The “High Efficiency Optical Amplifier For On-Board Fiber Optic Subsystems Applications” project is divided in two clear phases:
- Phase 1: Trade off analysis of optical amplifiers – Selection of optical amplifier devices to be tested. In this work package, Thales Alenia Space performs a trade-off analysis of the performance characteristics of the available optical amplifiers technologies (mainly Erbium-Doped Fibre Amplifier (EDFA), Erbium-Doped Waveguide Amplifier (EDWA) and Semiconductor Optical Amplifier (SOA)), and assesses their potential for operation at the space environment. The objective requirements of the optical amplifiers have been classified in three different groups depending mainly on the maximum optical output power (18, 24 and 28 dBm). The output of this phase is a Technical Note with the results of this trade off analysis and the selection of devices to be tested.
- Phase 2: Procurement, Test plan procedures and Testing. After the approval of the selection of components, the selected samples were procured and in parallel the Test Plan and Test Procedures were prepared. The reason for this is that the tests to be implemented depended on the selected samples. After the TRR the devices were tested. The output of this phase is the Test Plan and Test Procedures documents, the Reports of the tests performed and the final conclusions and recommendations of the overall project.
- Trade off analysis is based on commercially available devices, but the technology state of the art and research activities have to be analyzed. The collaboration of the UPM was essential in this work.
- Size and weight is an essential factor in the selection of devices.
- Selection of devices for the testing phase has to be based not only on the technology and characteristics of the devices, but also on the willingness of the manufacturer to collaborate in this project and in future possible developments.
- The price of the devices is high and the budget for procurement is fixed. This conditions the selection of the samples.
The expected benefits are:
- To know the real characteristics of commercial optical amplifiers,
- To know the research trends for optical amplifiers,
- To know the possibilities of using commercial available optical amplifiers for space missions,
- To know which improvements have to be investigated or developed for allowing space usage of selected optical amplifiers,
- To know the willingness of commercial companies for the possible future development of a space qualified high optical output optical amplifier.
There is not any new architecture to be developed in this project because the main goal is to study the suitability of commercially available optical amplifiers for space missions.
- The project began with the Kick-off meeting on the 16th May 2006,
- Phase I including a selection of components ended in November 2006,
- Procurement lasted 4 months,
- TRR was held on 15th March 2007,
- Testing activities lasted till December 2007,
- Failure analysis and manufacturer consultancy lasted till November 2008,
- Conclusions and recommendations were ready one month after completion of the testing activities,
- Final presentation was in March 2009.
The project has been completed with the following General Conclusions:
- The EDFAs are clearly the best option due to gain, output optical power, bandwith, etc.
- The numbers of devices tested have been quite low (6 for two EDFAs and 1 for one EDFA, one SOA and two EDWAs), and many different tests have been performed. In the case of those amplifiers with one sample, the validity of the results is very limited. In the case of those with 6 samples, the measurements need further investigation.
- It is difficult to isolate the degradation source. There are several optical components involved, from connectors and spliced of fibers to pump lasers and doped fibers. In the case of having also electronics in the same package, the situation is worse. However, the collaboration of the manufacturers allowed the test of each individual optical component and this showed that the degradation was related to the doped fibers used.
- The most critical optical component for an optical amplifier is the doped fiber. It is proposed to carry an investigation of the behaviour of doped fibers for optical amplifiers by measuring the attenuation after several gamma radiation steps and also its behaviour when installed in an optical amplifier. The possibility of using optical connectors is proposed and should be evaluated, as this would allow radiating the fibers to check not only the attenuation but also their performance in a reference optical amplifier. It is proposed to test the behaviour of European and Canadian doped fibers under gamma radiation when installed in a reference optical amplifier not being radiated. This would allow the selection of the best fiber for future developments.
- The support from the manufacturers is needed for future developments of optical amplifiers prepared for space applications.
- It is recommended to develop and test, with the support of an optical amplifiers manufacturer, an optical amplifier specifically designed for space use for the 18dBm and another one for the 24 dBm range.
- The EDFA commercial optical amplifiers have shown generally good stability during mechanical tests, thermal vacuum and proton radiation.
- However, the gamma radiation has demonstrated to give an important degradation in most of the analyzed devices. This depends on the type of fiber used.
- As expected, the SOA does not provide fully linear amplification, and generates unwanted frequency-compounds through cross-gain saturation and Four-Wave Mixing processes.
- First, such frequency compounds were observed in the optical domain with LO-type signals. These non-linear effects increase as the input power increases and as the frequency separation decreases. In practice, this makes the SOA not well-suited for amplifying LO signals near saturation.
- Non-linear effects were also observed in the RF domain with telecom-type signals. These effects increase as the optical input power increases, and as the RF signal modulation index increases. In practice, these amplifiers are not easily usable for amplifying telecom signals.
- There has been a very limited test campaign for this type of amplifiers, but it is clear that the gamma radiation is also an issue for the EDWA technology.