Optical switch is an important function of the optical communication network devices, MEMS optical switch is a light switch one of the most promising. Introduction of different types on the basis of the principle characteristics of the optical switch, a detailed analysis of the current classification, structure, processes and performance of the major MEMS optical switches, and gives research and development in this field.
The advent and development of optical communication technology to the communications industry has brought a revolutionary change, about 85% of world traffic through the optical fiber transmission, long haul network and local relay networks has also been widely used fiber. Meanwhile, dense wavelength division multiplexing (DWDM) technology to develop and mature into the full application of optical fiber transmission bandwidth and capacity to develop a broad space, with high-speed, large bandwidth obvious advantages of DWDM optical communication networks have become the communication network development trend. Especially in recent years, to the IP-based Internet business showed explosive growth, this growth trend has not only changed the relationship between the IP network layer and the underlying transport network, but the entire network networking node design, management and control of proposed new requirements. An intelligent network architecture - Automatically Switched Optical Network (ASON: automatic switched optical networks) has become a hot research of today's systems, its core node consists of optical cross-connect (OXC: optical cross connect) equipment constituted by OXC, can be achieved dynamic wavelength routing and optical network flexibility, effective management. Optical cross-connect (OXC) technology is one of the key technologies in an increasingly complex DWDM networks, and optical switching device as a function of switching the optical path, it is a key part of OXC. Optical switching matrix is a core part of OXC, which enables dynamic optical path management, fault protection, wavelength dynamic allocation functions such as optical network, to solve complex network of wavelength contention, improve wavelength reuse, network flexible configurations there is significant.
OXC optical switch is not only the core of the device, it is widely used in the following areas.
(1) optical network protection switching system, the actual optical transmission system have left a spare fibers, when the working channel transmission interruption or performance degradation to a certain extent, the main signal light switch will automatically go to standby fiber optic transmission system, so that the receiving end can receive the signals do not feel normal network has a fault, it will be connected in a ring network nodes in order to further improve the survivability of the network.
(2) Real-time monitoring system network performance, the distal end of the optical fiber test points by 1 × N optical switch multiplexer connected to the plurality of optical fibers on the optical time-domain reflectometer, real-time network monitoring, optical switch switching sequence controlled by computer and time to achieve the detection of all fibers, and test results back to the network control center, once found a road problems can be handled from the network management center.
(3) Optical Switch also be used in optical fiber communication device testing system as well as metro, access of poor / division multiplexing and switching equipment. The introduction of the optical switch so that future all-optical network flexibility, intelligence, survivability. Optical switching technology has become the future of optical networking, optical switching key technology, in communications, automatic control and other fields are playing an increasingly important role.
Among the many types of light switches, micro-mechanical (MEMS) optical switch is considered most likely to become the mainstream optical switching device. In this paper, an overview of the principle characteristics of a variety of optical switch on the basis of the analysis focused on several major MEMS optical switches, and elaborated their respective structural and performance characteristics.
A variety of optical switch performance parameters, such as: fast switching speeds, high isolation, low insertion loss, polarization insensitive and reliability of the different areas of its requirements also vary. Its species are protected switching system commonly used in conventional optical mechanical switches, there are new optical switch of the rapid development in recent years, such as: thermo-optical switches, liquid crystal switches, optical switch, sound and light switches, MOEMS optical switch (MOEMS , micro optic electro mechanical systems), bubble switch. In the ultra-high-speed optical communications, as well as Mach - Zehnder (Maeh-Zehnder) interferometer type optical switch, non-linear loop mirror (NOLM, nonlinear optical fiber loop mirror) optical switch light control switch.
1, the mechanical optical switch
Works traditional mechanical optical switch: by heat, static electricity and other power, rotating micro-mirrors, reflecting light directly or sent to the output. Characterized by a relatively slow switching speed, good price, in many areas there is a market prospects, but bulky and difficult to scale integration of shortcomings limit its application in future optical communication field. On this basis, has developed rapidly in recent years is the MOEMS optical switch, which is micro-electromechanical systems and traditional optical technology combination of new switches, in particular data format of an optical signal having a transparent, independent of the polarization, the difference between loss, reliability, speed, ease of integration advantages.
2, the electro-optic effect switch
Optical waveguide electro-optic effect made of a material more switch phototransistor material (or other semiconductor materials such as LiNbO3), two connected MZ interferometer waveguide structure, the applied voltage can change the refractive index of the waveguide material, so as to control the phase arms, use to achieve the interference effect of light off. It is characterized by fast, but with polarization-dependent, the higher the cost. Works shown in Figure 1.
For 3dB coupler, the two light wave equation satisfy the mode coupling, so that the propagation constants of the two optical waveguides are equal, B0 = 0, at the output of the two 3dB couplers obtained:
|A3|2=|A0|2sin2(Ф/2)
|B32=|A0|2cos2(Ф/2)
Where: A0, B0-- input light wave amplitude; A3, wave amplitude B3-- output; Ф-- light phase.
Seen from the above equation, Ф and applied voltage, change the voltage, then Ф change, so that the light intensity obtained tuning. The switching speed depends on the phase difference between two light generating time that the optical waveguide refractive index change over time.
To high-speed, intelligent development stage, to address the slow response time of the electronic switches in modern communication systems, and ultra-high-speed transmission of data can not match the conflict, to achieve faster switching speeds and lower insertion loss, you can also use Quartz self-phase modulation or cross phase modulation optical fibers and semiconductor optical amplifier change in refractive index method, namely optical switch technology.
3, light control switch
Now more mature models: Based on NOLM SOA principles and nonlinear effects (such as XPM: cross phase modulation) made all-optical switch. Not only are they used ultrafast switching exchange, but also for ultrafast all-optical signal regeneration and wavelength conversion, is promising all-optical switching technology. In general, all kinds of ultrafast all-optical switch nonlinear effects are ultimately inseparable from the light, here to SOA-XPM an example to illustrate the experimental principle shown in Figure 2.
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