Linearization of optical intensity modulation systems
View Patent ↗Embodiments for improving the Signal to Noise and Distortion (SINAD) ratio in Pulse Amplitude Modulation (PAM)-M optical intensity modulation systems, to enable higher data rate communications, are provided. Embodiments can be used to improve the linearity and reduce the distortion of electrical and electro-optics components (including optical modulators) in optical intensity modulation systems. Embodiments are well suited for use with PAM-M optical intensity modulators, such as segmented Vertical Cavity Surface Emitting Laser (WSEL) and segmented Mach-Zehnder Modulator (MZM), for example.
1. An optical intensity modulation system, comprising:
a segmented optical intensity modulator having a plurality of segments;
a binary driver configured to receive an optical amplitude level and to convert the optical amplitude level to a plurality of binary bits, wherein each of the plurality of binary bits is configured to control an optical intensity output of a respective one of the plurality of segments of the segmented optical intensity modulator; and
a plurality of transmit paths each configured to couple a respective one of the plurality of binary bits to a respective one of the plurality of segments of the segmented optical intensity modulator,
wherein a first transmit path of the plurality of transmit paths includes a programmable delay element configured to equalize a delay between the first transmit path and at least a second transmit path of the plurality of transmit paths.
2. The optical intensity modulation system of claim 1 , wherein the first transmit path is further configured to couple a first binary bit of the plurality of binary bits to a first segment of the plurality of segments, wherein the second transmit path is further configured to couple a second binary bit of the plurality of binary bits to a second segment of the plurality of segments, and wherein a produced intensity level of the second segment is twice a produced intensity level of the first segment.
3. The optical intensity modulation system of claim 1 , wherein each of the plurality of binary bits is further configured to control the optical intensity output of its respective one of the plurality of segments between a low intensity level and a high intensity level.
4. The optical intensity modulation system of claim 1 , wherein the programmable delay element is further configured to compensate for a capacitive loading difference between the second transmit path and the first transmit path.
5. The optical intensity modulation system of claim 1 , wherein the programmable delay element includes a capacitor.
6. The optical intensity modulation system of claim 1 , wherein the first transmit path of the plurality of transmit paths further includes a DC offset module configured to equalize a DC offset between the first transmit path and at least the second transmit path of the plurality of transmit paths.
7. The optical intensity modulation system of claim 6 , further comprising:
a photo diode configured to receive a combined output of the plurality of segments; and
a controller configured to control at least one of the programmable delay element and the DC offset module responsive to the combined output of the plurality of segments.
8. The optical intensity modulation system of claim 1 , wherein a number of the plurality of segments is greater than 2.
9. The optical intensity modulation system of claim 1 , wherein the segmented optical intensity modulator includes a segmented Vertical Cavity Surface Emitting Laser (VCSEL) or a segmented Mach-Zelmder Modulator (MZM).
10. An optical intensity modulation system, comprising:
a segmented optical intensity modulator having a plurality of segments;
sub-binary radix driver configured to receive an optical amplitude level and to convert the optical amplitude level based on a sub-binary nominal radix to a plurality of binary bits, wherein each of the plurality of binary bits is configured to control an optical intensity output of a respective one of the plurality of segments of the segmented optical intensity,modulator: and
a plurality of transmit paths each configured to couple a respective one of the plurality of binary bits to a respective one of the plurality of segments of the segmented optical intensity modulator.
11. The optical intensity modulation system of claim 10 , wherein the plurality of segments include a first segment and a second segment, and wherein a produced intensity level of the second segment is equal to a product of the sub-binary nominal radix and a produced intensity level of the first segment.
12. The optical intensity modulation system of claim 10 , wherein the plurality of segments include a first segment and a second segment, and wherein a produced intensity level of the first segment is proportional to a first sub-binary radix (R i ) and a produced intensity level of the second segment is proportional to a second sub-binary radix (R i+1 ).
13. The optical intensity modulation system of claim 12 , wherein the produced intensity level of the first segment is equal to R i k and the produced intensity level of the second segment is equal to R i+1 k+1 , where k is an integer.
14. The optical intensity modulation system of claim 13 , wherein R i and R i+1 are equal or different.
15. The optical intensity modulation system of claim 10 , further comprising:
a photo diode configured to receive an output of at least one of the plurality of segments; and
a controller configured to control the sub-binary nominal radix responsive to the output.
16. The optical intensity modulation system of claim 10 , further comprising:
a controller configured to receive feedback from a receiver and to control the sub-binary nominal radix responsive to the feedback.
17. The optical intensity modulation system of claim 10 , wherein a first transmit path of the plurality of transmit paths includes a programmable delay element configured to equalize a delay between the first transmit path and at least a second transmit path of the plurality of transmit paths.
18. An optical intensity modulation system, comprising:
a segmented optical intensity modulator having a plurality of segments of equal produced intensity levels;
a binary-to-thermometer coding driver configured to receive an optical amplitude level and to convert the optical amplitude level to a plurality of binary bits, wherein each of the plurality of binary bits is configured to control an optical intensity output of a respective one of the plurality of segments of the segmented optical intensity modulator; and
a plurality of transmit paths each configured to couple a respective one of the plurality of binary bits to a respective one of the plurality of segments of the segmented optical intensity modulator.
19. The optical intensity modulation system of claim 18 , wherein the binary-to-thermometer coding driver is configured to set to a logic high a subset of the plurality of binary bits, and wherein a size of the subset is equal to the optical amplitude level.
20. The optical intensity modulation system of claim 18 , wherein a number of the plurality of segments is equal to a number of possible values of the optical amplitude level.