A new (to our knowledge) ultrashort laser pulse irradiation regime that allows us to directly modify and increase the refractive index of rare earth doped YAG polycrystalline ceramics has been identified. Single-mode buried channel waveguides in both Ho:YAG and Er:YAG ceramics at the near-IR wavelengths of 1.55 μm and 1.95 μm are demonstrated by fabricating positive square step-index cores. Minimum propagation losses of 1.5 dB cm(-1) at a 1.51 μm wavelength have been preliminarily obtained. Confocal microluminescence mapping reveals that the increased refractive index regions retain the near-IR spectral properties of Er3+ ions in the YAG crystalline matrix.

We propose a new method for the development of a tunable optical bandpass filter (TOBF) based on a linearly chirped fiber Bragg grating (LCFBG). A NiCr wire heater is used to heat the LCFBG at a small point to introduce a narrow passband within the stop band of the LCFBG. The central wavelength of the passband is tuned by scanning the wire heater along the LCFBG. As an example demonstrating the effectiveness of the proposed method, we demonstrate a TOBF with a very small 3-dB bandwidth of approximately 7 pm, a tuning range of 16.4 nm, and a rejection ratio of more than 25 dB. Compared with previously reported tunable-fiber-based bandpass filters, this method provides the advantages of a large tuning range, continuous tunability, a switchable passband, a simple tuning mechanism, low cost, and narrow bandwidth.

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Efficient passive Q-switching operation of a 1532 nm in-band pumped polycrystalline Er:YAG ceramic 1645 nm laser is demonstrated in this work. Graphene deposited on a quartz substrate was used as the saturable absorber for the Q-switching operation. Under an incident pump power of 4.14 W, an average output power of 528 mW was obtained, with the pulse energy and pulse repetition rate being 7.08 μJ and 74.6 kHz, respectively.