Posada-Roman Julio E, Garcia-Souto Jose A, Poiana Dragos A, Acedo Pablo
Department of Electronics Technology, Universidad Carlos III de Madrid, Av. Universidad 30, E-28911 Leganés, Madrid, Spain.
Sensors (Basel). 2016 Nov 26;16(12):2007. doi: 10.3390/s16122007.
Optical frequency combs (OFC) generated by electro-optic modulation of continuous-wave lasers provide broadband coherent sources with high power per line and independent control of line spacing and the number of lines. In addition to their application in spectroscopy, they offer flexible and optimized sources for the interrogation of other sensors based on wavelength change or wavelength filtering, such as fiber Bragg grating (FBG) sensors. In this paper, a dual-OFC FBG interrogation system based on a single laser and two optical-phase modulators is presented. This architecture allows for the configuration of multimode optical source parameters such as the number of modes and their position within the reflected spectrum of the FBG. A direct read-out is obtained by mapping the optical spectrum onto the radio-frequency spectrum output of the dual-comb. This interrogation scheme is proposed for measuring fast phenomena such as vibrations and ultrasounds. Results are presented for dual-comb operation under optimized control. The optical modes are mapped onto detectable tones that are multiples of 0.5 MHz around a center radiofrequency tone (40 MHz). Measurements of ultrasounds (40 kHz and 120 kHz) are demonstrated with this sensing system. Ultrasounds induce dynamic strain onto the fiber, which generates changes in the reflected Bragg wavelength and, hence, modulates the amplitude of the OFC modes within the reflected spectrum. The amplitude modulation of two counterphase tones is detected to obtain a differential measurement proportional to the ultrasound signal.
通过对连续波激光器进行电光调制产生的光学频率梳（OFC）提供了宽带相干光源，每条谱线具有高功率，并且谱线间距和谱线数量可独立控制。除了在光谱学中的应用外，它们还为基于波长变化或波长滤波的其他传感器（如光纤布拉格光栅（FBG）传感器）的询问提供了灵活且优化的光源。本文提出了一种基于单个激光器和两个光学相位调制器的双OFC FBG询问系统。这种架构允许配置多模光源参数，如模式数量及其在FBG反射光谱内的位置。通过将光谱映射到双频梳的射频光谱输出上可实现直接读出。该询问方案被提议用于测量快速现象，如振动和超声波。给出了在优化控制下双频梳操作的结果。光学模式被映射到可检测的音调上，这些音调是围绕中心射频音调（40 MHz）的0.5 MHz的倍数。用该传感系统演示了对超声波（40 kHz和120 kHz）的测量。超声波在光纤上引起动态应变，这会导致反射布拉格波长发生变化，从而调制反射光谱内OFC模式的幅度。检测两个反相音调的幅度调制以获得与超声信号成比例的差分测量结果。
