Optical modulator having a plurality of modulator segments
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.
1. A method for modulating an optical carrier wave, the method comprising:
propagating the optical carrier wave through a plurality of optical modulator segments; and,
electrically driving the plurality of optical modulator segments in accordance with differing limiting voltage transfer functions.
2. The method of claim 1 comprising propagating the optical carrier wave sequentially through the plurality of optical modulator segments.
3. The method of claim 2 wherein the plurality of optical modulator segments is monolithically integrated in a chip.
4. The method of claim 3 wherein the chip comprises semiconductor material.
5. The method of claim 1 comprising using the differing limiting voltage transfer functions to convert an input electrical signal into driving voltages for the plurality of optical modulator segments.
6. The method of claim 5 comprising:
for each optical modulator segment from the plurality of optical modulator segments, providing a control voltage defined by the input electrical signal; and
converting the control voltages into the driving voltages.
7. The method of claim 6 comprising applying the driving voltages to the plurality of optical modulator segments synchronously with propagation of the optical carrier wave therein.
8. The method of claim 7 comprising, for at least two of the driving voltages applied respectively to at least two of the optical modulator segments, limiting voltage variations to different sub-ranges of an operating voltage range of the control voltage.
9. The method of claim 8 wherein the at least two of the optical modulator segments comprise a first optical modulator segment and a second optical modulator segment, wherein the driving voltages comprise a first driving voltage applied to the first optical modulator segment and a second driving voltage applied to the second optical modulator segment, the method comprising:
varying the first driving voltage in accordance with the control voltage for the first optical modulator segment when the control voltage for the first optical modulator segment varies in a first sub-range of the operating voltage range; and
varying the second driving voltage in accordance with the control voltage for the second optical modulator segment when the control voltage for the second optical modulator segment varies in a second sub-range of the operating voltage range that differs from the first sub-range.
10. The method of claim 9 comprising suppressing variations of the first driving voltage when the control voltage for the first optical modulator segment varies outside of the first sub-range of the operating voltage range, and suppressing variations of the second driving voltage when the control voltage for the second optical modulator segment varies outside the second sub-range of the operating voltage range.
11. The method of claim 10 wherein the first and the second sub-ranges of the operating voltage range do not overlap.
12. The method of claim 8 wherein each of the driving voltages transitions between a low voltage and a high voltage when the control voltage passes an offset voltage, and wherein at least one of the low voltage, the high voltage, or the offset voltage differs for at least two of the optical modulator segments.
13. The method of claim 12 wherein at least some of the driving voltages are independent on the control voltage at the edges of the operating voltage range.
14. The method of claim 12 wherein at least some of the driving voltages are generally independent of the control voltage across most of the operating voltage range.
15. The method of claim 6 , comprising comparing the control voltage for one of the optical modulator segments to a threshold set therefor.
16. The method of claim 15 , comprising changing a driving voltage to the one of the optical modulator segments when the control voltage crosses the threshold.
17. The method of claim 12 , wherein the offset voltage for each successive optical modulator segment is greater than the offset voltage for a preceding optical modulator segment.