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We report on an electro-absorption modulator (EAM) integrated laser (EML) based real-time 112 Gbit/s (2 × 56.25 Gbit/s) 4-level pulse amplitude modulation (PAM-4) signal transmission in the C-band over 80 km of standard single-mode fiber (SSMF). Various operating conditions of the EAM were investigated to find the optimum driving conditions for PAM-4 modulation. When the EAM reverse bias was set to the inflection point of the transfer curve, which was −2.35 V, we obtained a bit error ratio (BER) of 4 × 10−8, which is well below the forward error correction (FEC) limit. The results demonstrate the feasibility of using EMLs for implementation in PAM-4 transceivers for inter-datacenter interconnection (inter-DCI) applications.

The effects of carrier phase estimation on IQ mismatch compensation are investigated and compared for coherent MIMO optical receiver. We investigate the impacts of phase IQ mismatch on required optical signal-to-noise ratio (OSNR) for coherent MIMO detection. The impacts of number of modes and analog-to-digital converter (ADC) resolution are also evaluated. The results show that decision-directed carrier phase estimator could compensate significant amount of IQ mismatch without employing additional compensation technique, and relaxes requirement of ADC resolution.

The 112 Gb/s dual-carrier differential quadrature phase shift keying (DC-DQPSK) optical transceiver, which does not need digital signal processing and coherent detection, is proposed for cost-effective 100G transport solution. In this paper, we describe upgrade schemes of 10 Gb/s-based WDM optical links by adopting 112 Gb/s DC-DQPSK transceiver, while the dispersion of the optical links is compensated 100% at each span. Method of introducing the DC-DQPSK signal into single grid of 100 GHz spaced WDM link is demonstrated. Performance sufficient for error-free operation after forward error correction is achieved over 640 km standard single mode fiber (SSMF) link. In another method, we experimentally investigate the transmission performance with co-propagating 10.7 Gb/s on-off-keying (OOK) signals over 1000 km of SSMF when the dual carriers occupy two channel grids separately. Excellent tolerance to the nonlinearities impacted by the OOK signals and low optical signal-to-noise ratio requirement are verified to demonstrate superior transmission performance in 10 Gb/s-based WDM links.

Impacts of in-phase/quadrature-mismatch (IQ-mismatch) in polarization division multiplexed-16 level quadrature amplitude modulation (PDM-16QAM) coherent optical receiver are investigated and the IQ-mismatch compensation by digital signal processing is examined. All the results are compared with those of PDM-quadrature phase shift keying (QPSK) receiver.

The feasibility of multicast-capable-reconfigurable optical add/drop multiplexer (MC-ROADM) based on broadcast-and-select switch is experimentally demonstrated. The MC-ROADM can support unicast connection as well as multicast connection, and can provide directionless switching and low insertion loss in path-through channel. We implement fully-reconfigurable multi-degree MC-ROADM based on wavelength selective switch, and evaluate multicasting performances by fully loading 40 × 10 Gbit/s wavelength division multiplexed (WDM) signals. For unicast and multicast operation, measured spectrum and bit-error-rate (BER) show good uniformity and no power penalty. After 1040 km transmission with 25 dB span loss, the measured BER is higher than forward-error-correction (FEC) limit for BER of 10−15.

Experimental demonstration of security-improved optical code-division-multiplexed-access (CDMA) scheme based on spectrally encoded incoherent broadband light source with bipolar coding is presented. Incoherent bipolar encoding is achieved with amplified spontaneous emission (ASE) noise of erbium-doped fiber amplifier. We show details of coding scheme and investigate security issues by measuring eye-diagrams and bit-error-rates for various cases. In addition, we present analytical and numerical simulation results for secure transmission of spectrally encoded incoherent optical CDMA signal.