The traffic on the data center network is mainly composed of intra-rack traffic, inter-rack traffic, and inter-data center traffic. The internal power consumption, equipment cost, and network congestion of the data center cannot be ignored. How to solve these problems has become a solution proposed by the main research. Using the interleaved filter range and subsequent received signal operation, a few fixed receivers (FFs) can receive multiple signals of arbitrary wavelengths at the same time, effectively reducing the cost. However, with the increase in the total number of wavelengths in the arrayed waveguide grating (AWG), the number (F) of FFs and receivers required by each node also increases, which will make a large number of receivers idle. Here we propose a scheme consisting of a tunable filter (TF) and a small number of FFs. This scheme can effectively reduce the number of filters and receivers required, save equipment costs, reduce equipment power loss, and improve signal demodulation efficiency.

Due to the cyclic wavelength routing feature of N×N AWG, each node can send signals to any other node through the wavelength tunable transmitter (WTT), so multiple nodes may send data to the same destination node. The relationship between node and transmission wavelength λ_(j-i)modN+1 is that node i sends data to node j. For example, node 1 sends data to node 2 (node N) through λ₂ (λ_N) (Fig. 1). In the rack of the data center, one AWG is connected to N servers, and the remaining one interface is used for signal communication inside and outside the rack. At a certain time, if servers 1, N-2, N-1, and N want to send data to server 2 at the same time, they will adjust their laser wavelengths to λ₂, λ₆, λ₅, and λ₄. After the signal is modulated by the Mach-Zehnder modulator, it enters the AWG. By using the AWG wavelength routing characteristics, each wavelength signal will be routed to the receiving end of server 2. The receiver of server 2 filters a wavelength of λ₂ through a TF and then sends the mixed signal of the remaining three wavelengths to the filter matrix for signal recovery (Fig. 2). The filtering range of each filter forms a receiver matrix. Whether each wavelength can be filtered corresponds to a column of the matrix, and the wavelength that each FF can filter corresponds to a row of the matrix. Specifically, 1 represents that the filter can filter the wavelength, and 0 indicates that the filter cannot filter the wavelength (Fig. 3).

When the transmission rate is 10 Gbit/s, the receiving sensitivity of the pure FF scheme (optical power of error-free transmission) is -7.1 dBm. The receiving sensitivity of the TF+FF scheme proposed in this study is -8.3 dBm, and the difference in optical receiving power is 1.2 dBm. When the transmission rate is 40 Gbit/s, the receiving sensitivity of the pure FF scheme is -3 dBm, and that of the TF+FF scheme is -3.8 dBm. The difference in optical receiving power is 0.8 dBm (Fig. 4). When pure FF reception is adopted, the receiving sensitivity of the scheme at a transmission rate of 10 Gbit/s is -8.2 dBm, and the receiving sensitivity of TF+FF scheme is -10.3 dBm. The optical receiving power difference between them is 2.1 dBm. When the transmission rate of 40 Gbit/s is adopted, the receiving sensitivity of the pure FF scheme is -4.7 dBm, and that of the TF+FF scheme is -6.3 dBm. The difference in optical receiving power is 1.6 dBm (Fig. 5). When the number of signals arriving at the same time is 2, and the transmission rate is 10 Gbit, the receiving sensitivity of the two schemes is -10.3 dBm and -15.4 dBm, and the difference in their optical receiving power is 5.1 dBm. When the transmission rate is 40 Gbit/s, the receiving sensitivity of pure FF scheme is -6.6 dBm, and that of the TF+FF scheme is -12.6 dBm. The difference in optical receiving power is 6 dBm. Our new TF+FF scheme can more effectively improve signal quality and reduce the bit error rate (BER). When the number of wavelengths arriving at the same time is less, the improvement of signal quality of the new scheme is more obvious (Fig. 6). When the second generation hard decision forward error correction coding (FEC) limit (BER is 3.8×10^-3) is reached, for the combination of two, three, and four wavelengths, the receiving sensitivities are -22.3, -19.8, and -16.5 dBm, respectively. The differences in optical receiving power are 2.5 and 3.3 dBm. After equalization, the receiving sensitivities are -22.9, -21.6, and -19.0 dBm for the combination of different wavelengths, and the differences in optical receiving power are 1.3 and 2.6 dBm, respectively (Fig. 8).

An improved multi-wavelength reception scheme is proposed. On the basis of AWG optical interconnection, the data center adopts a scheme involving a TF and several FFs at one receiving end, which can optimize the simultaneous received wavelength signal from four channels (M=4) to three channels (M=3). The difference between the number of filters required for demodulation in these two cases increases with the increase in the total number of wavelengths in the data center. The simulation results show that the improved scheme proposed in this study can significantly improve the signal quality, especially when the number of wavelength signals arriving at the same time is small. By calculating the power loss, it is concluded that the improved scheme under 10 Gbit/s can support the transmission of up to 100 wavelengths in the data center. This scheme can significantly reduce the number of FFs and their connected receivers by adding only one TF and can effectively reduce the equipment cost and the number of idle filters and receivers.