It is difficult to imagine contemporary science without sophisticated testing machines and other kinds of meticulously developed equipment. In this article we are going to touch upon the spectrometer or optical spectrum analyzer historical background, main characteristics, types and principles of work. Spectrometers are widely used in astronomy and some branches of chemistry, although their structure and functions can be interesting not only for scientists, but for wider audience.
The first optical devices performing spectrometer functions were simple prisms with markings indicating wavelengths of light. Pioneers in this sphere were Joseph von Fraunhofer, Gustav Robert Kirchhoff and Robert Bunsen. These scientists were first to make practical use of the spectrum analyzer which enabled them to discover new chemical elements (cesium and rubidium). With the development of photographic equipment, the more precise kind of spectrometer was invented. It used a camera instead of the viewing tube and was called a spectrograph. Modern optical analyzers are rather complicated devices, totally automated and controlled by a computer.
Optical Spectrum Analyzer in Work
OSA is used to divide the lightwave signal into constituents as well as to measure the optical power of the wavelengths. This means that it can provide an optical spectrum analysis of the signal with a set wavelength range. The analyzers’ output is usually displayed in the form of an X/Y plot (horizontal axis is for wavelength while the vertical one is for power). To make it clear, let’s illustrate this with a simple example. If scientists need to define unknown substance with the help of optical spectrum analyzer, they need to heat it to incandescence first. When heated, the material starts to emit light which is unique for each substance. The particular light frequencies emitted by the incandescent material resemble fingerprints – and if you have the sample in the database, you can unhesitatingly name the ‘perpetrator’. For instance, sodium has a very specific double yellow band which is always easily recognizable.
OSA may also incorporate additional optical devices called applications. These may include LED (light-emitting diode) light sources and testing lasers to enhance distribution of power, spectral purity and additional check of the transmission quality. Optical spectrum analyzer in combination with various applications is an invaluable testing device for laser modes analysis, high resolution measurements and telecommunication appliances.
Optical spectrum analyzers are divided into three categories: diffraction grating based and two interferometer based devices (Fabry-Perot and Michelson analyzers). The former are used to measure lasers’ and LEDs’ spectra, while the latter are applied for direct coherence length measurements and very precise wavelength estimation.
Thus, spectrometers or optical spectrum analyzers are very sophisticated devices used for spectral lines producing and wavelength intensities measuring. These can work with a very wide range of wavelengths, from gamma and X-rays to infrared.