Courtesy of Berkeley Nucleonics Corp
Cover photo. Optical mounts on a laser bench, and a red laser beam meeting an optic, the kind of setup this paper times.

Cover photo. Optical mounts on a laser bench, and a red laser beam meeting an optic, the kind of setup this paper times.

Fast edges and picosecond timing for laser and electro-optic benches

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Nov. 12, 2026
2 min read
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Abstract
On a photonics bench every timing quantity is also a length: 10 ps is 3.0 mm of free-space path. This paper derives the electrical requirements a pulse source must meet when it drives a laser trigger, an electro-optic gate and a detector window that have to coincide. It relates the two rise-time conventions, shows how oscilloscope bandwidth inflates a measured edge, explains why the jitter that matters is the jitter of the interval between two edges, and derives how much of a programmed pulse is usable once its edges are counted. A worked example budgets a 1 ns modulator gate around a short optical pulse. The reader will be able to write a pulse-source requirement, score any instrument against it and set up the bench to verify the result.

Who this paper is for. Laser, LiDAR and electro-optic test engineers who build pulsed benches, and the research staff who specify their timing. Design and test engineers get a requirements table they can lift into a specification; researchers get the derivations behind it.

David Brown, President, Berkeley Nucleonics Corp.

Key results

  • 3.0 mm: of free-space path per 10 ps of timing error
  • 30%: slow reading of a 105 ps (10% to 90%) edge on a 4 GHz oscilloscope, k = 0.35
  • 1/3 the specified interval jitter: with both edges on one timebase, under 10 ps RMS versus under 30 ps RMS through a trigger link
  • 895 ps: above 90% amplitude in a 1 ns gate with 105 ps (10% to 90%) edges

Timing on an optical bench is a length

In free space, light covers 3.0 mm in 10 ps or 30 cm in 1 ns. On a bench where a laser pulse, an electro-optic gate and a detector window must coincide, every timing quantity is therefore also a length. A 100 ps error in a detector gate is 3.0 cm of optical path, and in a time-of-flight measurement, where the light makes the trip twice, it is 1.5 cm of range. The conversion changes by no more than about a factor of 1.5 across the media on the bench, including the coaxial cable that carries the electrical pulse to the device.

Courtesy of Berkeley Nucleonics Corp
Ten picoseconds is 2 to 3 mm of path in every medium on the bench, so a picosecond timing budget is also a millimeter path budget.

Ten picoseconds is 2 to 3 mm of path in every medium on the bench, so a picosecond timing budget is also a millimeter path budget.

Computed as path = c × interval / n, with c = 299.79 mm/ns. The group index is typical of standard single-mode fiber near 1550 nm; the velocity factor is typical of solid polyethylene dielectric.

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