Hollow-core fiber with stable propagation delay between -150°C and +60°C.

Optical fibers with a low thermal coefficient of delay (TCD) have been developed for frequency and timing transmission/distribution. However, their temperature sensitivity changes as a function of temperature and, to date, no study of such fibers has demonstrated improved performance over extended temperature ranges, especially at sub-zero temperatures. Here, we show that a hollow core fiber (HCF) with a thin acrylate coating can have a TCD within ±2.0 ps/km/°C over a broad temperature range from -150°C to +60°C. In addition, this thinly coated HCF can be fully insensitive to temperature around -134°C, making it of interest, e.g., for laser stabilization close to cryogenic temperatures.