325, 2002.
[18]
M. Yi, K. Lee, J. Lim, Y. Hong, Y.-D. Jho, and J. Ahn, “Terahertz waves emitted from an optical fiber,” Optics Express, vol. 18, no. 13, pp. 13693–13699, 2010.
[19]
M. Qasymeh, M. Cada, and S. A. Ponomarenko, “Quadratic electro-optic Kerr effect: applications to photonic devices,” IEEE Journal of Quantum Electronics, vol. 44, no. 8, pp. 740–746, 2008.
[20]
H. An and S. Fleming, “Inverstigating the effectiveness of thermally poling optical fibers with various internal electrode configurations,” Optics Express, vol. 20, no. 7, pp. 7436–7444, 2012.
[21]
G. P. Agrawal, Nonlinear Fiber Optics, Academic Press, San Diego, Calif, USA, 4th edition, 2007.
[22]
S. Pereira and J. E. Sipe, “Nonlinear pulse propagation in birefringent fiber Bragg gratings,” Optics Express, vol. 3, no. 11, pp. 418–432, 1998.
[23]
Y. S. Kivshar and G. P. Agrawal, Optical Solitons: from Fibers to Photonic Crystals, Academic Press, San Diego, Calif, USA, 2003.
[24]
E. A. Saleh and M. C. Teich, Fundamental of Photonics, John Wiley & Sons, New York, NY, USA, 1991.
