Optical modulator having a plurality of modulator segments

• US 9,874,767 B2
• Filed: 11/09/2016
• Issued: 01/23/2018
• Est. Priority Date: 10/09/2014
• Status: Active Grant

• Current Assignee: Nokia Solutions and Networks US LLC (Nokia Corporation)
• Original Assignee: Elenion Technologies, LLC (Nokia Corporation)
• Inventors: Ding, Ran, Baehr-Jones, Thomas Wetteland, Magill, Peter D., Hochberg, Michael J., Rylyakov, Alexander
• Primary Examiner(s): KIM, ELLEN E
• Application Number:
  US15/347,202
• Publication Number:
  US 20170059888A1
• Time in Patent Office: 440 Days
• CPC Class Codes: G02F 1/011 in optical waveguides, not otherwise provided for in this subclass
• CPC Class Codes: G02F 1/0121 Operation of devices; Circuit arrangements, not otherwise provided for in this subclass
• CPC Class Codes: G02F 1/025 in an optical waveguide structure G02F1/017, G02F1/2257 take precedence
• CPC Class Codes: G02F 1/035 in an optical waveguide structure
• CPC Class Codes: G02F 1/225 in an optical waveguide structure

Abstract

An optical modulator apparatus may include a plurality of segment drivers, each segment driver having a unique offset voltage and driving but a portion or a segment of an electro-optical modulator. A modulating electrical signal may be applied to the segment drivers via a plurality of electrical delays. Parameters of the segment drivers may be selected so as to approximate a pre-defined transfer function, which may include a linear or a non-linear transfer function.

Claims

1. A modulator apparatus comprising:

an electrical input port for receiving an electrical signal to be modulated onto an optical carrier wave;

a succession of serially optically coupled optical modulator segments disposed in an optical path of the optical carrier wave and configured to successively modulate the optical carrier wave so as to obtain a modulated optical signal;

a plurality of segment drivers, wherein each segment driver is electrically coupled to one of the succession of the modulator segments and configured to apply a driving voltage V_d thereto in response to a control voltage V_c in accordance with a limiting voltage transfer function specific to the segment driver, wherein the driving voltage V_d transitions between a low voltage V_low, and a high voltage _high when the control voltage V_c passes an offset voltage V_os, that is specific to the segment driver; and

a plurality of electrical connections between the electrical input port and each segment driver.

2. The modulator apparatus of claim 1, wherein each segment driver is configured to generate the driving voltage V_d such that

V_d=V_low when V_c<

V_os−

V_th;

V_d=V_high when V_c>

V_os+V_th; and

V_d varies between V_low and V_high when V_c varies between V_os−

V_th and V_os+V_th, wherein V_th is a threshold voltage defining the width of a voltage transition region about the offset voltage V_os.

3. The modulator apparatus of claim 1, wherein each segment driver comprises a limiting amplifier characterized by the corresponding low voltage V_low, the corresponding high voltage V_high, the corresponding offset voltage V_os, and the corresponding threshold voltage V_th.

4. The modulator apparatus of claim 1, wherein each electrical connection has a corresponding delay Δ

T_electrical between the electrical input port and each segment driver; and

wherein the delays Δ

T_electrical are such that in operation, the application of the driving voltage V_d to individual optical modulator segments in the succession of optical modulator segments is substantially synchronized with propagation of the optical carrier wave therein.

5. The modulator apparatus of claim 1, further comprising a comparator module operationally coupled to the electrical input port and the plurality of segment drivers to provide individual control signals to the plurality of segment drivers when the control voltage V_c exceeds the offset voltages V_os of corresponding segment drivers of the plurality of segment drivers.

6. The modulator apparatus of claim 1, wherein the succession of serially optically coupled optical modulator segments comprises an optical waveguide and a succession of electrodes disposed along the optical waveguide and operationally coupled thereto.

7. The modulator apparatus of claim 1, wherein the plurality of electrical connections comprise a succession of serially electrically coupled electrical delay line segments,

wherein each progressive one of the succession of electrical delay line segments is electrically coupled to a segment driver of the plurality of segment drivers, and

wherein the segment driver is electrically coupled to a corresponding progressive one of the succession of optical modulator segments.

8. The modulator apparatus of claim 1, wherein the offset voltage V_os of the segment driver of each successive optical modulator segment is greater than the offset voltage V_os of the segment driver of an immediately preceding modulator segment, if any.

9. The modulator apparatus of claim 8, wherein the offset voltage V_os of the segment driver of each successive optical modulator segment is greater than the offset voltage V_os of the segment driver of an immediately preceding modulator segment, if any, by a same step voltage Δ

V_os.

10. The modulator apparatus of claim 2, wherein a slope of each segment driver, defined as (V_high−

V_low)/2V_th, is such that in operation, a degree of modulation of the modulated optical signal is substantially proportional to a magnitude of the electrical signal received at the electrical input port.

11. The modulator apparatus of claim 2, wherein at least one of the low voltage V_low, the high voltage V_high, and the threshold voltage V_th, of at least one segment driver of the plurality of segment drivers is substantially different from a corresponding one of the low voltage V_low, the high voltage V_high, and the threshold voltage V_th of another segment driver of the plurality of segment drivers.

12. The modulator apparatus of claim 6, further comprising a silicon photonic chip comprising the optical waveguide.

13. The modulator apparatus of claim 12, wherein the silicon photonic chip comprises the plurality of segment drivers.

14. The modulator apparatus of claim 1, wherein the low voltage V_low, the high voltage V_high, and a threshold voltage V_th defining the width of a voltage transition region in the corresponding limiting voltage transfer characteristic of each segment driver of the plurality of segment drivers are such that a degree of modulation of the modulated optical signal is a function of the electrical signal received by the electrical input port;

wherein the function is selected from the list consisting of quadratic, cubic, periodic, and an exponential function.

15. A method of modulating an optical carrier wave by an electrical signal, the method comprising:

propagating the optical carrier wave in a succession of serially optically coupled optical modulator segments;

coupling the electrical signal to a plurality of segment drivers, wherein each segment driver is electrically coupled to one of the succession of the modulator segments and is configured to apply a driving voltage V_d thereto in response to a control voltage V_c in accordance with a limiting voltage transfer function specific to the segment driver, wherein said control voltage V_c is defined by the electrical signal, and wherein the driving voltage V_d transitions between a low voltage V_low and a high voltage V_high when the control voltage V_c passes an offset voltage V_os that is specific to the segment driver; and

setting one or more parameters of the limiting voltage transfer function of each of the segment drivers so that an overall voltage transfer function of the plurality of segment drivers approximates a pre-defined linear or non-linear function, so as to provide a desired dependence of a degree of modulation of the optical carrier wave by the succession of serially optically coupled optical modulator segments upon the electrical signal.

16. The method of claim 15, wherein the limiting voltage transfer function of each of the segment drivers has associated:

a low voltage V_low;

a high voltage V_high;

an offset voltage V_os; and

a threshold voltage V_th,

and wherein for each of the segment drivers, the limiting voltage transfer function relating the driving voltage V_d and the control voltage V_c, is such that;

V_d=V_low when V_c<

V_os−

V_th;

V_d=V_high when V_c>

V_os+V_th; and

V_d varies between V_low and V_high when V_c varies between V_os−

V_th and V_os+V_th.

17. The method of claim 15 further comprising:

providing the electrical signal to each segment driver with a different electrical time delay Δ

T_electrical, wherein the electrical time delays Δ

T_electrical are such that the application of the driving voltages V_d to individual optical modulator segments in the succession of optical modulator segments is substantially synchronized with propagation of the optical carrier wave therein.

18. The method of claim 16, further comprising pre-selecting the offset voltage V_os of each successive segment driver to be greater than the offset voltage V_os of the immediately preceding segment driver, if any.

19. The method of claim 18, further comprising pre-selecting the low voltage V_low, the high voltage _high, the offset voltage V_os, and the threshold voltage V_th of each segment driver of the plurality of segment drivers such that V_low of each successive segment driver is substantially equal to V_high of the immediately preceding segment driver, if any.

20. The method of claim 18, further comprising pre-selecting a slope of each segment driver, defined as (V_high−

V_low)/2V_thso as to provide a degree of modulation of the optical carrier wave substantially proportional to a magnitude of the electrical signal received at the electrical input port.