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Frequently Asked Questions

Frequently Asked Questions If you see a rainbow pattern on a soap bubble or on a film of oil you...

Advantages of Multiple Band Pass Filters in Telecommunications Applications

In wavelength-division multiplexer (WDM) and passive optical network (PON) modular design, single band pass filters and multiple band pass filters are used for the same purpose: permitting narrow wavelength ranges to pass through while rejecting wavelengths outside that range (known as the filter’s upper and lower cutoff frequencies).

Multiple band pass filters are used to transmit two or more standard coarse wavelength division multiplexing (CWDM) channels, separating them from the other CWDM bands — replacing two or more single band pass filters with a single component.

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Effect of an optical coating on in-band and out-of-band transmitted and reflected wavefront error measurements

The wavefront error (WE) of a surface with an optical coating (“filter”) is ideally measured at the in-band wavelength of the filter. However, quite often this is not possible, requiring that the filter be measured at an out-of-band wavelength (typically 633 nm), assuming that the filter transmits (for transmitted WE, or TWE) or reflects (for reflected WE, or RWE) at this wavelength. This out-of-band TWE/RWE is generally assumed to provide a good estimation of the desired in-band TWE/RWE. It will be shown in this paper that this is not the case for a large class of filters (i.e., bandpass) where the group delay is significantly different at the in-band and out-of-band wavelengths and where the optical filter exhibits a thickness non-uniformity across the surface.

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Edge Filters for Raman Spectroscopy

Raman spectroscopy probes the molecular vibrational and rotational modes of a material in order to detect and identify the material. Typically, laser light is incident upon the material and the scattered light is measured.

The excitation source (laser line) intensity is often to orders of magnitude greater than the Raman scattered signal. Therefore, edge pass (or notch) filters are required to block the Rayleigh scattered laser light while transmitting the red-wavelength shifted (Stokes) and/or the blue-wavelength shifted (Anti-Stokes) Raman scattered signal.

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