Background technology
Optical communication is one of communication modes of applying the earliest of the mankind.Transmit signal from flames of war, to communication modes such as signal lights semaphores, be all the category of optical communication.But owing to being limited by factors such as sighting distance atmospheric attenuation landform stops, the slower development of optical communication.
Until nineteen sixty, after American scientist Maiman utility model First laser instrument in the world, provide good light source for optical communication.More than 20 year subsequently, optical transmission medium was tackled key problems by people, is finally made for low loss fiber, thus has established the foundation stone of optical communication.From this, optical communication enters the stage developed rapidly.
Fiber-optic transfer has many prominent advantages:
1. bandwidth
The width of frequency band represents the size of transmission capacity.The frequency of carrier wave is the highest, and the bandwidth that can transmit signal is the biggest.In VHF frequency range, carrier frequency is 48.5MHz~300Mhz.Bandwidth about 250MHz, can only transmit 27 set TVs and tens set frequency modulation broadcastings.The frequency of visible ray reaches 100000GHz, exceeds more than 100 ten thousand times than VHF frequency range.Although by optical fiber, the light of different frequency there is is different losses, make bandwidth be affected, but the bandwidth in lowest loss district is also up to 30000GHz.The bandwidth of single source only account for wherein small part (the most hundreds of megahertz of the frequency band of multimode fibre at present, good single-mode fiber is up to more than 10GHz), use advanced coherent light communication can arrange 2000 light carriers in the range of 30000GHz, carry out wavelength-division multiplex, up to a million channels can be accommodated.
2. loss is low
In the system of coaxial cable composition, best cable is when transmitting 800MHz signal, and the loss of every kilometer is all at more than 40dB.By contrast, fibre-optic loss is the most much smaller, the light of transmission 1.31um, if every kilometer is lost the light at below 0.35dB transmission 1.55um, every kilometer of loss is less, up to below 0.2dB.This is just little than the power attenuation of coaxial cable 100,000,000 times so that it is the distance that can transmit is much farther away.Additionally, fiber transmission attenuation also has two features, one is to have identical loss in whole cable television channels, it is not necessary to the equalizer that must induce one as cable trunk equalizes;Two is that its loss becomes little with temperature, does not worries causing the fluctuation of mains voltage because of variation of ambient temperature.
The most lightweight
Because optical fiber is the thinnest, single-mode fiber core line diameter is generally 4um~10um, external diameter also only has 125um, plus waterproof layer, reinforcement, sheath etc., it is less than 13mm with the optic cable diameter of 4~48 optical fiber compositions, more much smaller than the diameter 47mm of standard coaxial cable, it is glass fibre plus optical fiber, proportion is little, makes it have diameter feature little, lightweight, installs very convenient.
4. capacity of resisting disturbance is strong
Because the basis of optical fiber is quartz, only pass light, non-conductive, do not acted on by electromagnetic field, the optical signal transmitted wherein is not affected by electromagnetic field, therefore fiber-optic transfer has the strongest defensive ability/resistance ability to electromagnetic interference, industrial interference.The most Just because of this, the signal transmitted in a fiber is difficult to be ravesdropping, thus is beneficial to secrecy.
5. fidelity is high
Amplify because fiber-optic transfer typically need not relaying, new non-linear distortion will not be introduced because of amplifying.If the good linearity of laser instrument, so that it may with high fidelity transmitting television signals.Actual test shows, three beats of the carrier combination of good amplitude modulation fibre system are than C/CTB at more than 70dB, and intermodulation index cM is also at more than 60dB, far above the non-linear distortion index of general cable trunk line system.
6. reliable working performance
It is known that the reliability of a system is relevant with the number of devices forming this system.Equipment is the most, and the chance broken down is the biggest.Because the number of devices that fibre system comprises few (needing tens amplifiers unlike cable system), reliability is naturally also just high, life-span plus fiber plant is the longest, time between failures reaches 500,000~750,000 hours, wherein what the life-span was the shortest is the laser instrument in optical sender, and least life is also more than 100,000 hours.Therefore the service behaviour of the fibre system of design installation and debugging good, correct is the most reliable.
7. cost constantly declines
At present, it is thus proposed that new Moore's Law, also referred to as optical laws (Optical Law).This law is pointed out, the bandwidth of fiber-optic transfer information, within every 6 months, increases by 1 times, and price reduction 1 times.The development of optical communication technique, extraordinary basis has been established in the development for Internet broadband technology.This just uses fiber-optic transfer mode to clear away last obstacle for large-scale cable television system.The abundantest owing to making material (quartzy) source of optical fiber, along with the progress of technology, cost also can reduce further;And copper raw material needed for cable is limited, price can be more and more higher.Obviously, fiber-optic transfer will have comparative advantage from now on, become and set up the whole province, so that the main transmission means of national cable TV network.
Laser is the perfect light source of optical communication.Now, multiple laser instrument can be produced, the laser of multiple power and wavelength can be produced.
Owing to laser is the luminescence phenomenon based on the light amplification of stimulated radiation, with compared with the ordinary light source based on spontaneous radiation, there is many salient features.
1. monochromaticity is good
It is known that the light of different colours has different wavelength.One section of radiation that so-called monochromatic light, really wave-length coverage are the least.Breadth of spectrum line the narrowest (i.e. wave-length coverage is the least), the monochromaticity of light is the best.It should be noted that breadth of spectrum line here is the wave-length coverage that unmodulated front laser is comprised, it is two different concepts from the bandwidth after Laser Modulation.Breadth of spectrum line before modulation is the narrowest, and the bandwidth that can effectively utilize after modulation is the widest.
Because laser is the stimulated radiation realizing producing after population inversion between particular level, again through the frequency-selecting effect of resonator cavity so that it is the breadth of spectrum line of output light is the least, i.e. has good monochromaticity.
The monochromaticity utilizing laser is good, and spectral resolution is high, can be used to study the fine structure of the energy level of material and spectrum, and in making 1 year, error is less than the regulator of a microsecond.
2. good directionality
The angle of divergence that we generally use up is to describe its directivity, and the angle of divergence is the least, and directivity is the best.Searchlight best in ordinary light source, its angle of divergence is 0.1rad (radian).If it is irradiated on the moon of 400,000 kilometers of liftoff ball (this is the most impossible), its spot diameter has several ten thousand kilometers.In the laser, the direction luminous due to excited atom is identical with ambient light, adds resonator cavity and only allows the light along axis propagation to be amplified, and the directivity making Output of laser is fine, and the angle of divergence, up to 10 rad, is irradiated to it on the moon, and spot diameter is less than 2km.Utilize the good directionality of laser, can be used for finding range, position, navigation etc..
3. brightness is high
Owing to laser instrument can accomplish interrupted luminescence, can run up to happen suddenly out the most again, thus there is the highest power, maximum up to 10 W, add the good directionality of laser, making its brightness high, the strong flash of light also exceeding more than one hundred billion times, only h-bomb blast moment than the brightness of the sun could by comparison.Utilize the high brightness of laser, the high temperature of more than 100,000 degree can be produced at subrange, carry out punching, weld, perform the operation and controllable thermonuclear reaction etc..
4. coherence is good
So-called coherence refers to that two-beam can interfere, and forms the characteristic of stable light and dark interference image.The light sent due to stimulated radiation atom is all the same with external photon at aspects such as frequency, position phase, direction of vibration, makes laser have the electromagnetic wave that good coherence is comparatively close to preferably, is concerned with completely.General monochromater sends the coherence length of light and is less than O.1m, but the coherence length of laser is up to tens kilometers.Here coherence length refers to light beam to be divided into two bundles, allows them through different distances, it is possible to produce the maximum optical path difference interfered.Utilize the coherence of laser good, holography can be carried out, carry out accurate measurement.
Modern optical networking main line length is general longer (more than tens kilometers), and transmission channel is more, and from mass of system, reliability, and economically each side considers, all should select amplitude modulation fibre system.
Utility model content
The purpose of this utility model is that providing a kind of is applied to the Optical Time Division Multiplexing emission system that photoelectric communication processes, area of light carries out time division multiplex, the transmission time of signal is divided into time slot one by one, the optical signal do not gone the same way transmits in different time slots, it is possible to improve the efficiency of transmission of optic communication further.
This utility model is achieved through the following technical solutions: a kind of Optical Time Division Multiplexing emission system being applied to photoelectric communication process, including mode-locked laser, fiber amplifier, beam splitter, M-Z manipulator group and light delay circuit group, described mode-locked laser connects fiber amplifier, described fiber amplifier connects beam splitter, described beam splitter connects M-Z manipulator group, and described M-Z manipulator group connects light delay circuit group.
Further for preferably to realize this utility model, particularly being provided with following structure: described M-Z manipulator group includes n M-Z manipulator, n is the natural number more than or equal to 2.
Further for preferably to realize this utility model, particularly being provided with following structure: described smooth delay circuit group includes n-1 light delay circuit, n is the natural number of >=1.
Further for preferably to realize this utility model, it particularly is provided with following structure: the annexation between described M-Z manipulator and light delay circuit is followed M-Z manipulator n and is connected light delay circuit n-1.
Further for preferably to realize this utility model, particularly being provided with following structure: also include optical combiner, described smooth delay circuit group connects optical combiner, and one of them the M-Z manipulator in described M-Z manipulator group connects optical combiner.
Further for preferably to realize this utility model, it particularly is provided with following structure: also include that the first fiber amplifier, described optical combiner connect the first fiber amplifier.
Further for preferably to realize this utility model, it particularly is provided with following structure: also include that fiber optic backbone, described first fiber amplifier connect fiber optic backbone.
This utility model compared with prior art, has the following advantages and beneficial effect:
This utility model carries out time division multiplex in area of light, and the transmission time of signal is divided into time slot one by one, and the optical signal do not gone the same way transmits in different time slots, it is possible to improve the efficiency of transmission of optic communication further.