03 Jun 2025 Schäfter+Kirchhoff have launched a new fiber coupler series 60SMF. The couplers series 60SMF are high precision fiber couplers optimized for high coupling efficiency, high pointing stability and long-term stability. The couplers’ compact size as well as the high-resolution alignment mechanisms facilitate the highly efficient coupling of collimated laser radiation into single-mode and polarization-maintaining fiber. The straight-forward and intuitive coupling procedure results in vibration- and shock-insensitive and thermally stable fiber coupling with power stability of better than 3% for a temperature range of 15-35°C.
A large variety of coupling optics allows the optimum focal length and the best lens type for a single wavelength or a wavelength range to be selected for each application. All lenses are AR-coated. For an ideal Gaussian beam and standard fibers, coupling efficiencies up to 80% are reached.
The fiber couplers provide all degrees of freedom necessary to achieve optimal coupling efficiency: The angle between laser beam and lens/fiber end-face, the z-position of the lens, the orientation of the polarization axis of the fiber to that of the laser source and the centering of the lens with respect to the laser beam all are adjustable. The fiber couplers 60SMF therefore have a TILT adjustment, an independent focus adjustment, can be rotated by 360°, and allow for lateral adjustment using an appropriate adapter.
The TILT adjustment, maximizing the lateral overlap between the mode field of the fiber and the focused laser spot, is done through 3 adjustment screws. It has ceramic bearings and the adjustment screws have a super-fine thread to ensure an even more precise and easy adjustment. 3 locking screws are used for fine-adjustment and to lock the position for optimal mechanical stability.
Independent of the TILT adjustment, the distance between fiber end-face and coupling optics is adjusted by means of an eccentric key. The final focus setting is locked using two radially arranged clamping screws. Since the focus adjustment is independent, the z-position of the mode field diameter can be placed much more precisely.
The fiber couplers 60SMF have a receptacle of type LSA and are available as PC (for fibers with 0°-polish) and APC (for fibers with 8°-polish). The angled polish of connectors of type APC causes the beam to exit in an angle and not parallel to the optical axis of the fiber. This is corrected by the pre-angled mechanical coupling axis of the coupler that compensates the beam deflection and thus minimizes aberrations resulting from a non-ideal beam path through the lens.
The couplers are available in eco brass ® (standard) or in amagnetic titanium (µr=1.00005). In case of titanium, the linear coefficient of thermal expansion is close to that of the optics so that a thermal stability over a larger temperature range can be expected.
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