Asymmetric lithium niobate Mach-Zehnder interferometer and its applications in photonic analog-to-digital conversion
will be discussed. Two schemes based on the asymmetric interferometer will be proposed and analyzed. The first scheme
is the phase shift photonic analog-to-digital conversion using asymmetric interferometer and synchronized multiwavelength
optical sampling pulses. Because of the dispersion effect of the lithium niobate crystal, when multiwavelength
optical pulses enter into the interferometer, at the output port, different wavelengths will have different phase
differences between two arms. As a result, after interference, the transmission characteristics of different wavelengths
will have a phase shift between each other, and this is just the key issue of phase shift photonic analog-to-digital
conversion. The other scheme we will propose in this paper is a spectral encoded photonic analog-to-digital conversion.
The spectral transmission characteristic of the asymmetric interferometer will shift with the voltage change of the analog
signal, and this shift has an ideal linear relation with the analog voltage change. The peak wavelength of the transmission
spectrum can be detected to realize quantization of the applied analog signal. Using both schemes presented in this paper,
high sampling rate and high resolution optical analog-to-digital conversion can be realized.
An approach to generate ultrawideband (UWB) monocycle pulses is proposed and experimentally demonstrated, based on a dual-output intensity modulator and tunable optical time delay. Positive and negative pulses are obtained from two output ports of the modulator, respectively, and are coupled together through different time delays. The generated monocycle pulse has a 10-dB bandwidth of 6.5 GHz and a central frequency of 3.7 GHz.
In this paper, an interferometric autocorrelator based on two-photon-absorption (TPA) detector is demonstrated. It can be used in the measurement of ultrashort pulse at 1.55 um wavelength region. From the second order autocorrelation trace of optical field, we can infer the pulse width. Accompanied with a linear detector, we can fully characterize the optical pulse, including intensity and phase profiles. A novel phase retrieval algorithm is proposed. It is a combination of an iterative loop and an evolution process. Simulation results show that our algorithm converges stably and can give a
better approximation of the optical field than traditional algorithm.