OPTOELECTRONIC DEVICES: Waveguide holograms replace external laser optics

Dec. 1, 1996
Computer-generated waveguide holograms developed by Anders Larsson and coworkers at Chalmers University of Technology perform output coupling and beam shaping simultaneously in surface-emitting lasers. The holograms eliminate the need for external beam-shaping optics.

Computer-generated waveguide holograms developed by Anders Larsson and coworkers at Chalmers University of Technology (Göteborg, Sweden) perform output coupling and beam shaping simultaneously in surface-emitting lasers. The holograms eliminate the need for external beam-shaping optics.

In a standard grating-coupled surface-emitting laser, the eponymous grating converts the guided mode into a near-surface free-space mode, usually through first-order diffraction. With the holographic system, however, the grating area is divided into a number of grating cells or pixels. Spatial phase modulation is accomplished by shifting the position of the grating grooves within one pixel relative to those of neighboring pixels, referred to as grating dislocation. Spatial amplitude also can be controlled by varying the grating duty cycle.

The waveguide holograms are fabricated on an epitaxially grown indium gallium arsenide/aluminum gallium arsenide (InGaAs/AlGaAs) waveguide using electron-beam lithography and reactive ion-beam etching. These techniques allow a minimum step size for grating dislocation of 2.5 nm, which for a grating period of 300 nm results in a phase resolution of 0.05 radgiving a virtually continuous phase variation. Duty cycle can be varied from 15% to 80%, allowing a large range of amplitude variation.

Initial demonstrations show that effective beam shaping is achieved with the waveguide hologram. Examples include the conversion of a Gaussian waveguide mode into an asymmetric distribution of 20 equal intensity spots, produced as a focused image 10 cm above the surface. The hologram thus acts as an output coupler, beamsplitter, and focusing lens. The phase pattern required to do this is calculated using an iterative Fourier-transform algorithm, and this is converted into grating dislocation. In this example, the diffraction efficiency is 65% and the uniformity error is 8%.

The researchers have also demonstrated image-multiplexing capabilities, for which a patent application has been submitted. Here, images are produced in different directions and focused at different distances above the waveguide surface. Another development is the fabrication of computer-generated waveguide holograms capable of angular multiplexing. This process generates two images that are reconstructed by two guided laser beams.

About the Author

Bridget Marx | Contributing Editor, UK

Bridget Marx was Contributing Editor, UK for Laser Focus World.

About the Author

Rick DeMeis | Associate Editor, Technology

Rick DeMeis was Associate Editor, Technology for Laser Focus World from March 1995 through March 1997.

Sponsored Recommendations

Brain Computer Interface (BCI) electrode manufacturing

Jan. 31, 2025
Learn how an industry-leading Brain Computer Interface Electrode (BCI) manufacturer used precision laser micromachining to produce high-density neural microelectrode arrays.

Electro-Optic Sensor and System Performance Verification with Motion Systems

Jan. 31, 2025
To learn how to use motion control equipment for electro-optic sensor testing, click here to read our whitepaper!

How nanopositioning helped achieve fusion ignition

Jan. 31, 2025
In December 2022, the Lawrence Livermore National Laboratory's National Ignition Facility (NIF) achieved fusion ignition. Learn how Aerotech nanopositioning contributed to this...

Nanometer Scale Industrial Automation for Optical Device Manufacturing

Jan. 31, 2025
In optical device manufacturing, choosing automation technologies at the R&D level that are also suitable for production environments is critical to bringing new devices to market...

Voice your opinion!

To join the conversation, and become an exclusive member of Laser Focus World, create an account today!