Multi-wavelength optical data modulation

Abstract

According to an example aspect of the present invention, there is provided a multi-wavelength modulator, comprising an input waveguide arranged to convey light to plural waveguide Bragg gratings, each waveguide Bragg grating being configured to reflect light of a specific wavelength back to a distinct intermediate waveguide, each intermediate waveguide configured to convey reflected light from a respective waveguide Bragg grating to a specific waveguide modulator, each intermediate waveguide being coupled with a distinct waveguide modulator, and each waveguide modulator configured to modulate light received in the waveguide modulator from a respective intermediate waveguide according to a pattern to generate modulated light.

Description

MULTI- WAVELENGTH OPTICAL DATA MODULATIONFIELD

[0001] The present disclosure relates to the technical field of modulation of electromagnetic radiation.BACKGROUND

[0002] Data centres provide centralized processing platforms for many services which may be used by users from wide areas. Data centres have come to consume substantial energy resources for performing computing and cooling of computing units. In some solutions, data centres are placed in geographic locations which experience cold winter weather, to enable use of naturally cold fluid, such as air or water, to cool the data centre.

[0003] High-bandwidth optical interconnections in data centres are used to interface computing units, such as servers or supercomputer sub-units, with each other. This enables distributed processing of complex computing tasks. Applications such as video streaming, virtual meetings and machine learning have drastically increased the required data transfer capacity of data centres. The need for high bandwidth, low latency and low power consumption is ever more important.SUMMARY

[0004] According to some aspects, there is provided the subject-matter of the independent claims. Some embodiments are defined in the dependent claims.

[0005] According to a first aspect of the present disclosure, there is provided a multiwavelength modulator, comprising an input waveguide arranged to convey light to pluralwaveguide Bragg gratings, each waveguide Bragg grating being configured to reflect light of a specific wavelength back to a distinct intermediate waveguide, each intermediate waveguide configured to convey reflected light from a respective waveguide Bragg grating to a specific waveguide modulator, each intermediate waveguide being coupled with a distinct waveguide modulator, and each waveguide modulator configured to modulate light received in the waveguide modulator from a respective intermediate waveguide according to a pattern to generate modulated light.

[0006] According to a second aspect of the present disclosure, there is provided a multi-wavelength modulator, comprising an input waveguide arranged to convey light to a multi-wavelength waveguide Bragg grating configured to reflect light of a plural specific wavelengths back to an intermediate waveguide, the intermediate waveguide being provided with plural waveguide modulators, each waveguide modulator being configured to modulate one and only one of the plural specific wavelengths reflected into the intermediate waveguide, and a last one of the plural waveguide modulators being configured to provide the output of all the plural waveguide modulators to an output waveguide.

[0007] According to a third aspect of the present disclosure, there is provided a multi-wavelength demultiplexer, comprising a receive input waveguide arranged to convey light to plural receive waveguide Bragg gratings, each receive waveguide Bragg grating being configured to reflect light of a specific wavelength back to a distinct intermediate receive waveguide, and each intermediate receive waveguide configured to convey reflected light from a respective receive waveguide Bragg grating to a photodetector, each intermediate waveguide being coupled with a distinct photodetector.

[0008] According to a fourth aspect of the present disclosure, there is provided a multi-wavelength transceiver comprising a multi-wavelength modulator according to the first or second aspect, and a multi-wavelength demultiplexer, such as according to the third aspect, the transceiver integrated on a silicon chip, wherein dimensions of the transceiver, integrated on the silicon chip, are in a range of 0,3 to 0,8 square millimetre, mm2, surface area with a thickness between 0,75 and 1,25 mm.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIGURE 1 illustrates an example system in accordance with at least some embodiments of the present invention.

[0010] FIGURE 2A illustrates a first modulator architecture in accordance with at least some embodiments of the present invention;

[0011] FIGURE 2B illustrates a second modulator architecture in accordance with at least some embodiments of the present invention, and

[0012] FIGURE 3 illustrates a modulator architecture in accordance with at least some embodiments of the present invention.EMBODIMENTS

[0013] Energy usage and heat generation of high-bandwidth optical interconnections are of interest, since excessive heat generation makes data centres and other centralized computing solutions more difficult to manage. Herein are disclosed multi-wavelength modulators which receive light to be modulated from outside the multi-wavelength modulator itself, in other words, the multi-wavelength modulators do not comprise light sources, but are connectable to external light sources. The light is arranged into separate wavelength components using waveguide Bragg gratings, and the separate wavelength components are separately modulated in separate waveguide modulators. This solution produces significant benefits in terms of reduced heat dissipation and compact size when integrated on a single silicon chip. High-bandwidth cryogenic light modulators may be employed for optical links delivering control signals and reading out data in quantum computing. Here, ultra-compact size obtained by integration of a transceiver on a single silicon chip and lower power consumption are beneficial.

[0014] As will be disclosed herein, graphene -waveguide modulators with reflective waveguide Bragg gratings may be monolithically integrated. This approach provides multiwavelength light modulation in a highly compact silicon chip. Compared with earlier transceiver solutions, a significant reduction in power consumption and transceiver device footprint are obtained. In addition, since graphene is used in the multi-wavelength modulator itself, the herein disclosed approach is viable also for cryogenic applications.

[0015] FIGURE 1 illustrates an example system in accordance with at least some embodiments of the present invention. The scope of the present disclosure is limited by theclaims, whereas the structure included in FIGURE 1 serves to elucidate technical features of the present disclosure.

[0016] Computing substrates 101 and 102 may comprise servers or supercomputer sub-units, for example. The present disclosure is by no means limited to communication between computing substrates, rather, they are used here to describe technical features of the herein disclosed devices. Computing substrates 101, 102 may be in a data centre, for example, the data centre possibly comprising many such computing substrates in addition to the two illustrated in FIGURE 1.

[0017] Computing substrate 101 is provided with multi-wavelength transceiver 110, and computing substrate 102 is provided with multi-wavelength transceiver 120. Multiwavelength transceivers 110, 120 will be referred to as transceivers 110, 120 herein for the sake of brevity. Transceivers 110, 120 each comprise a respective multi-wavelength modulator and multi-wavelength receiver in the example of FIGURE 1 , although in some implementations it is possible that communication is one-way, in which case one of these devices could be a multi-wavelength modulator, and the other a multi-wavelength receiver.

[0018] Transceiver 110 is configured to receive light to modulate from light source 112 via waveguide 113. Waveguide 113 may be an optic fibre, for example. Light source 112 produces polychromatic light, the polychromatic light having plural spectral peaks or a continuous spectrum. Polychromatic light with plural spectral peaks may be generated using plural laser emitters or plural light-emitting diode, LED, emitters, for example. Light with a more continuous spectrum may be generated using a supercontinuum light source, for example. Laser emitters have sharper spectral peaks than LED emitters.

[0019] Transceiver 120 is configured to receive light to modulate from light source 122 via waveguide 123. Waveguide 123 may be an optic fibre, for example. Light source 122 produces polychromatic light, the polychromatic light having plural spectral peaks or a continuous spectrum. Like light source 112, also light source 122 may comprise laser or LED light emitters, for example.

[0020] The light sources 112, 122 need not be of a same type, for example, one of them may comprise laser emitters and the other LED emitters. The number of emitters may be two, four, eight or sixteen, for example. Also the number of emitters may differ between light source 112 and light source 122. In some embodiments, a same light source isarranged to provide light to be modulated to more than one multi-wavelength modulator. Placing the light source separate from the modulator(s) provides the benefit that heat generated in the light source is not generated close to a computing substrate or other device close to the multi-wavelength modulator.

[0021] Transceiver 110 is configured to receive patterns of data from terminal 111 via connection 114. A multi-wavelength modulator of transceiver 110 modulates light received in transceiver 110 from light source 112 in accordance with the patterns received from terminal 111. In other words, the pattern is the payload data the modulator encodes in the light. Likewise, transceiver 110 is configured to provide, via connection 114, to terminal 111 demodulated data it has received. Connection 114 may be an optical connection or an electrically conductive lead, for example. Terminal 111, comprised in computing substrate 101, may comprise a communication interface or a communication pin, or pins, of a processor of computing substrate 101, for example.

[0022] Transceiver 120 is likewise configured to receive patterns of data via connection 124 from terminal 121 for modulating light, and to provide to terminal 121, via connection 124, demultiplexed data it has received.

[0023] Transceivers 110 and 120 are interconnected by a link 130, which comprises at least one waveguide, e.g., an optical fibre, to enable multi-wavelength communication between transceivers 110 and 120. In some embodiments, interface 130 comprises plural waveguides, one for each wavelength of light used in the multi-wavelength communication between transceivers 110 and 120.

[0024] FIGURE 2A illustrates a first modulator architecture in accordance with at least some embodiments of the present invention. An input waveguide 210 is arranged to convey polychromatic light from a light source to the modulator 200. The light source may be, as illustrated in FIGURE 1 , external to modulator 200 and, optionally, also external to a transceiver which comprises modulator 200.

[0025] Input waveguide 210 conveys unmodulated polychromatic light to plural waveguide Bragg gratings 222, 224, 226. A waveguide Bragg grating may be referred to as a fibre Bragg grating. A waveguide Bragg grating is a wavelength selective filter which reflects back toward a source a specific wavelength, and allows other wavelengths to pass through the waveguide Bragg grating. In other words, a waveguide Bragg grating is a typeof distributed Bragg reflector constructed, for example, in a short segment of optical fibre that reflects a particular wavelength of light and transmits all others. This may be achieved by creating, for example, a periodic variation in the refractive index of the fibre core, which generates a wavelength-specific dielectric mirror. Hence a waveguide Bragg grating may be used as to block certain wavelengths, for sensing applications, or it can be used as wavelength-specific reflector. The waveguide Bragg gratings 222, 224, 226 may comprise shifted Bragg gratings applied to a silicon waveguide section, the gratings being deposited with a titanium dioxide, TiCh, surface layer. The titanium dioxide surface layer reduces index contrast and allows a narrower reflected bandwidth, increasing the frequency selectivity of the waveguide Bragg grating. Such a grating is described in publication [1], where a 2,2 nanometre, nm, spectrum peak width of reflected light is described. The shifted Bragg gratings may be asymmetric.

[0026] The waveguide Bragg gratings 222, 224, 226 are provided with adiabatic mode splitters for each waveguide Bragg grating 222, 224, 226 to convey the reflected light of the specific wavelength to a respective intermediate waveguide 232, 234, 236. In detail, a reflected wavelength from waveguide Bragg grating 222 is conveyed to intermediate waveguide 232. Similarly, the wavelength reflected from waveguide Bragg grating 224 is conveyed to intermediate waveguide 234, and the wavelength reflected from waveguide Bragg grating 226 is conveyed to intermediate waveguide 236. Thus the waveguide Bragg gratings 222, 224, 226 overall selectively and accurately convey distinct wavelength components of the incoming polychromatic light to intermediate waveguides 232, 234, 236, one and only one wavelength into each intermediate waveguide. In other words, the light in intermediate waveguides 232, 234, 236 is monochromatic in the sense that it has a single spectral peak, which is of the order of only a few nanometres, nm, wide. For example, it may be less than 2,5 nm, less than 3 nm, less than 4 nm or less than 5 nm wide, depending on the characteristics of the waveguide Bragg gratings 222, 224, 226. In some embodiments, the spectral width is not the same in all the intermediate waveguides 232, 234, 236. This would be a result of the waveguide Bragg gratings having different selectivity.

[0027] The waveguide Bragg gratings may further act as mode converters, by which it is meant that each grating is an antisymmetric grating in a two-mode waveguide and performs mode conversion (Ref. 1). This enables the reflected light, e.g., from the waveguide Bragg grating 222 to couple to the intermediate waveguide 232.

[0028] Intermediate waveguide 232 is coupled with waveguide modulator 242, which is configured to modulate the monochromatic light from intermediate waveguide 232 based on a pattern received via connection 260, which may correspond to, or be connected with, connection 114 of FIGURE 1. Connection 260 couples with all waveguide modulators 242, 244, 246, providing independent and different modulation patterns, despite being illustrated in FIGURE 2A in connection with waveguide modulator 246 only for the sake of clarity of the illustration. The modulation may comprise, for example, on- off modulation in accordance with the pattern, encoding bits zero and one as states of the light being on and off Modulated light is conveyed from waveguide modulator 242 to exit waveguide 252.

[0029] Waveguide modulator 242 may be a graphene-waveguide modulator [2], [3], which is an electro-absorption light modulator based on graphene on top of a planar waveguide. Both single- and dual-graphene layer modulator configurations may be used [2], [3], One applicable configuration of a graphene-waveguide modulator is based on micro-ring resonators with graphene on top of the micro-ring resonators [4], With this approach the interaction of light with graphene is enhanced. In addition, graphenewaveguide electro-absorption modulators have potential for operation at cryogenic temperatures, since they do not suffer from carrier freeze-out, which is a severe issue with common silicon-waveguide modulators based on p-n junctions..

[0030] The efficiency of a graphene-waveguide modulator may be increased by enhancing light interaction with graphene, which may be obtained with a cavity based on a distributed Bragg grating, DBR, structure. As in the case of a ring waveguide modulator, the waveguide cavity formed by DBR gratings enhances the interaction of light with graphene.

[0031] Likewise, waveguide modulator 244 modulates the monochromatic light it receives from intermediate waveguide 234 based on a pattern from connection 260 and outputs modulated monochromatic light to exit waveguide 254. Further, waveguide modulator 246 modulates the monochromatic light it receives from intermediate waveguide 236 based on a pattern from connection 260 and outputs modulated monochromatic light to exit waveguide 256. Waveguide modulators 244 and 246 may be graphene-waveguide modulators, graphene-waveguide electro-absorption modulators or bebased on micro-ring resonators with graphene on top, as described herein above concerning waveguide modulator 242.

[0032] The exit waveguides 252, 254, 256 may be coupled with a wavelength multiplexer configured to convey the modulated light of the specific wavelengths from the exit waveguides 252, 254, 256 to a single output waveguide. Alternatively, the exit waveguides 252, 254, 256 may be the output interface of the multi-wavelength modulator, corresponding to interface 130 of FIGURE 1. The wavelength multiplexer is not illustrated in FIGURE 2A.

[0033] The number of modulated wavelengths, corresponding in FIGURE 2A to the number of waveguide Bragg gratings, intermediate waveguides, waveguide modulators and exit waveguides, need not be three but may be two or more than three, such as four, eight or sixteen, for example. The multi-wavelength modulator of FIGURE 2A may be integrated on a chip such that it consumes only 0,5 square millimetres, mm, and a thickness of one mm. For example, the dimensions of the multi-wavelength modulator, when integrated on a silicon chip, may be 1 x 0,5 mm in area, and 1 mm thick. The area may be in the range of 0,3 to 0,8 square mm, for example, with the thickness between 0,75 and 1,25 mm. The multi-wavelength modulator so integrated on a silicon chip that it may be operated at a temperature as low as 4 kelvins.

[0034] FIGURE 2B illustrates a second multi-wavelength modulator architecture in accordance with at least some embodiments of the present invention. Eike numbering denotes like structure as in FIGURE 2A. The input waveguide 210 conveys polychromatic, unmodulated light from a light source external to multi-wavelength modulator 201 and, optionally, also external to a transceiver which comprises multi-wavelength modulator 201. Input waveguide 210 conveys the light to multi-wavelength mode-converting Bragg grating 228, which is configured to reflect into intermediate waveguide 238 plural specific wavelengths, and to admit other wavelengths possibly present in the incoming light to pass through multi-wavelength mode-converting Bragg grating 228.

[0035] Waveguide modulators 242, 244 and 246 are cascaded along intermediate waveguide 238. Waveguide modulators 242, 244 and 246 are each configured to modulate a specific one of the wavelengths reflected into intermediate waveguide 238 by multiwavelength mode-converting Bragg grating 228, and to allow other wavelengths to pass through. As was the case in FIGURE 2A, connection 260 couples with all waveguidemodulators 242, 244, 246, providing independent and different modulation patterns to these modulators. Waveguide modulators 242, 244 and 246 may be graphene -waveguide modulators based on micro-ring resonators, to minimize losses incurred by the wavelengths passing through modulators not configured to modulate them. A benefit of the architecture of FIGURE 2B is that the modulated output in all the modulated wavelengths is in a single exit waveguide 258, which removes the need for a separate wavelength multiplexer in case the modulated output is to be conveyed in a single waveguide. In general, use of graphene with, e.g., silicon nitride waveguides results in lower losses compared to silicon waveguides.

[0036] FIGURE 3 illustrates a demultiplexing architecture in accordance with at least some embodiments of the present invention. An input waveguide 310 conveys modulated, polychromatic light to plural waveguide Bragg gratings 322, 324, 326. The modulated polychromatic light may comprise plural narrow spectral peaks of specific wavelengths. A waveguide Bragg grating may be referred to as a fibre Bragg grating. A waveguide Bragg grating is, as described above concerning the modulator side, a wavelength selective filter which reflects back toward a source a specific wavelength, and allows other wavelengths to pass through the waveguide Bragg grating. A waveguide Bragg grating may be used as a wavelength-specific reflector. The waveguide Bragg gratings may comprise shifted Bragg gratings applied to a silicon waveguide section, the gratings being deposited with a titanium dioxide, TiCh, layer. The titanium dioxide layer reduces index contrast and allows a narrower reflected bandwidth, increasing the selectivity of the waveguide Bragg grating. Such a grating is described in publication [1], where a 2,2 nanometre spectral peak width of reflected light is described.

[0037] The waveguide Bragg gratings 322, 324, 326 are provided with adiabatic mode splitters for each waveguide Bragg grating 322, 324, 326 to convey the reflected light of the specific wavelength of modulated light to a respective intermediate waveguide 332, 334, 336. In detail, a reflected wavelength from waveguide Bragg grating 322 is conveyed to intermediate waveguide 332. Similarly, the wavelength reflected from waveguide Bragg grating 324 is conveyed to intermediate waveguide 334, and the wavelength reflected from waveguide Bragg grating 326 is conveyed to intermediate waveguide 336. Thus the waveguide Bragg gratings 322, 324, 326 overall selectively and accurately convey distinct wavelength components of the incoming polychromatic light to intermediate waveguides 332, 334, 336, one wavelength of modulated light into eachintermediate waveguide. In other words, the light in intermediate waveguides 332, 334, 336 is monochromatic in the sense that it has a single spectral peak, which is of the order of only a few nanometres, nm, wide. For example, it may be less than 2,5 nm, less than 3 nm, less than 4 nm or less than 5 nm wide, depending on the characteristics of the waveguide Bragg gratings. In some embodiments, the spectral width is not the same in all the intermediate waveguides 332, 334, 336. This would be a result of the waveguide Bragg gratings having different selectivity. The modulation used may comprise on-off modulation, representing bits zero and one by maintaining the light on and off.

[0038] The waveguide Bragg gratings may further act as mode converters, as described herein above in connection with the multi-wavelength modulator side.

[0039] Intermediate waveguide 332 is coupled with photodetector 342, which is configured to convert the monochromatic light from intermediate waveguide 232 to a pattern of bits. The pattern may be provided to a terminal using connection 260. The photodetector may count photons to determine, whether the monochromatic light in intermediate waveguide 332 is on or off during a specific time period. For example, the monochromatic light may be determined to be off in case the number of detected photon events is below a threshold, and otherwise the monochromatic light may be determined to be on.

[0040] Intermediate waveguide 334 is coupled with photodetector 344, which is likewise configured to convert the monochromatic light from intermediate waveguide 234 to a pattern of bits. The pattern may be provided to a terminal using connection 260. Intermediate waveguide 336 is coupled with photodetector 346, which is likewise configured to convert the monochromatic light from intermediate waveguide 236 to a pattern of bits. The pattern may be provided to a terminal using connection 260. Thus overall demodulator 203 converts a polychromatic incoming modulated light signal into a pattern of bits, which is provided over connection 260 to a suitable terminal. The number of modulated light components on different wavelengths may be two, three, four, eight or sixteen, for example. In some embodiments, the demultiplexer (or receiver) is configured to receive the distinct modulated wavelength components over separate input waveguides, in some cases even one wavelength component per waveguide, in which case no waveguide Bragg grating is needed to separate the wavelengths as they are already separate.

[0041] The photodetectors 342, 344, 346 may comprise hybrid semiconductor detectors or monolithically integrated germanium photodetectors, for example. A transceiver may comprise a multi-wavelength modulator affording to FIGURE 2A or 2B, and a multi-wavelength demultiplexer according to FIGURE 3. The multi-wavelength modulator and multi-wavelength demultiplexer may be integrated on a same silicon chip, to obtain a compact device capable of high-throughput bidirectional communication. In some embodiments, a transceiver integrated on a same silicon chip comprises a multiwavelength modulator affording to FIGURE 2 A or 2B, and a demultiplexer which need not be of the type illustrated in FIGURE 3.

[0042] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0043] Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

[0044] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0045] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the preceding description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0046] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0047] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", that is, a singular form, throughout this document does not exclude a plurality.INDUSTRIAL APPLICABILITY

[0048] At least some embodiments of the present invention find industrial application in multi-wavelength communication.ACRONYMS LISTDBR distributed Bragg reflection mm millimetre nm nanometreREFERENCE SIGNS LISTCITATION LIST[1] “Add-drop filter based on T1O2 coated shifted Bragg grating”, by Somnath, P., Vartiainen, I., Roussey, R., Saastamoinen, T., Tervo, J., Honkanen, S. andKuittinen, M., Optics Express, Vol. 24, No. 23, Nov. 14, 2016.[2] “Graphene photonics and optoelectronics”, by Bonaccorso, F., Sun, Z., Hasan, T., and Ferrari, A. C., Nature Photonics, Vol 4, Pages 611-622, 2010.[3] “Graphene-based integrated photonics for next-generation datacom and telecom”, Romagnoli M., Sorianello V., Midrio M., Koppens F. H. E.,Huyghebaert C., Neumaier D., Galli, P., Wolfgang Tempi, W., D’Errico, A., and Ferrari, A.C., Nat. Rev. Mater. 2018, Vol. 3, No. 10, Pages 392-414, 2018.[4] “Graphene electro-optic modulator with 30 GHz bandwidth”, by Phare, C., Daniel Fee, Y.H., Cardenas, J. and Eipson, M., Nature Photonics, Vol. 9,No. 9, Pages 511-514, 2015.

Claims

CLAIMS:

1. A multi-wave length modulator, comprising:- an input waveguide arranged to convey light to plural waveguide Bragg gratings, each waveguide Bragg grating being configured to reflect light of a specific wavelength back to a distinct intermediate waveguide;- each intermediate waveguide configured to convey reflected light from a respective waveguide Bragg grating to a specific waveguide modulator, each intermediate waveguide being coupled with a distinct waveguide modulator, and- each waveguide modulator configured to modulate light received in the waveguide modulator from a respective intermediate waveguide according to a pattern to generate modulated light.

2. The multi-wavelength modulator according to claim 1, wherein at least one of the waveguide modulators is a graphene waveguide modulator.

3. The multi-wavelength modulator according to claim 2, wherein all of the waveguide modulators are graphene waveguide modulators.

4. The multi-wavelength modulator according to any preceding claim, wherein each waveguide modulator is coupled with an exit waveguide, the exit waveguides being configured to convey modulated light from the multi- wavelength modulator.

5. The multi-wavelength modulator according to claim 4, wherein the exit waveguides are coupled with a wavelength multiplexer configured to convey the modulated light of the specific wavelengths from the exit waveguides to a single output waveguide.

6. The multi-wavelength modulator according to any preceding claim, wherein each waveguide modulator comprises a cavity based on Bragg reflector gratings.

7. The multi- wavelength modulator according to any preceding claim, wherein the input waveguide is provided with a separate adiabatic mode splitter for each waveguide Bragggrating to convey the reflected light of the specific wavelength to the respective intermediate waveguide.

8. The multi-wavelength modulator according to any of claims 1 - 7, integrated on a silicon chip, wherein dimensions of the multi-wavelength modulator, integrated on the silicon chip, are in a range of 0,25 to 0,7 square millimetre, mm2, surface area with a thickness between 0,75 and 1,25 mm.

9. A multi-wavelength demultiplexer, comprising:- a receive input waveguide arranged to convey light to plural receive waveguide Bragg gratings, each receive waveguide Bragg grating being configured to reflect light of a specific wavelength back to a distinct intermediate receive waveguide, and- each intermediate receive waveguide configured to convey reflected light from a respective receive waveguide Bragg grating to a photodetector, each intermediate waveguide being coupled with a distinct photodetector.

10. The multi-wavelength demultiplexer according to claim 9, wherein each photodetector is either a hybrid integrated semiconductor detector or a monolithically integrated germanium photodetector.

11. A multi-wavelength transceiver, comprising a multi-wavelength modulator according to any of claims 1 - 7 and a multi-wavelength demultiplexer according to any of claims 8 - 9.

12. A multi-wavelength modulator, comprising:- an input waveguide arranged to convey light to a multi-wavelength waveguide Bragg grating configured to reflect light of a plural specific wavelengths back to an intermediate waveguide;- the intermediate waveguide being provided with plural waveguide modulators, each waveguide modulator being configured to modulate one and only one of the plural specific wavelengths reflected into the intermediate waveguide, and- a last one of the plural waveguide modulators being configured to provide the output of all the plural waveguide modulators to an output waveguide.

13. The multi-wavelength modulator according to any claim 12, wherein the input waveguide is provided with a separate adiabatic mode splitter to convey the reflected light of the specific wavelengths to the intermediate waveguide.

14. The multi-wavelength modulator according to any of claims 12 - 13, integrated on a silicon chip, wherein dimensions of the multi-wavelength modulator, integrated on the silicon chip, are in a range of 0,25 to 0,7 square millimetre, mm2, surface area with a thickness between 0,75 and 1,25 mm.

15. A multi-wavelength transceiver comprising a multi-wavelength modulator according to any of claims l - 8 or l2 - 13 and a multi-wavelength demultiplexer, the transceiver integrated on a silicon chip, wherein dimensions of the transceiver, integrated on the silicon chip, are in a range of 0,3 to 0,8 square millimetre, mm2, surface area with a thickness between 0,75 and 1,25 mm.

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