Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/50—Amplifier structures not provided for in groups H01S5/02 - H01S5/30
  • H01S5/5009—Amplifier structures not provided for in groups H01S5/02 - H01S5/30 the arrangement being polarisation-insensitive
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S2301/00—Functional characteristics
  • H01S2301/14—Semiconductor lasers with special structural design for lasing in a specific polarisation mode
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
  • H01S5/062—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying the potential of the electrodes
  • H01S5/0625—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying the potential of the electrodes in multi-section lasers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
  • H01S5/1053—Comprising an active region having a varying composition or cross-section in a specific direction
  • H01S5/1064—Comprising an active region having a varying composition or cross-section in a specific direction varying width along the optical axis
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
  • H01S5/1082—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region with a special facet structure, e.g. structured, non planar, oblique
  • H01S5/1085—Oblique facets

Definitions

• the present invention relates to the amplification of optical signals. It typically finds application in fiber optic telecommunications networks.
• the signals transmitted by these networks consist of pulses carrying in binary form information to be transmitted. These pulses must be amplified to compensate for losses of power which they undergo during their propagation in these networks.
• Semiconductor amplifiers constitute a space-saving and integrable means to achieve this amplification. However, in the absence of special provisions, their gain is sensitive to the state of polarization of the light they receive, which will be more simply indicated below by mentioning the sensitivity of an amplifier to polarization.
• this invention finds an application whenever the sensitivity of an optical amplifier to polarization must be zero or limited.
• the invention applies more specifically to so-called “buried ribbon” amplifiers, known under the term of BRS (for Burried Ridge Structure in English).
• such a semiconductor optical amplifier (an illustration of which is given in FIG. 1) comprises a wafer 2 made up of layers of semiconductor materials having respective refractive indices and forming a common crystal lattice.
• networks formed respectively by these materials have characteristic dimensions constituting respective meshes of these materials.
• These layers follow one another in a vertical direction DV forming a trirectangle trihedron with two horizontal directions constituting a longitudinal direction DL and a transverse direction DT, these directions being defined with respect to this plate 2.
• These layers form a succession in an ascending direction of the vertical direction DV from a lower face 4 to an upper face 6.
• This plate 2 comprises at least the following layers or groups of layers or part of a layer:
• a substrate 8 consisting mainly of a semiconductor base material having a first type of conductivity. This substrate has a sufficient thickness to impose the dimensions of the mesh of the base material on the entire crystal lattice of the wafer 2.
• An active layer 10 including an active material capable of amplifying light by stimulated recombination of charge carriers of the two types injected into this material.
• a guiding structure 12 comprising at least one buried ribbon having a higher refractive index than that of surrounding materials.
• the strip 12 extends in the longitudinal direction DL to guide said light in this direction.
• This ribbon 12 has a width 1 and a thickness e respectively transverse and vertical.
• an upper confinement layer 18 made of a material having a second type of conductivity opposite to the first.
• This amplifier further comprises a lower electrode 20 and an upper electrode 22 respectively formed on the lower face 4 and the upper face 6 of the wafer 2. to allow to pass between these faces an electric current injecting said carrier • charging of two types in the active material.
• the basic materials of known semiconductor optical amplifiers are of the III-V type. Those are typically indium phosphide and gallium arsenide. Their active material is typically a ternary or quaternary material formed with the same chemical elements. It is generally desired that the width 1 of the ribbon 12 which guides the lights be close to a micrometer to facilitate the formation of this ribbon by etching and above all to facilitate the integration of the amplifier with other optical components on the same semiconductor wafer. The thickness e must then be much less than this width to ensure a mononodal guidance of the light whose wavelength is typically 1310 or 1550 nm. In the absence of special provisions, it is this rectangular shape of the section of the tape 12 which tends to cause the sensitivity to polarization previously mentioned.
• the active material constituting the light-guiding ribbon 12 is surrounded on all sides by a binary semiconductor material 14, 16.
• the latter has the advantage of conducting heat well, but its index of refraction is only slightly lower than that of the active material.
• the active material is homogeneous and is then said to be mass (or bulk material in English).
• the section of the buried ribbon 12 is strongly rectangular. Given the small difference in index between this ribbon 12 and the surrounding binary material 14, 16. The confinement of a wave with horizontal polarization is greater than that of a wave with vertical polarization, the difference between these two confinements being all the greater the greater the ratio of the width 1 to the thickness e of the strip.
• the confinement mentioned here in connection with a wave is considered in a transverse plane. It is the ratio of the power of the wave passing through the area occupied by the strip 12 to the total power of 'this wave.
• the confinement is defined for each polarization and for each wavelength by the shape and the dimensions of the section of the ribbon and by the refractive indices of the material of this ribbon and of the surrounding material. In the case of a rectangular ribbon section, it can be considered to be the product of a directional confinement in the horizontal direction by a directional confinement in the vertical direction, each of these two directional confinements depending on the polarization.
• the gain of the amplifier for a wave the greater the confinement of this wave. It follows that, if the ribbon material were a homogeneous material, and moreover isotropic, therefore insensitive to polarization, the gain of the amplifier would be greater for the waves with horizontal polarization and than for those with vertical polarization.
• Such an amplifier has a low sensitivity to polarization.
• the object of the present invention is to solve the drawbacks of the technology proposed in the aforementioned patent US 5,982,531.
• the present invention provides a structure such that the sensitivity to the polarization of the overall gain ⁇ G of the amplifier is easily controlled by current for an adjustment of this so-called “active” sensitivity.
• the optical amplifier according to the invention thus has at least two separate sections, each provided with an electrode, each section having a different geometry and / or voltage stress. so as to favor respectively a higher gain of the TE mode and of the TM mode.
• the transition between the two sections is abrupt which induces a non-adiabatic modification of the sizes of the modes propagating in the active layer and causes a reflection of the light waves at the level of this transition.
• the reflections in an SOA are not acceptable.
• the production of such a structure requires a step of etching the active layer which must be perfectly controlled as well as a step of epitaxial growth after this etching.
• a well-controlled etching requires dry etching followed by chemical etching.
• Such a technique is generally avoided on active materials because it induces surface recombination effects which affect the quality of the active layer.
• the regrowth step is particularly delicate on a thin active layer.
• the present invention seeks to resolve these drawbacks by proposing another structure with two sections favoring respectively a higher gain of the TE mode and of the TM mode for an “active” adjustment.
• the structure proposed by the invention consists in making two sections comprising an active layer of the same thickness, but subject to stresses of different tensions and / or having different geometries, while preserving a continuity of the effective indices of refraction of the active layer in the two sections for an adiabatic transition or without index jump.
• the present invention relates more particularly to a semiconductor optical amplifier comprising at least two amplifier sections each favoring, respectively, a higher gain of the TE mode and of the TM mode of polarization of the light to be amplified, said sections each comprising an active guiding structure having the same thickness, characterized in that the active guiding structure of the two sections is respectively subjected to different tension stresses and / or has a different geometry so as to make the overall gain of the amplifier insensitive to the polarization of said light at amplify, and in that the transition between the different sections presents a continuity of the effective indices of refraction.
• the active guiding structure of the different sections has a different respective width.
• the active guiding structure of at least one of the sections has a curvature.
• the active guiding structure of the different sections is subjected to different respective tension stresses.
• the active guiding structure is composed of a material having different stoichiometric ratios between the elements making up said material for the different sections.
• the material of the active guiding structures consists of a quaternary material.
• the quaternary material is InGaAsP.
• Figure 1 already described, illustrates schematically ent a buried ribbon amplifier produced according to the prior art
• Figure 2 is a schematic top view of an amplifier according to a first embodiment of the invention
• Figure 3 is a schematic top view of an amplifier according to a second embodiment of the invention
• Figure 4 is a schematic top view of an amplifier according to a third embodiment of the invention.
• the invention consists in producing an optical amplifier whose gain is independent of the polarization of the light to be amplified.
• the amplifier comprises two amplifier sections 30 and 40 each favoring, respectively, a higher gain of the TE mode and of the TM mode of polarization of the light to be amplified, each section 30 and 40 being respectively controlled by an electrode. separate 23 and 24.
• the amplifier comprises a single active guiding structure 12 consisting of an engraved and buried ribbon.
• This tape 12 is common to the different sections 30 and 40 and has the same thickness everywhere.
• the material constituting the guiding active structure is a quaternary material such as InGaAsP for example.
• the guiding active structure 12 nevertheless has specific features specific to each section 30 and 40 making it possible to favor one or the other polarization mode of the light to be amplified.
• the structure - active guide 12 has a different width li, 1 2 for each section 30 and 40.
• the confinement of the widest portion of tape will favor the TE propagation mode. while confining the narrowest portion of tape will favor the TM propagation mode.
• Such a tape 12 can easily be produced by etching with a suitable mask which defines the respective widths of each section 30 and 40.
• the width l ⁇ of the active guiding structure 12 of section 30 promoting a higher gain of the TE mode is between 0.8 and 1.2 ⁇ m
• the width 1 2 of the active guiding structure 12 of section 40 favoring a higher gain of the TM mode is between 0.6 and 1.0 ⁇ m, with the condition l ⁇ > l 2 always fulfilled.
• the active guiding structure 12 has a curvature 13 on the section 30 favoring the TE mode of propagation of the light to be amplified.
• the material of the active guiding structure is the same on the two sections 30 and 40, as well as its confinement.
• the curved section 13 of the ribbon 12 will favor the TE mode of light propagation while the straight sections will favor the TM mode (by the nature of the material constituting the ribbon).
• the straight ribbon sections 40 are separated by the curved section 13, in the example illustrated, but are electrically connected by electrodes 24, 24 'connected to each other.
• Such a ribbon 12 with a curvature 13 can easily be produced by etching with a suitable mask.
• an adiabatic transition of the modes between the two sections 30 and 40 is obtained, which eliminates the risks of reflection of the light waves.
• the active guiding structure 12 is subjected to different respective tension stresses on the different sections 30 and 40.
• the active guiding structure 12 is composed of a quaternary material.
• the difference in tension stress between the two sections 30 and 40 is obtained by a difference between the stoichiometric ratios of the elements constituting the material of said active structure 12.
• the use of the same material (InGaAsP) makes it possible to avoid jumps index from section to section and consequently the light wave reflections between these sections 30 and 40. It is the composition of this material which varies.
• the ribbon 12 is produced by a double epitaxy for each section according to the known and mastered technique of "butt-coupling".

Landscapes

• Physics & Mathematics (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• General Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Optics & Photonics (AREA)
• Semiconductor Lasers (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=8853659

Family Applications (1)

Country Status (5)

Families Citing this family (2)

Family Cites Families (9)

• 2000
  • 2000-08-22 FR FR0010818A patent/FR2813448A1/fr active Pending
• 2001
  • 2001-08-20 US US10/110,378 patent/US6751015B2/en not_active Expired - Fee Related
  • 2001-08-20 EP EP01963110A patent/EP1232550A1/fr not_active Withdrawn
  • 2001-08-20 JP JP2002522039A patent/JP2004507894A/ja not_active Withdrawn
  • 2001-08-20 WO PCT/FR2001/002632 patent/WO2002017454A1/fr not_active Application Discontinuation

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events