Sharp tunable and additional noise-free optical filter based on Brillouin losses

Abstract

In this paper, we propose an additional noise-free, independent center frequency and bandwidth tunable optical filter based on stimulated Brillouin scattering (SBS) losses. By suppressing the out-of-band signal with two broadened symmetric SBS losses, tunable pass bandwidths from 500 MHz to 9.5 GHz and the independent center frequency tunability are demonstrated. Considering the limited SBS interaction in the center frequency range, a flat-top response with minimum 0.3 dB ripple is achieved. Assisted by the extra suppression from polarization pulling, a maximum selectivity of 20 dB and an ultrahigh 250 dB∕GHz roll-off are reached. A gain-based SBS filter adds noise to the filtered signal. However, for our proposed filter setup, no additional noise is detected due to the transparency in the passband. Considering the wide independent bandwidth and center frequency tunability, flat-top response, and low-noise characteristic, our proposed filter can be perfectly used as a supplement of most commercialized conventional tunable optical single bandpass filters, whose minimum bandwidth is limited by 10 GHz.

High link performance of Brillouin-loss based microwave bandpass photonic filters

“…To relax the stringent requirement in high pump power, an additional optical filter with lower spectral resolution can be used to provide band spectrum rejection as pre-processing operations, followed by the SBS-loss-based high-resolution spectrum processing [19]. This configuration can pair the coarse processing capability of the pre-processing optical filter offers with the high resolution provided by SBS, allowing for broadband operation and highresolution signal processing with a lower pump power consumption.…”

“…1(a) and 1(b). To obtain broadband tunability, the SBS filter configuration could be combined with a tunable coarse optical filter, such as a fiber Bragg grating (FBG), with significantly reduced filter requirements [19]. To create multiple passbands and form different filter shape, additional pumps (comb lines group 3) with various frequencies and separations can be programmed by an AWG.…”

“…Previous realization of MWP bandpass filters based on SBS gain response have exhibited excessive in-band noise induced by the spontaneous emission associated with the SBS amplifications, leading to a high noise figure penalty, which makes the SBS-based MWP filter impractical for real-world applications [16][17][18]. There have been recent efforts to mitigate the additional SBS noise in the passband of an optical filter, using broadband SBS loss to suppress out-of-band signals, which enables the creation of a bandpass response, while avoiding added SBS amplification noise in the passband [19][20][21]. This approach offers a potentially noise-free passband solution for tunable microwave filter technology but needs to be implemented in a high-performance microwave photonic link and to provide desired programmable multi-bandpass MWP filter functionality.…”

“…Figure 1 shows the principle of the low-noise bandpass filter formed by SBS-based losses, without introducing extra losses in the filter passband. In this approach, the noise figure of the filter passband is unaffected by the noise generated through the SBS amplification process [19]. This contrasts with the MWP bandpass filter creation using SBS gain, which processes the signal of interest and introduces additional noise in the passbands [20].…”

The State-of-the-Art of Brillouin Distributed Fiber Sensing

“…(4) represents the power amplification of the probe wave, also known as the Brillouin gain spectrum (BGS), and can be expressed as: The full width at half maximum (FWHM) of the BGS Δν B ¼ Γ B = 2π ðÞ , also known as the natural Brillouin linewidth, is estimated to be several tens of MHz for SMF, as shown in Figure 1(b) for a 20 km SMF. The Brillouin linewidth can be engineered to several GHz with a broadened pump for applications such as SBSbased filters [18][19][20] and slow light [21][22][23] while it can also be narrowed to a record of 3.4 MHz with specific techniques [24][25][26][27][28].…”