초록 ▼

Advantageous methodologies are disclosed for embedding periodic patterns in optical waveguide elements such as optical fibers. Polarization independence in an elongated waist region of an add/drop coupler can be established by measuring polarization characteristics during fusion and elongation, and

Advantageous methodologies are disclosed for embedding periodic patterns in optical waveguide elements such as optical fibers. Polarization independence in an elongated waist region of an add/drop coupler can be established by measuring polarization characteristics during fusion and elongation, and controlling the elongation to impart a cross-sectional shape, such as a hybrid dumbbell-ellipsoid. Polarization dependence can also be minimized by angular deformation of the elements along the light transmissive axis. To write a pattern, an element having potential photosensitivity is markedly photosensitized in a hydrogen or deuterium environment pressurized to about 1000 to 5000 psi and a scanning UV beam that is transmitted through a photo mask and impinges on the coupler waist as the in-diffused gas is constantly replenished. Dimensional variations in the element which can affect spectral bandwidth are sensed by writing a preliminary test pattern in the element and then locally measuring the spectral properties of the test pattern and adjusting the local levels of background index of refractions so that the modal index of refraction is substantially constant along the length of the pattern. A relatively wide scanning writing beam tracks on a narrower waveguide element despite positional imprecision and temporal shifting by using a feedback signal derived from fluorescence induced in the element. To apodize the grating in accordance with a selected function, a constant power beam is directed through a rotating half-wave plate and divided by a polarizing beam splitter into two beams having oppositely varying DC amplitude characteristics. The two beams are separately varied to produce the desired apodization profile of the grating.

대표청구항 ▼

[ We claim:] [1.] The method of providing a wavelength selective optical coupler having a narrow bandwidth drop wavelength and high grating strength comprising the steps of:elongating a portion of one optical fiber pair each having a core and cladding to a narrow waist region in which the fibers are

[ We claim:] [1.] The method of providing a wavelength selective optical coupler having a narrow bandwidth drop wavelength and high grating strength comprising the steps of:elongating a portion of one optical fiber pair each having a core and cladding to a narrow waist region in which the fibers are longitudinally merged and the core is vestigial;tapering optical fiber transitions to and from the waist region adiabatically to a dimension such that the optical modes of original fibers evolve adiabatically into orthogonal modes within the waist region;modifying the polarization dependence of the propagation constants of the orthogonal modes to establish substantial polarization independence of the drop wavelength in the operation of the coupler;photosensitizing the waist region;writing an apodized reflection grating having a periodicity adapted for the drop wavelength in the waist region while maintaining the photosensitization.