Block1 Part1 Flashcards
What is meant by Refractive Index?
The refractive index n is a property of a transparent medium, relating to the speed of light v in the medium to the speed of light c in a vacuum.
v=c/n
Why is refractive index relevant to the construction of optical fibres?
If light is directed from one medium to another medium with a lower refractive index, and at a sufficiently shallow angle, the light is reflected back into the first medium.
Can achieve Total Internal Reflection
What is the decibel conversion formulae?
G= 10 log_10 * P_1/P_2
where
G is decibels dB
P_1 is power 1
P_2 is power 2
Velocity or speed equation
Distance = Velocity * Time
tera
10^12
T
Trillion
giga
10^9
G
Billion
mega
10^6
M
Million
kilo
10^3
k
Thousand
deci
10^-1
d
Tenth
centi
10^-2
c
Hundredth
milli
10^-3
m
Thousandth
micro
10^-6
μ
Millionth
nano
10^-9
n
Billionth
pico
10^-12
p
Trillionth
Bandwith
The amount of spectrum occupied by a signal called bandwidth.
It is equal to the difference between the highest and lowest frequencies
f_2 - f_1
Passband
The range of frequencies that a receiver responds best to
The inverse square law
A receiver that is n times as far from the transmitter will receive 1/n^2 of power
Wavelength
the distance between successive crests of a wave, especially points in a sound wave or electromagnetic wave
λ = c/f
where λ wavelength
c speed of light 3 x 10^8 m/s
f the frequency
What does Shannon’s equation measure?
Channel capacity (bits per second)
Shannon’s equation
C = W log_2(1 + S/N)
where,
C is channel capacity (bits per second)
W is the bandwidth in Hz
S/N is the signal to noise ratio
Relationship between frequency and wavelength
c=λν
where c = 2.998 x 10^8 m/s the speed of light
λ = lambda the wavelength in metres
ν = nu the frequency in Hz is per second
Amplitude Phase Keying (ASK)
A method of digital modulation in which different symbols are represented by segments of a carrier signal with different amplitudes.
The frequency and phase remain the same.
Frequency Shift Keying(FSK)
A method of digital modulation in which different symbols are represented by segments of a carrier signal with different frequencies.
The amplitude and phase remain the same
Phase Shift Keying (PSK)
A method of digital modulation in which different symbols are represented by segments of a carrier signal with different phases.
The frequency and amplitude remain the same
Quadrature Amplitude Modulation (QAM)
QAM, or quadrature amplitude modulation, is where sinusoidal symbols are used that can be viewed as appropriate combinations of in-phase (I) and quadrature (Q) sinusoidal segments.
The resulting symbols thus differ in amplitude and phase, but have a single frequency.
Bits per symbol in QAM
n = log_2M
where
n is the bits per symbol
M is the number of symbols
Define Baud
The term baud refers to the number of symbols per second, where one baud is one symbol per second
EG if 64-QAM used to transmit data at 48 Mbps
64-QAM is 6 symbols
48/6 is 8 symbols per second
Therefore baud rate is 8 Mbaud
Signal-to-noise
Signal power divided by noise power
ie power_s/power_n
Power density equation
Power density (W/Hz) = power (W) / bandwidth (Hz)
