GB2435137A

GB2435137A - An optical transceiver which modulates an optical source using digital control data, the modulator using output from a function generator

Info

Publication number: GB2435137A
Application number: GB0709470A
Authority: GB
Inventors: Sonia Ashmore; Jeremey Crouch
Original assignee: Avago Technologies Fiber IP Singapore Pte Ltd
Current assignee: Avago Technologies International Sales Pte Ltd
Priority date: 2003-09-11
Filing date: 2003-09-11
Publication date: 2007-08-15
Anticipated expiration: 2023-09-11
Also published as: GB2435137B; GB0709470D0

Abstract

An optical transceiver 100 modulates an optical source 210 such as a laser using a modulator 220. The modulator receives both content data and digital control data. The digital control data may be input to the transceiver using an electrical two-wire serial interface 520, 540. A processor 410 uses the digital control data as a basis for deriving modulation information, such as parameters of a tone signal. This modulation information is used by a function generator 460. Its output is passed through a digital-to-analogue converter 450 and then input to the modulator, optionally to provide a tone signal. The processor also receives control information from an analogue-to-digital converter (ADC), and uses this to control the modulation. The input to the ADC may include a signal representing both the output from a laser monitor 440 and a low pass filtered 430 version of an optical signal received at optical detector 310, as claimed in GB2406010.

Description

OPTICAL TRANSCEIVER WITE FUNCTION GENERATOR

The invention relates to an optical transmitter and receiver for use in optical communications networks, and S in particular to an integrated transceiver comprising a transmitter and a receiver.

It is commonplace to use optical transmitters, such as lasers, to transmit light signals over optical fibres.

The transmitted light is modulated in order to transmit data but it. is also known to superimpose a low frequency electrical signal onto the optical signal in order to enable the further transmission of control signals for network elements and network control systems.

According to the present invention, there is provided an optical transceiver as set out at claim 1.

The optical transmitter may comprise an optical source, a first modulation signal being applied to the optical source to modulate the output of the optical source, the first modulation signal representing content data to be transmitted by the optical transmitter and a second modulation signal being applied to the optical source to modulate the output of the optical source, the second modulation signal representing control data to be transmitted buy the optical transmitter, the optical transmitter being characterised in that the control data comprises a digital signal. The optical transmitter may further comprise a two-wire interface to apply the digital control data to the optical source.

The optical receiver may comprise an optical detector, the detector receiving an optical signal comprising a first modulation signal representing content data and a second modulation signal representing control data, the optical receiver recovering the content data and the control signal from the received optical signal, the optical receiver being characterised in that the control data comprises a digital signal. The optical receiver may further comprise a two-wire interface to transmit the digital control data from the optical receiver.

According to a third aspect of the invention there is provided an optical transceiver comprising an optical transmitter as described above and an optical receiver as described above.

Whilst the use of digital control signals per se is well known, in the present invention the use of the digital control signals in contrast to the conventional analogue tone signals enables the control signals to be sent over a conventional two-wire interface. This then allows the tone terminals to be removed from the transmitter and the receiver, allowing transceiver modules to be reduced in size and increasing the module density in equipment racks.

The use of digital control signals and a two-wire interface also enables the tone functions to be managed and controlled via the systems that are used to manage other aspects of module functiona1itY The invention will now be described, by way of example only, with reference to the following Figures in which: Figure 1 shows a schematic depiction of a known optical transceiver; and Figure 2 shows schematic depiction of an optical transceiver according to the present invention.

Figure 1 shows a schematic depiction of a known optical transceiver 10 comprising a transmitter module 20 and receiver module 30. The transmitter module 20 compriseS laser 21, 22, laser modulator 23, transmitter control means 24, first and second data input ports 25, 26 and tone input port 27. The receiver module 30 comprises detector 31, pre-amplifier 32, post amplifier 33, low-pass filter 34, amplifier 35, first and second data output ports 36, 37 and tone output port 38. The transceiver also comprises a two wire serial interface 50 comprising clock 52 and data 54 input/output ports. Such interfaces are known for transmitting control data and reporting back measured data to control systems, for example laser diode temperatures, power measured by optical monitors, etc. In Figure 1, the serial interface 50 is shown to interface with the laser 21 and the detector 31 but it will be understood that the serial interface may also interface with other components in the transceiver.

In use, data for transmission is presented at the first and second data input ports 25, 26 and is received by the laser modulator 23. The laser modulator determines the output of the laser 21 that is launched into first optical fibre 40 and is controlled by transmitter control means 24. The transmitter control means sends two signals to the laser modulator in order to control the behaviour of the laser modulator. The first signal controls the bias current applied to the laser, which determines the average optical power outputted by the laser, and the first signal is determined in relation to the signal sent from the laser monitor 22. The laser 21 is configured such that a small fraction of the optical output of the laser is detected by the laser monitor in order that the performance of the laser can be monitored and the bias current adjusted as necessary by the transmitter control means in order to achieve the desired average output power from the laser. The second signal controls the amplitude of the modulation current applied to the laser. This amplitude is maintained by the transmitter controller in a pre-determined ratio to the bias current in order to maintain the required difference in optical power between the 1 and 0 level used in data transmission.

The transmitter control means is also connected to the tone input 27, to which a low frequency analogue signal is applied. The transmitter control means superimposes this low frequency signal onto the amplitude signal to the laser modulator such that the 1 level of the optical output of the laser is also modulated with the low frequency tone signal.

Conventionally, the light transmitted over the first optical fibre 40 is received at a second optical transceiver (not shown), which will transmit data, which is received by transceiver 10 from the second optical fibre 45. The optical signal is received by the detector 31 and is converted into an electrical signal. The electrical signal passes through a pre-amplifier 32 and a post-amplifier 33 before the electrical signal is presented at the first and second data output ports. The data may then be transmitted to a terminal, such as a computer or a telephony switch, or it may be de-multiplexed prior to sending the data to one or more terminals.

In order to access the tone signal added to the data signal a fraction of the electrical signal is routed to a low-pass filter 34 to recover the tone signal, which is then amplified by amplifier 35 and can be accessed from tone output port 38.

Figure 2 shows schematic depiction of an optical transceiver 100 according to the present invention comprising a transmitter module 200, receiver module 300 and control module 400. The transmitter module 200 comprises a laser 210, a laser modulator 220 and first and second data input ports 230, 240. The receiver module 300 comprises detector 310, pre-amplifier 320, post-amplifier 330 and first and second data output ports 340, 350. The control module 400 comprises processing means 410, analogue to digital converter (ADC) 420, low-pass filter 430, laser monitor 440, digital to analogue converter (DAC) 450, function generator 460, clock input/output port 540 and data input/output port 520.

In use the transceiver 100 operates in a generally similar manner to the transceiver described above with reference to Figure 1. In particular, an electrical data signal will be applied to first and second data input ports and this data will be used by the laser modulator to modulate the optical output of the laser, which will be launched into first optical fibre 40. Similarly, optical signals received at the detector 310 will be converted into the electrical domain and will be amplified by the pre-amplifier and the post-amplifier before being presented at the first and second data output ports.

The present invention is distinguished over the prior art by the function and structure of the control module 400.

The laser monitor 440 measures a fraction of the light emitted by the laser and a signal representing this is transmitted to ADC 420. The processing means 410 then generates a first digital signal that is sent to the DAC 450, which converts the first digital signal into an analogue bias current signal that can be used to control the laser modulator 220. The processing means then also generates a second digital signal based on a pre-defined algorithm, which represents the modulation amplitude control signal. This in turn is sent to a DAC, which converts the second digital signal into an analogue modulation current control to the laser modulator.

The clock input/output port and data input/output port 520, 540 form a conventional two-wire serial interface 500 that can be used to transit commands to the processing means. The processing means can then interpret the commands, for example by comparing them against a look-up table, to determine one or tone signal parameters such as frequency, duty cycle, gain, etc. The processor then determines an appropriate signal, which added to the modulation current control and passed to the function generator and subsequently to the DAC in order to provide the required modulation current that is used by the laser modulator to add the modulation tone to the optical output of the laser.

The optical signal received by the detector 310 includes tone modulation and this information can be recovered by the control module 400. A portion of the electrical data signal is fed, having been amplified by the pre-amplifier 320, to the ADC 420 via a low-pass filter 430. The ADC sends a digital signal to the processing means 410 in response to the analogue signal received from the low-pass filter and the processing means interprets this digital signal to determine the transmitted tone signal. A signal may then be transmitted via the data input/output port and clock input/output port so that the received tone signal may be monitored and the information derived therefrom used to provide feedback.

In a preferred embodiment the processing means comprises 410 comprises memory means 415 that is capable of storing a number of tone parameters for both transmitted and received signals. The operator of the transceiver can use the data input/output port and clock input/output port, which may be a conventional two-wire serial interface, to write tone parameter values into the associated memory locations. When tone parameter values are detected within received signals then these values may be written into those associated memory locations. These parameters may be reported to a monitoring system or corrective action may be undertaken if, for example,, a parameter exceeds a defined threshold value.

The disclosures of the abstract and of GB 0321269.3 as filed (of which the present application is a divisional application), published as GB 2406010, are hereby incorporated by reference.

Claims

CLAIMS

1. An optical transceiver (100) comprising: an optical source (210); a modulator (220) operable to modulate the optical source in accordance with content data and digital control data; an optical detector (310); a processing means (410); an ADC (420); and a DAC (450) and a function generator (460) connected to the modulator, wherein the processing means is operable to control the modulator using the DAC and the function generator.

2. An optical transceiver according to claim 1, wherein the optical source comprises a laser.

3. An optical transceiver according to claim 2, comprising a monitor (440) for generating the signal indicative of the light emitted by the laser.

4. An optical transceiver according to any preceding claim, comprising a preamplifier (320) for amplifying a signal from the optical detector.

5. An optical transceiver according to claim 4, wherein the ADC is operable to receive the output of the preamplifier as a tone signal, indicative of digital control data, received by the optical detector.

6. An optical transceiver according to claim 5, wherein the ADC is connected to the pre-amplifier by a low pass filter (430).

7. An optical transceiver according to any preceding claim, comprising a two-wire interface (500, 520, 540), wherein the two-wire interface is operable to apply digital control data to the optical source.

-10 - 8. An optical transceiver according to any preceding claim, comprising a two-wire interface (500, 520, 540), wherein the two-wire interface is operable to transmit digital control data from the optical receiver.