DE19500135A1 - Opto-electronic component with feedback grating for e.g. semiconductor laser - Google Patents

Abstract

The component includes a optical feedback grating with an axially variable corrugation period which is formed from at least three layers of at least two different semiconductor materials and an optical waveguide. The feedback grating has at least one homogenous grating field in longitudinal direction, which is interrupted by in its periodicity in longitudinal direction by a quasi-abrupt phase shift at one point, at least. The characteristic lengths of the grating, locally lying in the region of the phase shift of the order number, are effectively changed in length by the curvature of the waveguide. A specified grating groove comprises the effective length change, due to the waveguide arcuation. The corrugation period is also changed.

Description

The solution according to the invention takes place in photonic Component application that is based on DFB (distributed feedback) grids, DBR (English = distributed Bragg reflector) grids or axially interrupted several times Lattice structures ("sampled grating") are based. For The following photonic components is the invention applicable: e.g. B. lasers, laser amplifiers, filters, couplers, Switches, wavelength converters, multiplexers, Waveguide branches (English splitter), waveguide Combiners, demultiplexers and Detectors. The present solution enables Realization of optical feedback gratings with quasi continuously variable corrugation period and therein contained quasi-abrupt phase shifts.

The following works, which are thematically related to the present Invention related, belong to the known prior art Technology:

• 1. The generation of abrupt phase shifts is known by holographic methods [e.g. B. T. Numai et. al., Yep J. Appl. Phys. 26, L 1910 (1987)] or by means of Electron beam lithography (EL). The whole The phase shift amount can also be several locally separated phase shift components (English multiple phase shifts) are distributed [z. B. S. Ogita et. al. J. Lightwave Technol 8, 1596 (1990)]. The However, individual partial phase shifts were found here quasi-abruptly using EL or holographic methods executed.  
• 2. Solutions are known from the literature that are abrupt Changes in the corrugation period in longitudinal Effect device direction. The central located section of the laser resonator with the Self-interference method a longer corrugation period realized as in the side sections [M. Okai et. al., IEEE J. Quantum Electron. 27, 1767 (1991)]. With this Abrupt corrugation periods Changes created, but not all advantages, which one offers continuous variation of the corrugation period, exhausted.
• 3. To a certain extent, the electron beam Litography (EL) the variation in the period of correlation in longitudinal direction. However, with this Procedure the difference between neighboring Grid periods limited to larger values (e.g. 2.5 nm) or small values can only be realized with great effort will. This means that only DFB grids can be used with EL are produced, which are a small number of different Have sections. Within these sections is the effective grid period is constant, it differentiates but from section to section. [H. Ishii et. al. IEEE Photonics Technol. Lett. 4, 393 (1993)]
• There can be no quasi-continuous variations of the Grid period can be reached with the location. Furthermore, EL is a complicated procedure and the EL write time very expensive.
• 4. Another known solution involves on homogeneous DFB gratings tilted waveguides, which one Deviation of the corrugation period in the waveguide from enable that of the original DFB grid. The Composition of the overall waveguide the differently tilted partial waveguides enables  Realization of a λ / 4 phase shift [Hirato Shoji, DE 36 43 361 A1, H 01 S 3/098-C (1987)].
• 5. Furthermore, it is known to have curved waveguides homogeneous DFB grid fields for the definition of grids with to use axially varied grating period (DE-42 33 500.0).

The aim of the invention is characteristic Properties of the photonic component for special Tailor the intended use cases. The Realization of optical feedback grids enables which is a smaller number of quasi abrupt Phase shifts included and additionally in the Areas that are free of phase shifts, one have continuously variable corrugation period.

The axial variation of the corrugation period (axial = direction of the waveguide curvature) is realized by means of a curved optical light waveguide, which lies in the area of an optical feedback grating. The feedback grating in the longitudinal direction (z-direction) has a number (n + 1) of homogeneous partial areas with a constant corrugation period and also contains a certain number n of quasi-abrupt phase shifts Δϕ _j (1 jn) between these areas. The longitudinal direction (z-direction) and axial direction are not identical in the present solution. The axial direction runs along the waveguide curvature and describes approximately the curved optical axis of the light guided in the waveguide. The generation of the axially variable corrugation period results from the targeted local tilting of the optical waveguide relative to the grating lines. This means that the optical waveguide does not intersect the grating lines at the same angle at every position on the z-axis within the photonic device. The effective, local corrugation period, which results from the local optical waveguide curvature, is closely linked to the angle ϑ (z). Here ϑ (z) is the angle between the perpendicular to the grid line adjacent to point z and the tangent to the optical waveguide at point z. As a result, the effective corrugation period at a point z at which none of the quasi-abrupt phase shifts is present is given by the following relationship: Λ (z) = Λ _z / cos [ϑ (z)]. Here Λ _{z is} the corrugation period of the homogeneous lattice areas. In the small areas seen in the z direction, in which the quasi-abrupt phase shifts are generated, the waveguide curvature causes extended or shortened grating trenches or stretched or shortened grating webs at the positions z _{si, j} and z _{gi, j} .

The characteristic lengths of the waveguide, which locally in the area of the phase shift of the Atomic number j are effective in their length defined where

• a lattice trench of atomic number i at position z _{gi, j} , viewed in the z direction, has the length g _{zi, j} , an effective change in length caused by the waveguide curvature g _{i, j} = g _{zi, j} / cos (ϑ (z _{gi, j} )),
• - A lattice web of atomic number i at position z _{si, j} , viewed in the z direction, has the length s _{zi, j} , an effective change in length caused by the waveguide curvature s _{i, j} = s _{zi, j} / cos (ϑ (z _{si, j} )), and wherein
• - A corrugation period at point z, viewed in the longitudinal direction, which has length Λ _z , has an effective length change Λ (z) = Λ _z / cos (ϑ (z)) caused by the waveguide curvature.

The solution according to the invention should be based on some Exemplary embodiments are explained in more detail. It shows:

Fig. 1 is a schematic representation of a section of the optical feedback grating in the xz plane, with a curved optical waveguide that runs in the vertical direction (y direction) above or below or within a homogeneous overall grating field. The dimensions (e.g. waveguide width, corrugation periods) are not drawn to scale. To illustrate the angles, the corrugation periods are e.g. B. exaggerated,

Fig. 2, the partial views of an optical feedback grating which n = 3 quasi-abrupt (j = 1, 2, 3) phase shifts and relative thereto the position of a curved optical waveguide. The dimensions (e.g. waveguide width, period of correlation) are not drawn to scale. The bottom sub-picture represents the cross-section of the optical feedback grating in the xz plane. The index i represents the ordinal number of the characteristic lengths occurring in each phase shift (grating bars, grating trenches),

Fig. 3 shows the example of an optical feedback grating with fully structured layer 2 in the yz plane,

Fig. 4 shows the example of an optical feedback grating with not completely structured layer 5 in the yz plane and

Fig. 5 shows the example of a section through a detail of the layered structure in a curved running plane from the vertical direction (y direction) and the direction is formed extending along the waveguide curvature (axial direction).

The example in FIG. 1 shows a section of an overall grid in the xz plane. The axial variation of the corrugation period is realized here by means of a quasi-ab rupen phase shift and a curved optical waveguide, which is in the region of an optical feedback grating.

The example in FIG. 1 shows a quasi-abrupt phase shift which has a broadened lattice web s _{zi, j} / cos (ϑ (z _{si, j} )).

Fig. 2 shows in the upper part of a grid structure in the xz plane with various quasi-abrupt phase shifts. Changes in the periodicity of the grating produce phase shifts e.g. B. by the local change in the lengths of the grid webs s _{zi, j} and / or the grid trenches g _{zi, j} in the z direction. There are three quasi-abrupt phase shifts shown in Fig. 2 (Δϕ₁, Δϕ₂ and Δϕ₃). They are referred to as quasi-abrupt, since the dimensions of the areas in the z-direction in which the quasi-abrupt phase shifts are generated are small compared to the dimensions of the homogeneous lattice fields in the z-direction. However, to illustrate the individual elements of the overall grid, the homogeneous grid areas in between in the z direction are shown in a greatly shortened form. Within each individual phase shift of the atomic number j, the length of the grid bars s _{zi, j} and the grid trenches g _{zi, j} change in length compared to the homogeneous grid _fields, with i denoting the individual characteristic lengths. The total grid field ( FIG. 2 above) is either produced holographically, defined with EL electron beam lithography or realized with ion beam lithography. In the middle part of FIG. 2, the curved optical waveguide is shown together with this overall grating field. The curved optical waveguide can be seen in the vertical direction (y-direction), above or below or within the grating field. Due to its curvature, the optical waveguide cuts the grating lines which follow one another in the z direction at different angles. The change of this angle takes place between adjacent grating lines in such small steps that one can speak of a continuous change of the angle and thus a continuous change of the axial effective corrugation period in the areas without phase shift. A section through the grid in the yz plane is shown in the bottom part of FIG. 2. It is very crucial that the light guided along the curvature (= axial direction) in the optical waveguide passes through a locally differently stretched and partly also unstretched image of the grating structure shown in the partial image below, as is shown schematically in FIG. 5.

On the other hand, the overall grid can also be DBR-like or have a sampled grating structure, with a certain number in the z direction grid-free areas exist.  

In Fig. 3 and 4 show two examples with different possibilities of realization of the feedback grating are each represented in a section schematically in the yz plane. The layers of material 1 , 2 , 3 , 4 and 5 generally have a different composition. In Fig. 3 z. B. the complex refractive index of layer 2 from that of layer 1 and that of layer 3 different. The complex refractive index of layers 1 and 3 can be identical in a special case. The feedback grid can e.g. B. also from a sequence of layers 1 , 2 , 3 ; 1 , 2 , 3,. . . be constructed, layers 1 and 3 can also be identical in a special case.

In FIG. 4, the complex refractive index of the layers is selected to 4 and 5 different.

The shape of the grid in the yz plane can either be triangular, rectangular or sinusoidal. Corresponding mixed shapes are also possible, as shown in FIGS. 3 and 4 (rectangular shape with rounded corners). In Fig. 5 the case of a sinusoidal cross-section is shown.

The mathematical function, which describes the curvature of the optical waveguide in the xz plane, is continuous and, if scattering losses are to be avoided, can also be differentiated. Only very moderate curvatures are required to generate strong changes in the corrugation period in the direction of the waveguide curvature (= axial direction). The illustrations in FIGS. 1 and 2 exaggerate the curvatures for clarification. Strong waveguide curvatures (small radii of curvature), as exaggerated in the figures, would lead to larger scattering losses. This is e.g. B. in semiconductor lasers and semiconductor laser amplifiers undesirable. In the following, a numerical example should in particular clarify how weakly the curvatures can be chosen for an axial variation of the corrugation period which is desirable in the application.

For the example, let L be the component length. L₁ and L₂ are the lengths of the waveguide in the z direction, which are not curved and perpendicular to the grating lines. The total length of the component is L = L₁ + 2L _B + L₂. The grating runs continuously from 0 z L. The waveguide curvature is defined in sections as follows:

The curvature function x (z) starts at z = 0 with an uncurved section of length L₁, in the middle the waveguide is curved over a length of 2L _B and ends at a length L₂ again without curvature and parallel to the z-direction. At z = L₁ + L _B the waveguide has a slope of -2 W / L _B. Let 2 L _B = 200 µm, L₁ = L₂ = 50 µm, W = 2.83 µm, Λ _z = 240 nm and thus L = 300 µm. Radii of curvature of approximately 2 mm result if the total phase shift generated solely by the waveguide curvature in the homogeneous grating field regions should be, for example, λ / 4 [the homogeneous grating field regions do not include the quasi-abrupt phase shifts]. In the case of components with longer areas 2 L _B , with an identical total phase shift of λ / 4, the required radii of curvature are still much larger and thus even more advantageous. If, for example, 2 quasi-abrupt phase shifts of λ / 16 each are added to the overall grid, the curvature required for a total phase shift amount of λ / 4 is even weaker, ie instead of W = 2.83 µm, as stated above, is sufficient W = 1.999 µm.

By means of the solution according to the invention it is possible to occurring geometric and compositional parameters to optimize so that the parameters of the photonic Component can be significantly improved. For one Semiconductor lasers can, for example, improvements in Regarding the following properties and parameters achieved will:

• - smaller line widths of the optical emission,
• - customized spatial hole burning,
• - targeted influence on the stability of the oscillation single spectral modes,
• - targeted change of the radio frequency properties:
  • - reduced frequency chirp,
  • - higher cut-off frequencies under high-frequency modulation,
  • - implementation of flat frequency modulation characteristics,
• - Realization of more stable axial single-shaft also high output power,
• - possible lowering of the main current threshold current and possible increase in threshold current of the side modes,  
• - linearization of the light-current characteristic,
• - Increasing the yield of photonic components certain specifications,
• - Increase in the emitted optical power
• - Extended wavelength tunability.

An extremely precise variation of the can be achieved Corrugation period and the local phase shift. Furthermore, the distribution of the phase shift in axial direction can be set very precisely.

The process is regardless of the special designs different photonic components applicable if these are based on optical feedback gratings. Laser structures with stronger lateral wave guidance, such as e.g. B. buried laser structures ("buried laser structures "), but allow stronger ones Waveguide curvatures and waveguide tilt compared to the grid lines and are therefore preferable. Laser structures with weaker lateral wave guidance (e.g. "Ridge" laser structures) enable accordingly not so small radii of curvature.

Reference list

L
L₁ specific lengths of the waveguide in
L₂ z direction
L _B characteristic length in the curved part of the waveguide in the z direction
x lateral direction of the component
y vertical direction of the component
z longitudinal direction of the component
Λ (z) effective grating period in the direction of the curved waveguide (axial direction) at the location z
Λ _z corrugation period of the homogeneous lattice regions in the z direction
ϑ (z) Angle at the point z between the perpendicular to the neighboring grating and the tangent to the optical fiber
λ wavelength of light
Δϕ₁
Δϕ₂
Δϕ₃ designation of various quasi-abrupt
Δϕ _i phase shifts
g _z trench width in the z direction of the homogeneous grid field
s _z grid web width in the z direction of the homogeneous grid field
Λ _z lattice period of the homogeneous lattice field in the z direction
i Number of modified and unmodified corrugation periods within the range in which the quasi-abrupt phase shift is generated. This means that the individual grid bars and grid trenches are numbered with i, which are located within one of the quasi-abrupt phase shifts
j atomic number of the quasi-abrupt phase shifts
z _h Position on the z-axis in the area of the homogeneous grid fields
s _{zi, j} grid _web width with the ordinal number i from the quasi-abrupt phase shift with the ordinal number j in the z direction
g _{zi, j} trench width with the ordinal i from the quasi-abrupt phase shift with the ordinal j in the z direction
z _{si, j} position on the z-axis in the region of the quasi-ab rupten phase shift with the ordinal number j at the point at which the grid web with the ordinal number i lies.
z _{gi, j} position on the z-axis in the area of the quasi-ab rupte phase shift with the ordinal number j at the point at which the trench with the ordinal number i lies.

Claims (13)

1.Optoelectronic component with a feedback grating with an axially variable corrugation period, which is constructed from at least three layers of at least two different semiconductor materials and an optical waveguide, the region of the waveguide in which the intensity of the guided light is clearly different from zero Feedback grating with its grating lines arranged perpendicular to the longitudinal direction, characterized in that the optoelectronic component has an optical feedback grating with at least one quasi-abrupt phase shift in combination with a curved optical waveguide, the optical feedback grating in the longitudinal direction (z) at least one homogeneous overall grid field has that this field is interrupted at least at one point in its periodicity in the longitudinal direction by a quasi-abrupt phase shift (Δϕ _j ) that the characteristic lengths of the grating, which are locally in the range of the phase shift of the atomic number j, are effectively changed in length by the waveguide curvature, so that there is a grating trench of the ordinal number i at the position z _{gi, j} , which is in the z direction considered the length g _{zi, j} has an effective length change caused by the waveguide curvature g _{zi, j} = g _{zi, j} / cos (ϑ (z _{gi, j} )) has that a grid web of atomic number i at the point z _{si, j} , which, viewed in the longitudinal direction, has formed the length s _{zi, j} , has an effective length change s _{i, j} = s _{zi, j} / cos (ϑ (z _{si, j} )) caused by the waveguide curvature and that there is a Corrugation period at point z, which has a length Λ _z when viewed in the longitudinal direction, has an effective length change Λ (z) = Λ _z / cos (ϑ (z)) caused by the waveguide curvature. 2. Optoelectronic component according to claim 1, characterized characterized in that in the longitudinal direction (z) additionally a defined number of grid-free Areas is arranged, creating a DBR structure or a "sampled grating" structure is created. 3. Optoelectronic component according to claim 1 and 2, characterized in that the mathematical Curvature function of the optical waveguide at least one straight, d. H. curvilinear Section contains, and that the straight section of the optical waveguide an intersection with the Includes dashes that range from 60 ° to 120 ° is defined. 4. Optoelectronic component according to claim 1 and 2, characterized in that for the realization of the curved optical waveguide in itself consistent lithography mask set is used, the waveguide curvature according to any mathematical functions, and that the Waveguide structure in the on the surface of the Semiconductor structure applied photoresist layers is defined by means of optical mask lithography.   5. Optoelectronic component according to claim 1 and 2, characterized in that the curved waveguide Structure in the on the surface of the Semiconductor structure applied photoresist layers defined directly by means of electron beam lithography becomes. 6. Optoelectronic component according to claim 1 and 2, characterized in that the curved waveguide Structure in the on the surface of the Semiconductor structure applied photoresist layers is defined directly by means of ion beam lithography. 7. Optoelectronic component according to claim 1 and 2, characterized in that the coupling of the grid is complex and refractive index and profit coupling includes. 8. Optoelectronic component according to claim 1 and 2, characterized in that the coupling of the grid is complex and refractive index and loss coupling includes. 9. Optoelectronic component according to claim 1 and 2, characterized in that the coupling of the grid is purely imaginary and involves profit coupling. 10. Optoelectronic component according to claim 1 and 2, characterized in that the coupling of the grid is purely imaginary and involves loss coupling. 11. Optoelectronic component according to claim 1 and 2, characterized in that the coupling of the grid is real and represents pure index coupling.   12. Optoelectronic component according to claim 1 and 2, characterized in that the pulse duty factor of the homogeneous grating g _z / Λ _z varies in the range between 0 and 1. 13. Optoelectronic component according to claim 1 and 2, characterized in that the characteristic lengths located in the phase shifts s _{zi, j} and g _{zi, j have} different lengths from one another.