Single Monochromator vs double Monochromator-Difference Single Monochromator and double Monochromator

This page compares Single Monochromator vs double Monochromator and mentions difference between Single Monochromator based OSA and double Monochromator based OSA(Optical Spectrum Analyzer).

As we know Optical Spectrum Analyzer is used to plot the optical signal. In order to plot the optical signal, incoming light signal is first passed through the wavelength tunable optical filter (either monochromator or interferometer type) This filter resolves individual spectral components of the light signal.
Refer Optical Spectrum Analyzer basics➤.

There are different types of Optical Spectrum Analyzer(OSA) as mentioned below:
• Interferometer based OSA (e.g. Fabry Perot and Michelson types)
• Diffraction grating based OSA

The most common OSA uses monochromator as tunable optical filter. In monochromator, diffraction grating separates different wavelengths of light signal with less attenuation. This results into better resolution of wavelength.

Diffraction grating based OSA consists of any one of the following monochromator types:
• Single Monochromator
• Double Monochromator
• Double Pass Monochromator

Single Monochromator based Optical Spectrum Analyzer

single monochromator OSA

Figure-1 depicts single monochromator used in OSA. It takes light signal as input and ptovides electrical output.

Here 2nd concave mirror is used to focuse desired wavelength at aperture. The aperture width is variable and will determine wavelength resolution of the OSA instrument.

Double Monochromator based Optical Spectrum Analyzer

double monochromator OSA

Figure-2 depicts double monochromator used in OSA. It also does the same function as single monochromator. It is equivalent to a pair of sweeping type of filters.

It is developed to increase the dynamic range achieved using single monochromator. The limitation of double monochromator is its degraded sensitivity due to losses.

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