using michelson interferometer to measure the wavelength of light

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Optical bandpass filter technique Optical spectrum analysis using a grating-based filter (previous chapter) or Fabry-Perot (FP) filters Wavelength calibrator cells are used to improve the accuracy of these measurements 2.

Interferometric fringe-counting techiques Commonly used for high accuracy application 3.

Wavelength discriminator technique A sloping insertion loss versus wavelength function can be used to determine optical wavelength Common ways to display the results of a laser wavelength measurement Vacuum wavelength, vac Standard dry air wavelength, air Frequency speed of light vac f or Wavenumber or spatial frequency 1 vac.

Calculate the corresponding coherence time and the spectral width, f12.

Ans ps, 6 THz Question An unmodulated DFB laser has a coherence time of 32 ns.

Is it practical to build a variable length arm into a Michelson interferometer to directly measure the coherence length Ans.

Lc 9.59 m.

What is the maximum frequency that can be displayed without aliasing effects Ans THz For a 30 mm sweep range, what is the frequency spacing of the data points in the Fourier domain Ans.

GHz What is the resolution of the system Ans.

GHz.

Maximum path-length change in the variable arm of the interferometer Longer path-length difference better accuracy Ability to count fractional fringes valuable wavelength information is lost if the remainder from the round function (to the nearest integer number) of the interference fringes is thrown away 2.

Knowledge of the ratio of the index of refraction at the reference wavelength to the index of refraction at the unknown wavelength The index of refraction of air is a function of humidity, temperature, gas content etc 3.

The wavelength accuracy of the reference source will ultimately limit the accuracy of the measurement of the unknown.

What is the exact number of fringes Ans If the fringe fraction is not counted, what wavelength would the wavelength meter measure Ans What is the error in ppm (parts per million) Ans ppm.

The figure show a plot of how the index of refraction depends on wavelength for the standard dry-air conditions.

A further correction can be made to the index for water vapour content in the air Here h is the partial pressure of water vapour in Torr.

The figure in the next slide shows how the index of refraction varies as a function of the three most common variables: pressure, temperature and humidity It is seen that pressure variations have the largest effect on the index of refraction for reasonable values of the environmental variables.

Calculate the worst case wavelength offset in the unit of parts-per-million (ppm).

Ans ppm.

However, this stabilization results in an appreciable increase in the cost of the laser Other Wavelength References HeNe lasers with similar wavelength accuracies are available at nm, nm and nm These other wavelengths offer lower gain per unit length requiring a significantly longer laser tube.

A similar interference occurs on the reflected signals form the interferometer The filtering function is accomplished by interfering the initially transmitted signal with many delayed versions of the input signal.

The index of refraction between mirrors is n, the mirror spacing is L, and the angle of the input light with respect to the perpendicular is.

Pearson, Justin T.

Schultz, Daniel Sidor, Michael.

Filippas 1, E. Fokitis 1, S.

Maltezos 1, K. Patrinos 1, and M.

Davenport 2.

Filippas 1, E.

Fokitis 1, S. Maltezos 1, K.

Patrinos 1, and M.

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Using Michelson Interferometer To Measure The Wavelength Of Light