1. Introduction

Wavelength-tunable light sources, born from advances in science and technology, are innovative technologies utilized in spectroscopic analysis and the characterization of optical components.
Wavelength-tunable light sources offer flexibility in wavelength limitations, providing stability and versatility not found in conventional lasers that generate only specific wavelengths.
This article explains the differences between wavelength-tunable light sources and conventional lasers, along with examples of their applications.

2. What is a wavelength-tunable light source (laser)?

A wavelength-tunable light source is a light source that is not fixed to a specific wavelength and can freely change its wavelength, primarily using a wavelength-tunable laser.
Due to its ability to arbitrarily adjust the wavelength, it is also sometimes called a tunable laser.
Wavelength-tunable light sources are broadly categorized into two types. One type uses grading or filters as wavelength selection elements to vary the light source’s wavelength. The other type changes the wavelength of the light source itself.
Wavelength-tunable light sources have diverse applications in research and industry, with various manufacturers releasing products featuring different characteristics.

Product Introduction
　KLS-601A Series：Tunable Diode Laser(High Resolution Model)
　KLS-201A Series：Tunable Diode Laser(Standard Model)

3. Differences between conventional lasers and wavelength-tunable light sources

The decisive difference between conventional lasers and wavelength-tunable light sources is the tunability of the oscillation wavelength.
Conventional lasers have a fixed oscillation wavelength determined by a specific laser medium, based on the principles and physical properties of that medium.
In contrast, wavelength-tunable light sources offer the major feature of freely changing the wavelength of the emitted light. They can be adjusted to any wavelength using various methods such as free-electron lasers, dye lasers, and wavelength-tunable semiconductor lasers, making them applicable in a wide range of uses.
While conventional lasers are suited for applications requiring a specific wavelength, wavelength-tunable light sources are used in situations demanding flexibility in wavelength control.

4. Types of wavelength-tunable light sources

Wavelength-tunable light sources are primarily classified into three types: free-electron lasers, dye lasers, and wavelength-tunable semiconductor lasers.

4-1. Free-electron laser (FEL)

A free-electron laser is a type of laser that utilizes a mechanism where electrons move freely.
When accelerated electrons meander through a specific range of magnetic fields, synchrotron radiation is generated. This synchrotron radiation is amplified within a resonator, emitting an extremely powerful laser beam.
The wavelength tuning range of free-electron lasers is extremely broad, and they are primarily utilized in research fields such as medicine and science.

4-2. Dye laser

Dye lasers use organic dyes, which exist as solids or liquids, as their laser medium.
The principle of dye lasers involves supplying light energy to dye molecules to excite them, thereby inducing laser oscillation. This characteristic enables oscillation across a broad wavelength range and provides excellent wavelength tunability.
Because they can be realized at relatively low cost, they are widely used lasers in laboratories and industrial settings.

4-3. Tunable semiconductor laser

Wavelength-tunable semiconductor lasers are lasers that oscillate using semiconductor devices, allowing their wavelength to be freely controlled and changed externally.
Typically, the wavelength is altered using externally placed wavelength-selective elements such as gratings or filters. This enables continuous adjustment of the laser’s oscillation wavelength.
Wavelength-tunable semiconductor lasers offer the advantage of easy wavelength control and the capability for high-speed wavelength sweeping, making them conducive to miniaturization and low-cost production.
Due to these characteristics, they play a vital role in a wide range of optical applications, communication technologies, and medical fields.

5. Characteristics of wavelength-tunable light sources differing based on grading and filter presence

Wavelength-tunable light sources come in two types: those using grading or filters in the wavelength-selective element, and those that change the emission wavelength of the light source itself.
We will explain the characteristics of each in detail.

・Type using grading or filters as wavelength selection elements
In wavelength-tunable light sources using grading or filters as wavelength selection elements, the light source itself emits a specific wavelength. This mechanism narrows down the output wavelength using grading (slits or filters) to select a specific wavelength band.
This type of wavelength-tunable light source is highly valued in research applications requiring precise wavelength adjustment, as it allows for fine-grained selection and generation of specific wavelength ranges.
While offering a broad wavelength band, an extremely small emission point, ultra-high brightness, and high stability, the light output of the source itself remains constant.

・Type that changes the light source’s own emission wavelength
Wavelength-tunable light sources that do not use grading change the emission wavelength of the light source itself.
For example, the laser’s oscillation wavelength can be adjusted continuously or discretely via external control.
This type of wavelength-tunable light source is widely used for investigating specific regions of the spectrum or conducting experiments at specific wavelengths.

Product Introduction
AWVF：Automatic Wavelength Variable Tunable Filter
VTFM/FC：Visible Light Wavelength Tunable Filter with Exchangeable Filter
TFM/FC：Wavelength Tunable Filter with Exchangeable Filter (Cassette Type)
TMUX：3-port Transmission/Reflection Filter Module
ITF-201A：Wavelenth/FWHM Tunable Filter

6. Applications of wavelength-tunable light sources

Wavelength-tunable light sources are primarily utilized in research fields requiring control over light source wavelength and intensity for experiments and observations, as well as in industrial applications such as evaluating optical component characteristics and verifying the operation and performance of optical fiber sensors.

Research Applications of Wavelength-Tunable Light Sources
• Spectral analysis
• Research on biological rhythms
• Productivity studies
• Fluorescence observation

Industrial Applications of Wavelength-Tunable Light Sources
• Characterization of optical components
• Evaluation of sensing devices
• Transmission testing of optical fiber sensors
• Evaluation of high-density integrated circuits
• Film thickness measurement

7. Summary

The wavelength-tunable light source discussed here differs from conventional lasers with a fixed wavelength, as it allows flexible external adjustment of its wavelength.
Capable of generating a wide range of wavelengths, it is utilized in diverse applications such as spectroscopic analysis and optical component characterization across research and industrial fields.

Optical Shinshinkogyo provides low-noise wavelength-tunable semiconductor lasers with narrow linewidth, low RIN, and excellent monochromaticity.
By integrating wavelength-tunable semiconductor lasers with PC-based measurement systems, we achieve precise optical characteristic measurements unattainable with spectrum analyzers.
If you are seeking a wavelength-tunable light source with superior stability or cannot find one in your desired wavelength band, Koshinshinko Kogyo also accepts custom and OEM orders. We encourage you to take this opportunity to contact us.