采用频率差在太赫兹范围的双波长激光器进行泵浦, 利用光纤的四波混频效应, 得到结构紧凑、频率可调的窄带太赫兹波源。为减小光纤材料对太赫兹波的吸收, 采用了表面发射机制。从耦合波理论出发, 详细分析了保偏光纤中的四波混频过程, 得到了太赫兹波输出功率的解析表达式, 并讨论了实现相位匹配的条件。结果表明, 太赫兹波功率与泵浦光功率和光纤长度成正比, 与太赫兹波长的3次方成反比。当泵浦光峰值功率为1 kW, 在6 THz处得到的太赫兹波峰值功率达350 mW, 功率转换效率约为0.01%。通过合理设置泵浦波长, 可以实现太赫兹辐射在3～8 THz 范围内连续调谐。该方案提供了一种新型的高功率、紧凑型的窄带太赫兹辐射源。

This paper proposes theoretically a novel terahertz source based on polarization-maintaining optical fibers. Utilizing the dual-wavelength laser as the pump source and four-wave-mixing effect in the optical fibers, a compact wide-tunable narrowband terahertz source can be constructed. The surface-emitting scheme is used to decrease the absorption loss of terahertz waves in the optical fibers. The four-wave mixing process and the phase-matching conditions are discussed through the coupled-wave theory, and the analytical expression of terahertz output power is obtained. It is shown that when the pump peak power is about 1 kW, the terahertz peak power is about 350 mW at 6 THz, and the power conversion efficiency is about 0.01%. This scheme provides a possibility to realize a high-power, compact narrowband terahertz source.