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).

MEMS Optical Devices — MEMS OXC

Application of OXC
Optical cross connect is a matrix switch usually with N×N ports. The OXC can be used to construct a CDC ROADM (Colorless, Directionless, and Contentionless Reconfigurable Optical Add/Drop Multiplexer), as shown in Fig.1 [1].

Fig.1 CDC ROADM based on WSS and OXC [1]

OXC Constructed by 1×N Optical Switches
The OXC can be constructed by 1×N optical switches, as shown in Fig.2. It requires 2N 1×N optical switch to construct a N×N OXC. Thus the size and cost of the OXC module increase rapidly with the incensement of port number N. OXC of this structure is usually limited to below 32×32 ports.

MEMS Optical Devices — MEMS Optical Switch

Optical switches are widely employed in optical fiber communication systems. The approaches for an optical switch are variable, including mechanical optical switch, thermos-optic switch, acousto-optic switch, electro-optic switch, magneto-optic switch, liquid crystal optical switch, MEMS optical switch, et. al. MEMS optical switches are characterized by compact size, low power consumption and good scalability, which enable their wide applications.

Optical switch is a multiport device. The port configurations include 2×2, 1×N, N×N. Optical switch with N×N ports is usually called OXC (optical cross connect). According to the difference in port configurations, different MEMS chips are employed for realization of the devices. We will discuss optical switches with 2×2 and 1×N ports in this paper.

MEMS Optical Devices — MEMS VOA

MEMS technologies are widely employed in optical fiber communication system. The combination of MEMS and optical technologies is usually named MOEMS (Micro-Opto-Electro-Mechanical Systems). The most widely applied MOMES devices include VOA (Variable Optical Attenuator), OS (Optical Switch), TOF (Tunable Optical Filter), DGE (Dynamic Gain Equalizer), WSS (Wavelength Selective Switch) and OXC (Optical Cross Connect).

VOA is widely employed in optical fiber communication system for optical power equalization. Among the variable approaches, MEMS VOAs are characterized by small size, low cost and easy fabrication. There are mainly two types of MEMS VOAs in applications, MEMS shutter and MEMS mirror. The first is usually thermally actuated and the second is usually actuated by electrostatic force.

MEMS Optical Devices – Introduction of MEMS Technologies

MEMS is a micro-electro-mechanical system fabricated with IC process. It is usually based on Si-wafer. The mechanical structures are fabricated with processes such as lithography, ion-beam etching, chemical etching and wafer bonding. Meanwhile, electrodes are fabricated along with the mechanical structures for electrical controlling.

MEMS in Life
The fist rotary MEMS motor was born in UC Berkley in 1988, as shown in Fig.1 [1]. Then in 1989, the first lateral comb drive emerged in Sandia National Laboratories, where the structures move laterally to the surface [2].