Comb Light Source/Imaging spectrometer for advanced Spectral Domain Optical Coherence Tomography

随着光学相干层析成像技术的发展，人们对功能成像的研究也越来越感兴趣 (10月)。这些功能成像方法中的许多都依赖于OCT的精密相位敏感度 干涉仪。这些技术包括成熟的技术，如多普勒OCT测量血流以及 用于测量机械性能的OCT弹性成像和磁动车式OCT等新兴应用 以及用于分子成像的光热OCT。我们自己的兴趣在于振动测量领域。 扫描激光系统是有利的，因为它们允许使用马赫-曾德尔类型干涉仪 平衡探测器。这提供了共模噪声、DC分量和 自相关伪影。市面上最先进的扫描激光器也有很长的 相干长度(&gt；1米)，因此信号滚降作为深度的函数可以忽略不计。将这些品质结合在一起 产生的图像具有较少的伪影和较高的信噪比，并伴随着高的相位稳定性 和振动敏感性。大多数商用扫描激光器都存在激光扫描不稳定的问题 这样每次扫描都需要校准，以保持高的相位稳定性。我们自己和他人 已经开发了实现这一点的方法，但代价是大量的硬件复杂性和 复杂的算法，以确保作为时间函数的波数k(T)对于每个 扫地。在我们的经验中，系统、环境的微小变化以及激光的正常老化，都会迫使 频繁地对系统进行“调整”，以保持最高的相位稳定性。一家公司开发了一种扫地式 激光，其中k(T)是线性的，并且具有很高的重复性。我们已经证明，这个源提供了高相位- 稳定性，不需要复杂的硬件/软件算法。这种激光系统的缺点是 其有限的光谱带宽(通常为90-95 nm)及其有限的可用性。另一方面， 基于分光计的系统提供高相位稳定性，但通常具有相对较短的相干长度(1-3 Mm)，并且没有平衡检测的优点。然而，它们可以提供较宽的频谱带宽 具有更高的分辨率，同时保持高的相位稳定性。 在这里，我们建议开发一种新型的基于梳状光源光谱仪的系统，它具有所有的优点 具有扫描激光系统的特性，但具有基于分光计系统的固有相位稳定性。目标1：制定 以~1300 nm为中心的梳状激光光源，带宽125-150 nm，在~200以上有1024条离散线 NM。每条线的相干长度将至少为8厘米，提供4厘米3分贝的滚降。目标2：制定 放大倍数为0.5的成像光谱仪，可在200纳米范围内线性分散光线(单位为k) 使用定制复合棱镜的带宽，具有147 kHz的线速。目标3：集成光源 和光谱仪组成的平衡光谱域OCT系统，进行性能验证，并开发了FPGA代码 用于差分信号的流水线实时计算。

There is a growing interest in the development of functional imaging with Optical Coherence Tomography (OCT). Many of these approaches to functional imaging rely on the exquisite phase sensitivity of the OCT interferometer. These include well established techniques like Doppler OCT for measuring blood flow as well as emerging applications like OCT elastography for measuring mechanical properties, and Magnetomotive OCT and Photothermal OCT for molecular imaging. Our own interest lies in the area of vibrometry. Swept laser systems are advantageous because they enable the use of Mach-Zehnder type interferometers with balanced detectors. This provides for cancelation of common mode noise, the DC component, and autocorrelation artifacts. The most advanced commercially available swept lasers also have a very long coherence length (>1 m), hence signal roll-off as a function of depth is negligible. Taken together these qualities result in images that have fewer artifacts and increased signal-to-noise with concomitant high phase stability and vibrational sensitivity. Most commercially available swept lasers suffer from instabilities in the laser sweep such that every sweep needs to be calibrated in order to maintain high phase-stability. Ourselves and others have developed methods to accomplish this, but at the expense of substantial hardware complexity and sophisticated algorithms to ensure that wavenumber as a function of time, k(t), is known precisely for each sweep. In our experience, small changes in the system, environment, and the normal aging of the laser, forces frequent “tweaking” of the system to maintain the highest phase-stability. One company has developed a swept laser, where k(t) is linear and highly reproducible. We have shown that this source provides high phase- stability without the need of the complex hardware/software algorithms. The drawback to this laser system is its limited spectral bandwidth (typically 90-95 nm) and its limited availability. On the other hand, spectrometer based systems offer high-phase stability, but typically with relatively short coherence lengths (1-3 mm) and without the advantages of balanced detection. However, they can provide wide spectral bandwidth with concomitant higher resolution while maintaining high phase-stability. Here we propose to develop a novel comb light source spectrometer based system that has all of the advantages of a swept laser system, but with the inherent phase-stability of a spectrometer based system. Aim 1: Develop a comb laser source centered at ~1300 nm, with a bandwidth of 125-150 nm, and 1024 discrete lines over ~200 nm. The coherence length of each line will be at least 8 cm, providing a 4 cm 3 dB roll-off. Aim 2: Develop an imaging spectrometer with a magnification of 0.5 that disperses the light linearly (in k) over the 200 nm bandwidth using a custom compound prism, having a line rate of 147 kHz. Aim 3: Integrate the light source and spectrometer into a balanced spectral domain OCT system, validate performance, and develop FPGA code for pipelined real-time computation of the differential signal.