We have experimentally demonstrated a direct-detection (DD) 112-Gbit/s 16 quadrature amplitude modulation (QAM) transmission over single-span 140-km standard single mode fiber (SSMF) with Kramers-Kronig receiver and a sparse I/Q Volterra filter (VF). The sparse I/Q VF was proposed in our previous work and it is based on dual-input real-valued Volterra series and ℓ1-regularization method. In this paper it is used for compensating the nonlinear distortion in a short-reach DD optical 16-QAM signal transmission system. In back to back case, sparse I/Q VF represents the great compensation ability to the saturation effect of the electrical amplifiers and the nonlinear sinusoidal transfer function of I/Q modulator. It provides around 1-order magnitude improvement of BER when reducing 84% complexity from full I/Q VF. For fiber transmission case, sparse I/Q VF can mitigate the fiber nonlinearity effectively and it achieves single-span 140-km transmission at hard-decision forward error correction (HD-FEC) threshold of 3.8 ×10-3 with less than half complexity of full I/Q VF. Besides, optical signal noise ratio (OSNR) performance at 120 km is measured and sparse I/Q VF reduces the required OSNR at HD-FEC threshold by 1.3 dB. In a word, we investigate the performance of sparse I/Q VF in short-reach optical 16-QAM transmission system and sparse I/Q VF reveals its potential in the growing short-reach applications, such as data center inter-connection and metropolitan area network.
We demonstrate a novel distributed optical fiber sensor system based on phase-sensitive optical time-domain reflectometry (Φ-OTDR). Both the phase and the amplitude of the Rayleigh scattering (RS) light can be demodulated based on I/Q demodulation and heterodyne detection using commercial available 100G integrated coherent receiver (ICR). The polarization fading problem in Φ -OTDR can be avoided by considering the RS signal from both polarizations. The dynamic strain sensing with a sensing range of 9.8 km and a spatial resolution of 15 m is experimentally demonstrated.
In this paper, we propose guard-band-shared direct-detection (GBSDD) scheme to simultaneously receive multi-band 100-Gb/s direct-detection optical signal with only one conventional 40-GHz photodiode. The modulation format of orthogonal frequency-division multiplexing based on offset quadrature amplitude modulation (OFDM/OQAM) is selected to provide signal spectrum with high side-lobe suppression ratio, which can effectively reduce the electrical subband frequency interference. In GBSDD scheme, only one guard band is required to accommodate the overlapped signal-to-signal beat interference (SSBI) induced by all the multi-band optical signals. Three different GBSDD schemes are experimentally demonstrated with total data rate of 100-Gb/s and OFDM/OQAM modulation format. The first one uses 6 subbands with transmission distance of 320 km and hybrid 32-QAM and 16-QAM formats. 6 lasers are used as the pilot carriers to beat the signal. The seconds utilizes only 2 subbands with 64-QAM format in 80-km fiber transmission, which are assigned onto two orthogonal polarizations. Only one optical pilot carrier is inserted to beat with the 2 subbands on the two polarizations. The 2 subbands are located on the one side of the optical carrier. Comparing with the first scheme, the bandwidth usage of the PD is enhanced from 1/2 to 2/3. In the third scheme, the 100-Gb/s optical signal includes 4 subbands with 32-QAM format after 880-km fiber transmission. The 4 subbands locate at the two sides of the optical pilot subcarrier. Under this condition, the bandwidth usage of the PD is further improved from 2/3 to 4/5.
We propose and experimentally demonstrate a novel all-optical microwave filter with high quality factor (Q). It is based
on a recirculating delay line (RDL) loop in which a semiconductor optical amplifier (SOA) is followed by a tunable
narrow-band optical filter and a 1x2 10:90 optical coupler. Converted signal used as a negative tap is generated through
wavelength conversion employing the cross-gain modulation (XGM) of the amplified spontaneous emission (ASE)
spectrum of the SOA. The converted signal can circulate in the RDL loop so that the proposed filter realizes a high Q
factor response after photo-detection. The 1x2 10:90 coupler is employed to extract 10% optical power from the loop as
output. A frequency response with a high Q factor of 543, a rejection ratio of 40 dB is experimentally demonstrated.
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