Abstract
An innovative all-fiber low-pedestal spectral compression scheme based on a two-stage structure employing a high nonlinear fiber (HNLF) connected with a nonlinear optical loop mirror (NOLM) is proposed and demonstrated. Both numerical and experimental results showed that the spectral pedestal and side-lobe component after spectral compression in the HNLF can be efficiently suppressed by the NOLM, simultaneously improving the spectral compression ratio. The measured spectral compression ratio increases by a factor of 2 from 3.39 to 6.91 and the side-lobe level is reduced from –7.47 to –9.36 dB. The spectral pedestal ratio is 15.7% using the proposed scheme, which is nearly one-third of that using the conventional feedthrough HNLF alternative.
Highlights
All-optical analog-to-digital conversion (ADC) in which the whole process is realized in the optical domain is the key technique to convert optical analog signals into optical digital ones
The basis of the spectral compression in an optical fiber is the compensation between the initial negative chirp of an optical pulse and the positive chirp introduced by the selfphase modulation (SPM) effect
Both numerical and experimental results indicate that spectral compression with a larger compression ratio and a lower pedestal can be achieved in the proposed two-stage structure, compared to its feedthrough high nonlinear fiber (HNLF) alternative
Summary
All-optical analog-to-digital conversion (ADC) in which the whole process is realized in the optical domain is the key technique to convert optical analog signals into optical digital ones. In an all-optical ADC based on a soliton selffrequency shift (SSFS) quantization scheme, the resolution, one of the vital factors, can be effectively enhanced by compressing the spectrum after SSFS.[1] Spectral compression, a common technology in passive picosecond pulse shaping,[2] can be achieved by passing an initially negative-chirped optical pulse through an optical fiber. The HNLF realizes the first-stage spectral compression, while the NOLM is employed for the second-stage spectral compression and pedestal suppression due to its chirp-related spectrum filtering effect. Both numerical and experimental results indicate that spectral compression with a larger compression ratio and a lower pedestal can be achieved in the proposed two-stage structure, compared to its feedthrough HNLF alternative
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