MZM linear driver for silicon photonics device characterized as two-channel wavelength combiner and locker

Patent metadata

Field	Value
Publication number	US-9874800-B2
Application number	US-201615247091-A
Country	US
Kind code	B2
Filing date	Aug 25, 2016
Priority date	Aug 28, 2014
Publication date	Jan 23, 2018
Grant date	Jan 23, 2018

Abstract

The present invention includes a Mach-Zehnder modulator (MZM) linear driver configured in a differential form with two waveguides carrying two traveling waves which supports a two-channel spectral combiner integrated with a wavelength locker. By coupling a DC current source supplied with a modulation voltage with each segment thereof for providing electrical modulation signal overlapping with each of the two traveling waves. The modulated traveling waves in the two waveguides then are combined in one output signal by a multimode interference coupler. Two optical signals at ITU grid channels are separately modulated by two MZMs and combined into a silicon waveguide-based delayed-line interferometer built on a SOI substrate to produce an output signal having a free spectral range equal to twice of the spacing of the two ITU grid channels. Two dither signals can be added respectively to the two optical signals for identifying and locking corresponding two channel wavelengths.

First claim

What is claimed is:

1. A MZM linear driver applicable for wavelength combiner and locker through silicon photonics, the MZM linear driver comprising:
a first MZM material having a first length connecting a first electrode to a second electrode to transmit a first optical wave split from an input optical signal by a 1×2 MMI coupler;
a second MZM material having the first length connecting a third electrode to a fourth electrode to transmit a second optical wave split from the input optical signal by the 1×2 MMI coupler;
a DC coupled current source configured to couple between the first electrode and the third electrode to supply a modulation current flowing through respectively the first MZM material and the second MZM material driven by a modulation voltage coupled in-parallel the second electrode and the fourth electrode;
a middle electrode having a second length disposed in parallel to the first MZM material and the second MZM material and subjecting to a bias voltage effectively on a first p-n junction across the middle electrode and the first MZM material of the first length and a second p-n junction across the middle electrode and the second MZM material of the first length, the second length being greater than or equal to the first length.

2. The MZM linear driver of claim 1 wherein the first MZM material and the second MZM material are substantially a same silicon-based material formed on a buried oxide layer in a SOI structure and doped with n-type electrical impurity.

3. The MZM linear driver of claim 1 wherein the middle electrode comprises a semiconductor material doped with p-type electrical impurity.

4. The MZM linear driver of claim 1 wherein the first MZM material and the second MZM material forms a differential Mach-Zehnder modulator to provide an amplitude modulation respectively to a first traveling wave through the first MZM material and a second traveling wave through the second MZM material.

5. The MZM linear driver of claim 4 wherein the amplitude modulation is based on a format selected from a NRZ format or a PAM format.

6. The MZM linear driver of claim 4 wherein the amplitude modulation comprises a swing voltage ranged between the modulation voltage and the modulation voltage minus the modulation current times a resistance associated with the first length of the first and the second MZM material.

7. The MZM linear driver of claim 4 further comprising a pair of thermo-optical controllers located after the second end of each of the first MZM material and the second MZM material for setting operating point on a transfer function associated with each of the first traveling wave and the second traveling wave and tuning a splitting ratio of optical power between the first traveling wave and the second traveling wave for getting an power offset and a chirp during transmission.

8. The MZM linear driver of claim 4 further comprising a 2×2 multimode interference (MMI) coupler having two input branches to combine the first traveling wave and the second traveling wave after NRZ or PAM modulation and a first output branch for outputting an output optical signal with amplitude modulation and a second output branch terminated by a photodetector for generating a feedback control signal.

9. The MZM linear driver of claim 1 wherein the DC coupled current source is configured to have an electrical ground decoupled from the bias voltage applied from the middle electrode.

10. The MZM linear driver of claim 1 wherein the first/second p-n junction is electrically equivalent to a first/second plurality of diodes connected in parallel between the middle electrode and the first/second MZM material and subjected to the bias voltage to set a minimum level of NRZ or PAM modulation.

11. A silicon photonics device on a substrate for combining two optical signals modulated by MZM while locking corresponding wavelengths, comprising:
a first waveguide having a first path length from a first end to a second end laid in a first region of the substrate;
a second waveguide having a second path length from a third end to a fourth end, the second path length being longer than the first path length by a delayed-line length laid in a second region of the substrate;
a heater component overlying substantially entire second region of the substrate;
a first 2×2 MMI coupler having a first input branch receiving a first optical signal of a first wavelength modulated by a first MZM linear driver of claim 1 and a second input branch receiving a second input optical signal of a second wavelength modulated by a second MZM linear driver of claim 1 , and having a first output branch connected to the first end of the first waveguide and a second output branch connected to the third end of the second waveguide;
a second 2×2 MMI coupler configured to connect the second end of the first waveguide and the fourth end of the second waveguide and to output an output optical signal either to a first output port or to a second output port or to both ports in complementary manner tunable by the heater component, the output optical signal comprising a first interference spectrum of the first optical signal with a first free spectral range associated with the first wavelength interleaved with a second interference spectrum of the second optical signal with a second free spectral range associated with the second wavelength;
wherein the delayed-line length is configured to determine the first free spectral range being equal to the second free spectral range and equal to twice of difference between the first wavelength and the second wavelength as the first wavelength and the second wavelength are respectively locked to corresponding channels of ITU grid by tuning the heater component.

12. The silicon photonics device of claim 11 wherein the first optical signal comprises a laser signal at the first wavelength selected from any channel of ITU grid and the second signal comprises a laser signal at the second wavelength selected from any channel of ITU grid excluding the first wavelength.

13. The silicon photonics device of claim 12 wherein the ITU grid comprises a channel spacing selected from 50 GHz, 25 GHz, and 12.5 GHz.

14. The silicon photonics device of claim 11 wherein each of the first interference spectrum and the second interference spectrum comprises a passband characterized by the first wavelength and the second wavelength respectively at a peak of the passband.

15. The silicon photonics device of claim 11 wherein the first waveguide laid in a first region of the substrate comprises silicon material arranged in a linear shape having a length substantially equal to the first path length.

16. The silicon photonics device of claim 11 wherein the second waveguide laid in a second region of the substrate comprises silicon material arranged in a double spiral linear shape having a cross dimension of about half of the first path length.

17. The silicon photonics device of claim 11 wherein the first optical signal and the second optical signal are configured to respectively mix with a first dither signal employed in the first MZM linear driver and a second dither signal employed in the second MZM linear driver, each of the first dither signal and the second dither signal having a different frequency from either the first optical signal or the second optical signal.

18. The silicon photonics device of claim 17 further comprising a low percentage tap coupler connecting to the second output port terminated by a photodiode for collecting and converting a fraction of optical power of the outp

Assignees

• Inphi Corp

Inventors

• Nagarajan Radhakrishnan L

Classifications

• G02F2001/212

  Physics · mapped topic

• G02F1/225

  in an optical waveguide structure · CPC title

• G02F1/0121

  Operation of devices; Circuit arrangements, not otherwise provided for in this subclass · CPC title

• G02F1/0123

  Circuits for the control or stabilisation of the bias voltage, e.g. automatic bias control [ABC] feedback loops · CPC title

• G02F1/025

  in an optical waveguide structure (G02F1/017, {G02F1/2257} take precedence) · CPC title