CN100504456C - Stress-free and thermally stable dielectric filters - Google Patents

Abstract

A multilayer optical interference filter having a multiplicity of optical cavities separated by a dielectric reflector stacks to achieve either a very narrow passband region or sharp transition between the passband and reflective region is substantially free of stress to preserve the desired optical performance upon fabrication into miniature discrete filter elements. The substantial stress reduction is achieved by removing the filter from the substrate used in the deposition process in a controlled manner to preserve the structural integrity of the resulting free standing multilayer film structure. The structure can be further bonded or attached to other optical components to suppress a thermal shift in center wavelength without reintroducing stress or interposing a massive substrate in the optical path through the filter.

Description

Stress-free and thermally stable dielectric filters

technical field

The field of the invention relates to multilayer optical interference filters and devices incorporating such filters, particularly having strong applicability in optical communication networks.

Background technique

Using wavelength division multiplexers, multilayer optical interference filtering is widely used in optical communication systems. This filter is currently a popular method of separating or combining optical signal channels into different optical wavelengths according to the grid of the International Telecommunication Union. However, due to the minimum insertion loss caused by this method, these optical signal channels will propagate under a common waveguide. However, increasing the number of signal channels that can be used in existing fiber optic structures requires reducing the optical distance between adjacent channels. It is also necessary to reduce the size of active and passive components, such as filters in switches, and reduce the cost of the overall device by combining filters with other components. Therefore, the performance requirements of optical interference filters have become more important. However, while this performance requirement can be met by increasing the number of layers, its physical properties such as the thickening of the filter pose a greater challenge to reduce the volume of the filter and the overall device volume after being combined with other devices.

Another requirement of this filter is that its optical properties, ie its propagation characteristics as a function of wavelength, must not cause large changes in the ambient temperature. The maximum propagation area or central wavelength position drift is a feature of the thermal stability of the filter, that is to say, when the temperature range is between 0°C and 70°C, the maximum propagation area or central wavelength position drift is less than 2pm/°C, which is more preferable It is desirable that the center wavelength shift by less than about 0.5 pm/°C within the above temperature range.

Placing thin-film optical materials on a substrate makes an optical interference filter, but this inevitably produces a pure residual stress state in the multilayer structure. This residual stress may be intrinsic, that is to say a property inherent in the materials themselves when they are placed in thin film form. Another type of residual stress is external and is caused by the different coefficients of thermal expansion between the base and membrane materials. When these useful optical materials are placed into multilayer films, their intrinsic properties are inevitably pure residual stress states. Since increasing the number of layers can improve the performance of thin-film optical fiber, and the bending time is the product of thickness and stress, the pure residual stress effect increases the bending degree of thin-film and base. Residual stresses place limits on the available foundations. The base must be thick enough to avoid buckling of the base due to residual stresses in the thin layer.

Simply increasing the thickness of the base in an attempt to minimize peripheral deformation is unacceptable for several reasons;

The use of thicker spacers prevents packing something reliable and efficient into a smaller device, and hinders the integration of the filter with other active or passive components. Thick spacers also increase insertion loss due to the optical properties of the spacer. Stress-induced confinement does not limit fiber bending due to defocusing effects especially due to reflections or fast signals; stress induces birefringence within the coating layer producing polarization-dependent loss (PDL) and position-induced CWL changes.

Residual stress may also be a factor in device failure and may limit future increases in signal power density, which can be increased through the development of laser emitters.

For thermally stable interference filters, the importance of choosing a good thermal plate is obvious. As H. Takahashi (whose name was misspelled as Takashashi in the original text) stated in pages 667 to 675 of his book "Applied Optics 34 (40)" published in 1995: By choosing a linear expansion coefficient material to change or stabilize The central wavelength multilayer dielectric bandpass filter that allows the beam to pass through changes the temperature of the surrounding environment.

Since about 1995, many high thermal expansion glass and glass/ceramic materials have been either used in other inventions or developed as optical performance susceptor materials for commercial use. Representative commercial products for different types of glass are as follows:

i) "F7" and "DWDM-12" made by Schott glass process.

ii) "WMS-01" and "WMS-02" produced by Ohara Glass Co., Ltd.

iii) Among other glasses, there are "WMS-11", "WMS-12" and "WMS-13" manufactured by Ohara Glass Co., Ltd.

Among these glasses, the four mentioned above are the real glasses. To a large extent, the high linear expansion coefficients of these four glasses are due to their alloy composition, which contains a large amount of alkali oxides. However, these alkaline components will reduce the stability of the environment around the glass. This instability may have a rather adverse effect on the environmental performance of the finished device.

Group (iii) is representative of glass/ceramic composite structures, "WMS-11", "WMS-12" and "WMS-13" are such glasses. By proper material selection and processing under corresponding processing conditions, the base can be made with the required high coefficient of expansion. Like most traditional glasses, these materials do not use alkaline components to achieve the corresponding high expansion properties, which in turn stabilize the ambient temperature more. These materials also have the advantage of being relatively hard, which can make them more resistant to the high stresses caused by the thin-film structure. However, properties of hybrid glass/ceramics reduce their overall propagation capabilities, such as at the interface between phase scattering and infrared.

A few simple coatings are removed from the spacer to create a pigment with unique optical properties. As described in U.S. Patent No. 4,434,010 (by Ash et al.), removing a layer of metal/insulating filter from the carrier spacer of the filter makes the spacer a very small sheet with reflective dyes of various colors . There are many such examples. But Ash found that the optical properties of the coating were attenuated, and suggested that this approach is only suitable for low-handling applications.

Another similar example is a method invented by U.S. Patent No. 4,826,553 (Armitage et al.), which removes a mirror coating from a mirror-coated carrier and completely coats the coating on another base To change the shape (curvature) of the insulating mirror. In a later publication, Schmidt et al. (in "Optical Spectrum", May 1995) stated that this approach was applicable to some lower operating performance telecommunication filters.

Another method proposed by Solberg et al. in US Pat. Nos. 5,944,964 and 5,930,046 is to balance the pressure of silica and reduce stress by crystallizing high-reflectivity materials. Titania and zirconia are two common high reflectivity oxide materials. The usual practice of hardening and stabilizing the titania and zirconia thin film layers involves a post-placement annealing process. Since these thin layers are fixed on a base that does not shrink, tensile stresses are induced in the thin film layers during hardening. In fact, the total tensile stress may exceed the total stress of silica due to excessive net tensile stress in the multilayer film due to lack of mechanical integrity or low optical properties. Furthermore, crystallization induced during annealing may cause optical dispersion, which may also degrade optical properties.

Solberg notes that this combination of processes minimizes many of the detrimental effects of crystallization, which is used as a way to reduce the net stress induced by plating into the film. However, this method is not suitable for use in wave-division multiplexer (WDM) filtering as a crystallization process in pass-through filters, because this will cause light dispersion and stress birefringence, because this will reduce Propagation capability, in turn, increases polarization-dependent loss (PDL).

Another requirement of WDM filters is that the optical performance, ie the propagation characteristics as a function of wavelength, should be spatially uniform over the area illuminated by the optical signal beam. So far, apart from the strong spatial non-uniformity in the propagation around the periphery of higher-performance WDM filters, this non-uniformity has been shown to limit the miniaturization of the filters in the assembly of advanced applications. While it would be somewhat desirable to reduce the filter size to less than a beam smaller than 500 microns, doing so would degrade device performance. Unless the spatial inconsistency at the edges is corrected to some extent, the optical signal path within the beam will be moderated over the area illuminated by the beam, depending on the average performance of the filter.

Therefore, it is necessary to invent a multilayer thin-film filter that can have stable wavelength characteristics in a large ambient temperature range, and has high propagation at the central wavelength, and has low dispersion characteristics and will Insertion loss and polarization dependent loss (PDL) are minimized.

Another corresponding need is to reduce the size of such optical interference filters so that they can be combined with passive and active optical devices such as lenses, switches, lasers, regulators, photodetectors, etc. Therefore, another object of this invention is to find out and eliminate the source of the inconsistency in the WDM filter.

Although the source of the spatial non-uniformity and residual stress has been found, another object of the invention is to substantially reduce the residual stress while retaining the characteristics of the optical interference filter suitable for WDM.

Contents of the invention

Leaving aside this theory, we also found that very thick multilayer optical interference filters have spatial inconsistencies in propagation that generate high residual stress. This non-uniformity is a limitation on the packaging of advanced application devices, which limits the miniaturization of filters. Miniaturizing such a filter to accommodate a small beam would then cause spatial changes across the beam.

A specific application of this invention, a stand-alone optical filter, is to place film layers sequentially on a first spacer. The thin film layers are then removed layer by layer from the pad to make the pad a monolithic integrated circuit, which releases the residual stress. And it has been proved that this specific application case can further miniaturize the optical filter device.

Removing the optical coating from the submount has several benefits due to losses and/or beam aberrations caused in the original submount. While the thermal stability of this separate filter is reduced, it is another aspect of this invention to attach a second submount so that these smaller submounts will generate propagation and Inconsistency between reflected heat and space. The second base and the way it is attached provides a way to thermally stabilize the filter.

Another aspect of the invention is a component having a center drift of less than 2pm/°C over a temperature range of 0 to 70°C, in which the light path passing through the multilayer dielectric interference filter does not pass through the second base. In this particular device, the second base is a frame or annulus with a so-called aperture opening. In this way, the optical hole of the multilayer dielectric interference filter is not supported. The frame is chosen to provide thermal stability at the center wavelength position.

Description of drawings

All of these and other features, aspects and advantages of this invention will be better understood from the following description, appended claims and its drawings.

Figure 1 is a transmission diagram of a "4-skip-0" type bandpass filter plated on a substrate 6 inches in diameter and 10 mm thick.

Fig. 2 is a propagation diagram of a "4-skip-0" type bandpass filter in which the base with a radius of 6 feet in Fig. 1 is made into a smaller square spacer with a radius of 1.5 mm and a thickness of 1.4 mm.

Figure 3 shows that after removing the film layer for the first time, an independent optical filter is formed, and then pasted on a square gasket with a length of 1.5 mm and a thickness of only 1 mm in the form of optical contact, the "4-skip-" in Figure 1 Propagation diagram of a 0" type bandpass filter.

Figure 4 is a schematic cross-sectional view of the bond between the gasket and the release and protective layers on which the multilayer bandpass filter is placed.

Fig. 5 is a diagram showing the relationship between the positions of the unfixed independent filter and the periphery of the independent filter on a ring frame, the position of the two at the center wavelength of the band pass and the temperature. The central wavelength shift of the non-fixed multilayer dielectric bandpass filter is greater than 9pm/°C, while that of the edge-fixed filter is less than 0.5pm/°C.

Fig. 6 is a schematic diagram of a stand-alone filter whose periphery is fixed on a ring frame.

Fig. 7 is a schematic diagram of placing the independent filter thin layer between two frames. The edges of each frame are glued to opposite sides of the filter.

Fig. 8 is a perspective view of fixing the outer periphery of an independent multilayer dielectric filter to a ring frame.

Detailed ways

There may be several factors that produce internal stress in a thin layer. Intrinsic stresses develop when depositing thin layers due to the formation of specific microstructures within the thin layer. Another important factor for the generation of stress is caused by the thermal expansion coefficient of the thin layer being different from that of the gasket or the thermal expansion and contraction of different materials caused by adjacent thin layers. Because the typical coating temperature is higher than the ambient temperature, when the temperature changes, the stress also starts to change. Even plating these thin layers at room temperature has the potential to generate heat in the base during placement and concentration. Finally, changes in temperature during use can also cause changes in stress. Due to the different thermal expansion coefficients of the thin layer and the base material, the stress induced by the thermal expansion signal will vary from high to low, and possibly from low to high. Therefore, there are many factors that affect the overall net stress of the optical coating layer.

The multi-layer film bond composed of high reflectivity oxide material and low reflectance material oxide is the first choice material for optical coating layer or filter, and the arrangement order of these materials can be reversed. To bond materials to form multiple optical film layers, environmental stabilization of the filter is necessary, and bonding multiple optical film layers creates inherent stress. Excessive stress within the optical coating due to the flexing of the base can crack or delaminate the coating. Then, for the particularly thick optical coating layer, such as the film layer is thicker than 20 μm, it is not suitable for WDM application devices due to the excessive pressure of these multi-layers.

Optical coatings with net tensile stress will develop a concave pad curvature while coatings in stress will develop a convex curvature. For this reason, the net laminar stress in the filter may be approximately the value of the net curvature of the coated shim, that is, the difference in stress from a bare shim to a bent shim after coating. For example, one way to measure curvature is to use an interferometer to pick a wavelength and measure the number of fringes and convert this information into a stress value. Conventionally, photoplating consists of a silicon and high-reflectivity metal oxide material substrate coated with multiple layers and can be exchanged. These photoplating layers usually have some net stress. Whether it is pressure or tension depends on the application technology and the specific misalignment. The layer placed material. However, the net stress in the thin layer material is generated by the placement method. For example, because the coated film layer is thicker and more stable, and can change the surrounding environment, coating by sputtering or ion methods is a narrow bandpass filter. the preferred method for . However, the pressure of these thick coating layers containing staggered silicon layers and high-reflectivity metal oxides greatly exceeds 100 x 10 ⁶ Pa (N/m ² ), or 100 MPa.

In the previously invented filter, since the thickness of the filter is thicker than 40 micrometers, it is difficult to apply this filter to an actual device. In such designed devices, internal stresses in the dielectric layer can distort the substrate to such an extent that potential signal sources are lost or dissipated, and can also increase insertion loss. High stresses also make the filter impossible to make smaller or thinner devices at all, since the stresses may indeed exceed the breaking force that the substrate can withstand.

Even when the substrate and filter are made to the desired size, another limitation arises; stress variations arising from the edges of the small filter, but not in contact with other devices, spread across the entire surface of the device and deform the substrate, thus This narrows the transmit and reflect bandpass regions, which is unacceptable.

Figure 1, Figure 2 and Figure 3 illustrate this limitation with a high-performance WDM filter named "4-skip-0". This design results in a highly spread wavelength range, the so-called "bandpass" where 4 optical signal channels separated by 100GHz in wavelength will be transmitted. Due to the square edges of this plot and the very large difference in transfer function between adjacent 100 GHz, the next adjacent optical channel outside the bandpass range is reflected. Thus among these spaced channels, none or zero channels are not transmitted or rejected by the filter.

Figure 1 shows the propagation of a filter plated on a substrate 6 inches in diameter and 10 mm thick as a function of wavelength. The actual propagation is very close to the theoretical performance extrapolated from the optical parameters.

Figure 2 shows the propagation of a 1.5 mm square filter obtained by reducing the thickness of a 6 inch diameter substrate from 10 mm to 1.4 mm. At the edge of the bandpass region, high net stresses make the filter's emission function less than ideally square and the ring edge is reduced as the size of the filter. This "4-skip-0" design is only suitable for 2 mm square filters, thus limiting the design to be applied to corresponding bulky devices. However, in theory, the shape of the filter can be changed arbitrarily by increasing the number of layers, but simply increasing the number of layers will increase the stress, which will make the problem more complicated.

We also found that thick multilayer dielectric filters, especially multilayer-cavity bandpass filters, can be removed from the substrate in a free-standing thin layer, and this movement can greatly reduce the stress. Once removed from the substrate, the filter's inherently strong inherent stress is released. The detrimental effect of the strong net stress that previously limited multilayer dielectric bandpass filters in many important applications no longer limits the optical design of the filter or places any special demands on the volume of the device.

Figure 3 is a diagram of the propagation of the filters in Figures 1 and 2, but the optical film layer is removed from the original substrate and then adhered to another square glass substrate with a thickness of 1 mm and a width of 1.5 mm Later propagation diagram. This almost square bandpass region is partially restored to the form in Figure 1, which is a more ideal or theoretical shape than the situation in Figure 2.

Removing the substrate facilitates the miniaturization of the device and can improve the optical performance of the device by eliminating the spatial variation of the center wavelength within the filter. Despite these and other advantages of stand-alone multilayer dielectric bandpass filters, the high thermal expansion variation of the central wavelength makes such structured devices unsuitable for high-performance applications such as telecom WDM systems. Optical properties that can vary with temperature are especially important. If the thermal expansion of the packaged optical device is not stable enough, it will not be suitable for WDM applications. In particular, there is a large variability in the center wavelength of the self-contained filter as a function of temperature, which makes the self-contained filter unsuitable for many telecommunication applications.

Stand-Alone Filter Practices

Filters are traditionally done with an appropriate substrate. However, before the multilayer bandpass filter is plated, the substrate is used to minimize the adhesion of the substrate to the film layers that make up the bandpass filter, which facilitates removal of the filter. This removal method may be a thin layer of a material that will be removed from the substrate or film layer so that the entire bandpass filter is separated at an appropriate point in the fabrication process. The separated substrate may be destroyed or damaged so that it becomes soluble, otherwise it is difficult to adhere to the underlying substrate.

As shown in Figure 4, the pipetting method currently used is to apply a thin layer 42 of water soluble, preferably inorganic material. Although there are many materials suitable as a mobile layer, we are currently using sodium chloride. During operation, the mobile release layer 42 is preferably placed in a vacuum chamber. Because of the air humidity, this water-soluble material is very fragile. In order to avoid the influence of the environment, it is better to coat the mobile release layer 42 with a thin protective layer 43 . Since this layer or layers will be separated as the release layer 42 and become part or all of the first layer of the finished multilayer dielectric bandpass filter, its thickness will be controlled accordingly, so its thickness Should be at least 100mm. The thickness of the sodium chloride layer is preferably controlled between 10 and 20 mm.

The protective layer 43 is to prevent the mobile release layer 42 from being fragile due to environmental changes when it is in use in the filter system.

The substrate 41 prepared together with the release layer 42 is then used as a conventional plating system, which meets the requirements of the ideal application device and meets the quality requirements used in the production of multilayer dielectric filters. Multilayer dielectric filters are plated in the usual way, using the accepted physical vapor deposition (PVD) or chemical vapor deposition or physical vapor deposition/chemical vapor deposition (PVD/CVD) hybrid method.

After the coated substrate is removed from the coating apparatus, it may be placed in a suitable controlled environment (such as a small portable vacuum vessel) until the next procedure.

This coated substrate can simplify the subsequent construction of individual filters, if desired. Such post-ordering may include, for example, imitation of filters. Mimicry, although not an essential process of this invention, assists in the latter process of release of the filter layer by providing unique features or allowing the filter material to be released from the substrate in a predetermined size and shape. Filter materials of this size are not easy to handle, but can be designed for future assembly or assembly with other optics.

Another way to make this thin filter of suitable specification is to model the substrate before plating the filter, and this method produces the same effect as the former.

Although in real-world applications, either material would interfere with the adhesion of the substrate, the thin layer deposited later acts as a release layer that can be easily activated by a specific device to bond multiple layers together. The dielectric bandpass filter is removed from its temporary base in a controlled and settable pattern, and the removal of the filter layer does not cause cracks, heat, or other defects at all.

Therefore, for NaCl, the currently favored release method is to scrape a place on the coating layer to form a small, deep groove. This causes a layer of delamination before the groove, which continues to the release layer to separate the filter from the base. Whether this delamination spreads slowly or quickly on the surface depends on the design of the filter and the degree of residual stress.

Today, available bandpass filters exist in bulk form and are large enough to be picked up by conventional methods (eg, with tweezers). And the filter can be cut again to the required size and shape. Residues left on the release layer can be removed in a suitable solution (for NaCl, de-ionized ionized water).

Furthermore, before or after the release layer is removed from the base, the filter can be annealed to stabilize its optical properties.

Another release layer can be made of water soluble materials such as other salts like metal halide salts (especially silver chlorides), and water soluble polymers and the like. Other materials for release layer can be organic photosensitive material (this material is easily decomposed or dissolved by organic solvent), and thin metal layer (this layer is easy to react with acid and be destroyed or dissolved) and other materials.

thermal stabilization method

We have also found a way to improve the thermal stability of such a freestanding filter without introducing another undesired stress layer. This may necessitate the selection of an additional base to provide the necessary thermal stability and/or to simplify future handling or assembly methods.

Thus, in another embodiment of the invention, the free-standing filter is removed from the first base and bonded to the second base. The second base can be selected from optical glass with a relatively large coefficient of thermal expansion, such as the material previously designed for direct placement. It is worth noting that most thin layer materials and coefficients of thermal expansion CTE are much smaller than those used to thermally stabilize the base. Silica glass is considered to be a representative of thin-layer materials, and its CTE is 4.5 x 10 ^-7 /°K, but after the glass is made into a wavelength division multiplexer (WDM), its CTE is 50 to 115 x 10 ^-7 /°K Between K. In some cases, silicon can provide sufficient thermal stability since its CTE is 26 x 10 ^-7 /°K higher than that of silica glass.

Bonding method of optical fiber components

Once the unplated thin layer is removed from the base, it can be glued to another base. The second base can be another fiber optic device to provide the required overall adhesion through miniaturization while interacting with active components such as autofocus lenses, prisms, mirrors, detectors, photodiodes, waveguides, lasers, regulators, etc. or a combination of passive components. Alternatively, bonding such a free-standing filter to at least part of the precise armature can be used as a reflective device in a small electrical switch, as described in PCT Applications WO/0039626 entitled "Wavelength-selected Such a switch was invented in the article "Electric Switch" (written by Scobey et al.), and this switch is used as a reference in the present invention.

Potential rebonding methods include mechanical coupling and bonding methods, depending on the chemical properties of the device, or through a dielectric layer, such as the familiar optical adhesive. Those skilled in fiber optic assembly can find many possible bonding methods. Optical contact methods such as those taught by Meissner in US Patent Nos. 5,846,638 and 5,441,803 or by Eda (Electronic Design Automation) in US Patent No. 5,5,485,540 are particularly preferable because dielectric bonding layers are avoided in their discussions The use of , which is also an example of which the present invention is incorporated by reference.

Method of bonding to base frame

We have found that the free-standing lamina does not need to be completely rebonded to another optical base, which reduces or eliminates thermal shift at the center wavelength. As shown in the schematic diagram in Figure 6, the free-standing filter 64 can be thermally stabilized by assembling a component 61, wherein the filter 64 is connected together with a base frame 63, and the base frame has at least one plane connected to the periphery of the filter , so that the unbonded filter portion forms a light aperture across the opening in the base frame. Since the opening of the base frame expands when heated, this geometrical property provides the same effect as would occur if a glass with high thermal expansion was attached to the entire surface of the filter.

Fig. 5 is a graph showing the relationship between the position of the center wavelength of the light beam passing through and the temperature after the independent filter is not fixed and the periphery of the independent filter is fixed on a ring frame. The central wavelength shift of the movable multi-layer dielectric beam through the filter is greater than 9pm/°C, while the central wavelength shift of the edge-fixed filter is less than 0.5pm/°C.

Part 61 is done by removing a comparable sized bandpass filter from the base of the filter to relieve net residual stress. The filter is then bonded to the base frame 63 or the washer with a highly adhesive adhesive 62 such as epoxy glue. Since only the outer ring of the filter is bonded to the base frame 63 or the annular ring, it is preferable to coat the base frame with an adhesive material, which avoids contamination of the uncontacted central portion of the filter.

Additionally, solder plating, other adhesives or bonding materials may be placed on the annular surface of the frame, or these materials may be placed in modules on the surface of the filter 64 depending on the shape of the frame. Other bonding methods include bonding with dry glue, optical contact, mechanical coupling and the like. Mechanical coupling can be done by mounting the filter on a frame of a certain size or by compressing or frictionally attaching the filter to a third thin layer to connect the filter. The frame structure is not required to be a separate device, but may be formed in other parts of an optical device for further miniaturization of future devices.

The base frame is preferably ring-shaped, such as a thermal ring, and this ring frame has a relatively appropriate thermal expansion coefficient, which can stabilize the central wavelength of the filter in a large temperature range. At the same time, due to the relief of the residual stress of the coating layer and the deformation of the first pedestal, the bandpass still maintains its required square shape.

Choose a spare ring of comparable size. The ring is made of a material with environmental stability and corresponding thermal expansion coefficient, and α is selected as the thermal expansion coefficient, so that the synthesized device has the inherent d(CWL)/d T of the filter itself and the larger The equilibrium state between the external tensions caused by the α value. While ceramic or optical glass can be used as the base for a free-standing filter, a metal ring is more ideal, as is a common gasket. The metal ring, which has a large differential coefficient of thermal expansion relative to the metal oxide in the film layer, will stretch the filter to balance the CWL drift of the filter itself. Stainless steel is a particular material of choice because it can be graded based on its CTE, which exceeds the grade range of the preferred optical glass used in WDM. For example, the CTE of SS410 grade is 103 x 10 ^-7 /°K and the CTE of SS302 is 179 x 10 ^-7 /°K.

Alternatively, the filter can be glued to a chosen substrate before removing it from its temporary base, but is not permanently attached to the coated surface. For example, the frame can be coated with a thermoplastic or a thermosetting resin, such as an epoxy glue of suitable viscosity. Thus, the release layer is activated, removing the filter from its base and securing it to the associated frame member. Each filter can be permanently affixed to the frame with a cured adhesive. This approach is highly throughput compatible since a frame-based assembly is easily separated from each other in a coplanar array and can be secured simultaneously to remove individual sized filters. Due to the viscous nature of the epoxy, each free-standing layer is only temporarily in an initial stress state, and heating the epoxy to curing temperature reduces the viscosity so that the net stress from the base remains permanently in place. This permanent bonding is a necessary condition to stabilize the filter.

This frame assembly provides a degree of manufacturing simplification for later handling and quality assurance steps since no separate handling of the still small and self-contained filter components is required. For example, future disassembly of coplanar array devices will remove a large number of individual filter or frame devices, and the individual filter/frame substrates will be removed and simultaneously incorporated into a larger optical device .

Since Figure 6 is intended as an illustration and not a limiting scope illustration, it should be noted that a symmetrical thermal stress in the structure may be obtained in some applications and accordingly a second frame layer may be adhered or connected to The other opposite surface of the filter can be made into a thin layer structure as shown in FIG. 7 . The optical assembly 71 includes a frame substrate 72 that is fixed or bonded to a first surface of the filter 74 by an adhesive layer 73a, and another is bonded to a second surface of the filter 74 by an adhesive layer 73b. 75 on the frame base. Alternatively, the second frame substrate 75 may be glued or secured to the filter 74 and the first frame substrate. Clamps and functional adhesive filter 74 may be used to bond or secure the first frame substrate to the second frame substrate, reducing reliance on adhesive layers 73a and/or 73b.

Fig. 8 is a perspective view of fixing the outer periphery of a self-contained multilayer insulation filter to a ring frame.

The advantage of the frame/filter components in Figures 6 and 7 is that the layering of the base avoids Nell reflections from the other surface of the base (this surface is opposite the first end, rather than placing the multilayer interference filter on on the first surface is connected to the first end face). Thus, the additional cost and complexity of providing a second surface of the submount with high anti-reflection properties is eliminated when the interference coating is not in contact with another surface of the optical device.

Although the invention has been described in considerable detail with a certain amount of optimized means (versions), other versions are also possible, e.g. it is desirable to stabilize the spectral characteristics of the fiber since no constraints are imposed on the bandpass filter , therefore, the spirit and scope of the appended claims should not be limited to the preferred optimized device (version) described herein.

Claims (11)

1. one kind forms the method that filter assembly is used, and this method comprises following step:

A) a multilayer optical wave filter is deposited in the substrate;

B) the multilayer optical wave filter is separated with this substrate;

C) first frame element is fixed to the discontinuous part of the outside surface of described multilayer optical wave filter, thereby multilayer optical wave filter and putting covers on the aperture that described first frame element limits;

Wherein said first frame element has thermal expansivity to vary with temperature the centre wavelength of stablizing the multilayer optical wave filter.

2. method according to claim 1 wherein provided the measure with the demoulding before the described multilayer optical wave filter of deposition.

3. method according to claim 2, wherein the measure of this demoulding is a release layer, described release layer with discontinuous patterned deposition in described substrate, thereby make each independently multilayer optical wave filter demoulding from the described substrate, and the lateral dimension of described substrate is corresponding with this discontinuous pattern.

4. according to the process of claim 1 wherein that described first frame element comprises toroidal frame.

5. comprise second frame element is fixed on the surface of the multilayer optical wave filter opposite with first frame element according to the process of claim 1 wherein.

6. according to the method for claim 1, wherein first frame element is installed on the described multilayer optical wave filter forming suitable epoxy glue before removing described substrate with thermoplastics or thermosetting resin, wherein said method also comprise solidify described thermoplastics or thermosetting resin with bonding described framework permanently to described multilayer optical wave filter.

7. optical filter assembly comprises:

A) first frame element with first plane surface, and this plane surface is basically around wherein central opening;

B) a free-standing multi-coated interference wave filter, it separates to discharge internal stress from substrate, and its first surface is connected with the plane surface of said frame element, to limit an expedite optical aperture that supplies described multi-coated interference wave filter to pass through;

Wherein said first frame element has thermal expansivity to vary with temperature the centre wavelength of stablizing the multi-coated interference wave filter.

8. optical filter assembly according to claim 7, wherein said first frame element comprises toroidal frame.

9. optical filter assembly according to claim 7 also comprises lip-deep second frame element of the multi-coated interference wave filter opposite with first frame element.

10. optical filter assembly according to claim 7, wherein this first frame element is made of the material of its thermal expansivity greater than at least a material coefficient of thermal expansion coefficient of forming described multi-coated interference wave filter.

11. optical filter assembly according to claim 7, wherein said first frame element comprises stainless steel.

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