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Active Filters

Active Filters

Active filters are electronic circuits that use operational amplifiers (op-amps), resistors, and capacitors to filter out unwanted frequency components from a signal. A first-order low-pass active filter is designed to pass signals with a frequency lower than a certain cutoff frequency and attenuate frequencies higher than that cutoff frequency. The transfer function for a first-order low-pass active filter is:

Passive Filters

Passive Filters

Passive filters are utilized to shape the frequency spectrum of signals across a diverse array of applications. These filters, using only passive elements like resistors (R), inductors (L), and capacitors (C), are capable of selectively allowing or blocking certain frequency ranges without the need for external power sources.
Low-Pass Filters
Low-pass filters are designed to transmit signals with frequencies lower than the cutoff frequency, ωc, and attenuate those above it. The cutoff frequency...

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Related Experiment Video

Updated: Jun 19, 2026

Design and Characterization Methodology for Efficient Wide Range Tunable MEMS Filters

Design and Characterization Methodology for Efficient Wide Range Tunable MEMS Filters

Published on: February 4, 2018

Tunable optical filter having a large dynamic range.

Ofir Aharon¹, I Abdulhalim

¹Department of Electro-Optic Engineering, Ben Gurion University, Beer Sheva, Israel. oaharon@bgu.ac.il

|October 14, 2009

Summary

A novel tunable birefringent filter using liquid-crystal retarders was developed. This high dynamic range filter offers broad spectral tunability for biomedical optical imaging.

Area of Science:

Optics and Photonics
Materials Science

Background:

Tunable filters are crucial for spectral imaging.
Existing filters often have limitations in dynamic range or tunability.
Liquid crystals offer unique electro-optic properties for filter applications.

Purpose of the Study:

To propose and demonstrate a novel tunable birefringent filter.
To achieve a high dynamic range and broad spectral tunability.
To explore its potential in biomedical optical imaging.

Main Methods:

A stack of liquid-crystal retarders with varying thicknesses in an arithmetic sequence was used.
Each retarder was placed between crossed polarizers with a 45-degree azimuthal orientation.
Nematic liquid crystals were employed for filter fabrication.

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Main Results:

The filter demonstrated tunability over an 800 nm range.
The tunable range covers visible and near-infrared spectrum.
The device exhibits a high dynamic range.

Conclusions:

The proposed liquid-crystal-based birefringent filter is a novel concept.
The filter offers significant spectral tunability and high dynamic range.
It holds potential for advanced biomedical optical imaging applications.