Lifetime Effective Active Region Refractive Index Parameter
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Modeling and characterization of a Semiconductor Optical Amplifier
KAMAL HUSSAIN
RAHUL MUNSHI
P K DATTA
INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR
What is a SOA ? • •
SOA is an optoelectronic device that amplifies an input light signal using the energy of the current injected into the active region. Two main types of SOAs are
The Fabry-Perot SOA
• •
•
and
The travelling wave SOA
The SOA output is accompanied by noise in the form of amplified spontaneous emission (ASE) and ripples due to reflection from the facets. Quantum well (Single quantum well, GRIN single quantum well, Multiple quantum well, Modified multiple quantum well) SOAs have superior gain bandwidths and are less polarization dependant. SOA gain dynamics are determined by carrier recombination lifetime (of the order of a few hundred picoseconds) and the gain saturation may cause the output bandwidth to be severely affected.
INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR
Gain saturation occurs as the carriers in the active regions get depleted leading to decrease in amplifier gain.
3dB
Gain(dB)
•
P o,sat Output signal power(dBm)
•
Nonlinearities in SOAs are primarily due to carrier density changes and can be responsible for effects like frequency chirping and higher order intermodulation products. Four main types of SOA nonlinearities are: Cross Gain Modulation (XGM), Cross Phase Modulation (XPM), Self Phase Modulation (SPM), Four Wave Mixing(FWM).
•
The most simple SOA structures are Double layered Semiconductor Heterostructures. Modern enhancements include Angled facet structure, Window facet structure, Ridge waveguide structure for high saturation output power, strained-layer super lattices to handle polarization sensitivity, Gain-clamped strucures to reduce crosstalk in multichannel applications.
INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR
Applications • • •
• •
Main advantages are transparency to data rate and modulation format, bi-directionality, WDM capability, simple mode of operation, low power consumption and compactness. Used as Booster amplifier, Pre amplifier, In-line amplifiers and amplifier cascade. Using four-wave-mixing (FWM) technique, cross-phase and cross-gain modulation mechanisms SOA can be used in wavelength converters which play an important role in broadband all-optical networks. SOAs can be used to construct high speed optical switches for future WDM and TDM optical communication systems. SOAs can be configured to realize all-optical logic gates.
INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR
• •
Mode-locked fiber ring laser incorporating an SOA is used to generate high repetition-rate wavelength tunable pulses, at high frequencies which are required in high-speed OTDM. SOA based MZI switches are required in ADMs required by optical time division multiplexed optical network nodes. Dc bias
40 Ghz pulse train 30 %
SOA
70 %
Fabry-Perot filter
Bias Tee
Fabry-Perot laser
High dispersion fiber
Polarization controller
Isolator
10Ghz gain-switched pulses
Optical pulse generation using a mode-locked fiber ring laser incorporating an SOA
• •
Due to its compactness and cost effectiveness SOAs find wide applications in Photonic Integrated Circuits (PIC) and in remote optical components. They can be used for format conversion of input signal such as DPSK to NRZ.
INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR
Comparison Chart Features
SOA
EDFA
Raman Amplifier
Internal gain
Low
High
High
Pump source
Electrical
Optical
Optical
Nonlinear effects
Yes
Negligible
Negligible
Noise figure
High
Low
Lower
Saturation output power
High
Low
High
Polarization sensitivity
Yes (< 2dB)
No
No
3dB gain bandwidth
Wide range
Small range
Small range
To make integrated circuits
Yes
No
No
To make functional devices
Yes
No
No
INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR
Analytical Static Modeling For our simulation involving analytical modeling we have considered the geometrical and material parameters of the SOA obtained from Mitsubishi Electric Co. Ltd.. Symbol
Parameter
Value
L
Length of the SOA
1800µm
w
SOA active layer width
1.4µm
d
SOA active layer thickness
0.32µm
β
Spontaneous emission coefficient
10-4
Γ
Optical confinement factor
0.439
c
Group velocity
0.95×108 ms-1
λs
Signal wavelength
1580 nm
a
Material gain constant
3.0×10-20 m2
R1
Input facet reflectivity
10-3
R2
Output facet reflectivity
10-3
τ
Carrier recombination lifetime
1ns
Effective active region refractive index
3.4
neff
INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR
Injection current=39mA
Spatial variation of carrier density of a TW-SOA
Gain ripple variation with input signal power
Injection current=39mA
Injection current=39mA
The variation of gain with input signal power
The variation of output power with input power for the TW SOA
INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR
Low Signal power = -60dBm
Injection current=39mA
Injection current=39mA
High Signal power = -10dBm
Spatial variation of amplified spontaneous emission
Injection current=39mA
Injection current=39mA High Signal power = -10dBm
Low Signal power = -60dBm
Spatial variation of signal photon density INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR
Conclusion and Reference • • • •
We have presented an analytical model of a semiconductor optical amplifier with low facet reflectivity taking into account the non-uniform spatial gain distribution. We have shown the carrier density variation inside the active region of the SOA for various input signal powers. The asymmetric nature of forward and backward ASE variation with high injection currents is observed. The saturation effect of the gain and output power with increasing input signal power has been shown . The maximum attainable gain of the amplifier is limited by the ASE.
REFERENCE • • •
P. Brosson, “Analytical model of a semiconductor optical amplifier”, J. Lightwave Technol. 12, 49-54 (1994). D. Marcuse, “Computer model of an injection laser amplifier”, IEEE J. Quantum. Electron. 19, 63-73 (1983) M. J. Connelly, “Wideband semiconductor optical amplifier steady-state numerical model”, IEEE J. Quantum. Electron. 37, 439-447 (2001). INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR
KAMAL HUSSAIN
RAHUL MUNSHI
P K DATTA
INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR
What is a SOA ? • •
SOA is an optoelectronic device that amplifies an input light signal using the energy of the current injected into the active region. Two main types of SOAs are
The Fabry-Perot SOA
• •
•
and
The travelling wave SOA
The SOA output is accompanied by noise in the form of amplified spontaneous emission (ASE) and ripples due to reflection from the facets. Quantum well (Single quantum well, GRIN single quantum well, Multiple quantum well, Modified multiple quantum well) SOAs have superior gain bandwidths and are less polarization dependant. SOA gain dynamics are determined by carrier recombination lifetime (of the order of a few hundred picoseconds) and the gain saturation may cause the output bandwidth to be severely affected.
INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR
Gain saturation occurs as the carriers in the active regions get depleted leading to decrease in amplifier gain.
3dB
Gain(dB)
•
P o,sat Output signal power(dBm)
•
Nonlinearities in SOAs are primarily due to carrier density changes and can be responsible for effects like frequency chirping and higher order intermodulation products. Four main types of SOA nonlinearities are: Cross Gain Modulation (XGM), Cross Phase Modulation (XPM), Self Phase Modulation (SPM), Four Wave Mixing(FWM).
•
The most simple SOA structures are Double layered Semiconductor Heterostructures. Modern enhancements include Angled facet structure, Window facet structure, Ridge waveguide structure for high saturation output power, strained-layer super lattices to handle polarization sensitivity, Gain-clamped strucures to reduce crosstalk in multichannel applications.
INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR
Applications • • •
• •
Main advantages are transparency to data rate and modulation format, bi-directionality, WDM capability, simple mode of operation, low power consumption and compactness. Used as Booster amplifier, Pre amplifier, In-line amplifiers and amplifier cascade. Using four-wave-mixing (FWM) technique, cross-phase and cross-gain modulation mechanisms SOA can be used in wavelength converters which play an important role in broadband all-optical networks. SOAs can be used to construct high speed optical switches for future WDM and TDM optical communication systems. SOAs can be configured to realize all-optical logic gates.
INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR
• •
Mode-locked fiber ring laser incorporating an SOA is used to generate high repetition-rate wavelength tunable pulses, at high frequencies which are required in high-speed OTDM. SOA based MZI switches are required in ADMs required by optical time division multiplexed optical network nodes. Dc bias
40 Ghz pulse train 30 %
SOA
70 %
Fabry-Perot filter
Bias Tee
Fabry-Perot laser
High dispersion fiber
Polarization controller
Isolator
10Ghz gain-switched pulses
Optical pulse generation using a mode-locked fiber ring laser incorporating an SOA
• •
Due to its compactness and cost effectiveness SOAs find wide applications in Photonic Integrated Circuits (PIC) and in remote optical components. They can be used for format conversion of input signal such as DPSK to NRZ.
INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR
Comparison Chart Features
SOA
EDFA
Raman Amplifier
Internal gain
Low
High
High
Pump source
Electrical
Optical
Optical
Nonlinear effects
Yes
Negligible
Negligible
Noise figure
High
Low
Lower
Saturation output power
High
Low
High
Polarization sensitivity
Yes (< 2dB)
No
No
3dB gain bandwidth
Wide range
Small range
Small range
To make integrated circuits
Yes
No
No
To make functional devices
Yes
No
No
INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR
Analytical Static Modeling For our simulation involving analytical modeling we have considered the geometrical and material parameters of the SOA obtained from Mitsubishi Electric Co. Ltd.. Symbol
Parameter
Value
L
Length of the SOA
1800µm
w
SOA active layer width
1.4µm
d
SOA active layer thickness
0.32µm
β
Spontaneous emission coefficient
10-4
Γ
Optical confinement factor
0.439
c
Group velocity
0.95×108 ms-1
λs
Signal wavelength
1580 nm
a
Material gain constant
3.0×10-20 m2
R1
Input facet reflectivity
10-3
R2
Output facet reflectivity
10-3
τ
Carrier recombination lifetime
1ns
Effective active region refractive index
3.4
neff
INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR
Injection current=39mA
Spatial variation of carrier density of a TW-SOA
Gain ripple variation with input signal power
Injection current=39mA
Injection current=39mA
The variation of gain with input signal power
The variation of output power with input power for the TW SOA
INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR
Low Signal power = -60dBm
Injection current=39mA
Injection current=39mA
High Signal power = -10dBm
Spatial variation of amplified spontaneous emission
Injection current=39mA
Injection current=39mA High Signal power = -10dBm
Low Signal power = -60dBm
Spatial variation of signal photon density INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR
Conclusion and Reference • • • •
We have presented an analytical model of a semiconductor optical amplifier with low facet reflectivity taking into account the non-uniform spatial gain distribution. We have shown the carrier density variation inside the active region of the SOA for various input signal powers. The asymmetric nature of forward and backward ASE variation with high injection currents is observed. The saturation effect of the gain and output power with increasing input signal power has been shown . The maximum attainable gain of the amplifier is limited by the ASE.
REFERENCE • • •
P. Brosson, “Analytical model of a semiconductor optical amplifier”, J. Lightwave Technol. 12, 49-54 (1994). D. Marcuse, “Computer model of an injection laser amplifier”, IEEE J. Quantum. Electron. 19, 63-73 (1983) M. J. Connelly, “Wideband semiconductor optical amplifier steady-state numerical model”, IEEE J. Quantum. Electron. 37, 439-447 (2001). INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR
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