Design and fabrication of a refractometric chemical sensor using heterodyned widely tunable lasers.

摘要

In a time of increased concern over biological weapons and infectious diseases, a device which can rapidly and reliably determine whether a foreign substance is harmful or benign is strongly desired. Many of the most established technologies and processes for identifying a substance require treatment of the sample with fluorescent markers before testing; therefore, these devices have a slow response time and are inconvenient outside of a laboratory. Additionally, the quantification of pathogen concentration and detection of small amounts of a substance is less reliable if the human eye is the detector.; A new class of sensors uses optical techniques to detect the existence of a pathogen. These existing technologies for chemical index sensing require the use of external light sources, optics, and detectors. This requirement limits the portability and versatility of these devices and, therefore, restricts the incorporation of biosensors into field applications, doctors' offices, and consumers' homes. By leveraging the knowledge and sophistication of the telecommunications industry, integrated sensors can be fabricated which exhibit fast detection, a small footprint, and a good sensitivity to small concentration changes.; This thesis will discuss progress in using an established telecommunications platform for high sensitivity chemical sensing. The fabricated devices use a sensor design with frequency tunable lasers, heterodyne spectrometers, and an integrated waveguide photodetector. Slight changes in the refractive index surrounding the laser are measured through corresponding changes in the lasing frequency. By reducing the waveguide ridge width in one section of the laser, referred to as the sensing region, the transverse modal overlap increases by 10--20x, increasing the sensitivity by the same ratio. A frequency shift of 80 GHz/RIU was measured when temperature effects were removed. The long-term frequency stability of this sensor is as low as 1.6 MHz leading to a minimum detectable index difference of 2x10-5. This figure is comparable to many existing technologies which use external sources.