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