REG: Infrared Laser, TV Camera and Fabry Perot for MM-Wave Modulator Research

美国国家科学基金会工程研究设备补助金将用于购买钕钇铝钇铝合金红外激光器、红外电视摄像机、以及用于加州理工学院新型电光调制器研究的红外扫描法布里·珀罗光谱分析仪。将行波电光调制器扩展到100 GHz （3mm）区域的严重困难是由于调制器材料晶体铌酸锂的色散造成的。光波通过晶体的速度比调制波快得多；因此，调制过程在这些高频处不同步。加州理工学院正在研究的一项技术将调制传输线分成许多短段，并通过集成在晶体表面的微小偶极子天线驱动每段。天线由波导发射的平面波激发，以正确的角度入射，使调制波平均与光波保持同步。作为奖励，使用天线和辐射而不是同轴连接器和键合线将调制耦合到传输线，消除了在毫米波范围内非常有害的寄生电子元件。调制频率高达63 GHz （4.8 m）已与18mm长的铌酸锂调制器一起使用，效率很高。这些最初的实验使用633纳米的红色激光。然而，实际使用这种调制器进行信息传输的光纤系统（电话、有线电视、雷达信号等）都在1320或1550纳米处工作。这笔拨款将允许将这种波耦合调制器的研究扩展到这些波长。

This NSF Engineering Research Equipment Grant will enable the purchase of a Neodymium-YAG infrared laser, an infrared TV camera, and an infrared scanning Fabry Perot optical spectrum analyzer for novel electro-optical modulator research at Caltech. A serious difficulty in extending the operation of travelling-wave electro-optical modulators into the 100 GHz (3mm) region is caused by dispersion in the modulator material, crystalline lithium niobate. The optical wave travels through the crystal much faster than the modulation wave; as a consequence, the modulation process gets out of step at these high frequencies. A technique being studied at Caltech breaks the modulation transmission line into a number of short segments, and drives each segment from its own tiny dipole antenna integrated on the surface of the crystal. The antennas are excited by a plane wave radiated from a waveguide, incident at just the correct angle to keep the modulating wave in step with the optical wave on the average. As a bonus, using antennas and radiation rather than coax connectors and bond wires to couple the modulation to the transmission lines eliminates parasitic electrical elements that would be very detrimental in the mm- wave range. Modulation frequencies as high as 63 GHz (4.8 m) have been used with an 18 mm long lithium niobate modulator with good efficiency. These initial experiments employed red laser light at 633 nm. Practical fiber optical systems that use such modulators for information transmission (telephone, CATV, radar signals, etc.) all operate at 1320 or 1550 nm, however. This grant will allow the extension of this wave-coupled modulator research to those wavelengths.