Optical add-drop multiplexers compatible with very dense WDM optical communication systems

• US 5,982,518 A
• Filed: 04/25/1997
• Issued: 11/09/1999
• Est. Priority Date: 03/27/1996
• Status: Expired due to Term

• Current Assignee: Ciena Corporation
• Original Assignee: Ciena Corporation
• Inventors: Mizrahi, Victor
• Primary Examiner(s): NEGASH, KINFE MICHAEL
• Application Number:
  US08/846,086
• Time in Patent Office: 928 Days
• Field of Search: 359/124, 359/127, 359/130, 359/173, 385/24
• US Class Current: 398/84
• CPC Class Codes: G02B 6/2932 comprising a directional router, e.g. directional coupler, circulator
• CPC Class Codes: G02B 6/29322 Diffractive elements of the tunable type G02B6/02195 takes precedence; optical modulation devices based on a change of the optical properties of the medium G02F1/00
• CPC Class Codes: G02B 6/29383 Adding and dropping
• CPC Class Codes: H04J 14/0204 Broadcast and select arrangements, e.g. with an optical splitter at the input before adding or dropping
• CPC Class Codes: H04J 14/0205 Select and combine arrangements, e.g. with an optical combiner at the output after adding or dropping
• CPC Class Codes: H04J 14/0206 Express channels arrangements
• CPC Class Codes: H04J 14/0209 Multi-stage arrangements, e.g. by cascading multiplexers or demultiplexers
• CPC Class Codes: H04J 14/021 Reconfigurable arrangements, e.g. reconfigurable optical add/drop multiplexers [ROADM] or tunable optical add/drop multiplexers [TOADM]
• CPC Class Codes: H04J 14/0213 Groups of channels or wave bands arrangements

Abstract

The present invention provides add-drop multiplexers which are compatible with dense wavelength division multiplexed (WDM) systems having large numbers of optical channels. The add-drop multiplexers employ sets of Bragg gratings separated by an optical isolator to reliably add or drop optical channels without crosstalk. The Bragg grating sets and the optical isolator are interposed between first and second optical couplers. Optical channels to be dropped from a WDM optical signal are reflected by the first set of Bragg gratings and exit the add-drop multiplexer through the first coupler. Optical channels to be added to a WDM optical signal enter the add-drop multiplexer through the second optical coupler.

Claims

1. An optical add-drop multiplexer for a wavelength division multiplexed optical communication system comprising:

a first optical coupler having at least first, second, and third input-output ports;

a first optical transmission path optically communicating with the first coupler input-output port for carrying a wavelength division multiplexed optical signal which includes one or more optical signals to be dropped from the transmission path;

a second optical transmission path optically communicating with the second coupler input-output port of the first optical coupler, the second optical transmission path having positioned therein a first set of one or more Bragg gratings configured to reflect one or more optical wavelengths included in a wavelength division multiplexed optical communication signal carried by the first optical transmission path and having positioned therein a second set of one or more Bragg gratings configured to reflect one or more optical wavelengths, the first and second sets of Bragg gratings being separated by optical isolation means;

a third optical path optically communicating with the third coupler input-output port of the first optical coupler, the third optical transmission path configured to receive optical wavelengths corresponding to channels to be dropped from the wavelength division multiplexed optical communication signal;

a second optical coupler having at least first, second, and third coupler input-output ports and configured such that the second optical transmission path optically communicates with the first coupler input-output port;

a fourth optical transmission path optically communicating with the second input-output port of the second optical coupler and configured to carry optical wavelengths to be added to through channels from the first optical transmission path;

a fifth optical transmission path optically communicating with the third coupler output port for receiving the combined optical signals from the first and second input-output ports of the second optical coupler.

2. An add-drop multiplexer for a wavelength division multiplexed optical communication system as recited in claim 1 in which the set of Bragg gratings includes one or more tunable Bragg gratings.

3. An add-drop multiplexer for a wavelength division multiplexed optical communication system as recited in claim 1 in set of Bragg gratings comprises one or more in-fiber Bragg gratings.

4. An add-drop multiplexer for a wavelength division multiplexed optical communication system as recited in claim 1 wherein the set of one or more Bragg gratings comprises a single chirped grating.

5. An add-drop multiplexer as recited in claim 1 further comprising an optical loss element positioned in the second optical transmission path downstream of the set of Bragg gratings.

6. An add-drop multiplexer as recited in claim 1 wherein the first optical coupler is an optical circulator.

7. An add-drop multiplexer as recited in claim 1 wherein the second optical coupler is an optical circulator.

8. An add-drop multiplexer as recited in claim 1 wherein the first and second optical couplers are optical circulators.