Planar waveguide grating device and method having a passband with a flat-top and sharp-transitions

A waveguide grating device comprising:

• a first port for receiving an optical signal having a plurality of channels therein, channels separated by a channel spacing within the frequency domain;
• a plurality of second ports for receiving optical signals each having a single channel;
• and,
• a grating region comprising a plurality of grating elements within the waveguide, the grating elements disposed for varying a phase of light propagating between the first port and one of the plurality of second ports via the grating elements, the phase variation between adjacent grating elements different than a multiple of 2π selected to provide a spectral response of the waveguide grating device including any effects of field distribution profiles of the first port and of the second ports of the device having a substantially flat spectral response within a passband of the device and having steep sloping edges within the spectral response about the passband.

A waveguide grating device comprising:

• a first port for receiving an optical signal having a plurality of channels therein, channels separated by a channel spacing within the frequency domain;
• a plurality of second ports for receiving optical signals each having a single channel;
• and,
• a grating region comprising a plurality of grating elements within the waveguide, the grating elements disposed for varying the phase of light propagating between the first port and any of the second ports via the grating elements, the phase and amplitude variations other than multiples of 2π, multiples of π and determined in a predetermined manner in order to, in conjunction with the amplitude variation, result in a spectral response of the waveguide device substantially similar within a working spectral range to a target spectral response.

A waveguide grating device comprising:

• an input port receiving light including a plurality of different signals each at a different wavelength and for providing the light with a first field distribution;
• a plurality of grating elements within a grating region for receiving the light having a first field distribution and for dispersing the light in dependence upon a wavelength of the light incidence upon each grating element with a first spectral response dependent upon a phase variation of the light introduced by each grating element;
• a plurality of output ports each for receiving light of a predetermined wavelength and for providing therefrom the light having a second field distribution,
• wherein a combination of the first spectral response, the first field distribution and the second field distribution form a substantially flat spectral response within a passband of the device and steep sloping edges within the spectral response about the passband and substantially zero response elsewhere within a working spectral range.

A method of designing a waveguide grating device having an input port, an output port, and a plurality of grating elements comprising the steps of:

• a) calculating a modulus product of a grating plane amplitude distribution of light diffracted from the input port and an inverse Fourier transform of a field distribution of the output port;
• b) providing a target spectral response for the waveguide grating device;
• c) determining a phase distribution for grating elements forming the waveguide grating such that the phase distribution at the output grating plane in conjunction with the field distribution of the output port results in a spectral response of the waveguide grating device substantially similar to the target spectral response within a working spectral range;
• and,
• d) providing the determined phase distribution of the grating elements as the design.

A method of designing a waveguide grating device having an input port, an output port, and a plurality of grating elements comprising the steps of:

• a) calculating a modulus product of a grating plane amplitude distribution of light diffracted from the input port and an inverse Fourier transform of a field distribution of the output port;
• b) providing a target spectral response;
• c) providing an initial estimate of spectral phase;
• d) determining a complex spectrum based on the target spectral response and the provided spectral phase;
• e) determining grating phase distribution using an inverse Fourier transform of the complex spectrum;
• f) determining an effective complex grating plane amplitude based on the grating phase distribution and the product calculated in step (a);
• g) performing a Fourier transform of the complex grating plane amplitude to determine a spectral amplitude and a new estimate of spectral phase;
• and,
• h) iterating steps (d) through (g) until a predetermined condition is met;
• i) providing the determined phase distribution of the grating elements as the design when the spectral amplitude is within predetermined limits with respect to the target spectral response.

A method of designing a waveguide grating comprising the steps of:

• a) calculating the modulus product of a grating plane amplitude distribution of light diffracted from the input port and the inversed Fourier transform of the field distribution of the output port;
• b) providing a target spectral response;
• c) providing a working spectral range less than the free spectral range of the waveguide grating;
• d) determining an initial estimate of a complex spectrum;
• e) determining grating phase distribution using an inverse Fourier transform of the complex spectrum;
• f) determining an effective complex grating plane amplitude from the grating phase distribution and the product calculated in step (a);
• g) determining a spectral amplitude and a new spectral phase using the Fourier transform of the complex grating plane amplitude;
• h) determining a complex spectrum within the working spectral range based on the target spectral amplitude and the determined spectral phase and having complex spectrum portions outside the working spectral range substantially similar to those resulting from a current iteration;
• and,
• i) iterating steps (e) through (h) until the spectral amplitude is within predetermined limits with respect to the target spectral response.