Most research efforts to date on optical networks have concentrated on wavelength division multiplexing (WDM) techniques where the information from different channels is routed via separate optical wavelengths. WDM can be used in conjunction with optical time division multiplexing (OTDM) to further increase the network capacity. In these WDM/OTDM network, every interconnecting node requires optical add/drop multiplexer as well as wavelength converters to solve the contention problem. All-optical gating switch, wavelength selective add/drop multiplexer, all optically tunable wavelength converter based on second-order nonlinear optic, three-wave mixing process in titanium indiffused periodically poled lithium niobate (Ti:PPLN) channel waveguides were theoretically and experimentally investigated in this thesis.
Optically controlled all-optical gating switch was demonstrated employing sum frequency generation (SFG) process. One of the continuous wave (cw) and pulsed input signals (pulse width τ = 5 ps, $f_{rep}$ = 10 GHz) was depleted by a cw gating pump wave with an extinction ratio of -32 dB and -7 dB, respectively. The lower extinction ratio for the pulsed signal case is due to the broader spectral bandwidth ($\tri\lambola_{3dB}$ ~ 0.67 nm) of pulses compared with a SFG phase-matching acceptance bandwidth ($Δλ_{accept}$ ~ 0.2 nm). Because of the narrow acceptance bandwidth of the SFG process, all-optical gating switch based on SFG have a wavelength selective characteristic, and due to this, time resolved operation can also be achieved. Using two signals of different wavelength, wavelength selective operation in channel dropping was demonstrated. We obtained less than -22 dB extinction ratio of the signal with a pump power of 170 mW.
All-optical wavelength selective add/drop multiplexer was demonstrated exploiting the optically induced (π -phase shift, which is obtained when the incident signal is regenerated by back conversion process, following complete depletion by SFG. The required switching power for transferring data between two orthogonal polarization states was 1.12 W. The rejection ratio of the signal was -20.2 dB and 85.3 % of the initial signal was recovered at different polarization states. By using two different signals which have 4.2 nm channel spacing, each signal was selectively switched from one polarization state to the other and vice versa, depending on the pump wavelength. -20 dB of rejection ratio was obtained with 1.12 W.
For the first time, all-optical, optically tunable wavelength converter, exploiting cascaded sum and difference frequency generation (cSFG/DFG) between five different wavelengths, was proposed and demonstrated in the Ti:PPLN channel waveguide. With coupled pump power of 780 mW, we obtained -3.3 dB of conversion efficiency, defined as the ratio of generated idler power to the transmitted signal power at the zero pump power level. The proposed wavelength converter has a tuning range of 60 nm.
