JP4003658B2 - Lens array spot size conversion optical circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical circuit in which a core layer of an optical waveguide and a core of an optical fiber are connected so that their optical axes coincide.
[0002]
[Prior art]
Many glass waveguide optical components having optical circuits such as AWG (Arrayed Waveguide Grating) filters, splitters, and optical switches have already been put into practical use because they are easily mass-produced by using a semiconductor process. Research and development for further miniaturization and cost reduction is underway.
[0003]
As an example, a reduction in size and cost reduction due to a high relative refractive index difference (high Δ) of a glass waveguide optical component has been studied. As a specific example, the relative refractive index difference Δ is 1.5% or more, About 2.5% of optical components are being studied.
[0004]
Here, the relative refractive index difference Δ is expressed by the following formula ₁ , where n ₁ is the maximum refractive index of the core layer and n ₂ is the refractive index of the cladding layer.
[0005]
[Expression 1]
Δ (%) = {(n ₁ −n ₂ ) / n ₁ } × 100 (%)
However, the optical circuit body made of a glass waveguide has a high Δ, whereas the optical fiber connected to it is a normal single mode optical fiber, and Δ ranges from 0.3% to 1%. Of these, those having a low Δ are used. Therefore, there is a problem that mode mismatching occurs between the optical circuit body and the optical fiber.
[0006]
In order to solve this, conventionally, two means as shown in FIGS. 5 and 6 have been used.
[0007]
5 and 6 are explanatory diagrams for explaining a conventional mode conversion method.
[0008]
As shown in FIG. 5, the first means is that the optical circuit body 50 in which the core layer 53 with a high refractive index is covered with a cladding layer 54 with a low refractive index is connected to the side connected to the optical fiber (the left side in the figure). In this method, the heater 52 is disposed, and a holding member 55 for circulating the cooling water w is attached to the opposite side (in this case, the right side) to form the mode conversion unit 51 (see, for example, Patent Document 1).
[0009]
Specifically, the refractive index control dopant (GeO ₂ ) in the core layer 53 of the optical circuit body 50 is heated by heating the end face side of the optical circuit body 50 to a high temperature (1300 ° C.) for a long time with the heater 52. Then, the mode converter 51 is formed by diffusing to the clad layer 54 side covering the core layer 53.
[0010]
In the second method, as shown in FIG. 6, one end of a high Δ single mode optical fiber 56-1 (56-2) is connected to a high Δ optical circuit body 60, and the optical fiber 56-1 (56 -2) A low-Δ single-mode optical fiber 57-1 (57-2) is heated and fusion-bonded using the TEC (Thermal Expand Core) technology to the other end of 2), and mode conversion is realized by the TEC connection part 58. (For example, refer to Patent Document 2).
[0011]
[Patent Document 1]
Japanese Patent Laid-Open No. 6-43330 [Patent Document 2]
Japanese Patent Laid-Open No. 5-257032
[Problems to be solved by the invention]
However, the conventional mode conversion system has the following problems.
[0013]
The method of forming the mode conversion unit 51 by heating with the heater 52 shown in FIG. 5 has a problem that the size of the optical circuit becomes very large and it is difficult to reduce the cost. Further, since it is difficult to finely process the core layer 53 with the heater 52, the loss of the optical circuit is increased, which is not practical.
[0014]
Further, the method of realizing mode conversion by the TEC connection unit 58 shown in FIG. 6 has an advantage that it can be realized with low loss, but a high Δ optical fiber 56-1 (56-2) must be separately manufactured. It becomes costly because it does not become. Further, the mounting cost is high, and it is difficult to reduce the cost. Furthermore, since the length of each optical fiber must be increased by at least several tens of centimeters, there is a restriction on miniaturization.
[0015]
Accordingly, an object of the present invention is to solve the above-described problems of the prior art, and to provide a lens array spot size conversion type optical circuit in which an optical fiber and an optical waveguide are connected with low loss and can be reduced in size and cost. It is to provide.
[0016]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention of claim 1 is an optical circuit in which an optical waveguide and an optical fiber are connected so that an optical axis of a core layer of the optical waveguide and an optical axis of a core of the optical fiber coincide with each other. The end face of the core layer on the side of the optical waveguide connected to the optical fiber is covered with a clad layer, and the optical fiber from the optical waveguide is placed on the optical axis of the core layer in the cladding layer covering the end face of the core layer. a plurality of substantially with the waveguide side spot size converting portion for chromatic gradually increased converts the spot size of the spherical lens medium is formed, the connecting portion near the optical fiber core gradually change the refractive index towards the among the optical fiber side spot size converting portion for gradually reducing convert have a plurality of substantially spherical lens medium which gradually changes the refractive index toward the optical waveguide from the optical fiber spot size is formed, the waveguide And spot size at the connection end of the optical fiber side spot size converting unit of the spot size conversion unit, also the spot size at the connection end of the waveguide side spot size conversion portion of an optical fiber-side spot size converting unit equal It is.
[0017]
According to a second aspect of the present invention, in addition to the configuration of the first aspect, the relative refractive index difference between the core layer and the clad layer of the optical waveguide is in the range of 2.0% to 4.0%, and the optical fiber The relative refractive index difference between the core and the clad is in the range of 0.3% to 1.5%, and the waveguide-side spot size converter is a substantially spherical lens toward the end face connected to the optical fiber. Preferably, the refractive index of the medium gradually decreases, and the refractive index of the substantially spherical lens medium gradually increases toward the end face connected to the optical waveguide in the optical fiber side spot size converter.
[0018]
According to a third aspect of the present invention, in addition to the configuration of the first or second aspect, the waveguide-side spot size conversion unit includes a plurality of substantially spherical lens media in a desired interval toward the end face connected to the optical fiber. It is preferably formed so as to have a desired diameter and a desired refractive index.
[0019]
In addition to the structure according to any one of claims 1 to 3, the invention of claim 4 has at least one connection portion between the optical waveguide and the optical fiber, and waveguide-side spot size conversion in the vicinity of each connection portion. It is preferable that the part and the optical fiber side spot size conversion part are respectively formed.
[0020]
According to a fifth aspect of the present invention, in addition to the configuration according to any one of the first to fourth aspects, the connection surface between the core layer of the optical waveguide and the core of the optical fiber is processed obliquely with respect to the perpendicular to the optical axis. Preferably it is.
[0021]
According to a sixth aspect of the present invention, in addition to the structure according to any of the first to fifth aspects, the lens medium has a pulse width in the range of 30 fs to 200 fs and a pulse repetition frequency in the range of 1 kHz to 250 kHz. It is preferably formed by changing the beam spot size and irradiation energy of the ultrashort pulse laser beam and condensing and irradiating.
[0022]
According to the configuration of the first aspect, since the spot size gradually changes from the optical waveguide toward the optical fiber by the plurality of lens media, the ultrahigh Δ optical waveguide with Δh of about 2% to about 4%, It becomes possible to connect an optical fiber having Δl in the range of 0.3% to 1.5% with mode field matching.
[0023]
According to the configuration of the second aspect, an ultra-high Δ optical waveguide is realized that is miniaturized from 1/20 to 1/40 compared to a conventional low Δ (Δ: about 0.75%) optical waveguide. It becomes possible.
[0024]
According to the configuration of claim 3, since the spot size conversion unit does not change the spot size abruptly, the refractive index and the cross-sectional area of the core do not change abruptly, and a very low loss connection is realized. Can do.
[0025]
According to the configuration of the fourth aspect, there is provided a small lens array spot size conversion type optical circuit in which an end face of an optical fiber is connected to an input / output end of an optical waveguide having multiple input / multiple output ports such as an AWG filter and a splitter. It becomes feasible.
[0026]
According to the configuration of the fifth aspect, since the connection surface between the optical waveguide and the optical fiber is processed obliquely and connected, the influence of the reflection of the signal light from each end surface can be removed. It is possible to suppress the influence of reflection on the end face of the optical circuit, and an optical circuit with low crosstalk and low reflection can be realized.
[0027]
According to the configuration of the above sixth aspect, the optical circuit can be further reduced in loss and processed at the final mounting or assembly stage. That is, the optical circuit can be processed while monitoring the optical characteristics, and an improvement in yield when manufacturing an ultrahigh Δ optical circuit can be expected.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0029]
1A is a front sectional view of a lens array spot size conversion type optical circuit showing an embodiment of the present invention, and FIG. 1B is a sectional view taken along line Ib-Ib in FIG. 1A. FIG. 1C is a diagram showing the refractive index distribution of the Ic-Ic line in FIG. In FIG. 1C, the vertical axis indicates the refractive index, and the horizontal axis indicates the position in the optical circuit.
[0030]
As shown in FIG. 1A, the lens array spot size conversion type optical circuit has a high relative refractive index difference Δ (Δh: within a range of 2% to 4%, spot size: within a range of about 4 μm to about 2 μm. ) An optical circuit body 5 made of a glass waveguide, and an optical fiber 6 optically connected to the optical circuit body 5 and having a low relative refractive index difference Δ (Δl: 0.3%, spot size: about 10 μm). Has been.
[0031]
The optical circuit body 5 has a lower cladding layer (for example, SiO ₂ glass layer) 2d having a low refractive index nu on a substrate (for example, anhydrous quartz glass substrate) 1, and a high refractive index nw on the lower cladding layer 2d. The pattern of the core layer 3 (for example, SiO ₂ —GeO ₂ —P ₂ O ₅ glass layer) 3 having a substantially rectangular cross section is formed, and the upper portion of the low refractive index nu is covered so as to cover the core layer 3 and the lower cladding layer 2d. The clad layer (for example, a glass film obtained by adding GeO ₂ and B ₂ O ₃ to SiO ₂ ) 2u is formed.
[0032]
The optical circuit body 5 has a core layer 3 shown in a straight line pattern for the sake of simplicity, but actually comprises an optical signal processing circuit including a curved pattern, such as a waveguide grating grating, a directional coupler. , Couplers, filters, ring resonators, Y branching devices, and the like.
[0033]
The core layer 3 has a refractive index nw of the core layer 3 such that the refractive index gradually decreases to a value substantially equal to the refractive index of the core 7 of the optical fiber 6 toward the connection end surface 11A with the optical fiber 6. Two substantially spherical lens media 5a and 5b having different refractive indexes and diameters are spaced apart from each other by a predetermined distance (if the number is at least one, the number is not limited to two, and it is located on the connection end surface 11A). A spot size conversion unit 4 is formed which is formed and gradually converts the spot size to an intermediate value Dgm (4 μm to 6 μm) gradually (see FIG. 1C).
[0034]
Specifically, as shown in FIG. 1B, a lens having a diameter Rgb and a refractive index ngb in the cladding layer 2u, which is fgb away from the end of the core layer 3, in the vicinity of the connection end surface 11A with the optical fiber 6. A medium 5b is formed, and another lens medium 5a having a diameter Rga and a refractive index nga is formed in the clad layer 2u that is fga + fgb away from the lens medium 5b and fga away from the connection end face 11A.
[0035]
The optical fiber 6 has a structure in which a cladding 8 having a refractive index ncl lower than that of the core 7 is formed on the outer periphery of the core 7 having a refractive index nc.
[0036]
In the core 7 of the optical fiber 6, in the vicinity of the connection end face 11 </ b> A of the optical circuit body 5, the refractive index gradually increases to a value almost equal to the refractive index of the core layer 3 of the optical circuit body 5. Two substantially spherical lens media 9a and 9b having a refractive index and a diameter higher than the refractive index nc of the core 7 and different in diameter are formed at a predetermined interval (the number is not limited to two as long as it is at least one). In addition, a spot size conversion unit 9 is formed which converts the spot size gradually to an intermediate value Dm (4 μm to 6 μm) (see FIG. 1C).
[0037]
Specifically, as shown in FIG. 1B, a lens medium 9b having a diameter Rb and a refractive index nb is formed in the core 7 which is fb away from the connection end surface in the vicinity of the connection end surface of the optical fiber 6. Further, another lens medium 9a having a diameter Ra and a refractive index na is formed in the core 7 which is away from the lens medium 9b by fa + fb.
[0038]
That is, the spot size conversion unit 100 includes a glass waveguide type spot size conversion unit 4 on the optical circuit body 5 side and an optical fiber spot size conversion unit 9 on the optical fiber 6 side.
[0039]
First, a specific design example by approximation calculation of the spot size conversion unit 9 on the optical fiber 6 side will be described.
[0040]
As the optical fiber 6, for example, a core 7 having a diameter of 10 μm and a refractive index n2 = 1.4619 and a clad 8 having a diameter of 125 μm and a refractive index n1 = 1.4575 are step-type refractive index distributions (Δl = 0.3%). The case where the one having the above is used will be described.
[0041]
With this structure, the condition that the spot size (about 10 μm) of the beam propagating in the core 7 can be converted into a small beam spot size Dm at the emission end (connection end face of the optical fiber) is expressed by the following equations 2 to 4. Calculate using an approximate expression.
[0042]
The calculation is performed assuming that the spot size in the core 7 at a position away from the lens medium 9a by fa is wi.
[0043]
[Expression 2]
Dm = fb · wi / fa
[Equation 3]
fa = na · Ra / [2 (na−n2)]
[Expression 4]
fb = nb · Rb / [2 (nb−n2)]
Here, if wi = 10 μm, na = 1.4722, Ra = 4 μm, nb = 1.4977, Rb = 2 μm, Dm can be narrowed down to 3.3 μm.
[0044]
As another example, if wi = 10 μm, na = 1.4722, Ra = 4 μm, nb = 1.4797, Rb = 1.25 μm, Dm can be narrowed down to 2.0 μm.
[0045]
However, the optical circuit main body of ultrahigh Δ with Δh of 4% only by the spot size conversion unit 9 on the optical fiber 6 side (refractive index of the core layer 3: 1.5182, thickness and width of the core layer 3: 1.5 μm) It is difficult to get close to a spot size of 5 (about 1.3 μm). Therefore, the spot size conversion unit 4 is also formed on the optical circuit body 5 side as in the present embodiment. A method for realizing the spot size conversion unit 4 will be described below.
[0046]
First, a part of the core layer 3 in the vicinity of the input end (connection end face 11A) on the optical circuit body 5 side is cut and removed, and the cut and removed part and the entire core layer 3 are embedded with the clad layer 2u, and the cut core The ultrashort pulse laser beam is focused and irradiated in the region of the cladding layer 2u on the extension line of the end of the layer 3, and the diameter Rgb and the refractive index are formed in the cladding layer 2u separated from the end of the core layer 3 by fgb. An ngb lens medium 5b is formed, and another lens medium 5a having a diameter Rga and a refractive index nga is formed in the clad layer 2u which is separated from the lens medium 5b by fga + fgb and fga from the end face 11A.
[0047]
The conditions under which the spot size wgi (about 1.3 μm) of the beam propagating in the core layer 3 of the optical circuit body 5 having such a structure can be converted into a large beam spot size Dgm at the emission end (connection end face 11A) are as follows. It calculates using the approximate expression of Formula 5 to Formula 7.
[0048]
[Equation 5]
Dgm = fga · wgi / fgb
[Formula 6]
fga = nga · Rga / [2 (nga-nu)]
[Expression 7]
fgb = ngb · Rgb / [2 (ngb−nu)]
Here, if wgi = 1.3 μm, nga = 1.4722, Rga = 4.4 μm, ngb = 1.4977, Rgb = 2 μm, Dgm can be increased to 3.3 μm, and the optical fiber 6 side Can be made equal to the beam spot size Dm of the spot size converter 9.
[0049]
That is, the optical fiber 6 and the optical circuit body 5 can be connected by mode field matching.
[0050]
This method realizes beam spot conversion for an ultra-high Δ optical circuit having Δ of up to 4%, which has never been realized until now.
[0051]
Next, the manufacturing method of the ultra-high Δ optical circuit of FIG. 1A will be described together with the operation with reference to FIGS. 2A to 2J.
[0052]
2A to 2E are front sectional views of an intermediate body for explaining a method of manufacturing a lens array spot size conversion type optical circuit, and FIGS. 2F to 2J are diagrams. It is a right view of 2 (a) to FIG.2 (e).
[0053]
When manufacturing an ultra-high Δ optical circuit, first, as shown in FIGS. 2A and 2F, by a plasma CVD method using an alkoxide-based source, at a low temperature (for example, 400 ° C.), For example, a lower cladding layer (SiO ₂ glass layer) 2d having a thickness of 20 μm, for example, is formed on an anhydrous quartz glass substrate 1 having a diameter of about 10.16 cm (4 inches), and a core layer (SiO ₂ —GeO) is formed on the lower cladding layer 2d. ₂₋ P ₂ O ₅ glass layer) 3a is formed to a thickness of 1.5 μm, for example, and an optical waveguide having a relative refractive index difference Δ of about 4% between the core layer 3a and the lower cladding layer 2d is produced.
[0054]
Next, although not shown, a WSi film having a thickness of about 0.5 μm is formed on the core layer 3a by a sputtering method, a photoresist is applied on the WSi film, and photolithography is performed using a photomask. A photoresist pattern is formed by the process, and then the WSi film is patterned by a dry etching process using the photoresist pattern as a mask.
[0055]
Thereafter, as shown in FIGS. 2B and 2G, the core layer 3 processed into a core pattern (optical signal processing circuit) having a substantially rectangular cross-sectional shape by using a WSi film pattern (not shown) as a mask. Form. Also, the vicinity of the end face of the lower cladding layer 2d is removed by etching to form the stepped portion 11.
[0056]
Then, as shown in FIGS. 2C and 2H, an upper clad layer 2u is formed on the lower clad layer 2d so as to cover the core layer 3. This is the upper cladding layer 2u a glass film added with the GeO ₂ and B ₂ O ₃ to SiO _2, GeO ₂ so that the refractive index becomes a value of about the same as the glass film of SiO ₂ and B ₂ O ₃ The amount of addition is controlled.
[0057]
Further, as shown in FIGS. 2D and 2I, an ultrashort pulse laser beam 14 having a wavelength of 800 nm (pulse width: 150 fs, pulse at a position fgb away from the position 12A at the end of the core layer 3. A lens having a refractive index of ngb and a lens diameter Rga at a position separated by a predetermined distance fgb from the position 12A at the end of the core layer 3 is condensed and irradiated by the lens 15 in the cladding layer 2u. 5b is formed, and then the light collecting and irradiating position is shifted from the position 12A of the end portion of the core layer 3 to the position 12B of the end face of the optical circuit body 5 by a predetermined distance fga + fgb as indicated by the arrow 13, and the refractive index nga, lens diameter An Rga lens medium 5a is formed.
[0058]
Then, as shown in FIGS. 2 (e) and 2 (j), an ultrashort pulse laser beam 14 (pulse width: 150 fs, pulse repetition) having a wavelength of 800 nm is now placed at a predetermined position in the core 7 of the optical fiber 6. A lens medium 9a having a refractive index na and a lens diameter Ra is formed by increasing the refractive index in the core 7 by condensing and irradiating a frequency of 200 kHz and an average output of 600 mW. Next, a predetermined distance fa + fb is shifted in the direction of the end face of the optical circuit body 5 as indicated by an arrow 16, and the lens medium 9 b having the refractive index nb and the lens diameter Rb is formed by similarly condensing and irradiating the core 7 to increase the refractive index. Thus, a lens array spot size conversion type optical circuit is manufactured.
[0059]
The refractive indexes and diameters of the lens media 9a and 9b are controlled by changing the power of the laser beam 14, the spot diameter, the irradiation time, and the like. Specifically, the diameters of the lens media 9a and 9b depend on the spot diameter of the laser beam 14, and can be adjusted by the spot diameter. Further, the refractive indexes of the lens media 9a and 9b depend on the irradiation energy (irradiation time, irradiation power, pulse width, pulse repetition frequency) of the laser beam 14, and the higher the energy, the larger the refractive index. When energy is increased, saturation tends to occur, and when the energy is further increased, voids are generated in the core 7. Therefore, the maximum refractive index that can be realized by irradiation with the laser beam 14 is about 1.485, and the refractive indexes used in the equations (3), (4), (6), and (7) can be sufficiently achieved.
[0060]
The ultrashort pulse laser beam 14 has a wavelength in the range of 400 nm to 980 nm, a pulse width in the range of 30 fs to 250 fs, a pulse repetition frequency in the range of 1 kHz to 250 kHz, and an average output in the range of 200 mW to 800 mW. preferable.
[0061]
By forming the spot size conversion part in this way, it becomes possible to process while monitoring the optical characteristics, it is possible to realize further reduction in loss of the optical circuit, and to process at the final mounting and assembly stage Will be able to. That is, an improvement in yield when manufacturing an ultrahigh Δ optical circuit can be expected.
[0062]
In the optical circuit of the present embodiment, the spot size of the signal light propagating in the optical fiber 6 is changed from a large spot size of about 10 μm, which is substantially equal to the core diameter, to a spot size having an intermediate value Dm toward the end face. The spot size of the core layer 3 in the optical circuit body 5 is also converted to an intermediate value Dgm toward the end face 11A, so that the optical circuit body 5 and the optical fiber 6 are low. It will be connected with loss.
[0063]
Furthermore, since two or more lens media 5a, 5b, 9a, 9b having different diameters are used as the spot size conversion units 4, 9, the length of the spot size conversion units 4, 9 in the optical axis direction is shortened. In addition, since the spot size conversion units 4 and 9 do not abruptly convert the spot size, the refractive index of these spot size conversion units 4 and 9 and the cross-sectional area of the core do not change abruptly. A very low loss connection can be realized.
[0064]
Further, an optical circuit body 5 having an ultrahigh Δ having Δh of 2% or more and 4% or less and an optical fiber 6 having Δl in the range of 0.3% to 1.5% are connected by mode field matching. Therefore, it becomes possible to realize an ultrahigh Δ optical circuit that is reduced in size from 1/20 to 1/40 compared to a conventional low Δ (Δ: about 0.75%) optical circuit. . As a result, the production amount of the optical circuit is increased by 20 times or more, the power cost required for the optical circuit production is reduced to 1/20 or less, and the cost of the optical circuit can be reduced to 1/15 or less. .
[0065]
Next, another embodiment of the present invention will be described in detail.
[0066]
FIG. 3 is a front cross-sectional view of a lens array spot size conversion type optical circuit showing another embodiment of the present invention.
[0067]
As shown in FIG. 3, in this lens array spot size conversion type optical circuit, both end portions 23a and 23b of the core layer 23 of the optical circuit body 25 are formed in the vicinity of different end faces 21A and 21B. Portions 24a and 24b are formed. Further, optical fibers 26 and 26 having spot size conversion portions 29 and 29 are connected to both end faces 21A and 21B of the spot size conversion portions 24a and 24b, respectively.
[0068]
Similar to the optical circuit body shown in FIG. 1A, the optical circuit body 25 has a lower clad layer 22d with a low refractive index nu on the substrate 21, and a high refractive index on the lower clad layer 22d. A pattern of the core layer 23 having a substantially rectangular cross section of nw is formed, and an upper cladding layer 22u having a low refractive index nu is formed so as to cover the core layer 23 and the lower cladding layer 22d. Similarly to the optical fiber shown in FIG. 1A, the optical fiber 26 has a structure in which a cladding 28 having a refractive index ncl lower than that of the core 27 is formed on the outer periphery of the core 27 having a refractive index nc. .
[0069]
Similarly, the lens media 25a and 25b of the spot size conversion units 24a and 24b of the optical circuit body 25 are configured so that the refractive index of the core layer 23 changes toward the connection end faces 21A and 21B with the optical fibers 26 and 26, respectively. Is arranged.
[0070]
With this configuration, it can be applied to, for example, an optical circuit having a multi-port input / output such as an AWG filter, a splitter, and an optical switch.
[0071]
In this case, N and M spot size conversion units (N, M: ≧ 1) may be provided on the both end surfaces 21A and 21B side of the optical circuit body 25 in accordance with the number of input and output of the optical circuit to be applied. .
[0072]
FIG. 4 is a front cross-sectional view of a lens array spot size conversion type optical circuit showing another embodiment of the present invention.
[0073]
As shown in FIG. 4, this lens array spot size conversion type optical circuit has the same basic configuration as the optical circuit shown in FIG. 1A, but the connection between the optical circuit body 35 and the optical fiber 36. The difference is that the end faces 35A and 36A are each processed obliquely with respect to the perpendicular to the optical axis.
[0074]
Specifically, θ is preferably in the range of 2 ° to 8 °, where θ is the inclination angle of the optical axis of the signal light propagating over the optical circuit body 35 and the optical fiber 36 with respect to the perpendicular.
[0075]
Then, by connecting the optical circuit body 35 and the optical fiber 36, the influence of unnecessary reflection of the signal light from the respective connection end faces 35A, 36A can be removed, and the influence of reflection on the other end faces is suppressed. Thus, an optical circuit with low crosstalk and low reflection can be obtained.
[0076]
Further, the interval between the connecting portions is preferably 10 μm or less in order to reduce transmission loss.
[0077]
The present invention is not limited to the above-described embodiment.
[0078]
First, Δl of the optical fibers 6, 26, and 36 having a low relative refractive index difference Δ (Δl) can be selected from a range of 0.3% to 1.5%. A high Δ optical circuit can be realized. As this Δl is larger, the refractive index of the lens medium 9a, 9b, 25a, 25b formed in the core 7, 27, 37 can be increased. As can be seen from the equations (3) and (4), The diameters Ra and Rb can be reduced to reduce the beam spot size Dm. Further, since the Dgm of the spot size conversion units 4, 24a, 24b, 34 on the optical circuit main bodies 5, 25, 35 side may be small, the very low loss spot size conversion units 4, 24a, 24b, 34 are provided. Can be configured.
[0079]
Moreover, as optical fiber 6,26,36 used for this invention, the coating | coated material may be formed in the outer peripheral part of optical fiber 6,26,36. For example, a polymer material such as a pre-coating material or a secondary coating material may be coated. Also, the core diameters of the optical fibers 6, 26, and 36 can be in the range of several μm to 10 μm other than 10 μm. In the equations (2) to (7), the values of fa, fb, na, nb, Ra, Rb, fga, fgb, nga, ngb, Rga, Rgb, etc. can be selected from a wide range. For example, Ra and Rb can be selected from the range of 1 μm to 10 μm, and na and nb can be selected from the range of 1.458 to 1.490.
[0080]
Furthermore, in the present embodiment, the spot size conversion units 4, 9, 24a, 24b, 29, 34, 39 are constituted by two or three lens media. good. Further, the optical fibers 6, 26, and 36 may be processed into a tapered structure so as to taper toward the tip portion. Further, the optical fibers 6 and 26 may have a tip processed into a spherical shape.
[0081]
Further, as the substrates 1 and 21 of the optical circuit bodies 5, 25 and 35, in addition to the glass substrate, a semiconductor substrate such as a Si substrate or a GaAs substrate, a ferroelectric substrate such as LiNbO ₃ or LiTaO ₅ , a ceramic substrate, or a plastic substrate A substrate or the like may be used.
[0082]
Furthermore, Δh of the optical circuit bodies 5, 25, and 35 can be 1.5% to 4.0%, but if Δl of the optical fibers 6, 26, and 36 is high, It can also be applied to those having a higher Δh.
[0083]
【The invention's effect】
In short, according to the present invention, it is possible to provide a lens array spot size conversion type optical circuit in which an optical fiber and an optical waveguide are connected with low loss and can be reduced in size and cost.
[Brief description of the drawings]
1A is a front cross-sectional view of a lens array spot size conversion type optical circuit showing an embodiment of the present invention, and FIG. 1B is a cross-sectional view taken along line Ib-Ib in FIG. (c) is a figure which shows the refractive index distribution of the Ic-Ic line | wire of (b).
FIGS. 2A to 2E are front sectional views of an intermediate body of a lens array spot size conversion type optical circuit, and FIGS. 2F to 2J are right side views of FIGS. is there.
FIG. 3 is a front cross-sectional view of a lens array spot size conversion type optical circuit showing another embodiment of the present invention.
FIG. 4 is a front cross-sectional view of a lens array spot size conversion type optical circuit showing another embodiment of the present invention.
FIG. 5 is an explanatory diagram for explaining a conventional mode conversion method;
FIG. 6 is an explanatory diagram for explaining a conventional mode conversion method;
[Explanation of symbols]
2u, 2d Clad layer 3 Core layer 4 Spot size converter 5 Optical circuit body 5a, 5b Lens medium 6 Optical fiber 7 Core 9 Spot size converter 9a, 9b Lens medium

Claims (6)

  In the optical circuit in which the optical waveguide and the optical fiber are connected such that the optical axis of the core layer of the optical waveguide coincides with the optical axis of the core of the optical fiber, the optical waveguide is connected to the optical fiber. The end surface of the core layer is covered with a cladding layer, and the refractive index is gradually increased from the optical waveguide toward the optical fiber on the optical axis of the core layer in the cladding layer covering the end surface of the core layer. A waveguide-side spot size conversion unit having a plurality of changed substantially spherical lens media and gradually converting a spot size is formed, and the optical fiber is connected to the core near the connection part of the optical fiber. An optical fiber side spot size conversion unit that has a plurality of substantially spherical lens media whose refractive index is gradually changed toward the optical waveguide and converts the spot size gradually to a smaller size is formed. The spot size at the connection end of the optical fiber side spot size conversion unit with the optical fiber side spot size conversion unit is equal to the spot size at the connection end of the optical fiber side spot size conversion unit with the waveguide side spot size conversion unit. A lens array spot size conversion type optical circuit. The relative refractive index difference between the core layer and the cladding layer of the optical waveguide is in the range of 2.0% to 4.0%, and the relative refractive index difference between the core and the cladding of the optical fiber is 0.3%. The refractive index of the substantially spherical lens medium gradually decreases toward the end face connected to the optical fiber, and the waveguide-side spot size conversion unit 2. The lens array spot size conversion type optical circuit according to claim 1, wherein the fiber side spot size conversion unit gradually increases the refractive index of a substantially spherical lens medium toward an end surface connected to the optical waveguide.   The waveguide-side spot size conversion section is formed by forming a plurality of substantially spherical lens media having a desired interval, a desired diameter, and a desired refractive index toward an end face connected to the optical fiber. 3. A lens array spot size conversion type optical circuit according to 1 or 2.   The waveguide-side spot size conversion section and the optical fiber-side spot size conversion section are formed in the vicinity of each connection section, respectively, with at least one connection section between the optical waveguide and the optical fiber. The lens array spot size conversion type optical circuit according to any one of 1 to 3.   The lens array spot size conversion type optical circuit according to any one of claims 1 to 4, wherein a connection surface between the core layer of the optical waveguide and the core of the optical fiber is processed obliquely with respect to a normal to the optical axis. .   The lens medium is condensed and irradiated by changing the beam spot size and irradiation energy of an ultrashort pulse laser beam having a pulse width in the range of 30 fs to 200 fs and a pulse repetition frequency in the range of 1 kHz to 250 kHz. 6. The lens array spot size conversion type optical circuit according to claim 1, wherein the lens array spot size conversion type optical circuit is formed.

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