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Swept Light Sources

Optical Sensing for Industry

Swept Light Sources
Overview

What Is a Swept Light Source?

Overview

A swept light source is a light source that emits laser light with a continuously shifting wavelength. It is suitable for shape measurement and displacement measurement utilizing OFDR (Optical Frequency Domain Reflectometry), an optical sensing method using the coherence of laser light.

Swept light sources are utilized as light sources for sensing in a wide range of fields, such as precision measurement, vibration measurement, surface inspection, industrial applications such as OCT, medical applications such as ophthalmology OCT and intravascular OCT, infrastructure/plant measurement applications such as displacement/fluctuation of large structures, and length measurement.

The swept light sources of Anritsu provides high-coherence wavelength swept light by performing continuous and mode hopping-free wavelength sweeping on a single longitudinal mode with narrow linewidth. These swept light sources can be used to measure with wider distance and higher precision.

Anritsu swept light sources improve the standard Littman arrangement with a unique optical arrangement so MEMS scanning mirrors can be used to achieve high-speed wavelength sweeping. In this optical system, the area from the effective cavity end facet to the reflection surface of the MEMS scanning mirror is comprised of an external cavity, and of the multiple vertical modes determined by the cavity length, only one mode obtained by the wavelength selectivity of the diffraction grating is selected for oscillation.


Overview of Anritsu swept light
Overview of Anritsu swept light

The graph below schematically depicts the wavelength selectivity of the diffraction grating caused by the rotation of MEMS scanning mirror, and how the selected oscillation mode changes.

Oscillation mode changes of Anritsu swept light sources
Oscillation mode changes of Anritsu swept light sources

Typical Specs

  • Sweeping center wavelength: 1,550 nm (or 1,060 nm)
  • Wavelength sweep frequency: Typ. 150 Hz or 1,250 Hz
  • Wavelength sweep range: less than 100 nm
  • Average optical output: 10 dBm or less
  • Coherence length: less than 100 m

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Benefits of Using OFDR (Swept Light Sources) >

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Applications

Precision Thickness Measurement

  • Optical component thickness measurement: Measuring the thickness of transparent objects such as glass and lenses
  • Thickness measurement and surface roughness measurement of film and steel plates
  • Thickness measurement of semiconductor wafers

Vibration Measurement

  • Rotating body vibration width measurement: Measuring the eccentricity and surface run-out of drills and disks, etc.
  • Vibrating body vibration width measurement and frequency measurement: Speakers, etc.

Surface Inspection

  • Inspecting workpieces for burrs and scratches
  • Fine bump measurement of solder surfaces

OCT (Optical Coherence Tomography)

OCT utilizes optical interference to perform tomography on the inside of objects and human bodies and can also be used with beam scanning to measure three-dimensional structures in detail. It utilizes near infrared light to perform non-destructive and non-contact imaging, which is used for inspecting thin film products for defects and inspection for ophthalmological treatment.


OCT for Industry

  • Thickness measurement of resin/plastic products and inspection for bonding areas
  • Thickness measurement of semiconductor wafers

OCT for Medicine

  • Eye axial length measuring instrument (biometer)
  • Intravascular OCT: Higher resolution tomography than IVUS (Intravascular Ultrasound)

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Lineup
Category Oscillation Mode Center Wavelength * [nm] Sweep Width [nm] Sweep Rate [Hz] typ. Output Power [dBm] Note
Swept Light Source Single-mode,
Mode-hop-free
1,550 110(30 to 110) 1,250 10 dBm or more Scheduled to be released in 2020
Swept Light Source Single-mode,
Mode-hop-free
1,550 70(15 to 70) 150 10 dBm or more Scheduled to be released in 2020
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