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Fiber Light Sources

ASE Light Sources
 

Product description

Amplified Spontaneous Emission

In a laser medium with large gain, the luminescence from spontaneous emission can be amplified to high power levels. This amplified luminescence may be used in applications where light with low temporal coherence but good spatial coherence (see below) is required. It also occurs in lasers, even when operated below the laser threshold.

Whereas luminescence originally goes in all spatial directions, ASE can be strongly directional for gain media with a large aspect ratio. As an extreme case, consider a fiber laser or fiber amplifier, where ASE propagating along the fiber can be much more powerful than the omnidirectional luminescent emission.

In lasers and particularly in high-gain amplifiers, amplified spontaneous emission is usually an unwanted effect. It tends to limit the gain achievable in a single stage of a fiber amplifier to the order of 40–50 dB. Higher gain values are possible e.g. for amplification of pulses, if several amplifier stages are used, which are separated by filters, Faraday isolators, and/or optical modulators (switches). Particularly in some fiber lasers, ASE can prevent lasing at extreme wavelengths, if the gain at other wavelengths is high enough for generating strong ASE. Such problems can often be overcome by optimizing the overall laser design, with special attention to fiber length, doping level and the like, and ASE at unwanted wavelengths may be suppressed with certain fiber designs (e.g. photonic crystal fibers) exhibiting high propagation losses outside the desired spectral region. Similar challenges arise in the context of some bulk lasers, e.g., Nd:YAG lasers operating at 946 nm, where strong ASE at 1064 nm can suppress 946-nm lasing.

Even if amplified spontaneous emission in an amplifier is not strong enough to extract significant power, it can contribute significantly to the noise of the amplified signal. The noise figure of a laser amplifier can be considered to be limited by ASE. Note that for quasi-three-level gain media this ASE effect is stronger than for four-level media.

Sources ASE autres bandes

C-Band ASE Light Source

Sources ASE bande C et L