Micro photonics is the successor of electronics .It has many advantageous features for application in space through the combination of micro, nano integrated optics and fiber optic technologies .Based on current technical feasibility, potential impact on space systems and significant benefits; it is proposed that micro photonic satellite navigation systems can be developed with the target of a space demonstration flight .The proposed methodology is generic to the needs of all space craft; can provide significant mass ,volume and power saving micro satellite systems.
The objective of micro-PICs is to integrate the various optical subcomponents in a common photonic chip. This minimizes the number of external fiber-optic interconnects; minimizing the overall system size and mass, while optimizing the system reliability. The small size of micro-Picks facilitates parallel device redundancy for greater fault tolerance in the space environment.
Micro photonics has many advantageous features for applications in space through the combination of micro, nana, integrated-optic and fiber-optic technologies. However, there are also many issues and challenges. The proposed approach is to select an advantageous application for space that has a feasible solution based on the current micro photonic technical status and to target the initial development towards a flight demonstration of this micro photonic solution. The purpose of this document is to provide a proposal for a technically-feasible concept, and a corresponding roadmap for its development and implementation, in order to facilitate the space technology demonstration of a micro photonic system and its significant benefits for space systems. Based on the current technical feasibility, potential impact on space systems and significant benefits; it is proposed that a micro photonic satellite navigation system be developed with the target of a space demonstration flight of the system on Proba-3. Here, it can also serve as a backup autonomous guidance system for the mission formation flying. The proposed technology demonstration is generic to the needs of all spacecraft; can provide a significant mass, volume and power saving relative to current spacecraft navigation systems; and addresses the needs of the evolving small and micro-satellite systems
. The basic components comprising the selected micro photonic space demonstrator can serve as the initial building blocks to target long-term space requirements and opportunities for applying the micro photonic technologies as solutions.
Significant achievements were demonstrated with respect to the basic components for an
optical integrated photonic circuit that can offer high functional densities. This includes a practical implementation of photonic band-gap theory using new concepts in high-order structures to provide wavelength selective filters, tunable PBG devices and MEMS optical switches employing PBG concepts. In parallel to this, IMEC has considered the integration of Incas with SOI to facilitate active devices.
This proposal considers a non-competitive teaming of resources and capabilities to facilitate
Accelerated development of micro photonic technologies that target the needs of the space sector.
Rather than a chaotic approach to the development, as currently exists, a systematic, more focused approach is suggested that builds on what is currently feasible and extends this through targeted long-term development.
It is important to recognize that there will be differences in the packaging and component requirements for microphotonic applications in space relative to terrestrial applications. For example, many terrestrial optical communications applications are fiber to fiber, i.e. fiber-input/ processor/ fiber-output. This still entails considerable alignment and coupling challenges with a significant optical power-loss factor. Many space applications can be addressed using a light-source/processor/photo-detector architecture that can avoid the fiber-coupling losses and provide a more efficient system.
One must also consider new design methodologies for micro photonic components rather than a simply a scaling in size of current bulk-optic systems, that build on the unique capabilities provided by the SOI integrated waveguide structures and the parallism afforded by the miniaturization and integration.
1.1 Micro photonic Systems
Guided-wave optics facilitate significantly higher information processing and transmission-bandwidths than electronic systems (> 100 GHz) with the added benefits of scalable WDM signal multiplexing, immunity from electro-magnetic interference (EMI) and electrical discharges (ESD), and lightweight fiber-optic signal-distribution harnesses. The benefits of fiber-optic photonic systems for space include:
Â¢ Reduced susceptibility of systems to EMI, electrical discharges and charged particles
Â¢ Substantial reduction in the weight of signal harnesses (< 1/20 of electrical).
Â¢ Substantially higher information transmission capacity (GHz).
Â¢ Substantially reduced weight and improved performance of microwave systems using optical microwaves.
Â¢ Opto-isolation of critical spacecraft subsystems.
Â¢ High-speed optical processing of RF and microwave signals
Â¢ Low high-frequency signal attenuation (< 0.1 dB/km)
Space systems entail a high mass-cost penalty during the launch of payloads into orbit that can be upwards of $100,000 US per pound. Therefore, the use of micro/nano technologies to miniaturize bus and payload subsystems, and to provide higher functional densities than traditional technologies can have a tremendous long-term payback benefit for the space sector. This can be translated into a higher frequency of missions, greater redundancy in mission-critical components to ensure the success of missions, and greater scientific or commercial benefit per mission.
Photonics has advanced from the historic bulk-optic systems that were organized on an optical bench using many separate optical components, to relatively compact fiber-optic and integrated-optic devices that can combine several optical functions on one fiber or waveguide substrate. Integrated optical technologies offer significant improvements in terms of manufacturing costs, size, weight, processing speed and power consumption over distributed bulk and micro-optic systems. Coupling to external optical I/O fibers is a major source of optical signal loss and mechanical reliability concerns for integrated optical devices. Minimization of external optical interconnects through multi-function optical device integration on a single optical wafer can substantially improve the net system optical throughput and reliability.
The objective of micro-PICs is to integrate the various optical subcomponents in a common photonic chip. This minimizes the number of external fiber-optic interconnects; minimizing the overall system size and mass, while optimizing the system reliability. The small size of micro-PICs facilitates parallel device redundancy for greater fault tolerance in the space environment. The main technical requirements are:
Â¢ Ability to process micro photonic materials to provide the desired optical functions
Â¢ Miniaturization of the basic integrated-optic devices (signal splitters, optical switches, modulators),
Â¢ Integration of microphotonics with fiber-optics, optical sources and photo-detectors,
Â¢ Compatibility of the fabrication process for different micro photonic functional blocks,
Â¢ Sustainability of microphotonics in the space environment,
Â¢ Hybrid integration of microphotonics with other technologies.
Â¢ Lithographic patterning and micromachining of fine PBG structures.
Micro photonics currently has a strong theoretical basis with various concepts being
developed for photonic crystal devices. In terms of experimental technical readiness, it is still at the development level of the basic building blocks. The main issues are the accuracy (resolution) of the lithographic patterning to define PBG and nana structures; fabrication processes; I/O coupling to optical fibers and/or photo-detectors and laser diodes; integration (hybrid and/or monolithic) of active InGaAs and SOI device structures.
1.1.1 Technical Challenges
There are a number of key challenges for the integration of photonic systems to realize micro-PIC. Firstly, different material systems, namely lithium niobate, silicon, silica and III-V compound semiconductors (Incas) are generally used in the photonics industry to generate, modulate, multiplex, amplify, and detect the optical signal. Each of these material systems entails somewhat different manufacturing tools and processes, as well as design rules. While there is also a wide range of functions to be performed in microelectronics, silicon has become the dominant substrate material. This common platform has allowed equipment manufacturers to create a standard set of fabrication tools and processes, simulation tools and device libraries.
A second challenge arises from the complexity of interconnecting to single mode fiber; the alignment tolerances differ vastly from wire bonding to semiconductor elements. Unlike the semiconductor industry where electronic packaging is a small fraction of the product cost, packaging represents a large portion of optical-component cost and its automation remains a challenge for the photonics industry.
A third technical challenge is the physical size of active devices employed for traditional integrated optics. This is illustrated by the following table for various NxM optical switches.
Table 1-1: Comparison of waveguide optical switches.
Switch Technology Substrate Switching
Speed Channel Capacity Size Functional
Electro-optic LiNbO3 < n sec 6 x 6 350 0.03
Amplification Switch III-V n sec 4 x 4 0.04 400
Thermo-optic Silica, SOI 2 m sec 16 x 16 110 2.4
Total Internal Reflection Silica, SOI 5 to 10
m sec 32 x 32 6 171
MPB 2x2 PBG/MEMS SOI m sec to s 12 x 12
(36 2x2 junctions) < 1 > 144
Electro-optic switches on LiNbO3 offer the best switching times but consume the most substrate real-estate on a per channel basis. This is due to the relatively large
interaction length required between two channel waveguides at a switching node (about 1 cm) to provide efficient switching. Optical switches based on controlling active optical amplification in III-V compound semiconductors, and total internal reflection using liquid bubbles in SOI can facilitate the highest functional density. The TIR switches are analogous to MEMS micro-mirror arrays but employ prealligned channel waveguides with an insertable index-matching micro-bubble at the crossing junctions. Amplification amplifiers in III-V compound semiconductor materials are based on switching active waveguide optical amplifiers on/off.
A further limiting factor in passive signal distribution within traditional waveguide devices is the bend radius of the channel waveguides. The minimum bend radius depends on the relative difference in the refractive index of the waveguide core and cladding. For materials such as LiNbO3, this difference is small (0.05) and the optical signal is very weakly confined to the core. As a result, a large bend radius must be employed to distribute the optical signal on the substrate, requiring considerable substrate area. Increasing the refractive index of the waveguide core, such as provided by Si in SOI structures facilitates strong optical confinement and relative sharp bends, up to 90o. This facilitates much more compact integrated-optic structures.
Traditional integrated optic components, such as 1x2 passive signal splitters, are relatively large, limiting the achievable functional density on a micro-optic chip. Several leading-edge micro and nana-optic technologies, can be considered to realize micro-optic integrated chips with high functional densities. The basic miniaturization technologies, based on the consensus developed include:
1. High-index integrated guided-wave optics on SOI,
2. MEMS miniature electro-mechanical systems
3. 1-D and 2-D photonic bandgap technologies (use lowest dimension that solves the problem)
4. Hybrid integrated Incas electro-optic materials and devices on SOI
5. Optically-active smart materials
The main constraint on miniaturization is the optical throughput and optical coupling
to the technology, and the resulting optical power and optical amplification requirements. In this respect, one must consider the size and power budget of the complete system, including the optical signal sources and amplifiers. Certain technologies, such as two dimensional photonic band-gap structures, while very compact, are currently associated with optical losses of the order of 10 dB/mm and tremendous optical coupling challenges. Therefore, considerable development is required in terms of both the fabrication methodology and design methodology before their use is practical.
Fig. 1-2: Technology Suite for micro-PICS
1.1.2 MPB Technology Demonstrator and BIP
The MPB demonstrator micro-PIC showed the feasibility of simultaneously fabricating several different active and passive microphotonic components and technologies (integrated-optic devices, MEMS devices, photonic bandgap structures) on a single substrate, including several novel and innovative devices. The MPB prototype demonstrator micro-PIC includes various innovative miniaturization technologies:
Â¢ Total-Internal Reflection (TIR) waveguide structures
Â¢ Optical test bench for tunable 50 to 100 nm-thick smart materials (VOn) for high-speed signal switching and modulation
Â¢ Miniature 50:50 T-bar optical beam splitters (< 100 m x 100 m)
Â¢ WDM Photonic band-gap concepts (1-D)
Â¢ miniature Machzender interferometer based on the T-bar splitter
Â¢ integration of MEMS, guidewave and PBG concepts to provide unique, tunable PBG devices
Â¢ unique 2x2 PBG/MEMS optical switches (1 x 1 mm) for either broad-band or selective optical signal switching
These devices provide the basic blocks that can be subsequently interconnected to provide various micro-Photonic Integrated Circuits (PIC), such as MEMS/waveguide integrated-optic cross-connects; optical buses and local-area networks; optical add/drop nodes; programmable, variable optical time delay lines for optical beam forming or pulse shaping of RF signals; and interferometric optical sensing systems for "lab on a chip" scientific payloads. Variable phase delays can be obtained by using switches to reconfigure the relative optical path lengths.
Fig. 1-3: Schematic of the innovative MEMS/PBG multifunction Technology Demonstrator integrating various passive and active devices on a single SOI platform. (a) to (d): Photographs of the MPB micro-PIC technology demonstrator testing and selected components.
(a) Photograph of micro-PIC under optical testing. (b) SEM micrograph of fabricated PBG/MEMS 2x2 optical switch.
Ã‚Â© SEM micrograph of miniature T-bar signal splitter. (d) SEM micrograph of wavelength-selective high-order linear PBG structure with defect.
1.2 Development of Micro photonics for Space
The main driving force for the use of microphotonics terrestrially is high-volume batch fabrication to minimize unit cost. An example is the hybrid micro-optic laser CD and DVD scanner/reader that employs binary optics, laser diode and photo-detector technologies in a miniature hybrid structure.
Some examples of the potential space application of microphotonics include:
Â¢ Optical processor for multichannel optical sensor systems and smart structures.
Â¢ Optical high capacity downlinks (reconfigurable repeaters and scalable WDM communications nodes).
Â¢ Optical WDM intersatellite links and WDM optical transceivers, reconfigurable transmitters and add/drop nodes for intersatellite communications and optical downlink communications.
Â¢ Optical space-wire intra-satellite communications networks using lightweight fiber-optic harnesses for interconnection of subsystems on a spacecraft (active optical cross-connects).
Â¢ Multi-channel configurable optical RF signal distribution and processing (microwave photonics, programmable true-time delay, filtering).
Â¢ Advanced optical satellite navigation systems (optical accelerometers, optical gyroscope, sun sensor, earth sensor).
Â¢ Miniature scientific payloads on a chip for planetary and deep-space exploration..
Â¢ Optical processors for distributed sensors/actuators for smart microsystems, composite and membrane structures.
Â¢ Optical distribution and processing of RF signals for advanced phase-array antennas.
Â¢ Optical processor for rocket propulsion monitoring system.
Â¢ Advanced nana-satellites, miniature scientific payloads and planetary explorers.
Â¢ Miniature high-performance spectrometers and advanced data processing for Earth observation and planetary exploration (atmospheric studies, hyperspectral earth and planetary observation).
Â¢ High speed optical A/D converters for RF and microwave signals.
The development and design of microphotonics for space must consider the systems needs of the space sector, the space operating environment and the technical feasibility. Based on the systems needs for space, a basic library of components needs to be optimized in terms of their design, size and fabrication process. The two possible platforms are silicon-on-insulator (SOI) and InGaAsP. The main difference is the higher cost and less mature fabrication technologies for the III-V compound semiconductors. Therefore, for most cases, SOI would be the preferred substrate for the integration of the microphotonic technologies for various space applications.
The most efficient methodology of introducing the microphotonic technologies into spacecraft systems, as shown schematically in fig. 1-4, is to select an opportune and technically feasible application, such as the proposed satellite navigation system, to identify the basic required components and to proceed with optimization of the required engineering model and to subsequently provide fight heritage on a technology demonstrator mission. Based on the space experience, the device design could be iterated. As the component library and space heritage is built up, subsequent designs for other applications will be less costly and have a higher probability of success in the space environment.
Fig. 1-4: Schematic of Proposed micro-PIC Development Methodology for Space
In terms of technical feasibility, one can first consider hybrid systems for space that combine micro-optic, integrated-optic and electro-optic elements to provide performance/mass/power benefits relative to current systems and demonstrate the basic principles and benefits. Based on long-term technology development, one can then progressively increase the degree of integration. For example, the current Pentium electronic processors are the results of for decades of technology development.
CURRENT SATELLITE NAVIGATION SYSTEMS
The spacecraft navigation subsystem system is a generic critical component of all spacecraft. The exact details may vary based on the pointing requirements of a satellite for its payload and/or guidance requirements of a launcher or lander. Navigation is the art of knowing where you are, how fast you are moving and in which direction; and of positioning yourself in relation to your environment to meet the payload requirements.
The basic parameters include:
1. Spacecraft Altitude
2. Geographical Position
3. Orbit trajectory and current velocity.
4. Orientation and pointing wrt Sun and Earth
5. Acceleration and rotation status.
6. Relative position for formation flying.
Fig. 2.1: Schematic of basic spacecraft guidance and navigation subsystems.
Inertial navigation is accomplished by integrating the output of a set of sensors to compute
position, velocity, and attitude. The sensors used are gyroscopes and accelerometers. Gyros measure angular rotational rates with respect to inertial space, while accelerometers measure linear acceleration with respect to an inertial frame. Typically, an inertial reference unit (IRU) will contain three gryroscopes and three accelerometers. For space system applications, additional redundancy is required.
An example of a current navigation system for spacecraft is the SIRU. This is an internally redundant inertial unit using a hemispherical Resonator gyroscope, two single-axis accelerometers and the corresponding electronics and power supplies.
SIRI-CORE Inertial Reference Mass/Power Budget and Environmental Characteristics:
Size 12.8 x 8.6 x 4.5 inches
Mass 5.5 kg
Power Consumption 22 W
Input Voltage 28 V
Radiation Hardness 100 krad
Vibration (survival) 20 gâ„¢s rms
Survival temperature range -34 to +71 C
Relative to the available mass and power budgets of smaller spacecraft platforms, the for the resource requirements for the current inertial navigation systems are relatively high
INTEGRATED MICROPHOTONIC SENSOR SYSTEM FOR SPACECRAFT NAVIGATION
The following example shows the potential of the proposed micro-PIC technology development. The main required components are largely based on those employed for the MPB technology demonstrator. As shown in fig. 3-1, The spacecraft navigation micro-PIC is a multifunction optical integrated circuit that integrates a number of critical functions on a single SOI chip. These could include:
1. linear FBG/PBG guided-wave temperature sensors
2. chemical/leakage sensors
3. waveguide optical radiation sensor
4. multiple dual-axis waveguide/MEMS optical accelerometers
5. Si Sun sensor or VOn bolometric IR Earth sensor quadrant arrays
6. waveguide optical gyroscope (optional development)
The end result is an orders of magnitude saving in the system mass and volume. This facilitates greater device redundancy to reduce the possibility of a systems failure. Moreover, redundancy can also be used to improve the net performance and accuracy of the navigation measurement systems.
Fig. 3-1: Preliminary concept of two-axis spacecraft navigation micro-PIC.
The PBG/MEMS structure devised by MPB for the 2x2 switch function can be modified to provide an optically interrogated accelerometer. By using several of these PBG/MEMS optical accelerometer devices in series, the effects of acceleration on the resulting opical measurands, such as a change in the relative transmittance intensity or wavelength, can be intensified to increase the device accuracy, as shown by the following preliminary simulations, given in fig. 13-2, for 1,3 and 6 PBG/MEMS devices in series.
Fig. 3.2: Transmitted intensity ratio versus acceleration for PBG/MEMSD optical accelerometer.
Table 3-1 compares the PBG/MEMS accelerometer to a bulk accelerometer based on strain sensors and to an electrical MEMS accelerometer. The PBG/MEMS optical accelerometer can be made much smaller and robust that the traditional MEMS electrical accelerometer. Traditional MEMS accelerometers rely on many interdigitated fingers to convert acceleration to a change in the capacitance of the device. This requires considerable substrate area, complex electronics and results in a complex electrode structure. In contrast, the optically read PBG/MEMS accelerometer employs a much simpler and more reliable MEMS actuator structure. By using N of the PBG/MEMS accelerometers in parallel, the measurement accuracy can be improved by a factor of 1/SQRT(N). Thus, in principle, it should be possible to also improve the measurement accuracy.
A further benefit, is that the micro-PIC could contain accelerometers tuned for different acceleration ranges through the design of the MEMS springs, such as micro-g, nominal g, and high. Therefore, the overall accuracy could be much better than current systems, despite the small size of the optical integrated circuit.
A similar parallel methodology could be used to improve the attainable accuracy of waveguide gyroscopes. A ring structure could be formulated based on the t-bat structure and the waveguide tapered collimators.
Table 3-1: Comparison of accelerometers.
Sensor Type Size Mass Power Range Resolution
(Analog Devices) 10 x 15 mm 1 g 10 mW +/- 40 g 0.4% F.S.
(Summit) 25 x 25 x 25 mm 35 g 60 mW +/- 40 g 0.25% F.S,
PBG/MEMS 1 x 2 mm
(per device) 100 g 100 W 0 to 1200 g 0.4% F.S.
Devices 0.4/SQRT(N) % F.S.
The satellite navigation micro-PIC is comprised of a number of basic components or functional blocks that are interlinked using the SOI channel waveguides. The basic components consist of:
1. Input fiber/waveguide coupler
2. SOI ridge channel waveguide
3. T-bar split
4. T-bar Machzender interferometric radiation sensor
5. PBG temperature sensor
6. PBG/MEMS optical accelerometer
7. Waveguide optical gyroscope.
8. Si PIN detector array for sun sensor
9. VOn bolometer array for Earth sensor
10. Output coupling or hybrid integration with InGaAs or Ge detectors
Since the output coupling is directly to photo detectors, fiber/waveguide output coupling is not an issue and the net signal throughput and SNR can be very high.
The optional additional development is for new concepts for waveguide optical gyroscopes. The two current optical approaches are
Â¢ Fiber-optic gyroscopes or FOGs
Â¢ Ring laser gyroscopes
FOGs require many loops of optical fiber to convert the rotation rate to a phase shift using the Sagnac effect. Ring laser gyroscopes convert the Doppler wavelength shift of two counter-propagating laser signals to the rotation rate using a four-mirror cavity. By considering the unique capabilities of high-index microphotonic systems and WDM systems, perhaps an elegant microphotonic gyroscope concept can be developed that is feasible and can provide the required resolution for the determination of rotation rates. MPB has been done some work in this respect through a previous contract with CSA.
3.1 Estimated Spacecraft Resource Requirements
Based on the FSD analysis, the microphotonic multi-axis inertial guidance system with supplementary GPS positioning and electronics could be achieved within the following envelope:
Total System Mass: < 1.2 kg
Total System Power: < 2.5 W
This represents a substantial mass and power reduction relative to current systems such as the SIRU-CORE.
3.2 PBG Sensors
The high-order PBG structure developed by MPB during the ESA project could be applied to facilitate various types of sensors that would be useful for both spacecraft status measurements and space exploration. The following schematic shows a sensor consisting of a linear PBG structure that is chemically treated to react with a specific biochemical. The presence of the target chemical results in a reaction that shifts the spectral characteristics of the sensor. Since the area of each sensor is very small, many sensors could be used in arrays to facilitate detection of a broad range of biomarkers, for example, as a miniature laboratory on a chip. The potential applications are vast and almost limitless.
Fig. 3.3: MPB concept for PBG biochemical sensor
MICRO- PIC TECHNOLOGY DEMONSTRATOR SYSTEM
The preliminary definition of the microPIC spacecraft navigation system is shown in fig. 4.1. The concept is a complete, compact navigation system, including the laser optical source, micro-PIC inertial and pointing sensors, the microprocessor and signal interfacing and acquisition subsystems. A hybrid system is envisioned that combines inertial guidance as provided by the integrated-optic accelerometers and gyroscopes with GPS positioning data from the NAVSTAR or future Galileo satellite systems. The two micro-PICS provide inertial navigation data in the two orthogonal planes (X-Y and Y-Z). This provides data about the instantaneous state and trajectory of the spacecraft. This can be supplemented using miniature GPS receiver chips to provide geographically linked positional data based on the NAVSTAR and/or future Galileo navigation systems. Using differential GPS, position accuracies to about +/- 2 m are feasible, with typical accuracies of about 10 m.
Fig. 4-1: Preliminary schematic of microPIC spacecraft navigation system for Proba-3.
The main subsystems include:
1. 16 bit microprocessor for system control with data acquisition and processing electronics .
2. X-Y and Y-Z inertial sensing micro-PICS with redundant sensors.
3. Tunable fiber-laser using 980 nm redundant pumps.
4. Triple redundant GPS receivers for spacecraft position determination and validation.
The tunable laser provides the signal source and the interrogation system for the micro-PIC sensors. Typically, the micro-PIC sensors convert the desired physical parameter, such as an axial acceleration, to a shift in the spectral wavelength. This significantly reduces the effects of variations in signal levels on measurement accuracy.
The system microprocessor and tunable fiber laser may be based on those proposed for the FSD technology demonstrator. These will gain flight heritage through the Proba-2 mission.
The additional components that could be considered for integration on the navigation micro-PICS include:
1. InGaAs detector array through hybrid integration
2. Schottky or PIN array for Sun sensing and tracking.
3. VOn/MEMS bolometer Earth sensor array.
4. Waveguide optical gyroscope.
The tunable fiber laser provides the interrogation of the micro photonic sensors on the two micro-Picks. Measurands such as the axial acceleration and chip temperature are converted to wavelength shifts and are thus independent of the signal intensity. The laser interrogation system offers some new potential for optical waveguide gyroscopes by facilitating the Sagnac phase shift measurements versus the optical wavelength.
Some of the basic micro photonic components required for the technology demonstrator have been addressed. These are still at a prototype stage and will require some design iteration to optimize their performance
Basic Component Applications
High index contrast Si ridge channel waveguide Interconnection of components.
Time delay lines.
T-bar 1x 2 splitter 1xN signal splitters for signal distribution.
90:10 signal sampling.
Signal reference lines.
Gyroscope optical cavities.
Linear high-order PBG WDM filters operating in transmission.
Tunable gratings for external cavity DFB laser diodes.
PBG/Waveguide/MEMS integration Optical accelerometers.
Configurable PBG structures.
Optical switches for programmable add/drop, reconfiburable repeaters and programmable time-delay lines.
Wavelength-selective optical switches.
Polarization selective optical splitters and switches.
T-bar Machzender interferrometer Optical modulator.
Variable optical attenuator.
Chemical and biochemical sensors.
VOn structures High-speed optical switch for time division multiplexing and optical A/D.
High-frequency optical modulators.
Variable optical attenuators.
Programmable cavity mirrors.
PRELIMINARY MICRO-PIC TECHNOLOGY DEMONSTRATOR DEVELOPMENT PLAN
The proposed conceptual design and subsequent technology development for a flight technology demonstration could be conducted through an initial GS study for the technology review and design concept and through a subsequent GSTP program in two Phases for the engineering and flight models. The development is targeted towards a specific space application that focuses the component and fabrication requirements.
Through the proposed teaming, there are considerable I.P resources to minimize the project risk and maximize the end benefits.
The new concepts and development work (optimization) inherent in the proposed project consists of:
1. Multi-axis PBG/MEMS optical accelerometers.
2. Integration of InGaAs detector arrays with SOI waveguides.
3. Er doped silica waveguides for waveguide lasers and optical amplifiers.
4. Novel concepts for a waveguide optical gyroscope (FOGS, ring laser, new approach).
This may entail developing new design concepts that employ the unique advantages of miniaturization, parallism and redundancy that is afforded by microphotonics. That is, the approach to microphotonics design should not be simply a scaling of a larger bulk-optic or fiber-optic system. One has to consider the new design opportunities that the micro photonic approach presents. As an example, a single waveguide gyroscope may not offer the performance of a large bulk optic system. However, using WDM and parallel architectures, it may be possible to devise a system of parallel miniature waveguide gyroscopes that together can match the performance of much larger systems.
Action Suggested Program Estimated Duration
Review requirements for selected space application. GS â€œ 12 Month Program 2 months
Trade-offs, r eview and define subcomponents required for microPIC demonstrator and perform preliminary conceptual system design and specifications (optical accelerometers and gyroscopes). 3 months
Detailed system design simulation. Review design of critical subsystem components with technology demonstrator fabrication and testing. 7 months
Engineering model detailed design and simulations. GSTP â€œ Phase 1: 18 Month Program 6 months
Engineering model fabrication and iteration. 8 months
Engineering model testing.. 4 months
Flight model design iteration and fabrication for Proba-3 GSTP â€œ Phase 2: 18 Month Program 12 months
Flight model pre-flight qualification. 4 months
Demonstrator Flight 2011-2012
The overall project study plan and experimental methodology is shown in the following flow chart. This methodology minimizes risk and costs and results in a
technology development that is focused and that meets the requirements for successful space application of microphotonics through a road-map that is technically feasible and does not required expensive basic technology development.
BENEFITS OF PROPOSED DEVELOPMENT
The proposed micro-PIC system will provide the next-generation spacecraft navigation and guidance that can meet the power and mass budgets of todayâ„¢s smaller platforms such as micro-satellites and enable greater functionality than current navigation systems for the future usage of spacecraft in coherent formations.
The overall benefits of the proposed work include:
1. Targeted development of microphotonics for space,
2. Development of generic microphotonuic components for spacecraft navigation and guidance,
3. Development of packaging methodologies for microphotonics for operation in space.
4. Development of novel hybrid integration concepts for InGaAs detectors with SOI integrated-optics,
5. Optimization of the PBG/MEMS concepts,
6. Demonstration of multi-function micro-PIC:
Â¢ Dual-axis PBG/MEMS optically interrogated accelerometers
Â¢ PBG temperature sensor
Â¢ Machzender radiation sensor
7. Development of novel concepts and architectures for waveguide optical gyroscopes.
8. Complete functional system with electronics and interfacing.
9. Technically feasible for space demonstration within relatively short timeframe of 4 to 5
10. Link to the requirements for Proba-3 for formation flying, and for future microsat and small-sat systems.
The micro-PIC navigation system could ultimately provide sufficient spacecraft guidance to facilitate relatively autonomous operation in future spacecraft systems. The proposed spacecraft microphotonic navigation system provides:
1. Order of magnitude reduction in mass and power requirements relative to current spacecraft navigation systems systems (i.e. SIRU core), providing a significant benefit for future space missions and satellite systems.
2. High sensor redundancy.
3. Single tunable-laser interrogation system.
4. Minimal moving parts with simplified mechanical subsystems for higher reliability than current navigation systems
5. Hybrid use of inertial and active (GPS) navigation that can facilitate greater autonomous operation of spacecraft.
Micro-integrated optic circuits increase the integration of optical components on a single Si substrate, to provide multi-function optical processing and switching similar to electronic integrated circuits. This minimizes the number of external optical interconnections required and sensitivity to external vibrations; maximizing the system information capacity, optical throughput, and reliability,
while minimizing the overall system size and weight. Batch fabrication can facilitates a substantial cost-reduction relative to current technologies on a per unit basis, even for moderate quantities. System integration entails a critical review of the architecture of optical subsystems to minimize size within the constraints of adequate optical transmission. Technology development is currently converging on the SOI platform. This benefits from compatibility with high-speed CMOS integrated electronics as well as a broad foundation of established design and fabrication tools. The recent demonstration of super-lattice strained interfaces that enable the deposition of single-crystal LiNbO3 and GaAs on SOI has further enhanced the appeal of SOI.
The proposed SOI MEMS/waveguide integrated-optic technology for micro-PICS has many significant advantages for space and terrestrial applications:
- One common SOI platform (7 Ã‚Âµm Si/2 Ã‚Âµm SiO2/ Si)
- Integration of several different active and passive components on a single substrate
- Employs several different miniaturization technologies on a single substrate: TIR waveguides,
- 1-D PBG concepts, thin-film electrochromic active optics, MEMS
- Novel 1-D PBG wavelength selector for WDM systems
- Novel T-junction beamsplitter - 160 x 200 mm
- Novel VOn/SOI optical switch
- Novel polarization-independent SOI/MEMS optical switch
- Integration of MEMS actuators and optical waveguides on a single substrate
- Large potential library of subcomponents for provide high functionality
- Feasibility, with development, of integrating InGaAs active components
- Feasibility, with development of Er-doped silica waveguides for active optical waveguide amplifiers and waveguide lasers.
A roadmap is proposed for the development and space demonstration of a functional microphotonic system. This targets a space application where microphotonics can provide significant benefits, and employs a systematic, technically feasible methodology that combines fully integrated micro-PIC components with hybrid integration to provide the necessary functionalities. The proposed micro-PIC inertial sensor development is generic to the needs of all spacecraft and can facilitate an order of magnitude reduction in the mass (< 1 kg) and power (< 2 W) requirements relative to current spacecraft navigation systems; while meeting the future navigation needs for small-sat and micro-sat formation and constellation systems.
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