Patent Grant
10142029
The invention relates to a device for modulating the intensity of an optical signal on four different levels.
The intensity of a monochromatic optical signal is the product of the optical field E of this optical signal by the conjugate of this optical field E. The optical field corresponds to the electrical field E in the context of the electromagnetic waves and Maxwell equations. In the case of a polychromatic optical signal, the optical intensity is calculated for each of the wavelengths of this signal. The intensity of the optical signal is expressed in Watts.
The modulation of the intensity of a monochromatic optical signal on four different levels is known by the acronym 4-PAM (“4-Pulse Amplitude Modulation). The 4-PAM modulation modulates only the intensity of the optical signal on four different levels and does not modulate its phase. It offers the advantage of simplifying the production of the receiver. In effect, the latter need only measure an intensity level out of only four different levels to demodulate the optical signal. Thus, this receiver is much simpler than, for example, a receiver implemented in the context of a QAM (Quadrature Amplitude Modulation). In effect, in the latter case, the intensity and the phase of the optical signal are modulated. It is therefore necessary also to synchronise the operation of the receiver with that of the modulation device in order to recover the information coded in the intensity and the phase of the received optical signal.
In the case of the polychromatic optical signals, the 4-PAM modulation can be implemented simultaneously for several monochromatic optical signals of different wavelengths which make up the polychromatic optical signal. Such a modulation is known by the acronym 4-PAM-WDM (4-Pulse Amplitude Modulation—Wavelength Division Multiplexing).
In the following article, a 4-PAM modulation device has already been proposed that uses a resonant ring modulator: Dubray O. et al., “20 Gb/s PAM-4 transmission from 20 to 90° C. by modulating a silicon ring resonator modulator with 2V”, Optical Society of America, Mar. 2015. Hereinbelow, this article is referred to by the expression “Dubray 2015”.
The modulation device of the Dubray 2015 article offers numerous advantages. In particular, by virtue of the use of a resonant ring modulator its bulk is very small. In particular, its bulk is much smaller than that of the 4-PAM modulation devices using Mach-Zender modulators.
By contrast, to implement the 4-PAM modulation device described in the Dubray 2015 article, it is necessary to generate an electrical control signal for the resonant ring modulator exhibiting four different voltage levels. Each of these voltage levels codes two information bits. To generate such an electrical signal from one or more binary information signals to be transmitted, it is therefore necessary to use a digital-analogue converter. Now, such digital-analogue converters are extremely bulky and consume a lot of energy. That limits the possibilities of application of the 4-PAM modulation device described in the Dubray 2015 article.
Prior art is also known from:
The invention aims to remedy this drawback while retaining the advantages of the 4-PAM modulation device of the Dubray 2015 article and, in particular, a small bulk. Its subject is therefore a 4-PAM modulation device.
The above 4-PAM modulation device comprises two resonant ring modulators, each controlled by a binary control signal. Thus, contrary to the 4-PAM modulation device described in the Dubray 2015 article, there is no need to use an electrical signal that can take four different voltage levels. It is consequently not necessary to use a digital-analogue converter capable of generating, from the binary information signal or signals to be transmitted, a corresponding voltage level. In the modulation device claimed, the binary information signal or signals can be directly transmitted to the control ports of the resonant ring modulators. It is consequently no longer necessary to use such a digital-analogue converter to do the 4-PAM modulation while using resonant ring modulators. Consequently, the bulk of the device claimed remains still much smaller than the bulk of the modulation devices using Mach-Zender modulators. Furthermore, the device claimed eliminates the need to have to use a bulky digital-analogue converter to make it operate.
Moreover, the above device combines the optical signals obtained from the second output port of the first resonant ring modulator and from the output port of the second resonant ring modulator. Thus, whatever the state of the first resonant ring modulator, the intensity of the first optical signal to be modulated is always combined constructively with the intensity of the second modulated optical signal. By virtue of that, the four intensity levels of the modulated optical signal extend over a wide intensity range which facilitates the decoding thereof by the receivers.
The embodiments of this device can further offer the following advantages:
The invention will be better understood on reading the following description, given purely as a nonlimiting example, and with reference to the drawings in which:
In these figures, the same references are used to designate the same elements. Hereinafter in this description, the features and functions well known to those skilled in the art are not described in detail.
The device 2 typically takes the form of an electronic chip in which all the optical and electrical components are produced on one and the same semiconductor substrate such as a piece of silicon. The dimensions of the device 2 are very small. For example, the area of the face on which all its components are produced is less than 2.5 mm2 or 1 mm2 or 500 μm2. Typically, the device 2 is produced by the same fabrication methods as those used to fabricate the microprocessors or other microelectronic devices. The device 2 modulates the intensity of a signal Sin as a function of two binary information signals V1 and V2 to be transmitted to obtain a modulated optical signal Sout. In the signal Sout, each pair of bits, formed by a bit of the signal V1 and a bit of the signal V2, is coded by a single intensity level of this signal.
Each binary signal is typically an electrical signal in which the value of each information bit is coded by a voltage level. This electrical signal is a binary signal, that is to say that each information bit is coded by its own voltage level and therefore that each voltage level codes only the value of a single information bit.
The signal Sout exhibits at most four different intensity levels each coding a different pair of bits. The device 2 does not use the phase of the optical signal to code and transmit information bits.
Typically, the signal Sout is transmitted via an optical fibre 11 to a receiver 12. To decode the signal Sout received, the receiver 12 only needs a sensor 14 which measures the intensity of the signal Sout. For example, the sensor 14 is a simple photodetector. Thus, given that the information is only coded by the four intensity levels, the latter is particularly simple to decode on the receiver 12 side.
To this end, the device 2 comprises:
The input 10 is optically coupled to an output of a laser source 16 which generates the signal Sin.
In this text, “optically coupled” describes the fact that two optical components are directly or indirectly coupled to one another via a waveguide or several waveguides. If the two optical components are produced on one and the same silicon substrate, this waveguide is typically a silicon waveguide surrounded by a material with a refractive index that is lower than that of the material of the waveguide. Also, consequently, the expression “directly optically coupled” describes the fact that a first and a second optical component are directly coupled optically to one another by one or more non-instrumented waveguides, that is to say waveguides incapable of modifying the optical signal which passes through them as a function of an external control signal.
The laser source 16 is, for example, an external laser optically coupled to the input 10 by an optical fibre/waveguide coupler. The signal Sin delivered by the source 16 is not intensity-modulated or phase-modulated.
The input 10 is directly optically coupled to an input 20 of an optical power divider 22 equipped with two outputs 24 and 26. The divider 22 divides the signal Sin into two optical signals to be modulated S1 and S2 delivered, respectively, by the outputs 24 and 26. The two signals S1 and S2 are identical to the signal Sin except that they each have an intensity lower than the intensity of the signal Sin. Here, the intensities of the signals S1 and S2 are respectively denoted P1 and P2. The intensity of the signal Sin received on the input 20 is denoted Pin. The sum of the intensities P1 and P2 is less than or equal to the intensity Pin. Preferably, the sum of the intensities P1 and P2 is greater than or equal to 0.9×Pin or 0.95×Pin or 0.98×Pin. The intensities P1 and P2 are each greater than or equal to 0.05×Pin and, preferably, greater than or equal to 0.15×Pin or 0.25×Pin. The divider 22 therefore acts as an intensity divider.
In this embodiment, the intensity Pin is divided into equal parts between the outputs 24 and 26. The intensities P1 and P2 are therefore equal.
The divider 22 is for example produced as described in the following article: C. S. Hsiao et AL, “Design for beam splitting components employing silicon-on-insulator rib waveguide structures”, Optics letter, C.S. Vol. 30, n° 23, Jan. 12, 2005.
The output 24 is directly optically coupled to an input port 30 of a resonant ring modulator 32 equipped with two output ports 34 and 36. The resonant ring modulators are well known and only a few production and operation principles are reviewed with reference to
The modulator 32 switches, in response to an electrical control signal received on its port 38, between an “Off” state, and an “On” state. In the “Off” state, the intensity P3 is maximum and the intensity P6 is minimum. Typically, in the “Off” state, the intensity P3 is at least greater than 0.5×P1 and, preferably, greater than 0.8×P1 or 0.9×P1 and the intensity P6 is at least three or five times less than the intensity P1. Conversely, in the “On” state, the intensity P3 is minimum and the intensity P6 is maximum. Typically, in the “On” state, the intensity P6 is at least greater than 0.5×P1 and, preferably, greater than 0.8×P1 or 0.9×P1 and the intensity P3 is at least three or five times less than the intensity P1. Because of this behaviour of the intensity of the signal S6 in relation to the intensity of the signal S3, it is said that the signal S6 is the complementary signal of the signal S3.
The control signal received on the port 38 is, here, a binary electrical signal V1. The voltage of the signal V1 therefore varies only between two voltage levels Vmax and Vmin each of which codes a value of an information bit. For example, Vmax is equal to 0 Vdc and Vmin is equal to −3 Vdc. The modulator 32 is in the “On” state when the voltage of the signal V1 is equal to Vmin and in the “Off” state when the voltage of the signal V1 is equal to Vmax. Thus, in response to the voltage variations of the signal V1, the modulator 32 simultaneously modulates the intensities of the signals S3 and S6.
The modulator 32 is associated with a controllable electric tuner 40 capable of modifying the transfer functions FT31 and FT61 of the intensity between the ports 30, 34 and 36. The function FT31 is the transfer function of the intensity of the optical signal between the ports 32 and 34. This function FT31 is represented in
More specifically, the tuner 40 is capable of shifting the wavelength λ0 for which the function FT31 exhibits a minimum. This tuner is also capable of at the same time shifting the wavelength λ0 for which the function FT61 exhibits a maximum. In effect, the functions FT31 and FT61 are intimately linked and depend on one another. For example, to this end, the tuner 40 comprises a radiator capable of heating up and/or cooling down the modulator 32. In effect, the refractive index of the ring of the modulator 32 varies as a function of the temperature, which therefore modifies its transfer function.
A sensor 44 of the intensity P3 is also provided. For example, the sensor 44 comprises an optical coupler 46 with one input and two outputs 50, 52 as well as a photodetector 54 directly optically coupled to the output 52. The input of the optical coupler 46 is directly optically coupled to the output 34. The output 52 delivers an optical signal identical to the signal S3 but with an intensity that is only a fraction of the intensity of the signal S3. Typically, the intensity of the optical signal delivered by the output 52 is less than 10% and, preferably, less than 5% or 3% of the intensity P3. The output 50 returns the remaining part of the signal S3. After that, the intensity taken by the coupler 46 from the signal S3 is considered as negligible. Consequently, the intensity of the signal S3 delivered by the output 50 is considered as being equal to the intensity P3 of the signal S3 delivered on the output 34.
The photodetector 54 converts the optical signal delivered on the output 52 into an electrical signal representative of the intensity P3. It is this electrical signal which therefore constitutes the measurement of the intensity P3.
The output 50 is directly optically coupled to an input 60 of an optical assembler 62. An optical assembler is also known as “optical combiner” or “optical field combiner”.
The output 26 of the divider 22 is directly optically coupled to an input 70 of a controllable phase-shifter 72. The phase-shifter 72 is capable of modifying the phase of the signal S2 as a function of an adjustment electrical signal. The phase-shifter 72 also comprises an output 74 on which it delivers the signal Sz, the phase of which has been adjusted. By contrast, the phase-shifter 72 does not modify the intensity P2 of the signal S2.
One possible embodiment of the phase-shifter 72 is described in the following article: Nicholas C. Harris et Al., “Efficient, compact and low loss thermo-optic phase shifter in silicon”, Optics Express, 2014.
For example, in a particular embodiment, the phase-shifter 72 comprises:
In response to the adjustment signal, a potential difference is applied to this resistive metal, which generates heat. The resistive metal therefore varies the temperature of the waveguide and therefore its refractive index. This modifies the phase of the signal S2 which passes through this waveguide.
The output 74 is directly optically coupled to an input 80 of the assembler 62.
The assembler 62 also comprises an output 82 on which it delivers an optical signal S4. The signal S4 results from the field combination of the signals S3 and S2.
Here, the assembler 62 is a summer of optical fields. It therefore adds up the optical fields of the signals S3 and S2 to obtain the signal S4. For example, the assembler 62 is an MMI (Multi-Mode Interference) assembler with two inputs 60, 80 and with one output 82. An MMI assembler is also sometimes called “interferometer”. The MMI assemblers are well known. For example, the interested reader can refer to the following article: Lucas B. Soldano et al “Optical multi-mode interference devices based on self-imaging: principles and applications”, Journal of Lightwave Technology, Volume 13, n° 4 Apr. 1995.
To limit the losses in the assembler 62, the optical signals received on the inputs 60 and 80 must preferably be in phase. Here, the assembler 62 is an MMI coupler with −3 dB of loss. Consequently, the intensity P4 of the signal S4 as a function of the intensities P3 and P2 is given by the following relationship when the signals S3 and S2 are in phase at the inputs 60 and 80: P4=(√{square root over (P3+)}√{square root over (P2)})2/2.
A sensor 86 of the intensity P4 is directly optically coupled to the output 82 of the assembler 62. Here, this sensor 86 is identical to the sensor 44. It therefore comprises an input directly optically coupled to the output 82 and an output which delivers the signal S4 from which a negligible fraction of its intensity has been taken for the measurement. As for the sensor 44, the sensor 86 comprises an optical coupler 88 and a photodetector 90 identical, respectively, to the optical coupler 46 and to the photodetector 54.
The output of the sensor 86 is directly optically coupled to an input port 100 of a resonant ring modulator 102. This modulator 102 is, for example, identical to the modulator 32. It therefore comprises two output ports 104 and 106. The ports 100, 104 and 106 are, respectively, the “In”, “Through” and “Drop” ports of the modulator 102.
The modulator 102 also comprises a control port 108 which receives the control binary electrical signal V2. The port 106 delivers an optical signal S5, the intensity of which is denoted P5.
In a way similar to what has been described for the modulator 32, the modulator 102 is associated with a controllable electrical tuner 109. This tuner 109 is identical to the tuner 40 except that it is capable of modifying the transfer functions of the modulator 102 and not those of the modulator 32.
Only a sensor 110 is directly optically coupled to the port 104 of the modulator 102. In particular, no power divider or no optical coupler is directly optically coupled to the port 104. Consequently, in this embodiment, the sensor 110 can use all of the intensity of the signal delivered on this port 104 when the modulator 102 is in its “Off” state. For example, to this end, the sensor 110 comprises a photodetector 112 directly optically coupled to the port 104.
The port 106 is directly optically coupled to an input 116 of a controllable phase-shifter 118. The phase-shifter 118 makes it possible to adjust the phase of the signal S5 as a function of an adjustment signal. The signal S5, the phase of which has been adjusted by the phase-shifter 118, is delivered on an output 120. Here, the structure of the phase-shifter 118 is identical to that of the phase-shifter 72.
The output 120 and the port 36 of the modulator 32 are directly optically coupled, respectively, to inputs 124 and 125 of an optical assembler 126. The assembler 126 recombines the signals S5 and S6 by summing their optical field and delivers the duly obtained optical signal on an output 128. Here, the assembler 126 is, for example, identical to the assembler 62.
A sensor 130 measures the intensity of the optical signal delivered on the output 128. For example, the sensor 130 is identical to the sensor 86 except that its input and its output are directly optically coupled, respectively, to the output 128 and to the output 14. Thus, the sensor 130 measures the intensity Pout of the signal Sout. The coupler and the photodetector of this sensor 130 bear, respectively, the numeric references 132 and 134.
By way of illustration, in this embodiment, the signals V1 and V2 originate from a source 142 of binary electrical signals external to the device 2. The source 142 comprises two outputs 144 and 146 electrically coupled, respectively, to the inputs 12A and 12B to supply the signals V1 and V2 to the device 2. For example, the source 142 comprises two microprocessors which each generate, independently of one another, one of the signals V1 and V2. The outputs 146 and 148 of the source 142 can also correspond to two outputs of a demultiplexer. The inputs 12A and 12B are electrically coupled, respectively, to the ports 38 and 108.
Finally, the device 2 comprises an electronic circuit 150 for adjusting the phase of the signals S2 and S5 and for setting the modulators 32 and 102. The circuit 150 is electrically coupled to the sensors 44, 86, 110 and 130 to receive the intensities measured by these sensors. The circuit 150 is also electrically coupled to the tuners 40 and 109 and to the phase-shifters 72 and 78 to control them. For example, the circuit 150 comprises a programmable microprocessor 152 produced on the same substrate as the other components of the device 2. Here, the microprocessor 152 is programmed to implement the method of
The port 164 is known as the “Add” port.
The ring 166 is optically coupled on one side to the waveguide 160 and, on another side, to the waveguide 162. A detailed description of such a ring and of its operation is given in the appendix to the application EP2843468. For example, the characteristics of the modulator 32 are as follows:
The points designated by the symbols “ON” and “OFF” in
In
In this embodiment, the extinction rate of the modulator 32 for the port 34, that is to say the deviation between the values in decibels of the ratio P3/P1 in the, respectively, “Off” and “On” states, is equal to 4 dB to within plus or minus 20%. For example, the insertion rate of the modulator 32, that is to say the deviation between 0 dB and the value in decibels of the ratio P3/P1 in the “Off” state is equal to 1.3 dB to within plus or minus 20%.
For example, the extinction rate and the insertion rate of the modulator 32 for the port 36 are equal, respectively, to 4 dB and 4.1 dB to within plus or minus 20%.
The operation of the device 2 will now be described with reference to the method of
The method begins with a phase 170 of setting of the modulators 32 and 102. For that, in a step 172, the source 142 is controlled to maintain, throughout the duration of the phase 170, the modulators 32 and 102 in their “On” state. In other words, the signals V1 and V2 are each maintained at their level Vmin.
In parallel, throughout the duration of the phase 170, in a step 174, the sensors 44 and 110 measure the intensities of the optical signals delivered on the ports, respectively, 34 and 104. These sensors transmit the measured intensities to the circuit 150.
Also in parallel, in a step 176, the circuit 150 sets the modulator 32. To this end, the circuit 150 controls the tuner 40 to progressively shift the transfer function FT31 and, in particular, the wavelength λ0 for which this transfer function exhibits a minimum. Thus, when the wavelength λ0 approaches the wavelength λ0 of the signal Sin, the intensity measured in parallel by the sensor 44 decreases. Conversely, as soon as the wavelength λ0 moves away from the wavelength λin, the intensity measured in parallel by the sensor 44 increases. The circuit 150 therefore varies the wavelength λ0 until the latter corresponds to a power minimum measured by the sensor 44. When the intensity measured by the sensor 44 is minimum, the wavelength λ0 is equal to the wavelength λin and the extinction rate of the modulator 32 is maximised. The control signal of the tuner 40 which minimises the intensity measured by the sensor 44 when the modulator 32 is in the “On” state is then stored.
Then, in a step 178, the circuit 150 sets the modulator 102. This step 178 is identical to the step 176 except that it is the sensor 110 and the tuner 109 which are used instead, respectively, of the sensor 44 and of the tuner 40.
Next, in a phase 180, the circuit 150 adjusts the phases of the signals S2 and S5 for these signals to be in phase, at the inputs 80 and 124, with, respectively, the signals S3 and S6.
For that, in a step 182, the source 142 is controlled to maintain, throughout the duration of the phase 180, the modulators 32 and 102 in their “Off” state.
In parallel, in a step 184, the sensors 86 and 130 permanently measure the intensities P4 and Pout. These sensors transmit in real time their measurements to the circuit 150.
In a step 186, the circuit 150 adjusts the phase of the signal S2 for it to be equal to the phase of the signal S3 at the inputs of the assembler 62. For that, the circuit 150 controls the phase-shifter 72 to progressively vary the phase of the signal S2. When the phase of the signal S2 approaches the phase of the signal S3 at the inputs 60, 80, the intensity measured by the sensor 86 increases. Conversely, when the phase-shift between the signals S2 and S3 increases at the inputs 60 ad 80, the intensity measured by the sensor 86 decreases. The circuit 150 therefore varies the adjustment signal of the phase-shifter 72 until the adjustment signal which maximises the intensity measured by the sensor 86 is found. This adjustment signal found is then stored.
Next, in a step 188, the circuit 150 adjusts the phase of the signal S5 for it to be in phase with the signal S6 at the inputs of the assembler 126. The step 188 is identical to the step 186 except that it is the phase-shifter 118 and the sensor 130 which are used instead of the phase-shifter 72 and the sensor 86.
Once the device 2 has been calibrated, the method continues with a phase 190 of modulation of the intensity of the signal Sin on four different levels as a function of the signals V1 and V2 to be transmitted. Throughout the duration of this phase 190, the circuit 150 applies to the modulators 32 and 102 the setting signal stored in the phase 170 and also applies the adjustment signal stored in the phase 180 to the phase-shifters 72 and 118.
In the phase 190, the signals V1 and V2 are applied to the input ports 38 and 108 of the modulators 32 and 102 respectively.
In parallel, the laser source 16 generates the signal Sin and transmits it to the input 10 of the device 2. The signal Sin is then divided into two signals S1 and S2 of the same power by the divider 22. The intensity of the signal S1 is then modulated by the modulator 32 as a function of the control signal V1 so as to obtain the modulated optical signal S3. The signal S3 is then combined with the signal S2 by the assembler 62 to obtain the signal S4 received on the port 100 of the modulator 102. At the same time, the complementary signal of the signal S3, that is to say the signal S6, is delivered on the port 36.
The module 102 once again modulates the intensity of the signal S4, but this time as a function of the control signal V2 to obtain the signal S5.
The signals S5 and S6 are then combined together by the assembler 126 to obtain the signal Sout, the intensity of which is modulated on four different levels. In the signal Sout, each intensity level codes both the value of a bit of the signal V1 and of a bit of the signal V2.
The table below presents, for each possible combination of the states of the modulators 32 and 102, the values of the intensities P1 to P6 and Pout calculated for a power Pin of the signal Sin. To simplify this calculation, the losses of intensities in the optical components of the device 2 have all been disregarded except those caused by the optical assemblers 62 and 130. Consequently, for the calculation of the intensity Pout of the signal Sout, the contribution of the maximum intensity of the optical signals S3, S5 and S6 is considered as negligible. Thus, in the table below, the minimum intensity of these signals is taken to be equal to 0 W.
The intensity range over which the four intensity levels are distributed therefore extends from 0 to 0.73×Pin. Furthermore, the four possible intensity levels are practically uniformly distributed over this intensity range.
At predetermined intervals, the circuit 150 once again reiterates the phases 170 and 180 to permanently adapt the calibration of the device 2 to the current operating conditions of this device 2.
Here, the block 202 comprises three resonant ring modulators 210 to 212. These modulators 210 to 212 are identical to the modulator 32 except that the wavelengths, respectively denoted λ1, λ2 and λ3, for which their transfer functions exhibit a minimum are different. Here, the wavelengths λ1, λ2 and λ3 are spaced apart from one another by an interval Δ greater than or equal to 1 nm and, preferably, greater than or equal to 2 or 5 nm. Furthermore, generally, the interval Δ is less than or equal to 10 nm or 15 nm. Thus, the modulator 210 is incapable of modulating the intensity of the optical signals at the wavelengths λ2 and λ3. The same applies for the modulators 211 and 212 which cannot modulate the optical signal at the wavelength λ1. Consequently, the series connection of the modulators 210 to 212 in no way alters the modulation method for a given wavelength of the signal Sin.
The block 204 comprises the same modulators 210 to 212 coupled in series. However, here, in the direction of circulation of the optical signal which passes through the “Through” ports of these modulators, the modulators 210 to 212 are arranged in reverse direction relative to that which was done in the block 202.
Each of the modulators of the blocks 202 and 204 is controlled by its own control binary electrical signal. Here, these control binary electrical signals are denoted V1, V2, V3, V4, V5 and V6. To generate these signals V1, V2, V3, V4, V5 and V6, the source 142 is replaced by a source 220 of binary electrical signals which generates the six signals V1 to V6.
To simplify
For each wavelength λ1, λ2 and λ3, the operation of the device 200 is the same as that of the device 2. It will however be noted, in the case of the device 200, the laser source 16 has to be replaced by a multichromatic laser source 222 which simultaneously generates three monochromatic optical signals not modulated at the wavelengths λ1, λ2 and λ3. For example, to this end, the source 222 comprises three monochromatic sources of different multiplexed wavelengths. Similarly, the receiver 12 has to be replaced by a receiver 224. The receiver 224 typically comprises a wavelength demultiplexer 226 which isolates the optical signals at the wavelengths λ1, λ2 and λ3. This demultiplexer 226 then transmits the optical signal isolated at each of these wavelengths λ1, λ2 and λ3 to respective photo detectors 228 to 230.
It is possible to arrange the modulators and the optical assemblers of the device 2 differently to obtain variations of this device 2 which offer the same advantages and, in particular, a small bulk and four intensity levels distributed over a wide intensity range. Three examples of such variants are represented in
The table below summarises the values of the intensities P1 to P6 and Pout obtained for the different possible states of the modulators 32 and 102 of the device 230.
In the device 230, the port 106 of the modulator 126 is not used. That increases the variability of the signal Sout.
The table below summarises the values of the intensities P1 to P6 and Pout obtained for the different possible states of the modulators 32 and 102 of the device 240.
As the table above shows, in the embodiment of
The table below indicates the values of the intensities P1 to P6 and Pout obtained for the different possible states of the modulators 32 and 102 of the device 250.
In each embodiment, the role and the optical couplings of the two output ports of the same modulator can be reversed. That is for example what has been done to switch from the embodiment of
Many other embodiments are possible. For example, the divider 22 can be replaced by any other type of optical component making it possible to divide the intensity of the signal Sin. In particular, this power divider can be replaced by a Y-junction.
It is not necessary for the divider 22 to uniformly distribute the intensity of the signal Sin between the signals S1 and S2. As a variant, the intensities of the signals S1 and S2 are different. For example, preferably, the intensity P1 is strictly greater than the intensity P2. Thus, in other embodiments, the intensity P1 is greater than 1.5×P2 or 2×P2. For example, in a particular case, the intensity Pin is equal to ⅔×Pin and the intensity P2 is equal to ⅓×Pin. In this case, the four intensity levels are no longer uniformly spaced apart from one another.
The optical assemblers such as the assemblers 62 and 126 can exhibit losses different from −3 dB. For example, there are optical assemblers with losses that are higher or, on the contrary lower. These assemblers can be used in place of the assemblers 62 and 126.
In place of the modulators described, it is possible to use modulators that are identical but in which the “On” state is obtained when the voltage applied to the control port is equal to Vmin and the “Off” state is obtained by applying the voltage Vmax. It is then necessary to adapt the control signal accordingly if necessary.
The binary control signal of the modulators is not necessarily an electrical signal. As a variant, it is replaced by a mechanical signal which switches a modulator between its “Off” and “On” states.
The fibre 11 can be replaced by a silicon or polymer waveguide produced on the same chip as that of the device 2 if the receiver 12 is also located on this chip.
In the device 200, the order in which the resonant ring modulators are coupled to one another in each block 202, 204 can be modified.
There are numerous possible embodiments for the resonant ring modulators 32 and 102. For example, as a variant, each of these modulators is produced as described in the application EP2843468. In this case, each modulator does not modify the phase of the optical signal that it modulates in intensity. Consequently, the phase-shifters 72 and 118 and the sensors 86 and 130 can be omitted because they are no longer necessary.
The phase-shifters 72 and 118 can be coupled to the other input of the assembler. In another variant, a phase-shifter is placed in front of each input of the assemblers 62 and 126. Other embodiments of an optical phase-shifter are possible. For example, one such other embodiment is described in the application EP1782123.
It is also possible to omit one or more of the optical phase-shifters. For example, it is possible to omit the phase-shifter 72 if the length of the waveguide between the output 24 and the input 80 has been adjusted to compensate the phase-shift introduced by the modulator 32. By proceeding likewise, it is also possible to omit the phase-shifter 118.
In another embodiment, at least one of the tuners 40, 109 is omitted. In this case, the sensor 44 or 110 used to control this tuner is also omitted.
The sensor 44 can be directly coupled to the port 36 to measure the intensity P6 instead of the intensity P3. In this case, the modulator 32 is tuned to the wavelength λin when the intensity of the signal S6 is maximum and the modulator 32 is in its “On” state.
| Number | Date | Country | Kind |
|---|---|---|---|
| 15 60976 | Nov 2015 | FR | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5369383 | Takahashi | Nov 1994 | A |
| 20030128415 | Kalluri | Jul 2003 | A1 |
| 20080219614 | Gill et al. | Sep 2008 | A1 |
| 20090244685 | Hoshida | Oct 2009 | A1 |
| 20150316794 | Hayakawa | Nov 2015 | A1 |
| 20170059893 | Lemaitre | Mar 2017 | A1 |
| Number | Date | Country |
|---|---|---|
| 2 843 468 | Mar 2015 | EP |
| Entry |
|---|
| Lucas B. Soldano et al. Optical Multi-Mode Interference Devices Based on Self-Imaging: Principles and Applications, Journal of Lightwave Technology, vol. 13, No. 4, 1995, 13 pages. |
| C.S. Hsiao et al. “Design for beam splitting components employing silicon-on-insulator rib waveguide structures” Optics Letters, vol. 30, No. 23, 2005, 3 pages. |
| French Preliminary Search Report dated Aug. 22, 2016 in French Application 15 60976, filed on Nov. 16, 2015 (with English Translation of Categories of Cited Documents and Written Opinion). |
| Nicholas C. Harris et al. “Efficient, Compact and Low Loss Thermo-optic Phase Shifter in Silicon”, Physics. Optics, 2014, 6 pages. |
| O. Dubray et al. “20Gb/s PAM-4 Transmission from 35 to 90° C. by modulating a Silicon Ring Resonator Modulator with 2Vpp”, OFC 2015, OSA 2015, 2015, 3 pages. |
| Bishanka Brata Bhowmik et al. “Silicon Micro-Ring Resonator Based 16-Qam Modulator for WDM Transmission Systems”, 2013 IEEE, 5 pages. |
| M. Ashkan Seyedi et aI. “Data Rate Enhancement of Dual Silicon Ring Resonator Carrier-Injection Modulators by PAM-4 Encoding”, Photonics in Switching 2015, Optical Switching Technology & Devices, 2015, 3 pages. |
| Number | Date | Country | |
|---|---|---|---|
| 20170141852 A1 | May 2017 | US |
