The optical switch performance parameters are many, such as: the fast switching speed, high isolation, low insertion loss, polarization insensitive and reliability, the different areas of its requirements also vary. Protection switching system used in traditional optical mechanical switch its kind, the past few years the rapid development of a new type of optical switch, such as: thermo-optical switch, the LCD switch, optical switch, sound and light switch, MOEMS optical switch (MOEMS, micro optic electro mechanical systems), bubble switch or the like. In the field of ultra-high-speed optical communication Mach – Zehnder (Maeh-Zehnder) interferometer type the optical switch, nonlinear loop mirror (NOLM nonlinear optical fiber loop mirror) light switch and light control switch.
Traditional mechanical optical switch works: by the power of heat, electrostatic, rotary micro-mirror, the light sent directly to or reflected to the output. Characterized by relatively slow switching speed, good price, market prospects in many areas, but bulky and not easy to scale integration shortcomings limit its application in future optical communication field. On this basis, in recent years, developed rapidly MOEMS optical switch, it is the combination of a new switch of the micro-electromechanical systems and conventional optical technology, particularly those having the data format of the optical signal and transparent, with the polarization-independent, differential loss is small,good reliability, speed, easy integrated advantage.
2.Electro-optic effect switch
Optical switch of the electro-optical effect and more by photoelectric crystalline material (such as LiNbO3 or other semiconductor material) waveguide material, two waveguide connected MZ interferometer structure, the applied voltage can change the refractive index of the waveguide material, to thereby control the phase difference of the arms,interference effects of the optical off. It is characterized by fast polarization and higher costs. For the 3dB coupler, the two lightwave equation satisfy the mode coupling, so that the propagation constants of the two optical waveguides are equal, B0 = 0, at the output terminal of the the 3dB coupler 2 is obtained:
In the equation A0, B0 – input light wave amplitude; A3, B3 – output light wave amplitude; Ф – Lightwave phase.
3.Light control switch
Now more mature models: the production of all-optical switch based on the the NOLM principle and SOA nonlinear effects (such as XPM: cross phase modulation). They are not only used for ultra-fast switching exchange, but also for all-optical signal regeneration and ultrafast wavelength conversion is a promising all-optical switching technology.
SOA respectively disposed in the two arms of the MZ interferometer, the switch control pulse injection arm, pulse changes will cause the change in refractive index of the SOA, causing arms retardation change △ Ф, that is: △Ф=-(2π/l)(dn/dN)(τe/[1+(wτe)2]1/2L×Vg×g×△S×cos(wτ-q)
Wherein, L – the signal wavelength; dn/dN- refractive index set the amount of change of the carrier density; L-SOA cavity length; the τe-carrier lifetime; VG-group velocity; g-gain coefficient; △ the S-the amplitude of the carrier density changes; the phase delay between the change and the modulation signal of the Q-carrier density.