# US 11,309,973 B2 · Optical burst monitoring

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- Number: US 11,309,973 B2
- Document ID: US11309973B2
- Status: Granted
- Kind: B2
- Application number: 15/885,385
- Filed: 2018-01-31
- Published: 2019-08-01
- Granted: 2022-04-19
- Earliest claimed: 2018-01-31
- Assignees: Nokia Solutions and Networks Oy
- Applicants: Nokia Solutions and Networks OY
- Inventors: Vincent Houtsma; Doutje van Veen
- Web page: https://patentgrep.com/patent/US11309973B2

## CPC

- H04B 10/07957: {Monitoring or measuring wavelength}
- H04B 10/64: Heterodyne {, i.e. coherent receivers where, after the opto-electronic conversion, an electrical signal at an intermediate frequency [IF] is obtained}
- H04B 10/0795: {Performance monitoring; Measurement of transmission parameters}
- H04B 10/572: Wavelength control
- H04J 14/02: Wavelength-division multiplex systems
- H04J 14/08: Time-division multiplex systems
- H04B: TRANSMISSION
- 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

A passive optical network having an optical-signal monitor configured to monitor carrier-wavelength drifts during optical bursts transmitted between the optical line terminal and optical network units thereof. In an example embodiment, the optical-signal monitor uses heterodyne beating between two differently delayed portions of an optical burst to generate an estimate of the carrier-wavelength drift during that optical burst. The passive optical network may also include an electronic controller configured to use the estimates generated by the optical-signal monitor to make configuration changes at the optical network units and/or implement other control measures directed at reducing to an acceptable level the amounts of carrier-wavelength drift during the optical bursts and/or mitigating some adverse effects thereof.

## Claims

### Claim 1

An apparatus comprising an optical receiver, the optical receiver having an optical burst monitor and being configured to receive data-modulated optical signals from a plurality of optical transmitters operable in optical burst mode; and
wherein the optical burst monitor comprises:
an optical mixer configured to generate an optical output signal by optically mixing a first portion of an optical burst and a second portion of the optical burst, the second portion being delayed with respect to the first portion;
a photodetector configured to convert the optical output signal into a corresponding electrical signal; and
a signal processor configured to generate an estimate of carrier-wavelength drift during the optical burst based on a beat frequency of said corresponding electrical signal.

### Claim 2 (depends on 1)

The apparatus of claim 1, wherein the optical mixer comprises:
a first optical coupler configured to power-split light of the optical burst to generate the first and second portions thereof;
a delay element configured to delay the second portion with respect to the first portion; and
a second optical coupler configured to power-combine the first portion and the second portion delayed by the delay element to generate the optical output signal.

### Claim 3 (depends on 2)

The apparatus of claim 2, wherein the delay element is controllably tunable to change a relative delay time between the first and second portions.

### Claim 4 (depends on 2)

The apparatus of claim 2, wherein the optical burst monitor further comprises an optical band-pass filter connected to filter the light to apply the optical burst to the first optical coupler.

### Claim 5 (depends on 4)

The apparatus of claim 4, wherein the optical band-pass filter is controllably tunable to change a pass band thereof to allow for sequential testing of carrier-wavelength drifts of different ones of the respective optical transmitters.

### Claim 6 (depends on 1)

The apparatus of claim 1, wherein the signal processor is configured to generate the estimate of the carrier-wavelength drift using one of more of the following:
a set of values representing the beat frequency;
an estimate of a minimum carrier wavelength during the optical burst;
an estimate of a maximum carrier wavelength during the optical burst; and
an estimate of a magnitude of the carrier-wavelength drift during the optical burst.

### Claim 7 (depends on 1)

The apparatus of claim 1, further comprising an electronic controller configured to generate one or more control signals in response to receiving from the optical burst monitor an input signal indicative of the estimate of the carrier-wavelength drift, the one or more control signals including a control signal directed to a corresponding one of the optical transmitters.

### Claim 8 (depends on 7)

The apparatus of claim 7, wherein the control signal directed to the corresponding one of the optical transmitters is configured to change an operating configuration of a laser source thereof.

### Claim 9 (depends on 8)

The apparatus of claim 8, wherein a change of the operating configuration includes a change for the corresponding one of the optical transmitters of one or more of the following:
duration of an optical burst;
duration of an inter-burst interval;
a carrier wavelength to which the corresponding one of the optical transmitters is tuned at a beginning of an optical burst;
a data modulation format used during an optical burst;
a duty cycle used during an optical burst;
a baud rate used during an optical burst;
one or more laser bias voltages;
one or more laser injection currents; and
an optical power of an optical burst.

### Claim 10 (depends on 7)

The apparatus of claim 7, wherein the one or more control signals include a control signal configured to change a TDMA transmit schedule for at least some of the optical transmitters.

### Claim 11 (depends on 7)

The apparatus of claim 7, wherein the electronic controller is configured to generate the one or more control signals in a manner that causes a carrier-wavelength drift during an optical burst to be smaller than a fixed threshold.

### Claim 12 (depends on 1)

The apparatus of claim 1, further comprising an optical line terminal that comprises the optical receiver.

### Claim 13 (depends on 12)

The apparatus of claim 12, wherein the optical line terminal comprises a WDM receiver configured to recover data encoded in the optical bursts.

### Claim 14 (depends on 12)

The apparatus of claim 12, further comprising a passive optical router having a first optical port and a plurality of second optical ports, the first optical port being externally connected to the optical line terminal, and each of the second optical ports being externally connected to a respective one of the plurality of optical transmitters.

### Claim 15 (depends on 1)

The apparatus of claim 1, wherein:
the first portion is a first attenuated copy of the optical burst; and
the second portion is a second attenuated copy of the optical burst.

### Claim 16 (depends on 3)

The apparatus of claim 3, wherein the delay element is controllably tunable to change the relative delay time such that the relative time delay is between ten and one hundred signaling intervals.

### Claim 17 (depends on 1)

The apparatus of claim 1, wherein the optical receiver is configured to receive the data-modulated optical signals from the plurality of optical transmitters in accordance with a TDMA transmit schedule.