Efficient reflective multiplexer arrangement

• US 5,450,511 A
• Filed: 07/25/1994
• Issued: 09/12/1995
• Est. Priority Date: 04/29/1992
• Status: Expired due to Term

• Current Assignee: AT&T IPM Corp. (AT&T, Inc.)
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: Dragone, Corrado
• Primary Examiner(s): Bovernick, Rodney B.
• Assistant Examiner(s): NGO, HUNG NHAT
• Application Number:
  US08/279,982
• Time in Patent Office: 414 Days
• Field of Search: 385/10, 385/31, 385/37, 385/15, 385/24, 385/38, 385/39, 385/47, 385/59, 385/54, 385/20, 359/115, 359/117, 359/124, 359/130
• US Class Current: 385/37
• 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 6/12019 characterised by the optical interconnection to or from the AWG devices, e.g. integration or coupling with lasers or photodiodes coupling integrated waveguide to fibre G02B6/30, to optoelectronic element G02B6/42; monolithic integration of integrated waveguides with other optical elements G02B6/12004

Abstract

The efficiency and freedom from cross-talk achieved by transmissive multiplexer/demultiplexer devices is achieved in a reflective multiplexer/demultiplexer device. The reflective geometry avoids the large size devices necessitated by transmissive geometries handling a large number of optical channels. The reflective geometry also avoids long bends in waveguides used in optical gratings in high efficiency transmissive geometries. Integrated optical multiplexers/demultiplexers in accordance with this invention comprise a plurality of waveguides for carrying unmultiplexed optical signals interleaved with a plurality of waveguides for carrying multiplexed optical signals. The two pluralities of waveguides are connected to the boundary of a free space region. The pluralities of waveguides communicate through the free space region with an optical grating comprising a plurality of waveguides each terminated in a reflective element. The length of each waveguide in the grating differs from the lengths of adjacent waveguides in the grating by a predetermined amount to introduce predetermined path length differences for the optical signals traveling in the waveguides of the grating. Unmultiplexed optical signals, introduced into one or more of the input waveguides for carrying unmultiplexed optical signals, travel through those waveguides into the optical grating and are reflected towards one or more of the output waveguides for carrying multiplexed optical signals. When the device is used as a multiplexer in this fashion, it causes the optical signals introduced into the device to be multiplexed together and appear in a predetermined one or more of the waveguides for carrying multiplexed signals. Multiplexed optical signals introduced into one or more of the waveguides for carrying multiplexed signals are directed through the free space region to the optical grating and are reflected toward one or more of the output waveguides for carrying unmultiplexed optical signals. When the device is used as a demultiplexer in this manner, input signals which comprise a mixture of optical frequencies are demultiplexed so that the individual optical frequencies are separated from one another and appear at one or more predetermined waveguides for carrying unmultiplexed optical signals.

Claims

1. An apparatus, comprising:

a first waveguide;

a grating comprising a plurality of second waveguides, each of the second waveguides in the grating having two ends and each of the second waveguides in the grating differing in length from each of the other second waveguides in the grating by a predetermined amount;

a first end of each of the second waveguides being coupled to the first waveguide so that electromagnetic energy flowing in the first waveguide illuminates a plurality of the first ends of the second waveguides in the grating; and

a reflective element connected to a second end of each of the second waveguides in the grating.

2. The optical apparatus of claim, 1, in which the at least one reflective element comprises a Bragg reflector.

3. The optical apparatus of claim 2, in which each of the second plurality of waveguides is substantially straight.

4. The optical apparatus of claim 1, in which the at least one reflective element comprises an optical diffraction grating attached to an end of at least one of the waveguides in the second plurality of waveguides.

5. The optical apparatus of claim 1 in which the at least one reflective element comprises an optical diffraction grating machined into an end of at least one of the waveguides in the second plurality of waveguides.

6. A method of multiplexing a plurality of optical wavelengths, comprising the steps of:

receiving, in each of a plurality of input waveguides for carrying input optical signals, an optical signal of a predetermined wavelength;

directing, through a free space region, the optical signals received in the plurality of waveguides toward a reflective optical grating comprising a plurality of unequal length waveguides each terminated in a reflective element; and

reflecting the optical signals directed to the optical grating toward a single one of a plurality of waveguides for carrying multiplexed optical signals interleaved with the plurality of waveguides for carrying unmultiplexed optical signals.

7. A method of demultiplexing a multiplexed plurality of optical wavelengths, comprising the steps of:

receiving, in one of a plurality of input waveguides for carrying input optical signals, a plurality of multiplexed optical signals;

directing, through a free space region, the input optical signals toward a reflective optical grating comprising a plurality of unequal length waveguides, each terminated in a reflective element; and

reflecting each of the multiplexed optical signals from the grating toward a respective one of a plurality of output waveguides for receiving unmultiplexed optical signals interleaved with the plurality of waveguides for carrying multiplexed opticals signals.

8. An apparatus, comprising:

a first plurality of waveguides;

a second plurality of waveguides coupled to the first plurality of waveguides so that electromagnetic energy flowing in at least one of the first plurality of waveguides illuminates a first end of each of the second plurality of waveguides; and

at least one reflective element directly connected to a second end of at least one of the second plurality of waveguides;

in which the first plurality of waveguides comprises a first group of input waveguides and a second group of output waveguides interleaved with the first group of input waveguides.

9. An apparatus, comprising:

a first plurality of waveguides;

a second plurality of waveguides coupled to the first plurality of waveguides so at electromagnetic energy flowing in at least one of the first plurality of waveguides illuminates a first end of each of the second plurality of waveguides; and

a reflective element directly connected to a second end of each of the second plurality of waveguides;

in which the reflective elements each comprises a Bragg reflector; and

in which each of the second plurality waveguides is curved so that each Bragg reflector is displaced with respect to every other Bragg reflector by only linear displacements.

10. An communication system, comprising:

a means for producing one or more optical signals for carrying information from a transmitter to a receiver;

at least one multiplexing/demultiplexing device for receiving the one or more optical signals comprising;

a first plurality of waveguides;

a second plurality of waveguides coupled to the first plurality of waveguides so that electromagnetic energy flowing in at least one of the first plurality of waveguides illuminates a first end of each of the second plurality of waveguides; and

at least one reflective element directly connected to a second end of at least one of the second plurality of waveguides; and

a means for transmitting output signals from the multiplexing/demultiplexing device to a receiver.