Bragg gratings in femtosecond fiber lasers: from programmable pulse shapers to compact volume-grating pulse compressors

Fiber-based lasers constitute next-generation in the ultrashort-pulse sources due to the significant practical advantages offered by fibers, such as high efficiency, compactness and robust all-fiber packaging of complex laser systems. In fact fiber technology has led to the first truly practical and compact mode-locked laser oscillators, which are fully compatible with rigorous reliability requirements of industrial use. However, majority of pulse-shaping and compression techniques conventionally employed for ultrashort pulse generation and control are based on using various bulk optical components (diffraction gratings in particular) and, therefore, are poorly compatible with fiber based laser systems. Here we describe our recent work on developing novel compact pulse-shaping and pulse-compression devices, which are fully compatible with fiber technology. The unifying theme of these efforts is that they use various implementations of chirped Bragg-reflection gratings. The first class of devices, pulse shapers, use combination of chirped fiber gratings and programmable MEMS arrays integrated into a single chip, to arbitrary manipulate the phase of ultrashort optical pulses on a temporal and absolute-phase magnitude scales exceeding those of conventional diffraction-grating based pulse shapers. In contrast, the second type of devices are based on volume chirped Bragg gratings to achieve pulse stretching and recompression between femtosecond to subnanosecond time scales. Use of volume gratings here offers a unique advantage of providing with compact devices which are also compatible with very high pulse energies. We have demonstrated that broad-bandwidth high-reflectivity gratings can be made in photo-thermal glass with apertures of several millimeters (and potentially much larger) thus permitting ∼mJ fiber-amplified and recompressed ultrashort-pulse energies. Fiber-based chirped pulse amplification systems demonstrated using these novel pulse stretchers and compressors, combine advantages of being compact, robust, efficient, and providing with very high average power and high pulse energy ultrashort pulses.