mach zender modulator
DESCRIPTION
A popular Optic-electric modulatorTRANSCRIPT
MACH-ZEHNDER MODULATOR
OUTLINE
INTRODUCTION TYPES WORKING PRINCIPLE BASIC ATTRIBUTES APPLICATION CONCLUSION
INTRODUCTION
Electro-Optic ModulatorAn optical device
Modulates beam of light by the use of electric field
Mach-Zehnder ModulatorAmplitude modulator based on Mach-Zehnder Interferometer
Beam Splitter divides Laser light into two paths
One or both of the beams passed through phase modulator
Beams are recombined at output
Constructive or Destructive Interference controls intensity or Amplitude of Exiting Light
SCHEMATIC DIAGRAM
SCHEMATIC DIAGRAM
DETAIL CONSTRUCTION
MZ MODULATOR
A Voltage applied to arm cause a change in refractive index according to the electro optic effect (E Δn): Pockel’s Effect
The changing refractive index phase modulates the propagating beam through arms (Δ n Δ φ): Self Phase Modulation
The phase modulation gets converted to intensity modulation by combining the two paths (Δ φ ΔI)
Medium
Mach Zehnder Modulator based on Lithium Niobate (LiNbO3)
Stable over wide temperature range
Very low bias voltage drift rate
Mach Zehnder Modulator based on Indium Phosphide (InP)Higher electrical bandwidth up to 60 GHz
Lower driving voltage 2.2 V
Configuration
Push Pull Configuration
Obtained by applying a data (vm) and bias voltage (VB)on one arm
Inverted data (-vm) and bias voltage (-VB) in the other arm
Phase change in two arm are equal and opposite
Chirp free intensity modulation
Configuration
Asymmetric ConfigurationModulating Signal and Bias Voltage are applied in
only one arm
May be same or opposite arm
WORKING PRINCIPLE
Consider an electric field of light propagating in z-direction
In phasor form
Let the light be passed through 50:50 beam splitter of Mach-Zehnder ModulatorArm 1:
Arm 2:
WORKING PRINCIPLE
Output of Mach-Zehnder Modulator
where,
and
Intensity ratio
Phase generated by applied voltage V
WORKING PRINCIPLE
Net phase change
Output Intensity
, k is constant related to geometrical parameters; l is the optical wavelength (in vacuum) and L is the length of waveguide or electrode
MZM Transfer Function