Fiber-based access networks have become in recent years the dominant technology for building access networks. In particular, all-fiber FTTH (Fiber to the home) networks with GPON protocol see the most growth. Most telecom operators strive to provide in such networks the Triple Play service (Internet-TV-Phone). Typically, in FTTH networks the 1310/1490 nm wavelengths are utilized for delivering the Internet and phone services (via the GPON protocol), whereas the TV service is broadcast on a dedicated 1550 nm wavelength over the same single fiber strand (an approach known as the RF overlay).

Since the RF overlay technology is a typical broadcast technology, the TV signal at the 1550 nm wavelength reaches all subscribers, including those who have not subscribed to the service, allowing them to have a potentially unauthorized  access. To prevent this, telecom operators may use 1550 nm optical blocking filters.

Although filter technologies (e.g. TFF - Thin Film Filters) which allow blocking the 1550 nm band are well-known and commercially available for many years, their use involves cost of around 20 USD/subscriber, which is an unacceptable amount in most cases.

Design of filters for telecom applications has to meet a variety of practical and nontrivial requirements and restrictions, such as controllable center wavelength, wide stop band, low attenuation in other spectrum bands (in the 1260-1610 nm region). Equally important is sufficient stability of spectral characteristics in the presence of mechanical stress and temperature changes. At the same time, a cost-effective and repetitive technology is required for commercial applications. Fibrain has designed GPON-compatible blocking filters and developed technology for their mass-production.

The manufacturing method is characterized by a relatively low cost of the manufacturing equipment, only a slight mechanical weakening of the fiber and low insertion and polarization dependent losses. The developed process lends itself easily to designing blocking filters for different applications.

Fiber-based access networks have become in recent years the dominant technology for building access networks. In particular, all-fiber FTTH (Fiber to the home) networks with GPON protocol see the most growth. Most telecom operators strive to provide in such networks the Triple Play service (Internet-TV-Phone). Typically, in FTTH networks the 1310/1490 nm wavelengths are utilized for delivering the Internet and phone services (via the GPON protocol), whereas the TV service is broadcast on a dedicated 1550 nm wavelength over the same single fiber strand (an approach known as the RF overlay).

Since the RF overlay technology is a typical broadcast technology, the TV signal at the 1550 nm wavelength reaches all subscribers, including those who have not subscribed to the service, allowing them to have a potentially unauthorized  access. To prevent this, telecom operators may use 1550 nm optical blocking filters.

Although filter technologies (e.g. TFF - Thin Film Filters) which allow blocking the 1550 nm band are well-known and commercially available for many years, their use involves cost of around 20 USD/subscriber, which is an unacceptable amount in most cases.

Design of filters for telecom applications has to meet a variety of practical and nontrivial requirements and restrictions, such as controllable center wavelength, wide stop band, low attenuation in other spectrum bands (in the 1260-1610 nm region). Equally important is sufficient stability of spectral characteristics in the presence of mechanical stress and temperature changes. At the same time, a cost-effective and repetitive technology is required for commercial applications. Fibrain has designed GPON-compatible blocking filters and developed technology for their mass-production.

The manufacturing method is characterized by a relatively low cost of the manufacturing equipment, only a slight mechanical weakening of the fiber and low insertion and polarization dependent losses. The developed process lends itself easily to designing blocking filters for different applications.

Full band measurement of a typical manufactured filter.