Source: Physics Stack Exchange

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The Concept of Transform-Limited Pulses

In ultrafast optics, the transform limit (or Fourier limit, Fourier transform limit) refers to the minimum pulse duration achievable for a given optical spectrum of a pulse. A pulse at this limit is termed transform limited, indicating a frequency-independent spectral phase, maximum peak power, minimum time–bandwidth product, and absence of chirp.

Significance of Transform-Limited Pulses

For a specific pulse duration, transform-limited pulses have the narrowest spectral width possible. This property is crucial in applications like optical fiber communications, where emitting pulses close to the transform limit helps minimize chromatic dispersion effects during transmission, thereby enhancing the achievable transmission distance.

Generation and Maintenance of Transform-Limited Pulses

Many mode-locked lasers, especially soliton mode-locked lasers, can produce pulses close to the transform limit. However, factors such as chromatic dispersion and optical nonlinearities during pulse propagation can introduce chirp, leading to non-transform-limited pulses. Techniques like dispersion compensation, involving modification of spectral phase through chromatic dispersion adjustment, can restore these pulses to the transform limit, enabling temporal compression.

Dispersion Compensation

For pulses with broad spectra, compensation of higher-order dispersion may be necessary, in addition to second-order dispersion compensation, to approach the transform limit effectively.

Conclusion

Understanding and achieving transform-limited pulses are essential in various ultrafast optics applications to optimize performance and transmission quality.

Source: Nagwa
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