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For the first time to our knowledge, we experimentally demonstrate a clock signal transmission using a counter-propagating Raman pump as a transmitter and concurrently utilize the same pump to amplify a data signal. A 1548nm vertical cavity surface emitting laser (VCSEL) was modulated with a pseudorandom bit sequence (2${}^7-1$) and coupled into an optical fiber. A 1448nm Raman pump in the backward scheme was also modulated with a 10kHz clock and used to boost the VCSEL data signal so as to improve the reach of the transmission. Clock distribution in a telescope network such as the Square Kilometre Array (SKA) is essential for the proper operation of the digitizers as well as dish synchronization. In the SKA phase 1, long transmissions involving baselines extending up to 100km may need amplification. We propose the use of counter-Raman configuration to amplify the signal carrying received astronomical data while transmitting a clock to the receptors. This is a cost-effective bi-directional transmission suited for telescope network applications.

Focal ratio degradation (FRD), the decrease of light’s focal ratio between the input into an optical fiber and the output, is important to characterize for astronomical spectrographs due to its effects on throughput and the point spread function. However, while FRD is a function of many fiber properties such as stresses, microbending, and surface imperfections, angular misalignments between the incoming light and the face of the fiber also affect the light profile and complicate this measurement. A compact experimental setup and a model separating FRD from angular misalignment was applied to a fiber subjected to varying stresses or angular misalignments to determine the magnitude of these effects. The FRD was then determined for a fiber in a fiber positioner that will be used in the Subaru Prime Focus Spectrograph (PFS). The analysis we carried out for the PFS positioner suggests that effects of angular misalignment dominate and no significant FRD increase due to stress should occur.