Patent Description:
Current photonic technologies based on pluggable modules are not suitable for future radio base stations utilising optical communication for intra-system and intraunit interconnection due to the low energy efficiency and the high frequency dependent channel loss between the transceiver and the ASICs. To make these pluggable modules work at high bit rate (> <NUM> Gbps) very complex, costly, and power-hungry equalization circuits and modulation formats are needed to reduce inter-symbol interference. A new photonic interconnect technology needs be developed with a higher level of integration between photonics and electronics, higher energy efficiency, based on solutions that are compatible with mass production in existing production lines for electronics. This technology relies on a new concept of system in package devices based on multi-chip modules (MCM) including, in the same substrate, digital ASICs and co-packaged optical transceivers with high throughput that are used as ASIC I/O interfaces.

Co-packaged optics, CPO, has been proposed to reduce the cost of packaging and power consumption by shortening the electrical lines between the optical module and the ASIC. It is estimated that the cost of packaging accounts for the <NUM>% of the total cost of a transceiver according to IPSR <NUM>. An additional cost reduction comes from the integration of multiple laser sources into a single optical transceiver with multiple channels. Nevertheless, the co-packaged solution presents some drawbacks in terms of serviceability and thermal management of the laser sources.

An integrated laser source dissipates a small thermal load of approximately <NUM> mW, however, because the lasers are very small in size (typically few hundreds of microns), the device-level heat flux dissipated per laser is large, around <NUM> kW/cm2. Removing this level of heat flux locally through an acceptable thermal resistance is extremely challenging and this may reduce the level of integration that can be achieved.

Currently, the approach adopted in optical transceivers to address the thermal management of laser sources is the use of solid state thermo-electric cooler, also indicated as macro-TEC. The TEC acts to maintain a reference temperature of the photonic chip and avoids the decay of laser performances during operation. Semiconductor lasers performances depend strongly on temperature. The threshold current of semiconductor lasers increases fast with temperature and their yield generally decreases above <NUM>. Additionally, laser lifetime decreases with exposure to high temperature according to the Arrhenius model.

Additionally, the integration of laser sources poses the problem of serviceability; in case of failure of a single laser source the whole module must be replaced since an integrated laser cannot be replaced. This may severely reduce any economic advantage of the co-packaged solution.

Standby/spare lasers have been proposed to address the issue of laser failure in integrated photonic chips e.g. in <CIT> which describes the replacement of failed lasers with auxiliary lasers that are included on the photonic chip so that when a failure is detected on a working laser the standby/spare laser can take over. Document <CIT> discloses an example of an optical module using internal replacement lasers to mitigate laser induced temperature failure.

External laser sources have been proposed for CPO as an alternative to integrated laser sources, to address the issue of serviceability and thermal stress in co-packaged modules, as reported in the CPO joint development forum, JDF, guidance document "Co-packaged Optics External Laser Source Guidance Document v1. <NUM>": http://www. copackagedoptics. com/wp-content/uploads/<NUM>/<NUM>/ELS-Guidance-Doc-v1. <NUM>-FINAL.

It is an object to provide an improved communications network optical apparatus. It is a further object to provide an improved method of providing optical signals for an optical module in a communications network.

An aspect of the invention provides communications network optical apparatus comprising an optical module and a controller. The optical module comprises optical modulators, internal lasers, an input port, optical routing devices and a temperature sensor. The optical modulators are arranged to modulate optical signals. The internal lasers arranged to generate internal optical signals to be modulated by the optical modulators. The input port is arranged to receive an external optical signal from an external laser. The optical routing devices are arranged to route internal optical signals from internal lasers to optical modulators and to route an external optical signal from the input port to at least one of the optical modulators. The temperature sensor is arranged to sense a temperature of the internal lasers and to generate a temperature reporting signal. The controller comprises processing circuitry and memory containing instructions executable by said processing circuitry whereby said controller is operative to perform operations. The operations include receiving the temperature reporting signal. The operations additionally include determining that a thermal protection condition exists based on the temperature of the internal lasers. The operations additionally include, in response to the determining, generating control signals configured to cause the external optical signal to be provided to at least one optical modulator and to cause an operating power of at least one respective internal laser to be reduced.

The apparatus enables thermal stress relief for lasers integrated within optical modules where dissipation of heat is particularly difficult by switching from using the internal laser to using an external optical signal when a thermal stress condition occurs. The apparatus may be particularly advantageous for use in applications where internal lasers experience thermal stress for a limited time relative to their total time of operation. The apparatus may enable an optical module to switch to an external optical signal when the optical module's internal lasers are experiencing thermal stress that is limited in space and time, to mitigate the thermal stress experienced by an internal laser. Mitigating the thermal stress in this way may mitigate reduction in the operating lifetime of the internal laser and may mitigate a reduction in the performance of the internal laser. The apparatus may advantageously enable the optical module to operate most of the time with the cost-effective internal lasers and to use an external optical signal from an external laser occasionally, for example when a peak in traffic causes a large temperature increase in the optical module.

In an embodiment, the control signals comprise a first control signal and a second control signal. The first control signal is for providing power control commands to an external laser. The second control signal is for providing power control commands to the at least one internal laser. The controller is caused to generate the first control signal to provide a power-on control command to the external laser in response to the determining that a thermal protection condition exists. The controller is additionally caused to subsequently generate the second control signal to provide at least one power control command configured to cause the operating power of the at least one respective internal laser to be reduced. The apparatus may advantageously enable the external laser to be switched on only when an external optical signal is required. Reducing the internal laser operating power after causing the external laser to switch on may advantageously enable the optical module to alternate the use of an internal laser and an external laser without causing bit errors or performance degradation in the optical module.

In an embodiment, the operating power of the at least one respective internal laser is reduced by switching off the operating power, by gradually reducing the operating power and then switching off the operating power, or by gradually reducing the operating power to zero. The apparatus is thus advantageously able to perform an instantaneous hand-over from the internal laser to the external optical signal or a gradual hand-over.

In an embodiment, the first control signal provides a power-on control command configured to cause the external laser to gradually increase a power of the external optical signal up to an operating power as the operating power of the internal laser is gradually reduced. This may avoid any fluctuation in the optical power received at the optical modulator.

In an embodiment, the optical module further comprises an optical tap configured to route a portion of an external optical signal received at the input port to the at least one respective internal laser for injection locking the at least one internal laser with the external optical signal. The second control signal is generated subsequently to the injection locking. In this way the wavelength of the internal optical signal may be matched to the wavelength of the external optical signal, to within the wavelength tolerance of an optical channel, before the external optical signal takes over from the internal optical signal. Injection locking may also enable the phase of the internal optical signal to be aligned to the phase of the external optical signal before the external optical signal takes over from the internal optical signal. Use of injection locking may avoid optical interference occurring between the internal optical signal and the external optical signal when the internal and external optical signals are coexisting.

In an embodiment, the external optical signal has a first frequency and the internal optical signals have frequencies different to the first frequency by a frequency difference that is greater than a defined detection bandwidth. This may advantageously cause any optical beat signal generated between coexisting internal and external optical signals to be outside a defined detection bandwidth.

In an embodiment, the optical routing devices comprise a first optical waveguide, a second optical waveguide, a third optical waveguide and at least one directional phase-shifting coupler. The first optical waveguide is coupled to an optical modulator. The second optical waveguide is coupled to an internal laser. The third optical waveguide is coupled to the input port. The at least one directional phase-shifting coupler is for coupling the second optical waveguide to the first optical waveguide or the third optical waveguide to the first optical waveguide. The control signals further comprise a third control signal for providing control commands to the at least one directional phase-shifting coupler. The controller is caused to generate the third control signal, after generating the first control signal. The third control signal is configured to provide control commands. The control commands are to cause the at least one directional phase-shifting coupler to couple the internal optical signal into the first optical waveguide with a first phase. The control commands are additionally to cause the at least one directional phase-shifting coupler to stop coupling the internal optical signal into the first optical waveguide. The control commands are additionally to cause the at least one directional phase-shifting coupler to couple the external optical signal into the first optical waveguide with the first phase. This may avoid any fluctuation in the optical power received at the optical modulator. This may also avoid optical interference occurring between the internal optical signal and the external optical signal when the internal and external optical signals are coexisting.

In an embodiment, the third control signal is additionally configured to provide further control commands. The further control commands are to cause the at least one directional phase-shifting coupler to gradually reduce to nothing the coupling of the internal optical signal into the first optical waveguide. The further control commands are additionally to cause the at least one directional phase-shifting coupler to gradually increase the coupling of the external optical signal into the first optical waveguide with the first phase. This may avoid any fluctuation in the optical power received at the optical modulator.

In an embodiment, the optical routing devices comprise an all-optical switch and the optical module further comprises an optical tap. The all-optical switch has a first input connected to an internal laser, a second input connected to the input port and an output connected to an optical modulator. The optical tap is configured to route a portion of an external optical signal received at the input port of the optical module to the all-optical switch as a switching signal for the all-optical switch. The all-optical switch has a first switch condition in which the first input is connected to the output and a second switch condition in which the second input is connected to the output. The all-optical switch is arranged to switch from the first switch condition to the second switch condition responsive to receipt of a said switching signal. An all-optical switch may enable fast switching which may avoid any fluctuation in the optical power received at the optical modulator and may avoid transmission downtime.

In an embodiment, not part of the claimed invention, the all-optical switch has a switching time for switching between the first switching condition and the second switching condition. The switching time is less than 10ps. The all-optical switch may advantageously enable very fast switching, effectively between bits modulated onto the optical signal, which may avoid any fluctuation in the optical power received at the optical modulator, due to interference caused by the coexistence of internal and external optical signals at the same wavelength, and any loss of bits.

In an embodiment, the apparatus further comprises a second optical module and a variable power coupler. The variable power coupler is configured to receive the external optical signal from the external laser and is configured to power split the external optical signal to send a first portion of the external optical signal to the optical module and second portion of the external optical signal to the second optical module. A single external optical signal, provided by a single external laser, may thus be used to provide external optical signals to two optical modules, reducing the cost as compared to providing an external laser for each module.

In an embodiment, the controller is further operative to perform further operations. The further operations include receiving a further temperature reporting signal. The further operations additionally include determining that a thermal protection condition no longer exists based on the temperature of the internal lasers. The further operations additionally include, in response to said determining, generating control signals configured to stop the external optical signal being provided to the at least one optical modulator and to cause the reduction in the operating power of the at least one respective internal laser to be reversed. The apparatus may advantageously return to operation using the internal laser once a thermal stress condition has ended.

In an embodiment, the apparatus comprises a plurality of optical modules and an optical switch apparatus configured to receive external optical signals. The controller is operative to receive temperature reporting signals from the optical modules and to determine that a thermal protection condition exists at an optical module based on the temperature of its internal lasers. The control signals are further configured to cause the optical switch apparatus to route one of the external optical signals to the optical module having said thermal protection condition. The apparatus may reduce the number of external lasers that are necessary to provide external optical signals to protect the internal lasers of an optical module. Also, this may increase the reliability of the apparatus because in case of failure of an external laser source an external optical signal from another external laser source can be used.

In an embodiment, the apparatus further comprise at least one external laser arranged to generate at least one external optical signal.

In an embodiment, not part of the claimed invention, the apparatus further comprises a plurality of external lasers arranged to generate the external optical signals. The plurality of external lasers and the optical switch apparatus are located remote from the plurality of optical modules. The apparatus may advantageously enable the optical module to operate most of the time with the cost-effective internal lasers and to use external optical signals from a pool of shared external lasers occasionally, for example when a peak of traffic causes a large temperature increase in the optical module. Also, this may increase the reliability of the apparatus because in case of failure of an external laser another one of the external lasers can be used.

In an embodiment, an optical module is a co-packaged optics, CPO, module. The apparatus may advantageously enable combining the cost-saving of using a CPO optical module with serviceability and reliability with a solution where the external optical signal is used only in the cases where internal lasers are under thermal stress.

In an embodiment, an optical module is provided in a Radio Unit.

Corresponding embodiments and advantages also apply to the method described below.

An aspect of the invention provides a method of providing optical signals for an optical module in a communications network. The method comprises the following steps. A step of generating an internal optical signal at an internal laser of the optical module. A step of providing the internal optical signal to an optical modulator of the optical module for optical modulation. A step of monitoring a temperature of the internal laser. A step of determining that a thermal protection condition exists based on the temperature of the internal laser. A step of, in response to the determining, causing an external optical signal to be provided to the optical modulator and causing an operating power of the internal laser to be reduced.

The same reference numbers will be used for corresponding features in different embodiments.

Referring to <FIG>, an embodiment provides communications network optical apparatus <NUM> comprising an optical module <NUM> and a controller <NUM>.

The optical module <NUM> comprises optical modulators <NUM>, internal lasers <NUM>, an input port <NUM>, optical routing devices <NUM> and a temperature sensor <NUM>.

The optical modulators are arranged to modulate optical signals. The internal lasers are arranged to generate internal optical signals to be modulated by the optical modulators. The temperature sensor is arranged to sense a temperature of the internal lasers and to generate a temperature reporting signal.

The input port is arranged to receive an external optical signal <NUM> from an external laser. The optical routing devices are arranged to route internal optical signals from internal lasers to optical modulators and to route an external optical signal from the input port to at least one of the optical modulators.

The controller comprises processing circuitry <NUM> and memory <NUM> containing instructions which when executed by the processing circuitry cause the controller to perform operations including:.

In an embodiment, the control signals comprise a first control signal <NUM> for providing power control commands to an external laser and a second control signal <NUM> for providing power control commands to the internal laser.

The controller <NUM> is caused to generate the first control signal to provide a power-on control command to the external laser in response to determining that a thermal protection condition exists. The controller is also caused to subsequently generate the second control signal, after generating the first control signal, to provide at least one power control command configured to cause the operating power of the internal laser to be reduced.

The handover of the light input from the internal laser to the external optical signal is performed in a way that the optical power input to the optical modulator is maintained.

In an embodiment, the operating power of the internal laser is reduced by switching off the operating power. In an alternative embodiment, the operating power of the internal laser is reduced by gradually reducing the operating power and then switching off the operating power. In an alternative embodiment, the operating power of the internal laser is reduced by gradually reducing the operating power to zero.

In an embodiment, illustrated in <FIG>, the communications network optical apparatus <NUM> further comprises an external laser <NUM> arranged to generate the external optical signal <NUM>.

An embodiment provides communications network optical apparatus <NUM> as illustrated in <FIG>.

In this embodiment the optical module additionally comprises an optical tap <NUM>. The optical tap is configured to route a portion of an external optical signal <NUM> received at the input port <NUM> to the internal laser <NUM>. The portion of the external optical signal is used to injection lock the internal laser with the external optical signal.

The second control signal is generated subsequently to the injection locking, to provide at least one power control command configured to cause the operating power of the internal laser to be reduced after it has been injection locked with the external optical signal.

Since the internal optical signal and the external optical signal co-exist during handover, it is necessary to avoid the generation of interference or beat signal. This can be achieved by ensuring the overlap of the two inputs, in terms of frequency and phase, by injection locking.

Injection locking enables high spectral overlap to be achieved between the external optical signal and the internal optical signal. The internal laser <NUM> (the 'slave' laser) is tuned to the frequency of the external optical signal by injecting a small amount of the external optical signal into the resonant cavity of the internal laser.

Additional controls may also be used to find the best alignment of the phase of the external optical signal and the phase of the internal laser. Phase alignment is relevant only in the case where the frequency of the external optical signal and the frequency of the internal optical signal are set to be the substantially the same (i.e. to have a high percentage of spectral overlap), means that interference may occur if the phases are not aligned.

In an embodiment, the external optical signal <NUM> has a first frequency and the internal optical signals have frequencies different to the first frequency. The frequencies of the internal optical signals are different to the first frequency by a frequency difference that is greater than a defined detection bandwidth.

The internal optical signal and the external optical signal co-exist during handover, setting this frequency means that any beat signal is generated between the internal and external optical signals does not fall within a defined detection bandwidth, so it is not detected by a receiver. Controlling the frequencies may be easier to implement and more robust than phase control, however it may be less suitable for use in a dense wavelength division multiplexing, DWDM, system since it would necessarily increase the bandwidth required by each channel. It may be easily adopted in 'gray optics' systems used in interconnect/data centers or course WDM, CWDM, systems.

<FIG> illustrate embodiments <NUM>, <NUM>, <NUM> of the optical routing device <NUM>. Each embodiment supports gradual handover from the internal laser <NUM> to the external optical signal <NUM>, and vice versa, to maintain the optical power output of the optical module <NUM>. Each optical routing device couples the internal optical signal and the external optical signal into a common waveguide <NUM>, <NUM>, <NUM> that in turn feeds an optical modulator <NUM> in the optical module.

In the embodiment of <FIG>, the optical routing device <NUM> is a passive power coupler, such as a Y-branch coupler. A first input branch <NUM> is coupled to the internal laser <NUM>, a second input branch <NUM> is coupled to the input port <NUM>, to receive the external optical signal <NUM>, and a common output branch <NUM> is coupled to the optical modulator <NUM>. An optical tap <NUM> is also provided to deliver a small percentage of the output light to a monitor photodiode, PD, not shown.

The monitor photodiode will detect an increase in output optical power when the external optical signal is present and output a photodiode signal to the controller <NUM>. The controller <NUM> is operable, in response to receiving a photodiode signal indicating an increase in output optical power, to generate the second control signal <NUM> to provide at least one power control command configured to cause the bias current of the internal laser to be reduced to zero.

Similarly, when the thermal protection condition has ended and the internal laser takes over again from the external optical signal, the photodiode signal may be used to cause the controller <NUM> to generate a first control signal <NUM> comprising power control commands to drive the gradual shut down of the external laser providing the external optical signal.

In the embodiment of <FIG>, the optical routing device <NUM> comprises a first optical waveguide <NUM>, a second optical waveguide <NUM>, a third optical waveguide <NUM> and a directional phase-shifting coupler <NUM>.

The first optical waveguide is coupled to the optical modulator <NUM>, the second optical waveguide is coupled to the internal laser <NUM> and the third optical waveguide is coupled to the input port <NUM>. The directional phase-shifting coupler <NUM> is configured to couple the second optical waveguide to the first optical waveguide or to couple the third optical waveguide to the first optical waveguide. The directional phase-shifting coupler also includes a phase shifter configured to match the phase of the external optical signal to the phase of the internal optical signal.

The controller <NUM> is additionally caused to generate a third control signal, after generating the first control signal. The third control signal is for providing control commands to the directional phase-shifting coupler.

The internal laser <NUM> generates the internal optical signal at a first wavelength (optical frequency) and a first phase. The external optical signal <NUM> is at the first wavelength and a second phase, which will in general be different to the first phase. The third control signal is configured to provide control commands to:.

The optical routing device <NUM> can be used to avoid destructive interference between the internal and external optical signals during handover from the internal optical signal to the external optical signal, and back.

In an alternative embodiment, the optical routing device <NUM> comprises a passive directional coupler, configured to transfer <NUM>% of the external optical signal into the first waveguide <NUM>.

Using a passive directional coupler, destructive interference of internal and external optical signals during handover can be addressed by managing the wavelengths of external and internal optical signals.

In an embodiment, the control commands cause the directional phase-shifting coupler <NUM> to gradually reduce to nothing the coupling of the internal optical signal into the first optical waveguide and gradually increase the coupling of the external optical signal into the first optical waveguide with the first phase. This may enable a consistent optical power to be output from the optical routing device to the optical modulator.

In the embodiment of <FIG>, the optical routing device <NUM> comprises a first optical waveguide <NUM>, a second optical waveguide <NUM>, a third optical waveguide <NUM>, a first directional phase-shifting coupler <NUM> and a second directional phase-shifting coupler <NUM>.

The first optical waveguide is coupled to the optical modulator <NUM>, the second optical waveguide is coupled to the internal laser <NUM> and the third optical waveguide is coupled to the input port <NUM>. The first directional phase-shifting coupler <NUM> is configured to couple the second optical waveguide to the first optical waveguide, to couple the internal optical signal into the first optical waveguide. The second directional phase-shifting coupler <NUM> is configured to couple the third optical waveguide to the first optical waveguide, to couple the external optical signal into the first optical waveguide. The directional phase-shifting couplers also include phase shifters configured to match the phase of the external optical signal to the phase of the internal optical signal.

The controller <NUM> is additionally caused to generate a third control signal, after generating the first control signal. The third control signal is for providing control commands to the directional phase-shifting couplers. The internal laser <NUM> generates the internal optical signal at a first wavelength (optical frequency) and a first phase. The external optical signal <NUM> is at the first wavelength and a second phase, which will in general be different to the first phase. The third control signal is configured to provide control commands to:.

In an embodiment, the control commands cause the first directional phase-shifting coupler <NUM> to gradually reduce to nothing the coupling of the internal optical signal into the first optical waveguide and cause the second directional phase-shifting coupler <NUM> to gradually increase the coupling of the external optical signal into the first optical waveguide with the first phase. By matching the gradual increase/decrease a consistent optical power may be output from the optical routing device to the optical modulator.

In an embodiment, the third control signal is configured to provide control commands to cause the first directional phase-shifting coupler <NUM> to apply a phase-shift to the internal optical signal so that has a third phase, different to the first and second phases. The control commands also cause the second directional phase-shifting coupler <NUM> to apply a phase-shift to the external optical signal so that also has the third phase.

This active control of the phases is the most efficient configuration for the avoidance of destructive interference during handover since it is possible to control both the phase of the internal optical signal and the phase of the external optical signal.

The controller <NUM> may also be configured to generate a fourth control signal to provide control commands to perform the opposite handover, from external optical signal to internal optical signal, when the thermal protection condition no longer exists at the internal laser <NUM>.

<FIG> illustrates an embodiment in which the optical routing device comprises an all-optical switch <NUM> and the optical module <NUM> further comprises an optical tap <NUM>.

The all-optical switch <NUM> has a first input <NUM> connected to the internal laser <NUM>, a second input <NUM> connected to the input port <NUM> and an output <NUM> connected to the optical modulator <NUM>. The optical tap is configured to route a portion of the external optical signal received at the input port <NUM> to the all-optical switch as a switching signal for the all-optical switch.

The all-optical switch has a first switch condition in which the first input is connected to the output and a second switch condition in which the second input is connected to the output. The all-optical switch is arranged to switch from the first switch condition to the second switch condition responsive to receipt of a switching signal. The all-optical switch is arranged to switch from the first switch condition to the second switch condition responsive to the switching signal no longer being present.

The all-optical switch <NUM> enables a 'switched handover' which avoids the need for managing the co-existence of the internal and external optical signals in terms of beat and interference.

In an embodiment, the all-optical switch <NUM> has a switching time, for switching between the first switching condition and the second switching condition, that is less than 10ps The switching time is thus small enough to prevent the occurrence of transmission error, i.e. the loss of bits, during handover.

In an embodiment, illustrated in <FIG>, the optical module <NUM> of the communications network optical apparatus <NUM> comprises a plurality of internal lasers <NUM>, optical routing devices <NUM> and optical modulators <NUM>. The optical module <NUM> also comprises three passive Y-branch couplers <NUM>, <NUM>, <NUM> provided between the input port <NUM> and the optical routing devices <NUM>, arranged to power split the external optical signal <NUM> received at the input port into four external optical signals. The external optical signal <NUM> can therefore be used to replace one or more of the respective internal optical signals generated by the internal lasers <NUM>.

In an embodiment, illustrated in <FIG>, the communications network optical apparatus <NUM> comprises two optical modules - optical module <NUM> and optical module two <NUM>(<NUM>) - and a variable power coupler <NUM>.

The variable power coupler may, for example, be a directional coupler with thermo-optic variation of the refractive index or may be a double micro-ring coupler. The variable power coupler is configured to receive the external optical signal <NUM> and is configured to power split the external optical signal to send a first portion of the external optical signal to the optical module <NUM> and a second portion of the external optical signal to the second optical module <NUM>(<NUM>). The external optical signal <NUM> can therefore be used to serve both optical modules.

The controller <NUM> is caused to generate a further control signal <NUM> to provide a control command to the variable power coupler. The control command is configured to set the percentage of received external optical signal that is routed to each of the optical modules.

The optical modules are independent, therefore a thermal protection condition may occur at different times for each module. The variable power coupler is operable to send a portion of the external optical signal to the optical module where it is needed. The external optical signal is split and distributed in a single step using the variable power coupler that acts as a switch that also regulates the percentage of laser power that passes from one waveguide to the other.

The variable coupler in this case is a variant of switch node in the switch matrix used for the routing of the light from the external laser sources towards the modules.

For power saving purposes the laser power of the external laser <NUM> may be variable. The controller <NUM> is caused to generate the first control signal <NUM> to provide an operating power control command, so that the external laser <NUM> is configured to fulfil the power needs of the optical modules to be served. For example, if the external laser is serving only the optical module <NUM>, the power control command is configured to cause the external laser power to be set to a first value P=p1. If, instead, the external laser is required to serve optical module <NUM> and optical module <NUM>(<NUM>), the power control command is configured to cause the external laser power to be set to a higher value, P=p1+p2.

In this scenario, the controller is operable to respond to requests by simultaneously controlling the external laser power, to serve the totality of the optical modules, and configuring the variable coupler to send the required fraction of external laser power to each optical module.

In an embodiment, the controller is further operative to perform further operations including:.

In an embodiment, illustrated in <FIG>, the communications network optical apparatus <NUM> comprises a plurality of optical modules <NUM> and an optical switch apparatus <NUM>.

The optical switch apparatus is configured to receive a plurality of external optical signals <NUM>.

The controller <NUM> is operative to receive temperature reporting signals from the optical modules <NUM> and to determine that a thermal protection condition exists at an optical module based on the temperature of its internal lasers <NUM>. The control signals are further configured to cause the optical switch apparatus to route one of the external optical signals to the optical module having the thermal protection condition. It will be understood that a thermal protection condition may exist at more than one optical module at the same time and the control signals are configured to cause the optical switch apparatus to route a respective external optical signal to each optical module at which a thermal protection condition exists.

<FIG> illustrates the logical scheme of an optical switch apparatus <NUM>, external lasers <NUM> and optical modules <NUM> of a further embodiment of communications network optical apparatus similar to the apparatus <NUM> illustrated in <FIG>.

The optical switch apparatus <NUM> is configurable to conditionally connect a set of N external lasers <NUM> to M optical modules <NUM>. The optical switch apparatus <NUM> comprises a plurality of optical switch nodes <NUM> which may be configured to route an external optical signal from an external laser <NUM> to an optical module <NUM>. A <NUM>:K optical splitter <NUM> is provided between each external laser <NUM> and the optical switch nodes, to power split the external optical signal from each external laser <NUM>. A high power external laser may therefore be used to service a variable number (from <NUM> to k; k = <NUM> in this example) optical modules.

The outputs of the optical switch apparatus are connected to the M optical modules <NUM> by M optical fibers <NUM>.

The optical switch apparatus <NUM> is configurable to conditionally connect a set of N variable power external lasers <NUM> to M optical modules <NUM>. The optical switch apparatus <NUM> comprises a plurality of optical switch nodes <NUM> which may be configured to route an external optical signal from an external laser <NUM> to an optical module <NUM>. Each optical switch node <NUM> is configurable to route a portion of an external optical signal received from a respective external laser <NUM> to a respective optical module <NUM>. A variable power external laser may therefore be used to service a variable number of optical modules. Up to K optical switch nodes may be activated at the same time.

In an embodiment, an optical module <NUM> is a co-packaged optics, CPO, optical module.

In an embodiment, an optical module <NUM> is provided in a Radio Unit of a communications network. The typical scenario where a laser undergoes thermal stress for a limited time in proportion with the total time of operation, is found in the application of co-packaged optical transceivers in Radio Units that are part of a mobile radio base station. In a Radio Unit typically there is no forced ventilation for cooling; the operating temperature is dependent on the environment temperature and is directly related to the power dissipation of the unit.

While instantaneous traffic at a Radio Unit changes within milliseconds, the temperature of the equipment can be considered related to average traffic in downlink due to thermal inertia of the Radio Unit, that can be assumed to be in the range of tens to hundreds of seconds order of magnitude, depending on the size of the Radio Unit. Traffic load typically varies during the day, with one or two peak hours within the <NUM> hours.

In an embodiment, not part of the claimed invention, illustrated in <FIG>, the communications network optical apparatus <NUM> further comprises a pool of N external lasers <NUM> arranged to generate the external optical signals <NUM>.

In an embodiment, the external lasers <NUM> and the optical switch apparatus <NUM> are located remote from the optical modules <NUM>.

In an embodiment, each of the optical modules <NUM> comprises a plurality of internal lasers <NUM>, one or more of which may be handed over to an external optical signal when a thermal protection condition exists.

The controller <NUM> is caused to perform operations to control handover from an internal laser <NUM> to an external laser <NUM> and subsequent off of the internal laser. The handover comprises the following functions:.

The controller <NUM> is caused to perform operations including:.

The choice of external laser may be based on criteria including, for example: distance, power, and operating wavelength. The external lasers may be located in proximity to the optical modules (from some cm to meters) or very far in a remote location up to km away from the optical modules to be served. In the first case the external laser could be connected to the module via a polarization maintaining fiber, so to avoid addressing polarization diversity in the photonic chip of the module. For long distances instead, polarization agnostic laser sources are preferrable, such as the remote laser source described in <CIT>.

The pool of external lasers provides a number of external sources N to a set of M optical modules <NUM> via switching of optical switch nodes of the optical switch apparatus <NUM>. The choice of N and M depends on the statistics of the protection condition and the number of internal lasers in each optical module. The response of the optical switch apparatus is not time-critical, since the handover will not take place until the external optical signal has reached the optical module.

There are different options for the choice of the type of external lasers <NUM>: the external lasers can be a high-power laser, that can be split to serve many optical channels (i.e. optical modulators) or a low power laser to serve a single channel.

In the case of a high-power external laser provides a high power external optical signal to replace multiple internal optical signals in the same optical module <NUM>, since all of the internal lasers <NUM> will suffer a similar thermal stress, the external laser can be switched on following detection of the thermal protection condition. In the case where the external laser serves more than one optical module extra controls are needed to deliver the required optical power to each optical module independently. These controls may include the external laser power variation and variable optical power splitting described above.

In the case of the use of low power external lasers the control is simpler as the external optical signal can be simply routed towards the respective optical modulator of a single optical channel and switched off when not in use.

In both cases, the external laser may be a wavelength tunable laser to increase flexibility.

The handover from an internal optical signal generated by an internal laser to an external optical signal generated by an external laser is performed such that the optical power input to the respective optical modulator is maintained, with a preference towards a slight increase of optical power in the case of a gradual power up of the external laser or when the internal laser switch off and external laser switch on cannot be synchronized and symmetric.

The controller <NUM> is caused to generate control signals to switch from/to the use of the light of the external source and the internal laser gradually, with a coexistence of the two light inputs to feed the optical transmitter, or to exclude the internal laser at the inset of the external laser. These two approaches, gradual handover and switched handover, have different advantages and drawbacks as explained in the following, and the convenience of one over the other may depend on the use case.

For the case where the handover is gradual, the apparatus <NUM> may exploit known control systems used to control the average optical power output by an optical module. For example, automated power control loops that change the bias current of the internal laser <NUM> in response to the light power received from a monitor photodiode, e.g. where the bias current is changed to maintain the photo-diode current. This type of control is generally present in optical modules to compensate for temperature variation and aging of the laser.

The controller <NUM> may be caused to perform operations including:.

The optical tap <NUM>, <NUM>, <NUM> within the optical routing device <NUM>, <NUM>, <NUM> sends a % of light to a monitor photodiode that detects the light intensity increase caused by the merging of the external optical signal with the internal optical signal. The controller <NUM> is further caused to general a second control signal comprising power control commands to cause a decrease of the bias current of the internal laser in response to the photodiode signal.

In an embodiment, the M optical modules <NUM> are provided within a cluster of Radio Units, sharing the pool of N external lasers <NUM>. The external lasers are connected to the Radio Units with optical fibers of up to <NUM>-<NUM> of length.

Referring to <FIG>, an embodiment provides a method <NUM> of providing optical signals for an optical module in a communications network.

Claim 1:
Communications network optical apparatus (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) comprising:
an optical module (<NUM>) comprising:
optical modulators (<NUM>) arranged to modulate optical signals;
internal lasers (<NUM>) arranged to generate internal optical signals to be modulated by the optical modulators;
an input port (<NUM>) arranged to receive an external optical signal (<NUM>) from an external laser;
optical routing devices (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) arranged to route internal optical signals from internal lasers to optical modulators and to route an external optical signal from the input port to at least one of the optical modulators; and
a temperature sensor (<NUM>) arranged to sense a temperature of the internal lasers and to generate a temperature reporting signal; and
a controller (<NUM>, <NUM>) comprising processing circuitry (<NUM>) and memory (<NUM>) containing instructions executable by said processing circuitry whereby said controller is operative to:
receive the temperature reporting signal;
determine that a thermal protection condition exists based on the temperature of the internal lasers; and
in response to the determining, generate control signals (<NUM>, <NUM>, <NUM>) configured to cause the external optical signal to be provided to at least one optical modulator and to cause an operating power of at least one respective internal laser to be reduced.