Spatially distributed optical fibre based transmission link and method thereof

1 . A method for reducing and/or minimizing the energy consumption and/or the cost of an optical fiber based transmission link characterized by having an optical signal-to-noise-ratio (OSNR) and desired total capacity C Total , the method comprising:

calculating a received signal-to-noise ratio (SNR 01 ) in a single spatial channel in the transmission link based on the OSNR of the transmitted optical signal through the link, or assuming a given SNR 01 , as determined by a given link design, wherein the single spatial channel has only one optical fiber;

calculating the corresponding capacity C 01 of the single spatial channel, determined by the SNR 01 , and calculating a number of single spatial channels (N fiber ) required in the link to obtain a predefined desired total capacity C Total =N fiber ·C 01 ;

whilst maintaining the same total capacity of the link, distributing the total capacity C Total of the link in S=m·N fiber spatial fiber channels, calculating a required signal-to-noise ratio SNR 0m for each of the S spatial fibre channels to support the capacity C Total /S, where m is between 1 and 2, or 2, or greater than 2, and wherein S is an integer;

for each fiber calculating a required repeater spacing in each spatial fibre channel to obtain the required SNR 0m ; and

determining the number of m that provides the minimum number of repeaters.

2 . The method according to claim 1 , wherein each of the S spatial fiber channels is independent from each other in such a way that there is no cross-talk from any one of the S spatial fiber channels to any of the other spatial fiber channels and wherein the total capacity of the S independent spatial fiber channels is the sum of the capacities of each of the S independent spatial fiber channels.

3 . The method according to claim 1 , wherein the total capacity of a fiber link with N fiber single spatial fiber channels is defined as C Total =N fiber ·C 01 , where C 01 =B·log 2 (1+SNR 01 ) is the capacity of each single spatial fiber channel, and the same total capacity for the optimized optical fiber based transmission link with S spatial fiber channels is defined as C Total =N fiber ·m·B·log 2 (1+SNR 0m ) and, in case of two spatial fiber channels C Total =N fiber ·2·B·log 2 (1+SNR 0m ), wherein B is the bandwidth of the data signal.

4 . The method according to claim 3 , wherein SNR 0m is related to SNR 01 according to the following equation

SNR

0

⁢

m

=

[

1

+

SNR

01

]

1

m

-

1

,

wherein SNR 0m practically reduces to

SNR

0

⁢

m

≈

1

m

⁢

ln

[

1

+

SNR

01

]

for m>=10.

5 . The method according to claim 3 , wherein SNR 01 is defined as

SNR

01

=

B

ref

R

S

·

OSNR

01

,

and SNR 0m is defined as

SNR

0

⁢

m

=

[

1

+

SNR

01

]

1

m

-

1

,

wherein B ref is a reference bandwidth, R S is the symbol rate, and OSNR 01 is the optical signal to noise ratio of the single spatial channel.

6 . The method according to claim 3 , wherein SNR 01 is defined as

SNR

01

=

B

ref

R

s

⁢

P

launch

(

1

2

)

[

P

launch

OCNR

laser

]

+

2

⁢

n

sp

⁢

hvB

ref

⁢

K

link

(

G

link

-

1

)

,

wherein P launch is the power launched in the fiber, OCNR laser is the optical carrier to noise ratio of the transmission laser, n sp is the spontaneous emission factor of the optical amplifiers in the link, h is Planck's constant, υ is the optical frequency, K link is the number of repeaters, G link is the gain of the optical amplifiers, within each repeater, used to exactly compensate for the transmission loss within the repeater spacing.

7 . The method according to claim 3 , wherein the transmission loss G link is defined as G link =10 −α dB L EDFA /10 , wherein L EDFA is the repeater spacing and αdB is the fiber transmission loss per kilometer in dBs.

8 . The method according to claim 3 , wherein L tot is the total length of the fiber based transmission link, and wherein K link,m =L tot /L EDFA,m is the number of repeaters for the fiber based transmission link with S spatial fiber channels, K link1 =L tot /L EDFA1 is the number of repeaters for the fiber based transmission link with one fiber channel (single spatial fiber channel), L EDFAm is the repeater spacing for the fiber based transmission link with m spatial fiber channels and L EDFA1 is the repeater spacing for the fiber based transmission link with one fiber channel and wherein K linkm /K link1 =m/(L EDFAm /L EDFA1 ) and wherein the following constraint is used to obtain an optimum value of m:

L

EDFAm

L

EDFA

1

>

m

.

9 . The method according to claim 1 , wherein energy and/or cost reduction and optimization are achieved by reducing and minimizing the total number of repeaters on the optical fiber based transmission link.

10 . The method according to claim 1 , wherein energy and/or cost reduction and optimization are achieved by maximizing the total length of the repeaterless optical fiber based transmission link, and wherein the SNR 0m is less than the SNR 01 .