Optical module

Abstract

The present disclosure provides a structure for integrating a plurality of optical waveguide chips into one optical module at high density. Specifically, provided is an optical module comprising: N optical waveguide chips that each include an optical waveguide having a core for propagating an optical signal and a connection auxiliary component and are stacked, N being an integer of 2 or more; N optical fiber blocks that each include grooved glass and lid glass and are connected to the N optical waveguide chips, an optical fiber being disposed between the grooved glass and the lid glass; and a housing in which the N optical waveguide chips and the N optical fiber blocks are housed and are fixed. For an integer i from 2 to (N-1), a first main surface of an i-th connection auxiliary component corresponding to an i-th optical waveguide chip is connected to a second main surface of an (i-1)-th optical waveguide chip, and a second main surface of the i-th connection auxiliary component is connected to a first main surface of the i-th optical waveguide chip.

Description

Optical Module

[0001] The present disclosure relates to an implementation form of an optical module, and more particularly to a structure in which multiple optical waveguide chips are integrated into one module.

[0002] With the expansion of data communication networks such as the Internet, optical communication networks are expected to have ever higher capacity. To meet this expanding network demand, wavelength division multiplexing (WDM) communication has been put into practical use. The key to the practical application of WDM communication in the mid-1990s was the erbium-doped optical fiber amplifier (EDFA) and the arrayed-waveguide grating (AWG), a wavelength multiplexer / demultiplexer. Previously, in order to compensate for optical attenuation in long-distance transmission, an OEO (Optical-Electrical-Optical) repeater was required, which received the optical signal, converted it into an electrical signal, and then converted it back into an optical signal before transmitting it. In WDM systems, however, OEO repeaters were required for the number of wavelengths, but the advent of EDFAs made it possible to transmit long distances economically without OEO repeaters. In addition, AWGs, which multiplex and demultiplex wavelengths at the transmitting and receiving ends, contributed to expanding the number of wavelengths multiplexed, which had previously been limited to about 4 channels, to about 100 channels, and became the basis for large-capacity communications.

[0003] AWGs manufactured using silica-based optical waveguides are generally in practical use. This is because silica-based optical waveguides, which are made from the same silica-based glass as optical fibers, are well matched to optical fibers and can multiplex and demultiplex signals of different wavelengths with low excess loss. However, silica-based optical waveguides have the disadvantage that their relative refractive index difference is low, at around 1 to 2%, and the bending radius of the optical waveguide cannot be made small, limiting their miniaturization. This disadvantage is an issue not only for AWGs but also for general optical devices using silica-based optical waveguides.

[0004] Fig. 1 shows a portion of the structure (subassembly 100) of a conventional optical device module using a silica-based optical waveguide disclosed in Non-Patent Document 1. In Fig. 1, optical fibers 103a and 103b are connected to both ends of a silica-based optical waveguide 101 via optical fiber blocks 102a and 102b. The connection is generally made using an optical adhesive such as an epoxy adhesive. The bonding between the silica-based optical waveguide 101 and the optical fiber blocks 102a and 102b is reinforced by auxiliary members 104a and 104b placed near the connection end faces on the silica-based optical waveguide 101.

[0005] As shown in Figure 2, an optical module is actually provided with the subassembly 100 of Figure 1 housed in a housing 201. Unlike the schematic diagram of Figure 1, Figure 2 shows optical fiber blocks 102a and 102b connected to one end of a silica-based optical waveguide 101, but the essence remains the same. When the subassembly 100 is assembled into the optical module housing 201, protective members (hereinafter referred to as boots) 202a and 202b are installed in the housing 201 to protect the optical fibers, in order to prevent external force from being applied to the adhesive portions between the silica-based optical waveguide 101 and the optical fiber blocks 102a and 102b. Note that Figure 2 shows the configuration of a conventional optical module to aid in understanding the present disclosure, and although a control electrical board and the like are shown, they are not directly related to the invention of the present disclosure.

[0006] Patent No. 6175106 Patent No. 6467339

[0007] Akira Himeno, Kuniharu Kato, and Tetsuo Miya, “Silica-Based Planar Lightwave Circuits,” IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 4, NO. 6, pp.913-924, NOVEMBER / DECEMBER 1998

[0008] As described above, in an optical module, it is the silica-based optical waveguide 101 that exhibits its functions, but peripheral components such as optical fiber blocks 102a, 102b and boots 202a, 202b that are necessary to connect the silica-based optical waveguide 101 and the optical fibers 103a, 103b are required, and the peripheral components limit the packaging density of the optical module.

[0009] 2 in a narrow optical transmission device, multiple subassemblies 100 must be arranged in the same space, which poses a problem that the footprint (area) of the optical module reduces space utilization efficiency. In other words, to improve space utilization efficiency, it is necessary to reduce the area occupied by the optical module and increase integration.

[0010] One method for improving the efficiency of space utilization within an optical module is to stack optical waveguide chips. Examples of stacking optical waveguide chips are disclosed in Patent Documents 1 and 2. Although these examples are not intended to increase integration density, they are also effective for increasing the integration of optical modules.

[0011] FIG. 3(a) shows the stacked arrangement of optical waveguide chips disclosed in Patent Document 1, and FIG. 3(b) shows the stacked arrangement of optical waveguide chips disclosed in Patent Document 2. Patent Document 1 discloses a method of stacking two optical waveguide chips 1a and 1b with their surfaces on which optical circuits are present facing each other, and then aligning the optical circuits on the two optical waveguide chips 1a and 1b by placing a positioning joint member between the two. Furthermore, Patent Document 2 discloses a method of integrating multiple optical circuit chips by inserting them into grooves formed in frames 10 and 20. However, the methods disclosed in these patent documents are insufficient or have limitations in integration capability in the following respects. With the method disclosed in Patent Document 2, the gap between the optical waveguides can be made very narrow, allowing the thickness of the optical module to be reduced, but it is difficult to stack three or more chips because the surfaces on which the optical circuits are present must face each other.

[0012] The present disclosure has been made in view of the above points, and provides a structure for integrating a plurality of optical waveguide chips into one module at high density.

[0013] The present invention provides an optical module comprising: N stacked optical waveguide chips, each including an optical waveguide having a core for propagating an optical signal and a connection auxiliary component, where N is an integer of 2 or greater; N optical fiber blocks connected to the N optical waveguide chips, each including a groove glass and a lid glass, with an optical fiber arranged between the groove glass and the lid glass; and a housing that houses and fixes the N optical waveguide chips and the N optical fiber blocks, wherein for an integer i between 2 and (N-1) inclusive, the first main surface of the i-th connection auxiliary component corresponding to the i-th optical waveguide chip is connected to the second main surface of the i-1-th optical waveguide chip, and the second main surface of the i-th connection auxiliary component is connected to the first main surface of the i-th optical waveguide chip.

[0014] An optical module is provided in which the sum of the distance from the core of the optical waveguide of the i-th optical waveguide chip to the first main surface of the i-th optical waveguide chip and the distance from the core of the optical waveguide of the i-th optical waveguide chip to the second main surface of the i-th connection auxiliary component is the same as or greater than the sum of the distance from the core of the optical fiber to the second main surface of the groove glass and the distance from the core of the optical fiber to the first main surface of the lid glass.

[0015] The optical module further includes at least one elastic auxiliary component disposed between two adjacent optical waveguide chips among the N optical waveguide chips.

[0016] A plurality of optical waveguide chips can be integrated into one module at high density, allowing the device to be miniaturized.

[0017] FIG. 7( a ) is a diagram showing an optical device using a conventional optical waveguide; FIG. 7( b ) is a diagram showing an optical module in which an optical device using a conventional optical waveguide is mounted; FIG. 8( a ) shows the internal configuration of a conventional optical module, with FIG. 3( a ) being a cross-sectional view of the optical module shown in Patent Document 1, and FIG. 3( b ) being a cross-sectional view of the optical module shown in Patent Document 2; FIG. 8( b ) is a perspective view showing an optical module according to this embodiment; FIG. 8( b ) is a cross-sectional view of the optical module according to another embodiment; FIG. 9( a ) is a cross-sectional view of the optical module according to this embodiment; FIG. 9( b ) is a cross-sectional view of the optical module according to another embodiment; FIG. 9( c ) is a composite cross-sectional view when the optical waveguide chip and the optical fiber block are connected; FIG. 9( a ) is a cross-sectional view of the optical module according to this embodiment when a plurality of optical waveguides are stacked; and FIG. 9( c ) is a cross-sectional view of the optical module according to another embodiment when a plurality of optical waveguides are stacked.

[0018] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the drawings are schematic and are intended to conceptually explain functions or structures. Furthermore, the present invention is not limited to the embodiments shown below. In the drawings, the same reference numerals are used to refer to the same or similar components whenever possible.

[0019] 4 is a perspective view of the inside of an optical module 400 having a configuration in which a plurality of optical waveguide chips 101a, 101b, and 101c are stacked in multiple stages according to an embodiment of the present disclosure. While Fig. 4 shows a configuration in which three optical waveguide chips are stacked as an example of an embodiment, the number of optical waveguide chips may be greater.

[0020] As shown in FIG. 4, the optical module 400 includes a plurality of optical waveguide chips 101a, 101b, and 101c, a plurality of optical fiber blocks 102a, 102b, and 102c, a plurality of optical fiber bundles 103a, 103b, and 103c, at least one boot 202 through which the plurality of optical fiber bundles 103a, 103b, and 103c pass, and a housing 201.

[0021] (Optical Waveguide Chip) The optical waveguide chip will be described with reference to Figures 4 and 5. Figure 5 is a cross-sectional view of the optical module 400 shown in Figure 4 when viewed from the Y direction. Each of the optical waveguide chips 101a, 101b, and 101c includes an optical waveguide 501a, 501b, or 501c and a connection auxiliary component 502a, 502b, or 502c, respectively. Figure 4 shows the optical waveguide chips 101a, 101b, and 101c as being the same size and having optical fiber blocks 102a, 102b, and 102c, i.e., optical fiber connection positions, at the same positions on the chip. However, this is just an example, and the size of each of the optical waveguide chips 101a, 101b, and 101c and the connection positions of the optical fiber blocks 102a, 102b, and 102c may vary depending on the actual implementation environment and conditions.

[0022] The optical waveguide chips 101a, 101b, and 101c are stacked (layered) in the thickness direction (e.g., the Z direction in FIGS. 4 and 5 ) and fixed to the housing 201. Fixing can be performed using, for example, adhesive, double-sided tape, pressure welding, anodic bonding, or other methods. Furthermore, the optical waveguide chips 101a, 101b, and 101c are connected to optical fiber blocks 102a, 102b, and 102c, respectively, and are taken out of the optical module 400 via the boot 202.

[0023] As described above, the optical module 400 has multiple optical waveguide chips 101a, 101b, and 101c. In the following description, the optical waveguide chips are sequentially referred to as the (i-1)th (e.g., 101a), the i-th (e.g., 101b), and the (i+1)th (e.g., 101c) optical waveguide chips, starting from the bottom one in the stacked structure. For ease of explanation, only one optical waveguide chip 101b of the multiple optical waveguide chips 101a, 101b, and 101c will be described, but the other optical waveguide chips 101a and 101c have the same structure.

[0024] The i-th optical waveguide chip 101b includes an optical waveguide 501b and a connection auxiliary component 502b, and one side of the optical waveguide chip 101b is adhesively fixed to one side of the optical fiber block 102b in surface contact. The adhesive fixation can generally be performed using an optical adhesive such as an epoxy adhesive. At this time, the core formed in the optical waveguide 501b and the core of the optical fiber or optical fiber bundle 103b disposed via the optical fiber block 102b are connected so as to be able to propagate an optical signal.

[0025] The auxiliary connection part 502b is connected to one main surface of the optical waveguide 501b (for example, the lower surface of the optical waveguide 501b) and extends in the Y direction. The width (X direction) and length (Y direction) of the auxiliary connection part 502b can be designed as desired to match the size of the optical waveguide 501b. Furthermore, it is preferable that the thickness (Z direction) of the auxiliary connection part 502b be small in order to miniaturize the optical module 400.

[0026] Furthermore, it is preferable to provide the auxiliary connection part 502b at one location on one main surface of the optical waveguide 501b, because the linear expansion coefficient of the housing 201 and the linear expansion coefficient of the optical waveguides 501a, 501b, and 501c generally differ. As shown in Figure 5, one main surface of the connection auxiliary component 502a in the (i-1)th optical waveguide chip 101a is fixed to one surface inside the housing 201 with adhesive or double-sided tape, and the other main surface is fixed to the optical waveguide 501a of the (i-1)th optical waveguide chip 101a. However, for example, as shown in Figure 6, if there are two or more connection auxiliary components for one optical waveguide 501a, for example, the connection auxiliary component 502a and an additional connection auxiliary component (hereinafter referred to as an elastic auxiliary component) 602a, the difference in expansion between the housing 201 and the optical waveguide 501a that occurs due to temperature changes from the time of mounting will induce internal stress in the optical waveguide 501a, affecting the optical circuit characteristics.

[0027] However, providing two or more auxiliary connection components 502a and elastic auxiliary components 602a for one optical waveguide 501a may be advantageous in improving the mechanical and / or structural stability of the optical module 400. Therefore, when the design of the optical module 400 requires two or more auxiliary connection components, one of the elastic auxiliary components, for example, 602a, can be made of an elastic material to absorb or release the internal stress that occurs.

[0028] (Optical fiber block) The optical fiber blocks 102a, 102b, and 102c will be described with reference to Fig. 5. As with the optical waveguide chip described above, for convenience of explanation, only one optical fiber block 102b among the multiple optical fiber blocks 102a, 102b, and 102c will be described, but the other optical waveguide chips have the same structure.

[0029] The optical fiber block 102b includes a groove glass 503b having a V-groove formed therein in which the optical fiber 103b is to be placed, and a lid glass 504b for fixing the optical fiber 103b. The connection end of the i-th optical waveguide chip 101b and the optical fiber block 102b is polished at an angle as shown in Fig. 5. This is the same as in the prior art shown in Fig. 1, and is done to prevent reflection from the end face.

[0030] (Housing) The housing 201 houses and modularizes the optical waveguide chips 101a, 101b, and 101c and the optical fiber blocks 102a, 102b, and 102c, and also protects the optical waveguide chips 101a, 101b, and 101c. In order to eliminate or reduce the internal stress that occurs as described above, it is preferable that the linear expansion coefficient of the housing 201 is equal to or the difference between the linear expansion coefficients of the optical waveguide chips 101a, 101b, and 101c is negligibly small. For example, when optical waveguide chips 101a, 101b, and 101c using a quartz-based planar lightwave circuit or silicon photonics with a silicon substrate are optically modularized, the linear expansion coefficient of the silicon substrate is 3.9×10 －６ Kovar (linear expansion coefficient 4.5 × 10 －６) is preferably selected as the material for the housing 201. By doing so, it is possible to avoid internal stress caused by the linear expansion coefficient and to manufacture an optical module 400 with high fixing strength.

[0031] (Stacked Structure) To increase the capacity of optical communication networks, multiple optical waveguide chips 101a, 101b, and 101c can be stacked (arranged). For example, as shown in the cross-sectional view of optical module 400 in FIG. 5, the (i-1)th optical waveguide chip 101a is arranged in the bottom layer of the stacked structure, and the bottom surface of the (i-1)th optical waveguide chip 101a is connected to and fixed to the housing 201. Furthermore, the top surface of the (i-1)th optical waveguide chip 101a is connected to and fixed to the bottom surface of the (i-1)th optical waveguide chip 101b. In the same manner, the bottom surface of the (i-1)th optical waveguide chip 101b is connected to and fixed to the top surface of the (i-1)th optical waveguide chip 101a, and the top surface of the (i+1)th optical waveguide chip 101a is connected to and fixed to the bottom surface of the (i+1)th optical waveguide chip 101c.

[0032] Fig. 7(a) is a cross-sectional view of the connection surface of the i-th optical waveguide chip 101b when the optical module 400 shown in Fig. 4 is viewed from the X direction, Fig. 7(b) is a cross-sectional view of the connection surface of the optical fiber block 102b, and Fig. 7(c) is a composite cross-sectional view when the optical waveguide chip 101b and the optical fiber block 102b are connected.

[0033] The optical waveguide 501b constituting the optical waveguide chip 101b has a core 701b through which an optical signal propagates, and the core 701b can be coupled to coincide with the core of the optical fiber 103b installed in the optical fiber block 102b. As a result, an optical signal input from the outside via the optical fiber 103b propagates through the optical waveguide chip 101b.

[0034] When the distance from the center of the core 701b of the optical waveguide 501b to the back surface of the optical waveguide 501b is t1, the distance from the core 701b to one main surface of the connection auxiliary component 502b is t2, the distance from the center of the core of the optical fiber 103b installed in the optical fiber block 102b to the back surface of the groove glass 503b is t3, and the distance from the center of the core of the optical fiber 103b to the top surface of the lid glass 504b is t4, the distances t1, t2, t3, and t4 are determined so that the following equation 1 holds.

[0035]

[0036] The above formula 1 indicates that the optical waveguide chip 101b has a thickness equal to or greater than that of the optical fiber block 102b. If formula 1 is not satisfied, it indicates that in a configuration in which multiple optical waveguide chips 101a, 101b, and 101c are stacked, the optical waveguide chips are not in close contact with each other, and each layer is fixed between the multiple optical fiber blocks 102a, 102b, and 102c.

[0037] Generally, the optical fiber blocks 102a, 102b, and 102c are components made of glass material and are generally more fragile than the optical waveguide chips 101a, 101b, and 101c. If the optical module 400 is constructed by bonding the optical fiber blocks 102a, 102b, and 102c together, the optical waveguide chips 101a, 101b, and 101c, which have large mass, will be held by the fragile optical fiber blocks, and mechanical strength will not be maintained. Therefore, it is preferable to fix the optical waveguide chips 101a, 101b, and 101c together while maintaining Equation 1.

[0038] Furthermore, with reference to FIG. 8, Equation 1 must satisfy the relationship of the following Equation 2.

[0039]

[0040] The condition of the above formula 2 is that one main surface of the lid glass 504b is not positioned below one main surface of the connection auxiliary component 502b. If formula 2 is not satisfied, the optical waveguide chips 101a, 101b, and 101c will be fixed to the housing 201 via the optical fiber blocks 102a, 102b, and 102c, and for the same reason as above, the mechanical strength will not be maintained.

[0041] (Embodiment 2) Another embodiment in which the optical module 400 described in the above embodiment 1 is modified will be described with reference to Fig. 9. Fig. 9 shows the optical module 400 in which the positions of the optical waveguides 501a, 501b, and 501c and the connection auxiliary components 502a, 502b, and 502c in the respective optical waveguide chips 101a, 101b, and 101c are reversed.

[0042] In the case of another embodiment, the condition of the following formula 3 must be satisfied in order to fix the optical waveguide chips 101a, 101b, and 101c to each other.

[0043]

[0044] In another embodiment, the rear surface of the optical waveguide 501a of the lowest optical waveguide chip is fixed to the entire inner surface of the housing 201, thereby ensuring mechanical and / or structural stability.

[0045] Additional Considerations The foregoing description of embodiments of the present invention has been presented for purposes of illustration and is not intended to be exhaustive or to be limited to the precise form disclosed. Those skilled in the art will recognize that many modifications and variations are possible in light of the above disclosure.

[0046] Finally, the language used herein has been selected primarily for readability and instructional purposes, and may not have been selected to delineate or limit the subject matter of the invention. Accordingly, it is intended that the scope of the invention be limited not by this detailed description, but rather by the appended claims. Accordingly, the disclosure of embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the claims.

[0047] 100 Subassembly 101, 101a, 101b, 101c Optical waveguide chip 102a, 102b, 102c Optical fiber block 103a, 103b, 103c Optical fiber 104a, 104b Auxiliary member 201 Housing 202, 202a, 202b Boots 400 Optical module 501a, 501b, 501c Optical waveguide 502a, 502b, 502c Connection auxiliary part 503a, 503b, 503c Groove glass 504a, 504b, 504c Lid glass 602a, 602b, 602c Elastic auxiliary part 701a, 701b, 701c Optical waveguide core

Claims

1. An optical module comprising: N stacked optical waveguide chips, each including an optical waveguide having a core for propagating an optical signal and a connection auxiliary component, where N is an integer of 2 or greater; N optical fiber blocks, each including a groove glass and a lid glass, connected to the N optical waveguide chips, with an optical fiber disposed between the groove glass and the lid glass; and a housing that houses and fixes the N optical waveguide chips and the N optical fiber blocks, wherein, for an integer i between 2 and (N-1), inclusive, the first main surface of the i-th connection auxiliary component corresponding to the i-th optical waveguide chip is connected to the second main surface of the i-1-th optical waveguide chip, and the second main surface of the i-th connection auxiliary component is connected to the first main surface of the i-th optical waveguide chip.

2. The optical module described in claim 1, wherein the sum of the distance from the core of the optical waveguide of the i-th optical waveguide chip to the first main surface of the i-th optical waveguide chip and the distance from the core of the optical waveguide of the i-th optical waveguide chip to the second main surface of the i-th connection auxiliary component is the same as or greater than the sum of the distance from the core of the optical fiber to the second main surface of the groove glass and the distance from the core of the optical fiber to the first main surface of the lid glass.

3. An optical module as described in claim 1 or 2, wherein the first main surface of the first connection auxiliary component corresponding to the first optical waveguide chip or the second main surface of the Nth connection auxiliary component corresponding to the Nth optical waveguide chip is fixed to the entire interior surface of the housing.

4. An optical module as described in claim 3, wherein the distance from the core of the optical waveguide of the i-th optical waveguide chip to the second main surface of the i-th connection auxiliary component is greater than the distance from the core of the optical fiber to the first main surface of the lid glass.

5. An optical module as described in claim 3, wherein the distance from the core of the optical waveguide of the i-th optical waveguide chip to the first main surface of the i-th optical waveguide chip is smaller than the distance from the core of the optical fiber to the second main surface of the groove glass.

6. The optical module according to claim 1, further comprising at least one elastic auxiliary component disposed between two adjacent optical waveguide chips among said N optical waveguide chips.

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