We used a commercially available 75 MHz regeneratively amplified laser system emitting 50 femtosecond pulses of
energies up to 3nJ at a wavelength of 800 nm. All waveguides were fabricated by focussing the femotsecond pulse train
polarised parallel to the x-axis to a distance of approximately 125 μm below the sample surface using a 0.65 NA, ×40
microscope objective and translating the sample along the y axis. To find the optimum waveguide fabrication parameters
the translation speed was varied from 2 to 100 μm/s. We introduces a method of measuring the refractive index of
optical waveguide in ten micrometer. Useing CCD to measure the two-dimensional near-field light intensity distribution
of the output cross-section of the waveguide, by measuring the two-dimensional near-field light intensity distribution of
the output cross-section of the waveguide can be calculated the two-dimensional distribution of refractive index of
waveguides. The context detailedly gives measurement results about femtosecond laser inducing the near-field intensity
of lithium niobate optical waveguide cross-section and calculations of refractive index of optical waveguide. The results
show that the refractive index of waveguides showed a large central, gradually reduce and the change of refractive index
in the range of 0.001. This method is of great significance to measure the optical waveguide refractive index
distribution.
The bend waveguide is one of the key components of photonic integration. In this paper, by using
tightly focused femtosecond laser pulses with repetition rate of 76 MHz, pulse duration of 50 fs, average output
power about 270mW, and the focus lens NA=0.65, we put forward a structure of waveguide that bent it to be 1/4
round, and research its mechanism by performing experiments. Under the above conditions, when the vertical
scanning speed of the laser system is 0.8 mm / s, the width of the bend optical waveguide is about 10μm, the
loss reaches a minimum value about 1dB/cm when the bend way’s radius is about 5mm. Based on the
experimental results of the above parameters, we can fabricate a 1/4 round vertical bend fiber coupler, which
can be applied to the connection between the chips or inter-level optical .The results showed that the bend
lithium niobate waveguides can be applied in the field of optical communication and has important implications
for the production of low loss, low cost and small size optical waveguide gratings , vertical fiber coupler, optical
switches and other devices .
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