Optical switch, multiplexer, and demultiplexer

• US 5,136,671 A
• Filed: 08/21/1991
• Issued: 08/04/1992
• Est. Priority Date: 08/21/1991
• Status: Expired due to Term

• Current Assignee: American Telephone & Telegraph Company (AT&T, Inc.)
• Original Assignee: AT&T, Inc.
• Inventors: Dragone, Corrado
• Primary Examiner(s): Lee, John D.
• Assistant Examiner(s): PALMER, PHAN T H
• Application Number:
  US07/748,131
• Time in Patent Office: 349 Days
• Field of Search: 385/46, 385/17, 385/37, 385/16, 385/42-45, 385/39
• US Class Current: 385/46
• CPC Class Codes: G02B 6/12011 characterised by the arrayed waveguides, e.g. comprising a filled groove in the array section
• CPC Class Codes: G02B 6/124 Geodesic lenses or integrated gratings

Abstract

An N×N integrated optical interconnection apparatus capable of switching, multiplexing, or demultiplexing a large number of input and output wavelength channels achieves low levels of crosstalk and insertion loss. Two substantially identical N×M star couplers are connected by an optical diffraction grating comprising M unequal length waveguides spaced from one another by predetermined amounts. Each coupler comprises a dielectric slab defining a free space region between two periodic arrays of waveguides, each radially directed toward a virtual focal point. The arrays are configured so that their respective foci are located at a predetermined distance away from and outside the free space region to minimize phase errors caused by mutual coupling between adjacent waveguides. Specifically, the focal point of each array connected to each star coupler may be located so that it coincides with the phase center of the other array connected to each coupler. Residual phase errors may be reduced by appropriately setting the lengths of the waveguides in the optical grating between the two star couplers. The length difference between any two adjacent waveguides in the grating is not constant throughout the grating.

Claims

1. An optical interconnection apparatus comprising:

a first plurality of input waveguides radially directed from a plurality of input ports toward a first focal point;

a first star coupler having an input connected to the plurality of input waveguides;

a first plurality of ouput waveguides radially directed to a second focal point and connected to an output of the first star coupler;

an optical grating comprising a plurality of unequal length waveguides having inputs connected to the first plurality of output waveguides;

a second plurality of input waveguides radially directed to a third focal point and connected to outputs of the optical grating;

a second star coupler having an input connected to an output of the second plurality of input waveguides; and

a second plurality of output waveguides radially directed from a plurality of output ports toward a fourth focal point and connected to an output of the second star coupler;

the first and second focal points being located predetermined distances from the first star coupler and the third and fourth focal points being located predetermined distances from the second star coupler.

2. The optical interconnection apparatus of claim 1, in which the predetermined distances of the focal points from the star couplers are such that phase errors are reduced.

3. The optical interconnection apparatus of claim 1, in which the predetermined distances of the focal points from the star couplers are such that aberrations caused by mutual coupling between waveguides is reduced.

4. The optical interconnection apparatus of claim 1, in which the input and output radially directed pluralities of waveguides each define respective phase centers;

the focal points of the input waveguides substantially coincide with the phase centers of the output waveguides; and

the focal points of the output waveguides substantially coincide with the phase centers of the input waveguides.

5. The interconnection apparatus of claim 2, in which the difference in length between adjacent waveguides in the optical grating is not the same for all adjacent waveguides throughout the grating so as to reduce residual phase errors in the apparatus.

6. An optical interconnection apparatus, comprising:

a free space region of predetermined geometry;

a first array of waveguides radially directed toward a first focal point located a predetermined distance outside the free space region so as to reduce phase errors caused by mutual coupling between the waveguides in the first array;

a second array of waveguides radially directed toward a second focal point located a predetermined distance outside the free space region so as to reduce phase errors caused by mutual coupling between the waveguides in the second array; and

an optical grating connected to the second array of waveguides and having a plurality of optical waveguides each having a predetermined length which differs from the predetermined lengths of the other waveguides in the grating, the length difference between two adjacent waveguides in the grating not being constant throughout the grating and the lengths of the waveguides in the grating being such that residual phase errors are reduced.

7. An optical transmission system, comprising:

a plurality of input ports at least one of which receives optical communication signals;

a plurality of output ports at least one of which transmits optical communication signals;

a first plurality of input waveguides radially directed from the plurality of input ports toward a first focal point;

a first star coupler having an input connected to the plurality of input waveguides;

a first plurality of output waveguides radially directed to a second focal point and connected to an output of the first star coupler;

an optical grating comprising a plurality of unequal length waveguides having inputs connected to the first plurality of output waveguides;

a second plurality of input waveguides radially directed to a third focal point and connected to outputs of the optical grating;

a second star coupler having an input connected to an output of the second plurality of input waveguides; and

a second plurality of output waveguides radially directed from the plurality of output ports toward a fourth focal point and connected to an output of the second star coupler;

the first and second focal points being located predetermined distances from the first star coupler and the third and fourth focal points being located predetermined distances from the second star coupler so as to reduce phase errors caused by mutual coupling between the waveguides in the array of input and output waveguides.

8. The optical transmission system of claim 7, in which the optical grating comprises a plurality of optical waveguides each having a predetermined length which differs from the predetermined lengths of the other waveguides in the grating, the length difference between two adjacent waveguides in the grating not being constant throughout the grating and the lengths of the waveguides in the grating being such that residual phase errors are reduced.