Optical noise is common in optical systems such as fiber amplifiers and fiber laser systems because both include the amplification process. Amplification of optical signals generates optical noise through the spontaneous emission process.

The process of spontaneous emission occurs when the light produced by the spontaneous decay of excited erbium ions is coupled to the optical fiber waveguide. This spontaneous emission of light gets amplified by the medium gain and increases significantly.

Since optical noise is dangerous for fiber lasers and fiber amplifiers, we need something that can help reduce or eliminate this optical noise.

The best way to reduce or eliminate optical noise is to use fiber bandpass filters.

Why is optical noise bad for optical systems?

Optical amplifiers are naturally subjected to generate optical noise spontaneously, also called amplified spontaneous emission (ASE). This amplified spontaneous emission when added to the modulated signal consequently degrades the quality of the signal transmission. Therefore, it is critical to quantify and eliminate the level of ASE in any given optical transmission system.

The optical signals and noise levels are usually characterized by the optical signal-to-noise ratio. While the optical signal may be polarized, the noise is typically not. Based on the receiver polarization sensitivity, the optical noise must be considered with a single or two polarizations.

As a result, any active or passive optical device amplifies or attenuates simultaneously the incoming signal and the incoming noise. Besides, it also adds noise, making its output optical signal-to-noise ratio lower than the input one.

This degradation in optical signal-to-noise value is referred to as noise factor and is expressed in dB. The relative importance of added noise strongly depends on the input noise level, the noise factor is only an intrinsic parameter of the optical device and independent of the input signal and noise.

For polarization-insensitive devices, input noise and output noise depend on polarization, which makes noise figure independent of polarization concerns.

What are bandpass filters? How do they reduce optical noise?

In optical transmission systems, fiber lasers, and fiber amplifiers, it is important to use PM bandpass filters. Bandpass filters are micro-optic components designed to block out unwanted noise signals. They are made based on environmentally-stable thin-film filter technology.

A bandpass filter is designed to allow signals of certain wavelengths and absorb or reflect unwanted optical signals. They allow you to transmit only desired light signals while blocking all other unwanted light signals such as ASE signals.

Optical bandpass filters are named so because they transmit a specific range or band of signals.

A typical optical bandpass filter can be characterized by various characteristics, such as blocking level, peak transmission, and central wavelength.

In addition to these characteristics, an ideal optical bandpass filter is also characterized by high isolation, low insertion loss, high return loss, impressive environmental stability, and high-power handling capability.

At DK Photonics, you can find bandpass filters with different central wavelengths, such as 1064nm bandpass filters, 1030nm bandpass filters, 1053 PM bandpass filters, and more. If you have any queries related to the purchase of optical fiber bandpass filters, please feel free to contact us.