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demonstrated the transmission of polarization-division-multiplexing (PDM) 224 Gbps 4-PAM signals at 1310 nm over 10 km SMF using a single IM laser and DD multi-input multi-output (MIMO) DSP-based receiver. developed scalable and fast optical switching system for 1310 nm optical interconnect carrying 4×25 Gbps, 4-PAM signals. The negligible chromatic dispersion of the SMF at this wavelength enables higher bit rate transmission distance product compared with 1550 nm link and this can be achieved without using any dispersion compensation techniques which are usually adopted in 1550 nm links. Recently, there is interest to investigate 1310 nm-optical links for data centers. Higher bit rates can be achieved by applying wavelength-division-multiplexing techniques. The 112 Gbps bit rate has been achieved using 4-PAM and 8-PAM signaling. These experiments have been demonstrated using multimode fibers or single mode fiber SMFs and DMLs or EIMs. These features have encouraged different research groups to demonstrate successfully 4- and 8-PAM optical interconnects for data centers and short reach applications at 1550 nm wavelength.
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Further, it can be implemented using DML which highly preferred due its low cost and simple implementation.
OFDM EQUALIZATION OPTISYSTEM FREE
One of the modulation formats which drawn significant attraction for optical interconnect is multilevel PAM which can be incorporated easily in IM/DD system and it is free of digital-to-analog converter. An active research topic in this field is to design low-cost version of optical interconnect based mainly on IM/DD system adopting advanced modulation formats and to enhance the operating rate above 400 Gbps. These links are expected to play key role in data centers and short-reach communication. Optical interconnects operating at 100 Gbps and 400 Gbps have attracted significant research efforts and standardization activities, such as the IEEE 802.3bs 400 Gbps Ethernet Task Force. Advanced in photonic and optoelectronic technology leads to design DML and EIM operating at bit rates above 100 Gbps. The intensity modulation can be achieved using directly modulated laser (DML) or external intensity modulator (EIM). Again, the intensity modulation (IM)-based optical transmitter is cheaper as compared with coherent optical transmitter. Further, DD receivers work efficiently with optical pulse amplitude modulation (PAM) signaling where the information is encoded on the intensity of the transmitted pulses. The DD receiver is considered cheaper than coherent optical receivers since it does not use a local laser acting as a local oscillator to be synchronized with the transmitter laser. This type of receivers uses a photodiode, for optical-to-electrical conversion, followed by an electrical receiver.
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Low cost optical interconnects usually implemented using direct-detection (DD) optical receivers. Further, the capacity of these links can be enhanced using different multiplexing techniques such as wavelength-division multiplexing (WDM), , optical orthogonal frequency-division multiplexing (O-OFDM), space-division multiplexing (SDM), and hybrid multiplexing. These links apply the main features and advantages of optical fiber communication for short-reach applications. Introduction Optical fiber links attract increasing interest for high-bit rate inter- and intra-connects for advanced data centers. These are to be compared with 40 and 28 km, respectively, for 224 Gbps data rate.ġ.
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Simulation results obtained using Optisystem software show that maximum distance of 45 and 37 km can be achieved for 4- and 8-PAM system, respectively, when 112 Gbps bit rate and 0 dBm transmitter launch power are used. Analytical expressions are derived to characterize the bit error rate (BER) floor and it dependence on the relative intensity noise (RIN) of the transmission laser source. Polarization-division multiplexing (PDM) technique is applied to the EML-based link to double the bit rate without degradation the transmission distance. Results are presented for both directly modulated laser (DML)- and externally modulated laser (EML)-based links operating with 4- and 8-PAM signaling and carry bit rate of 56, 112, and 224 Gbps. This paper addresses the transmission performance of PAM-based optical interconnect operating at 1310 nm without using optical amplifications. Optical links incorporating multilevel pulse amplitude modulation (PAM) with intensity modulation/direct detection (IM/DD) scheme have shown promising features when used as low-cost data center interconnects.