OCAM3

Question 1

What is Optical Modulation?

Answer 1

The process by which the carrier wave of an electromagnetic wave is altered to impose information onto the wave for transmission. The carrier wave transmits the data to a destination where it is extracted (detection)

Question 2

What are the type of modulation?

Answer 2

1) Direct - varying the laser current (on/off) on low speed networks
2) Indirect - varying the output of laser components - requires additional components

Question 3

What properties of a carrier wave can be varied?

Answer 3

1) Amplitude: signal power
2) Phase: Point in a wave cycle from a reference point
3) Polarisation: Direction of the oscillations of a wave as it propagates

Question 4

What are the benefits of dual polarisation modulation?

Answer 4

1) Higher bit rates
2) Tighter wavelength spacing
3) longer distances
4) reduced Optical-Signal-to-Noise-Ratio (OSNR)

Question 5

What are common modulation techniques? (QIDD)

Answer 5

1) Intensity Modulation ON/OFF keying (IM-OOK)
2) Differential Binary Phase Shift Keying (D-BPSK)
3) Dual Polarisation Quadrature Phase Shift Keying (DP-QPSK)
4) Quadrature Amplitude Modulation (QAM)

Question 6

Properties of IM-OOK

Answer 6

1) Laser
2) Direct modulation
3) up to 10Gbps

Question 7

Properties of D-BPSK

Answer 7

1) Laser Constant
2) Indirect modulation, dual polarised
3) 40Gbps

Question 8

Properties of DP-QPSK

Answer 8

1) Laser Constant
2) Indirect, dual polarised
3) 40-100Gbps

Question 9

Properties of QAM

Answer 9

1) Laser Constant
2) Indirect, dual polarised
3) 400Gbps-1Tbps

Question 10

How does modulation convey information?

Answer 10

By the use of symbols. A symbol is one or more data bits

Question 11

What is a data bit?

Answer 11

A binary digit expressed a 0 or 1. Bit rate is the number of bits that can be expressed per second

Question 12

Define symbol rate

Answer 12

1) Number of symbols per second
2) Expressed at Baud (Bd)
3) Does not always equal bit rate