Not far is the time when 4K HDTV would be streamed to the residential users. Together with 24-channel audio support it would demand at least 1 Gbps bandwidth per user. Technology supporting such great amounts of bandwidth is already available today and is called WDM-PON. It has promising cost-to-performance ratio, wavelengths of less than 12.5 GHz spacing, and simple architecture. Instead of using splitters/combiners, it relies on energy saving filters. It can provide stable 1 Gbps signal for up to 192 subscribers over the distance of 60 km.

WDM-PON can offer dedicated wavelength for each customer if necessary. However, capacity of one wavelength is more than enough for one customer, which allows to use free wavelengths to build virtual private networks. Next generation of wired broadband access solution, can offer different wavelength densities as shown in Figure 1

Figure 1. WDM-PON example.

TDM/TDMA can be used in WDM-PON to allocate the capacity. Another option is the use of the SCM-WDM (SubCarrier Modulation WDM) that allow users to send upstream signals using same wavelength in different frequency slots. It is achieved with the help of OFDM-WDM (Orthogonal Frequency Division Multiplexing WDM).

Third way of capacity allocation is the implementation of OCDM-WDM (Optical Code Division Multiplexing WDM), which provides access of multiple users to the single wavelength without help of the central controller.

Since there is no necessary to share wavelength between users, it is easier to provide privacy of the communication link. ONUs/ONTs cannot receive data sent on different wavelengths only if the optical isolation among ONUs is on the high level.