11.3 Optical MEMS for displays and imaging systems

Optical MEMS revolutionize displays and imaging systems. These tiny devices manipulate light using micromirrors, scanners, and spatial light modulators. They enable advanced projection systems, adaptive optics, and compact optical switches for improved image quality and communication.

MOEMS integrate mechanical and optical components on a single chip. This technology powers micro-interferometers for precision measurements and enables the development of smart, adaptive optical systems for various applications in consumer electronics and telecommunications.

Micromirror and Projection Systems

Digital Micromirror Devices (DMDs) and Spatial Light Modulators

• Digital micromirror devices (DMDs) consist of an array of tiny mirrors that can be individually tilted to reflect light and create an image
  • Each mirror represents a pixel in the projected image
  • DMDs are used in digital light processing (DLP) projectors (movie theaters, home theaters)
• Spatial light modulators (SLMs) control the amplitude, phase, or polarization of light waves
  • Can be used to modulate light for various applications such as holography, optical computing, and adaptive optics
  • Liquid crystal on silicon (LCoS) is a common type of SLM used in projectors and displays

MEMS Scanners and Pico Projectors

• MEMS scanners use tiny mirrors to scan a laser beam and create an image
  • Can be used to create compact, portable projectors known as pico projectors
  • Pico projectors can be integrated into smartphones, tablets, and other mobile devices (Samsung Galaxy Beam, Sony MP-CL1A)
• MEMS scanners can also be used for 3D scanning and imaging applications
  • By scanning a laser beam over an object and measuring the reflected light, a 3D model of the object can be created
  • Used in applications such as industrial inspection, reverse engineering, and medical imaging

Adaptive Optics and Optical Switching

Adaptive Optics for Improved Imaging

• Adaptive optics correct distortions in optical systems caused by atmospheric turbulence or other factors
  • Uses a deformable mirror or spatial light modulator to compensate for distortions in real-time
  • Improves image quality in astronomical telescopes, microscopy, and ophthalmology (retinal imaging)
• Adaptive optics can also be used for free-space optical communication
  • Corrects for atmospheric distortions to improve signal quality and reduce bit error rates
  • Enables high-speed, long-distance wireless communication using laser beams

Optical Switches and Tunable Lasers

• Optical switches route optical signals between different fibers or waveguides
  • Can be used to create reconfigurable optical networks and improve network flexibility
  • MEMS-based optical switches use tiny mirrors to redirect light beams between different ports (2D and 3D MEMS switches)
• Tunable lasers can adjust their output wavelength over a range of values
  • Used in wavelength-division multiplexing (WDM) systems to increase bandwidth and network capacity
  • MEMS-based tunable lasers use a movable mirror or grating to select the output wavelength (external cavity lasers, distributed Bragg reflector lasers)

MOEMS and Interferometry

Micro-Interferometers for Precision Measurement

• Micro-interferometers use the interference of light waves to measure small displacements or changes in optical path length
  • Can detect sub-nanometer displacements and measure surface roughness, film thickness, and refractive index
  • Fabry-Perot interferometers use two parallel mirrors to create an optical cavity (used in fiber optic sensors, spectrometers)
• Michelson interferometers split a light beam into two paths and recombine them to create an interference pattern
  • Used in gravitational wave detectors (LIGO), surface profilers, and Fourier transform infrared (FTIR) spectrometers
  • MEMS-based Michelson interferometers can be integrated into compact, portable devices for on-site measurements

MOEMS: Integrating MEMS and Optical Components

• MOEMS (Micro-Opto-Electro-Mechanical Systems) integrate MEMS structures with optical components on a single chip
  • Enables the creation of compact, low-cost optical systems with improved performance and reliability
  • Examples include MEMS-based spectrometers, optical switches, tunable filters, and adaptive optics
• MOEMS can be fabricated using standard microfabrication techniques such as photolithography, etching, and thin film deposition
  • Allows for mass production and integration with electronic circuits
  • Enables the development of smart, adaptive optical systems for a wide range of applications (consumer electronics, automotive, medical devices)