Spot Size Converting Fiber Arrays

Spot size converters (SSCs) provide an efficient coupling from arrays of optical fibers to photonic integrated circuits (PICs). They reduce the mode field using lithographically defined waveguides. PHIX offers v-groove fiber arrays with a pre-attached spot size converter. Depending on the required mode field, these can be made from ion exchanged glass (a partnership with TEEM Photonics) or Silicon Nitride (a cooperation with LioniX International). These lithographic transposers can be interfaced to PICs of any common material.

Traditional ways to reduce the mode field of an optical fiber are the use of high numerical aperture fibers, lensed fibers or specially tapered fibers. These solutions work well for single fibers, but they provide serious alignment challenges when applied to multi-channel configurations. Variations in core concentricity and cladding diameter would inevitably result in high losses.

Our SSCs, on the other hand, offer a low-loss multi-channel solution. They exhibit lithographic accuracy at the chip interface and therefore demonstrate a minimal waveguide to waveguide loss. PHIX has an automated process for attachment of spot size converters to our fiber arrays. This method is similar to how we assemble fiber arrays to PICs with integrated SSCs directly.

Our spot size converters can be polished under various angles, for edge or surface coupling. As an example, a 45-degree orthogonal coupling arrangement is great for wafer-scale testing of silicon photonics that have etched facets. The resulting probe is polarization maintaining, very durable, and low loss.

fiber array with adiabatic taper
spot size converting optical fiber array


  • Output mode field sizes between 1.5 and 10 µm
  • Conversion loss less than 1.5dB
  • Polarization maintaining
  • Optical pitch down to 10 µm
  • 1, 4, 8, 16 and 28 channels available off the shelf
  • Polishing angles for edge or surface coupling
  • Chip can be shaped
  • Large optical bandwidth, from visible light to mid-infrared

Advantages over lensed or tapered fibers

  • Higher channel counts don’t increase the complexity
  • The channels are positioned with lithographic accuracy
  • Cost-effective, especially for higher channel counts
mode field reduction
spot size converter configurations

Off-the-shelf configurations for spot size converters. Other channel counts and dimensions are available on request.

spot size converter fitted to an optical fiber array