With the application of DWDM systems and the development of optical communication technology, optical networking has become the trend of network development. The realization of optical network technology depends on optical devices such as optical switches, erbium-doped fiber amplifiers (EDFA) and Wavelength Division Multiplexers (WDM ), and the improvement of optical technology. DWDM (Dense Wavelength Division Multiplexing) technology is the key factor promoting all optical network development, while optical network put great opportunity and challenge in front of equipment manufacturers and telecom operators.

Optical switch is the key in all-optical switching that can achieve routing switching, wavelength selection, OXC and self-healing protection in the all-optical layer. At present, optical switches main applications are:

OXC (optical cross connect). Composed of optical switches arrays, OXC can realize dynamic optical path management, optical network fault protection and flexible new business addition. OXC requires low insertion loss, low crosstalk, short switching time and non-blocking operation. Currently, MEMS technology is put into use.

Realizing network automatic protection switching by optical switch. When fiber breaks or transmission fails, optical switch, like 1x2 optical switch, can change the transmission path to achieve business protection.

Network monitoring by 1xN optical switch. At the optical fiber test points of distal end, 1xN optical switch connects several fibers with OTDR (optical time-domain reflectometer) so as to achieve monitoring of all fibers. Or use the network analyzer to achieve network on-line analysis.

Optical fiber communication device testing. When testing optical device, fiber cable and system product, optical switch is able to test several devices so that thus simplifies the test and increases the efficiency.

OADM. It is mainly used in circular MAN, to achieve a single wavelength and a plurality of wavelengths transmitted in the optical path up and down freely. Optical switch OADM can control any dynamic wavelength up and down by software to boost the flexibility of network configuration.

Conventional optical switching technology mainly uses two technologies: solid state waveguide and optomechanical. Because of high crosstalk and power loss, solid state waveguide is limited in a switches array, not suitable to expansion in a large-scale switch array. While optomechanical has low insert loss and crosstalk, it is also not suitable to large-scale switch array for its large equipment and ordinary expansibility. So far, a lot of new technologies have emerged, mainly including MEMS, Inkjet bubble optical switch, the liquid crystal optical switch, thermo-optic effect switch, acousto-optic switches, holographic switches and so on.
The following specifications are used to examine an optical switch: switching time, array size, insert loss, reliability, expansibility and so forth. The developments of different technologies vary with the different applications. The following is a summary on the major optical switches types and their applications.

MEMS Optical Switches. MEMS (micro-electromechanical system) is likely to be one of the mainstreams of the core optical switch devices, because it is less affected by the format, wavelength, protocols, modulation, polarization and optical signal transmission direction, but performs better than other types in loss and scalability, which is consistent with the trend of the future development of optical network. The principle is to switch the light route by static electricity or other controls driving the movable micro mirror rotate. In spite of complicated production process, MEMS used IC technology to achieve mass-produces and decrease the individual cost.

Magneto-optic Switches. As technology developing fast and expanding its horizon to wider fields, magneto-optic switches emerge as the times require. Magneto-optic switches boast higher switching speed, better durability, higher reliability, low voltage drive, and fail-safe latching. The sophisticated micro-technique is a push to high-technology industry. The applications are promising in high-end science, such as aerospace, military, fire monitoring, oil field detection, medical science and so on. Thus, a manufacture’s strength is reflected in whether it masters the magneto-optic switch technology and is able to produce it.

PON. Optical switches are widely used in PON monitoring system to build up all optical networks nowadays. PON is necessary to fulfill FTTx. With zero natural environment influence like thunder and lightning, PON is the best choice to meet the need of present networking. PON is composed of OLT, ONU, ONT and ODN, while optical switches integrated in these devices play great role to transmit mass data and monitor the networking in case of fault and ensure signal transmission.

Multi-channel Optical Switches. Optical switches can be integrated into an optical switch module or an equipment as multi-channel optical switches featured wide wavelength range, low crosstalk, high stability, high reliability and modularized design. At present, there are 1x4, 1x8, 1x16, 4x4, 1xN, MxN and module-type multi-channel optical switches.

Micro Optical Switches.  It is the fundamental and widely used optical component, including 1x1, 1x2, 2x2A, 2x2B, D1x2, D2x2B, S1x8, 2x2F and so on. Micro optical switch is famous for its high performance, low insertion loss and compact dimension. It is an ideal component for OADM, OXC, system monitoring and protection. With compact package, it can be easily integrated into a high density optical communication system.

With the popularization of optical networking concept, optical switch technology has become the key to the future all optical network. This article briefly introduces the optical switch technology and application to help understand what is in the optical networking.