Athermal tunable filter with wavelength and intensity responses based on volume phase hologram

#The invention relates to athermal tunable filters. More specifically, it relates to athermal tunable filters with wavelength and power responses based on volume phase hologram.

#The wide acceptance of the Internet is creating a fast growth in communication bandwidth demand, and many carriers are turning to wavelength division multiplexing (WDM) to achieve the necessary increase in the capacity of their existing fiber networks. The next generation of the dense WDM (DWDM) components will be tunable devices. Low cost, compact reconfigurable optical add/drop multiplexers (ROADM), Dynamic Gain Equalizers (DGE), Variable Optical Attenuators (VOA), tunable lockers and tunable lasers will be required for the next generation WDM systems, especially in the access and metro networks, to increase network usage efficiency and reduce the operation cost by eliminating the cost of service personnel traveling to manually reconfigure the network. In addition, firmware can be updated or replaced remotely without service interruption.

#Volume Phase Hologram-based Filters (VPHF) recently emerged as an enabling technology for the next generation tunable devices in DWDM network and bio-photonics applications.

#These and other features, aspects and advantages of the present invention will become better understood with regard to the following description and accompanying drawings wherein:

#FIG. 1 is an athermal VPHF based reconfigurable OADM;

#FIG. 2 is a plot of the Bragg resonant wavelength as a function of the ambient temperature, the solid line being without using a temperature compensation technique and the dashed line being with the temperature compensation technique of the present invention;

#The present invention proposes an innovative use of the photosensitive glass that is the Ge-doped fused silica optic fiber preform and is currently widely used for optic fibers and fiber Bragg gratings (FBGs) as the material for the VPHF. This material has proven long term stability and reliability for both the material properties and the UV photosensitive index modulation.

#The present invention also uses an innovative self-compensation optical architecture. The thermal drift of the optical grating period (i.e. nΛ) is automatically compensated by the thermal drift of the incident light beam angle. Thus, a total athermal operation is achieved.

#The OADM is useful in the WDM network to add or drop specific predetermined wavelengths into and from the through traffic fiber. The next generation of OADM must be reconfigurable and highly integrated, and should dynamically select which wavelengths are added or dropped.