Novel geometry fibres for use in optical communications and high power lasers

The progress Multi-element Fiber (MEF) for applications such as space-division-multiplexed transmission and multi-port amplifiers is reviewed. Error-free transmission of 1014GBps in a Ge-doped 3-element MEF (3-MEF) with an effective length of 28.5km has been demonstrated. Er-doped 3-MEF and 7-element MEF have been operated as core-pumped amplifiers with each element providing an average gain of 33dB with a NF of 20dB gain in the wavelength range of 1536-1615nm (80nm) bandwidth. Further, the progress towards Multi Trench Fiber (MTF) has been reviewed. This fiber can provide single mode operation for effective area (Aeff) as large as 10,000µm2 in rod-type configuration on the other hand it can provide 1000µm2 in bend configuration. MTF offers certain advantages of easy fabrication, easy splicing and cleaving over other fibers. A 30µm core MTF has been demonstrated, which shows a 50dB suppression of higher order modes. Modified version of MTF (Single trench fiber) can also be used in bend configuration for single mode operation while having core refractive index to be higher than cladding. This further reduces the fabrication cost associated with the fiber, hence makes it suitable for mass production. A single trench fiber laser of 20µm core (Aeff~400µm2) has been demonstrated to provide very high suppression of HOMs (~32dB using S2 measurement). Further, Hybrid-MTF with additional resonators has been investigated to tailor the dispersion.