DE10047681A1 - Manufacturing procedure for optical waveguide array with periodic refractive index modulations, involves radiation of maximum and minimum intensity extending transversely to part zones - Google Patents

Abstract

A method for the manufacture of optical waveguide arrays with periodic refractive index modulations of the individual waveguides, involves fabricating waveguides (111 - 11n) on one substrate, and the electromagnetic or particle radiation should extend over the total width of the laterally adjacent part-zones (151 - 15n) of the waveguides, and have lines (17) of maximum- and minimum-intensity in the plane of the waveguides (111 - 11n).

Description

The invention relates to a method for producing an optical waveguide array with periodic refractive index modulations of the individual optical fibers with the Features of the preamble of claim 1.

Optical fiber with a periodic refractive index modulation in the longitudinal Axes are used in particular as a filter or as an external grating for a laser dung. The periodic refractive index modulation can be used as an optical fiber Bragg Grid be formed. The periodicity of a Bragg grating determines the wavelength gene characteristic of the through the optical fiber with axially periodic refraction index modulation formed optical element, which in relation to the transmit light acts as a bandstop and, in relation to the reflected light, acts as a bandpass or the other way around. For example, a bandpass with respect to the transmitted light by periodic refractive index modulation with a phase jump between two areas with constant local period are generated.

The production of fiber Bragg gratings can follow, for example, that a Single-mode optical fiber with a core made of UV-sensitive germanium do quartz glass from a substantially radial direction (or at least one direction with a radial component) is irradiated with UV light, which in periodic intensity minima and the axis of the irradiated optical waveguide -maxima. Correspondingly, periodic swans are created in the optical waveguide of the refractive index in the axial direction.

The periodic fluctuations in intensity of the radiation used to irradiate the optical waveguide UV light used can be generated in different ways: for example  it offers itself in the manufacture of single-mode optical fibers in integrated Optics, d. H. as a substantially planar structure, the optical waveguide in the Be rich in which the periodic refractive index modulation is to be generated with a mask, for example made of etched photoresist, and cover with UV light irradiate. The intensity fluctuations in the axial direction of the optical waveguide can also be generated by the interference of two UV laser beams, which enclose a given angle. The bisector is here preferably perpendicular to the axis of the optical waveguide to maximum levels and to generate minimum intensity of UV light that is perpendicular to the axis of the Optical fiber run. The local period of the intensity fluctuations is included depending on the angle that the two interfering laser beams enclose. A Another possibility for generating periodic fluctuations in intensity of the Irradiation used UV light consists in the use of holographic tech techniques.

Optical fiber arrays are also used in a variety of configurations. For example, an optical wavelength division multiplexer or demultiplexer can be used as Arrayed Waveguide Grating (AWG) can be formed. Such an AWG consists of an optical fiber array, in which the individual optical fibers for generation corresponding phase differences have different lengths. This is it for example possible an optical wavelength multiplex signal of a light wave lenleiters via a coupling area in the optical fiber array, wherein after decoupling the signal carried over the array by means of an output Coupling area the individual optical sub-signals of different carrier wavelengths can be coupled into different optical fibers. itself of course, such an AWG can also be used in the opposite way as a multiplexer be used when the optical signal of a particular carrier wavelength fed to the coupling area via the optical fibers in question and into the light waveguide array is coupled. After passing through the fiber optic  Arrays can contain the individual optical signals of different carrier wavelengths one or more output optical waveguides are coupled.

When using AWGs, it can prove to be an advantage if the light wave guide ter array, which via the coupling waveguide with the actual phase differences bounding generating central array is coupled in each of the individual waveguides has an integrated filter structure, for example in the form of a Bragg grating. This improves the crosstalk attenuation of the individual channels, in particular then if this optical fiber array is the output of the whole AWG acts (i.e. when operating the AWG as a demultiplexer). Serves the matching array for coupling the light of different lasers into a single light world lenleiter (operation of the AWG as a multiplexer), so the aforementioned problem of Improvement of the crosstalk attenuation at most a subordinate role, since As a rule, extremely narrow-band lasers are used, whose center wavelength lies within the bandpass range of the respective filter structure. An improvement However, the transmission properties of the overall system can result if the transmission spectrum of the respective laser changes due to temperature influences or Dynamic influences of the laser control changes so that the spectral power changes in the edge areas of the wavelength characteristic of the respective filter structure increased. When using appropriate filter structures in the input fiber optic Arrays of an AWG (i.e. when operating the AWG as a multiplexer) can be used as external Resonators for the lasers are used, whose signals in the off optical fiber should be coupled. Since the whole arrangement of one AWG and the transmitter laser can be manufactured in integrated optics, here results due to the advantage of a rational and cost-saving structure.

However, the generation of the filter structures, ie. H. the light waveguide areas with periodic refractive index fluctuations highlighted because the optical fibers of the array are closely adjacent. Because with a multiplexer The center wavelength of the filter structures of the individual optical fibers is very precisely defined  and must be different in each case, it is for the manufacture of the filter structures required, the refractive index fluctuations with different, exact local wavelength to be observed.

This can be done when using the exposure technique explained above Masks are still technically well implemented. However, the creation of the mask is complete speaking elaborate, because in the laterally closely adjacent areas of light waveguide of the array a "radiation grating" with different periodicity must be generated.

The use of two interfering laser beams (see above) is also appropriate Adequate, because there is a sufficient axial area of the light in question waveguide must be irradiated without the closely adjacent light wel conductor are also recorded.

The holographic radiation technology (see above) is also hardly involved in this way reasonable effort. The structure of a hologram, which for perio of each of the closely adjacent optical waveguides in sufficient axial areas Identity fluctuations generated different periodicity is very complicated In addition, the image that can be generated by this hologram in the The plane of the (axes of) the optical fibers can be positioned very precisely.

The object of the invention is therefore based on this prior art based on a method for producing an optical waveguide array with periodic to create the refractive index modulations of the individual optical fibers with such an optical waveguide array in a simple manner and with relative little effort with sufficient accuracy and with sufficient optical Properties can be produced.  

The invention is based on the knowledge that the generation of the axial regions of the Optical fibers with different periodic refractive index modulations simple way is possible that the electromagnetic or particle beam procure with which the optical fibers are irradiated from the side fen is that they extend over the entire width of the laterally adjacent subregions of the Optical fiber and the entire axial length over which the refractive dex modulations are to be generated. The electromagnetic or particle beam lung shows maximum and mini lines in the plane of the axes of the optical waveguides painterly intensity, which run across the areas in which the bre index modulations are to be generated, and which in each sub-area an optical waveguide in the axial direction of a predetermined different have local periodicity.

In this way it is particularly using a holographic process rens possible with relatively little effort, the required structures of the Bre generating index modulations.

At this point it should be noted that under axially periodic refractive index Modulations can also be understood as structures in which the length of the local che period is modulated or phase jumps are provided.

According to the preferred embodiment of the invention, the electromagnetic or Obtain particle radiation to generate the refractive index modulations so that the lines of maximum and minimum intensity on one of the outer parts areas a minimum periodic distance and at the other the outside partial areas a maximum periodic distance in the axis of the respective Have partial areas. This results in a very simple structure of the required chen radiation. In particular, the lines of maximum and minimum intensity in the simplest case run straight.  

The periodicity of the refractive index in the axis of the respective partial areas of the Optical waveguide can be produced in accordance with one embodiment of the invention that the sub-areas of the optical waveguides are essentially straight and run in parallel. In this case you have to create different periodic tables would be used in the individual optical fibers radiation, the Li no maximum and minimum width straight and not parallel or curved run.

According to one embodiment of the invention, the radiation can be designed such that A line of maximum in the axially central area of the partial areas of the optical waveguides or minimum intensity is substantially perpendicular to the optical fibers and the lines of maximum or minimum intensity that are adjacent on both sides a predetermined angle with the substantially perpendicular line lock in.

This has the advantage that the axially front or rear Areas of the periodic refractive index modulations the light guidance in the light affect the waveguide only slightly. Because an optimal structure of the bre Index modulation is given when the levels are constant Refractive index each run perpendicular to the axis of the optical waveguide. The bigger the angle that these planes (or the lines of maximum and minimum intensity in the plane of the axes of the optical fibers) with the axis of the optical fibers close, the greater the losses of the optical structure in question.

According to a further embodiment of the invention, the adjacent parts can reach the waveguide straight and enclose a predetermined angle eat and / or run differently curved. In this case you can also use a electromagnetic or particle radiation are irradiated in the plane of the Axes of the optical waveguide lines running parallel maximum and minimum Intensity. Of course, the lines can be maximum and minimum  In this case, however, the intensity is additionally rectilinear under predetermined win curled or curved.

Further embodiments of the invention result from the subclaims.

The invention is explained in more detail below using an exemplary embodiment shown in the drawing. Show in the drawing

Fig. 1 is a schematic representation of an arrayed waveguide gratings (AWG) with an input or output light waveguide and n output or input light waveguides and

Fig. 2 shows an enlarged portion of the AWG in Fig. 1, wherein the n output or input optical fibers in combination with an optical fiber array are coupled with periodic refractive index modulations of the individual optical fibers.

. The arrayed waveguide grating (AWG) 1 illustrated in Fig 1 comprises a central portion having an optical waveguide grating 3, which is formed so that the one individual optical waveguide 3 ₁ - 3 _m each have a different length. In this way, a light wave coupled in at the respective input of the optical waveguide array 3 can be applied with different phase delays to the respective output of the optical fiber array 3 . The optical fiber array 3 thus outputs a grid-like function. In comparison with a conventional optical grating, however, there is, to put it simply, the advantage that the grating-like behavior which is to be used for separating the wavelengths of an input signal is already a zero-order diffraction maximum. An AWG thus has the advantage of a much lower insertion loss compared to the use of a conventional optical grating for building a multiplexer or demultiplexer.

The optical waveguide array 3 is connected via coupling waveguides 5 at one end to a single input or output optical waveguide 7 and at its other end to n output or input optical waveguides 9 .

When operating as a demultiplexer, the AWG 1 can be supplied with a multiplex signal of the carrier wavelengths λ ₁ to λ _n via the input optical waveguide 7 . The optical partial signals of the carrier wavelengths λ ₁ to λ _n then occur at the output optical waveguides 9 , divided between the individual output optical waveguides 9 .

Conversely, the AWG 1 can be operated as a multiplexer if optical signals of the carrier wavelengths λ ₁ -λ _{n are} coupled into the input optical waveguides 9 and the corresponding multiplex signal is coupled out at the output of the AWG 1 in the output optical waveguide 7 .

FIG. 2 shows the right part of the AWG shown in FIG. 1, the output or input optical waveguide 9 being coupled to an optical waveguide array 11 . In the embodiment shown in FIG. 2, each optical waveguide 11 ₁ to 11 _{n of} the optical waveguide array 11 is connected to a laser diode 13 ₁ to 13 _n . The laser diodes 13 ₁ to 13 _n are driven with a corresponding electrical signal, with each laser diode coupling the electrically / optically converted signal with a carrier wave length λ ₁ to λ _n into the optical waveguide 11 ₁ to 11 _{n in question} .

Each of the optical waveguides 11 ₁ to 11 _n is provided in a partial region 15 ₁ to 15 _n with a periodic refractive index modulation in the axial direction.

According to the invention, the refractive index modulation in the individual optical waveguides 11 ₁ to 11 _n is produced in that the optical waveguides, the core of which has a corresponding UV-sensitive doping material, are irradiated with UV light. The direction of the radiation has at least one component perpendicular to the plane of the drawing in FIG. 2.

In general, of course, electromagnetic radiation or particle radiation of a different wavelength can also be used if the core of the optical waveguide 11 ₁ to 11 _{n has} a corresponding sensitive component.

The radiation takes place in such a way that the entire area of the laterally adjacent partial areas 15 ₁ to 15 _n is irradiated simultaneously. The radiation is such that there are intensity fluctuations in the plane of the optical waveguides (preferably in the plane of the axes of the optical waveguides), the lines (or planes) of maximum and minimum intensity extending transversely to the partial regions 15 ₁ to 15 _n and in each partial area of an optical waveguide 11 ₁ to 11 _{n have} a predetermined different local periodicity in the axial direction thereof.

The local periodicity or the local wavelength Λ ₁ to Λ _n is different for each optical waveguide and is selected so that the center wavelength of the filter structure in question has the desired distance from the respective neighboring center wavelength. The optical grating produced in this way can, in the embodiment shown in FIG. 2, serve as an external resonator for the lasers 13 ₁ to 13 _n . Of course, the structure shown in FIG. 2 can be modified in an analogous manner so that instead of the lasers 13 ₁ to 13 _n, corresponding receive diodes are connected to the optical waveguides 11 ₁ to 11 _n . In this case, the filter structures in the partial areas 15 ₁ to 15 _n serve to improve the crosstalk attenuation of the individual channels.

As indicated in FIG. 2, the refractive index modulations in the partial areas 15 ₁ to 15 _{n can} be produced in that the lines of maximum or minimum intensity 17 each enclose a small constant angle with one another. In the case of parallel to each other in Fig. 2 extending optical waveguides 11 ₁ to 11 _n then the portions 15 ₁ to 15 _n is obtained in each one Bragg grating with the local Peri ode Λ ₁ Λ _n. The local wavelength decreases from Λ ₁ to Λ _n . Depending on the desired distances between the center wavelengths of the resonator structures or structures with periodic refractive index modulations in the subregions 15 ₁ to 15 _n , the lateral distances of the optical waveguides 11 ₁ to 11 _{n can} be selected accordingly. In this way, the desired distance of the center wavelengths can be set even with straight lines of maximum or minimum intensity 17 .

Of course, the structure of the field used for irradiating the partial areas 15 ₁ to 15 _n can also be selected such that the lines of maximum or minimum intensity 10 are curved. In addition, the optical waveguides 11 ₁ to 11 _n can also be designed such that they do not run parallel and / or curved. The essence of the present invention is to choose the radiation so that the lines of maximum or minimum intensity (understood in the general sense) run across the partial areas 15 ₁ to 15 _n and in each partial area in its axial direction (which are also curved) can be) have a predetermined different local wavelength λ ₁ to λ _n .

This results in a relatively simple in most practical applications che structure of the required radiation, so that this also using a holographic process can be generated with relatively little effort can.

Claims (8)

1. Method for producing an optical waveguide array with periodic refractive index modulations of the individual optical waveguides,

• a) in which optical waveguides ( 11 ₁ to 11 _n ) are produced on a substrate,
• b) which in essentially laterally adjacent partial areas ( 15 ₁ to 15 _n ) receive an essentially axially periodic modulation of the refractive index in the area of the respective light-guiding part of each optical waveguide in that each axial partial area ( 15 ₁ to 15 _n ) of an optical waveguide with an electromagnetic or particle radiation is applied which has a corresponding periodicity (Λ ₁ to Λ _n ) in its intensity in the axial direction of the partial area,

characterized by

• a) that the electromagnetic or particle radiation is such that it extends over the entire width of the laterally adjacent sub-regions ( 15 ₁ to 15 _n ) of the optical waveguide ( 11 ₁ to 11 _n ) and the entire axial length over which the refractive index Modulations are to be generated, and
• b) that the electromagnetic or particle radiation in the plane of the optical waveguide ( 11 ₁ to 11 _n ) has lines 17 of maximum and minimum intensity, which run transversely to the partial areas ( 15 ₁ to 15 _n ) and which in each partial area of an optical waveguide whose axial direction has a predetermined different local periodicity (Λ ₁ to Λ _n ).

2. The method according to claim 1, characterized in that the lines ( 17 ) ma ximal and minimum intensity at one of the outer partial areas a minimum periodic distance (Λ _n ) and on the other of the outside the partial areas ( 15 ₁ ) are maximum have periodic spacing (Λ ₁ ) in the axis of the respective partial area. 3. The method according to claim 1 or 2, characterized in that the lines ( 17 ) of maximum and minimum intensity are rectilinear. 4. The method according to any one of the preceding claims, characterized in that the subregions ( 15 ₁ to 15 _n ) of the optical waveguides ( 11 ₁ to 11 _n ) essentially run in parallel. 5. The method according to claim 4, characterized in that in the axially central region of the partial regions ( 15 ₁ to 15 _n ) a line of maximum or minimum intensity runs substantially perpendicular to the optical waveguides ( 11 ₁ to 11 _n ) and the lines adjacent on both sides ( 17 ) maximum or minimum intensity each include a predetermined angle with the substantially vertical line. 6. The method according to any one of claims 1 to 3, characterized in that each adjacent sub-regions ( 15 ₁ to 15 _n ) of the waveguide ( 11 ₁ to 11 _n ) ge straight and include a predetermined angle and / or run differently curved. 7. The method according to claim 6, characterized in that the lines ( 17 ) maximum or minimum intensity run parallel. 8. The method according to any one of the preceding claims, characterized in that the electromagnetic radiation is generated holographically.