Experimental Demonstration of Long-Haul Transmission Using Silicon-Based IC-TROSA

In this letter, we apply high-bandwidth silicon-based integrated coherent Transmit & Receive Optical Sub-Assembly (IC-TROSA) in long-haul fiber transmission systems. G.654E fiber and Raman amplifiers are employed in the fiber link to reduce the transmission loss and the nonlinear interference. In the experimental demonstration, the silicon-based IC-TROSA can provide similar performance as commercial coherent transceivers. In addition, G.654E fiber can achieve longer transmission distance than G.652D fiber. Moreover, 16 Tb/s ( $80\times 200$ Gb/s) Nyquist DP-QPSK and 20 Tb/s ( $50\times 400$ Gb/s) Nyquist DP-16QAM transmission over 10000 km and 4000 km fiber distance have been successfully achieved under the threshold of soft-decision forward error correction (SD-FEC) codes with 20% overhead, respectively.

I. Introduction

In the past 20 years, the capacity of single fiber transmission system has increased by 20% every year [1]. This is mainly because coherent detection technologies are used at the receiver side, which can preserve the whole optical fields. Therefore, the channel impairments such as chromatic dispersion (CD), polarization mode dispersion (PMD) can be effectively compensated via digital signal processing (DSP) techniques. In coherent detection scheme, advanced optical modulation formats considering both the amplitude and phase have been generated and transmitted in wavelength division multiplexing (WDM) systems to increase the total channel capacity [1]. Currently, one challenge of high-capacity system is the limited transmission distance due to fiber nonlinear noise, which can seriously degrade the transmission performance in WDM systems [2]. In order to mitigate the fiber nonlinear noise, several advanced digital signal processing (DSP) techniques have been proposed at the receiver side including digital back-propagation [3], perturbation-based nonlinear noise cancellation [4] and machine learning assisted techniques [5]. However, these nonlinearity mitigation techniques suffer from high computational complexity and power consumptions, which cannot satisfy the low-cost requirement in the industry community. Furthermore, these DSP techniques are less effective under WDM scheme. Therefore, the industry community has now focused more on the optimization of fiber link than the DSP techniques for fiber nonlinear noise mitigation. For example, new type of single mode fiber with lower loss and larger effective area can be used in the fiber link instead of traditional G.652D fiber. The new type of fiber can have smaller fiber nonlinearity coefficient, resulting in smaller fiber nonlinear noise [6]. Raman optical amplifier with lower noise figure instead of erbium-doped fiber amplifier (EDFA) [7] can also be considered in the fiber link to enhance the signal-to-noise ratio of the optical signal. Another challenge of high-capacity system is the complexity of coherent transceiver scheme, resulting in much higher cost when compared with intensity modulation and direct detection scheme. In order to solve this issue, silicon-based integrated coherent transceivers using mature processing technology have been applied in coherent transmission systems [8]. Fig. 1.

(a) Schematic of the silicon-based coherent transceiver, (b) Graph of integrated coherent receiver.