Research On Electro-optical Tunable ROADM With Titanium Diffused Lithium Niobate Waveguides

Reconfigurable optical add/drop multiplexer (ROADM) shows its significancegradually in recent years while the optical network evolving as an all-optic andintelligent one. The ROADM, which adds or drops optical signals by wavelengthscales, supports the business develop in wavelength level with the ability of remotecontrol and configuration and the convenience of network planning and preserving,which benefit the network operation by launching new business and depressing theoperating cost. It has a structure composed of wavelength multiplexer, de-multiplexerand optical switch array as its mainstream technology, which has the defects of lowresponse speed and low configuration level at present. As an alternative strategy, theone based on optical tunable filters is still in the lab because of its high crosstalk anddisability of multi-channel downloads. In order to solve those problems, anelectro-optical tunable ROADM with titanium diffused lithium niobate waveguides isproposed in this article with the innovation points and main contents as following.A novel structure of electro-optical tunable ROADM with titanium diffused lithiumniobate waveguides was proposed. It contains two symmetrical polarization beamsplitters fabricated on the Ti: LiNbO3 waveguides and electrode zone composed ofinterdigital electrodes and phase shifting electrodes which induce the polarizationconversion with E-O grating and tune the wavelength respectively. This scheme has amore rapid response speed, wider tuning range, narrower bandwidth and lowercrosstalk compared with the similar technologies while providing the capacity ofdownloading multi-wavelength synchronously.The apodizing technologies are transplanted from acousto-optic tunable filter, whichsuppress the sidelobe with less than 30 dB. Several methods of adjusting the fullwidth at half maximum (FWHM) are proposed including regulating the parameter ofGauss window function and altering the effective length of electrodes. Calculationproves that both of them are incapable of adjusting the FWHM precisely orduplicabilityto adapt the 100GHz or 200GHz channel spacing.New tuning methods are presented with sinusoidal or cosine function weightedinterdigital electrode voltages. They are able to tune the download wavelength atlower voltage but wider tuning range compared to the one with phase shifters. Theysimplify the electrodes structure and circuit as well. Moreover, the arbitrary double-wavelength download and multi-wavelength download such as fourwavelengths and even eight wavelengths is practicable with or without apodizing.Several combinations of interdigital and phase-shifting electrodes are putting forwardwith different application expect those mentioned above. A comb wavelength filterwith unequal width is designed with two interdigital electrodes and a ROADM withflat-top download spectrum is structured with special interdigital electrodes voltageconfiguration, the latter of which is a rare application with the polarization conversionwith refractive index grating.