Ultraviolet curing adhesive-based optical fiber feedthrough for ultrahigh vacuum systems

We present an inexpensive, simple, and robust method of making an optical fiber feedthrough for ultrahigh vacuum UHV systems. This system is particularly devoted for cold atom experiments. A drilled standard UHV DN16CF flange allows us to pass a fiber inside an UHV chamber. An optical ultraviolet UV curing adhesive is simultaneously used for holding the fiber through the flange and as a vacuum sealant. A vacuum down to 10−9 mbar is currently observed, while the optical insertion loss of the feedthrough is monitored and does not exceed 0.01 dB. In most of light-matter interaction experiments, laser light must pass through ultrahigh vacuum chambers. Although light beams can be propagated in free space through glass view-ports, more and more recent cold atom experiments use optical fibers to carry or collect light to or from a well defined area. This covers a wide variety of experiments such as atom-surface interactions or atomic samples guided inside hollow-core fibers. This kind of experiments requires continuous fibers through the vacuumatmosphere interface. A feedthrough for optical fiber based on a Teflon ferrule has been successfully demonstrated. However, this technique has several drawbacks. It requires a very high drilling precision, and as a consequence, must be accurately designed for a specific fiber diameter. As the ferrule must avoid any leaks, a constraint is applied to the fiber, which can induce birefringence and excess losses. Furthermore, as the polymer coating of the fiber ages under mechanical constraints, leaks might appear with time. We have developed a simple method to realize an optical fiber feedthrough completely free of those problems. It is based on a commercially available UV curing adhesive. The realization is easy and does not require accurate mechanical pieces. A multiple-fiber configuration is also achievable.