Monitoring a multiplexed laser array in an optical communication system

Patent metadata

Field	Value
Publication number	US-9455782-B2
Application number	US-201414456124-A
Country	US
Kind code	B2
Filing date	Aug 11, 2014
Priority date	Aug 11, 2014
Publication date	Sep 27, 2016
Grant date	Sep 27, 2016

Abstract

Individual channels of a multiplexed laser array in a multi-channel optical transmitter are monitored at an output of an optical multiplexer. The monitoring may be used to confirm proper operation of each of the channels in the multiplexed laser array and/or to perform wavelength locking on each of the channels. Monitoring at the output of the optical multiplexer avoids the use of multiple photodetectors coupled directly to multiple lasers in the multiplexed laser array. The multiplexed laser array generally includes a plurality of laser emitters optically coupled to an optical multiplexer such as an arrayed waveguide grating (AWG). An optical transmitter with a monitored multiplexed laser array may be used, for example, in an optical line terminal (OLT) in a wavelength division multiplexed (WDM) passive optical network (PON) or in any other type of WDM optical communication system capable of transmitting optical signals on multiple channel wavelengths.

First claim

What is claimed is:

1. A multi-channel optical transmitter comprising:
a plurality of laser emitters having electrical inputs for receiving electrical signals including data signals and optical outputs for outputting modulated optical signals, wherein each of the laser emitters is associated with a channel and a channel wavelength;
an optical multiplexer including a plurality of input ports optically coupled to the optical outputs of the laser emitters, respectively, the optical multiplexer being configured to receive the modulated optical signals from the laser emitters and to produce a multiplexed optical signal including the modulated optical signals at a plurality of different channel wavelengths, respectively;
a monitoring signal generator coupled to the electrical inputs of the laser emitters, the monitoring signal generator being configured to generate a monitoring signal and to provide the monitoring signal to the electrical input of one of the laser emitters, wherein the monitoring signal generator is configured to provide the monitoring signal to each of the laser emitters consecutively for a predefined period of time; and
a monitoring system optically coupled to an output of the optical multiplexer, wherein the monitoring system includes a photodetector for detecting a portion of the multiplexed optical signal, a filter for separating the monitoring signal, and a power monitor for monitoring a power level of the monitoring signal to determine if the one of the laser emitters outputting the modulated optical signal including the monitoring signal is emitting at the associated channel wavelength.

2. The multi-channel optical transmitter of claim 1 wherein the laser emitters include distributed feedback (DFB) lasers configured to emit light at the channel wavelengths associated with the DFB lasers, respectively.

3. The multi-channel optical transmitter of claim 1 wherein each of the laser emitters includes a Fabry-Perot (FP) laser for emitting light across a range of wavelengths including multiple channel wavelengths, and wherein the optical multiplexer is configured to filter the light from each of the FP lasers at the associated channel wavelength.

4. The multi-channel optical transmitter of claim 1 wherein each of the laser emitters includes a gain region for emitting light across a range of wavelengths including the channel wavelengths and a back reflector for reflecting light from the laser emitters, wherein the optical multiplexer is configured to filter light received on each of the input ports, respectively, at the different channel wavelengths and to provide the filtered light to the output port, and further including an exit reflector coupled to the output port of the optical multiplexer, the exit reflector being configured to reflect at least a portion of the filtered light back to the gain regions in the respective laser emitters such that lasing cavities are formed between the back reflectors of each of the laser emitters and the exit reflector and lasing occurs at each of the channel wavelengths reflected back to the respective gain regions of the respective laser emitters.

5. The multi-channel optical transmitter of claim 1 wherein the laser emitters include an array of Fabry-Perot (FP) gain chips, and further including an exit reflector at an output of the optical multiplexer, wherein external laser cavities are formed between the FP gain chips and the exit reflector, wherein the external laser cavities are configured to emit light at the channel wavelengths, respectively.

6. The multi-channel optical transmitter of claim 1 wherein the optical multiplexer is an arrayed waveguide grating (AWG).

7. The multi-channel optical transmitter of claim 1 wherein the laser emitters are tunable to one of the channel wavelengths, and further comprising a wavelength tuning system coupled to the monitoring system and to each of the laser emitters, the wavelength tuning system being configured to tune at least one of the laser emitters to one of the channel wavelengths in response to the power level of the monitoring signal obtained from the multiplexed optical signal.

8. The multi-channel optical transmitter of claim 7 wherein the wavelength tuning system includes a temperature control system configured to control a temperature of the laser emitters for tuning the laser emitters.

9. A method of monitoring a multiplexed laser array, the method comprising:
modulating a plurality of channels of the multiplexed laser array with respective data signals and multiplexing to produce a multiplexed optical data signal at an output of the multiplexed laser array;
consecutively modulating each of the channels of the multiplexed laser array for a predefined period of time with a monitoring signal to produce a monitoring optical signal together with the multiplexed optical data signal at the output the multiplexed laser array, wherein the monitoring signal has a lower amplitude and frequency than the data signals;
tapping a portion of an optical output of the multiplexed laser array;
detecting the portion of the optical output of the multiplexed laser array;
filtering the detected portion of the optical output of the multiplexed laser array to obtain the monitoring signal; and
determining a power of the monitoring signal to consecutively monitor each of the channels of the multiplexed laser array to determine if the one of the laser emitters outputting the modulated optical signal including the monitoring signal is emitting at the associated channel wavelength.

10. The method of claim 9 wherein the multiplexed laser array includes an arrayed waveguide grating (AWG) and a plurality of distributed feedback (DFB) lasers coupled to respective inputs of the AWG and configured to emit light at different channel wavelengths.

11. The method of claim 9 wherein the multiplexed laser array includes an arrayed waveguide grating (AWG), an array of Fabry-Perot (FP) gain chips coupled to respective inputs of the AWG, and an exit reflector at an output of the AWG, wherein external laser cavities are formed between back reflectors of the FP gain chips and the exit reflector, and wherein each of the external laser cavities is configured to emit light at a different channel wavelength.

12. The method of claim 9 further comprising tuning the at least one channel of the multiplexed laser array to a channel wavelength in response to the power of the monitoring signal at the output of the multiplexed laser array.

13. A multi-channel optical transceiver module comprising:
a transceiver housing;
a multi-channel receiver optical sub-assembly (ROSA) located in the transceiver housing, the ROSA being configured to receive a wavelength division multiplexed (WDM) optical signal on multiple channel wavelengths; and
a multi-channel transmitter optical sub-assembly (TOSA) located in the transceiver housing, the TOSA being configured to transmit a wavelength division multiplexed (WDM) optical signal on multiple channel wavelengths, the TOSA comprising:
a plurality of laser emitters having electrical inputs for receiving electrical signals including data signals and optical outputs for outputting modulated optical signals, wherein each of the laser emitters is associated with a channel and a channel wavelength;
an optical multiplexer including a plurality of input ports optically coupled to the optical outputs of the laser emitters, respectively, the optical multiplexer being configured to receive the modulated optical signals from the laser emitters and to produce a multiplexed optical signal including the modulated optical signals at a plurality of different channel wavelengths, respecti

Assignees

• Applied Optoelectronics Inc

Inventors

• Zheng Jun
• Wang Yi
• Ho I-Lung
• Anselm Klaus Alexander
• Zhang Huanlin

Classifications

• H01S5/0683

  by monitoring the optical output parameters · CPC title

• H04J14/02

  Wavelength-division multiplex systems · CPC title

• H04B10/07955 Primary

  Monitoring or measuring power · CPC title

• H01S5/4025

  Array arrangements, e.g. constituted by discrete laser diodes or laser bar (H01S5/42 takes precedence) · CPC title

• H04B10/503

  Laser transmitters · CPC title