Manufacturing method of rod with optical thin film and rod block for use in the method

A method for manufacturing a rod with an optical thin film which comprises forming a rod block by arranging a plurality of rods each having a circular cross section in parallel to one another along the axis of each rod and by allowing a resin to enter gaps between rods adjacent to one another to fix the rods to one another. The rod block is cut into a predetermined length. The endfaces of each rod positioned on the cut endface of the rod block are then polished. An optical thin film is formed on the polished endfaces of each rod. The resin has a melting point higher than the temperature used in forming the film. The rods are separated from one another by removing the resin from the rod block.

BACKGROUND OF THE INVENTION

The present invention relates to a method for manufacturing a rod with an optical thin film, and also relates to a rod block for use in this method.

Conventionally, there has been known a technology for previously forming a filter on an endface of a gradient index rod lens and thereby eliminating problems with alignment of the rod lens and the filter element and making the optical system more compact. For example, refer to Japanese Laid-open Patent Publication No. 54-56851.

Furthermore, Japanese Laid-open Patent Publication No. 2002-255580 discloses a technology for integrating with a resin, such as wax, a plurality of slender rod lens preforms having a predetermined refractive index distribution, and cutting off the rod lens preforms into a predetermined length at one time. After each cut endface of the rod lens preforms is subjected to a polishing process and the like, a desired optical film is formed on each endface of the rod lens preforms.

Further, in Japanese Examined Patent Publication No. 3-14590, there is known a technology in which, prior to the film formation, a resin, such as wax for fixing a plurality of rod lens preforms, is removed to separate the rod lens preforms from one another and the separated rod lens preforms are fixed to a jig piece by piece. The reason for separating the rod lens preforms from one another before the film formation is that in the case of integrating the rod lens preforms with a resin, the resin is melted by heat applied during the film formation, and as a result, the rod lens preforms cannot be integrally held, or there is the possibility that the melted wax flows out onto the surface of the rod lens to inhibit the film formation, or the vaporized wax adsorbs on the rod lens endface to cause deterioration in film quality.

However, as for the removal of resin and separation of the rod lens preforms from one another before the optical film formation, and for the fixing of the separated rod lens preforms to a jig, it takes a lot of time to conduct the preliminary work and a long working time is required.

Furthermore, there is the possibility that due to the preliminary work before the film formation, defects are produced, leading to the reduction of the yield. This is because during the preliminary work, there arise problems in that the individual rod lens preforms contact one another, tweezers or the like for clipping small rod lens preforms come into contact with the rod lens preforms and damage the lenses, or small rod lens preforms scatter in all directions and are lost.

SUMMARY OF THE INVENTION

The present invention has been made by taking notice of these conventional problems, and the object of the present invention is to provide a method for manufacturing a rod with an optical thin film, in which steps of from cutting to film formation are performed in a state where a plurality of rods are fixed, thereby improving manufacturing efficiency and yield. The object of the present invention also includes providing a rod block for use in this method.

To achieve the foregoing and other objective and in accordance with the purpose of the present invention, a method for manufacturing a rod with an optical thin film is provided. A plurality of rods are integrally fixed with a resin so as to have axes running in parallel to one another. The method includes sequentially performing: cutting the rods into a predetermined length; polishing the cut endfaces of the rods; and forming an optical thin film on the polished endfaces of the rods, wherein the resin has a melting point higher than the temperature to which the rods are exposed during said forming.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

One embodiment of the method for manufacturing a rod with an optical thin film embodied in the present invention is described below by referring to the drawings. The method for manufacturing a rod with an optical thin film comprises a block forming step, a block cutting step, a polishing step, a film forming step, and a lens separating step.

As shown inFIG. 1, andFIGS. 2(a) and2(b), in the present embodiment, a plurality of glass rod lens preforms21are integrally fixed with a thermoplastic resin so as to have optical axes running in parallel to one another and thereby producing a rod assembly, namely, a glass rod block30. Each of the rod lens preforms21has a predetermined refractive index distribution.

In the glass rod block30of this embodiment, the rod lens preforms21are arranged in two rows so as to have optical axes running in parallel to one another, and integrally fixed with the thermoplastic resin.

In the block forming step in this embodiment, as shown inFIG. 1, the rod lens preforms21are each arranged in a row between an upper holding plate22and an intermediate holding plate23, and between the intermediate holding plate23and a lower holding plate24. Side plates25,26,28and29are each arranged on the outside of the rod lens preforms21in each row. The holding plates22to24and the side plates25,26,28and29are each made of glass, for example, soda-lime glass.

Thermoplastic resin films27are each arranged on the upper side and lower side of the rod lens preforms21in each row. Each resin film27has a width which covers a part of from almost the middle part of the left upper side plate25to almost the middle part of the right upper side plate26, more specifically, a width (t1+t2+t3) resulting from adding an approximately half width (t2, t3) of both the side plates25and26to the whole width (t1) along the alignment direction of the rod lens preforms21, that is, the film27each has a length L which covers almost the entire length of the rod lens preforms21.

As the resin film27, there is used a resin film having heat resistance such that a fixed state of the rod lens preforms21can be kept even at the maximum temperature (a process temperature during the film formation, e.g., 200° C.) in the step of forming an optical thin film. In short, the resin film27has a melting point higher than the process temperature during the film formation. The materials of the resin film27include polycarbonate, polysulfone, polyether sulfone or polyolefin. These resins become sufficiently soft at a temperature of 350° C. or lower, where characteristics of the rod lens preforms21are not deteriorated, so that the resins can enter gaps between the rod lens preforms21. Further, the resins are sufficiently hard so as to be capable of holding the rod lens preforms21without problems when the temperature is around the process temperature during the film formation, and the amount of a gas generated in a vacuum atmosphere is also sufficiently small so as to exert no influence on the film formation. The process temperature during the film formation varies depending on the film formation apparatus or the object, therefore, a resin suitable for the apparatus must be selected for the resin film27.

The order of arrangement for each holding plate, side plate, and resin film is not particularly limited, and stacking is usually performed starting from the bottom, for example, in the order of the lower holding plate24, the resin film27, the lower rod lens preforms21, the right and left side plates28and29, the resin film27, the intermediate holding plate23, the resin film27, the upper rod lens preforms21, the right and left side plates25and26, the resin film27, and the upper holding plate22.

Next, the side plates25and26, and the side plates28and29are each pressed against the rod lens preforms21, so that the rod lens preforms21in each row are brought into contact with one another. In this state, while applying a pressing force to the upper and lower holding plates22and24, the entire assembly is heated to about 250° C., kept for about 30 minutes and then, cooled to an ordinary temperature.

The heating temperature and heating time in this case are applicable to a case of selecting polycarbonate as a material for the resin film27. Due to the heating, the resin film27enters the gaps between the rod lens preforms21and the entire periphery thereof as shown inFIGS. 2(a) and2(b). Via the resin film27, the rod lens preforms21arranged in two rows, the holding plates22,23and24, and the side plates25,26,28and29are integrally fixed to form the glass rod block30. Respective holding plates22,23and24, and respective side plates25,26,28and29construct a holding frame60for the rod lens preforms21.

The heating temperature and heating time of the resin film27are suitably set according to the type of resin selected. The heating temperature is about 300° C. in the case of selecting polysulfone, about 350° C. in the case of selecting polyether sulfone and about 300° C. in the case of selecting polyolefin, in place of polycarbonate as the material for the resin film27. The heating time is not changed in these cases.

In the next block cutting step, the entire glass rod block30produced in the above-described block forming step is cut into a predetermined length to produce a lens block31as shown inFIG. 3andFIG. 4. By cutting the entire glass rod block30into a predetermined length, all the rod lens preforms21integrally fixed with the resin film27are simultaneously cut into a predetermined length.

Next, in the polishing step, cut endfaces31aand31bof the lens block31shown inFIG. 3andFIG. 4are ground such that the endfaces of all the rod lens preforms21positioned on the cut endfaces31a,31bare ground into a predetermined shape, for example, a flat surface perpendicular to the optical axes or an inclined surface inclined at a predetermined angle with respect to the optical axes, and then the ground endfaces are polished, whereby the lens block31for use in the sequential film forming step is produced.

In the next film forming step, an optical thin film, for example, a CWDM band pass filter is formed on each endface of the rod lens preforms21held by the polished lens block31by the use of a sputtering method, or the like. CWDM is an abbreviation for “Coarse Wavelength Division Multiplexing.”

Next, in the lens separating step, the resin film27in the lens block31is dissolved or swollen with a solvent to dismantle the lens block31after completion of the film forming step, whereby the rod lens preforms21are separated from one another. Thus, a plurality of gradient index rod lenses40as a rod with an optical thin film, wherein each has a predetermined length and comprises an endface (a filter formed face)40ahaving formed thereon an optical thin film, are formed as shown inFIG. 7.

In the method for manufacturing a rod with an optical thin film according to this embodiment, the following advantages are provided.

(1) According to this embodiment, when the gradient index rod lenses40each comprising the endface having thereon an optical thin film are produced from the rod lens preforms21, the steps of from the cutting step to the film forming step can be performed in the state where the rod lens preforms21are integrally fixed with the resin film27.

(2) In the block formation step, the resin film27having heat resistance such that a fixed state of the rod lens preforms21can be kept at a process temperature during the film formation is used as a resin integrally fixing the rod lens preforms21to produce a glass rod block30comprising the rod lens preforms21integrally fixed with this resin film27. The resin film27has a melting point higher than the process temperature during the film formation. The glass rod block30is cut into a predetermined length, and the cut endface is polished to produce the lens block31. The thus obtained lens block31is used in the film forming step.

Thus, the steps of from the cutting step of cutting the rod lens preforms21into a predetermined length to the film forming step of forming an optical thin film on each endface of the rod lens preforms21can be performed in the state where the rod lens preforms21are integrally fixed with the resin film27. Therefore, work is not required such that during the film forming step, the rod lens preforms21are separated from one another, and the separated rod lens preforms21are fixed to a jig piece by piece. By virtue of this, the labor or man-hours for the preliminary work in the film forming step can be reduced and at the same time, damage, scattering and loss of the rod lens preforms21, which have been generated by the work, can be avoided. Accordingly, improvement in production efficiency and yield can be attained.

(3) After completion of the step of forming an optical thin film, the resin film27is dissolved or swollen with a solvent to dismantle the lens block31, whereby the rod lens preforms21, each comprising an endface having formed thereon an optical thin film, can be easily separated from one another.

(4) The glass rod block30shown inFIG. 2(a) is produced by a method where the rod lens preforms21, and the holding plates22to24and side plates25,26,28and29constructing the holding frame60for holding the rod lens preforms21are integrally fixed with the resin film27. Further, the glass rod block30is cut into a predetermined length and the cut endface is polished to produce the lens block31. Therefore, rigidity of the glass rod block30and the lens block31, which is demanded in conducting each step other than the lens separating step, can be secured by the holding frame60, and further the holding frame60can prevent the rod lens preforms21from getting scratched.

(5) The holding frame60is composed of three holding plates22to24for sandwiching the whole plurality of rod lens preforms21in each row and four side plates25,26,28and29for sandwiching the rod lens preforms21at both the sides in each row. Therefore, the arrangement can be easily performed so that the optical axes of the rod lens preforms21are parallel and the adjacent rod lens preforms21contact one another. Further, since the holding plates and side plates constructing the holding frame60are made of glass, for example, soda-lime glass, the glass rod block30and lens block31having rigidity and heat resistance at the same time can be obtained.

(6) To outer peripheral surfaces of the gradient index rod lenses40(seeFIG. 7) after passing through the lens separating step, a film formation material used for the optical film formation in the endface40ais not adhered. This is because during the film formation in the endface40a, the thermoplastic resin fills in the gaps between the rod lens preforms21to cover the whole periphery of each base material21with the resin.

(7) The lens block31ofFIG. 4, produced by cutting the glass rod block30shown inFIGS. 2(a) and2(b) into a predetermined length and polishing the cut endface, is used as it is without dismantlement, and the formation of the optical thin film is performed. Therefore, all the filter formed surfaces of the respective rod lens preforms21within the lens block31are aligned on the same flat plane. Thus, variations of the film thickness and the quality can be reduced at each of the rod lens preforms21during the formation of a multilayer film or a thick film such as the filter.

EXAMPLE

The Example is described below by referring toFIG. 1toFIG. 7.

In this Example, the glass rod block30shown inFIGS. 2(a) and2(b) is produced by using three holding plates22,23and24, four side plates25,26,28and29, four resin films27and forty-eight rod lens preforms21as shown inFIG. 1. Each of the holding plates22,23and24has a thickness of 4 mm, a width of 50 mm and a length of 150 mm, and is made of soda-lime glass. Further, each of the side plates25,26,28and29has a thickness of 1.7 mm, a width of 5 mm and a length of 150 mm, and is made of soda-lime glass. The thermoplastic resin film27is a polycarbonate film having a thickness of 200 μm, a width of 47 mm and a length of 115 mm. Each of the rod lens preforms21has a diameter of 1.8 mm and a length of 117 mm.

Using these members, while applying a pressing force to the upper and lower holding plates22and24in the state of bringing the adjacent rod lens preforms21in each row into contact with one another, the whole block was heated to about 250° C., kept for about 30 minutes and then, cooled to an ordinary temperature, whereby there was formed the glass rod block30where the rod lens preforms21were arranged in two rows, the holding plates22,23and24and the side plates25,26,28and29were integrally fixed with the resin film27.

Next, the whole glass rod block30was cut into a predetermined length to produce the lens block31shown inFIG. 3andFIG. 4.

Next, the cut endfaces31aand31bof the lens block31shown inFIG. 3andFIG. 4were ground and then, the ground endfaces were polished, whereby the lens block31for use in the sequential film forming step was produced. Next, the thus produced 100 pieces of lens blocks31were fixed to a coating jig50as shown inFIG. 5and by a sputtering method, CWDM band pass filters were formed all at one time on each endface of 4800 pieces in total of the rod lens preforms21held in each lens block31. On an inner periphery of the coating jig50, a supporting face50a, where each of the lens blocks31were arranged, was formed as shown inFIG. 5andFIG. 6. When fixing each of the lens blocks31to the coating jig50, each of the lens blocks31may be only arranged on the supporting face50aso as to face upward the filter formed faces of the rod lens preforms21held in each of the lens blocks31.

In this Example, the man-hours (minute×man) required for the preliminary work for the formation of the CWDM band pass filters on each endface of 4800 pieces of the rod lens preforms21was 12 minutes per one worker in terms of 1 coat lot (equivalent to 4800 pieces of rod lenses). Further, adhesion due to shifting of the film formation materials onto an outer peripheral surface of the gradient index rod lens40shown inFIG. 7was observed by a microscope at a magnification of 20 times, and as the result was that no shifting was observed. Further, the outer diameters of the band pass filter formed portion in the gradient index rod lens40were compared before and after the film formation, and the results thereof are shown in the following Table 1. The standard deviation σ in a center wavelength λc of the band pass filter formed within the same lot is also shown in Table 1. The center wavelength λc is a wavelength between two wavelengths of λ1 and λh where transmittance is 50%, as shown inFIG. 12and the standard deviation σ in the center wavelength λc expresses variations of the center wavelength.

Comparative Example

The Comparative Example is described below by referring toFIGS. 8(a) and8(b) toFIG. 11.

In this comparative example, a glass rod block30A shown inFIGS. 8(a) and8(b) is produced by using three holding plates22A,23A and24A, four side plates25A,26A,28A and29A, and forty-eight rod lens preforms21A. Each of the holding plates22A,23A and24A has a thickness of 4 mm, a width of 50 mm and a length of 150 mm, and is made of soda-lime glass. Further, each of the side plates25A,26A,28A and29A has a thickness of 1.7 mm, a width of 5 mm and a length of 150 mm, and is made of soda-lime glass. Each of the rod lens preforms21A has a diameter of 1.8 mm and a length of 117 mm.

Using these members, the glass rod block30A shown inFIGS. 8(a) and8(b) was produced by the following procedures.

First, the rod lens preforms21A were arranged in a row between two holding plates22A and23A, and two holding plates23A and24A, respectively, and the side plates25A,26A,28A and29A were arranged outside both the ends in the row direction of the rod lens preforms21A in each row.

Next, heated and molten wax27A was poured into the gaps between the rod lens preforms21A in each row to cover the whole periphery of each rod lens preform21A and the whole base material block was cooled to solidify the wax27A, whereby the rod lens preforms21A arranged in two rows, the holding plates22A,23A and24A and the side plates25A,26A,28A and29A were integrally fixed with the wax27A to produce the glass rod block30A.

The whole glass rod block30A produced in this manner was cut into a predetermined length to produce the lens block31A shown inFIG. 9. Then, the lens block31A was dipped in ethanol for 24 hours to dissolve the wax27A and thereby, the rod lens preforms21A were separated from one another.

Next, 4800 pieces of the separated rod lens preforms21A were thoroughly washed and fixed to the coating jig50A as shown inFIG. 10. On each endface of 4800 pieces of the rod lens preforms21A fixed to the coating jig50A, CWDM band pass filters were simultaneously formed by a sputtering method or the like.

In this Comparative Example, the man-hours required for the preliminary work for the formation of the CWDM band pass filters on each endface of 4800 pieces of the rod lens preforms21A was 330 minutes per one worker in terms of 1 coat lot (equivalent to 4800 pieces of rod lenses). Further, adhesion due to shifting of the film formation materials onto an outer peripheral surface of the obtained rod lens40A was observed by a microscope at a magnification of 20 times, and as a result, shifting of the film formation material70was confirmed in the range of 0.1 to 0.5 mm from the film-formed endface as shown inFIG. 11. Further, the outer diameters of the band pass filter formed portions of the gradient index rod lenses40and40A in the Example and the Comparative Example were compared before and after the film formation, and the results thereof are shown in Table 1 above. The standard deviation σ in the center wavelength λc of the band pass filter formed within the same lot is also shown in Table 1.

Comparison between the Example with the Comparative Example has revealed the following. As shown in Table 1, the man-hours required for work in the preliminary stage was 12 minutes per one worker in the Example, whereas it was 330 minutes per one worker in the Comparative Example. From the results above, it can be understood that according to the Example, the working time in the preliminary stage could be greatly reduced.

Further, in the Example, the shifting of the film formation materials onto the outer peripheral surface of the gradient index rod lens40was not observed as shown in Table 1, whereas the shifting was observed in the Comparative Example. From the results above, it is presumed that the gradient index rod lens comprising the outer peripheral surface to which the film formation materials did not adhere, was produced by the manufacturing method of a rod with an optical thin film according to the present invention.

Further, in the Example, the outer diameter in the filter formed portion of the gradient index rod lens40was 1.800 mm before the filter formation, whereas it was 1.801 mm after the filter formation as shown in Table 1. In other words, the outer diameter of the filter formed portion was insignificantly changed before and after the filter formation. On the contrary, the outer diameter in the filter formed portion of the gradient index rod lens40A was 1.835 mm after the filter formation in the Comparative Example.

Furthermore, as shown in Table 1, the standard deviation σ (nm) in the center wavelength λc of the band pass filter formed within the same lot was 1.3 in Example, whereas it was 4.1 in Comparative Example. From the results above, it can be understood that when the steps of the cutting step to the film forming step were continuously carried out in the state of integrating the (4800 pieces) rod lens preforms21as in the Example, many gradient index rod lenses40, having extremely reduced variations in their characteristics, could be produced.

The present invention is applicable also when producing a rod with an optical thin film by the use of a homogeneous glass rod in place of the gradient index rod.

As the resin film27, a resin other than the above-described resin may be used if it has a property of sufficiently softening, at least at a temperature where characteristics of the rod lens preform21or the glass rod do not deteriorate, for example, at a temperature of 350° C. or less, and has a hardness at such a level so as to be able to sufficiently hold the rod lens preform21or the glass rod at the process temperature.

In the case of fixing the rod lens preforms21with the thermoplastic resin film27, in place of the resin film27, a molten thermoplastic resin may be poured into the gaps between the rod lens preforms21arranged in the mold or between the holding plates or the side plates.

In the illustrated embodiment, auxiliary energy such as heat or ultrasonic waves may be preferably used in dismantling the lens block31, whereby the rod lens preforms21may be separated more easily in a shorter time from one another after completion of the step of forming an optical thin film.

In the above-described block formation step, a filler may be mixed into the resin film27for the purpose of preventing the rod lens preforms21from cracking or becoming chipped due to heat shrinkage of the resin film27at the time of cooling the whole glass rod block30to room temperature. Examples of the filler include glass fiber, glass flake (thin leaf) or fine glass particles. For the same purpose, a glass rod as a dummy may be inserted into the gaps between the rod lens preforms21.

In place of forming the glass rod block30and the lens block31into a rectangular parallelepiped, these blocks may be shaped to have three side surfaces, or five or more side surfaces containing two side surfaces in parallel to the optical axes and at an angle with respect to one another.

The holding frame may be formed with a cylindrical glass pipe and the rod lens preforms21may be arranged in a space within the same glass pipe so as to have the optical axes running in parallel to one another.