Segmented optical modulator

• US 20080089634A1
• Filed: 10/09/2007
• Published: 04/17/2008
• Est. Priority Date: 10/07/2006
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Sioptical Inc. (Cisco Systems, Inc.)
• Inventors: Montgomery, Robert, Gothoskar, Prakash, Mosinskis, Paulius
• Granted Patent: US 7,515,778 B2
• Time in Patent Office: Days
• US Class Current: 385/3
• CPC Class Codes: G02F 1/0121 Operation of devices; Circuit arrangements, not otherwise provided for in this subclass
• CPC Class Codes: G02F 1/2255 controlled by a high-frequency electromagnetic component in an electric waveguide structure
• CPC Class Codes: H04B 10/5051 using a series, i.e. cascade, combination of modulators
• CPC Class Codes: H04B 10/50575 to control the modulator DC bias

Abstract

An optical modulator is formed to include an adjustable drive arrangement for dynamically adjusting the effective length of the optical signals path(s) within the modulator. Each modulator arm is partitioned into a plurality of segments, with each segment coupled to a separate electrical signal driver. Therefore, the effective length of each modulator arm will be a function of the number of drivers that are activated for each arm at any given point in time. A feedback arrangement may be used with the plurality of drivers to dynamically adjust the operation of the modulator by measuring the extinction ratio as a function of optical power, turning “on” or “off” individual drivers accordingly.

Claims

1. An external modulator for an optical input source, creating a modulated optical output signal, the external modulator comprising

an input waveguiding section for receiving a continuous wave (CW) optical input signal;

an input optical splitter, coupled to the output of the input waveguiding section for dividing the CW optical input signal into a pair of CW optical input signals;

a pair of optical waveguides coupled to the outputs of the input optical splitter, the pair of optical waveguides forming a pair of modulator arms for supporting the propagation of the optical signal, each modulator arm partitioned into a plurality of N modulator segments;

a plurality of modulator electrodes disposed adjacent to each modulator segment of the plurality of N modulator segments;

a plurality of N separate electrical drive signal sources, each source coupled through modulator electrodes to a separate modulator segment of the plurality of N modulator segments, each drive signal source capable of being separately energized/de-energized to control the phase shift present between the optical signals propagating along each arm of the pair of modulator arms, providing at the output of the pair of modulator arms a pair of modulated optical signals;

an output optical combiner for combining the pair of modulated optical signals into a modulated optical output signal; and

an output waveguiding section coupled to the output of the output optical combiner for supporting the propagation of the modulated optical output signal.

2. An external modulator as defined in claim 1 wherein an isolation region is formed between adjacent modulator segments.

3. An external modulator as defined in claim 2 wherein each isolation region comprises a dielectric material disposed between adjacent modulator electrodes to provide the isolation between adjacent modulator segments.

4. An external modulator as defined in claim 2 wherein each isolation region comprises a lightly-doped optical waveguiding section, where each modulator segment comprises a heavily-doped optical waveguiding section.

5. An external modulator as defined in claim 2 wherein each isolation region is coupled to a DC bias source.

6. An external modulator as defined in claim 2 wherein each isolation region is coupled to a low frequency electrical signal source.

7. An external modulator as defined in claim 1 wherein the external modulator further comprises a feedback path between the output waveguiding section and the plurality of N electrical drive signal sources, where the measured output optical power is used to control which signal sources are enabled and which signal sources are disabled, to adjust the extinction ratio of the modulated optical output signal on an on-going basis.