Testing of the convex delivery exit with flat mirror joint-type transducer

posted Apr 7, 2013, 5:39 PM by Tiberius Brastaviceanu   [ updated Apr 7, 2013, 5:49 PM ]
Today, Tibi created a setup to test the convex delivery exit with flat mirror joint-type transducer. A 1550nm Mosquito (with Chinese parts: LD+isolator, PD and a 50/50 Y coupler in between them) was used, in conjunction with the LabJack. The Chinese laser with isolator was driven by Frederic's laser driver. The delivery fiber tip was rounded using the fiber splicer. Two reusable ST connectors were used to connect a piece of fiber with a rounded tip with the Mosquito. A "perfect" mirror (silver, surface coated) mounted on a gimbal was used to simulate the joint-type transducer. 

Before testing this device, a flat fiber was put in front of the mirror. The Mosquito signal showed large fluctuations due to resonance within the cavity. 

The flat fiber was replaced with a rounded tip fiber and the same test was performed, showing a great reduction in fluctuations. 

Unfortunately, the laser or Frederic's laser driver started to act funny, and no quantitative data was extracted. In conclusion, the rounded tip of the delivery fiber reduces signal fluctuations. 

What is the nature of these signal fluctuations? Is this a Fabry Perot effect, sending more or less light to the detector based on the conditions of the cavity? Are these fluctuations related to the laser, as it get's more or less feedback? are they a combination of those? 

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