DISTRIBUTED TRAVELLING-WAVE MACH-ZEHNDER MODULATOR DRIVER
A distributed traveling-wave Mach-Zehnder modulator driver having a plurality of modulation stages that operate cooperatively (in-phase) to provide a signal suitable for use in a 100 Gb/s optical fiber transmitter at power levels that are compatible with conventional semiconductor devices and conventional semiconductor processing is described.
This application claims priority to and the benefit of co-pending U.S. patent application Ser. No. 16/398,422, filed Apr. 30, 2019, now allowed, which claims priority to and benefit of U.S. patent application Ser. No. 16/220,203, filed Dec. 14, 2018, now U.S. Pat. No. 10,320,488, which claims priority to co-pending U.S. patent application Ser. No. 16/108,857, filed Aug. 22, 2018, now U.S. Pat. No. 10,205,531 which claims priority to and benefit of co-pending U.S. patent application Ser. No. 15/830,351, filed Dec. 4, 2017, now U.S. Pat. No. 10,084,545, which claims priority from U.S. patent application Ser. No. 15/234,359, filed Aug. 11, 2016, now U.S. Pat. No. 9,853,738, which is a continuation-in-part of and claims priority from U.S. patent application Ser. No. 14/618,989, filed Feb. 10, 2015, issued as U.S. Pat. No. 9,559,779, which claims priority to U.S. Provisional Application No. 61/937,683 filed Feb. 10, 2014, each of which is hereby incorporated by reference herein in its entirety.
FIELD OF THE INVENTIONThe invention relates to optical transmitters in general, and particularly to an optical driver for a Gigabit/second transmitter.
BACKGROUND OF THE INVENTIONOptical interconnects offer promising solutions to data transmission bottlenecks in supercomputers and in data-centers as well as other applications. Adopting higher channel data rates can greatly reduce the complexity in optical communication systems and/or further improve interconnect capacity and density.
The most important requirement on the driver amplifier is the output voltage swing. The state-of-the-art driver amplifier in CMOS/BiCMOS can output 3 Vpp at 40 Gb/s, consuming 1.35 W DC power. See for example, C. Knochenhauer, J. Scheytt, and F. Ellinger, “A Compact, Low-Power 40-GBit/s Modulator Driver With 6-V Differential Output Swing in 0.25 um SiGe BiCMOS,” Solid-State Circuits, IEEE Journal of, vol. 46, no. 5, pp. 1137-1146, 2011.
At higher data rates it is difficult to maintain or improve the available drive voltage without substantial advances in the fabrication process. This trend is at odds with the increasingly higher drive voltage required by modulators at higher speed.
There is a need for improved drivers for use in optical data handling systems.
SUMMARY OF THE INVENTIONAccordingly, the present disclosure relates to a modulator, comprising: an optical input waveguide for receiving an input optical signal and splitting the input optical signal into a first portion and a second portion; a plurality of sequential modulators connected to the optical input waveguide for receiving the first portion and the second portion; an optical output port for recombining the first portion and the second portion into a modulated output optical signal; a differential electrical data input connected to a data source; a plurality of driver-amplifier stages, each including a respective differential driver amplifier input, a respective differential driver amplifier output, and a respective differential signal output connected to a respective one of the sequential modulators, the respective differential driver amplifier input of a first of the plurality of driver-amplifier stages connected to the differential electrical data input; and a plurality of delay/relay stages, each including a respective differential delay/relay input connected to the respective differential driver amplifier output of a previous one of the plurality of driver-amplifier stages, and a differential delay/relay output connected to the respective differential driver amplifier input of a following one of the plurality of driver-amplifier stages.
An optical delay of each of the plurality of sequential modulators along with optical waveguide wiring therebetween matches a delay between the driver amplifier stages so that modulations constructively add.
The foregoing and other objects, aspects, features, and advantages of the invention will become more apparent from the following description and from the claims.
The objects and features of the invention can be better understood with reference to the drawings described below, and the claims. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the drawings, like numerals are used to indicate like parts throughout the various views.
As illustrated in
We describe systems and methods to provide ultra-high channel rate (40 to 100 Gb/s) optical transmitters in silicon-based electronics and photonics technology.
We have described another design of a traveling wave modulator in Ran Ding, Yang Liu, Qi Li, Yisu Yang, Yangjin Ma, Kishore Padmaraju, Andy Eu-Jin Lim, Guo-Qiang Lo, Keren Bergman, Tom Baehr-Jones, and Michael Hochberg, “Design and characterization of a 30-GHz bandwidth low-power silicon traveling-wave modulator,” Optics Communications (available online Feb. 7, 2014).
In various embodiments of the present invention, the following assumptions are made: Cpn is 230 fF/mm, Rpn is 5.5 Ω-mm, Vπ Lπ is 2.0 V-cm, device bandwidth is 70% data rate, a differential-drive geometry is used, and an equivalent of Vπ/3 swing generate acceptable optical modulation amplitude. As an example, we describe a distributed TWMZ driver that can be fabricated in a 130-nm SiGe BiCMOS process in order to bridge the gap between the increasingly higher drive-voltage required by modulators and limited available driver output voltage swing from electronics at higher data rates.
As shown in the circuit block diagram in
In the preferred embodiment of
In other embodiments, one can use other kinds of optical phase shifters in place of the TWMZ, so long as the number of optical phase shifters is greater than or equal to 2.
In one embodiment, the integration interface between silicon TWMZ sections and the driver circuits is expected to be flip-chip bump-bonding. A 40 fF parasitic capacitance is assumed for each signal connection. The optical delay of each TWMZ section plus optical waveguide wiring matches the delay between the amplifier stages so that the modulations constructively add. As an additional step to improve the performance, we have incorporated pre-amplification in the driver output to extend the length of TWMZ sections that can be driven at 100 Gb/s by about 40%. The driver pre-amplifier stage 254a and 254b is shown in
The example circuit described above consumes 1.5 W power overall. The DC bias structures illustrated on the right of the chip (
In the embodiment shown in
Post-layout simulations at 100 Gb/s is shown in
In the driving scheme used in the embodiment of
In operation, an optical wave (or an optical signal) to be modulated is expected to be received at an input port such as 220, subjected to a succession of N modulations performed by successive ones of a plurality N a plurality N of optical phase-shifters connected in series connection as N sequential modulators, where N is greater than or equal to 2, each of the N−1 phase shifts after the first of the N phase shifts delayed by a time calculated to apply each of the N−1 phase shifts after the first of the N phase shifts at a respective time when the optical signal passes a respective one of the N−1 sequential modulators after the first modulator, and providing a modulated optical signal at an optical output port, such as port 240.
The apparatus described above can be used for performing such optical modulation as just described.
DefinitionsUnless otherwise explicitly recited herein, any reference to an electronic signal or an electromagnetic signal (or their equivalents) is to be understood as referring to a non-volatile electronic signal or a non-volatile electromagnetic signal.
Theoretical DiscussionAlthough the theoretical description given herein is thought to be correct, the operation of the devices described and claimed herein does not depend upon the accuracy or validity of the theoretical description. That is, later theoretical developments that may explain the observed results on a basis different from the theory presented herein will not detract from the inventions described herein.
Any patent, patent application, patent application publication, journal article, book, published paper, or other publicly available material identified in the specification is hereby incorporated by reference herein in its entirety. Any material, or portion thereof, that is said to be incorporated by reference herein, but which conflicts with existing definitions, statements, or other disclosure material explicitly set forth herein is only incorporated to the extent that no conflict arises between that incorporated material and the present disclosure material. In the event of a conflict, the conflict is to be resolved in favor of the present disclosure as the preferred disclosure.
While the present invention has been particularly shown and described with reference to the preferred mode as illustrated in the drawing, it will be understood by one skilled in the art that various changes in detail may be affected therein without departing from the spirit and scope of the invention as defined by the claims.
Claims
1-19. (canceled)
20. A modulator, comprising:
- an optical input waveguide for receiving an input optical signal and splitting the input optical signal into a first portion and a second portion;
- a plurality of sequential modulators connected to the optical input waveguide for receiving the first portion and the second portion;
- an optical output port for recombining the first portion and the second portion into a modulated output optical signal;
- a differential electrical data input connected to a data source;
- a plurality of driver-amplifier stages, each including a respective differential driver amplifier input, a respective differential driver amplifier output, and a respective differential signal output connected to a respective one of the sequential modulators, the respective differential driver amplifier input of a first of the plurality of driver-amplifier stages connected to the differential electrical data input; and
- a plurality of delay/relay stages, each including a respective differential delay/relay input connected to the respective differential driver amplifier output of a previous one of the plurality of driver-amplifier stages, and a differential delay/relay output connected to the respective differential driver amplifier input of a following one of the plurality of driver-amplifier stages;
- wherein an optical delay of each of the plurality of sequential modulators plus optical waveguide wiring matches a delay between the driver-amplifier stages so that modulations constructively add.
21. The modulator according to claim 20, wherein each respective differential signal output is configured to comprise an open-collector driver for driving sequential modulators with different impedances.
22. The modulator according to claim 20, wherein each respective differential signal output is configured to comprise an open-collector cascode driver for driving the sequential modulators with different impedances.
23. The modulator according to claim 22, wherein each respective differential signal output is configured to comprise an open-collector driver for driving the sequential modulators with both 25Ω and 50Ω impedances.
24. The modulator according to claim 20, further comprising:
- a plurality of DC bias structures, each DC bias structure configured to individually control one of said plurality of delay/relay stages;
- wherein each DC bias structures is configured to control an on state and an off state of a respective delay/relay stage for shutting down individual delay/relay stages.
25. The modulator according to claim 24, wherein the DC bias structures are also configured to control on and off states of a respective on of the plurality of driver-amplifier stages for shutting down individual driver amplifier stages.
26. The modulator according to claim 24, wherein each DC bias structures is also configured to control variation in biasing voltages of a respective one of the driver-amplifier stages.
27. The modulator according to claim 20, further comprising:
- a plurality of DC bias structures, each DC bias structure configured to individually control one of the plurality of driver amplifier stages;
- wherein each DC bias structures is configured to control an on state and an off state of a respective one of the driver-amplifier stages for shutting down individual driver amplifier stages.
28. The modulator according to claim 27, further comprising:
- wherein each DC bias structures is also configured to control variation in biasing voltages of a respective one of the driver-amplifier stages.
29. The modulator according to claim 20, further comprising:
- a plurality of DC bias structures, each DC bias structure configured to individually control one of the plurality of driver amplifier stages;
- wherein each DC bias structures is configured to control variation in biasing voltages of a respective one of the driver-amplifier stages.
30. The modulator according to claim 20, wherein each one of the driver-amplifier stages includes only a single type of transistor to enable high-speed operation.
31. The modulator according to claim 20, wherein each one of the plurality of driver amplifier stages includes a pre-amplifier stage.
32. The modulator according to claim 20, wherein the plurality of sequential modulators comprise a plurality of optical phase-shifter pairs connected in series.
33. The modulator according to claim 32, wherein each one of the plurality of phase-shifter pairs comprises a fixed optical length.
34. The modulator according to claim 32, wherein each one of the plurality of optical phase shifter pairs comprises a Mach-Zehnder interferometer modulator.
35. The modulator according to claim 20, wherein each of the first portion and the second portion comprise equal intensities.
36. The modulator according to claim 20, wherein the plurality of driver amplifier stages comprises four, and the plurality of delay/relay stages comprises three.
37. The modulator according to claim 20, wherein each one of the plurality of driver amplifier stages includes:
- a first pair of emitter followers including termination resistors connected to the respective differential driver amplifier input;
- a pre-amplifier comprising a differential pair;
- a buffer comprising a second pair of emitter followers; and
- means for splitting a differential input signal into first and second differential output signals for output the respective differential driver amplifier output, and the respective differential signal output, respectively.
38. The modulator according to claim 20, wherein the plurality of sequential modulators, the optical input waveguide, and the optical output port are integrated on a semiconductor chip; and wherein the differential electrical data input, the plurality of driver amplifier stages, and the plurality of delay/relay stages comprise drive circuitry attached to the semiconductor chip.
39. The modulator according to claim 38, further comprising flip-chip bump bonding for attaching the drive circuitry to the semiconductor chip.
Type: Application
Filed: Nov 28, 2019
Publication Date: Jun 11, 2020
Inventors: Ran Ding (New York, NY), Thomas Wetteland Baehr-Jones (Arcadia, CA), Michael J. Hochberg (New York, NY), Alexander Rylyakov (Staten Island, NY)
Application Number: 16/699,082