Periodic Reporting for period 2 - VERTIGO (VERy high Throughput Satellite-Ground Optical Link)
Reporting period: 2020-06-01 to 2022-11-30
The telecommunication industry is more and more orientated towards mobile devices and broadband connectivity with its associated challenges the cost reduction per bit supplied to customers (€/Gbps) and the higher capacity of broadband. To stay competitive and face the concurrence of the ground fibered networks but also deliver similar telecommunication services to people in unserved or underserved regions by ground network (bridging the digital divide), operators have to propose services of comparable performance and quality to ground operators offer.
One of the first technological response coming from the Space industry is to develop more competitive solutions like Very High Throughput Satellite (VHTS). But in order to prevent the foreseeable congestion of more conventional (RF) frequency bands and to prepare for the future in the longer term, others are already envisaged such as the W band and a leap to optical technologies is considered as a serious alternative.
Optical feeder links (OFL) are thus considered as a promising technology. Nevertheless, they are still facing some implementation uncertainties, beyond the obvious issue of nebulosity which can be alleviated through site diversity approach. Indeed atmospheric propagation impairments and their mitigation techniques together with high power generation and management as well as efficient modulations are of primary importance in the design and sizing of OFLs. In the past several experimentations on ground or in-flight have demonstrated part of these concepts and subsystems but simultaneous combination of all of them in comprehensive demonstrations has however not been implemented yet.
VERTIGO ambition was to establish the required breakthrough by developing the on-board and ground concepts and technologies enabling for a drastic increase of the link throughput towards and beyond 1 Tbps. VERTIGO major objectives were: 1) Throughput increase by using advanced modulation schemes with higher spectral and power efficiency than currently 1bit/symb approach. 2) High optical power generation to close the demanding link budgets by developing on-board and ground means to raise the transmitted optical power. 3) Mitigation of atmospheric propagation impairments, to make full use of throughput and power increases, implementing optical strategies and digital processing to enhance the robustness of future optical feeder links.
The project successfully addressed these 3 pillars through a total of 4 demonstrations detailed hereafter.
One of the first technological response coming from the Space industry is to develop more competitive solutions like Very High Throughput Satellite (VHTS). But in order to prevent the foreseeable congestion of more conventional (RF) frequency bands and to prepare for the future in the longer term, others are already envisaged such as the W band and a leap to optical technologies is considered as a serious alternative.
Optical feeder links (OFL) are thus considered as a promising technology. Nevertheless, they are still facing some implementation uncertainties, beyond the obvious issue of nebulosity which can be alleviated through site diversity approach. Indeed atmospheric propagation impairments and their mitigation techniques together with high power generation and management as well as efficient modulations are of primary importance in the design and sizing of OFLs. In the past several experimentations on ground or in-flight have demonstrated part of these concepts and subsystems but simultaneous combination of all of them in comprehensive demonstrations has however not been implemented yet.
VERTIGO ambition was to establish the required breakthrough by developing the on-board and ground concepts and technologies enabling for a drastic increase of the link throughput towards and beyond 1 Tbps. VERTIGO major objectives were: 1) Throughput increase by using advanced modulation schemes with higher spectral and power efficiency than currently 1bit/symb approach. 2) High optical power generation to close the demanding link budgets by developing on-board and ground means to raise the transmitted optical power. 3) Mitigation of atmospheric propagation impairments, to make full use of throughput and power increases, implementing optical strategies and digital processing to enhance the robustness of future optical feeder links.
The project successfully addressed these 3 pillars through a total of 4 demonstrations detailed hereafter.
Based on a reference very high capacity mission scenario, the main requirements for an operational feeder link were derived to feed the design phase of the different subsystems. The feeder link capacity was assessed for both digital and analog modulation formats and under different propagation conditions, preliminary SWaP features were evaluated and a preliminary eye safety analysis was also carried out. From the system assumptions, different building blocks were then designed, developed or upgraded and tested with the aim to be implemented in laboratory and outdoor demonstrations of high data rate optical links :
- Optical transmitters and receivers breadboards were developed and tested addressing several modulation formats including both digital and analog: OOK (10G and 25G), DPSK (25G) and DQPSK (50G), DP-QPSK to 16QAM coherent modulation and analog intensity modulation.
- 2 x 50W and 1 x 10W high optical power amplifiers and a high power multiplexer breadboard (3 channels up to 10W/ch) were developed. A setup able to coherently combine two beams of up to 50W was also integrated to generate 100W-class transmissions.
- Two types of optical ground station (OGS) setups were upgraded: a 35cm diameter single-aperture OGS (SA-OGS) equipped with Adaptive Optics and a 4 x 20 mm multi- apertures OGS (MA-OGS) with tip/tilt correction and digital signal combining as two optical approaches for the mitigation of atmospheric impairments. Concurrently, (de)coding/ (de)interleaving FPGA boards were developed as a digital mean to reduce the impact of residual atmospheric impairments on the communication signal.
Most of breadboards and setups developments and upgrades were preceded by simulation analysis and/or tests at components level in order to predict performance in the relevant upcoming environment (e.g. adaptive optics performance were evaluated based on topographic map on the line of sight to be encountered in the frame of the outdoor demo).
Finally, four demonstrations were deployed each addressing a combination of key technologies for the development of operational optical feeder links:
- A first demonstration took place in Switzerland between the high altitude station of Jungfraujoch in the Swiss Alps and the Zimmerwald observatory near Bern implementing a space terminal emulator in Jungfraujoch and the SA-OGS in Zimmerwald. An optical downlink over 53 km of free-space propagation was established successfully conveying telecom data based on previously mentioned modulation formats and a record transmission speed was achieved at 1 Tbit/s over a single wavelength.
- A second demonstration took place in Switzerland between Zimmerwald hosting the MA-OGS and the Castle of Thun hosting a space terminal emulator. Up- and downlink were both tested over a 18 km line-of-sight, transmitting data at 10G based on OOK modulation.
- A third demonstration was deployed in Berlin between two buildings implementing a 2x200m round-trip and successfully demonstrating the coherent combining of optical signals received from each of the four apertures and conveying telecom signals based on 10G OOK modulation.
- Transmissions at high and very high optical power were addressed in the frame of a secure laboratory demonstration set up in Palaiseau (France) for obvious laser safety reasons. OOK and DPSK transmissions up to 25 Gbit/s were successfully tested and a record transmission of telecom data at 97W optical power was achieved.
All the results achieved in the frame of the project were widely disseminated through international conferences, workshops, journal papers and press releases.
- Optical transmitters and receivers breadboards were developed and tested addressing several modulation formats including both digital and analog: OOK (10G and 25G), DPSK (25G) and DQPSK (50G), DP-QPSK to 16QAM coherent modulation and analog intensity modulation.
- 2 x 50W and 1 x 10W high optical power amplifiers and a high power multiplexer breadboard (3 channels up to 10W/ch) were developed. A setup able to coherently combine two beams of up to 50W was also integrated to generate 100W-class transmissions.
- Two types of optical ground station (OGS) setups were upgraded: a 35cm diameter single-aperture OGS (SA-OGS) equipped with Adaptive Optics and a 4 x 20 mm multi- apertures OGS (MA-OGS) with tip/tilt correction and digital signal combining as two optical approaches for the mitigation of atmospheric impairments. Concurrently, (de)coding/ (de)interleaving FPGA boards were developed as a digital mean to reduce the impact of residual atmospheric impairments on the communication signal.
Most of breadboards and setups developments and upgrades were preceded by simulation analysis and/or tests at components level in order to predict performance in the relevant upcoming environment (e.g. adaptive optics performance were evaluated based on topographic map on the line of sight to be encountered in the frame of the outdoor demo).
Finally, four demonstrations were deployed each addressing a combination of key technologies for the development of operational optical feeder links:
- A first demonstration took place in Switzerland between the high altitude station of Jungfraujoch in the Swiss Alps and the Zimmerwald observatory near Bern implementing a space terminal emulator in Jungfraujoch and the SA-OGS in Zimmerwald. An optical downlink over 53 km of free-space propagation was established successfully conveying telecom data based on previously mentioned modulation formats and a record transmission speed was achieved at 1 Tbit/s over a single wavelength.
- A second demonstration took place in Switzerland between Zimmerwald hosting the MA-OGS and the Castle of Thun hosting a space terminal emulator. Up- and downlink were both tested over a 18 km line-of-sight, transmitting data at 10G based on OOK modulation.
- A third demonstration was deployed in Berlin between two buildings implementing a 2x200m round-trip and successfully demonstrating the coherent combining of optical signals received from each of the four apertures and conveying telecom signals based on 10G OOK modulation.
- Transmissions at high and very high optical power were addressed in the frame of a secure laboratory demonstration set up in Palaiseau (France) for obvious laser safety reasons. OOK and DPSK transmissions up to 25 Gbit/s were successfully tested and a record transmission of telecom data at 97W optical power was achieved.
All the results achieved in the frame of the project were widely disseminated through international conferences, workshops, journal papers and press releases.
The VERTIGO project was the opportunity to combine and demonstrate in an unprecedented manner the different key building blocks necessary for the deployment of very high throughput optical feeder links. In particular, very high speed data transmissions (up to a record 1 Tbit/s) through a very challenging propagation channel (due to high level of turbulence imputable to topographic configuration and line-of-sight) was demonstrated. A key aspect demonstrated in the frame of VERTIGO is the transmission of telecom data (based on 25G DPSK) on an optical beam at a record power of 97W opening the way to 100W-class telecom data transmission. Further activities, following VERTIGO end of project are investigating in particular the combination of high power transmission and coherent modulation.
The development and the demonstration in an unprecedented combination manner of key technologies in the frame of VERTIGO strongly contributes to operational deployment perspectives of leading-edge optical feeder link system solutions. VERTIGO paves the way towards very high throughput satellite systems (expected to contribute to bridge the digital divide) and contributes to maintain EU technological leading edge and industry competitiveness.
The development and the demonstration in an unprecedented combination manner of key technologies in the frame of VERTIGO strongly contributes to operational deployment perspectives of leading-edge optical feeder link system solutions. VERTIGO paves the way towards very high throughput satellite systems (expected to contribute to bridge the digital divide) and contributes to maintain EU technological leading edge and industry competitiveness.