What are the current mainstream all-optical technology solutions- Part II

There are two ways of optical network in Ethernet ：

One 、 White light （ Also called gray light ） The way

The wavelength of light fluctuates within a certain range , This method is called white light or gray light . White light is the most widely used in optical networks , It is also the most mature way , The corresponding optical transceiver modules are universal .

Two 、 Color light mode

use WDM（Wavelength Division Multiplexing, Wavelength division multiplexing ） technology , The way in which a series of different wavelengths of light are synthesized and propagated in the optical fiber is called color light mode , It is often used in the transmission network of operators , Realize capacity expansion without increasing the number of optical fibers . In the color light system , Each different wavelength of light has its own standard wavelength , Do not use random wavelengths .

chart 1 Schematic diagram of color light system

From the figure 1 so , The color light system emits light of different wavelengths , After the wave combiner is combined into one channel of light, it is transmitted on the optical fiber , after , The light enters the wave splitter before reaching the receiving end , Separate the multi-path light , The separated light is exactly the same as the light emitted by the color light system , The restoration of color light after long-distance transmission is realized .
We need to pay attention to , Color light system is used to transmit and receive light of different wavelengths , Each light receiving and emitting module is Special optical modules , Only receive or transmit light of the wavelength that you support , Can't mix , Then there are n Lu Guang , You need to be prepared 2n Different optical modules .
Practical application , Information is transmitted in both directions , Therefore, it is necessary to adopt the two-way or single core two-way mode to send and receive information .

chart 2 Schematic diagram of color light bidirectional communication mode

However , Not all wavelengths are suitable for transmission in optical fibers , Light has different wavelengths , The loss in the core is different , After study , Most suitable for transmission in optical fiber “ Low loss wavelength region ” by 1260nm~1625nm Range of light , This region is further divided into five bands , Namely O Band 、E Band 、S Band 、C Band and L Band , The rule between optical fiber transmission loss and optical wavelength is verified , Pictured 3.

chart 3 Schematic diagram of transmission loss in low loss wavelength region （ Source network ）
The most commonly used is C Band , Low loss .L Band loss second , Will be in C When the band does not meet the bandwidth requirements, it acts as C Band supplement .PON The network downlink wavelength is S Band , The uplink wavelength is O Band .E The band has an obvious loss surge region , Because in 1370-1410nm Band , Hydroxyl ion （OH-） absorption , The loss has increased dramatically , This is also called the water peak , This phenomenon leads to E There are certain restrictions on the use of wavebands .
In order to avoid overlapping interference of light with different wavelengths due to certain deviation , There is a certain interval between the central wavelength of each path of light and the central wavelength of the adjacent path of light . According to the center wavelength interval width ,WDM It is divided into CWDM（ Coarse wavelength division multiplexing ） and DWDM（ DWDM ） Two types of .

• CWDM, It is wavelength division multiplexing with large wavelength spacing .CWDM Center wavelength used from 1270nm To 1610nm, The central wavelength interval of adjacent light waves 20nm, Reusable 18 A wave , Due to the above water peak problem ,1370nm and 1390nm Great loss , Generally do not choose to use , Then the reusable is 16 A wave , At present, the largest number of operators are commercial 1270nm~1370nm Of 6 A wave .CWDM Suitable for short distance transmission , It is generally used in Gigabit Ethernet , The cost of equipment and optical modules is relatively low .

chart 4 CWDM Sketch Map

• DWDM, It is wavelength division multiplexing with small wavelength spacing .DWDM There are standard bands and wavelength intervals defined by different operators , The band will be fully utilized 1550nm Nearby low loss area , The wavelength interval is generally less than or equal to 1.6nm, At the very least 0.2
  nm, Far less than CWDM, Can reuse up to 192 Lu Guang , Suitable for long distance transmission , It is generally used in man , But the cost of equipment and optical modules is relatively high .

chart 5 DWDM Sketch Map （ contrast CWDM）
According to the wavelength division multiplexing technology introduced above , It can be seen that , It is suitable for use in the Ethernet all-optical network in the park CWDM The way .
Actually in PON In the network , Wavelength division multiplexing technology will also be used , The uplink and downlink light with different wavelengths are wavelength division multiplexed , Even the 1G PON and 10G PON Wavelength division multiplexing of light , Can play the role of reuse ODN The Internet , The effect of reducing fiber input , I won't go into that here .

Ethernet all-optical switch products and Ethernet light are used in the Ethernet all-optical network AP As the node of photoelectric conversion in the network , Use white light or color light products to receive luminous signals .
Ethernet all-optical switch products are in the near future 20 It was launched years ago , The models are very rich , The two most basic categories are box and box .
The frame type adopts Ethernet all-optical single board , It can not only be connected with other business boards （ Include PON The Internet OLT Veneer ） One box fusion deployment , You can also expand the capacity by increasing the number of boards . Generally, it serves as the core of the park or converges , Reliability can be achieved by stacking and other technologies .
The box Ethernet all-optical switch has a wide range of product models ：

• It is generally used as an access switch , Products entering the room need to be silent without fans , Smaller size , It can be placed in the indoor information box or on the desktop . It also needs to support standards POE, For indoor AP Power supply .

• The box type Ethernet all-optical switch with stronger performance can also be used as building convergence switch , Deployed in the building machine room .

• There is also a special type of box access switch , It is called central switch and asteroid switch , These two must be used together , The central switch is connected to the asteroid switch through the photoelectric hybrid cable , While supplying power to the asteroid switch and conducting optical communication , You also need to manage and configure the asteroid switch , The asteroid switch can also be AP Conduct POE Power supply . This method is due to the high price of optoelectronic hybrid cables 、 The wire diameter is thick , Not suitable for a large number of vertical routes , Moreover, the advantages of the optical fiber itself are reduced after the cable is connected , The transmission distance is from 10KM Level 1 is back to the 100 meter level in the era of network cable .

Etheric light AP product , There are two types of products , One is in the ether AP The product supports optical ports , It can be directly connected to the building through optical fiber , Take power through local power supply or centralized power supply ; The other is in the ether AP The product supports the optoelectronic hybrid cable connection port , The above central switches must be configured to use , Power is supplied through photoelectric hybrid cable , There is also the problem of the deployment of the above-mentioned optoelectronic hybrid cables . Etheric light AP In addition to providing wireless access , At the same time, it can provide a small number of wired interfaces , One can meet the needs of the dormitory 、 Hotel rooms and other dense room scenes , Wired and wireless network requirements in a single room .
White light products are various types of Ethernet light modules , Common are SFP、SFP+、XFP etc. , Optical modules of the same type must be used at both ends of an optical fiber , At the same time, according to the port rate and fiber type of the Ethernet optical switch （ Monomode / multimode ） Select the appropriate optical module .
Color light products , The most important are the color light module and the combiner and splitter .
The color light module is divided into sending light module and receiving light module , And each standard wavelength has corresponding transmitting optical module and receiving optical module . The transmitting optical module enables the light emitted by the Ethernet optical switch to be transmitted according to the standard wavelength , The receiving optical module receives the light of standard wavelength and sends it to the Ethernet optical switch for processing . The transmitting and receiving optical modules cannot be mixed , Optical modules of different wavelengths cannot be mixed .
The combiner and splitter are usually used in pairs , Passive equipment , No power supply is required , Built in standard color light transceiver module . The combiner and splitter on the Ethernet optical switch side and the user side are generally different devices , In order to synthesize the delay error caused by different wavelengths of light going through different optical paths in optical devices . Scenarios with low delay requirements , The same combiner and splitter can also be used on both sides .
We need to pay attention to , The optical fiber connection from the color light module of the Ethernet optical switch to the combiner must correspond to the correct color light module one by one , Once the connection is wrong, the reception will fail .
meanwhile , In management and operation and maintenance , Since the combiner and the splitter are passive devices , Cannot be managed by the network management system , Moreover, there is no redundant backup mechanism between the combiner and the splitter , In actual use , The operation and maintenance of the color light system will be more difficult . The white light method will not have this problem .

Ethernet all-optical network is the biggest transformation of traditional Ethernet , It is to directly deploy optical fiber into the room from the converged all-optical switch in the central machine room or building machine room / Access corridor , It saves the investment and operation and maintenance of the weak current room on the floor .

chart 6 Typical networking diagram of white light scheme

chart 7 Typical networking diagram of color light scheme
From the figure 7 It can be seen from the typical networking of color light scheme , Even if color light technology is used , Still does not change the point-to-point nature of Ethernet connections , Only the transmission medium is multiplexed . The color optical scheme enables the network to access the core switch without convergence , The probability of bandwidth collision is small , But the normal network will generally adopt 1:2.5~4 Convergence ratio between , And colored light is 1:1 Access core switch , No convergence , Therefore, a large number of expensive core switch interface resources are occupied , Low resource utilization .