44.2 Tb / s over fiber - how does it work?

On May 22, 2020, Nature Communications published an article by scientists representing research and scientific institutions in Australia, China and Canada, entitled "Ultra-dense optical data transmission over standard fiber with a single chip source".

Naturally, such a headline did not fit for a wide audience, therefore, in the news everyone wrote about 44.2 Tb / s - the result that was achieved (some did not read and TB / s appeared in the headings, but the correct value was terabits / s). Let's figure it out together how it was done and what the researchers actually wrote about.

Let's get started!

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Table of contents

01. Abstracts
02. Experiment
03. Results
04. Comparison with other results
05. Useful links
06. Afterword

I will try to explain the key points of the study, including terms, devices and so on. In addition, at the end of my publication there will be a list of links, through which you can read more.

100% . , , . ( 05).

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01.

[l-1] ( ):

Micro-combs – optical frequency combs generated by integrated micro-cavity resonators – offer the full potential of their bulk counterparts, but in an integrated footprint. They have enabled breakthroughs in many fields including spectroscopy, microwave photonics, frequency synthesis, optical ranging, quantum sources, metrology and ultrahigh capacity data transmission. Here, by using a powerful class of micro-comb called soliton crystals, we achieve ultra-high data transmission over 75 km of standard optical fibre using a single integrated chip source. We demonstrate a line rate of 44.2 Terabits s−1 using the telecommunications C-band at 1550 nm with a spectral efficiency of 10.4 bits s−1 Hz−1. Soliton crystals exhibit robust and stable generation and operation as well as a high intrinsic efficiency that, together with an extremely low soliton micro-comb spacing of 48.9 GHz enable the use of a very high coherent data modulation format (64 QAM — quadrature amplitude modulated). This work demonstrates the capability of optical micro-combs to perform in demanding and practical optical communications networks.

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75 . , "" (76.6 ) , .

:

- (micro-comb)
— ( "") . , ( ). , . , [l-2], (81 , , , ). [n-1].

, . [n-2].

(soliton crystal)
, "" . .

(QAM)
, . $$$\pi / 2$— , "". 64 . [n-3].

, , .

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02.

. 1. [l-1].

a. " ", .
b. (5 9 , $$$1/4$) + 2 AUD (20.5 ) . . , , , .
c. . (CW [n-4]) (1.8 ) (48.9 FSR [n-5]), - . ( ) [n-6], . , EDFA (. ) ( ).

. 1 :

• ECL — edge-coupled laser — , ;
• WSS — wavelength-selective switch — , [n-7];
• Rx — receiver;
• EDFA — Erbium Doped Fiber Amplifier — , [n-8].

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. 2. . , [l-1].

a. . , .
b. , . "" - , ( ). , . C- .
c. 10 ( . 10 ). ± 0.9 , , .

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- 80 C- ( 32 1 536 1 567 , 3.95 ). 160 ( 24.5 ). ( ).

(6 ). 64 QAM, [n-9] 23 [n-10], 94% .

2 75 . [n-11].

1. .
2. , .

. 3. [l-1].

a. , 12.5 , .
b. 75 . 50 . ( 150 ), -, ( , ).
c. 76.6 . 50 .
d. [n-12] 193.4 (1550.1 ) (X Y). "Back-to-back" (B2B) , "75 km in-lab fibre" — (b) "76.6 km field fibre" — ().

. 3 :

• BER — bit error rate — [n-13];
• $$$Q^2$( [n-14]) — .

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03.

. 4. (BER), (GMI) [n-15] [l-1].

a. BER . B2B , — , — . 20% SD FEC, LDPC. FEC $$$4*10^{-2}$. , , .
b. GMI . GMI , - . 10% 20% (OH). (SE) GMI . GMI , BER. GMI (SE) B2B 11.3 / (10.6 //) 10.9 / (10.3 //). ( ) 11.0 / (10.4 //) 10.7 / (10.1 //). .

. 4 :

• FEC — forward error correction — [n-16];
• SD FEC — soft decision FEC;
• LDPC — low-density parity-check code — [n-17].

, 44.2 /. ( ) 40.1 / (B2B ), 39.2 / ( ) 39.0 / (" "). 10.4, 10.2 10.1 // .

50% , [l-3]. , 3.7 .

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04.

. 1. .

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05.

l-1. Ultra-dense optical data transmission over standard fiber with a single chip source (OpenAccess)
l-2. Micro-combs: A novel generation of optical sources (OpenAccess)
l-3 Microresonator-based solitons for massively parallel coherent optical communications
l-4. High-order coherent communications using mode-locked dark-pulse Kerr combs from microresonators (OpenAccess)
l-5. Microresonator frequency comb optical clock (OpenAccess)

May be useful (Wikipedia)

n-1. Frequency comb
n-2. Soliton (optics)
n-3. Quadrature amplitude modulation (QAM)
n-4. Continuous wave (CW)
n-5. Free spectral range (FSR)
n-6. Multiplexing
n-7. Wavelength selective switching (WSS)
n-8. Doped fiber amplifiers (DFA, EDFA)
n-9. Symbol rate
n-10. Baud
n-11. Single-mode optical fiber (SMF)
n-12. Constellation diagram
n-13. Bit error rate (BER)
n-14. Error vector magnitude
n-15. Multivariate mutual information (MMI, GMI)
n-16. Forward error correction (FEC)
n-17. Low-density parity-check code (LDPC) I

also recommend that you look at links to other robots in this area used in the publication [l-1] .

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06. Afterword

Achieving a data transfer rate of 44.2 Tb / s (even if in practice it is 39.0 Tb / s) is an impressive achievement in modern science.

And even though we are unlikely to be able to use it in life soon, the ability to transfer data at high speed is one of the few areas of science that does not raise ordinary people with the question “why are you doing this?” or "how to apply it in our life?".

I hope you were interested. Thank you for the attention!

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