光有源器件
&
光无源器件
光器件,光通信网络的基础
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光 有 源 器 件
光 无 源 器 件
关键技术,SD H A T M
TDM
WD M
TDM
WD M
支撑基础：
光有源器件
定义,需要外加能源驱动工作的光电子器件
– 半导体光源 (LD,LED,DFB,QW,SQW,VCSEL)
– 半导体光探测器 (PD,PIN,APD）
– 光纤激光器（ OFL:单波长、多波长）
– 光放大器 (SOA,EDFA)
– 光波长转换器 (XGM,XPM,FWM)
– 光调制器（ EA）
– 光开关 /路由器
光无源器件
定义,不需要外加能源驱动工作的光电子器件
– 光纤连接器（固定、活动,FC/PC,FC/APC）
– 光纤定向耦合器 /分支器
– 光分插复用器（ OADM)
– 光波分 /密集波分复用器（ WDM/DWDM)
– 光衰减器（固定、连续）
– 光滤波器（带通、带阻）
– 光纤隔离器与环行器（偏振有关、无关）
– 光偏振态控制器、光纤延迟线、光纤光栅
光器件与电器件的类比
电线 光纤 调制器 光调制器
电阻 光衰减器 三通 （多通） 光耦合器
二极管 光隔离器 混频器 光波分复用器
放大器 光放大器 频率转换器 光波长转换器
滤波器 光滤波器 电源 光源
电接插件 光连接器 探头 光探测器
开关 光开关 集成电路 集成光路
多波长光源
DWDM
光调制器
光隔离器
光耦合器
光波长转换
光放大
DWDM
光色散补偿
光隔离器
光环行器
光波长转换
OADM
DWDM
光隔离器
光环行器
光开关
光器件的应用
可调谐滤波
DWDM
OXC
光耦合器
光调制解调
光器件的分类
? 光电变换器件
? 光开关与调制器件
? 光放大器件
? 光色散补偿器件
? 光网络器件
光电变换器件
? F-P腔激光二极管 (LD)
? 分布反馈布拉格激光器 (DFB)
? 分布布拉格反射激光器 (DBR)
? 外腔激光器与 Q开关激光器
? 发光二极管 (LED)
? 光纤激光器 (OFL)
? 垂直腔表面发射激光器 (ECSEL)
? 多波长光源与波长可调谐激光器
? 光电探测器 (PD,PIN,APD)
光调制器件
? 幅度调制
– 机械调制
– 电光调制
– 直接调制
– 电吸收光调制 (EA)
? 相位调制
? 偏振调制
? 光电集成芯片 (OEIC)
? 光子集成芯片 (PIC)
光放大器件
? 掺铒光纤放大 (EDFA)
? 掺镨光纤放大 (PDFA)
? 掺钕光纤放大 (NDFA)
? 分布式光纤放大
– 喇曼光纤放大 (SRFA)
– 布里渊光纤放大 (SBFA)
? 半导体光放大 (SOA)
光色散补偿器件
? 色散控制
– 色散位移单模光纤
– 非零色散位移单模光纤
– 大有效截面单模光纤
– 色散平坦单模光纤
? 色散补偿
– 色散补偿光纤模块
– SOA色散补偿
– 光纤光栅色散补偿
? 色散管理
光网络器件
? 光耦合透镜 （ 自聚焦透镜, 玻璃球透镜 ）
? 光连接器与光耦合器
? 光隔离器与光环行器
? 光滤波与光波分复用器件
? 光起偏器与偏振控制器
? 光波长转换与光波长路由器件
? 光调制解调器 （ Modem）
? 光衰减器与光延时器件
? 光开关与光交叉连接器件
? 微光电机械芯片
元件,Components
器件,Devices
模块,Modules
系统,Systems
Optical Component
Technologies
? Optical fibre technology
? Microoptic technology
? Planar waveguide technology
? Micro-Optic-Electronic-Mechanic
technology
Fibre Technology
? Fibre is not only a transmission medium,
? Many devices such as amplifiers and
filters can be made from fibre,
? Components usually end up connected
to a fibre for transmission,
Microoptics
? Devices are made using traditional
optical components (such as lenses,
prisms and diffraction gratings)
assembled together,
? Making very small,very high precision
components and assembling them into
useful devices to tolerances well less
than one micron is very difficult and
expensive to accomplish,
Planar Waveguide Technology
? Devices are constructed on the surface
of a flat piece of material such as silica
or semiconductor crystal using the
techniques of semiconductor chip
manufacturing,
Planar Optical Devices
Advantages
? Build a devices much more efficiently and
with much lower cost,
? Physically quite small and be built with very
great precision,
? Critical dimensions can be controlled much
more accurately
? There are a number of devices that can't be
built any other way,
? Many devices can be made together on a
single large substrate and later cut up into
individual devices,
Difficulties
? Need to control dimensions accurately to
about,25 of a micron,
? When diagonal waveguides have regularly
ccurring steps in their sides,you happen to
chance on a resonant wavelength,
? Many complex devices can't be done in planar
technology because a planar device is made
from a uniform material,
? It is costly and difficult to connect these devices
to fibres,
Fabrication of
Planar Optical Devices
? Diffusion of a dopant into a flat ubstrate,
? Deposition/etching techniques similar to
those used in making semiconductors,
? Direct writing of waveguides using a
powerful laser beam and photosensitive
dopant in the material (such as germanium
in silica glass),
Deposition/Etching
Diffusion Techniques
? A silica or glass substrate (rather than a
silicon one) is used,
? The surface is covered with a mask to cover
the parts of the device that we don't want to
become waveguiding,
? The blank is then subjected to prolonged
exposure (usually at a high temperature) to a
material which can diffuse its way into the
surface and so form a waveguide,
Ion Exchange Techniques
? An example of the ion exchange technique
would be where soda glass (with a high
sodium content) is used as the substrate,
After masking,the substrate is immersed in
molten potassium nitrate,Potassium ions
diffuse into the unmasked parts of the glass
and sodium ions diffuse out,Thus the ions
are exchanged - K replaces Na,this
increases the RI and forms a waveguide,
Direct Writing with
a UV Beam
? A small sheet of fused silica doped with
germanium is used,
? This,blank” is polished until the surface is
very flat,
? A UV laser beam (244 nm) at very high
intensity is then used to expose the areas on
the surface that are to be of higher RI,
Optical Amplifiers
What is an Optical Amplifier
? An optical amplifier is a device which
amplifies the optical signal directly
without ever changing it to electricity,
The light itself is amplified,
How to make an OA
? Amplifiers can be built in semiconductor,
Semiconductor Optical Amplifiers (SOAs),
– Almost any semiconductor laser can be made into an
amplifier with a few modifications -
? Amplifiers can be built in fibres,Fibre Amplifiers
– EDFA,Erbium Doped Fibre Amplifiers
– PDFA,Praseodymium Doped Fibre Amplifiers
– NDFA,Neodymimum Doped Fibre Amplifiers
– SRFA,Stimulated Raman Fibre Amplifiers
– PFA,Plastic Fibre Amplifier
Principle
光信号( I n ) 光信号( O u t )
泵浦能源
Pumping Energy
Signal in Signal out
1550
EDFA 增益窗口 30nm ~ 60nm 光 放
大
器
增
益
光
纤
衰
减
除去 OH 峰外
>300nm 低损耗窗口
波长
nm 850 1310
PDFA
SOA
SRA
Development of OA
增益窗口30n ~ 60n
S
EDFAs
Energy Level States
of Erbium
Technical Characteristics
of EDFAs
? Efficient pumping
? Minimal polarisation sensitivity
? Low insertion loss
? High output power (this is not gain but raw
amount of possible output power)
? Low noise
? Very high sensitivity
? Low distortion and minimal interchannel
crosstalk
Definitions
? Gain (amplifier), the ratio in decibels
of input power to output power,
? Gain Coefficient,the small signal gain
divided by the pump power,
? Bandwidth,the range of wavelengths
over which the amplifier will operate,
Definitions
? Gain Saturation,the point where an increase
in input power ceases to result in an increase
in output power,
? Polarisation Sensitivity,the difference in
gain of an input signal in one polarisation to
the gain in the orthogonal polarisation,
(typical,01 ~,1 dB),
? Noise Figure,the ratio of the SNR at the
input to the SNR at the output (in decibels),
Gain Characteristics of EDFAs
Response of Cascaded EDFAs
Flattening the Gain Curve
? Operating the device at 77oK,
? Introducing other dopant materials (such as
aluminium or ytterbium) along with the erbium
into the fibre core,
? Amplifier length is another factor influencing
the flatness of the gain curve,
? Controlling the pump power (through a
feedback loop) is routine to reduce ASE,
Flattening the Gain Curve
? Adding an extra WDM channel locally at the
amplifier,This is called,gain clamping”,
? Manipulating the shape of the fibre
waveguide within the amplifier,Fibres with
dual cores have recently been shown to
produce much superior gain flatness
characteristics,
Flattening the Gain Curve
? Using,blazed” fibre Bragg gratings as filters
to reduce the peaks in the response curve,In
other words,reduce the response at all
wavelengths to that of the worst wavelength,
This approach has been reported to work well
in field trials,
? Using channel preemphasis on the signals as
they are transmitted,That is,transmit different
WDM channels at different power levels to
compensate for later amplifier gain
characteristics,
LPG for Flattening the Gain
Gain Clamping EDFA
Coupler
Filter
Coupler
EDFA光放大器增益锁定技术
泵浦源功率控制
饱和光控制技术
光功率
检测控制
输入光功率
检测
输出光功率
检测
Pin Pout
泵浦激光器
EDF
Wideband EDFAs
? usual gain window (S- & C-band)
– 1525 - 1565 nm
? Second gain window (L-band)
– 1570 - 1610 nm
– Using co-dopants,principally aluminium
and phosphorus
? Wideband EDFAs
– 80 nm,
Gain Saturation
Co-Dopants
? Common co-dopants
used are aluminium (Al),
ytterbium (Yb) and
germanium (Ge),
? Ge co-doping produces
1536 nm and 1550 nm
gain peaks,
? Al broadens and flattens
the gain spectrum in the
region 1540 nm to1560
nm,
Design of Amplifier Length
? Both the signal power level and the pump
power level vary along the length of the
amplifier,signal travels stronger; pump power
level decreases,
? Single wavelength operation,
Lopt=f(Psig,Ppump,Ce,G)
? WDM operation,the flatness of the gain,
? The gain spectrum at any point along the
amplifier will be different from the spectrum at
any other point along the amplifier,
Select Pump Wavelengths
? 980 nm is almost twice as efficient,as
a pump wavelength,than 1480 nm,
– 1480 is within the gain spectrum
– 1480 is a two-level laser system
– 1480 is temperature-sensitive
? disadvantage of 980 nm,quite narrow
pump bandwidth
Warning
? Pumps need to produce an output of up
to 250 mW,
? Unless the laser is very carefully
designed to protect it you can burn the
end facet and erode the LD,
Pumping Direction
Cladding Pumps
Output powers of up to 10 watts!
MultiStage EDFAs
1) To increase the power output whilst retaining low noise
2) To flatten the total amplifier gain response
3) To reduce ASE noise
Remote Pumping
?Two fibres are used in the connection - one for the
signal and one for the pump,
?to pump at 1480 nm
?In a typical undersea system to extend the distance
from around 100 km to 150 or even 200 km,
EDFA System Resilience
? Signal passes through the failed
amplifier relatively unchanged!
Using OTDRs in Amplified Links
? To diagnose link condition right
through the amplifier,
Amplifier Applications
? Preamplifiers
? Power Amplifiers
? Line Amplifiers
Second-Generation EDFAs
? An amplifier with any of the following
characteristics is,second-generation”,
– Multi-stage designs
– Use of co-dopants such as ytterbium
– Use of multiple pumps
– Use of gain-equalisation techniques
Summary of EDFA
Characteristics
? It is significantly simpler than a repeater
and will have a much longer mean time
to failure,
? It is significantly lower in cost than a
repeater,
? It will operate at almost any speed,
? It can be made physically small enough
to fit on a printed circuit card,
Summary of EDFA
Characteristics
? It will produce a gain in optical signal
of about 25 dB,Some amplifiers can
produce a gain of 50 dB or even
higher,
? It will amplify many different
wavelengths simultaneously (with
some small limitations),
Summary of EDFA
Characteristics
? Both amplitude (pulse) modulated and
coherent (frequency modulated) light as
well as cable TV signal could be amplified
without distortion,
? There is effectively no delay in the amplifier,
? It is possible to do end-to-end diagnosis of
link faults right through an EDFA,
? Amplifiers (like their electrical counterparts)
can saturate,
Summary of EDFA
Characteristics
? There are of course some limitations,
– The amplifier itself adds some noise,
– Wavelength range limitation
– The gain spectrum is not perfectly flat,
– Amplifiers do not re-create pulses,
– amplifiers must be placed closer together (30
kilometres) than repeaters (50 kilometres)
? Transmission at 2.4 Gbps over a distance
of 21 000 kilometres was reported
Praseodymium (Pr) Doped
Fibre Amplifiers
? Operate in the 1300 nm band
? The gain available in commercial
PDFAs is only around 12 dB
? Fluorozirconate (ZBLAN) glasses are
used instead of silica,
? Nd:YLF at 1047 nm pumps are the ones
used in commercial PDFAs,
Neodymium (Nd) Doped
Fibre Amplifiers
? Nd will amplify over the range 1310 to
1360 nm in ZBLAN glass and between
1360 and 1400 nm 67 in silica,
? Efficient pump wavelengths are at 795
and 810 nm,
Erbium Doped Planar Devices
Semiconductor Optical/Laser
Amplifiers (SOAs/SLAs)
&
光无源器件
光器件,光通信网络的基础
用
户
网
传
输
网
交
换
网
接
入
网
光 有 源 器 件
光 无 源 器 件
关键技术,SD H A T M
TDM
WD M
TDM
WD M
支撑基础：
光有源器件
定义,需要外加能源驱动工作的光电子器件
– 半导体光源 (LD,LED,DFB,QW,SQW,VCSEL)
– 半导体光探测器 (PD,PIN,APD）
– 光纤激光器（ OFL:单波长、多波长）
– 光放大器 (SOA,EDFA)
– 光波长转换器 (XGM,XPM,FWM)
– 光调制器（ EA）
– 光开关 /路由器
光无源器件
定义,不需要外加能源驱动工作的光电子器件
– 光纤连接器（固定、活动,FC/PC,FC/APC）
– 光纤定向耦合器 /分支器
– 光分插复用器（ OADM)
– 光波分 /密集波分复用器（ WDM/DWDM)
– 光衰减器（固定、连续）
– 光滤波器（带通、带阻）
– 光纤隔离器与环行器（偏振有关、无关）
– 光偏振态控制器、光纤延迟线、光纤光栅
光器件与电器件的类比
电线 光纤 调制器 光调制器
电阻 光衰减器 三通 （多通） 光耦合器
二极管 光隔离器 混频器 光波分复用器
放大器 光放大器 频率转换器 光波长转换器
滤波器 光滤波器 电源 光源
电接插件 光连接器 探头 光探测器
开关 光开关 集成电路 集成光路
多波长光源
DWDM
光调制器
光隔离器
光耦合器
光波长转换
光放大
DWDM
光色散补偿
光隔离器
光环行器
光波长转换
OADM
DWDM
光隔离器
光环行器
光开关
光器件的应用
可调谐滤波
DWDM
OXC
光耦合器
光调制解调
光器件的分类
? 光电变换器件
? 光开关与调制器件
? 光放大器件
? 光色散补偿器件
? 光网络器件
光电变换器件
? F-P腔激光二极管 (LD)
? 分布反馈布拉格激光器 (DFB)
? 分布布拉格反射激光器 (DBR)
? 外腔激光器与 Q开关激光器
? 发光二极管 (LED)
? 光纤激光器 (OFL)
? 垂直腔表面发射激光器 (ECSEL)
? 多波长光源与波长可调谐激光器
? 光电探测器 (PD,PIN,APD)
光调制器件
? 幅度调制
– 机械调制
– 电光调制
– 直接调制
– 电吸收光调制 (EA)
? 相位调制
? 偏振调制
? 光电集成芯片 (OEIC)
? 光子集成芯片 (PIC)
光放大器件
? 掺铒光纤放大 (EDFA)
? 掺镨光纤放大 (PDFA)
? 掺钕光纤放大 (NDFA)
? 分布式光纤放大
– 喇曼光纤放大 (SRFA)
– 布里渊光纤放大 (SBFA)
? 半导体光放大 (SOA)
光色散补偿器件
? 色散控制
– 色散位移单模光纤
– 非零色散位移单模光纤
– 大有效截面单模光纤
– 色散平坦单模光纤
? 色散补偿
– 色散补偿光纤模块
– SOA色散补偿
– 光纤光栅色散补偿
? 色散管理
光网络器件
? 光耦合透镜 （ 自聚焦透镜, 玻璃球透镜 ）
? 光连接器与光耦合器
? 光隔离器与光环行器
? 光滤波与光波分复用器件
? 光起偏器与偏振控制器
? 光波长转换与光波长路由器件
? 光调制解调器 （ Modem）
? 光衰减器与光延时器件
? 光开关与光交叉连接器件
? 微光电机械芯片
元件,Components
器件,Devices
模块,Modules
系统,Systems
Optical Component
Technologies
? Optical fibre technology
? Microoptic technology
? Planar waveguide technology
? Micro-Optic-Electronic-Mechanic
technology
Fibre Technology
? Fibre is not only a transmission medium,
? Many devices such as amplifiers and
filters can be made from fibre,
? Components usually end up connected
to a fibre for transmission,
Microoptics
? Devices are made using traditional
optical components (such as lenses,
prisms and diffraction gratings)
assembled together,
? Making very small,very high precision
components and assembling them into
useful devices to tolerances well less
than one micron is very difficult and
expensive to accomplish,
Planar Waveguide Technology
? Devices are constructed on the surface
of a flat piece of material such as silica
or semiconductor crystal using the
techniques of semiconductor chip
manufacturing,
Planar Optical Devices
Advantages
? Build a devices much more efficiently and
with much lower cost,
? Physically quite small and be built with very
great precision,
? Critical dimensions can be controlled much
more accurately
? There are a number of devices that can't be
built any other way,
? Many devices can be made together on a
single large substrate and later cut up into
individual devices,
Difficulties
? Need to control dimensions accurately to
about,25 of a micron,
? When diagonal waveguides have regularly
ccurring steps in their sides,you happen to
chance on a resonant wavelength,
? Many complex devices can't be done in planar
technology because a planar device is made
from a uniform material,
? It is costly and difficult to connect these devices
to fibres,
Fabrication of
Planar Optical Devices
? Diffusion of a dopant into a flat ubstrate,
? Deposition/etching techniques similar to
those used in making semiconductors,
? Direct writing of waveguides using a
powerful laser beam and photosensitive
dopant in the material (such as germanium
in silica glass),
Deposition/Etching
Diffusion Techniques
? A silica or glass substrate (rather than a
silicon one) is used,
? The surface is covered with a mask to cover
the parts of the device that we don't want to
become waveguiding,
? The blank is then subjected to prolonged
exposure (usually at a high temperature) to a
material which can diffuse its way into the
surface and so form a waveguide,
Ion Exchange Techniques
? An example of the ion exchange technique
would be where soda glass (with a high
sodium content) is used as the substrate,
After masking,the substrate is immersed in
molten potassium nitrate,Potassium ions
diffuse into the unmasked parts of the glass
and sodium ions diffuse out,Thus the ions
are exchanged - K replaces Na,this
increases the RI and forms a waveguide,
Direct Writing with
a UV Beam
? A small sheet of fused silica doped with
germanium is used,
? This,blank” is polished until the surface is
very flat,
? A UV laser beam (244 nm) at very high
intensity is then used to expose the areas on
the surface that are to be of higher RI,
Optical Amplifiers
What is an Optical Amplifier
? An optical amplifier is a device which
amplifies the optical signal directly
without ever changing it to electricity,
The light itself is amplified,
How to make an OA
? Amplifiers can be built in semiconductor,
Semiconductor Optical Amplifiers (SOAs),
– Almost any semiconductor laser can be made into an
amplifier with a few modifications -
? Amplifiers can be built in fibres,Fibre Amplifiers
– EDFA,Erbium Doped Fibre Amplifiers
– PDFA,Praseodymium Doped Fibre Amplifiers
– NDFA,Neodymimum Doped Fibre Amplifiers
– SRFA,Stimulated Raman Fibre Amplifiers
– PFA,Plastic Fibre Amplifier
Principle
光信号( I n ) 光信号( O u t )
泵浦能源
Pumping Energy
Signal in Signal out
1550
EDFA 增益窗口 30nm ~ 60nm 光 放
大
器
增
益
光
纤
衰
减
除去 OH 峰外
>300nm 低损耗窗口
波长
nm 850 1310
PDFA
SOA
SRA
Development of OA
增益窗口30n ~ 60n
S
EDFAs
Energy Level States
of Erbium
Technical Characteristics
of EDFAs
? Efficient pumping
? Minimal polarisation sensitivity
? Low insertion loss
? High output power (this is not gain but raw
amount of possible output power)
? Low noise
? Very high sensitivity
? Low distortion and minimal interchannel
crosstalk
Definitions
? Gain (amplifier), the ratio in decibels
of input power to output power,
? Gain Coefficient,the small signal gain
divided by the pump power,
? Bandwidth,the range of wavelengths
over which the amplifier will operate,
Definitions
? Gain Saturation,the point where an increase
in input power ceases to result in an increase
in output power,
? Polarisation Sensitivity,the difference in
gain of an input signal in one polarisation to
the gain in the orthogonal polarisation,
(typical,01 ~,1 dB),
? Noise Figure,the ratio of the SNR at the
input to the SNR at the output (in decibels),
Gain Characteristics of EDFAs
Response of Cascaded EDFAs
Flattening the Gain Curve
? Operating the device at 77oK,
? Introducing other dopant materials (such as
aluminium or ytterbium) along with the erbium
into the fibre core,
? Amplifier length is another factor influencing
the flatness of the gain curve,
? Controlling the pump power (through a
feedback loop) is routine to reduce ASE,
Flattening the Gain Curve
? Adding an extra WDM channel locally at the
amplifier,This is called,gain clamping”,
? Manipulating the shape of the fibre
waveguide within the amplifier,Fibres with
dual cores have recently been shown to
produce much superior gain flatness
characteristics,
Flattening the Gain Curve
? Using,blazed” fibre Bragg gratings as filters
to reduce the peaks in the response curve,In
other words,reduce the response at all
wavelengths to that of the worst wavelength,
This approach has been reported to work well
in field trials,
? Using channel preemphasis on the signals as
they are transmitted,That is,transmit different
WDM channels at different power levels to
compensate for later amplifier gain
characteristics,
LPG for Flattening the Gain
Gain Clamping EDFA
Coupler
Filter
Coupler
EDFA光放大器增益锁定技术
泵浦源功率控制
饱和光控制技术
光功率
检测控制
输入光功率
检测
输出光功率
检测
Pin Pout
泵浦激光器
EDF
Wideband EDFAs
? usual gain window (S- & C-band)
– 1525 - 1565 nm
? Second gain window (L-band)
– 1570 - 1610 nm
– Using co-dopants,principally aluminium
and phosphorus
? Wideband EDFAs
– 80 nm,
Gain Saturation
Co-Dopants
? Common co-dopants
used are aluminium (Al),
ytterbium (Yb) and
germanium (Ge),
? Ge co-doping produces
1536 nm and 1550 nm
gain peaks,
? Al broadens and flattens
the gain spectrum in the
region 1540 nm to1560
nm,
Design of Amplifier Length
? Both the signal power level and the pump
power level vary along the length of the
amplifier,signal travels stronger; pump power
level decreases,
? Single wavelength operation,
Lopt=f(Psig,Ppump,Ce,G)
? WDM operation,the flatness of the gain,
? The gain spectrum at any point along the
amplifier will be different from the spectrum at
any other point along the amplifier,
Select Pump Wavelengths
? 980 nm is almost twice as efficient,as
a pump wavelength,than 1480 nm,
– 1480 is within the gain spectrum
– 1480 is a two-level laser system
– 1480 is temperature-sensitive
? disadvantage of 980 nm,quite narrow
pump bandwidth
Warning
? Pumps need to produce an output of up
to 250 mW,
? Unless the laser is very carefully
designed to protect it you can burn the
end facet and erode the LD,
Pumping Direction
Cladding Pumps
Output powers of up to 10 watts!
MultiStage EDFAs
1) To increase the power output whilst retaining low noise
2) To flatten the total amplifier gain response
3) To reduce ASE noise
Remote Pumping
?Two fibres are used in the connection - one for the
signal and one for the pump,
?to pump at 1480 nm
?In a typical undersea system to extend the distance
from around 100 km to 150 or even 200 km,
EDFA System Resilience
? Signal passes through the failed
amplifier relatively unchanged!
Using OTDRs in Amplified Links
? To diagnose link condition right
through the amplifier,
Amplifier Applications
? Preamplifiers
? Power Amplifiers
? Line Amplifiers
Second-Generation EDFAs
? An amplifier with any of the following
characteristics is,second-generation”,
– Multi-stage designs
– Use of co-dopants such as ytterbium
– Use of multiple pumps
– Use of gain-equalisation techniques
Summary of EDFA
Characteristics
? It is significantly simpler than a repeater
and will have a much longer mean time
to failure,
? It is significantly lower in cost than a
repeater,
? It will operate at almost any speed,
? It can be made physically small enough
to fit on a printed circuit card,
Summary of EDFA
Characteristics
? It will produce a gain in optical signal
of about 25 dB,Some amplifiers can
produce a gain of 50 dB or even
higher,
? It will amplify many different
wavelengths simultaneously (with
some small limitations),
Summary of EDFA
Characteristics
? Both amplitude (pulse) modulated and
coherent (frequency modulated) light as
well as cable TV signal could be amplified
without distortion,
? There is effectively no delay in the amplifier,
? It is possible to do end-to-end diagnosis of
link faults right through an EDFA,
? Amplifiers (like their electrical counterparts)
can saturate,
Summary of EDFA
Characteristics
? There are of course some limitations,
– The amplifier itself adds some noise,
– Wavelength range limitation
– The gain spectrum is not perfectly flat,
– Amplifiers do not re-create pulses,
– amplifiers must be placed closer together (30
kilometres) than repeaters (50 kilometres)
? Transmission at 2.4 Gbps over a distance
of 21 000 kilometres was reported
Praseodymium (Pr) Doped
Fibre Amplifiers
? Operate in the 1300 nm band
? The gain available in commercial
PDFAs is only around 12 dB
? Fluorozirconate (ZBLAN) glasses are
used instead of silica,
? Nd:YLF at 1047 nm pumps are the ones
used in commercial PDFAs,
Neodymium (Nd) Doped
Fibre Amplifiers
? Nd will amplify over the range 1310 to
1360 nm in ZBLAN glass and between
1360 and 1400 nm 67 in silica,
? Efficient pump wavelengths are at 795
and 810 nm,
Erbium Doped Planar Devices
Semiconductor Optical/Laser
Amplifiers (SOAs/SLAs)
