# US 8,571,410 B2 · Mutual wavelength locking in WDM-PONS

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- Number: US 8,571,410 B2
- Document ID: US8571410B2
- Status: Granted
- Kind: B2
- Application number: 11/546,747
- Filed: 2006-10-11
- Published: 2008-04-17
- Granted: 2013-10-29
- Earliest claimed: 2006-10-11
- Assignees: Novera Optics, Inc.
- Applicants: Wayne V. Sorin; Pavle Sedic
- Inventors: Wayne V. Sorin; Pavle Sedic
- Web page: https://patentgrep.com/patent/US8571410B2

## CPC

- H04J 14/0305: {in end terminals}
- H04J: MULTIPLEX COMMUNICATION (transmission in general H04B; peculiar to transmission of digital information H04L5/00; systems for the simultaneous or sequential transmission of more than one television signal H04N7/08; in exchanges H04Q11/00; stereophonic systems H04S)

## Abstract

Methods and apparatuses to provide wavelength locked WDM Passive Optical Networks (“PONs”) are described. A first transceiver transmits a set of optical signals in a first direction along a wavelength channel. A second transceiver transmits another set of optical signals along the same wavelength channel in another direction. The wavelength of the first transceiver is locked using an optical power of the optical signals of the second transceiver. The wavelength of the second transceiver is locked using the optical power of the optical signals of the first transceiver. A WDM MUX/De-MUX is coupled between the first transceiver and the second transceiver. An in-line gain element can be coupled to the WDM MUX/De-MUX to amplify the optical signals. The first transceiver and the second transceiver operate in a saturated gain condition.

## Claims

### Claim 1

An apparatus, comprising:
a first transceiver to transmit a first set of optical signals in a first direction along a first wavelength channel; and
a second transceiver coupled to the first transceiver to transmit a second set of optical signals along the first wavelength channel in a second direction opposite to the first direction, wherein the first transceiver is wavelength locked using the second set of optical signals from the second transceiver and the second transceiver is wavelength locked using the first set of optical signals from the first transceiver, wherein the first transceiver saturates gain within a first response time to output the first set of optical signals, wherein the first response time is of the same order of magnitude or shorter than a first time period of data modulation onto the second set of optical signals to remove effects of the data modulation in the second direction that cause noise in the first direction, and the second transceiver saturates gain within a second response time to output the second set of optical signals, wherein the second response time is of the same order of magnitude or shorter than a second time period of the data modulation onto the first set of optical signals to remove effects of the data modulation in the first direction that cause noise in the second direction, wherein the first transceiver and the second transceiver are mutually saturated due to wavelength locking.

### Claim 2 (depends on 1)

The apparatus of claim 1, further comprising:
a wavelength division multiplexing (“WDM”) multiplexer/de-multiplexer (“MUX/De-MUX”) coupled between the first transceiver and the second transceiver.

### Claim 3 (depends on 1)

The apparatus of claim 1, further comprising:
an in-line gain element coupled to the first transceiver.

### Claim 4 (depends on 1)

The apparatus of claim 1, further comprising:
a scrambler coupled to the first transceiver.

### Claim 5 (depends on 1)

The apparatus of claim 1, wherein the transceiver is to operate in a saturated gain condition.

### Claim 6 (depends on 1)

The apparatus of claim 1, wherein the transceiver includes a light source that is a Fabry-Perot laser, a reflective semiconductor optical amplifier, or a vertical cavity laser.

### Claim 7 (depends on 1)

The apparatus of claim 1, wherein the transceiver is polarization insensitive.

### Claim 8 (depends on 1)

The apparatus of claim 1, wherein the first transceiver and the second transceiver are designed to be identical.

### Claim 9

A system, comprising:
a first wavelength division multiplexing multiplexer/de-multiplexer (“WDM MUX/De-MUX”) having a first wavelength channel;
a first transceiver to send a first set of optical signals in a first direction along the first wavelength channel;
a gain element coupled to the WDM MUX/De-MUX; and
a second transceiver coupled to the gain element to send a second set of optical signals in a second direction along the first wavelength channel, wherein the second direction is opposite to the first direction, wherein the first transceiver is wavelength locked using the second set of optical signals, and the second transceiver is wavelength locked using the first set of optical signals, and wherein the first transceiver saturates gain within a first response time to output the first set of optical signals, wherein the first response time is of the same order of magnitude or shorter than a first time period of data modulation onto the second set of optical signals to remove effects of the data modulation in the second direction that cause noise in the first direction and the second transceiver saturates gain within a second response to output the second set of optical signals time, wherein the second response time is of the same order of magnitude or shorter than a second time period of the data modulation onto the first set of optical signals to remove effects of the data modulation in the first direction that cause noise in the second direction, wherein the first transceiver and the second transceiver are mutually saturated due to wavelength locking.

### Claim 10 (depends on 9)

The system of claim 9, further comprising
a monitor to monitor an optical power of the second set of the optical signals to control the gain element.

### Claim 11 (depends on 9)

The system of claim 9, further comprising
a scrambler coupled to the WDM MUX/De-MUX to scramble an optical frequency, an optical polarization, or both.

### Claim 12 (depends on 9)

The system of claim 9, wherein the first transceiver is wavelength locked using an optical power of the second set of the optical signals, and the second transceiver is wavelength locked using an optical power of the first set of the optical signals.

### Claim 13 (depends on 9)

The system of claim 9, wherein each of the first transceiver and the second transceiver is to operate in a saturated gain condition.

### Claim 14 (depends on 9)

The system of claim 9, further comprising
a first power splitter coupled to the first transceiver to split an optical power of the second set of the optical signals; and
a second power splitter coupled to the second transceiver to split the optical power of the first set of the optical signals.

### Claim 15 (depends on 14)

The system of claim 14, wherein the first transceiver and the first power splitter are integrated into an optical chip.

### Claim 16 (depends on 9)

The system of claim 9, wherein the gain element is an Erbium Doped Fiber Amplifier (“EDFA”), a Raman Amplifier, a semiconductor optical amplifier (“SOA”), or any combination thereof.

### Claim 17 (depends on 9)

The system of claim 9, wherein the transceiver is polarization insensitive.

### Claim 18 (depends on 9)

The system of claim 9, further comprising
a second WDM MUX/De-MUX coupled to the gain element;
a third transceiver coupled to the second WDM MUX/De-MUX, and
a third power splitter coupled to the second WDM MUX/De-MUX to send the first set of the optical signals along the first wavelength channel to the second transceiver and the third transceiver using a Time-Division Multiplexing (“TDM”) scheme.

### Claim 19 (depends on 9)

The system of claim 9, wherein the first WDM MUX/De-MUX and the gain element are integrated into an optical chip.

### Claim 20 (depends on 9)

The system of claim 9, wherein a first transmitter of the first transceiver and a second transmitter of the second transceiver are integrated into an array on an optical chip.

### Claim 21 (depends on 9)

The system of claim 9, wherein the first transceiver and the first WDM MUX/De-MUX are integrated into the optical chip.

### Claim 22 (depends on 9)

The system of claim 9, wherein a first receiver of the first transceiver and a second receiver of the second transceiver are integrated into an array on an optical chip.

### Claim 23 (depends on 9)

The system of claim 9, further comprising a saturating laser coupled to adjust a gain of the gain element.

### Claim 24 (depends on 9)

The system of claim 9, further comprising a pump coupled to adjust a gain of the gain element.

### Claim 25

A method, comprising:
transmitting a first set of optical signals along a first wavelength channel in a first direction from a first transceiver;
transmitting a second set of optical signals along the first wavelength channel in a second direction from a second transceiver, wherein the second direction is opposite to the first direction;
locking a first wavelength of the first transceiver using the second set of the optical signals; and
locking a second wavelength of the second transceiver using the first set of the optical signals, wherein the first transceiver saturates gain within a first response time to output the first set of optical signals, wherein the first response time is of the same order of magnitude or shorter than a first time period of data modulation onto the second set of optical signals to remove effects of the data modulation in the second direction that cause noise in the first direction, and the second transceiver saturates gain within a second response time to output the second set of optical signals, wherein the second response time is of the same order of magnitude or shorter than a second time period of the data modulation onto the first set of optical signals to remove effects of the data modulation in the first direction that cause noise in the second direction, wherein the first transceiver and the second transceiver saturate each other due to mutual wavelength locking.

### Claim 26 (depends on 25)

The method of claim 25, further comprising amplifying the set of the optical signals.

### Claim 27 (depends on 25)

The method of claim 25, further comprising scrambling the set of the optical signals.

### Claim 28 (depends on 25)

The method of claim 25, further comprising operating the transceiver in a saturated gain condition.

### Claim 29 (depends on 25)

The method of claim 25, further comprising controlling a mode of the transceiver.

### Claim 30 (depends on 25)

The method of claim 25, further comprising
transmitting a third set of the optical signals along a second wavelength channel from a third transceiver;
multiplexing the first set and the third set to transmit along a transmission medium;
de-multiplexing the first set and the third set to send to the second transceiver and the fourth transceiver;
transmitting a fourth set of the optical signals along the second wavelength channel from a fourth transceiver;
multiplexing the second set and the fourth set to transmit along the transmission medium; and
de-multiplexing the second set and the forth set to send to the first transceiver and the third transceiver.

### Claim 31 (depends on 28)

The method of claim 28, further comprising
routing the first set of the optical signals to the second transceiver using a Time Division Multiplexing (“TDM”) scheme.

### Claim 32

An apparatus, comprising:
means for transmitting a first set of optical signals along a first wavelength channel in a first direction from a first transceiver;
means for transmitting a second set of optical signals along the first wavelength channel in a second direction from a second transceiver, wherein the second direction is opposite to the first direction;
means for locking a first wavelength of the first transceiver using the second set of the optical signals; and
means for locking a second wavelength of the second transceiver using the first set of the optical signals, wherein the first transceiver saturates gain within a first response time to output the first set of optical signals, wherein the first response time is of the same order of magnitude or shorter than a first time period of data modulation onto the second set of optical signals to remove effects of the data modulation in the second direction that cause noise in the first direction, and the second transceiver saturates gain within a second response time to output the second set of optical signals, wherein the second response time is of the same order of magnitude or shorter than a second time period of the data modulation onto the first set of optical signals to remove effects of the data modulation in the first direction that cause noise in the second direction, wherein the first transceiver and the second transceiver are mutually saturated due to wavelength locking.

### Claim 33 (depends on 32)

The apparatus of claim 32, further comprising means for amplifying the set of the optical signals.

### Claim 34 (depends on 32)

The apparatus of claim 32, further comprising means for scrambling the set of the optical signals.

### Claim 35 (depends on 32)

The apparatus of claim 32, further comprising means for operating the transceiver in a saturated gain condition.

### Claim 36 (depends on 32)

The apparatus of claim 32, further comprising
means for transmitting a third set of optical signals along a second wavelength channel from a third transceiver;
means for multiplexing the first set and the third set to transmit along a transmission medium;
means for de-multiplexing the first set and the third set to send to the second transceiver and the fourth transceiver;
means for transmitting a fourth set of the optical signals along the second wavelength channel from a fourth transceiver;
means for multiplexing the second set and the fourth set to transmit along the transmission medium; and
means for de-multiplexing the second set and the forth set to send to the first transceiver and the third transceiver.

### Claim 37 (depends on 33)

The apparatus of claim 33, further comprising
means for splitting the first set of the optical signals to the second transceiver using a Time Division Multiplexing (“TDM”) scheme.