## 3 High-Capacity DWDM PDM-16 QAM Optical Switch
### Experimental Setup  
Figure 7 shows the experimental setup of a transmitter for DWDM, PDM-16 QAM-modulated optical packets. As light sources, we used an array of 64 lasers, ranging from 1537.0 to 1562.23 nm on the 50 GHz grid spacing. The continuous waves of the 32 odd and 32 even channels were collectively modulated by two independent DPMZMs, respectively. The modulators generated 20 GBd single polarization 16-QAM optical packets with an aggregated bit rate of 80 Gbit/s per channel and per polarization. To generate the optical packet train, the continuously modulated signal was gated by two MZM modulators to remove the bogus PRBS data used in the guard time between packets. Then, packets were polarization-multiplexed by a polarization beam combiner (PBC) with a decorrelation of 12 symbols between polarizations. As a result, waveband optical packets at a rate of 10.24 Tbit/s were generated. A train of eight packets of different lengths, ranging from 1000 to 4000 symbols, was generated and each packet had either a PSK label A or label B, as shown in the inset of Figure 7. For label generation, 10 GHz optical pulses generated by a mode-locked laser diode (MLLD, 1530 nm) were modulated using known timing from the coherent packets payload pattern by an intensity modulator. The pulses were input to a 200 Gchip/s multiple optical encoder (MOE) to generate optical phase-shift keying (PSK) codes. The MOE has an AWG configuration [42; 43] with 16 inputs and 16 outputs, and behaves like a transversal filter to simultaneously generate 16-chip PSK codes. When a short pulse is sent into one of input ports of MOE, 16 different PSK codes are generated from each output port [43]. In this demonstration, two PSK codes were chosen and named label A and label B. After coupling of even and odd channels by a wavelength interleaver (100 GHz to 50 GHz), each packet was sandwiched by the PSK labels. Figure 6: (**a**) time-resolved BER measurement of the packet payload; (**b**) same as (**a**), but a median filter has been applied to smooth the curves. The packet train was then split into two to simulate two different transmitters, named TX1 and TX2, as shown in Figure 8. In this experiment, we used two 1 \(\times\) 2 PLZT switches for the label-switching (2 \(\times\) 2 OPS without buffer), designed to forward optical packets with label A only input from TX1 and TX2. Each 1 \(\times\) 2 PLZT optical switch had a PDL ranging from 0.3 to 1 dB. When multiple optical decoders (MODs) [42; 43] recognized an input label as label A, an output gate signals an FPGA based buffer manager. The buffer manager sends open or close signals to two switches for TX1 and TX2. As a result, four-packet trains with label A were output to each port. To demonstrate a packet addition process, a delayed four-packet train of TX2 was added to a four-packet train of TX1. Output packets after the packet addition process were input to a polarization-diverse coherent receiver, shown in Figure 8, using a free-running tunable laser as local oscillator (LO) with linewidth of approximately 100 kHz. The four-channel electrical signal after photo detection was then digitized at 50 GS/s, and the offline processing was performed with MATLAB (version R2015b, The MathWorks, Inc., Natick, MA, USA) for easy prototyping. Figure 8: Experimental setup of the optical packet switching node, configured to forward packets with label A and drop packets with label B. (insets) Constellation diagram of the packet header and waveform of the received eight packets. Figure 7: Transmitter setup for the generation of DWDM PDM-16 QAM modulated optical packets and 64 wavelength channels, (inset) diagram of the generated eight-packet train. The inset of Figure 8 shows a diagram of the optical packet train at the receiver. Each optical packet had a header of 64 symbols (128 samples) followed by a variable-length PDM-16 QAM payload.