Second harmonic generation via periodically-poled nonlinear materials offers an efficient means of generating high-quality
visible light at wavelengths that would be otherwise unattainable with traditional laser sources. While this
technology has the potential for implementation in many mass-industrial applications, temperature stability
requirements, often as restrictive as 0.1°C, can make packaging with a pump source problematic. In this work we are
investigating the use of synthesised response PPLN gratings to create crystals that are better suited to visible SHG. Our
route towards addressing this issue is to convert the standard sinc-shaped temperature-tuning response of a uniform
grating to a flat-top temperature tuning function with widths of up to several degrees. We have achieved a
computationally efficient means of designing such gratings with a required temperature tuning profile based on a
simulated annealing algorithm using repeated local changes of grating layout and subsequent Bloembergen-style
analysis of the second harmonic, successive iterations of which quickly lead to the desired temperature tuning profile.
Using our high fidelity poling technique we have fabricated synthesised response PPLN with precise placement of poled
domains in Lithium Niobate based on the designs from our mathematical models. Measurements on these initial devices
provide more than 4°C flat-top temperature stability, albeit with a corresponding loss in operational efficiency. Our aim
is to implement improved designs in magnesium-doped Lithium Niobate for packaging with near-room temperature
diode-based pump sources, as could be applied towards RGB TV and projector applications.
We demonstrate a practical ultra-fast Nd-doped fiber laser operating in the 894-909 nm spectral range, in both soliton and stretched pulse dispersion supporting regimes. Using purposely designed semiconductor saturable absorbers, a truly self-started mode-locking regime of operation with clean, transform limited pulses, was achieved.
The taper (i.e. thin fiber with transitions from large to small diameter) is created during pulling of the molten fiber. Its shape depends on many parameters of the pulling process, such as pulling speed, pulling temperature, pulling stages step, etc. This paper attempts to describe the taper shape as a function of pulling parameters and provide comparison for different heating methods.
The paper presents a practical method for fabricating wavelength-selective fused-type couplers. The detailed procedure is described, which allows for reliable fabrication of coupler with arbitrary parameters of wavelength channels. The simple model for the single-mode fused tapered coupler was used to validate the method and to define the technological limits.