Passive Optical Devices for 5G Application(Part II)

With the rise of 5G technologies and massive deployment of 5G base stations, wireless access of terminals with high speed and large capacity is realized. Meanwhile, the traffic in optical fiber network increases rapidly. It is predicted that the current optical fiber network will become the bottleneck of information exchange in the future 12-18 months. The upgrading of optical fiber network is urgent. The representative trend is that the technologies for long-haul network (LHN) will be sunk to metropolitan area network (MAN), including DWDM (Dense Wavelength Division Multiplexing), ROADM (Reconfigurable Optical Add-Drop Multiplexer) and coherent receiving techniques. This paper discusses some of the passive optical devices for the coming 5G applications.

Tunable Optical Filter (TOF) for Coherent Receiving
In DWDM optical network, tunable optical filter (TOF), as one of the most important dynamic optical devices, is used to realize such functions as channel selection, optical performance monitoring (OPM) and optical channel monitoring (OCM) in the wavelength domain. The requirements of optical network for TOF include low loss, wide tuning range and good filtering characteristics.

WDM Devices — AWG with Flat Response

Why Is Flat Response Required?
In the all optical network (AON), the optical signals passed tens of nodes before reaching the destination node, as shown in Fig.1. The ROADM nodes are usually composed of wavelength selective switches (WSS), multiplexers/demultiplexers and optical switches. The wavelength multiplexers/demultiplexers are optical filters, including TFF-based WDM devices, arrayed waveguide gratings (AWG) and optical interleavers.

The Structures of ROADM

What’s CDC-F ROADM?
A ROADM node has a network node interface (NNI) and a user network interface (UNI). The NNI interconnects DWDM signals from/to multiple directions. The DWDM signals are switched between different directions in wavelength granularity. The UNI downloads signals designated to the node and uploads signals from the node in wavelength granularity. In order to realize non-blocking switching and adding/dropping of wavelengths, the new generation of ROADM nodes are required to be colorless, directionless and contentionless (CDC ROADM).

What is All Optical Network (AON)?

Review of Optical Fiber Communication
Based on industrial view, the development of optical fiber communication has experienced four stages and is now in the fifth stage. In 1970, the emergence of optical fiber with low loss and laser diode operating at room temperature initialized optical fiber communication.

However, the wide application of optical fiber communication was in 1990s. USA government released the plan named “National Information Infrastructure (NII)” in 1993. Optical fiber communication technologies were important parts supporting NII and were developed rapidly. The symbolic technology in the period is DWDM, which expands the transmission capacity of optical fiber communication by tens of times. The development of optical fiber communication slowed down in 2001 with the burst of internet bubble.