EP4237906A1

EP4237906A1 - Systems for emitting uncooled light

Info

Publication number: EP4237906A1
Application number: EP21805903.8A
Authority: EP
Inventors: Hélène DEBRÉGEAS
Original assignee: Almae Technologies
Current assignee: Almae Technologies
Priority date: 2020-11-02
Filing date: 2021-11-02
Publication date: 2023-09-06
Also published as: CN117120916A; WO2022090569A1; CA3200694A1; FR3115893A1; JP2023548612A; FR3115893B1

Abstract

According to one aspect, the present description relates to an uncooled light-emitting system (100) comprising a light-emitting device (400) comprising at least a first set of layers of semiconductor materials (403) which emits light and is optimised for operation at a nominal temperature; and a heater (460) extending in a first active area (401) and located at a predetermined maximum distance from the first active area (401), the distance being less than or equal to about 100 micrometres, the heater being configured to heat the first active area; means (500) for determining the temperature of the device; and a control unit (600) configured to operate the heater (460) only when the temperature of the device is strictly lower than a predetermined set temperature lower than or equal to the nominal temperature, the heat produced by the heater raising the temperature of the device to about the set temperature value.

Description

Uncooled light emitting systems

Technical field of the invention

The invention relates to uncooled light emitting systems, in particular uncooled light emitting systems for telecommunications systems.

State of the art

Telecommunication systems generally include semiconductor optical devices for transmitting an optical signal that can be modulated. Depending on the distance over which the optical signal must be transported, these devices may include: continuous wave (LC) lasers, direct modulation (LMD) lasers which have an active area allowing the emission of a directly modulated optical signal and externally modulated lasers (LME) comprising an active zone allowing the emission of an optical signal (hereinafter "laser part" or simply "laser") and an active zone allowing the modulation of this optical signal (hereinafter " modulator part" or simply "modulator"). The modulator of an LME is for example an electro-absorption modulator (ME A).

In general, a zone is said to be "active" in an optical semiconductor device when it is capable of generating a modification of an optical property of a light beam when it is subjected to a current source or tension. An active zone is thus, for example, configured for light emission or light modulation.

The laser of an LMD or an LME is characterized in particular by two quantities, the laser gain curve g(Æ) which represents the gain of the laser as a function of the wavelength and the wavelength of laser emission. For optimum output laser power, the laser is optimized for operation at a nominal temperature for which the maximum of the gain curve is close to the laser's emission wavelength and has a sufficient level to allow a power output suitable for the applications.

When the laser is placed in an environment subject to temperature variations, the wavelength corresponding to the maximum gain of the laser and the emission wavelength of the laser vary differently with the temperature of the device. Thus, as shown in FIG. 1, when the device temperature deviates from the nominal temperature, the emission wavelength of the laser is shifted with respect to the maximum gain of the laser. This implies an increase in the threshold current of the laser and a decrease in the optical power emitted by the laser, which is detrimental for the applications.

Moreover, the gain tends to decrease when the temperature of the device moves away from the nominal operating temperature, which also degrades the optical power. In the case of an LME, the performance of the modulator is characterized in particular by a curve of evolution of the optical power transmitted by the modulator (extinction curve) at an operating wavelength (for example the length of emission wave of the laser) as a function of a supply voltage of the modulator. The extinction curve also varies with temperature.

In particular, as illustrated in FIG. 2, for use at a nominal temperature, the extinction curve 202 is steep and configured so that two modulator supply voltages, for example 0 V and -IV, make it possible to switch between two states of the modulator corresponding to two levels different absorption levels: a state allowing light to pass at the operating wavelength (on state, low absorption by the modulator) and a state allowing little light to pass through at the operating wavelength (blocking state, strong absorption by the modulator). On the other hand, for a temperature deviating from the nominal temperature, the modulator may absorb too much of the light it receives from the laser in the on-state, which reduces the output power of the LME (as shown by curve 204), or not absorbing enough light in the blocking state (as shown by curve 206), which means using a higher supply voltage (e.g. -2V instead of -IV) and therefore greater energy consumption.

The aforementioned optical devices are therefore generally integrated into a cooled light emission system in which they are combined with a temperature regulation system (for example a Peltier effect thermoelectric system) capable of heating and cooling the laser parts and/or or modulators of the devices and ensuring that they are maintained at the nominal temperature. In practice, a chosen nominal temperature is often around 45° C. because such a temperature is in the middle of a usual range of temperature variations to which the environment of the device is subjected. However, in these systems, temperature control is a major contributor to overall power consumption. In particular, the cooling function consumes a lot of energy when the desired temperature variation is high, which is often the case in installations containing a large number of electrically powered devices.

Therefore, systems without a temperature cooling function, called uncooled systems in the present description, are preferred for applications such as access networks which must be low cost, or data centers which consume a lot of power. of energy.

In these systems, it is therefore sought to limit the variations in performance of the light-emitting device when the system is placed in an environment subject to typical temperature variations, for example a temperature range extending between approximately 0° C. and about 85°C for LMDs, and between 20°C and 70°C for LMEs.

In the state of the art, several solutions are proposed to reduce the technical problems mentioned above and to obtain a device emitting an optical signal whose characteristics are not too degraded during temperature variations, without however requiring cooling. of the device.

The document N. Sasada et al. [Ref. 1], discloses a technique for maintaining high laser gain at high temperature by optimizing an active area of a light-emitting device. This solution makes it possible, for example, to achieve operation of the laser part of an optical device up to 80°C with sufficient gain. However, the technique does not solve the problem of variation in the emission wavelength of the laser part with respect to the gain curve, which nevertheless degrades the emission power of the laser during a temperature variation.

The document Y. Nakai et al. [Ref. 2], discloses a solution to minimize variations in the extinction curve of the MEA of an LME. In this solution, the active zone which constitutes the MEA is optimized to form a vertical structure with multi-quantum wells making it possible to obtain a very steep extinction curve of the MEA, so that the modulation performances remain correct despite the variations of temperature. This solution makes it possible to achieve good performance in the temperature range 20-70°C; nevertheless, at high temperature, the absorption of the modulator becomes too high and at low temperature the modulation voltage of the MEA must be increased to obtain satisfactory switching.

Furthermore, in order to reduce the variations in extinction of the MEA with the temperature, it has been proposed to implement a heater along an optimized MEA at high temperature, as disclosed in the patent document EP 1 281 998. However this last document is not interested in maintaining the performance of a laser during a temperature variation.

An objective of the present description is to propose a new uncooled light emission system allowing to solve the problems of the state of the art.

Summary of the invention

In this description, the term "include" means the same as "include" or "contain", and is inclusive or open-ended and does not exclude other items not described or shown.

Furthermore, in the present description, the term "about" or "substantially" is synonymous with (means the same as) a lower and/or upper margin of 10%, for example 5%, of the respective value.

According to a first aspect, the present description relates to an uncooled light emission system comprising:

- a light-emitting device comprising: at least a first set of layers made of semiconductor materials configured to form at least a first active zone capable of emitting light, said first active zone being optimized to operate at a nominal temperature ; and a heater, extending at least along said first active area, and located at a predetermined maximum distance from said first active area, said heater being configured to produce, in operation, a heating of said first active area;

- Means for determining the temperature of the device; and

- a control unit configured to operate said heater only when said temperature of the device is strictly lower than a predetermined setpoint temperature, lower than or equal to said nominal temperature, the heating produced by the heater allowing a rise in the temperature of the device up to approximately the set temperature value. According to one or more exemplary embodiments, the maximum distance between the active zone and the heater is a distance less than or equal to 100 micrometers, for example a distance less than or equal to 100 micrometers over at least 70% of the length of the first zone active.

According to one or more examples, the maximum distance between the active zone and the heater is a distance between about 5 micrometers and about 100 micrometers, preferably between about 5 micrometers and about 20 micrometers, for example over at least 70% of the length of the first active area.

Such a distance allows the heater to be able to effectively heat the first active zone while leaving sufficient space between a contact electrode of the laser and the heater to prevent electrical conduction between these two components.

In the present description, the temperature of the device is understood as being the average temperature of the device; this temperature can be considered as substantially equal to the temperature of the active zone(s) of the device, also called the junction temperature of the device by those skilled in the art.

In this description, the device temperature rating is the device temperature for which the device was optimized during manufacture to perform optimally, i.e. the device temperature for which the device emits the highest optical power. This temperature is usually indicated by the manufacturer.

In the absence of heating of the active zone or zones by the heater, the temperature of the device is close to a temperature outside the device, that is to say a temperature of an environment in which the device is placed, or substantially higher due to the heating of the device during its operation. Thus, the temperature of the device is subject to variations in the outside temperature and can deviate from the nominal operating temperature, which degrades the performance of the device.

The operation of the heater only when the temperature of the device is strictly lower than a predetermined setpoint temperature, lower than or equal to the nominal temperature, allows an improvement in the performance of the system compared to a system of the prior art while maintaining reduced power consumption. The setpoint temperature is a temperature selected so that the device has an operation approaching optimal operation when the heater is in operation, that is to say a temperature of the device closer to the nominal temperature than the temperature of the device which would be obtained if the device did not have a heater, or that the heater was not in operation.

According to one or more exemplary embodiments, said setpoint temperature is approximately equal to the nominal operating temperature of the device.

This is particularly advantageous in the case where the nominal operating temperature is approximately equal to an estimated maximum value of the temperature of the environment. Indeed, Heating of the active zone(s) maintains the device at the nominal operating temperature and the variations in performance of the device during variations in the outside temperature are cancelled. In particular, the device's emission wavelength during variations in the outside temperature remains stable, which makes it possible to use telecommunications channels that are narrower in terms of wavelength in order to increase the overall throughput of an optical telecommunications network.

According to one or more exemplary embodiments, said setpoint temperature is strictly lower than said nominal operating temperature of the device. This makes it possible to limit the range of variation of the temperature of the device with respect to the range of variation of the outside temperature and to reduce the electrical overconsumption of the heater because the range of outside temperature for which the heater is in operation is restricted. This improves the performance of the device compared to a device of the prior art while reducing the electrical overconsumption of the heater.

According to one or more exemplary embodiments, the means for determining the temperature of the device comprise a temperature sensor.

According to one or more examples, the temperature sensor is in thermal contact with said at least one first active zone of the device.

By virtue of this thermal contact, the sensor makes it possible to precisely measure the temperature of the device. For this, the sensor can for example be arranged on the same base as the light-emitting device. According to one or more exemplary embodiments, the temperature sensor is thermally insulated from said at least one first active zone of the device. The sensor then measures the outside temperature.

As the temperature of the device is substantially equal to the outside temperature when the heater is not in operation, the measurement of the outside temperature thus makes it possible to estimate the temperature of the device and to determine whether it is useful to put the heater on. working.

The temperature sensor can for example be placed in the same box as the device, but at a sufficiently large distance from the device so that the heating produced by the heater does not influence the temperature measurement by the temperature sensor.

In other exemplary embodiments, the sensor can be physically separated from the device by a thermally insulating material so that the heating produced by the heater does not influence the temperature measurement by the temperature sensor. The thermal insulation is typically sufficient if the sensor is not heated by more than 5°C due to heating of the heater.

According to one or more exemplary embodiments, and in particular in exemplary embodiments where the temperature sensor measures the outside temperature, it is useful to perform a prior calibration of the control unit to determine an electrical power to be supplied to the heater so that the heating produced by the heater raises the temperature of the device to the set temperature.

According to one or more exemplary embodiments, the means for determining the temperature of the device comprise a device for measuring the wavelength (or the frequency) of the light emitted by the light-emitting device.

As the wavelength emitted by the light-emitting device depends on the temperature of the device, the measurement of said wavelength makes it possible to determine the temperature of the device and to deduce therefrom whether it is useful for the heater be put into operation. For this, the temperature of the device deduced from the wavelength measurement is compared to the value of the set temperature and, if the temperature of the device is strictly lower than the set temperature, the heater is put into operation.

According to one or more exemplary embodiments, said first set of layers made of semiconductor materials is configured to form, in addition, a second zone active capable of receiving and modulating the light emitted by said first active zone, said second active zone being optimized to operate at said nominal temperature; and said heater further extends along said second active area and is disposed at said maximum distance from said second active area, said heater being further configured to produce heating of said second active area.

This makes it possible to heat the first active zone and the second active zone of the device so that the temperature of the device approaches the nominal operating temperature. This makes it possible in particular to improve the performance of a light-emitting device comprising both a laser and a modulator during an outside temperature variation.

According to other exemplary embodiments, the device may comprise a second set of layers of semiconductor material to form a second active zone capable of receiving and modulating the light emitted by said first active zone, said second active zone being optimized to operate at said rated temperature, and the heater further extends along said second active area and is disposed at said maximum distance from said second active area, said heater being further configured to produce heating of said second active area . Said second set of layers made of semiconductor materials is arranged so as to be able to receive the light emitted by the first set of layers made of semiconductor materials. The arrangement of the first and second sets of layers in semiconductor materials can be, for example, manufactured using the “butt-joint” technique, that is to say that the first and second sets of layers made of semiconductor materials are arranged end to end, with their active areas aligned relative to each other and in contact according to a technique known to those skilled in the art.

According to one or more exemplary embodiments, said second active zone forms an electro-absorption modulator.

According to one or more exemplary embodiments, said first active zone constitutes a distributed Bragg grating laser.

According to one or more exemplary embodiments, the heater comprises a metal strip placed on an outer layer of said set of layers made of semiconductor materials. The applicants have shown that the metal strip allows the active zone(s) of the device to be heated, for example by the Joule effect.

According to one or more exemplary embodiments, the heater is made in layers of the set of layers of semiconductor materials and forms a PN or PIN diode.

The applicants have shown that this PN or PIN diode produces heating in the set of layers made of semiconductor materials, facilitating the heating of the active zone(s) of the device.

According to one or more exemplary embodiments, said heater comprises at least one ground electrically connected with a ground of said set of layers made of semiconductor materials and at least one electrical contact electrically insulated from said ground.

This makes it possible to have only one common ground for the device, which simplifies the electrical connection and the control of the device

According to one or more exemplary embodiments, said heater is controlled by a current command setpoint.

According to one or more exemplary embodiments, said heater is controlled by a voltage control setpoint.

According to a second aspect, the present description relates to a method for controlling the temperature in an uncooled light-emitting system according to the first aspect, said method comprising:

- the choice of a setpoint temperature lower than or equal to said nominal temperature of the device;

- determining the temperature of the device;

- the operation of the heater by the control unit only when said temperature of the device is strictly lower than said setpoint temperature, the heating produced by the heater allowing a rise in the temperature of the device to approximately the value of the set temperature.

According to one or more exemplary embodiments, the method further comprises a prior calibration of the control unit, said calibration comprising the establishment of a power-heating characteristic which characterizes the rise in temperature of the device as a function of an electric power supplied to the heater by the control unit to produce a heating. Brief description of figures

Other advantages and characteristics of the invention will appear on reading the description, illustrated by the following figures:

[FIG. 1], already described, represents the spectral power of the “laser” part of an example of a light-emitting device according to the state of the art for a temperature varying from 20° C. to 80° C.;

[FIG. 2], already described, schematically represents a curve of the transmitted power (extinction curve) of the "modulator" part of an example of a light-emitting device according to the state of the art in the case of a use at a nominal temperature, for example 45°C, in the case of a temperature much higher than the nominal temperature, for example 80°C, and in the case of a temperature much lower than the nominal temperature, for example 20 °C.

[FIG. 3A] shows a diagram of an example of a light emitting system according to the present description, in which the means for determining the temperature of the device comprise a temperature sensor thermally isolated from the active zone of the emitting device from light ;

[FIG. 3B] shows a diagram of an example of a light emitting system according to the present description, in which the means for determining the temperature of the device comprise a temperature sensor in thermal contact with the active zone of the device. light emission;

[FIG. 4A] schematically represents a top view of an example of a light-emitting device, according to the present description, in which the heater comprises a metal strip;

[FIG. 4B] schematically represents a sectional view of the light-emitting device illustrated in FIG. 4A;

[FIG. 5] schematically represents a sectional view of an example of a light-emitting device according to the present description, in which the heater comprises a PN diode;

[FIG. 6] schematically represents a top view of an example of a light-emitting device according to the present description comprising two active zones.

Detailed description of the invention

In the figures, certain elements are not shown to scale for better visibility. FIGS. 3A-3B schematically represent uncooled light-emitting systems 100 according to the present description, comprising a light-emitting device 400 with a heater 460, a control unit 600 and means for determining the temperature of the device, comprising for example a temperature sensor 500.

The light-emitting device 400 is a device based on semiconductor materials configured to emit light. According to one or more embodiments, the device 400 can perform one or more optical functions, for example, emitting continuous light or emitting modulated light.

The light-emitting devices according to the present description are devices comprising semiconductor materials forming one or more active zones allowing the emission of light.

According to the present description, the operation of one or more active zones of the device is optimized at a given nominal temperature and the device is provided with a heater so that, when the temperature of the device is below a set temperature, it is heated the active zone(s) of the device to raise the temperature of the device to said setpoint temperature, generally close to the nominal temperature.

In practice, in a light-emitting device according to the present description, it is possible to provide a "high" nominal temperature, that is to say a nominal temperature higher than the nominal temperatures used mainly in the devices according to the state of the art, for example a temperature greater than about 45°C, preferably greater than or equal to about 70°C.

The control unit 600 comprises for example an electronic circuit configured to send electrical signals to the light-emitting device 400 in order to control optical functions of the device 400. In particular, the control unit 600 can activate or deactivate the emission of light, or the modulation of the light emitted.

The control unit 600 is furthermore configured to supply an electric power allowing the activation or not of the heater and heating of the heater producing the rise in temperature of the device up to the setpoint temperature. The device 400 can be fixed on a base 303 configured to allow the connection between the electrodes of the device 400 and the electrical signals emitted by the control unit 600.

The device 400 can be fixed on the base 303 by means of a layer of solder which can comprise, for example, a Gold-Tin alloy.

The base 303 can comprise Aluminum Nitride (AIN) or Silicon and has dimensions of a few mm ² (for example between around 4 mm ² and around 2 mm ² ). The uncooled light emission system 100 can include an optical box 301 (for example of the TOSA type after the English acronym for “Transmit Optical SubAssembly”) comprising for example the base 303 on which the device is arranged. 400 and, optionally, the temperature sensor 500, the box being configured to allow optical coupling of the optical signal (light) emitted by the device 400 with optical components (not shown), for example optical fibers. The control unit 600 is arranged outside the box.

In general, the heater 460 is configured to be put into operation when the temperature of the device is strictly lower than a set temperature, for example between approximately 40° C. and approximately 85° C. for a nominal temperature of between approximately 60° C. and approximately 85° C., and produce a heating enabling the temperature of the device to be raised to the set temperature.

The means for determining the temperature of the device are configured to estimate or measure the temperature of the device and activate or not activate heating of the heater.

The means for determining the temperature of the device can comprise a sensor 500 enabling temperature measurement, for example a thermistor. In certain embodiments, an example of which is shown in FIG. 3A, the means comprise a temperature sensor 500 arranged in the optical box 301 but thermally insulated from the device 400, and more precisely from the active zone of the device. In particular, the temperature sensor is not fixed on the base 303 to avoid thermal contact with the device 400. The sensor therefore measures the temperature of the environment in which the box 301 is placed, i.e. say the outside temperature. In the absence of heating by the heater, the temperature of the device is substantially equal to the outside temperature and the temperature sensor 500 makes it possible to estimate the temperature of the device. When the heater is on operation and heats the device, the temperature of the device can be evaluated from the prior calibration for determining the characteristic power injected into the heater - heating of the device.

In certain embodiments, an example of which is illustrated in FIG. 3B, the means may comprise a temperature sensor placed directly on the base 303 and in thermal contact with the active zone(s) of the device to allow precise measurement of the temperature of the device.

In other embodiments, the means 500 for determining the temperature of the device can comprise a device (not shown in the figures) which measures the wavelength emitted by the device and gives an output estimate of the temperature of the device. device from said measure the wavelength.

In embodiments of the device where the determining means comprise a temperature sensor thermally insulated from the active zone or zones of the device, a prior calibration of the device can be carried out to establish the electrical power that the control unit will supply to the heater so that the heating of the heater can increase the temperature of the device to the value of the setpoint temperature.

Calibration can be performed by determining a power-heating characteristic that characterizes the rise in temperature of the device as a function of the electrical power supplied to the heater by the control unit.

The characteristic can for example be obtained by measuring the temperature variations of the device as a function of the electrical power supplied to the heater by the control unit. To do this, it is possible to proceed by injecting several current values I into the heater with the control unit and by measuring, for each, Intension U at the terminals of the heater as well as the wavelength emitted by the device in order to to deduce therefrom a coefficient a characterizing the variation of the wavelength X with the electrical power supplied by the control unit UI (the coefficient a being able to be expressed in nm/W). Thus, by using the coefficient a and a coefficient of variation of the wavelength emitted with the temperature of the device (for example equal to 0.09nm/°C), it is possible to calculate the temperature rise of the device in ° C as a function of the electrical power supplied by the control unit (in W), and to obtain the temperature rise characteristic controlled by the control unit in °C/W. In the case in particular where a temperature sensor is in thermal contact with the active zone(s), it is possible to proceed without prior calibration, by directly measuring the variations in the temperature of the device depending on the power supplied to the heater by the control unit.

According to one or more examples, the nominal temperature is greater than approximately 45° C., preferably greater than or equal to 70° C., and it is possible to choose a setpoint temperature approximately equal to said nominal temperature.

Thus, in the case for example of a nominal temperature equal to 70° and a variation in the temperature of the device from 70° C. to 20° C., due to use in a cold environment, the heater produces a temperature rise of approximately 50° C. to regain the nominal operating temperature of 70° C. and restore the nominal operating performance of the device 400 according to the present description.

The applicants have observed that, when the setpoint temperature is chosen approximately equal to the nominal operating temperature of the device 400, the heating produced by the heater 460 according to the above methods makes it possible to improve the performance of the device 400 by limiting the variations in the wavelength and the power emitted by the device 400 with respect to operation at nominal temperature.

In particular, maintaining the emission wavelength of the device during outside temperature variation makes it possible to use telecommunications channels that are narrower in terms of wavelength and therefore to increase the overall throughput of a communication network. tel ecommunications .

Alternatively, the applicants have shown that it is possible to choose a set temperature strictly lower than the nominal temperature.

The compensation for the temperature variation of the device 400 is then only partial but is sufficient to improve the performance of the device 400 compared to a device according to the state of the art and also makes it possible to reduce the electrical consumption of the heater 460 (and therefore of the device 400), which is advantageous for the applications described above.

It is thus possible to choose a setpoint temperature to select the temperature range of the device on which the heater 460 is in operation and therefore to choose the desired maximum electrical consumption. For example, in the case of a range of variation of the outside temperature between 20°C and 70°C, and for a device having a nominal temperature equal to 70°C, it is possible in a first operating mode, to choose a setpoint temperature approximately equal to the nominal temperature, that is to say approximately equal to 70° C., thus the heater 460 is in operation over the entire outside temperature range (between 20° C. and 70° C.). For example, for an efficiency of 50°C/W of the heater 460, it consumes a maximum of approximately 1W, because it must in particular produce a heating of the active zone of 50°C when the outside temperature is 20°C. . In a second mode of operation, if the chosen setpoint temperature is equal to 40° C. (that is to say strictly lower than the nominal temperature), then the temperature range of the device over which the heater 460 is in operation is reduced to an outside temperature range between 20°C and 40°C. The heater then only consumes a maximum of approximately 400 mW because it is, at most, necessary to produce a heating of the active zone of only 20° C. to reach 40° C., when the outside temperature is at 20° C.

FIGS. 4A-4B show a first example of a light-emitting device 400 according to the present description in a top view (FIG. 4A) and in a section perpendicular to the direction of propagation of the light in the device (FIG. 4B) .

According to the examples illustrated in FIGS. 4A-4B, the device 400 is an LC or LMD type device comprising a laser part but no part capable of modulating the light emitted by the laser part (such as, for example, an MEA).

In general, the device 400 comprises a set of layers of semiconductor materials 403, said set of layers forming in particular an active zone 401 configured for the emission of light.

As shown in FIG. 4B, the set of layers of semiconductor materials 403 comprises a lower layer 413, a layer 423 in which the active zone 401 is formed and an upper layer 404 opposite the lower layer with respect to layer 423.

The set of layers of semiconductor materials 403 can form, for example, a PIN junction type structure with P-doped or N-doped semiconductor materials and an active area 401 configured to emit light. The light emitted by the active area 401 is guided along the active area by index contrast with the layer 423 which can comprise materials different from the materials of the upper layer 404, such as for example semi-insulating material (InP doped with iron for example), or materials identical to layer 404 (InP doped P).

In the present description, also called laser or laser part, said set of layers of semiconductor materials 403 which notably form said active zone 401 allowing light to be emitted.

The laser is electrically powered in this example via two electrodes, one being the electrical contact electrode 407 for powering the laser and the other being the electrical ground of the device, for example the lower layer 413, opposite the contact 407 with respect to layer 423

The device 400 further comprises a heater 460 configured to heat the active zone 401 and allow the temperature of the device to be raised to the setpoint temperature, according to the operating modes described for example above. The heater 460 is arranged along the active area 401, for example at a distance at most equal to about 100 micrometers over more than about 70% of the length of the active area 401.

The applicants have observed that by placing the heater all along the active area 401 of the device, it is possible to maintain a uniform temperature over the entire length of the active area 401 in order, in particular, to maintain a constant refractive index. in the active area 401. A constant refractive index makes it possible in particular to maintain a stable laser emission length for the device.

The applicants have observed that the optimum distance between the heater 460 and the active zone 401 results from a compromise. A distance is sought that is as small as possible to optimize the efficiency of heating of the active layer 401 but sufficient to avoid electrical contact between the heater 460 and the electrode 407. The applicants have observed that a distance of between approximately 5 micrometers and 100 micrometers between the heater and the active zone 401 can satisfy said compromise. The heater 460 can be manufactured using different technologies.

In the example of FIG. 4A-4B, the heater 460 is for example a surface metal strip arranged on the set of layers of semiconductor materials 403, for example of Ni-Cr, with two electrical contact points 421, 422 at each end of the heater 460. The two electrical contact points 421, 422 are configured to receive an electrical voltage or current command used to control the heater 460, by means of a control unit (see FIG. 3 A, 3B), not shown on the FIGs. 4A, 4B. The electrical control makes it possible in particular to activate the production of heating by the Joule effect due to the electrical resistance of the metal strip. According to other embodiments, the heater can also be put into operation by supplying voltage via the electrical contact zone 422, the electrical contact 421 being connected to the electrical ground of the component.

In other embodiments, an example of which is shown in FIG. 5, the heater forms a diode 504 which is made in the assembly 403 of layers of semiconductor materials, for example a diode of the PN or PIN type, parallel to the waveguide formed by the active zone 401 and made in the layers of semiconductor materials of the device. The diode consumes electrical power when an electrical current or voltage is injected into it. The diode is made to preferentially emit very few or no photons, so that the electrical consumption results in self-heating by the Joule effect, thus making it possible to heat the active area 401 located nearby.

The diode is in this example electrically supplied via two electrodes, a surface electrode 507 arranged on the same side of the set of layers of semiconductor materials 403 as said contact electrode 407 and a ground electrode arranged on the opposite side, by example the lower layer 413 of the set 403 of layers of semiconductor materials.

The applicants have shown that the diode 504 has the advantage of being able to produce a heating in depth in the set of layers of semiconductor materials 403. That is to say that unlike a metal strip essentially heating an external surface of the set of layers 403, then by thermal conduction, the active area 401, the PN diode heats the inside of the set of layers 403, and therefore heats the active area 401 more efficiently.

FIG. 6 represents a second example of a light-emitting device. As in the first example shown in FIGs. 4A - 4B, the device comprises a set of layers in semiconductor materials 403. In this example however, the set of layers in semiconductor materials 403 is configured to form in addition to the first active area 401 a second active area 484 configured for receive and modulate the light emitted by the first active area 401. In FIG. 6, a dotted line 490 is indicated to indicate a boundary between the first active area 401 and the second active area 484.

In this example, the second active area 484 is electrically powered by two electrodes. One of said electrodes is a modulation contact electrode 480 configured to receive an electrical signal variable in voltage or current controlling the modulation of the light emitted by the first active area 401. The other electrode is the ground of the second active area 484 (not visible in FIG. 6), and can be electrically connected to the ground of the first active zone 401.

The device according to the second example can be configured to form a device of the LME type, comprising a first active zone 401 emitting light (laser part) and a second active zone 484 producing a modulation of this light (modulator part).

In the present description, a modulation of the light emitted by the assembly 403 is understood as the modification of a parameter of the light, for example the phase or the amplitude.

In the example of FIG. 6, the heater 460 extends along the first active zone 401 and the second active zone 484 in order to be able to produce, according to the methods presented above, a simultaneous and homogeneous heating of the two active zones 401, 484.

The applicants have shown that the simultaneous heating of the two active zones 401, 484 makes it possible, on the one hand, to limit the variations of the emission wavelength and of the power of the light emitted by the device 400 and, on the other hand, to maintain a satisfactory extinction curve. This therefore allows the device to maintain optimum performance during a variation in outside temperature, in particular in terms of optical power and depth of modulation of this optical power. In FIGs. 4A and FIG. 6, to illustrate the positioning of the waveguide 401 and the first and second active zones with respect to the heater 460, the waveguide 401 and the active zones are visible by transparency although they are not arranged on the upper layer of the first set of layers of conductive materials 403, as seen in FIG. 4B. In a general case, the waveguide 401 is not always visible on a top view of the device 400. In certain embodiments of the device 400 comprising a waveguide 401 of the buried type, the presence and arrangement of the waveguide 401 can however be identified indirectly on a top view of the device by a variation in relief on the visible surface of the device 400.

According to the first and the second example, the set of layers in semiconductor materials 403 is optimized to operate advantageously at a high nominal temperature, for example around 70° C. The optimization can include, for example, a choice of particular structures for the active areas 401, 484. In particular, said active areas can be configured to produce a strong confinement of the electrons in their conduction band to limit the impact of the device temperature on device performance.

Optimization can also be performed by choosing structures comprising materials with an energy bandgap allowing an optimal laser emission gain or extinction curve at high temperature.

Generally, the set of semiconductor material layers 403 can be configured to form different types of active areas, such as, for example, a distributed Bragg grating.

Moreover, alternatively to the example of FIG. 6, a second active zone can be formed by a second set of layers of semiconductor material (not shown in the figures), arranged so as to be able to receive the light emitted by the first set of layers of semiconductor material. The arrangement of the first and second sets of layers made of semiconductor materials can be, for example, manufactured using the so-called “butt-joint” technique, that is to say that the first and second sets of Semiconductor material layers are arranged end to end, with their active areas aligned relative to each other and in contact according to a technique known to those skilled in the art. In this example, the heater also extends along the second active zone formed by said second set of layers of semiconductor material.

Although described through a certain number of exemplary embodiments, the light emission systems according to the present description comprise various variants, modifications and improvements which will appear obvious to those skilled in the art, it being understood that these various variations, modifications and improvements fall within the scope of the invention as defined by the following claims. References

[Ref 1] SAS AD A, Noriko, NAKAJIMA, Takayuki, SEKINO, Yuji, et al. Wide-Temperature-Range (25-80° C) 53-Gbaud PAM4 (106-Gb/s) Operation of 1.3-pm Directly Modulated DFB Lasers for 10-km Transmission. Journal of Lightwave Technology, 2019, vol. 37, No. 7, p. 1686-1689.

[Ref 2] NAKAI, Yoshihiro, NAKANISHI, Akira, YAMAGUCHI, Yonyoshi, et al. Uncooled Operation of 53-GBd PAM4 (106-Gb/s) EA/DFB Lasers with Extremely Low Drive Voltage With 0.9 V pp. Journal of Lightwave Technology, 2019, vol. 37, No. 7, p. 1658-1662.

Claims

1. Uncooled light emitting system (100) comprising: a light emitting device (400) comprising: at least a first set of layers of semiconductor materials (403) configured to form at least a first zone active (401) capable of emitting light, said first active zone (401) being optimized to operate at a nominal temperature; and a heater (460), extending at least along said first active area (401), and located at a predetermined maximum distance from said first active area (401) less than or equal to about 100 micrometers, said heater being configured to produce, in operation, a heating of said first active zone (401); means (500) for determining the temperature of the device; and a control unit (600) configured to operate said heater (460) only when said temperature of the device is strictly lower than a predetermined setpoint temperature, lower than or equal to said nominal temperature, heating produced by the heater allowing an increase in the temperature of the device up to approximately the value of the set temperature.

2. System according to claim 1, in which the means (500) for determining the temperature of the device comprise a temperature sensor.

3. System according to claim 2, in which the temperature sensor is thermally insulated from said at least one first active zone of the device so as to measure a temperature outside the device (400).

4. System according to claim 2, in which the temperature sensor is in thermal contact with said at least one first active zone of the device (400).

5. A system according to any preceding claim, wherein said maximum distance between the active area (401) and the heater (460) is a distance between about 5 micrometers and about 100 micrometers.

6. System according to any one of the preceding claims, in which the said maximum distance between the active zone (401) and the heater (460) is a distance comprised between approximately 5 micrometers and approximately 20 micrometers.

7. System according to any one of the preceding claims, in which the means (500) for determining the temperature of the device comprise a device for measuring the wavelength of the light emitted by the light-emitting device.

8. System according to any one of the preceding claims, in which said setpoint temperature is strictly lower than said nominal temperature.

9. A system according to any preceding claim, wherein the heater (460) comprises a metal strip disposed on an outer layer of said first set of layers of semiconductor materials (403).

10. System according to any one of claims 1 to 8, in which the heater (460) is made in layers of the set of layers of semiconductor materials (403) and forms a PN or PIN diode.

11. System according to any one of the preceding claims, in which said heater (460) comprises at least one mass (421) electrically connected with a mass of said set of layers of semiconductor material (403) and at least one electrical contact (422) electrically isolated from said ground (421).

12. A system according to any preceding claim, wherein said first active area (401) forms a distributed Bragg grating laser.

13. System according to any one of the preceding claims, in which said first set of layers of semiconductor materials (403) is configured to form, in addition, a second active zone (484) capable of receiving and modulating the light emitted by said first active area (401), said second active area being optimized to operate at said nominal temperature; and said heater (460) further extends along said second active area (484) and is disposed at said maximum distance from said second active area (484), said heater being further configured to provide heating of said second active area (484).

14. System according to any one of claims 1 to 12, in which the device comprises a second set of layers of semiconductor material configured to form a second active zone capable of receiving and modulating the light emitted by said first active zone, said second active zone being optimized to operate at said nominal temperature; and said heater further extends along said second active area and is disposed at said maximum distance from said second active area, said heater being further configured to produce heating of said second active area.

15. System according to any one of claims 13 to 14, in which said second active zone forms an electro-absorption modulator.

16. A method of controlling the temperature in an uncooled light-emitting system according to any one of the preceding claims, said method comprising: choosing a setpoint temperature less than or equal to said nominal temperature of the device; determining the temperature of the device; and the operation of the heater by the control unit (600) only when said temperature of the device is strictly lower than said setpoint temperature, the heating produced by the heater allowing the temperature of the device to be raised to approximately the value of the setpoint temperature.

17. Method according to claim 16, further comprising: a prior calibration of the control unit (600), said calibration comprising the establishment of a power-heating characteristic which characterizes the rise in temperature of the device as a function of an electrical power supplied to the heater (460) by the control unit (600) to produce a heating.