Search

We experimentally demonstrate a modulation format identification (MFI) and optical signal-to-noise ratio (OSNR) monitoring method for digital coherent receivers by using the specific features of received signals' density distributions in Stokes axes combined with deep neural networks (DNNs). The features of received signals' density distribution fitting curves in S1 and S2 axes depend on the signal's modulation format and OSNR. The proposed technique extracts the features of these fitting curves' first-order derivation for MFI and OSNR monitoring, in order to improve the probability of format correct identification and OSNR estimation accuracy. Experimental results for 28Gbaud/s polarization-division multiplexing (PDM) quadrature phase-shift keying (QPSK), PDM 8 quadrature amplitude modulation (PDM-8QAM), PDM-16QAM, and 21.5Gbaud/s PDM-32QAM signals demonstrate OSNR monitoring over back-to-back transmission with mean estimation standard errors (SEs) of 0.21dB, 0.48dB, 0.35dB and 0.44dB, respectively. The MFI results over back-to-back transmission show that 100% identification accuracy of all these four modulation formats are achieved at the OSNR values lower or equal to their respective 7% forward error correction (FEC) thresholds. Similarly, 100% identification accuracy also is obtained for PDM-QPSK, PDM-8QAM, PDM-16QAM, and PDM-32QAM after 2000km, 2000km, 1040km, and 400km standard single-mode fiber (SMF) transmission within practical optical power ranges launched to the fiber, respectively.

We propose a four-linear state of polarization multiplexed intensity modulation and direct detection (IM/DD) scheme based on two orthogonal polarization division multiplexing (PDM) on-off keying systems. We also experimentally demonstrate a simple demultiplexing algorithm for this scheme by utilizing only a single Stokes analyzer. At the rate of 4×10 Gbit/s, the experimental results show that the power penalty of the proposed scheme is about 1.5 dB, compared to the single PDM-IM/DD for back-to-back (B2B) transmission. Compared to B2B, just about 1.7 dB power penalty is required after 25 km Corning LEAF optical fiber transmission. Meanwhile, the performance of the polarization tracking is evaluated, and the results show that the BER fluctuation is less than 0.5 dB with a polarization scrambling rate up to 708.75 deg/s.

Polarization is one of the key parameters to be utilized for large capacity and high spectral-efficient optical communication systems, especially the widely deployed polarization-division-multiplexing (PDM) scheme. To break the limitation of only two orthogonal polarization states that could be used for carrying data signals over the same wavelength, we experimentally demonstrate the first transmission of three-polarization-division-multiplexed DPSK signals at a rate up to 3×25 Gb/s over 300-km fiber link by using a single-carrier.

An all-fiber approach to generate triangular-shaped pulses based on frequency-to-time conversion is proposed and demonstrated. Two filter modules that have sinusoidal spectral responses are cascaded to create a triangular-shaped optical spectrum. Through the frequency-to-time conversion in a dispersive fiber, periodic triangular pulses with the same shape as the optical spectrum are obtained. The repetition rate and pulse width of the generated signals can be tuned by adjusting the modulation rate and the dispersion value, respectively.

We demonstrate simultaneous 10-Gb/s NRZ-to-RZ format conversion and multicasting from one to many data channels in a highly nonlinear fiber (HNLF) with only a single pump. Functionalities are achieved based on various nonlinear effects, such as four-wave-mixing (FWM), cross-gain-modulation (XGM) and cross-phase-modulation (XPM) between the pump channel and the NRZ data channel. Up to five and six converted data channels are error-free (10(-9) BER) as the wavelength spacing between the pump and the NRZ signal is set to 0.4-nm and 0.8-nm, respectively.

A large-ratio stretcher for ultra-short pulses is proposed based on photonic crystal fiber (PCF). Through proper design of the PCF structure, we obtain over 300-nm wavelength range with flattened dispersion characteristics. Analysis indicates that 1-km of such fiber can broaden over 10,000 times for ultra-short pulses with

We demonstrate simultaneous self-phase-modulation-based 2R regeneration of 2 x 10.65-Gb/s polarization-division-multiplexed (PDM) signals using a single section of highly nonlinear fiber (HNLF). Mitigation of inter-channel nonlinearities is achieved through a bidirectional configuration, rejecting of backward Stimulated Brillouin Scattering noise is obtained by signal re-polarizing before the offset filter and putting the center wavelength of filter at the short wavelength side of the signal. The power penalty improvement up to 2.0 dB for two PDM signals at 10(-9) BER is achieved.