Abstract: The dynamic sensors for speed and flow are applied in pathological physiological research of the cardiovascular system and for the study of blood flow in the capillaries. The use of laser Doppler anemometry (LDA) method is considered the major prospective for this application. This method is based on the Doppler shift of the frequency of laser radiation scattered by blood particles in movement. However, to have access to inner organs, a small-size delivery system and optical probe are necessary. In this paper, we report a novel miniature optical probe for the differential-type LDA, suitable for use in small blood vessels and in other small channels. For the construction of the probe, two-core single mode optical fiber was used. This fiber had two anisotropic 8 $mu cores, located symmetrically with respect to the fiber axis. The separation between them was 25 $mu@. In the fiber, a directional coupler was integrated near the fiber's remote end. The coupler was fabricated by heating of a small section of the fiber, with simultaneous elongation of this section. For heating, the carbon-dioxide laser was utilized. The carbon-dioxide laser was also used to fabricate a lens at the fiber tip. At the fiber entrance, the laser light was launched in one of the fiber's cores. The fiber was typically of several meters long. Near the fiber end, this radiation was splitted by the directional coupler, and the second core was excited too. At the fiber tip, the fused lens provided collimation of the emerging beams and secured their intersection in front of the fiber tip. In this intersection volume, the interference field was formed. In the flow, this periodic pattern resulted in Doppler frequency shift of the light scattered by moving particles. This probe was successfully used together with the LDA signal processing equipment for velocity measurement in small tubes for blood-flow simulation experiments. In the probe, the two cores are identical, and the between the directional coupler and the fiber tip is very small. Thereafter, all extrinsic fields and effects have identical influence on the propagation constant of each core. Hence, the resultant parasitic phase modulation, that is the main problem in the fiber-based differential LDA, is negligible in this probe. This is the principal advantage of this probe. However, its small size and integrated nature are also of value for biomedical applications. !22
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机译：摘要：速度和流量的动态传感器被用于心血管系统的病理生理研究以及毛细血管中血流的研究。激光多普勒风速计（LDA）方法的使用被认为是该应用的主要前景。该方法基于运动中血液颗粒散射的激光辐射频率的多普勒频移。但是，要接近内部器官，必须使用小型传送系统和光学探头。在本文中，我们报告了一种适用于小血管和其他小通道的新型微光学探头，用于差分型LDA。为了构造探头，使用了两芯单模光纤。该纤维具有两个各向异性的8μm芯，相对于纤维轴对称放置。他们之间的距离是25 $ mu @。在光纤中，定向耦合器集成在光纤远端附近。耦合器是通过加热一小段光纤并同时延长该段来制造的。为了加热，利用了二氧化碳激光器。二氧化碳激光器还用于在光纤尖端制造透镜。在光纤入口处，激光在光纤的一个纤芯中发射。光纤通常长几米。在光纤末端附近，该辐射被定向耦合器分开，第二个纤芯也被激发。在光纤尖端，熔融透镜提供了出射光束的准直，并将它们的交点固定在光纤尖端的前面。在该相交体积中，形成了干扰场。在流动中，此周期性模式导致通过移动粒子散射的光的多普勒频移。该探头已与LDA信号处理设备一起成功用于小管中的速度测量，以进行血流模拟实验。在探头中，两个纤芯是相同的，定向耦合器和光纤尖端之间的纤芯很小。此后，所有外部场和效应对每个核的传播常数具有相同的影响。因此，在该探头中可以忽略产生的寄生相位调制，这是基于光纤的差分LDA中的主要问题。这是该探针的主要优点。但是，它的小尺寸和集成特性对于生物医学应用也很有价值。 ！22
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