I.

INTRODUCTION

Photonics is progressively transforming from a highly-focused technology applicable to digital communication networks into a pervasive “enabling” technology with diverse non-telecom applications. However, the centre of mass on the R&D level is still mostly driven by, and invested in, by stakeholders active in the telecoms domain. This is due to the high level of investments necessary that in turn require a large and established market for reaching break-even and generation of revenues. Photonics technology and more specifically, fibre-optic technology is moving into non-telecom business areas with great success in terms of markets captured and penetration rates. One example that cannot be overlooked is the application of fibre-optics to industrial applications, where double-digit growth rates are recorded with fibre lasers and amplifiers constantly gaining momentum. In this example, several years of R&D efforts in creating high-power amplification solutions and fibre-laser sources by the telecom sector, were piggy-backed into industrial applications and laser cutting/welding equipment that is now a strong R&D sector on its own and commercially now displacing some conventional free space laser cutting/welding.

The space sector and associated market characteristics pose significant constraints on the levels of investment justifiable due to factors relating to expected revenues, high development costs due to “zero-failure” requirements and extensive testing and qualification required. Hence, technology development from TRL 1 within the space domain takes longer to mature and is harder to justify in terms of investments. The “rules of engagement” change radically when lower TRL technologies are piggy-backed into the space domain, hence exploiting investments already allocated and applying novel designs and required advancements starting from a higher TRL. Research and development is now required focusing on satellite communications that make use of high-power photonics technologies, exploiting the advances from telecommunications and fibre-optics in laser industrial applications.

II.

R&D ACTIVITIES AND WORKPLAN

HIPPO [1] is a 3-year research & development collaborative project co-funded by the European Union. The project aims to design and develop a new generation of robust and reliable high-power photonic components and modules, demonstrate applicability to space applications and prove that the technology can operate in the stringent requirements set by the space environment. HIPPO development plan includes active photonic components that rely on advanced semiconductor fabrication and packaging approaches developed by III-V LAB and G&H respectively. On the fibre side, development of new micro-structured optical fibres by FIBERWARE and passive fibre components by G&H are scheduled. Using the components developed, high-power amplifier modules are developed and tested by G&H. All HIPPO components and modules are then evaluated by the space vendor (Thales Alenia Space), exploiting its unique expertise and infrastructure on space systems. Table 2 shows the technology development activities foreseen within the program. HIPPO focuses on creating a powerful “made in Europe” technology base covering the complete spectrum of “high-power photonics”. In so doing, it will create a strong potential to capture significant market segments due to the vertically-integrated consortium. The HIPPO development phase starts with the system vendor and prime space contractor (Thales Alenia Space) for providing initial inputs on the space-born systems where HIPPO components would offer unique advantages not possible with competing technologies. According to these high-level set of performance metrics, the component manufacturers (III-V LAB, G&H TQY, FIBERWARE) and module vendor (G&H STG) provide the necessary design methodologies and device designs for realizing the specifications.

Table 1.

Photonic technologies and market drivers

Table 2.

Photonic technologies developed

Table 3.

Laser specifications

Table 4.

Detector specifications

Table 5.

Amplifier specifications

Fig. 1.

HIPPO project value chain

III.

APPLICATION SCENARIOS

The satellite communication field is facing new challenges: whilst future broadband communication satellites ask for higher throughput, extended coverage and flexibility, observation and scientific missions will need for larger data transfer capacity. In this context, photonic technologies are perceived as a credible alternative to traditional electronic counterparts and are expected to bridge the gap addressing different applications including on-board photonic signal handling and processing as well as free-space optical communications for near-Earth and deep space applications. HIPPO components are specifically designed for application in the following two future space markets:

IV.

COMPONENT SPECIFICATIONS

HIPPO will develop a complete family of high power components including DFB lasers, high power-handling photodiodes, pump lasers, passive fibre optic components and photonic crystal fibres. High-power optical fibre amplifier modules will be designed and developed through functional integration of HIPPO fibre-optic and optoelectronic components.

A.

Optoelectronic components

In the case of semiconductor lasers, the main way to increase optical power and efficiency is to reduce optical losses inside the optical cavity. In 1.55μm semiconductor lasers on InP, the two main sources of optical losses inside the cavity are re-absorption in quantum wells and intra-valence-band absorption (IVBA) in P-type doped layers.

Reduction of internal losses can be achieved by either a reduction of the optical mode overlap with quantum wells or the reduction of the optical mode overlap with p-type doped layers, which is the main path selected within HIPPO for increasing optical laser power.

Fig. 2.

(left) DFB experimental results from various devices within the 1^st fabrication run and (right) simulation of the back-side illuminated UTC photodiode versus absorber thickness (Wa)

The main challenge on HIPPO photodetectors relate to detecting high optical input power at microwave frequencies which sets challenges on bandwidth/saturation limitation, thermal dissipation and linearity. To fulfil such requirements one has to design an appropriate photodiode vertical structure by optimizing the active layer which should take into account the illumination scheme of the detection area. For such requirements, the candidate of choice is the UTC-type (Uni-Traveling-Carrier) vertical photodiode structure and more specifically, MUTC (for Modified UTC), which was recently introduced by III-V Lab to improve detector responsivity.

B.

High-power optical fiber amplifiers

High-power optical fibre amplifiers suitable for space flight environment will be designed and developed, exploiting the expertise available within the team. The R&D activity scheduled for the project aims at creating a new family of optoelectronic and fibre-optic components, supporting the requirements set by high-power amplifier modules. Within the HIPPO project, different generation of amplifier modules will be designed and developed using a variety of co-doped fibres employing micro-structured active fibres.

Fig. 3.

Preliminary modelling results using conventional silica Er/Yb co-doped fibre for the two amplifier models foreseen within the project.

The first phase of the workplan involves the investigation of the performance of the amplifiers using non micro-structured fibre and specifically Erbium/Ytterbium co-doped active fibres. The modeling and experimental results are to be used as a benchmark against the performance obtained from the new microstructured active fibres drawn within the project. The simulation results provide insight on the saturated output power achievable, the noise performance and the overall optical to optical conversion of the amplifier subassemblies.