The working principle of external modulation optical transmitter
Light modulator technology is laser (LD) emits a beam of a certain intensity, injection LiNbO3 (lithium niobate crystal made of the modulator, which treated radio frequency modulation signal is added to the modulator electrodes, under the influence of electric field, the beam of light intensity and phase modulation, the output light intensity of the modulator is changing with modulation signal and optical signals.Direct modulation and different parts of the modulation signal is added in the modulator, rather than on the light source, light output is light, and light source can be a LD light source, can also be a solid-state laser.Because there is no additional frequency modulated light source, outside the modulator and combination can effectively overcome the second distortion (CSO).
Outside light modulation method, in principle, although there are several but currently used in the cable television network in the modulator, wide power mainly application effect of Mach - effect of mach-zehnder interferometer (M - Z) type.Its structure is based on electro-optic crystal substrate, and then made pathway in a single mode optical waveguide on the substrate.Input light from the optical waveguide will light is divided into two pathways, in carries on the synthesis of produce interference is a h - mach-zehnder interference (M - Z).In Mach - mach-zehnder interferometer unilateral pathways, make use of electro-optical effect during phase change, the interference of light output can follow the phase difference of the change.To produce the electro-optic effect, in principle is a unilateral waveguide on the opposite side of the path, fitted with electrodes, coupled with the signal voltage.If is equal to the length of the two pathways, applied voltage is zero, so no phase difference can form additive synthesis, when the plus half wave voltage phase difference is л, produces offset, the output is zero.(unfinished)
A modulation effect, straight line is too long will affect index, and cannot be secondary amplifier, short circuits can also.Outside modulation optical transmitter is better, light amplification can cascade, but the price will be a little higher, domestic also has a diversion, but the main device is sure or foreign.Mainly is the transmission distance and price differences!
In this paper, published by shandong Wan Shuo photoelectric equipment co., LTD.