20 fs pulses cover telecoms range

17 Jun 2002

Researchers claim they have generated the shortest ever pulses in the 1.3 to 1.6 µm range.

Researchers in Germany and the US have generated 20 fs pulses from a Cr4+:YAG laser with a repetition rate of 110 MHz. The output covers the entire fibre-optic transmission band from 1.3 to 1.6 µm.

The group says that these are the shortest pulses ever generated in this range and at such a high repetition rate (Optics Letters 27 61).

Daniel Ripin of the Massachusetts Institute of Technology, US, made the system with colleagues at the universities of Karlsruhe and Darmstadt in Germany.

He told Optics.org: "Before this, the shortest pulses generated from Cr4+:YAG were 43 fs. That design used fused silica prisms for dispersion compensation. However, these leave high-order dispersion from the Cr4+:YAG crystal uncompensated."

To minimize intracavity pulse broadening caused by dispersion, Ripin and colleagues used double-chirped mirrors (DCMs) made by the Darmstadt group. This prismless design has three advantages: it is easier to align; it has lower intracavity loss; and it is more compact.

"However, our current laser design does not allow fine-tuning of intracavity dispersion for pulse-width minimization. The use of DCMs for coarse compensation and prisms for fine-tuning of the dispersion might allow [even] shorter pulses," said Ripin.

Ripin sees many applications for the system. He said: "A couple of groups have recently shown that a single phase-coherent pulse can be created by overlapping two synchronized lasers operating at different wavelengths. If few-cycle pulses from a Cr4+:YAG were synchronized and combined with few-cycle pulses from a Ti:sapphire laser it might be possible to generate pulses in the single-cycle regime. Pulses much shorter than two optical cycles have not been generated in the visible or in the infrared."

He also believes the Cr4+:YAG laser could generate a frequency chain covering communications wavelengths.

Ripin concedes that the main disadvantage of his group's system over other Cr4+:YAG lasers is the cost and availability of DCMs. However, German companies Nanolayer and Layertec are commercializing the mirror fabrication, so DCMs could become more widely available in the near future. The group also plans to replace the current Nd:YVO₄ pump laser with a diode laser.

Author
Nadya Anscombe is editor of Optics.org and Opto & Laser Europe magazine.