Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/35—Non-linear optics
  • G02F1/365—Non-linear optics in an optical waveguide structure
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/015—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on semiconductor elements having potential barriers, e.g. having a PN or PIN junction
  • G02F1/025—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on semiconductor elements having potential barriers, e.g. having a PN or PIN junction in an optical waveguide structure
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/015—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on semiconductor elements having potential barriers, e.g. having a PN or PIN junction
  • G02F1/0155—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on semiconductor elements having potential barriers, e.g. having a PN or PIN junction modulating the optical absorption
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F2202/00—Materials and properties
  • G02F2202/32—Photonic crystals

Definitions

• the invention relates to a modulator comprising a waveguide, for example an optical modulator, and an associated modulation method.
• Modulators are devices intended to control the transmission of a wave, for example light transmission in the case of optical modulators. This concept therefore covers devices that can vary the intensity of the wave transmitted continuously or discontinuously, for example all or nothing in the case of switches.
• Such a Mach-Zehnder device is for example described in the patent application US 2003/161565 according to which the group speed is varied in a branch of the device in order to obtain a phase shift of the signal in this branch with respect to the signal which goes through the other branch of the device.
• the resulting wave In both cases (displacement of a resonance or interference of out of phase waves), the resulting wave, and in particular its intensity, varies according to the density of the charge carriers, which can itself be controlled by a voltage .
• the modulations are obtained in these devices only on a narrow frequency band.
• Mach-Zehnder devices have a relatively complex structure because they use two branches which must also be coupled to the main guide of the electromagnetic wave.
• the invention proposes a modulator comprising a waveguide propagating an electromagnetic wave of a given wavelength with absorption, characterized by means capable of modifying the time of presence of the electromagnetic wave in the guide.
• the waveguide is made for example in an absorbent material at the given wavelength.
• the waveguide may also comprise, for example, nanostructures, which may be quantum dots or quantum wells of semiconductor material.
• the waveguide may have a periodic variation of the dielectric permittivity, which makes it possible to benefit from the physical properties of a dispersive structure, in particular the existence of slow propagation modes at the boundary or Brillouin zone center.
• the waveguide is a photonic crystal guide.
• Such a guide can for example be made by silicon die processes, which simplifies the integration of the modulator into a component.
• It can also be a guide type "rib” or "ridge” whose edges have a sinusoidal shape.
• the means capable of modifying the time of presence may in practice comprise means capable of modifying the refractive index of the electromagnetic wave in the guide. This solution makes it possible to reduce the group velocity by modifying the index, and this very importantly when one considers the case of the slow propagation modes mentioned above.
• the means capable of modifying the refractive index may comprise an electrical junction. This solution is also advantageous for integration into a component.
• the invention also proposes a method of modulating an electromagnetic wave having a given wavelength and propagating in an absorption waveguide, characterized in that it comprises a step of modifying the time of presence of the electromagnetic wave. electromagnetic wave in the guide.
• the step of modifying the presence time is for example obtained by modifying the refractive index of the electromagnetic wave in the waveguide.
• Such a method optionally possesses the characteristics and advantages already mentioned above with regard to the modulator.
• FIG. 1 represents a modulator produced in accordance with the teachings of the invention
• FIG. 2 represents a sectional view of the modulator of FIG. 1;
• FIG. 3 shows dispersion curves illustrating the operation of the device of FIG. 1.
• the modulator shown in FIG. 1 is an optical modulator which comprises an input region 2, a waveguide (here an optical guide) 4 and an output region 6.
• the guide 4 is formed in a photonic crystal 8 (made for example by periodic holes in a semiconductor material) and thus has a periodic variation of the dielectric permittivity.
• the waveguide 4 comprises nanostructures, for example quantum germanium on silicon (Ge / Si) boxes 5 (see FIG. 2), which allow absorption of the electromagnetic wave to be transmitted. Alternatively, this absorption could be obtained by choosing an absorbent material to make the guide.
• Ga / Si quantum germanium on silicon
• the intrinsic absorption of the materials is typically of the order of 1 cm -1 to 10 cm -1 .
• the photonic crystal 8 is placed in an electrical junction 11 to which an electric voltage can be applied to the means of two contacts 10, 12 located on either side of the photonic crystal 8.
• FIG. 2 represents a sectional view of the modulator which has just been described, in which the structure of the electrical junction 11 clearly appears.
• the electrical junction 11 is for example deposited on a substrate 20 with the interposition of an optical index layer. lower than the material of the electrical junction, for example an oxide layer 22, in particular of silicon oxide.
• the electrical junction is formed of a first layer 18 made of doped semiconductor (here Si-p) and deposited on the oxide layer 22 and in electrical contact with the contact 12, a second layer made of material semiconductor (here in Si) and deposited on the first layer 18, however without contact with the contact 12, and a third layer 14 doped semiconductor (here Si-n) and deposited on the second layer 16 without not entering contact with the contact 12.
• the contact 10 is deposited directly on the third layer 14, for joining this layer to ground according to the example shown in FIG.
• a second oxide layer 24 optionally covers the third layer 14.
• the first layer 18, the second layer 16 and the third layer 14 are traversed at regular intervals by recesses which form the holes of the photonic crystal 8 already mentioned.
• the second layer 16 made of semiconductor material comprises nanostructures (here quantum boxes 5) which generate absorption in the guide as already mentioned.
• the propagation of the electromagnetic wave in the photonic crystal guide 4 takes place with a group velocity determined by the slope at a point of a dispersion curve as shown in FIG.
• FIG. 3 illustrates the case where the charge carrier depletion (obtained thanks to the electrical junction 11) of relatively high-speed germanium-on-silicon quantum wells or boxes is used, in which case part of the dispersion curve is used. concavity turned down. However, depending on the material and absorption process used, one could use a concavity curve portion facing upwards.
• the dispersion curve of the waveguide 4 (which represents the energy as a function of the propagated mode wave vector) is not a straight line and therefore has a variable slope which cancels out at least one point due to the presence of optical modes of the photonic crystal 8 coupled to each other via the periodic character of the dielectric constant of this photonic crystal 8 (ie due to the band structure energy of the scatter plot).
• the energy displacement of the dispersion curve can be such that the slope of this curve at the point corresponding to the wavelength ⁇ considered becomes zero or almost zero, without requiring the application a high voltage due to the large curvature of the dispersion curve.
• This phenomenon makes it possible to reduce very significantly (division by 100) the group velocity of the wave propagated in the guide.
• the group speed can in fact be reduced from c / 3 to c / 100, or even c / 1000 (where c is the celerity of light).
• the very significant slowing of the light thus generated allows a corresponding increase in the time of presence of the electromagnetic wave in the guide, which leads to a very strong increase in the absorption generated overall by the passage of light through the guide. wave 4.
• the term - can become very important because of the periodic variation of the dielectric permittivity as already explained.
• the structure shown in FIG. 1, which comprises a single waveguide, can thus be used as an optical modulator without requiring the addition of a resonant structure or that of a parallel guide, as in devices of the Mach-Zehnder type. which avoids diffraction losses and widens the usable spectral range. It is further noted that the modification of the density of the charge carriers in the junction 11 in itself makes it possible to control the absorption of this material, in particular at the level of the guide 4 thanks to the quantum boxes 5.
• the arrangement of the photonic crystal guide 4 within the junction 11 thus makes it possible to combine the two following effects in order to modulate the transmission by the guide when a voltage is applied to the junction:
• the modulation of the propagation speed of the guided optical mode in order to increase the time of presence of the wave and thus to amplify the phenomenon of absorption by the guide.

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• Physics & Mathematics (AREA)
• Nonlinear Science (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

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• 2005
  • 2005-02-11 FR FR0501406A patent/FR2882161B1/fr not_active Expired - Fee Related
• 2006
  • 2006-02-09 EP EP06709283A patent/EP1856573A1/de not_active Withdrawn
  • 2006-02-09 JP JP2007554599A patent/JP2008530605A/ja active Pending
  • 2006-02-09 US US11/815,952 patent/US7650049B2/en not_active Expired - Fee Related
  • 2006-02-09 WO PCT/FR2006/000297 patent/WO2006084999A1/fr not_active Ceased
  • 2006-02-09 CN CNA2006800045858A patent/CN101116025A/zh active Pending

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