Wavelength selective modulator

• US 6,295,397 B1
• Filed: 02/18/2000
• Issued: 09/25/2001
• Est. Priority Date: 02/19/1999
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Augustsson, Torsten
• Primary Examiner(s): Ullah, Akm E.
• Application Number:
  US09/506,831
• Time in Patent Office: 585 Days
• Field of Search: 385/24-27, 385/147, 359/139, 359/128, 359/138, 359/158, 455/276.1, 455/139, 455/277.2, 455/304, 455/337
• US Class Current: 385/24
• CPC Class Codes: G02B 2006/12107 Grating
• CPC Class Codes: G02B 2006/12142 Modulator
• CPC Class Codes: G02B 6/12007 forming wavelength selective elements, e.g. multiplexer, demultiplexer
• CPC Class Codes: G02B 6/2813 based on multimode interference effect, i.e. self-imaging
• CPC Class Codes: G02B 6/29317 Light guides of the optical fibre type
• CPC Class Codes: G02B 6/29355 Cascade arrangement of interferometers
• CPC Class Codes: G02B 6/29395 configurable, e.g. tunable or reconfigurable switching G02B6/35
• CPC Class Codes: G02F 1/217 Multimode interference type
• CPC Class Codes: G02F 1/3136 of interferometric switch type

Abstract

The present invention relates to a device and to a method for modulating optical wavelength channels. The optical wavelength channels are switched to at least one access waveguide arranged on a first side of a first multimode waveguide (10). The wavelength channels are then transmitted through the multimode waveguide (10) and imaged on at least two connecting waveguides provided on an opposite side. The optical wavelength channels are then transmitted through the connecting waveguides. For each wavelength selective cross-switch structure (2, 4, 6, 8), the phase of a reflected wavelength is changed by two phase control elements (C1, C2, D1, D2, E1, E2, F1, F2) arranged in a first and a second connecting waveguide on a first side of said wavelength selective cross-switch structure (2, 4, 6, 8) over a given time period and slightly time shifted in relation to the second phase control element, at the same time as the phase of the reflecting wavelength remains relatively unchanged on a second side of said wavelength selective cross-switch structure (2, 4, 6, 8). For each wavelength selective cross-switch structure (2, 4, 6, 8), the phase of transmitting wavelengths is changed once in a first and a second direction per wavelength selective cross-switch structure (2, 4, 6, 8). The phase relationship between the optical signal in respective access waveguides arranged on the first side of the second multimode waveguide (20) determines where the optical signal will be focused on the opposite side.

Claims

1. A wavelength selective modulator (1) for modulating optical wavelengths and including at least two multimode waveguides (10, 20), at least one wavelength selective cross-switch structure (2, 4, 6, 8), at least two phase control elements (C1, C2, D1, D2, E1, E2, F1, F2), and at least four connecting waveguides, wherein the wavelength selective cross-switch structure is disposed between a first multimode waveguide (10) and a second multimode waveguide (20), wherein the first multimode waveguide (10) is connected to at least one access waveguide on a first side and to at least two access waveguides on a second side, wherein the second multimode waveguide (20) is connected to at least two access waveguides on a first side and to at least one access waveguide on a second side, wherein said wavelength selective cross-switch structure is connected to at least two access waveguides on a first side and on a second side, wherein in respect of a wavelength selective cross-switch structure a first access waveguide on the second side of the first multimode waveguide is connected to a first access waveguide on the first side of the wavelength selective cross-switch structure via a first connecting waveguide, a second access waveguide on the second side of the first multimode waveguide is connected to a first access waveguide on the second side of said wavelength selective cross-switch structure via a second connecting waveguide, a second access waveguide on the first side of the wavelength selective cross-switch structure is connected to a first access waveguide on the first side of the second multimode waveguide via a third connecting waveguide, and a second access waveguide on the second side of the wavelength selective cross-switch structure is connected to a second access waveguide on the first side of the second multimode waveguide via a fourth connecting waveguide, wherein the phase control elements are arranged in the connecting waveguides on one side of the wavelength selective cross-switch structure, wherein a first phase control element (C1) is adapted to effect a phase change for a given time period Δ

t1 that is as many time units τ

earlier than the time at which a second phase control element (C2) effects the phase change for a time period Δ

t2, said time difference corresponding to the time taken for the light to travel from a contemplated point (30) to the second phase control element (C2) or to the time taken for the light to travel from the first phase control element (C1) to the second phase control element (C1), wherein in the case of two or more wavelength selective cross-switch structures two phase control elements (D1, D2, E1, E2, F1 and F2) and two connecting waveguides are provided for each wavelength selective cross-switch structure, wherein each wavelength selective cross-switch structure has two phase control elements on the opposite side relative to a nearest adjacent wavelength selective cross-switch structure, and wherein the first of said phase control elements (D1, E1 and F1) is adapted to effect a phase change during a given time period Δ

t1 which is earlier than a phase change caused by the second phase control elements (D2, E2 and F2) during a time period Δ

t2 by a length of time corresponding to the time taken for transmitted or reflected light to travel to said second phase control elements (D2, E2 and F2) from the nearest adjacent phase control element, and wherein the wavelength selective cross-switch structures are mutually connected via connecting waveguides from one access waveguide on a first wavelength selective cross-switch structure to another access waveguide on an adjacent wavelength selective cross-switch structure, and wherein said access waveguides are chosen so as to lie closely adjacent one another and on mutually the same side.

2. A wavelength selective modulator (1) according to claim 1, characterised in that the multimode waveguide is an MMI waveguide.

3. A wavelength selective modulator (1) according to claim 2, characterised in that the wavelength selective cross-switch structure is symmetrical.

4. A wavelength selective modulator (1) according to claim 2, characterised in that the wavelength selective cross-switch structure (2, 4, 6, 8) is an MMI Bragg grating structure (100).

5. A wavelength selective modulator (1) according to claim 3, characterised in that the phase control elements (C1, C2, D1, D2, E1, E2, F1, F2) belonging to respective wavelength selective cross-switch structures change the phases to the same extent.

6. A wavelength selective modulator (1) according to claim 3, characterised in that the time duration Δ

t1 is equally as long as the time duration Δ

t2.

7. A wavelength selective modulator (1) according to claim 6, characterised in that all connecting waveguides have mutually the same length.

8. A wavelength selective modulator (1) according to claim 7, characterised in that for N-number of wavelength selective cross-switch structures, there are 2×

N number of different Mach-Zehnder paths for N-number of different wavelengths.

9. A wavelength selective modulator (1) according to claim 1, characterised in that a receiver (90) is connected to an output of the second multimode waveguide (20) via a bandpass filter (80).

10. A method of modulating optical wavelength channels in an optical network, characterised by switching the optical wavelength channels to at least one access waveguide arranged on a first side of a first multimode waveguide;

transmitting the optical wavelength channels through said first multimode waveguide and imaging said waveguide channels on at least two connecting waveguides arranged on an opposite side relative to said access waveguide;

transmitting said optical wavelength channels through said connecting waveguides;

changing the phase of a reflecting wavelength two times for each wavelength selective cross-switch structure with the aid of two phase control elements arranged in a first and a second connecting waveguide on a first side of said wavelength selective cross-switch structure, wherein said phase is changed by a first phase control element over a given time period Δ

t1 which is earlier than the phase change caused by a second phase control element during a time period Δ

t2 by a length of time that which corresponds to the time taken for the light to travel from a contemplated point (70) to the second phase control element, or the time taken for the light to travel from the first phase control element to the second phase control element, at the same time as the phase of said reflecting wavelength on a second side of the wavelength selective cross-switch structure remains relative unchanged;

changing the phase of transmitting wavelengths for each wavelength selective cross-switch structure once in a first and a second direction per wavelength selective cross-switch structure;

switching the optical wavelength channels via at least two connecting waveguides in a second multimode waveguide; and

wherein the phase relationship between the optical signal in respective access waveguides arranged on the first side of the second multimode waveguide determines where the optical signal will be focused on the second side of the second multimode waveguide for a given length-width ratio on said multimode waveguide.

11. A method according to claim 10, characterised in that the multimode waveguide is an MMI waveguide.

12. A method according to claim 10, characterised in that all connecting waveguides are of mutually the same length.

13. A method according to claim 10, characterised in that for N-number of wavelength selective cross-switch structures, there are 2×

N-number of different Mach-Zehnder paths for N-number of different wavelengths.

14. A method according to claim 10, characterised in that the time period Δ

t1 is of the same duration as the time period Δ

t2.