An integrated multi-wavelength tunable ultra-narrow bandwidth filter based on lithium niobate

An integrated multi-wavelength tunable ultra-narrow bandwidth filter on Lithium Niobate substrate is proposed and its performances are analyzed. The filter contains multiple sections of Bragg gratings and waveguides. The waveguides are interleaved between Bragg gratings. A pair of electrodes is fabricated on both sides of each waveguide. Multi-wavelength tunable function can be realized by applying voltages on different electrode pairs. In this paper, tunable filters with three wavelengths and five wavelengths are discussed. The filter with three wavelength contains three pairs of electrodes and the five wavelength filter contains five pairs of electrodes. The number of wavelengths is determined by the number of the electrode pairs. The number of the wavelength can be increased by adding electrode pairs. In the filers a section of waveguide with a pair of electrodes is located in the center of the structure, others are symmetrically distributed on both sides of it. The wavelength difference is influenced by the length of Bragg grating between the electrodes. The longer the Bragg grating, the smaller the wavelength difference. And the bandwidth of each wavelength is around a few pm. The tuning range of the filter is affected by the total length of the Bragg gratings. The longer the total length of the Bragg gratings the wider the tuning range. In addition, the tuning speed of the filter can reach the order of nanosecond due to the simultaneous response of electro-optical effect in Lithium Niobate. It is faster than other filters, based on elastic-optic effect (stress) and thermal effect (the temperature). The integrated multi-wavelength tunable ultra-narrow bandwidth filter based on Lithium Niobate is easy to achieve large-scale integrated. It has great potential application in dense wavelength division multiplexing (DWDM), optical arbitrary waveform generator (OAWG), tunable laser or other fields.