Slow Wave Electrooptic Light Modulators

这个项目的目标是展示使用新的调制器设计原理的极其高效和高度线性的微波到光转换。这一提议的理论基础是最近才发展起来的，而计划中的实验将建立在德克萨斯A&amp大学十多年来对导波光学铁电材料的研究基础上。所提出的电光调制器利用行波（TW）马赫-曾德干涉仪配置。每个干涉仪臂上的集成光栅反射器形成一个标准子，降低了向前方向的平均光传播速度。“慢”波导结构提供了两个特性，使得调制器性能优于传统的“快”TW设计：(1)具有高电光系数和介电常数的基片的光/微波速度匹配，以及(2)由于光在调制区域的“停留时间”而增强的电光相互作用强度。对于在传统铌酸锂（LN）衬底材料中制造的器件，这两个因素导致电功率耗散比传统速度匹配设计有一个数量级的潜在改进。使用钨青铜衬底，如铌酸锶钡（SBN），其电光系数比LN高得多，预计驱动功率会进一步降低几个数量级。在LN和SBN中使用慢波结构也可以改善干涉调制器的响应线性度。校准器N等距的反射镜(N _ 3)表现出高透光率在宽光谱范围被设计用于在慢波调节器。由于这种结构的透光率在光频上具有周期性，因此具有适当反射器间距的单个调制器可用于密集波分复用（WDM）通信系统中的任何信道。设计工作波长接近1.5 gm的调制器将在LN和SBN衬底上制造。传统的光刻、蚀刻和扩散技术将用于制作波导和电极图案。波纹光栅将在衬底表面通过反应离子蚀刻或离子铣削产生，使用全息相位掩模，以氩气激光器作为光源来定义0.35 gm周期图案。测量的电功率耗散、pi电压（Va）和响应线性度将与输入带宽为10 GHz的“快波”器件报告的结果进行比较。这些调制器有望在数字和模拟光纤通信系统中得到应用，在这些系统中，电力需求的数量级减少将对光传输设备的尺寸和成本产生重大影响。此外，由于不需要非常厚（~ 15-30 ~tm）的电极，集成光学芯片的成本可以大大降低。在GIfl状态下运行的模拟光纤链路也将受益于增强的动态范围，目前受微波放大器可用的最大驱动功率和集成光调制器响应线性度的限制。

The goal of this project is to demonstrate extremely efficient and highly linear microwave-to-optical conversion using new modulator design principles. The theoretical basis for this proposal was developed recently, while the planned experiments will build upon over a decade of research at Texas A&M in ferroelectric materials for guided wave optics. The proposed electrooptic modulators utilize a traveling wave (TW) Mach-Zehnder interferometer configuration. Integrated grating reflectors in each interferometer arm form an etalon which reduces the average optical propagation speed in the forward direction. The 'slow" waveguide structures provide two features which lead to improved modulator performance over conventional "fast" TW designs: (1) optical/microwave velocity matching in substrates with high electrooptic coefficients and dielectric constants, and (2) enhancement of electrooptic interaction strength due to the "dwell time" of the light in the modulation region. For devices fabricated in the conventional lithium niobate (LN) substrate material, these two factors lead to a potential improvement of an order of magnitude in electrical power dissipation over conventional velocity-matched designs. Additional orders-of-magnitude reduction in driving power is anticipated from the use of tungsten bronze substrates such as strontium barium niobate (SBN), which have much higher electrooptic coefficients than LN. Better response linearity in interferometric modulators is also possible using slow wave structures in both LN and SBN.Etalons with N equally spaced reflectors (N _ 3) which exhibit high transmittance over a wide spectral range have been designed for use in the slow-wave modulators. Since the transmittance of such a structure is periodic in optical frequency, a single modulator with appropriate reflector spacing could be used on any channel in a dense wavelength-division- multiplexed (WDM) communication system.Modulators designed to operate at a wavelength near 1.5 gm will be fabricated in LN and SBN substrates. Conventional lithography, etching, and diffusion techniques will be used to produce waveguide and electrode patterns. Corrugated gratings will be produced on the surface of the substrate by reactive ion etching or ion milling using a holographic phase mask with an argon laser as the light source to define the 0.35 gm-period patterns. Measured electrical power dissipation, pi-voltage (Va), and linearity of response will be compared with results reported for "fast-wave" devices in LNto bandwidths 10 GHz. These modulators are expected to find application in digital and analog fiber optic communication systems, where order-of-magnitude reductions in electrical power requirements would have a major impact on the size and cost of optical transmission equipment. Furthermore, since the need for very thick (~ 15-30 ~tm) electrodes is eliminated, the cost of the integrated optic chip can be reduced considerably. Analog fiber optic links operating in the GIfl regime would also benefit from enhanced dynamic range, which presently is limited by the maximum drive power available from microwave amplifiers and the linearity of response of integrated optic modulators.