MXPA00008129A - Fabrication of diffraction gratings for optical signal devices and optical signal devices containing the same - Google Patents

Abstract

Method of fabricating a wavelength filter on a substrate in which a phase mask having corrugations is placed over a polymeric substrate composed of at least two comonomers having different indexes of refraction and passing light through the phase mask to form light into two beams corresponding to different diffraction orders to form refractive gratings capable of reflecting light of a selective wavelength. Optical signal devices employing gratings fabricated in this manner are also disclosed.

Description

MANUFACTURE OF DIFRACTION GRIDS FOR OPTICAL SIGNAL DEVICES AND OPTICAL SIGNAL DEVICES THEY CONTAIN THE SAME FIELD OF THE INVENTION The present invention is generally directed to a method of manufacturing diffraction gratings that are used to isolate a narrow band of wavelengths in an optical signal device, such as Mach Zehnder device or a directional coupler. The manufacturing method employs a phase mask having corrugations that periodically retard the light that passes through it to a polymer substrate consisting of comonomers having different refractive indices. The present method and the optical signal devices produced therefrom result in less light loss than typical optical signal devices.

BACKGROUND OF THE INVENTION The optical signal devices for switching, addition / derivation and data orientation are known. Devices for adding and deriving signals encoded by wavelength (light of wavelength or specific wavelengths) are known in the art. Such devices employ optical fibers that are predominantly used in telecommunication systems in addition to local area networks, computer networks and the like. Optical fibers are capable of transmitting large amounts of information and it is the purpose of such optical devices to extract a select amount of information from the fiber, segregating the information transmitted in channels of different wavelengths. Devices of this type are comprised of a variety of components that together provide the desired segregation of signals encoded by wavelengths. The integrated optical couplers and especially the directional couplers have been developed to effect the evanescent directional coupling. The optical signals are coupled from one planar waveguide to another. The signals from the second planar waveguide propagate in the same direction as the signals in the first planar waveguide travel. The diffraction gratings (for example Bragg gratings) are used to isolate a narrow band of wavelengths. Such grid reflectors have made it possible to construct the device for use in adding or deriving a light signal with a predetermined centered wavelength to or from a fiber-optic transmission system, without disturbing other signals with other wavelengths. The Bragg grating systems of the patent of E.U.A. No. 5,574,807 to Elias Snitzer incorporated herein by reference. The '807 patent discloses a device for use in adding or deriving light signals with predetermined centered wavelengths to or from a wavelength division multiplex fiber-optic transmission system, which transmits signals with other wavelengths . A double-core fiber is fabricated which consists of two substantially identical, substantially identical fibers forming a coupling region, to provide substantially complete evanescent field light coupling from one core to the other in a predetermined range of wavelengths . The double-core fiber also influences a Bragg grating system that is substantially perpendicular to the axis of the double-core fiber. The exposed devices of the prior art, such as those described above, adoloce a number of disadvantages. One such disadvantage is that they are difficult to manufacture. A second disadvantage is that it is difficult to align Bragg gratings through the branches of the optical waveguides in the region of the gratings. It will therefore be a major advance in the technique of optical signal devices to provide a grid system that is relatively easy to manufacture and eliminate the problems associated with the alignment of the grids to minimize the loss of light.

BRIEF DESCRIPTION OF THE INVENTION The present invention is generally directed to optical signal devices and especially to optical signal devices that add and derive light signals. The present invention provides an improved grating system for more efficient derivation of light signals with less light loss than common optical signal devices. In particular, the present invention is directed in part to a method of manufacturing a wavelength filter (eg, a Bragg grid) on a substrate, comprising: a) placing a phase mask having corrugations on a polymeric substrate , said substrate consisting of a polymer composed of at least two comonomers having different refractive indices. b) passing a single beam of light through the phase mask to form two light beams corresponding to different diffraction orders to form refractive grids capable of reflecting the light of a selected wavelength. The present invention also encompasses optical signal devices with wavelength filters made in this manner.

BRIEF DESCRIPTION OF THE DRAWINGS The following drawings are illustrative of the embodiments of the invention and are not intended to limit the invention, encompassed by the claims forming part of the application.

Figure 1 is a vertical side view of an optical device of the present invention showing the relative positioning of the substrate, the coating layers and the core layers; Figure 2 is a schematic view of a first embodiment of the invention that includes a Mach Zehnder interferometer with several waveguides placed to be possible evanescent coupling in the two regions of 3-dB couplers of the device and a Bragg grid along the branches separated from each other in the middle of the device. Figure 3 is a graph showing the relationship between monomer conversion and time for a series of polymers useful for making grids according to the present invention; Figure 4 is a schematic view showing the placement of a phase mask on top of a substrate to create the gratings in an optical signal device according to the present invention; and Figure 5 is a graph showing a desirable wave function for the envelope of the modulation of refractive indices in the grid system of the present invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a method of manufacturing a reflection grating system with enhanced contrast (ie, greater modulation of indices) and more control over the wavelengths of the signals to be segregated from a light source of lengths Multiple wave Grids in optical signal devices are fine periodic variations of refractive indices that are used in numerous passive elements, including couplers, deflectors, reflectors, wavelength filters and mode converters. Such devices have many applications, but generally comprise a system for the control of wavelength optical signals. In accordance with the present invention, a wavelength filter in the form of a grating system is provided on a polymeric substrate through a phase mask having a series of corrugations. A beam of light is passed through a phase mask to form light in two phases corresponding to different diffraction orders to form refractive grids capable of reflecting the light of a selected wavelength. The substrate employed for manufacturing the optical signal device of the present invention can be selected from a variety of materials, including glass, silicon, plastic (for example polyurethane and polycarbonate) and the like. As shown in figure 1, the main layers comprising the optical signal device 2 include the substrate 4 as defined above having on it a layer of sub-coating 6 and layer of overcoating 8. Sandwiched between the layers of coating 6 and 8 is the core layer 10 in which the waveguides are printed (not shown). Referring to FIG. 2, an optical single channel addition / derivation optical signal in the form of a Mach-Zehnder device 20 that is formed on a substrate (see FIG. 1 for the relative position of the device) is shown as an example. substrate). The device 20 shown in Figure 2 in which evanescent coupling occurs in the coupling regions has two substantially identical planar waveguides 22, 24 which align with each other in two coupling regions 3-dB 26, 28 in the form of Directional couplers. Between the coupling regions 26 and 28 are the region of gratings 30 constituted in the grid system 32 (for example Bragg gratings), manufactured in accordance with the present invention. The arrangements in the waveguides that are printed on the core layer 10 are designed to provide an optical signal device in which a single wavelength of light from a light source of multiple wavelengths is segregated and discharged. of the optical signal device. The subcoat layer 6, the overcoat layer 8 and the core layer 10 are preferably made of polymeric materials consisting of comonomers that meet certain requirements as described hereinafter. In particular, the comonomers are selected such that refractive indices are different from each other, so that the difference of the refractive indices (? N) is large enough to allow a large difference in indices between the light fringes. and dark in the interference pattern formed by the light after it passes through a phase mask, since the relative amounts of the comonomers are different in areas that see light from areas that do not see light. The comonomers preferably have different diffusion rates, because one of the monomers has a tendency to move away from the light strips, while the other of the monomers tends to remain in the clear strips. In addition, it is desirable that the comonomers remaining in the clear fringes have high polymerization rates, while those monomers that are not in the clear fringes (dark regions) have a lower polymerization rate. Examples of various monomers and their conversion from the monomeric state to a polymer as a function of time are shown in Figure 3. Referring to Figure 3, it can be seen, for example, that the HDDA monomer has a higher conversion rate than the EBDA. This pair of monomers would be suitable for the formation of a polymeric material for use in the present invention. Conversely, the combination of EBDM and HDDA would not be as suitable, because the polymerization rates for the respective monomers are similar. Polymers that meet the requirements identified above are particularly suitable for receiving a filter or a wavelength grating according to the present invention. The phase mask through which the light source passes to the polymeric material can be selected from among a variety of materials, including glass and quartz. The phase mask is required to have a series of corrugations, so that the light beam passing through it passes through both the phase mask material (eg glass) and the air and is thus periodically retarded. , because the light passes through the phase mask material at a lower speed than that of the light passing through the air. Therefore, the light is diffracted and the two beams of light corresponding to different diffraction orders leave the phase mask at different angles. With reference to figure 4, a polymeric substrate 40 of the type described above having a phase mask 42 with a plurality of corrugations 44 therein is shown. A light source designated by the number 46 and as described hereinafter sends a light beam through the phase mask in which the diffraction of the light takes place in two beams 48 and 50. The two beams of light Light that come out of the phase mask interfere with each other to form light and dark regions. The period of the light and dark regions is equal to! of the period of the corrugations on the phase mask. In this way, for example, if the phase mask has a period of 1.040 nm, the two light beams emerging from the phase mask will form an interference pattern having a period of 520 nm. The wavelength of the light reflected in the grating system is determined according to the following formula:? = 2 NTff? where ? is the reflected wavelength, Neft is the effective refractive index in the waveguide and? is the period of the grid. Thus, for example, if the desired wavelength of the reflected light is 1.560 nm and the effective refractive index in the waveguide is 1.5, then the period of the grid should be 520 nm. According to the present invention, the light source for producing a light beam passing through the phase mask is a laser, preferably having a laser beam of relatively small diameter, preferably of approximately 2 to 3 millimeters of diameter. A preferred laser beam for use in the present invention is an argon ion laser beam. The use of the small beam provides better control over the placement of the grids. The wavelength of the preferred argon ion laser beam is from 350 to 365 nm. According to a further aspect of the present invention, the speed at which the phase mask is scanned can be varied, so that the amplitude of the grid can be varied equally. It is desirable to have the difference in refractive index of the comonomers (? N) more marked in the center than in the edges of the wave function, in order to derive more precisely a desired predetermined wavelength, reducing the lateral lobes around the Main peak in the reflection spectrum. The presence of several lateral lobes causes crosstalk between the wavelength channels. In this way, the grid of the present invention provides a large peak in the reflection spectrum at the desired wavelength and only small peaks at the sides. In a preferred embodiment of the invention, it is desirable that the envelope of the modulation of refractive indices in the grid have a synchronization profile where sinc (x) = [sin (x)] / x as indicated in figure 5 The resulting reflection spectrum has not only reduced the side lobes but also a central peak of rectangular or square shape that makes possible the operational stability in the derivation efficiency of the wavelength channels, despite slight fluctuations in the length wave of light generated by the light source of the communication system. According to another aspect of the present invention, apodization or any envelope can be obtained by varying the scanning speed of a small laser spot or by modulating the intensity of a large laser spot. In this way, using a small laser beam (2 to 3 mm) to scan through the phase mask by changing the speed, the local intensity of the grid can be varied resulting in a first type of apodization. This results in a strong peak in the reflection spectrum at the desired wavelength and the weakest peaks towards the sides of the main peak. By employing an envelope in the form of synchronization for the grid as discussed above, the natural lobes can be reduced thereby reducing crosstalk. An additional benefit is that a central peak of square or rectangular shape is obtained in the reflection spectrum, which makes it possible to derive all the light of the same wavelength or very similar in a desired bypass gate. In a further aspect of the invention, the grid is applied through both the coating layers and the core layer. It is known that as much as 25% of the light passing through the waveguides of the known optical signal device is propagated in the coating layers. The present invention provides for the reflection of light in the coating areas and therefore a significant reduction in the loss of light signals derived at levels considerably lower than 25%. In a preferred form of the invention, the comonomers which are used for the coating layers as well as the core layer are not completely cured before the formation of the gratings by the use of a phase mask. By keeping the comonomers in a semi-cured state, some movement is left available to the monomers, so that after treatment with the argon ion laser beam to provide the grids, the comonomers can still be moved in response to the diffracted light of the beam. To be. Subsequent to the manufacture of the grids according to the invention, complete curing can begin by the use of ultraviolet light and the like. Complete curing freezes the refractive indices of all materials in the waveguides and gratings.

In a further aspect of the invention, the grids are provided in the optical signal device after the overcoating layer has been placed over the core layer. It is known that polymerization is retarded by the presence of oxygen. By having the coating layer on the core layer and then providing the grid system, the overcoating layer acts as a barrier to oxygen penetration and therefore limits the availability of oxygen which would inhibit the termination of the polymerization of the reaction , when the grid system is installed. In this way, it is a preferred aspect of the invention, if the grid system is applied through the overcoating layer. The use of the polymer system for the coating and core layers according to the present invention provides a grating area having an average refractive index which is essentially the same as that of the areas outside the gratings (for example in the region of couplers) of the optical signal device. Maintaining the average refractive index substantially at the same value prevents the broadening of the blue side of the reflected peak, when apodization is used.

EXAMPLE 1 A silicon plate was used as the substrate. A negative-toned liquid photomonomer (from a mixture of 20.0 g of ethoxylated bisphenol diacrylate, 10.0 g of tripropylene glycol diacrylate, 0.6 g of Irgacure 651 photoinitiator, 0.09 g of Irganox 1010 antioxidant) was spin-coated in order to form a layer which was 10 μm thick and was subsequently cured by ultraviolet radiation uniformly under a mercury lamp (line / Hg, wavelength = 365 nm) forming a solid thin film with a refractive index of 1.4894 (when fully cured ) as a sub-coating layer. The exposure time was kept short (1 sec.) At this point to obtain a layer that is only partially polymerized. A negative-toned liquid photomonomer (from a mixture of 20.0 g of ethoxylated bisphenol diacrylate, 8.0 g of tripropylene glycol diacrylate, 2.0 diacrylate of 1,6-hexanediol, 0.6 g of Irgacure 651 photoinitiator and 0.09 g of antioxidant was revolvingly coated. Irganox 1010) on the sub-coating layer, in order to form a layer that was 6 μm thick, was placed in contact with a mask where the waveguide circuit (cascade four-channel add / drop device where each of the four addition / derivation elements in the cascade was a Mach-Zehnder interferometer) was free (the width of the waveguides in the mask was 6μ) and that the layer was subsequently cured by UV radiation so selective through the mask under the mercury lamp (for a short time of 3 seconds to ensure only partial polymerization), solidifying the core waveguide circuit that a refractive index of 1.4970 (when it was completely cured). The mask was removed and the unexposed sections were removed using methanol. The same photomonomer used for over coating on the core structures was rotatably coated to form a corresponding layer that was 10μ thick; this layer was subsequently exposed to UV radiation with a protective layer under the mercury lamp, forming a corresponding solid film with refractive index of 1.4895 (when fully cured) as an overcoat layer. This layer was also exposed for a short time (1 sec.) To ensure only partial polymerization at that stage. A phase mask with four grids was used to print (using an argon ion laser operating at 363.8 nm) a grid across the separated branches in each of the four Mach-Zehnder devices. The sample was maintained with the planar waveguide circuit parallel to the phase masks at 50μ of said mask. He directed the laser beam perpendicular to the mask and displayed it. The diameter of the laser beam was 3 mm (at an intensity of 1 / e2). The 3mm laser was scanned through the center of the 6mm long Mach Zehnder branches, creating gratings in the 3 layers of partially cured waveguides. The sample was finally subjected to a final UV cure in a nitrogen environment under the mercury lamp (60 seconds) and a final thermal cure (90 ° C for 1 hour), resulting in complete polymerization of all three layers. The evaluation of the sample revealed that all the grids were reflecting the desired wavelength channels.

Claims (22)

NOVELTY OF THE INVENTION CLAIMS

1. A method of manufacturing a wavelength filter on a substrate, comprising: a) placing a phase mask having corrugations on a polymeric substrate, said substrate consisting of at least one polymer made of at least two comonomers having different refractive indexes; and b) passing light from the light source through the phase mask to transform the light into two beams corresponding to different diffraction orders to form refractive grids on said substrate capable of reflecting light of selective wavelength.

2. The method according to claim 1, further characterized in that the light is an argon ion laser beam.

3. The method according to claim 1, further characterized in that the polymeric substrate comprises an overcoat layer, a sub-coating layer and a core layer therebetween, said method comprising forming the refractive grids on each of said layers.

4. The method according to claim 3, comprising placing an overcoat layer on the core layer and then applying the refractive grids to the substrate.

5. The method according to claim 1, further characterized in that the difference of the refractive indices is sufficient to allow a difference of indices between the light and dark stripes of the light passing through the phase mask.

The method according to claim 1, further characterized in that the comonomers have different diffusion rates, said difference being sufficient for one of the comonomers to move away from the light bands of the light passing through the phase mask , while all comonomers tend to remain in clear bands.

7. The method according to claim 1, further characterized in that the comonomers have different polymerization rates.

The method according to claim 3, which comprises partially curing the polymeric substrate, forming refractive grids on said layers and completely curing the polymeric substrate to thereby freeze all refractive indices.

9. The method according to claim 1, further characterized in that comonomers are selected from the group consisting of ethoxylated bisphenol diacrylate, tripopylene glycol diacrylate, 1,6-hexanediol diacrylate, ethoxylated bisphenol dimethacrylate and 1,6-dimethacrylate. hexanodiol.

10. The method according to claim 1, further characterized in that the phase mask of a material selected from the group consisting of glass and quartz is made.

11. The method according to claim 1, further characterized in that two light beams leaving the phase mask interfere with each other to form light and dark stripes where the period is equal to a half of the period of the corrugations of the phase mask.

The method according to claim 1, further characterized in that the light passing through the phase mask has a diameter of about 2 to 3 mm.

13. The method according to claim 2, further characterized in that the wavelength of the argon ion laser beam is from about 350 to 365 nm.

The method according to claim 1, further comprising varying the scanning speed of the light source through the phase mask to thereby vary the amplitude of the refractive grids formed on the substrate.

15. The method according to claim 1, further characterized in that the difference between the refractive indices of the comonomers is more marked at the center than at the edges of the wave function.

16. The method according to claim 1, further characterized in that the gratings have a refractive index modulation with an envelope having in synchronization profile represented by the formula sinc (x) = [sin (x) / x].

17. An optical signal device comprising: a) a substrate including optical waveguides for propagating an optical signal, said substrate consisting of at least one polymer composed of at least two comonomers having different refractive indexes; and b) a region of gratings traversing the substrate having a reflective grid or a plurality thereof in which the average refractive index of the grid region and the remaining portion of the substrate are approximately equal.

18. The optical signal device according to claim 17, further characterized in that the comonomers have different diffusion rates.

19. The optical signal device according to claim 17, further characterized in that the comonomers have different polymerization rates.

20. The optical signal device according to claim 17, further characterized in that the comonomers are selected from the group consisting of ethoxylated bisphenol diacrylate, tripopylene glycol diacrylate, 1,6-hexanediol diacrylate, ethoxylated bisphenol dimethacrylate and dimethacrylate di-methacrylate. 1,6-hexanediol.

21. The optical signal device according to claim 17, further characterized in that the difference between the refractive indices of the comonomers is more marked at the center than at the edges of the wave function.

22. The optical signal device according to claim 17, further characterized in that the gratings have a modulation of refractive indices having a synchronization profile represented by the formula sinc (x) = [sin (x) / x].