Optical filters are crucial elements in optical communications. The influence of cascaded filters in the optical signal will affect the communications quality seriously. In this paper we will study and simulate the optical signal impairment caused by different kinds of filters which include Butterworth, Bessel, Fiber Bragg Grating (FBG) and Fabry-Perot (F-P). Optical signal impairment is analyzed from an Eye Opening Penalty (EOP) and optical spectrum point of view. The simulation results show that when the center frequency of all filters aligns with the laser's frequency, the Butterworth has the smallest influence to the signal while the F-P has the biggest. With a -1dB EOP, the amount of cascaded Butterworth optical filters with a bandwidth of 50 GHz is 18 in 40 Gbps NRZ-DQPSK systems and 12 in 100 Gbps PM-NRZ-DQPSK systems. The value is reduced to 9 and 6 respectively for Febry-Perot optical filters. In the situation of frequency misalignment, the impairment caused by filters is more serious. Our research shows that with a frequency deviation of 5 GHz, only 12 and 9 Butterworth optical filters can be cascaded in 40 Gbps NRZ-DQPSK and 100 Gbps PM-NRZ-DQPSK systems respectively. We also study the signal impairment caused by different orders of the Butterworth filter model. Our study shows that although the higher-order has a smaller clipping effect in the transmission spectrum, it will introduce a more serious phase ripple which seriously affects the signal. Simulation result shows that the 2nd order Butterworth filter has the best performance.Keywords: optical filter, optical communication, differential quadrature phase shift keying (DQPSK), polarization multiplexed differential quadrature phase shift keying (PM-DQPSK), signal impairment
Optical filters are crucial elements in optical communication networks. Their influence toward the optical signal will affect the communication quality seriously. In this paper we will study and simulate the optical signal impairment and crosstalk penalty caused by different kinds of filters, which include Butterworth, Bessel, Fiber Bragg Grating (FBG) and Fabry-Perot (F-P). Signal impairment from filter concatenation effect and crosstalk penalty from out-band and in-band are analyzed from Q-penalty, eye opening penalty (EOP) and optical spectrum. The simulation results show that signal impairment and crosstalk penalty induced by the Butterworth filter is the minimum among these four types of filters. Signal impairment caused by filter concatenation effect shows that when center frequency of all filters is aligned perfectly with the laser's frequency, 12 50-GHz Butterworth filters can be cascaded, with 1-dB EOP. This value is reduced to 9 when the center frequency is misaligned with 5 GHz. In the 50-GHz channel spacing DWDM networks, total Q-penalty induced by a pair of Butterworth filters based demultiplexer and multiplexer is lower than 0.5 dB when the filter bandwidth is in the range of 42-46 GHz. Keywords-opticalfilter; optical communication; polarization multiplexed differential quadrature phase shift keying (PM-DQPSK); signal impairment; optical crosstalk
Tilted fiber Bragg grating, which has the advantages of both fiber Bragg grating and long-period fiber grating, has been widely studied for sensing in many fields, especially in the field of biochemistry. Calmodulin, which has a wide distribution in eukaryotes, can regulate several enzymes such as adenylate cyclase and guanylate cyclase and mediates several cellular processes such as cell proliferation and cyclic nucleotide metabolism. The abnormal levels of calmodulin in the body will result in serious effects from metabolism to nerve growth and memory. Therefore, it is important to measure the calmodulin concentration in the body. In this work, we propose and experimentally demonstrate a plasmonic tilted fiber Bragg grating-based biosensor for calmodulin detection. The biosensor was made using an 18° tilted fiber Bragg grating with a 50 nm-thick gold nanofilm coating the surface of the fiber, and transient receptor potential channels were bonded onto the surface of the gold nanofilm to serve as bio-detectors for calmodulin detection. Experimental results showed that the limit of detection using our biosensor was 0.44 nM. Furthermore, we also demonstrated that the interaction between calmodulin and transient receptor potential channels was quite weak without calcium in the solution, which agrees with the biology. Our proposed biosensor has a simple structure, is easy to manufacture, and is of small size, making it a good choice for real-time, label-free, and microliter-volume biomolecule detection.
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