Providing connection with micro machines and smart dust are challenging. Integrated circuits with wireless connection are preferred. Optical wireless communications is an attractive option. For low data rate communications modulated retro-reflectors are used. Low speed communication for smart dust without tracking.
According to figure Base Station is situated above a number of Smart Dust Motes (SDM). Light from the Base Station falls on a particular mote using holographic beam steering system. The light illuminates the Smart Dust Mote, and modulated to provide a downlink from the Base Station to the Smart Dust Mote. A Modulated Retro Reflector on the Smart Dust Mote reflects light back to the Base Station. Modulated radiation is detected using an imaging receiver that consists of a high frame rate CMOS camera and associated image processing.
Base Station Design
Base Station illuminate the SDM to provide power, intensity for the SDM downlink and power for uplink to operate. Holographic beam steering used for maximizing intensity. There is possibility to alter the divergence of beams, and correct for aberrations.
Optical design and link budget modelling
Light from a 670nm laser is polarized and illuminates the SLM. The SLM is arranged for binary phase modulation. Resulting wave front is Fourier transformed using a Fourier Lens. Two lenses are used to magnify the steering angle, to create a total view of 30 degrees. The simple optical system use enlarged, spots.
Intensity and link budgets
Three constraints which helps in the correct working of Smart Dust Mote are
- Illumination intensity from the beam to power the Smart Dust Mote
- Sufficient link margin for the downlink
- Sufficient link margin for the uplink.
Light passes through the aperture of the modulator is retro reflected and passes back through it once more. Power that passes back through the aperture to be re-emitted and propagate back to the base station.
SMART DUST MOTES
The SDM consists of
- Power photo diode
- Communications receiver
- Modulated retro reflector
- LC cells: to form the modulator
- LC drive directory