Source: tonmeister.ca

Understanding Timing Phase in Mode-Locked Lasers

Mode-locked lasers are a cornerstone in photonics, known for their ability to generate ultra-short pulses of light. These lasers are critical in various applications, from telecommunications to medical imaging. One of the essential parameters in analyzing the performance of these lasers is the timing phase, which can significantly affect the quality and stability of the generated pulses.

Defining Timing Phase

The timing phase is a critical concept when discussing the timing jitter of mode-locked lasers. It is defined as the power spectral density of the timing deviation, which is the difference between the expected and actual pulse arrival times. The timing phase is typically expressed in units of radians squared per Hertz (rad² Hz⁻¹).

Understanding the Pulse Train

To comprehend the timing phase, consider the emitted pulse train from the laser as a highly anharmonic oscillation of optical power. In an ideal, noiseless scenario, this can be represented as a Fourier series comprising a sinusoidal signal and its integer harmonics. This representation allows us to understand that one complete pulse period corresponds to a 2π change in the timing phase.

Importance of Power Spectral Density

The power spectral density (PSD) related to the timing phase is crucial for characterizing the stability of the laser. It provides insight into how noise affects the timing of the pulses. In practice, this is often expressed in decibels relative to the carrier per Hertz (dBc/Hz), which is ten times the logarithm to base ten of the PSD.

Timing Phase vs. Optical Phase

It is important not to confuse timing phase with optical phase, even though both concepts are crucial in the context of mode-locked lasers. Optical phase refers to the phase of the electromagnetic wave, while timing phase pertains to the timing of the pulse train. Misunderstanding these can lead to incorrect interpretations of laser behavior.

Conclusion

Understanding the timing phase in mode-locked lasers is vital for optimizing their performance. By analyzing the power spectral density of the timing phase, researchers and engineers can better understand and mitigate the effects of noise on pulse timing, ensuring the lasers operate as intended in their respective applications.

Source: ResearchGate
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