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 .
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.
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 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 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 . Then in 1989, the first lateral comb drive emerged in Sandia National Laboratories, where the structures move laterally to the surface .
As we know, physical contact is most important to ensure low IL and high RL for fiber connection. The evolution of endface polishing types experiences physical contact (PC), ultra physical contact (UPC) and angled physical contact (APC), as shown in Fig.1. All the endfaces are spherically polished. The UPC connector has a smaller radius of curvature than the PC connector. For the APC connector, the sphere surface is usually tilted by an angle of 8°. The RL guaranteed by PC, UPC and APC is 40dB, 55dB and 65dB, respectively.
Fiber optic connectors are the most basic optical passive components for optical fiber communication systems. The basic specification requirements for them are low insertion loss (IL) and high return loss (RL), i.e. low back reflection (BR). However, as the most widely employed components, low cost and easy connection are equal important as the specifications.
Alignment of Optical Fibers The core size of the single mode fiber (SMF) is about 8~10μm. The two connected fibers must be precisely aligned to ensure low loss. Fig.1 shows how much the lateral offset between two optical fibers influence the IL. The curve is exponential. A small lateral offset such as 2.4μm will introduce IL of 1dB. Thus the lateral offset between the two fibers must be kept <0.5μm for SMF fiber optic connectors.