The hierarchy of the standard SDH corresponds to that of SONET for ATM interfaces.
The hierarchy of flows is different on three continents (USA, EC, Japan) is a rate of 51.84 Mbps, which was chosen for form the first level of SONET: STS-1 (Synchronous Transport Signal, level 1). The other levels are called SONET OC-n (Optical Carrier level n). So there is just a gap between the levels of SDH and SONET: Level 1 SDH (155.52 Mb / s) is level 3 and level SONET 2 of SDH (622.08 Mb / s) is the level 12 of SONET.
Sunday, August 30, 2009
The virtual containers and types
To carry signals, using virtual containers (VC: Virtual Container). In the VC that are sections overload (POH: Path Overhead), which are used by pointers. The transport of containers on STM 1 STM 16 done by TDM. The couple VC-pointer, called AU (Administrative Unit) can therefore to carry both synchronous signals. Depending on the speed, the units are two levels Possible AU3 and AU4. Containers are managed in the SDH transmission network, regardless of the signals they carry. This packaging is called adaptation.
Types
There are two types of virtual containers:
• The virtual containers of lower order (VC-11 VC-12, VC-2
and VC-3) which are carried in virtual containers
higher order.
• The virtual containers of higher order (VC-3 and VC-4)
are multiplexed to form the resulting signal.
Types
There are two types of virtual containers:
• The virtual containers of lower order (VC-11 VC-12, VC-2
and VC-3) which are carried in virtual containers
higher order.
• The virtual containers of higher order (VC-3 and VC-4)
are multiplexed to form the resulting signal.
Saturday, August 29, 2009
The principle of SONET / SDH
The arrival of SDH
SDH offers significant advantages over the PDH. SDH based
on a digital frame that provides high level, in addition to the top
speed (higher than PDH):
• Greater flexibility as to the possibility of extracting or
to insert directly a component of said multiplex
• Ease of operation and maintenance (Flow
important for these functions)
• An opportunity to move towards high speed (frames
synchronous broadband are built by multiplexing
phase the basic entity. This entity defines the basic
implicitly all frames high speed, the limitation
is more than technological)
• An interconnection of broadband systems facilitated by the
normalization of the frame line and optical interfaces
corresponding
• The network architectures providing security against
the line faults or equipment
• The modularity of SDH equipment is more suited to
advances in technology.
The SDH frames
There are different frames in SDH. The base frame is called
STM-1 (Synchronous Transport Module level 1).
STM-1 to a length of 2430 bytes. Frequency transmission
is 125ns, which gives us a rate of:
2430 * 8 / 125 = 155.52 Mbit / s.
In this frame, 9 bytes are reserved for the management and
addressing, leaving a payload of 150.336 Mbit / s.
SDH offers significant advantages over the PDH. SDH based
on a digital frame that provides high level, in addition to the top
speed (higher than PDH):
• Greater flexibility as to the possibility of extracting or
to insert directly a component of said multiplex
• Ease of operation and maintenance (Flow
important for these functions)
• An opportunity to move towards high speed (frames
synchronous broadband are built by multiplexing
phase the basic entity. This entity defines the basic
implicitly all frames high speed, the limitation
is more than technological)
• An interconnection of broadband systems facilitated by the
normalization of the frame line and optical interfaces
corresponding
• The network architectures providing security against
the line faults or equipment
• The modularity of SDH equipment is more suited to
advances in technology.
The SDH frames
There are different frames in SDH. The base frame is called
STM-1 (Synchronous Transport Module level 1).
STM-1 to a length of 2430 bytes. Frequency transmission
is 125ns, which gives us a rate of:
2430 * 8 / 125 = 155.52 Mbit / s.
In this frame, 9 bytes are reserved for the management and
addressing, leaving a payload of 150.336 Mbit / s.
Saturday, August 22, 2009
OBJECTIVE OF TRAFFIC GROOMING
1.To combine low-speed traffic streams onto high-capacity wavelengths
2.Improve bandwidth utilization
3.Optimize network throughput
4.Minimize the network cost (transmitter, receiver, fiber link, OXC, ADM, amplifier,wavelength converter etc)
2.Improve bandwidth utilization
3.Optimize network throughput
4.Minimize the network cost (transmitter, receiver, fiber link, OXC, ADM, amplifier,wavelength converter etc)
TRAFFIC GROOMING
Traffic-grooming is a kind of multiplexing in optical signal by packing low speed traffic streams into higher-speed streams.
There is a significant advantage to groom the traffic.
1.Reduction of wavelengths : If each demand requires a light-path exclusively, we need a lot of wavelengths to be allocated.
2.Reduction of costs for installing WDMs and operating networks
There is a significant advantage to groom the traffic.
1.Reduction of wavelengths : If each demand requires a light-path exclusively, we need a lot of wavelengths to be allocated.
2.Reduction of costs for installing WDMs and operating networks
SONET
The evolution of flows of different services, the need for flexibility transmission network, the need to improve the functions of exploitationmaintenance, the continuous increase of transmission capacity on fiber optics and the need for interconnection between operators to high flows and Standardized have shown the limitations of the current hierarchy and led to standardization.
SONET or SDH?
Research on SONET lead each time on another Technology: SDH (Synchronous Digital Hierarchy). It should be clearly introduce the origins of SONET and the links between SONET, PDH (Plesiochronous Digital Hierarchy) and SDH.
Introduction to SONET
SONET (Synchronous Optical Networks) is an initial proposal Bellcore, which defines the transport layer of a physical architecture broadband. SDH (Synchronous Digital Hierarchy) is a vision specific SONET, requested by the Europeans and adapted to the ATM. We will focus our research rather SDH which is used in
Europe and more media on the internet. However, the differences between these
two technologies are very slim.
PDH to SDH
PDH is the technique that preceded SDH. It consists of multiplexer and carry bits of the lower flow transmitting at rates higher. The lower rates are high at a value higher order of bits of justification, with an indication of their presence in the resulting frame. The flow is not exact multiple of the returns but slightly more. It is what was described as plesiochronous (in Greek, Plesio = almost plesiochronous = almost synchronous). The main shortcoming of this technique is that multiplexing does not have access to information in a way directly without demultiplex all channels.
For example, to provide a line to 2Mbit / s more multiplexing and demultiplexing must be made to extract a fast channel 140Mbit / s. It was a defect in telephony but acceptable for use on optical networks, it becomes unacceptable.
SONET or SDH?
Research on SONET lead each time on another Technology: SDH (Synchronous Digital Hierarchy). It should be clearly introduce the origins of SONET and the links between SONET, PDH (Plesiochronous Digital Hierarchy) and SDH.
Introduction to SONET
SONET (Synchronous Optical Networks) is an initial proposal Bellcore, which defines the transport layer of a physical architecture broadband. SDH (Synchronous Digital Hierarchy) is a vision specific SONET, requested by the Europeans and adapted to the ATM. We will focus our research rather SDH which is used in
Europe and more media on the internet. However, the differences between these
two technologies are very slim.
PDH to SDH
PDH is the technique that preceded SDH. It consists of multiplexer and carry bits of the lower flow transmitting at rates higher. The lower rates are high at a value higher order of bits of justification, with an indication of their presence in the resulting frame. The flow is not exact multiple of the returns but slightly more. It is what was described as plesiochronous (in Greek, Plesio = almost plesiochronous = almost synchronous). The main shortcoming of this technique is that multiplexing does not have access to information in a way directly without demultiplex all channels.
For example, to provide a line to 2Mbit / s more multiplexing and demultiplexing must be made to extract a fast channel 140Mbit / s. It was a defect in telephony but acceptable for use on optical networks, it becomes unacceptable.
Saturday, August 15, 2009
CWDM optical multiplexing
In CWDM equipment, we can use lasers in unregulated temperature, lower cost and which emit at wavelengths spaced 20 nm in the transmission window 1270-1610 nm. CWDM is the subject of the ITU-T recommendation G.695, which provides for flexible and scalable solutions, including the solution of 8 to 16 channels with two optical fibers (one for each direction of transmision), offering data rates of 1.25 Gb / s to 2.5 Gb / s per channel.
However, systems CDWM not compatible with optical amplifiers, are limited in scope. Two lengths are indicative of connection specified in Recommendation G.695: up to 40 km and up to about 80 km, which is usually enough for the needs of metropolitan networks.
In contrast, in the record books in 2004, Alcatel was just topped mythical 10 Terabit / s, in a multiplex fiber Alcatel TeraLight 256 channels each operating at 40 Gb / s over a distance of 100 Km This error-free transmission was achieved by combining amplifiers hybrid Erbium / Raman.
In addition, Alcatel has managed to pass 3 terabit / s over a distance of 300 Km 7, in 300 multiplex channels each operating at 10 Gb / s, with optical amplifiers doped with erbium (EDFA) broadband
However, systems CDWM not compatible with optical amplifiers, are limited in scope. Two lengths are indicative of connection specified in Recommendation G.695: up to 40 km and up to about 80 km, which is usually enough for the needs of metropolitan networks.
In contrast, in the record books in 2004, Alcatel was just topped mythical 10 Terabit / s, in a multiplex fiber Alcatel TeraLight 256 channels each operating at 40 Gb / s over a distance of 100 Km This error-free transmission was achieved by combining amplifiers hybrid Erbium / Raman.
In addition, Alcatel has managed to pass 3 terabit / s over a distance of 300 Km 7, in 300 multiplex channels each operating at 10 Gb / s, with optical amplifiers doped with erbium (EDFA) broadband
ITU-T G.692 (Optical interfaces for multi-channel systems with optical amplifiers)
Recommendation ITU-T G.692 (Optical interfaces for multi-channel systems with optical amplifiers) has defined a comb of wavelengths allowed in the only window of 1530-1565 nm transmission. It normalizes the spacing in nanometer (nm) or Gigahertz (GHz) between two wave lengths permitted the window: 200 nm or 1.6 GHz and 100 GHz or 0.8 nm.
The technology is called dense WDM (DWDM) used when the spacing is equal to or less than 100 GHz. Systems at 50 GHz (0.4 nm) and 25 GHz (0.2 nm) to obtain respectively 80 and 160 optical channels.
For even lower densities, we refer to U-DWDM: Ultra - Dense Wavelength Division Multiplexing. Thus, systems
10 GHz (0.08) to obtain 400 optical channels.
Systems WDM / DWDM most marketed today include 8, 16, 32, 80 optical channels, which can reach capacities of 80, 160, 320, 800 Gb / s through a flow capacity of 10 Gb / s. You can reach a capacity of 4 000 Gb / s (4 Tera b / s) with 400 optical channels at 10 Gb / s, U-DWDM technology.
One of the key components of WDM / DWDM amplifier is the erbium-doped fiber (EDFA) which can compensate for losses due to insertion multiplexing / demultiplexing wavelengths.
However DWDM introduces non-linear phenomena which have the effect of limiting in practice the distance between amplifiers between 50 and 100 Km:
- Crosstalk between channels (XPM: Cross Phase Modulation),
- The blend quatre ondes (FWM Four Wave Mixing) which created the inter-modulation between the different optical channels,
- The Raman effect (SRS: Stimulated Raman Scattering), which increases the received power differences between channels and therefore produces a too large dispersion of the signal to noise ratio.
Over singlemode optical fiber 652 G non-linear effects do not appear in the 1550 nm window as the number of channels remains less than or equal to 32 channels and the power per channel remains below 1 mw.
Different techniques used to correct these phenomena: the case of the DCF (Dispersion Compensating Fiber) which is to introduce in the binding section of fiber producing a negative dispersion (around -100 ps / nm.km) compensation.
However, the technologies and DWDM DWDM-U have not yet reached their limits.
New techniques under development will further increase the capacity of optical systems:
- Soliton transmission allowing the transport of very narrow pulses over thousands of km without distortion, while maintaining a broad bandwidth;
- Pulse modulation, or duo-binary transmission, allowing the multiplication by two or three times the flow-mail, using pulse 2 or 3 levels binaries;
- Amplification and multiplexing in the 1300 nm window to improve returns on conventional optical fibers G652 experiencing limitations in the use of DWDM systems at 1550 nm.
In addition, devices such as multiplexers to insertion / extrat optics (Optical Add Drop Multiplexing: OADM) Reconfigurable:
brewers and optical (Optical Cross-Connect: OXC)
give operators flexibility to optimize their networks, primarily long-haul networks. Indeed, the price of these technologies can not be used on networks of local loops, where it should be more equipment. They particularly need to use cooled lasers. Therefore, it has grown quite recently another less expensive technology called CWDM (Coarse WDM) which saves about 30% over a DWDM system.
The technology is called dense WDM (DWDM) used when the spacing is equal to or less than 100 GHz. Systems at 50 GHz (0.4 nm) and 25 GHz (0.2 nm) to obtain respectively 80 and 160 optical channels.
For even lower densities, we refer to U-DWDM: Ultra - Dense Wavelength Division Multiplexing. Thus, systems
10 GHz (0.08) to obtain 400 optical channels.
Systems WDM / DWDM most marketed today include 8, 16, 32, 80 optical channels, which can reach capacities of 80, 160, 320, 800 Gb / s through a flow capacity of 10 Gb / s. You can reach a capacity of 4 000 Gb / s (4 Tera b / s) with 400 optical channels at 10 Gb / s, U-DWDM technology.
One of the key components of WDM / DWDM amplifier is the erbium-doped fiber (EDFA) which can compensate for losses due to insertion multiplexing / demultiplexing wavelengths.
However DWDM introduces non-linear phenomena which have the effect of limiting in practice the distance between amplifiers between 50 and 100 Km:
- Crosstalk between channels (XPM: Cross Phase Modulation),
- The blend quatre ondes (FWM Four Wave Mixing) which created the inter-modulation between the different optical channels,
- The Raman effect (SRS: Stimulated Raman Scattering), which increases the received power differences between channels and therefore produces a too large dispersion of the signal to noise ratio.
Over singlemode optical fiber 652 G non-linear effects do not appear in the 1550 nm window as the number of channels remains less than or equal to 32 channels and the power per channel remains below 1 mw.
Different techniques used to correct these phenomena: the case of the DCF (Dispersion Compensating Fiber) which is to introduce in the binding section of fiber producing a negative dispersion (around -100 ps / nm.km) compensation.
However, the technologies and DWDM DWDM-U have not yet reached their limits.
New techniques under development will further increase the capacity of optical systems:
- Soliton transmission allowing the transport of very narrow pulses over thousands of km without distortion, while maintaining a broad bandwidth;
- Pulse modulation, or duo-binary transmission, allowing the multiplication by two or three times the flow-mail, using pulse 2 or 3 levels binaries;
- Amplification and multiplexing in the 1300 nm window to improve returns on conventional optical fibers G652 experiencing limitations in the use of DWDM systems at 1550 nm.
In addition, devices such as multiplexers to insertion / extrat optics (Optical Add Drop Multiplexing: OADM) Reconfigurable:
brewers and optical (Optical Cross-Connect: OXC)
give operators flexibility to optimize their networks, primarily long-haul networks. Indeed, the price of these technologies can not be used on networks of local loops, where it should be more equipment. They particularly need to use cooled lasers. Therefore, it has grown quite recently another less expensive technology called CWDM (Coarse WDM) which saves about 30% over a DWDM system.
Antennas recycled
Near the village of Takahagi, Japan, two giant antennae installed in the early 1960s as part of the creation of the first Japanese telecommunications network, have a second life ... as observatories radio astronomy.
An unexpected partnership between a university and a village in 2007, it turned out when he learned that the telecommunications company converted to fiber optics, to close the two antennas. They found allies in Ibaraki University, who saw an opportunity to join an international network of observation of the cosmos, the Very Long Baseline Interferometry,
According to Science, this is not even the first time an old telecom antenna is "recycled" for radio-astronomy, and it will not be the last, as fiber optics spread throughout the world, edging out satellite communications.
An unexpected partnership between a university and a village in 2007, it turned out when he learned that the telecommunications company converted to fiber optics, to close the two antennas. They found allies in Ibaraki University, who saw an opportunity to join an international network of observation of the cosmos, the Very Long Baseline Interferometry,
According to Science, this is not even the first time an old telecom antenna is "recycled" for radio-astronomy, and it will not be the last, as fiber optics spread throughout the world, edging out satellite communications.
Sunday, August 9, 2009
The applications of optical fiber
Today, work stations are interconnected using network using fiber optics as its use allows for information flows faster and greater security in transmissions.
In telephony, coaxial cables are slowly replaced by fiber optiques.en Indeed, it is more economical on long and short distances and the number of components required is less important.
Its use is particularly interesting for the military because it gives them some advantages:
low-weight
-size of the fiber
-insensitivity to interference and detection
FIBER OPTICS
1.-The cable technique
The optical fiber was used for these connections, because of relatively long distances, its weakening low prevents the installation of repeaters, unlike coaxial and microwave links that were not interactive. France Telecom is responsible for receiving the programs and then transmits to the control of the operator. They are then sent via fiber to the center of France Telecom supervision and then to the distribution centers.
The first urban fiber network in 1980 in Paris, between two central electronic. The first series of orders were placed in 1982 and the beginning of the massive achievements in 1983. Since 1987 has used the new fiber. Currently three quarters of the fibers are installed in the Paris area . It operate without repeater to 34 Mbits / s. End 1988 150000 Km fiber was employed and 300 000 km ordered.
Approximately 200 000 km of fiber will be laid in intercity by 10 years.
The strategy of the Directorate General of national networks is as follows:
* Skip to the fiber axis for all major risk of saturation in the short and medium term.
* Search the optical connection.
* Aim for optical services in large cities.
2.-Areas of advanced telecommunications (ZTA)
Service very efficient telecommunications are available to offer to businesses: optical fiber networks connected to ISDN 2nd generation, possible reasons for the Telecom 1 satellites and IBS to American and European cities.
3 .- Vidéodyn
The name brings together all the resources available to either customers or subscribers for the occasional television transmissions. Urban networks used for routing fiber optic part in the big cities: they provide connections between telephone exchanges and fuel distribution centers neighborhoods. In addition to the images for the general public, these materials are capable of delivering on fiber, high-speed signals to broadband can be used to establish permanent or temporary connections between different devices.
4 .- The broadband ISDN
ISDN is based on a completely digital and optical. Digital satellite hubs connect analog phones and digital switches to digital. ISDN is established since 1987 in the northern coast. It is now in Paris and throughout France. The standard digital connections adapted to the volume of communication of each user for the transportation of voice, fax, videotex and the data twice 64kbit / s a single cable. The services on fiber optic networks to broadband therefore complement those of the first generation narrowband: banks allow multimedia video, downloading videos or software.
5 .- The domotics
Centralized technical management of a smart building can include fire, floods, gas leaks, alerting services, remote etc ... This requires a "home bus" based on fiber optics.
network type (example)
In telephony, coaxial cables are slowly replaced by fiber optiques.en Indeed, it is more economical on long and short distances and the number of components required is less important.
Its use is particularly interesting for the military because it gives them some advantages:
low-weight
-size of the fiber
-insensitivity to interference and detection
FIBER OPTICS
1.-The cable technique
The optical fiber was used for these connections, because of relatively long distances, its weakening low prevents the installation of repeaters, unlike coaxial and microwave links that were not interactive. France Telecom is responsible for receiving the programs and then transmits to the control of the operator. They are then sent via fiber to the center of France Telecom supervision and then to the distribution centers.
The first urban fiber network in 1980 in Paris, between two central electronic. The first series of orders were placed in 1982 and the beginning of the massive achievements in 1983. Since 1987 has used the new fiber. Currently three quarters of the fibers are installed in the Paris area . It operate without repeater to 34 Mbits / s. End 1988 150000 Km fiber was employed and 300 000 km ordered.
Approximately 200 000 km of fiber will be laid in intercity by 10 years.
The strategy of the Directorate General of national networks is as follows:
* Skip to the fiber axis for all major risk of saturation in the short and medium term.
* Search the optical connection.
* Aim for optical services in large cities.
2.-Areas of advanced telecommunications (ZTA)
Service very efficient telecommunications are available to offer to businesses: optical fiber networks connected to ISDN 2nd generation, possible reasons for the Telecom 1 satellites and IBS to American and European cities.
3 .- Vidéodyn
The name brings together all the resources available to either customers or subscribers for the occasional television transmissions. Urban networks used for routing fiber optic part in the big cities: they provide connections between telephone exchanges and fuel distribution centers neighborhoods. In addition to the images for the general public, these materials are capable of delivering on fiber, high-speed signals to broadband can be used to establish permanent or temporary connections between different devices.
4 .- The broadband ISDN
ISDN is based on a completely digital and optical. Digital satellite hubs connect analog phones and digital switches to digital. ISDN is established since 1987 in the northern coast. It is now in Paris and throughout France. The standard digital connections adapted to the volume of communication of each user for the transportation of voice, fax, videotex and the data twice 64kbit / s a single cable. The services on fiber optic networks to broadband therefore complement those of the first generation narrowband: banks allow multimedia video, downloading videos or software.
5 .- The domotics
Centralized technical management of a smart building can include fire, floods, gas leaks, alerting services, remote etc ... This requires a "home bus" based on fiber optics.
network type (example)
Saturday, August 8, 2009
The option put forward by Free multifibre is validated by ARCEP in France
About the future deployment of fiber optics in France, the regulatory authority for telecommunications (ARCEP) has taken a position on two key points. The first concerns the choice of technology FFTH (abandoned by most developed countries), which brings fiber to the subscriber's home. In its communiqué ARCEP said "the dynamics of the broadband market in France fixed and palatability of the operators in this market to invest in a new local loop fiber to the subscriber (FTTH) is a unique in Europe, particularly conducive to the development of high speed in the territory. "
The second point talks about the choice of options and monofibre multifibre defended by Orange and Free. In his opinion, the authority goes against the assertion of Orange, who judges the option multifibre too expensive, and formally introduced it in the opportunities available in each building so that this solution is installed each When an operator wishes.
The telecoms watchdog said that in the 148 municipalities, or 5.16 million homes, "any operator may request the operator of a building (ie the operator chosen by the co-ownership fibrer building) to have a dedicated fiber for each additional housing, with a pre-installation and co-financing of initial investment. "
The authority says both that this is "conducive to the dynamics of competition and (offer) a guarantee for the future without creating undue hardship for the operators" and that its additional cost is modest compared to monofibre architecture and encourages investment in the fiber properties, encouraging a sharing of costs and hence risk.
Finally for ARCEP 'point of view, the laying of fiber Supernumeraries can change more easily operator (without loss of service) and subscribe to services from different operators.
The second point talks about the choice of options and monofibre multifibre defended by Orange and Free. In his opinion, the authority goes against the assertion of Orange, who judges the option multifibre too expensive, and formally introduced it in the opportunities available in each building so that this solution is installed each When an operator wishes.
The telecoms watchdog said that in the 148 municipalities, or 5.16 million homes, "any operator may request the operator of a building (ie the operator chosen by the co-ownership fibrer building) to have a dedicated fiber for each additional housing, with a pre-installation and co-financing of initial investment. "
The authority says both that this is "conducive to the dynamics of competition and (offer) a guarantee for the future without creating undue hardship for the operators" and that its additional cost is modest compared to monofibre architecture and encourages investment in the fiber properties, encouraging a sharing of costs and hence risk.
Finally for ARCEP 'point of view, the laying of fiber Supernumeraries can change more easily operator (without loss of service) and subscribe to services from different operators.
Wednesday, August 5, 2009
Transmission systems over optical fiber
Compared to other existing transmission media, fiber has a nearly constant attenuation over a large frequency range (several thousands of gigahertz) and offers the advantage of huge bandwidth, for now consider the transmission of digital flow very large (several terabit / second) required by the multiplication of services and the increased need for transmission of images. Very fast too, it is apparent that the optical system, compared to coaxial cable systems of equivalent capacity, a significant gain on the distance between repeaters-regenerators, passing a few kilometers to several tens of kilometers. From 1978 installed systems were working at the optical wavelength of 0.8 m, delivering a throughput of between 50 and 100 Mbit / s with repeater spacing of 10 km, ie approximately three times more than coaxial cable systems of equivalent capacity.
The second generation of transmission systems over optical fiber, which emerged in the 1980s, follows directly from the development of single mode fiber and semiconductor laser at 1.3 m, wavelength for which the chromatic dispersion (ie the distortion on the signals induced by the spread) is minimal. Data rates exceeding 1 Gbit / s with repeater spacing of several tens of kilometers, are met. The scope of these systems are limited by the losses of the fiber, 0.5 dB / km at best, and the idea appears to develop sources emitting at a wavelength of 1.55 m for which l mitigation is minimal. However, this gain is destroyed by the effect of chromatic dispersion, all wavelengths can not propagate at the same speed. The chromatic dispersion of the material of the fiber is much higher than 1.3 m and it is that comes when the limitation of bandwidth and therefore the flow. Simultaneous progress on both the lasers emitting a single mode on the medium of transmission (dispersion shifted fiber) will bring solutions to these problems and the first systems working at 1.55 m appear in the late 1980s, with a throughput greater than 2 Gbit / s.
Emerged in the late 1980s and became very rapid industrial products, fiber amplifiers will bring a revolution in the field of optical fiber communications: inserted into the transmission line, they can compensate for the attenuation of the fiber and thus increase the range of transmission systems, at the cost of added noise. Used as preamplifiers, they increase the sensitivity of optical receivers. Finally, their huge bandwidth (30 nm and even more today) allows consideration of the amplification of multiple optical carriers in the spectrum juxtaposed, forming what is called a multiplex. Thus was born the concept of multiplexing wavelength (WDM Wavelength Division Multiplexing), each fiber carrying a multiplex of N channels is equivalent in capacity to N fibers each carrying a channel, and it is easily conceivable that this approach can potentially d increase the capacity of a network of very large without changing its physical infrastructure. Systems using this technique, mostly with a flow rate of 2.5 Gbit / s per channel, are now being installed in all major global players in their transport networks to cope with traffic growth expected in the coming years. Systems with N × 10 Gbit / s are offered by manufacturers and installed and the shift to multiplex large numbers of channels and (or) high capacity per channel will likely continue in the coming years, to address the need for capacity growth experienced by transport networks such as metropolitan networks.
Finally, the optical transmission can now achieve a quality (in terms of error rates) much higher than earlier systems, particularly microwave.
The optical fiber is also used in video communications networks to transmit a multiplex of sub-carrier electric intensity modulate a carrier perspective. Each of these sub-carrier, which corresponds to a television channel, is itself so analog modulated (frequency modulation, amplitude modulation single sideband) or digital (phase modulation, amplitude modulation on two quadrature carriers ...).
The second generation of transmission systems over optical fiber, which emerged in the 1980s, follows directly from the development of single mode fiber and semiconductor laser at 1.3 m, wavelength for which the chromatic dispersion (ie the distortion on the signals induced by the spread) is minimal. Data rates exceeding 1 Gbit / s with repeater spacing of several tens of kilometers, are met. The scope of these systems are limited by the losses of the fiber, 0.5 dB / km at best, and the idea appears to develop sources emitting at a wavelength of 1.55 m for which l mitigation is minimal. However, this gain is destroyed by the effect of chromatic dispersion, all wavelengths can not propagate at the same speed. The chromatic dispersion of the material of the fiber is much higher than 1.3 m and it is that comes when the limitation of bandwidth and therefore the flow. Simultaneous progress on both the lasers emitting a single mode on the medium of transmission (dispersion shifted fiber) will bring solutions to these problems and the first systems working at 1.55 m appear in the late 1980s, with a throughput greater than 2 Gbit / s.
Emerged in the late 1980s and became very rapid industrial products, fiber amplifiers will bring a revolution in the field of optical fiber communications: inserted into the transmission line, they can compensate for the attenuation of the fiber and thus increase the range of transmission systems, at the cost of added noise. Used as preamplifiers, they increase the sensitivity of optical receivers. Finally, their huge bandwidth (30 nm and even more today) allows consideration of the amplification of multiple optical carriers in the spectrum juxtaposed, forming what is called a multiplex. Thus was born the concept of multiplexing wavelength (WDM Wavelength Division Multiplexing), each fiber carrying a multiplex of N channels is equivalent in capacity to N fibers each carrying a channel, and it is easily conceivable that this approach can potentially d increase the capacity of a network of very large without changing its physical infrastructure. Systems using this technique, mostly with a flow rate of 2.5 Gbit / s per channel, are now being installed in all major global players in their transport networks to cope with traffic growth expected in the coming years. Systems with N × 10 Gbit / s are offered by manufacturers and installed and the shift to multiplex large numbers of channels and (or) high capacity per channel will likely continue in the coming years, to address the need for capacity growth experienced by transport networks such as metropolitan networks.
Finally, the optical transmission can now achieve a quality (in terms of error rates) much higher than earlier systems, particularly microwave.
The optical fiber is also used in video communications networks to transmit a multiplex of sub-carrier electric intensity modulate a carrier perspective. Each of these sub-carrier, which corresponds to a television channel, is itself so analog modulated (frequency modulation, amplitude modulation single sideband) or digital (phase modulation, amplitude modulation on two quadrature carriers ...).
Saturday, August 1, 2009
Acousto-optical modulator
The diffraction of light by an ultrasonic wave is used in the acousto-optical modulators.
The high frequency generator (F = 80 MHz) generated in the strong wave acoustic wavelength Λ = C / F where the acoustic velocity is C = 4200 m / s therefore Λ = 52.5 m. The laser beam is diffracted by the ultrasonic wave. Here we are dealing with the Bragg diffraction since the diffraction angle is such that we can not neglect the diffracting three-dimensional environment (ie in inside the crystal, the deviation of a light ray is such that it will through several periods of network noise, see below **). For a maximum intensity is diffracted in the order 1, we must direct the cell to have an angle of incidence equals the angle of Bragg:
θB = λ / 2Λ = 6.0 mrad = 0.35 °
The laser beam is then deflected a corner:
2 θB = λ / Λ = 12 mrad = 0.69 °
Network ** 2D or 3D? : There are in general two types of diffraction, following a laser beam diffracted or not returned in an adjacent layer of a thick network: In the 1st case it is Bragg diffraction (3D network) in the second case, we speak of the Raman-Nath (2D network). On moves from one regime to another for a network of thickness Ec. In the experiment described in the leaflet "Optical and acoustic,the light was diffracted by a 2D network (the frequency being much lower, the period is greater: Λ / 2 ≈ 0.7 mm
Thus Ec ≈ 1m). Here against the network period is very short short (Λ / 2 = 26 m,thus Ec ≈ 1 mm): we are here in a Bragg regime.
Measuring θB:
Adjust the orientation of the cell so as to have a maximum intensity in the order 1 (use a photodetector for further details). At a distance 245 cm from the cell, separating the two beams main (order 0 and 1) is 3.0 cm. We therefore measured
θB an angle 2 = 3.0 / 245 = 12 mrad in agreement with the value calculated above.
Measuring the effectiveness of the modulator:
In the absence of ultrasonic wave is measured by such a power P = 3.30 mW.
With the ultrasonic wave, the power measured in the order 1 is P1 = 2.40 mW.
Efficiency is therefore P1 / P = 2.40 / 3.30 = 73% (max efficiency = 85% according to the notice).
Modulation:
The amplitude of the ultrasonic wave can be modulated by an external (GBF 0-5 V connected to the "mod
input generator HF) frequency fmod (15 MHz max), which has the effect of the intensity diffracted in
Order 1. In this case, the HF generator switch must be set to "OFF" (in the "cw", the HF signal is not modulated). To demonstrate an application telecoms ", the adjustment can be made from the signal output of a radio (see montage below).
• Other applications: ACOUSTO-OPTIC DEFLECTOR:
By modulating this time not the amplitude but the frequency F of the HF signal, it changes the wavelength Ultrasonic Λ therefore the angle of diffraction. This allows to control the deflection of a laser beam by a signal electric. This effect is used in scanners for example. This experience can not be achieved with our hardware because we do not currently supply a variable frequency RF or deflector acoustooptique.
Indeed, for applications to the deflection, we use acousto-optic cells that operate on a acoustic mode of low speed of propagation, which allows for a low acoustic wavelength Λ and a wide angle of deflection (typically: C = 500 m / s therefore Λ m = 6 to F = 80 MHz and Δθ = 50 mrad at λ = 633 nm for a variation of the acoustic frequency ΔF = 40 MHz). For applications to modulation, is preferred by against using a sound speed (C = 4200 m / s) because the time between the laser beam in the
acoustic wavelength Λ, which limits the high frequency performance of the modulator, with typically 160 ns per mm laser beam to the modulator, 1μs/mm against the deflector (source: AA Optoelectronic).
The high frequency generator (F = 80 MHz) generated in the strong wave acoustic wavelength Λ = C / F where the acoustic velocity is C = 4200 m / s therefore Λ = 52.5 m. The laser beam is diffracted by the ultrasonic wave. Here we are dealing with the Bragg diffraction since the diffraction angle is such that we can not neglect the diffracting three-dimensional environment (ie in inside the crystal, the deviation of a light ray is such that it will through several periods of network noise, see below **). For a maximum intensity is diffracted in the order 1, we must direct the cell to have an angle of incidence equals the angle of Bragg:
θB = λ / 2Λ = 6.0 mrad = 0.35 °
The laser beam is then deflected a corner:
2 θB = λ / Λ = 12 mrad = 0.69 °
Network ** 2D or 3D? : There are in general two types of diffraction, following a laser beam diffracted or not returned in an adjacent layer of a thick network: In the 1st case it is Bragg diffraction (3D network) in the second case, we speak of the Raman-Nath (2D network). On moves from one regime to another for a network of thickness Ec. In the experiment described in the leaflet "Optical and acoustic,the light was diffracted by a 2D network (the frequency being much lower, the period is greater: Λ / 2 ≈ 0.7 mm
Thus Ec ≈ 1m). Here against the network period is very short short (Λ / 2 = 26 m,thus Ec ≈ 1 mm): we are here in a Bragg regime.
Measuring θB:
Adjust the orientation of the cell so as to have a maximum intensity in the order 1 (use a photodetector for further details). At a distance 245 cm from the cell, separating the two beams main (order 0 and 1) is 3.0 cm. We therefore measured
θB an angle 2 = 3.0 / 245 = 12 mrad in agreement with the value calculated above.
Measuring the effectiveness of the modulator:
In the absence of ultrasonic wave is measured by such a power P = 3.30 mW.
With the ultrasonic wave, the power measured in the order 1 is P1 = 2.40 mW.
Efficiency is therefore P1 / P = 2.40 / 3.30 = 73% (max efficiency = 85% according to the notice).
Modulation:
The amplitude of the ultrasonic wave can be modulated by an external (GBF 0-5 V connected to the "mod
input generator HF) frequency fmod (15 MHz max), which has the effect of the intensity diffracted in
Order 1. In this case, the HF generator switch must be set to "OFF" (in the "cw", the HF signal is not modulated). To demonstrate an application telecoms ", the adjustment can be made from the signal output of a radio (see montage below).
• Other applications: ACOUSTO-OPTIC DEFLECTOR:
By modulating this time not the amplitude but the frequency F of the HF signal, it changes the wavelength Ultrasonic Λ therefore the angle of diffraction. This allows to control the deflection of a laser beam by a signal electric. This effect is used in scanners for example. This experience can not be achieved with our hardware because we do not currently supply a variable frequency RF or deflector acoustooptique.
Indeed, for applications to the deflection, we use acousto-optic cells that operate on a acoustic mode of low speed of propagation, which allows for a low acoustic wavelength Λ and a wide angle of deflection (typically: C = 500 m / s therefore Λ m = 6 to F = 80 MHz and Δθ = 50 mrad at λ = 633 nm for a variation of the acoustic frequency ΔF = 40 MHz). For applications to modulation, is preferred by against using a sound speed (C = 4200 m / s) because the time between the laser beam in the
acoustic wavelength Λ, which limits the high frequency performance of the modulator, with typically 160 ns per mm laser beam to the modulator, 1μs/mm against the deflector (source: AA Optoelectronic).
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