6.2 PIC implementation of OLT/ONU and receiver circuits

The architecture comprises four lasers, four Mach-Zehnder modulators (MZM), and a number of filters. Two of the filters are for changing the operational frequency band (C band for upstream transmission and L band for downstream). Also, one filter is employed for tuning the four lasers to the correct wavelength. Besides, at the output, there is one filter working as a combiner of the four lasers. The band selection is made using the two semiconductor optical amplifiers (SOAs) that are placed after the band filters. It is noteworthy that the two SOAs are working as

switches and determine the chip's operating mode (i.e., OLT or ONU). Therefore, one of the SOAs is amplifying the light (active SOA), while the other is absorbing (passive SOA). Consequently, by this configuration, only one band filter is contributing to the setup. The employed lasers are built using laser cavities which contain SOAs that are being used for gain purposes, filters, and reflectors on both sides. The C þ L band filter helps in the selection of the downstream or upstream channel [39].

of the PIC, where a fiber will be aligned to collect the light, and subsequently, it will

Enabling Optical Wired and Wireless Technologies for 5G and Beyond Networks

This PIC has also a receiver circuit, but it is a simple one, with just a wavelength division multiplexer (WDM) filter which receives the light from the network and routes each NG-PON2 channel for a different PIN. The receiver circuit schematic is

Using the photonic design kit (PDK) from the foundry Smart Photonics and a software for PIC design (Phoenix Software at the time, meantime bought by synopsis) for the implementation, the final circuit masks of the chip are shown in

In this section, we present the obtained simulation results with further discussion on NG-PON2 physical layer architecture design and development based on PICs. Figure 13 shows the spectral simulation results obtained using advanced simulator for photonic integrated circuits (Aspic) software from filarete. On the left figure, there is the downstream operation (L band selected), and on the right there is the upstream (C band selected). In the figure, the spectra in blue, pink, orange, and green are the four channels. In both cases, it is possible to conclude that there is about 30 dB of suppression of replicas. The suppression facilitates smooth operation

The reason for using laser cavities is due to the limitations on the foundry. During the chip's design period, the Smart Photonics did not offer lasers on their process design kit (PDK). Consequently, improvements in the architecture can be undertaken to potentiate the results. For instance, the laser cavities could be replaced by distributed feedback (DFB) or distributed Bragg reflector (DBR) lasers that have narrow linewidth and a stable single mode operation. In this case, the cavity would disappear, and the filtering should be done after the lasing. In addition, the architectures can be simplified using only one modulator; nevertheless, it

be sent to the network [39].

depicted in Figure 11.

7. Results and discussion

Figure 12.

Figure 13.

161

6.2.1 PIC implementation of receiver circuit

DOI: http://dx.doi.org/10.5772/intechopen.85858

6.2.2 PIC implementation of OLT/ONU circuit

of the system by preventing intra-channel interference.

Optical spectra at the transmitter output (a) downstream and (b) upstream.

Moreover, the architecture includes also a multimode interferometer reflector (MMIR) before the band selection and another one after each gain SOA. These reflectors define the laser cavity limits. The second MMIR, after the gain SOAs, only reflects 50% of the light, and the remaining 50% is the laser cavity output and is sent to the MZM for modulation. After the modulation on the MZMs, all four channels are combined in just one, and the resulting light signal is sent to the output

Figure 11. Receiver block diagram.

Figure 12. OLT/ONU integrated transceiver design masks.

Enabling Optical Wired and Wireless Technologies for 5G and Beyond Networks DOI: http://dx.doi.org/10.5772/intechopen.85858

of the PIC, where a fiber will be aligned to collect the light, and subsequently, it will be sent to the network [39].

## 6.2.1 PIC implementation of receiver circuit

switches and determine the chip's operating mode (i.e., OLT or ONU). Therefore, one of the SOAs is amplifying the light (active SOA), while the other is absorbing (passive SOA). Consequently, by this configuration, only one band filter is contributing to the setup. The employed lasers are built using laser cavities which contain SOAs that are being used for gain purposes, filters, and reflectors on both sides. The C þ L band filter helps in the selection of the downstream or upstream channel [39]. Moreover, the architecture includes also a multimode interferometer reflector (MMIR) before the band selection and another one after each gain SOA. These reflectors define the laser cavity limits. The second MMIR, after the gain SOAs, only reflects 50% of the light, and the remaining 50% is the laser cavity output and is sent to the MZM for modulation. After the modulation on the MZMs, all four channels are combined in just one, and the resulting light signal is sent to the output

Telecommunication Systems – Principles and Applications of Wireless-Optical Technologies

Figure 11.

Figure 12.

160

OLT/ONU integrated transceiver design masks.

Receiver block diagram.

This PIC has also a receiver circuit, but it is a simple one, with just a wavelength division multiplexer (WDM) filter which receives the light from the network and routes each NG-PON2 channel for a different PIN. The receiver circuit schematic is depicted in Figure 11.

#### 6.2.2 PIC implementation of OLT/ONU circuit

Using the photonic design kit (PDK) from the foundry Smart Photonics and a software for PIC design (Phoenix Software at the time, meantime bought by synopsis) for the implementation, the final circuit masks of the chip are shown in Figure 12.
