Narrow band filter and method of making same

A method of fabricating a narrow band optical filter comprising the steps of:

• providing a first graded index lens having a substantially collimating end and a substantially focusing end;
• providing a second graded index lens having a substantially collimating end and a substantially focusing end;
• providing a wavelength selective means having a wavelength characteristic dependent upon on an angle of incidence between the substantially collimating ends of the first and second graded index lenses;
• positioning the first and second graded index lenses such that they are disposed in a coaxial relationship so that the graded index lenses have a common optical axis;
• coupling an optical waveguide to each substantially focusing end of the first and second graded index lenses, each at a location defining a port for porting a beam of light at each end face, the ports being on opposite sides of the common optical axis and substantially equidistant from the optical axis;
• launching a narrowband signal comprising of substantially the predetermined wavelength into one of said ports through one of the optical waveguides;
• allowing the signal to propagate through the wavelength selective means and through the lenses;
• receiving the signal from the other optical waveguide at the other of said ports;
• and,
• adjusting the location of at least one of said ports to determine a maximum intensity of the received signal.

A method of fabricating a narrow band optical filter for passing a narrow band optical signal having a predetermined centre wavelength, comprising the steps of:

• providing a first graded index lens having a substantially collimating end and a substantially focusing end;
• providing a second graded index lens having a substantially collimating end and a substantially focusing end;
• providing a wavelength selective means having a wavelength characteristic dependent upon on an angle of incidence between the substantially collimating ends of the first and second graded index lenses;
• coupling an optical waveguide to each substantially focusing end of the first and second graded index lenses, each at a location defining a port for porting a beam of light at each end face;
• launching an optical signal having at least the predetermined wavelength into one of said ports through one of the optical waveguides;
• allowing the signal to propagate through the wavelength selective means and through the lenses;
• receiving the signal from the other optical waveguide at the other of said ports;
• adjusting the location of at least one of said ports until the wavelength of the received signal is the predetermined wavelength, within predetermined limits;
• and,
• affixing the waveguides in place such that they are permanently and non-movably coupled with their adjacent lenses.