Abstract
In this paper, we experimentally demonstrate an optical frequency comb (OFC) based transmitter, employing directly modulated active demultiplexers, for data center interconnects. The results validate that the proposed transmitter has the potential to achieve aggregate data rates of 100 Gb/s (8 × 12.5 Gb/s) and 200 Gb/s (8 × 25 Gb/s) for systems employing 4- and 16- quadrature amplitude modulated (QAM) discrete multi-tone (DMT) modulation. An OFC based on an externally injected gain switched laser (EI-GSL) is used, providing excellent stability and flexibility in free spectral range (FSR). The OFC is followed by an injection locked active demultiplexer, which not only filters, but also amplifies individual comb tones, thus alleviating the need for an external optical amplifier to boost the low powered comb tones. Using the proposed configuration, we experimentally demonstrate a successful transmission of 12.5 Gb/s/λ 4-QAM DMT and 25 Gb/s/λ 16-QAM DMT signals over 40 km and 25 km of SSMF, respectively. In addition, we show that it is possible to filter and modulate comb lines that are 20 dB below the spectral peak, whilst achieving a BER below the hard decision (HD-) FEC limit of 3.8e-3. This gain flattening or comb expansion feature leads to a significant increase in the channel count, which in turn provides a reduction in the energy consumption and the footprint of the transmitter.
Highlights
OVER the past decade, the global demand for communication capacity has increased exponentially [1]
We experimentally demonstrate an optical frequency comb (OFC) based transmitter comprising an active demultiplexer directly modulated with 4- and 16-quadrature amplitude modulated (QAM) discrete multi-tone (DMT) signals
Through injection locking of a semiconductor laser with the desired OFC tone, the active demultiplexer acts as a filter, and as an optical amplifier and a data modulator of the filtered tone
Summary
OVER the past decade, the global demand for communication capacity has increased exponentially [1]. The authors in [10], demonstrated a 2 × 56 Gb/s PAM4 transmission over 100 km standard single mode fiber (SSMF) using directly modulated lasers Another impressive demonstration, reported in [11], entailed a four channel 50 Gb/s DMT signal transmission for short reach networks. An external optical amplifier is required to enhance the CLP, at the cost of degrading the optical signal to noise ratio (OSNR), due to amplified spontaneous emission noise To overcome this drawback, an active demultiplexing technique based on optical injection locking (OIL) has been widely researched [15]. By utilizing the comb tones with power 20 dB below the spectral peak, using a single EI-GSL OFC, the proposed system has the potential to achieve the aggregate data rates of 100 Gb/s (8 × 12.5 Gb/s) and 200 Gb/s (8 × 25 Gb/s) for 4- and 16-QAM DMT respectively. It is important to note that the proposed transmitter configuration lends itself to photonic integration, which can be used to realize a reduced form factor [19]
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