Global Optical Fibre can carry hundreds of terabits per second.

This capacity also increases by 25% every year.

Use of Spatial Division Multiplexing (SDM) over Multi-Core and Multi-Mode fiber increases the bandwidth capacity and ultra-high capacity transmission links.

There is also a trend of a higher number of shorter high-capacity links.

The central part for both is an optical source.

A single source offering all wavelengths is more beneficial rather than many parallel lasers for each wavelength.

An innovation of Micro-Combs has shown significant promise towards this technology.

Introduction of Micro-Combs:

In the last decade, optical frequency combs based on micro-resonators has become an active field of research.

The most significant property of these micro-combs is their ability to store information efficiently.

The underlying technology behind these optical micro-combs is dielectric optical resonators composed of different materials molded into different shapes.

The nonlinear optical behavior of micro-resonators makes this field for extensive research.

The discovery of micro-combs has made many breakouts in the field of spectroscopy, photonics, optical ranging, quantum sources, metrology, and many more.

The Director of the Optical Sciences Center at Swinburne University said that the advancement in the field of ultra-high bandwidth fiber optic telecommunications leads to innovations in the internet field.

Optical fiber technology also passed through critics.

In 2013, the Australian Government did not allow National Broadband Network (NBN) to run directly across the people’s houses which even they have developed by muti-technology.

The field then became questionable for future proof of the internet.

But innovations in the field of optical fiber technology arises due to rising demands in the internet field.

Recent Innovation in Micro-Combs:

The micro-combs enables the ability to phase-lock or mode-lock.

Different kinds of oscillation states are explored, including temporal soliton states, dark solitons, and DKS.

DKS states have the ability of transmission speed of 30 TB/s with a single device and 55 TB/s with a combination of two devices.

DKS states use C and L telecommunication bands.

Spectral efficiency has great importance, and it determines the limit of the data-carrying capacity of particular optical communication bandwidth.

Micro-comb termed soliton crystals are recently invented and form the basis for RF photonic and microwave devices.

Micro-combs are formed naturally by micro-cavities having appropriate mode-crossing, and there is no need for complex dynamic pumping and stabilization schemes.

These are stable due to the intra-cavity power.

Micro-combs are very close to the chaotic states, but very little change in intra-cavity power made these thermally stable.

The combination of intrinsic stability and higher efficiency makes it perfect for ultrahigh-capacity transmission.

Ultra-high bandwidth optical data transmission is carrying across the standard fiber having a single integrated chip source.

Soliton crystals realized in a CMOS-compatible platform are used to achieve the transmission speed of 44 TB per second from a single source having high spectral efficiency of 10.4 bits/s/HZ.

This is tested under a high modulation format of 64 QAM, comb – free spectral range (FSR) of 48.9 GHz, and telecommunications C-band.

This transmission is made over 75 km of fiber in the laboratory.

It is also tested over an installed network in the Metropolitan area of Melbourne, Australia.

These experiments provided positive results.

Importance of Micro-Combs:

Micro-combs are tiny devices that could replace the existing infrastructure of the internet one day.

It allows the user to acquire crazy download speeds, providing millions with ample data at the same time.

Micro-combs can work very fast, even during the busiest times.

This lightweight technology has passed through a test trial with a transmission speed of 44.2 Tb per second.

And these used only a single light source.

The extensive research on this field leads to the ways to slim down and speed up the technology behind the internet.

This high potential downloading speed allows us to max out data from each channel through this speed.

Theoretically, it can allow the user to download 1,000 movies in a single second.

This technology can lead to further enhancements in the future.

It also allows many improvements to the internet technology and can be used by data centers to connect with faster communication skills.

Experimental Verification of Micro-Combs:

A schematic experimental setup is arranged for the verification of transmission through Micro-combs.

An FSR spacing of 48.9 GHz is connected with a soliton crystal having spacing 0.4 nm over a bandwidth of more than 80 nm to produce a micro-resonator.

The resonator is then pumped with 1.8 W of continuous-wave (CW) power at 1550 nm.

Automatically tuning of the pump laser to a pre-set value generates a soliton crystal micro-comb.

Conceptual Diagram of a Soliton Crystal Micro-Comb Communications Experiment.

80 lines are then selected over the telecommunications C-band from these generated micro-combs.

These bands are then flattened with a spectral shaper.

After this, the number of wavelengths is doubled to 160 for the optimization of spectral efficiency.

Odd/even de-correlated test channels are generated by the use of a single side-brand modulation scheme.

With the same odd and even channel structure, a test band of 6 channels is loaded.

The comb is then modulated by a high order format of 64 QAM at a symbol rate of 23 Gigabaud.

The micro-comb avails 94% of the spectrum.

Soliton Crystal Generation

Two practical implementations are conducted for the verification of Micro-combs.

Data is sent over 75km of single-mode fiber in the laboratory.

Also, a successful trial is made possible across the Metropolitan area of Melbourne connecting the campuses of two universities.

Offline Digital Signal Processing (DSP) flow method is used for recovery at the receiver site.

Signal quality is also measured with a little bit of drop.

Soliton Crystal Super-Channel Spectra, and Indicative Signal Constellations

Experimental Results of Micro-Comb Transmission:

Scientists investigated three different kinds of scenarios.

  1. A direct connection between transmitter and receiver (B2B)
  2. In the laboratory across single optical fiber
  3. Over a field trial network across a metropolitan state

The overall result deducted from the practical experiments had given a raw bitrate of 44.2 TB per second.

This information is translated at a rate of 40.1 TB per second (in B2B), dropping to 39.2 TB per second for the lab, and 39.0 TB per second for field transmission experiments.

This is an almost 50% increase in efficiency than the highest reported result from a single integrated device.

The spectral efficiency is also 3.7 times higher. The net result in the form of statistics is shown below

Line Rate

Net Rate

Format

Spectral Efficiency

Transmission

44.2 TB/s 40.1 TB/s 64 QAM 10.4 b/s/Hz B2B (0 km)
44.2 TB/s 39.2 TB/s 64 QAM 10.2 b/s/Hz 75 km SMF in Lab
44.2 TB/s 39.2 TB/s 64 QAM 10.1 b/s/Hz 76.6 km SMF installed

Methods for Micro-Comb Production

Different kinds of methods are available

  • CMOS-compatible micro-comb source

CMOS compatible processes having doped silica glass waveguides are fabricated to produce combs.

There is a cross-section of 3 × 2 µm and a radius of 592 µm for MRR, which yields an FSR of 48.9 GHz and a Q factor of 1.5 million.

On-chip mode converters are then coupled to a single-mode fiber array. There is a 0.5 dB per facet fiber-chip coupling loss.

Statistical Studies shows that fabrication yield is another field in which fully CMOS-compatible platform are provided with stepper mask aligners on full wafers.

There is a shallow index contrast, which results in larger waveguide dimensions.

This makes the micro-combs less sensitive to fabrication error.

The typical yield of FSR and Q factor for CMOS-compatible micro-combs should be extremely high, even more than 90%.

This discovery achieves a deterministic generation of micro-combs that will yield new functionality.

  • Soliton Crystal Micro-Comb Generation:

Another method for the production of micro-comb is from the doped silica double bus micro-ring resonator.

This structure is packaged with a fiber array connection to all four devices.

The TM mode oscillates in a soliton crystal state.

Pump Light is inserted into the “through” port, which is then collected from the corresponding “drop” port.

The temperature of the MRR chip is maintained at 25º C with the help of a thermos-electric cooler.

Automated wavelength tuning leads to the production of soliton crystal Micro-combs.

This procedure is less complicated than other micro-comb generation schemes.

The internal efficiency of 42% for the whole spectrum and 30% when selecting only 80 lines over the C-band.

These combs are usually compatible with standard transmissions C-band equipment.

Soliton crystal combs usually show a nonuniform spectrum, and it is the main drawback of this procedure.

To overcome this problem, optical frequency combs are flattened in such a way that all lines are of equal power, which leads to the formation of a uniform spectrum.

Discussion on Recent Innovation in Micro-Combs:

The best result before this innovation was able to support 30.1 TB per second over the C and L bands.

This is done by the use of a standard tunable laser coherent receiver.

This innovation uses less than half of the spectrum and gives a higher data rate with much higher spectral efficiency (3.7x higher).

With the help of dark solitons, high modulation formats are also achieved.

In this new experiment, with the help of the on-chip board, a fully integrated system is produced.

The proprietary multicore file is used to achieve a 30-fold increase in bandwidth.

This innovation has high transmission capacity and spectral efficiency due to high conversion between the soliton crystal state and injected CW wave.

This new experiment is restricted to only C-band, but the bandwidth of soliton crystal combs increases more than 80 nm.

The comb lines between the other two S and L transmission bands can increase and enable transmission across all three bands.

This can lead to a threefold increase in the total data rate, and transmission speed can be increased to 120 TB per second from a single integrated device.

The quality of the signal improves at lower symbol rates.

The micro-combs with lower FSRs can support high spectral efficiencies than others.

This can lead to a narrow bandwidth of comb.

In this modern innovation, single side-band modulation has proceeded, which enables the multiplexing of two channels to a single light source.

In this way, the comb spacing is halved and leads to improvement in back to back (B2B) performance.

The stable nature of the soliton crystal combs made it very easy.

There is another option of using electro-optic modulation, which can be used for the sub-division of the repetition rate of micro-combs.

This procedure can help in enabling broader comb-bandwidths.

This procedure requires locking the comb spacing to an external RF source.

Laser cavity soliton micro combs can also lead to boosting comb generation efficiency.

This can lead to an improvement in the system capacity and signal quality even more.

Conclusion:

A very high-performance ultrahigh bandwidth optical transmission is made possible by a single integrated chip source using soliton crystal micro-combs recently.

This innovation supports the transmission of data with higher speed in a realistic and demanding environment.

The current system of transmission will face struggles for upcoming years.

The replacement of aging cables is a costly and time-demanding exercise.

Now, the world is focusing on other ways of improvement by which the transmission of signals is enhanced.

One such way is the generation of specific frequencies of light that carries data into our computer and smart devices.

Different frequencies allow a multitude of channels to cram information into the tiny optical fiber tubes.

The innovation in the field of micro-combs replaces all existing methods of creating these channels.

Only a single crystal waveform is generated that can be tuned to shape a rainbow of light waves.

The innovation allows the faster way of communication for data processing, which can be used for transportation and self-driving cars.

It can also help in medicine, finance, education, and e-commerce industries.

The high downloading speed can change the whole internet field allowing the user to download massive files even less than seconds.

The most significant importance of this innovation is in the field of algorithms and data-banks, where a massive amount of data is processed.

New deployed links with the combination of space division-multiplexing multicore fiber will allow us the data transfer rates of many petabytes per second from a single source in the near future.

It will be the most significant innovation in the communication field.

This research was published in Nature Communications.