Integrateable band filter using waveguide grating routers

• US 7,043,123 B2
• Filed: 09/01/2005
• Issued: 05/09/2006
• Est. Priority Date: 09/09/2003
• Status: Active Grant

• Current Assignee: WSOU Investments, LLC (WSOU Holdings, LLC)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Doerr, Christopher Richard
• Primary Examiner(s): KIANNI, KAVEH C
• Application Number:
  US11/217,625
• Publication Number:
  US 20060008209A1
• Time in Patent Office: 250 Days
• Field of Search: None
• US Class Current: 385/37
• CPC Class Codes: G02B 6/12021 Comprising cascaded AWG devices; AWG multipass configuration; Plural AWG devices integrated on a single chip

Abstract

The inventors propose herein a novel band filter design for planar lightwave circuits. In one embodiment of the present invention, the band filter includes two waveguide grating routers interconnected by a third waveguide grating, wherein waveguides comprising the third waveguide grating have unequal path lengths. In addition, the waveguides in the third grating are partitioned into sets of adjacent waveguides wherein each set corresponds to a particular wavelength band for the filter. The individual sets of waveguides are spaced at their connection to the second waveguide grating router such that optical signals within predetermined, different optical wavelength bands are routed to different output ports of the band filter. Some of the advantages of this novel band filter include compactness, sharp passband corners, low spectral ripple, and a lack of chromatic dispersion.

Claims

1. A band filter for filtering an optical signal having components in one or more passbands of the filter, comprising:

a first waveguide grating router;

a second waveguide grating router; and

a plurality of waveguides connecting the first waveguide grating router to the second waveguide grating router, the plurality of waveguides arranged as a waveguide grating, each waveguide having a center wavelength for supporting transmission of an optical signal;

wherein the plurality of waveguides is partitioned into at least two sets of waveguides, each set of waveguides corresponding to a particular passband in the band filter, the waveguides in a set having unequal path lengths, and the adjacent waveguides having a path-length difference defined as;

$L<br><br>\left(m\right)-L<br><br>\left(m-1\right)=\frac{A_{\mathrm{middle}}}{2<br><br>n}<br><br>\left[\mathrm{\lambda <br><br>}<br><br>\left(m\right)+\mathrm{\lambda <br><br>}<br><br>\left(m-1\right)\right]$

where L(m) is the path length of waveguide m, λ

(m) is the center wavelength supported for propagation by waveguide m, n is the waveguide refractive index, and A_middle is an integer grating order of the waveguide grating, where A_middle is chosen to be greater than or equal to order 5.

2. The band filter as defined in claim 1 wherein the first waveguide grating router includes a second waveguide grating of order A_left comprising M_left waveguides, wherein the second waveguide grating router includes a third waveguide grating of order A_right comprising M_right waveguides, and wherein A_middle is chosen to be less than one of either A_leftM_left/25 or A_rightM_right/25.

3. The band filter as defined in claim 2 wherein said band filter includes one input port and at least two output ports, the number of output ports corresponding to the number of waveguide sets, said input port disposed on an input side of the first waveguide grating router for receiving said optical signal comprising a plurality of optical channels, and said output ports disposed on an output side of the second waveguide grating router for outputting at least one channel of the optical signal from each output port.

4. The band filter as defined in claim 3 wherein said optical signal comprising a plurality of optical channels is a coarse wavelength division multiplexed signal.

5. The band filter as defined in claim 2 wherein said band filter includes at least two input ports and one output port, the number of input ports corresponding to the number of waveguide sets, said input ports disposed on an input side of the second waveguide grating router each for receiving said optical signal comprised of one or more of optical channels, and said output port disposed on an output side of the first waveguide grating router for outputting substantially all the optical channels carried by said optical signals in a wavelength division multiplexed format.

6. The band filter as defined in claim 5 wherein said wavelength division multiplexed format is a coarse wavelength division multiplexed format.

7. The band filter as defined in claim 1 wherein the plurality of waveguides in the waveguide grating traverse a substantially parabolic shape.

8. The band filter as defined in claim 7 wherein at least one of said at least two sets of waveguides exhibits a grating order that is different from the grating order from another one of the at least two sets of waveguides.

9. A band filter for filtering an optical signal having components in one or more passbands of the filter, comprising:

first means responsive to the optical signal for demultiplexing the optical signal into a plurality of first optical bands;

second means coupled an output side of the first means for supporting optical transmission of the plurality of first optical bands individually on a corresponding plurality of optical paths therein, the second means arranged to group adjacent optical paths in said plurality of optical paths together to form a plurality of groups of optical paths, said plurality of optical paths being larger in number than said plurality of groups of optical paths; and

third means coupled to the second means opposite to receive said plurality of groups of optical paths for multiplexing the first optical bands in each said group together so that each group of said first optical bands is output individually by the third means within a second optical band substantially equal to a sum of the first optical bands in the group;

wherein the optical paths within a group having unequal path lengths, and the adjacent optical paths having a path-length difference defined as;

$L<br><br>\left(m\right)-L<br><br>\left(m-1\right)=\frac{A_{\mathrm{middle}}}{2<br><br>n}<br><br>\left[\mathrm{\lambda <br><br>}<br><br>\left(m\right)+\mathrm{\lambda <br><br>}<br><br>\left(m-1\right)\right]$

where L(m) is the path length of optical path m, λ

(m) is the center wavelength supported for propagation by optical path m, n is the refractive index for the optical paths, and A_middle is an integer, where A_middle is chosen to be greater than or equal to 5.