The authors experimentally demonstrate stable pulse generation from a rational harmonic mode-locked fiber ring laser
that employs carrier-suppressed return-to-zero (CS-RZ) format as a modulation waveform. We obtain the CS-RZ format
by tuning the bias voltage of the LN intensity modulator and the RF driving amplitude. The rational mode-locking is
realized by detuning the modulation frequency in the laser system. We have observed the rational harmonic
mode-locking of up to the fifth order. The most stable pulses are generated at the rational harmonic order of two, where
the stability of the output pulses is evaluated by the sum of the normalized standard deviation of the voltage and that of
the time of the pulse leading edge.
We have developed polyimides for optical waveguide synthesized by block-copolymerization method. We demonstrated the optical waveguide with rather low refractive indices. Lower refractive indices make larger waveguide size and easier coupling to optical fibers. We applied polyimides with lower refractive indices with a fluorinated polyimide for the clad and polyimide of dedrimer structures for core. The refractive indices are precisely controlled as 0.01 by thermal conditions. This core polyimide has patterned by i-line process and formed optical waveguide.
Cascading of quadratic nonlinearity has been attracting great interests for its potential application to parametric devices,
such as phase conjugators or effective Kerr media. In most configurations, the device consists of a single nonlinear element
with uniform phase-mismatch. Cascading of several elements with different phase-mismatch has been theoretically investigated and predicted to improve performance of the device for classical applications. In this paper, amplitude squeezing in second-harmonic generation using cascaded quadratic nonlinear elements is numerically analyzed. The analyses are based on linearization of nonlinear coupling equations, where interacting fields are approximated as plane waves. Phase-mismatch of each element is varied independently and tolerance of squeezing performance to the fluctuation of the phase-mismatch is also investigated. It is predicted that the performance as a squeezing device can be also superior to that of a single element device, if a proper combination of the phase-mismatch of each element is chosen. For the fundamental wave, the tolerance to the fluctuation of the phase-mismatch will improve by nearly tenfold compared with the single element case. For the harmonic wave, squeezing beyond the limit of perfect phase-matched case (3dB) will be available, though the tolerance to the fluctuation of the phase-mismatch is quite small. These improvements can be attributed to the nonlinear phase rotation that keeps squeezed axis coincided with the amplitude phase in a stable manner.