Ajoy K. Kar

Ultrafast laser inscription of an integrated photonic lantern

We used ultrafast laser inscription to fabricate three-dimensional integrated optical transitions that efficiently couple light from a multimode waveguide to a two-dimensional array of single mode waveguides and back. Although the entire device has an average insertion loss of 5.7 dB at 1539 nm, only ≈0.7 dB is due to mode coupling losses. Based on an analysis which is presented in the paper, we expect that our device should convert a multimode input into an array of single modes with a loss of ≈2.0 dB, assuming the input coupling losses are zero. Such devices have applications in astrophotonics and remote sensing.

Optical waveguide fabrication in z-cut lithium niobate (LiNbO3) using femtosecond pulses in the low repetition rate regime

Waveguide structures are fabricated in z-cut lithium niobate (LiNbO3) using focussed femtosecond pulses. Two different types of waveguide structure are fabricated depending on the pulse energy used. In the first, guiding occurs in regions directly surrounding a visible laser-damage region. In the second, guiding occurs in a material modification region created at the focus. High confinement guiding at 1550nm is demonstrated in the first type of waveguide but found to be temporary, thus indicating that at least part of the refractive index change is due to phenomena such as stress that are subject to relaxation. Finally, the polarization dependent guiding properties of the structures are investigated.

Ultrafast-laser inscription of a three dimensional fan-out device for multicore fiber coupling applications

A three dimensional fan-out device has been fabricated using ultrafast laser inscription. The device allows each core of a multicore fibre to be addressed individually by a single mode fiber held in an FVA.

Three-dimensional mid-infrared photonic circuits in chalcogenide glass

We report the fabrication of single-mode buried channel waveguides for the whole mid-IR transparency range of chalcogenide sulphide glasses (λ ≤ 11 μm), by means of direct laser writing. We have explored the potential of this technology by fabricating a prototype three-dimensional three-beam combiner for future application in stellar interferometry that delivers a monochromatic interference visibility of 99.89% at 10.6 μm and an ultrahigh bandwidth (3-11 μm) interference visibility of 21.3%. These results demonstrate that it is possible to harness the whole transparency range offered by chalcogenide glasses on a single on-chip instrument by means of direct laser writing, a finding that may be of key significance in future technologies such as astrophotonics and biochemical sensing.

1.5 GHz picosecond pulse generation from a monolithic waveguide laser with a graphene-film saturable output coupler

We fabricate a saturable absorber mirror by coating a graphene- film on an output coupler mirror. This is then used to obtain Q-switched mode-locking from a diode-pumped linear cavity channel waveguide laser inscribed in Ytterbium-doped Bismuthate Glass. The laser produces 1.06 ps pulses at ~1039 nm, with a 1.5 GHz repetition rate, 48% slope efficiency and 202 mW average output power. This performance is due to the combination of the graphene saturable absorber and the high quality optical waveguides in the laser glass.

Ultrafast laser inscribed Yb:KGd(WO4)2 and Yb:KY(WO4)2 channel waveguide lasers.

We demonstrate laser action in diode-pumped microchip monolithic cavity channel waveguides of Yb:KGd(WO(4))(2) and Yb:KY(WO(4))(2) that were fabricated by ultrafast laser writing. The maximum output power achieved was 18.6 mW with a threshold of approximately 100 mW from an Yb:KGd(WO(4))(2) waveguide laser operating at 1023 nm. The propagation losses for this waveguide structure were measured to be 1.9 dBcm(-1).

Nonlinear optical properties of chalcogenide glasses: Observation of multiphoton absorption

We report observation of four- and five-photon absorption in the chalcogenide glasses at the telecommunication wavelengths. The nonlinear refractive index is sufficiently large that the optical switching criterion is satisfied.

Er:Yb-doped oxyfluoride silicate glass waveguide amplifier fabricated using femtosecond laser inscription

The authors report net gain from a channel waveguide fabricated in an Er:Yb-doped oxyfluoride silicate glass substrate using femtosecond laser waveguide inscription. To fabricate waveguides exhibiting low propagation and coupling losses, they used the recently demonstrated multiscan technique that allows the waveguide cross section and refractive index contrast to be controlled independently of each other. By doing so, the best waveguide exhibited a total background insertion loss, excluding absorption, of only 1.2dB at 1537nm. As a result, a fiber-fiber net gain of 0.72dB at 1537nm was measured for a 10mm long waveguide.The authors report net gain from a channel waveguide fabricated in an Er:Yb-doped oxyfluoride silicate glass substrate using femtosecond laser waveguide inscription. To fabricate waveguides exhibiting low propagation and coupling losses, they used the recently demonstrated multiscan technique that allows the waveguide cross section and refractive index contrast to be controlled independently of each other. By doing so, the best waveguide exhibited a total background insertion loss, excluding absorption, of only 1.2dB at 1537nm. As a result, a fiber-fiber net gain of 0.72dB at 1537nm was measured for a 10mm long waveguide.

70% slope efficiency from an ultrafast laser-written Nd:GdVO4 channel waveguide laser.

We report high efficiency continuous wave laser oscillations at 1063.6 nm from an ultrafast laser written Nd(3+):GdVO4 channel waveguide under the 808 nm optical excitation. A record 17 mm·s(-1) writing speed was used while the low propagation loss of the waveguide (~0.5 dB·cm(-1)) enabled laser performance with a threshold pump power as low as 52 mW and a near to quantum defect limited laser slope efficiency of 70%.

Femtosecond laser writing of waveguides in periodically poled lithium niobate preserving the nonlinear coefficient

Optical waveguides have been inscribed in periodically poled lithium niobate by femtosecond laser pulses with the multiscan technique. Second harmonic generation experiments from a fundamental wavelength of 1567nm demonstrate that the nonlinear optical coefficient in the waveguides is preserved, yielding a conversion efficiency of 18%W−1.