JP2024074480A - Method for manufacturing self-written optical waveguide - Google Patents

Abstract

The present invention provides a method for manufacturing a self-written optical waveguide capable of preventing coupling failure.
[Solution] A photocurable resin and two multicore fibers each having n cores (n: a natural number of 2 or more) are prepared. The photocurable resin includes a core portion-forming resin that is polymerized and hardened when light of a predetermined wavelength band is incident thereon and has a refractive index na, and a cladding portion-forming resin that is polymerized and hardened when light with an intensity equal to or greater than that of the light incident on the core portion-forming resin is incident thereon and has a refractive index nb after hardening of nb<na. The two multicore fibers are arranged opposite each other, and the photocurable resin is arranged between the multicore fibers. Light is incident from the cores of the two multicore fibers into the photocurable resin in order from the core of the multicore fiber to form the core portions. Next, the cladding portion is formed.
[Selected figure] Figure 3

Description

The present invention relates to a method for manufacturing a self-written optical waveguide.

With the advancement of optical technology in the fields of optical communications, optical information processing, electronic devices, and optical devices, the development of optical waveguides between various optical devices has become an issue. Various optical devices are optically connected by optical waveguides such as optical fibers, but these connections require extremely high positional accuracy. Conventionally, such connection work has been performed manually or using high-precision alignment equipment, which has led to the problem of increased connection costs.

To solve these problems, self-forming optical waveguides have been developed. These optical waveguides have a core that is self-formed from photocurable resin. The end of an optical fiber or the like is immersed in the photocurable resin, and light is irradiated from the optical fiber or the like into the photocurable resin, gradually hardening the resin, forming a self-forming optical waveguide at the end of the optical fiber or the like.

For example, Patent Document 1 is an example of such a self-forming optical waveguide. According to Patent Document 1, an optical connector includes at least a ferrule and n self-forming optical waveguides (n is a natural number not including 0). The ferrule includes n optical fiber insertion holes, and an optical fiber is inserted into each optical fiber insertion hole.

After the optical waveguide is formed, it is left for two minutes to promote mutual diffusion of the monomers at the boundary between the core and the cladding, and then the cladding is formed by UV irradiation. In the core region, only one of the monomers in the photocurable resin is consumed and polymerized, so a concentration gradient of the monomers occurs at the boundary between the core and the cladding, promoting mutual diffusion and fulfilling the function of the cladding. In addition, by irradiating the entire photocurable resin with UV, the entire core and cladding are cured and formed, resulting in the optical waveguide.

International Publication No. 2020/209364

However, when attempting to form multiple self-forming optical waveguides as in Patent Document 1, if light is irradiated simultaneously from the cores of each optical fiber into the photocurable resin, the self-forming optical waveguides formed by irradiating adjacent cores with light may bond together, resulting in poor coupling.

The present invention was made in consideration of the above problems, and aims to realize a method for manufacturing a self-written optical waveguide that can prevent poor coupling.

The above problem is solved by the present invention as described below. That is, in the manufacturing method of the self-forming optical waveguide of the present invention, a photocurable resin and two multicore fibers having n cores (n: a natural number of 2 or more) are prepared, the photocurable resin includes a core-forming resin having a refractive index na that is polymerized and hardened by light of a predetermined wavelength band being incident thereon, and a cladding-forming resin that is polymerized and hardened by light of an intensity equal to or greater than the intensity of the light incident on the core-forming resin, and has a refractive index nb after hardening of nb < na. The two multicore fibers are arranged opposite each other, and the photocurable resin is arranged between the multicore fibers. Light of an intensity capable of polymerizing only the core-forming resin is incident on the photocurable resin from the cores of the two multicore fibers in order, and polymerization and hardening of the core-forming resin are caused to occur to form the core of the optical waveguide in the photocurable resin, and then the cladding is formed, and n optical waveguides are self-formed in the photocurable resin.

The method for manufacturing a self-forming optical waveguide according to the present invention can prevent the cores formed by irradiating adjacent cores with light from bonding together in each multicore fiber, thereby preventing poor bonding between the cores.

1 is a front view showing a configuration of a multi-core fiber used in a method for manufacturing a self-written optical waveguide according to an embodiment of the present invention. 1 is an explanatory diagram showing a part of a state in which a photocurable resin is disposed between two multi-core fibers in a manufacturing method of a self-written optical waveguide according to an embodiment of the present invention; FIG. FIG. 3 is an explanatory diagram showing a state in which light is incident from each core of two multi-core fibers into a photocurable resin to form a core portion of a self-written optical waveguide, starting from the state shown in FIG. 2 . FIG. 4 is a perspective view showing the state of FIG. 3 excluding the photocurable resin and the transparent container. 4 is an explanatory diagram showing a state in which light is made incident on and propagates through the core portions, starting from the state shown in FIG. 3, and leakage light is generated from each core portion. FIG. FIG. 6 is an explanatory diagram showing a state in which each clad portion and a plurality of self-written optical waveguides are formed from the state shown in FIG. 5 . 7 is a stereomicroscope image showing the state of FIG. 6.

In the method for manufacturing a self-forming optical waveguide of the present invention, a photocurable resin and two multicore fibers having n cores (n: a natural number of 2 or more) are prepared, the photocurable resin includes a core-forming resin that is polymerized and hardened by light of a predetermined wavelength band being incident thereon and has a refractive index na, and a cladding-forming resin that is polymerized and hardened by light of an intensity equal to or greater than the intensity of the light incident on the core-forming resin and has a refractive index nb after hardening of nb < na. The two multicore fibers are arranged opposite each other, and a photocurable resin is arranged between the multicore fibers. Light (hereinafter, also simply referred to as "light") of an intensity capable of polymerizing only the core-forming resin is incident on the photocurable resin from the cores of the two multicore fibers in order, causing polymerization and hardening of the core-forming resin to form the core of the optical waveguide in the photocurable resin, and then a cladding is formed, thereby self-forming n optical waveguides in the photocurable resin.

In the above manufacturing method, light with an intensity sufficient to polymerize only the resin for forming the core portion can be incident on the photocurable resin, starting from the core of the multicore fiber.

The above manufacturing method can prevent the cores in each multicore fiber from bonding together when adjacent cores are irradiated with light, thereby preventing poor bonding between the cores.

As one embodiment of the present invention, a manufacturing method according to an embodiment will be described below with reference to Figs. 1 to 7, but the present invention is not limited to the following embodiment.

In the manufacturing method of this embodiment, first, a photocurable resin 1 and a multicore fiber (3a, 3b) having n cores (n: natural number of 2 or more) are prepared. Two multicore fibers (3a, 3b) having the same structure are prepared. n is a natural number of 2 or more, for example, 2 to 4. However, n is not limited to the range exemplified here.

The transparent container 4 is filled with photocurable resin 1, and one end of each multicore fiber (3a, 3b) is immersed in the photocurable resin 1. Thus, the photocurable resin 1 is disposed between the multicore fibers (3a, 3b), and the two multicore fibers (3a, 3b) are disposed facing each other with the photocurable resin 1 sandwiched between them.

The two multicore fibers (3a, 3b) each have a circular outer shape as shown in FIG. 1, a core diameter of 8.0 μm, a cladding diameter of 125 μm, and n=4 cores (3a1, 3a2, 3a3, 3a4, or 3b1, 3b2, 3b3, 3b4). As shown in FIG. 1, the four cores (3a1-3a4, or 3b1-3b4) are arranged in two rows x two cores at equal angles (90° in FIG. 1) and equal intervals on the circumference of a circle centered on the center of the multicore fiber (3a, 3b). In this embodiment, the interval d between each core (3a1-3a4, or 3b1-3b4) in the two multicore fibers (3a, 3b) is 50 μm. The interval d is the distance between the centers of the two cores.

For example, the cutoff wavelength is 1300 nm to 1500 nm, and the mode field diameter is 7.4 μm to 8.5 μm (propagating light wavelength 1550 nm).

The end faces (3a5, 3b5) of the multicore fibers (3a, 3b) immersed in the photocurable resin 1 are formed to have a planar shape perpendicular to the optical axis direction of each core (3a1 to 3a4 or 3b1 to 3b4) as shown in FIG. 2. The end faces (3a5, 3b5) are subjected to flat polishing.

The photocurable resin 1 includes a resin for forming the core portion and a resin for forming the cladding portion. The resin for forming the core portion has a refractive index na as a result of being polymerized and cured by light of a specific wavelength band being incident thereon. The resin for forming the cladding portion is polymerized and cured by light of the same or different wavelength band as the light incident on the resin for forming the core portion and of an intensity equal to or greater than that of the light incident on the resin for forming the core portion. Furthermore, the refractive index nb of the resin for forming the cladding portion after curing is nb<na.

For the resin for forming the core portion and the resin for forming the cladding portion, resins that undergo photopolymerization through different polymerization reactions are selected. In this embodiment, the resin for forming the core portion is an acrylic resin, and the resin for forming the cladding portion is an epoxy resin. In a combination of acrylic resin and epoxy resin, the polymerization reaction rate of the acrylic resin is faster than that of the epoxy resin, so only the acrylic resin is selectively polymerized by light of low intensity.

Acrylic resins and epoxy resins are solutions in which a photopolymerization initiator is added to a mixture of two or more types of monomers.

Next, light of a predetermined wavelength band is incident on the inside of the photocurable resin 1 from the cores (3a1-3a4 or 3b1-3b4) of the two multicore fibers (3a, 3b). The light incident on the photocurable resin 1 is laser light with an intensity sufficient to polymerize only the resin for forming the core portion. The wavelength λw of the light can be set arbitrarily depending on the photopolymerization initiator, but an example is 365 nm to 1675 nm, and in this embodiment, λw is set to 405 nm. Additionally, the wavelength band to which the photopolymerization initiator is sensitive is also set to around 405 nm.

The incidence of light from the cores (3a1 to 3a4 or 3b1 to 3b4) causes polymerization and hardening of the resin for forming the cores, the monomers of the resin for forming the cores become polymers, and multiple cores (2a1, 2b1, 2c1, 2d1) of the optical waveguide shown in Figures 3 and 4 are self-formed within the photocurable resin 1.

When light is incident from the cores (3a1 to 3a4, or 3b1 to 3b4) to the photocurable resin 1, light is incident on the n cores in each multicore fiber (3a, 3b) in sequence. Here, "in sequence" means that when light is incident on the n cores in each multicore fiber (3a, 3b) in sequence, during the time when light is incident on a certain core, light is not incident on any other cores of the same multicore fiber. For example, in the multicore fiber 3a, during the time when light is incident on the core 3a1, light is not incident on the cores 3a2, 3a3, and 3a4, and in the multicore fiber 3b, during the time when light is incident on the core 3b1, light is not incident on the cores 3b2, 3b3, and 3b4. Note that during the time when light is incident on the cores of one of the two multicore fibers (3a, 3b), light may or may not be incident on the cores of the other multicore fiber. In the example shown in Figures 1 to 3, cores are sequentially formed between each core in the order of core 3a1 (or 3b1) → 3a2 (or 3b4) → 3a3 (or 3b3) → 3a4 (or 3b2), and after the self-formation of the cores between each core is completed, the self-formation of the cores between the next cores is performed. The reason for using such a light incidence process is that it is possible to prevent the cores formed by the light irradiation of adjacent cores in each multi-core fiber (3a, 3b) from bonding with each other, and thus prevent poor bonding of the cores.

The diameter of the cores (2a1, 2b1, 2c1, 2d1) is preferably the same as the diameter of each core (3a1-3a4, or 3b1-3b4) of the multicore fiber (3a, 3b), and is preferably uniform in the optical axis direction of each core (2a1, 2b1, 2c1, 2d1). Furthermore, the mode field diameter of each core (2a1, 2b1, 2c1, 2d1) is the same (7.4 μm-8.5 μm) as the mode field diameter of each core (3a1-3a4, or 3b1-3b4) of the multicore fiber (3a, 3b).

Next, the self-formation of the cladding portion will be described. After the core portion (2a1, 2b1, 2c1, 2d1) is formed, the interdiffusion of monomers is generated in the cladding portion forming resin in the photocurable resin 1 around the core portion (2a1, 2b1, 2c1, 2d1) (the boundary surface between the core portion 2a1, 2b1, 2c1, 2d1 and the other photocurable resin 1). While the monomers are consumed and polymerized in the core portion (2a1, 2b1, 2c1, 2d1) region, the monomers in the photocurable resin 1 other than the core portion (2a1, 2b1, 2c1, 2d1) have not polymerized and are uncured and unconsumed, so a concentration gradient of the monomers is generated around the core portion (2a1, 2b1, 2c1, 2d1), and interdiffusion progresses. In this example, the core portions (2a1, 2b1, 2c1, 2d1) were left to stand for 2 minutes after formation to promote interdiffusion of the monomers.

Next, in this embodiment, laser light of the same wavelength band (λw = 405 nm) as the wavelength band in which the resin forming the core portion is polymerized is made to enter the core portion (2a1, 2b1, 2c1, 2d1) from each core (3a1-3a4 or 3b1-3b4) of the multicore fiber (3a, 3b) and propagates inside the core portion (2a1, 2b1, 2c1, 2d1). Light with an intensity equal to or greater than that of the light that polymerized the resin forming the core portion is made to enter the core portion (2a1, 2b1, 2c1, 2d1). Of course, this intensity is set to be an intensity capable of polymerizing the resin forming the cladding portion.

The light continues to propagate, causing light leakage from the cores (2a1, 2b1, 2c1, 2d1) to the uncured cladding resin around the cores (2a1, 2b1, 2c1, 2d1). The cladding resin around the cores (2a1, 2b1, 2c1, 2d1) is then polymerized and cured by the leaking light shown by the arrows in FIG. 5, and the cladding (2a2, 2b2, 2c2, 2d2) is self-formed in a form that surrounds the surface of the cores (2a1, 2b1, 2c1, 2d1). Note that the arrows in FIG. 5 are only shown for one core 2a1, but light leakage also occurs in the other cores (2b1, 2c1, 2d1). Although the cladding 2d2 is not shown, it is a self-formed cladding that surrounds the surface of the core 2d1.

After curing, the refractive index nb of the self-formed cladding (2a2, 2b2, 2c2, 2d2) is nb<na, where na is the refractive index of the core (2a1, 2b1, 2c1, 2d1). Thus, multiple self-formed optical waveguides (2a, 2b, 2c, 2d) are self-formed by the cores (2a1, 2b1, 2c1, 2d1) and cladding (2a2, 2b2, 2c2, 2d2). The self-formed optical waveguide 2a is made up of the core 2a1 and cladding 2a2. The self-formed optical waveguide 2b is made up of the core 2b1 and cladding 2b2, the self-formed optical waveguide 2c is made up of the core 2c1 and cladding 2c2, and the self-formed optical waveguide 2d is made up of the core 2d1 and cladding 2d2.

Finally, ultraviolet (UV) light is uniformly applied around the transparent container 4 to harden all of the unreacted photocurable resin 1 (see Figures 6 and 7).

The light for forming the cladding portions (2a2, 2b2, 2c2, 2d2) may be incident on all the core portions (2a1, 2b1, 2c1, 2d1) simultaneously from all the cores (3a1 to 3a4, or 3b1 to 3b4) of each multicore fiber (3a, 3b), or may be incident on each core portion (2a1, 2b1, 2c1, 2d1) one by one in sequence. By simultaneously incident on all the cores (3a1 to 3a4, or 3b1 to 3b4) on all the core portions (2a1, 2b1, 2c1, 2d1), complex incident time control is not required, and the time required for forming the cladding portions (2a2, 2b2, 2c2, 2d2) can be shortened, which is preferable.

As described above, by forming the cladding portions (2a2, 2b2, 2c2, 2d2) by the leakage of light from the core portions (2a1, 2b1, 2c1, 2d1), the occurrence of cure shrinkage of the entire photocurable resin 1 except for the core portions (2a1, 2b1, 2c1, 2d1) is prevented, and it is possible to limit the resin that cures when forming the cladding portions (2a2, 2b2, 2c2, 2d2) to the resin for forming the cladding portions. Therefore, the occurrence of stress in the entire photocurable resin 1 is prevented, deformation of the core portions (2a1, 2b1, 2c1, 2d1) can be suppressed, and an increase in the light insertion loss to the core portions (2a1, 2b1, 2c1, 2d1) can be suppressed.

Furthermore, as described above, by forming the cladding portions (2a2, 2b2, 2c2, 2d2) by light leakage, it becomes possible to control the diameter and thickness of each cladding portion, and it is also possible to stabilize the optical and mechanical properties of the self-forming optical waveguides (2a, 2b, 2c, 2d).

Furthermore, in this embodiment, when forming multiple self-forming optical waveguides (2a, 2b, 2c, 2d), the hardening of all clad portions (2a2, 2b2, 2c2, 2d2) can be completed without irradiating the photocurable resin 1 with UV light from the periphery when forming the clad portions (2a2, 2b2, 2c2, 2d2), so that an increase in the optical insertion loss for each core portion (2a1, 2b1, 2c1, 2d1) can be prevented.

After the self-forming optical waveguides (2a, 2b, 2c, 2d) were formed, light with a wavelength of 1550 nm was made to enter and propagate from each core (3a1-3a4) of the multicore fiber 3a into each optical waveguide (2a, 2b, 2c, 2d), and the optical output of the emitted light relative to the optical output of the incident light was measured with a power meter, and the optical insertion loss between the multicore fibers (3a, 3b) was measured.

The loss values are shown in Table 1. As shown in Table 1, it was confirmed that the optical insertion loss was improved to within the range of 0.2 dB to 1.2 dB in all four optical waveguides (2a, 2b, 2c, 2d). In Table 1, optical waveguide 2a is shown as channel 1, optical waveguide 2b as channel 2, optical waveguide 2c as channel 3, and optical waveguide 2d as channel 4. The length of each optical waveguide (2a, 2b, 2c, 2d) between the end faces (3a5, 3b5) of the two multicore fibers (3a, 3b) is 500 μm.

The present invention is applicable not only to the manufacturing method of self-forming optical waveguides between multicore fibers, but also to the field of high-density optical packaging, such as the manufacturing method of self-forming optical waveguides between multicore fibers and silicon optical waveguides, or between multicore optical fibers and polymer optical waveguides.

1 Photocurable resin 2a, 2b, 2c, 2d Self-forming optical waveguide 2a1, 2b1, 2c1, 2d1 Core portion 2a2, 2b2, 2c2, 2d2 Self-forming optical waveguide clad portion 3a, 3b Multicore fiber 3a1, 3a2, 3a3, 3a4, 3b1, 3b2, 3b3, 3b4 Core 3a5, 3b5 of multicore fiber End surface 4 of multicore fiber Transparent container d Spacing between each core of multicore fiber

Claims (1)

Two multi-core fibers each having a photocurable resin and n cores (n: a natural number of 2 or more) are prepared.
The photocurable resin includes a core portion forming resin which is polymerized and cured by light of a predetermined wavelength band being incident thereon and has a refractive index na, and a cladding portion forming resin which is polymerized and cured by light having an intensity equal to or greater than that of the light incident on the core portion forming resin and has a refractive index nb after curing such that nb<na,
Two of the multi-core fibers are arranged to face each other, and the photocurable resin is arranged between the multi-core fibers;
light having an intensity capable of polymerizing only the resin for forming the core portion is incident on the photocurable resin in sequence from the cores of the two multi-core fibers, thereby causing the polymerization and hardening of the resin for forming the core portion to occur, thereby forming a core portion of an optical waveguide in the photocurable resin;
Next, a cladding portion is formed, and the n optical waveguides are self-formed in the photocurable resin.