Integrated unaligned resonant modulator tuning

Patent metadata

Field	Value
Publication number	US-9780870-B1
Application number	US-201414502062-A
Country	US
Kind code	B1
Filing date	Sep 30, 2014
Priority date	Sep 30, 2014
Publication date	Oct 3, 2017
Grant date	Oct 3, 2017

Abstract

Methods and systems for tuning a resonant modulator are disclosed. One method includes receiving a carrier signal modulated by the resonant modulator with a stream of data having an approximately equal number of high and low bits, determining an average power of the modulated carrier signal, comparing the average power to a predetermined threshold, and operating a tuning device coupled to the resonant modulator based on the comparison of the average power and the predetermined threshold. One system includes an input structure, a plurality of processing elements, and a digital control element. The input structure is configured to receive, from the resonant modulator, a modulated carrier signal. The plurality of processing elements are configured to determine an average power of the modulated carrier signal. The digital control element is configured to operate a tuning device coupled to the resonant modulator based on the average power of the modulated carrier signal.

First claim

What is claimed:

1. A method for operating a resonant modulator having a tunable resonance, comprising the steps of:
receiving a stream of data encoded to have an approximately equal number of high and low bits;
in the resonant modulator, modulating a carrier signal having a carrier wavelength with the coded stream of data;
transmitting the modulated carrier signal;
from an extracted portion of the modulated carrier signal, determining an average power of the modulated carrier signal over a predetermined number of bits;
comparing the average power to a predetermined threshold equal to an expected power value based on the assumption that half the number of data bits in the modulated carrier signal are high bits;
incrementing a counter when the average power is greater than the predetermined threshold;
decrementing the counter when the average power is not greater than the predetermined threshold; and
operating a tuning device coupled to the resonant modulator based on a value of the counter;
wherein the average power is determined as a running average that varies over time;
wherein the comparing, the incrementing, the decrementing, and the operating of a tuning device are performed at repeated intervals without interrupting the receiving, the modulating, and the transmitting; and
wherein the tuning device is operated so as to optimize a non-zero frequency offset between the tunable modulator resonance and the carrier wavelength at which equal numbers of high and low data bits are in the modulated carrier signal.

2. The method of claim 1 , wherein
when the count value is greater than another predetermined threshold, the tuning device is turned on, and
when the count value is not greater than the other predetermined threshold, the tuning device is turned off.

3. The method of claim 1 , wherein the determining step comprises:
integrating the extracted portion of the modulated carrier signal with an integrator.

4. The method of claim 3 , wherein the counter is incremented or decremented once for every N bits of the data used to modulate the carrier signal, where N is a number from 10 to 500.

5. The method of claim 1 , wherein the determining step comprises:
counting a number of high bits in the extracted modulated carrier signal with another counter to obtain a running count value as the average power of the modulated carrier signal.

6. The method of claim 5 , wherein the counter is incremented or decremented once for every N bits of the data used to modulate the carrier signal, where N is a number from 10 to 500.

7. The method of claim 1 , wherein the tuning device is a heater configured to adjust a temperature of the resonant modulator.

8. A system comprising:
an encoder configured to produce a stream of encoded data having an approximately equal number of high and low bits;
a resonant modulator having a tunable resonance and configured to receive the encoded data stream from the encoder, to modulate the encoded data stream onto a carrier signal having a carrier wavelength, thereby providing a modulated carrier signal, and to transmit the modulated carrier signal;
an input structure configured to receive, from the resonant modulator, a portion of the modulated carrier signal;
a plurality of processing elements configured to determine a time-varying running average power of the modulated carrier signal over a predetermined number of bits of the stream of data; and
a digital control element configured to operate, at repeated intervals, a tuning device coupled to the resonant modulator based on the average power of the modulated carrier signal over the predetermined number of bits without interrupting the transmission of the modulated carrier signal by the resonant modulator; wherein:
the resonant modulator is configured to modulate the carrier signal at a non-zero frequency offset between the tunable modulator resonance and the carrier wavelength;
the digital control element is configured to urge the resonant modulator toward an optimal frequency offset at which equal numbers of high and low data bits are in the modulated carrier signal;
the plurality of processing elements includes an integrator and a counter;
the integrator is configured to integrate the modulated carrier signal to obtain a running average power value; and
the counter is configured to increment or decrement a count based on comparing the running average power value to a predetermined threshold equal to an expected power value based on the assumption that half the number of data bits in the modulated carrier signal are high bits.

9. The system of claim 8 , wherein the input structure comprises an evanescent coupling structure.

10. The system of claim 8 , wherein the plurality of processing elements include:
a first counter configured to count a number of high bits of the data used to modulate the carrier signal to obtain a running count value; and
a second counter configured to increment or decrement a count based on the running count value, wherein the count represents the average power of the modulated carrier signal.

11. The system of claim 8 , wherein the digital control element comprises a digital to analog converter.

12. The system of claim 8 , wherein the digital control element comprises a digital pulse-width modulator.

13. The system of claim 8 , wherein the tuning device is a heater configured to adjust a temperature of the resonant modulator.

14. The system of claim 13 , further comprising the heater.

Assignees

• Sandia Corp
• Sandia Llc Nat Tech & Eng Solutions

Inventors

• Zortman William A
• Lentine Anthony L

Classifications

• H04B10/572

  Wavelength control · CPC title

• H04B10/5057 Primary

  using a feedback signal generated by analysing the optical output · CPC title

• H04B10/516

  Details of coding or modulation · CPC title

• H04B10/524

  Pulse modulation · CPC title

• H04B10/07955 Primary

  Monitoring or measuring power · CPC title