Waveguide coupler produces stable light

Dec. 15, 2000
A WDM light source must both have a narrow spectral emission and be spectrally stable. Diffraction gratings, either in the light source itself or in the associated optical fiber, are what traditionally provide this control. Researchers at Stanford University (Palo Alto, CA), have devised a narrowband WDM light source that does not rely on gratings, and in the process have eliminated the necessity of butt-coupling the light source to a fiber.

A WDM light source must both have a narrow spectral emission and be spectrally stable. Diffraction gratings, either in the light source itself or in the associated optical fiber, are what traditionally provide this control. Researchers at Stanford University (Palo Alto, CA), have devised a narrowband WDM light source that does not rely on gratings, and in the process have eliminated the necessity of butt-coupling the light source to a fiber.

Simple in concept, the device is nothing more than a coupling of two waveguides--one an optical fiber, the other a semiconductor anti-resonant reflective optical waveguide (ARROW). The ARROW contains a light-emitting AlAs/AlGaAs slab core sandwiched between two distributed Bragg reflector mirrors, one of them only partially reflective but bounded by air, producing complete reflection.

The fiber is epoxied into a curved groove in a glass substrate and one side polished to within a few microns of its core. The two waveguides have very different dispersion characteristics, producing phase-matching at only specific wavelengths. When the fiber is contacted with the ARROW using index-matching fluid, its emission is coupled into the fiber at two discrete wavelengths corresponding to transverse electric (TE) and transverse magnetic (TM) resonances.

The 0.819-nm TE resonance has a narrower linewidth than the 0.837-nm TM resonance. When the researchers increased the injection current, they determined that although the TE spectrum shifted to longer wavelengths, the TM spectrum did not. Thus, for TM-polarized light, the device is truly wavelength stabilized. There was no linewidth narrowing with increasing input current.

The light output of the device at an injection current of 100 mA was 7 nW, for an efficiency of as low as 3 x 10-8. The ARROW has no lateral optical confinement, which means that many emitted photons take lateral paths that preclude coupling into the fiber. By producing a one-dimensional waveguide using lithographic techniques, all photons would be emitted collinear with the fiber, greatly boosting efficiency, say the researchers. Introducing optical feedback with the help of fiber Bragg gratings could result in a directly fiber-coupled wavelength-stabilized semiconductor laser. Useful as a WDM source, such a device could also be made into a fiber amplifier pump. Contact Erji Mao at [email protected].

About the Author

John Wallace | Senior Technical Editor (1998-2022)

John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.

Sponsored Recommendations

How to Tune Servo Systems: The Basics

April 10, 2024
Learn how to tune a servo system using frequency-based tools to meet system specifications by watching our webinar!

How Precision Motion Systems are Shaping the Future of Semiconductor Manufacturing

March 28, 2024
This article highlights the pivotal role precision motion systems play in supporting the latest semiconductor manufacturing trends.

Melles Griot® XPLAN™ CCG Lens Series

March 19, 2024
IDEX Health & Science sets a new standard with our Melles Griot® XPLAN™ CCG Lens Series fluorescence microscope imaging systems. Access superior-quality optics with off-the-shelf...

Spatial Biology

March 19, 2024
Spatial Biology refers to the field that integrates spatial information into biological research, allowing for the study of biological systems in their native spatial context....

Voice your opinion!

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