What is Center Wavelength? (CWL)

In the context of optical bandpass filters, CWL stands for Center Wavelength. It indicates the wavelength at the center of the filter's passband, representing the wavelength that experiences the highest transmission through the filter.

Here's a breakdown of CWL and how it relates to bandpass filters:

• Bandpass filter: Allows light within a specific range of wavelengths (passband) to pass through, while blocking other wavelengths (stopband).

• CWL: Measured in nanometers (nm), it identifies the central point of this passband, where the filter transmits light with the highest intensity.

• Relationship with FWHM: FWHM (Full Width at Half Maximum) tells you the width of the passband around the CWL.

• Importance of CWL: Choosing the right CWL depends on your application's needs. You may need to filter specific wavelengths based on the properties of the light you want to analyze or detect.

Some additional points to remember about CWL:

• CWL and FWHM together define the shape and performance of the passband.

• Filters with different CWLs can have the same FWHM, meaning they have the same bandwidth but transmit light around different central wavelengths.

• Some filter manufacturers might specify the peak wavelength instead of CWL. These are essentially the same for most practical purposes.

Choosing the appropriate CWL depends on your specific application:

• Targeting a specific wavelength: Select a CWL matching the target wavelength for precise filtering.

• Analyzing a range of wavelengths: Choose a CWL that falls within the desired range to capture relevant information.

• Combining filters: CWLs of different filters need to be carefully considered for multi-spectral analysis.