Optical transmitter modulation of the light source
We all know, information disposal are finished in the field of electricity, in optical fiber communication, we have necessary to convert optical signals into electrical signals, such ability on optical fiber transmission.In optical fiber communication system, information announced by leds or LD with light waves, light waves, is the carrier to load the information to the light wave is the process of modulation.Light modulator is to realize the conversion from electrical to optical signal equipment.
Modulation method is usually divided into two categories, namely analog modulation and digital modulation.
Analog modulation has two kinds, one kind is to use analog baseband signal directly to the light intensity modulation (D - IM);Another choose continuous or pulse radio frequency (RF) waves as subcarrier, analog baseband signal to the first of its ups and downs, frequency, or phase modulation etc., then use the modulated subcarrier to intensity modulated light source.Analog modulation strengths are briefly equipment, possession of a narrow bandwidth, but its anti-interference function is poor, relay when noise accumulation.
Digital modulation method is the first modulation of optical fiber communication, quantification, imitate signal sampling in binary digital signal "1" or "0" light carrier for on-off modulation, and pulse coding (PCM).Digital modulation strengths are strong anti-jamming capability, relay the impact of noise and the dispersion is not piled up, thus can realize long distance transmission, its defect is demand of wide frequency band, equipment and clutter.
According to the modulation method with light source, which has two kinds of direct modulation and external modulation.The former refers to direct power modulation signal to control the vibration parameters of semiconductor light source (light intensity, frequency, etc.), optical frequency amplitude modulation or frequency modulation wave, this is also called the modulation;The latter is to make the output light source fluctuation and frequency constant carrier of light through the optical modulator, optical signal through ups and downs of the modulator to achieve light carrier modulation, frequency and phase, light source modulation strengths are brief directly, but under the modulation rate by carrier lifetime and high rate of functional degradation of restrictions (such as frequency chirp, etc.).Modulation method needs outside modulator, layout is messy, but can obtain excellent modulation function, especially suitable for the high rate of use.
According to the parameters of the modulated light points: the intensity modulation, phase modulation, polarization modulation and so on.
In current optical fiber communication is the most used light source of the baseband directly intensity modulation, sub-carrier intensity modulation and digital modulation, choose outside when a high rate of modulation.
By the input interface, light source, drive circuit, control circuit, control circuit, its center is the light source and driver circuit.In digital communication, the input circuit of the input signals (such as PCM pulse) for plastic, after the transformation into suitable for wire type drive circuit source, perhaps to light modulator modulating successive waves of light source output.In order to secure uniform light power and working temperature of the output, often to set an active temperature control and power control circuit.
Specific knowledge about our product can be consulting optical transmitter manufacturers, they have their own technical staff, will know more in detail in this respect.
In this paper, published by shandong Wan Shuo photoelectric equipment co., LTD.