Mumbai University > Electronics and telecommunication > Sem 7 > optical communication and networks

Marks: 10

Years: DEC 2015

In specifying the performance of an optical coupler, one usually indicates the percentage division of optical power between the output ports by means of the splitting ratio or coupling ratio.

1) Coupling ratio or splitting ratio

$CR=\dfrac {\text {Power from any single output} P_t}{\text {Total power out to all ports}P_{T-out}}$

In dB for 2*2 Coupler

$CR=10\log_{10} (\dfrac {P_2}{P_1+P_2})$

3-dB coupler: $P_1 = P_2 = 0.5 P0 $

2)Excess Loss

The excess loss is defined as the ratio of the input power to the total output power.

$ L_e=\dfrac {\text {Input power P_i}}{\text{Total outpower } P_{T-out}}\\ L_e =10\log_{10} (\dfrac {P_0}{P_1+P_2})$

3) Insertion Loss

The insertion loss refers to the loss for a particular port-to-port path. For example, for the path from input port i to output port j, we have, in decibels,

$L_i=\dfrac {\text{Power from any single output}}{\text {Power Input}}=\dfrac {P_t}{P_i}$

4) Isolation Loss or Crosstalk or Directivity

Another performance parameter is crosstalk, which measures the degree of isolation between the input at one port and the optical power scattered or reflected back into the other input port.

In dB $\hspace {1cm} L_{iso} =\dfrac {\text{Input power at one port}}{\text {Reflected power back into other input port}}\\ L_{iso} =10\log_{10} (\dfrac {P_0}{P_3})$