Optical comb filters are widely used in wavelength-division-multiplexed optical communication systems, acting as multichannel isolation filters and wavelength selective filters, etc. The existing optical filters with fixed frequency interval between channels can’t satisfy today’s dynamic optical communication systems, but the tunable multi-wavelength filters can implement flexible filtering functions, thus become a hot topic in recent years. In addition, a comb filter with flat-top passbands and a high extinction ratio is indispensable to improve the signal stability, enhance tolerance to wavelength drift, and reduce the adjacent channel crosstalk.
Prof. Ming Tang and doctoral student Zhiyong Zhao at WNLO demonstrated a free spectrum range (FSR) tunable multi-wavelength filter based on ethanol filled photonic crystal fiber and programmable thermal printer head (TPH). Thanks to the high thermal-optical coefficient of ethanol, the thermal controllability of the ethanol-filled device is enhanced dramatically, and the tuning range of the channel interval is also greatly expanded. A high density (8 units/mm) TPH managed by a micro-controller unit (MCU) is used to precisely control the heating position along the ethanol-filled PCF to configure the propagating optical modal profile dynamically. The finite element method (FEM) based simulation result matches well with the experimental feature. We have demonstrated an all fiber multi-wavelength filter with programmable FSR and flat top; the proposed device owns the merits of wide dynamic range, high tuning precision, flexible operation and high sensitivity, etc.
The study has been published in Optics Letters, Vol. 39, Issue 7, pp. 2194-2197, (2014). This work is supported by the National Natural Science Foundation of China (Grant Nos. 61107087 and 61331010), the 863 High Technology Plan of China (2013AA013402), the National Basic Research Program of China (973 Program: 2010CB328305), the Fundamental Research Funds for the Central Universities’, HUST: 2013TS052 and the Program for New Century Excellent Talents in University (NCET-13-0235)