Optical frequency comb (OFC) is a spectrum that consists of a set of evenly spaced frequency components with a coherent and stable phase relationship. With the rapid development of optical communication technology, the generation of OFC is attracting lots of interests recently due to its wide applications, such as optical arbitrary waveform generation (OAWG), multi-wavelength ultra- short pulse generation and dense wavelength division multiplexing (DWDM). In such applications especially for OAWG, the number of comb lines, spectral flatness and optical tone-to-noise ratio (OTNR) represent key considerations.
Several researchers in Wuhan National Lab for Optoelectronics, including Prof. Xinliang Zhang, Prof. Jianji Dong, and Dr. Ting Yang, etc have experimentally demonstrated that self-phase modulation and cascaded four wave mixing processes in highly nonlinear fiber (HNLF) are effective ways for spectrum broadening. They have investigate some parameters affecting the performance of the output OFC in detail by comparing and analyzing several different OFC generation schemes. Several OFCs have been obtained with highly broad bandwidth and good flatness. All the OFC schemes appeared in the paper have the advantages of tunability of central wavelength and repetition frequency.
This work has been published in Optics Express (vol. 21, no. 7, pp.8508-8520, 2013). Relative work was partially supported by the National Basic Research Program of China (Grant No. 2011CB301704), the Program for New Century Excellent Talents in Ministry of Education of China (Grant No. NCET-11-0168), and the National Natural Science Foundation of China (Grant No. 60901006, and Grant No. 11174096).
Fig. 1. (a) The wide spectrum obtained by the HNLF (solid line) and the filter shape of the OBPF (dash line) and (b) the flat OFC generated after the OBPF, when the input optical power of HNLF is 970mW. (c) The wide spectrum obtained by the HNLF (solid line) and the filter shape of the OBPF (dash line) and (d) the flat OFC generated after the OBPF, when the input optical power of HNLF is 1.5W.