Optical side input / output circuit and optical connector

Abstract

The present application provides an optical side input / output circuit and an optical connector which have wavelength selectivity and are easily configured at multiple points in a transmission path. An optical side input / output circuit (301) includes a tapping section (10) in which a tapping waveguide (53) is formed, the tapping waveguide (53) outputting light of a high-order mode from a side surface of an optical fiber (50) from among light propagating in a core (51) of the optical fiber (50), and a grating section (20) located in front of the tapping section (10) in a propagation direction of the light, the grating section (20) having a grating (21) formed on the core (51) of the optical fiber (50), the grating (21) converting light of a desired wavelength from a fundamental mode into the light of the high-order mode.

Description

Technical Field

[0001] The present invention relates to a side-mounted input / output circuit for inputting and outputting light from the side of an optical fiber and an optical connector including the side-mounted input / output circuit. Background Technology

[0002] As an optical branching technology, wavelength multiplexing couplers using arrayed waveguide gratings are known. In addition, in order to realize optical sensing and monitoring of transmission channels, a side-output optical technology has been proposed, which forms an optical waveguide in an optical fiber by laser processing and outputs a portion of the power of the light from the core (see, for example, Non-Patent Literature 1).

[0003] Existing technical documents

[0004] Non-patent literature 1: Peng Ji et al, Optics Express, Vol. 26, No. 12, pp. 14972-14981, (2018)

[0005] Non-patent literature 2: Y. Shani et al, “Integrated Optic Adiabatic Devices on Silicon,” IEEE J. Quantum Electron., vol. 27, no. 3, pp. 556-566, 1991.

[0006] Non-Patent Document 3: Fundamentals of Optical Waveguides, Katsuyuki Okamoto (CORONA Corporation, 1992)

[0007] Non-patent document 4: A. Urushibara et al, "Experimental verification of mode-dependent loss reduction by mode coupling using long-period grating," OFC2017, Tu2J.6, 2017.

[0008] Non-patent literature 5: BY Kim et al., “All-fiber acousto-optic frequency shifter,” Optics Letters, vol. 11, no. 6, pp. 389-391, 1986

[0009] Known wavelength multiplexing couplers present challenges in multi-point configuration within the transmission channel due to their large size and increased reflections and losses at connection points. Furthermore, while existing tapped waveguides are easily configured at multiple points within the transmission channel, improving wavelength selectivity remains a challenge. Summary of the Invention

[0010] Therefore, in order to solve the aforementioned problems, the object of the present invention is to provide an optical side input / output circuit and an optical connector that are wavelength selective and can be easily configured at multiple points within the transmission channel.

[0011] To achieve the above objectives, the optical side input / output circuit of the present invention includes a tapped waveguide with wavelength selectivity.

[0012] Specifically, the optical side input / output circuit of the present invention includes:

[0013] A tapped head is formed with a tapped waveguide, which outputs higher-order modes of light propagating in the core of the optical fiber from the side of the fiber; and

[0014] A grating section, located in the front stage of the tap head in the direction of light propagation, has a grating formed on the core of the optical fiber that converts light of a desired wavelength from the basic mode to the higher-order mode.

[0015] Furthermore, the optical connector of the present invention includes the optical side input / output circuit.

[0016] This optical side-input / output circuit incorporates a long-period fiber grating to achieve wavelength selectivity in the tapped waveguide. Because it uses a tapped waveguide, it is easily configured at multiple points within the transmission channel. Furthermore, this optical side-input / output circuit can input and output light of the desired wavelength using the long-period fiber grating. Therefore, this invention provides an optical side-input / output circuit and optical connector that are wavelength selective and easily configured at multiple points within the transmission channel.

[0017] The optical side-input / output circuit of the present invention is characterized in that the normalized frequency V of the grating section at the desired wavelength is 2.4 or higher.

[0018] The tap head satisfies

[0019] d t / d c ≥0.24V-0.27

[0020] 0.33≤d t / d c ≤0.87、

[0021] 0.28V - 0.35 ≤ δn / (n core -n clad )≤0.03V+1.28, and

[0022] α≤-0.57V 2 +2.65V-1.48.

[0023] Where, dt d is the diameter of the tapped waveguide. c δn is the diameter of the core of the optical fiber, and n is the refractive index change of the tapped waveguide relative to the optical fiber. core and n clad These are the refractive indices of the core and cladding of the optical fiber, respectively, and α is the angle (°) between the core and the tapped waveguide of the optical fiber.

[0024] The optical side-input / output circuit of the present invention is characterized in that the refractive index of the core of the grating section is higher than the refractive index of the core of the tap. By exciting a higher-order mode in the grating section, light of the desired wavelength can be tapped by the tap even without propagating the higher-order mode.

[0025] The optical side-mounted input / output circuit of the present invention is characterized in that multiple groups of the taps and the grating portions are continuously arranged on the optical fiber. Furthermore, the optical side-mounted input / output circuit of the present invention is further characterized in that it includes a light receiver disposed on the side of the optical fiber to receive the light output from the taps. Taps can be made at multiple locations in the transmission channel, enabling control of the transmission channel path and multi-stage optical power supply.

[0026] Furthermore, the inventions described above can be combined in combination as much as possible.

[0027] The present invention provides optical side input / output circuits and optical connectors that are wavelength selective and can be easily configured at multiple points within the transmission channel. Attached Figure Description

[0028] Figure 1 This is a diagram illustrating the optical side input / output circuit of the present invention.

[0029] Figure 2 This is a diagram illustrating the characteristics of the optical side input / output circuit of the present invention.

[0030] Figure 3 This is a diagram illustrating the characteristics of the optical side input / output circuit of the present invention.

[0031] Figure 4 This is a diagram illustrating the characteristics of the optical side input / output circuit of the present invention.

[0032] Figure 5 This is a diagram illustrating the characteristics of the optical side input / output circuit of the present invention.

[0033] Figure 6 This is a diagram illustrating the characteristics of the optical side input / output circuit of the present invention.

[0034] Figure 7 This is a diagram illustrating the characteristics of the optical side input / output circuit of the present invention.

[0035] Figure 8 This is a diagram illustrating the characteristics of the optical side input / output circuit of the present invention.

[0036] Figure 9 This is a diagram illustrating the characteristics of the optical side input / output circuit of the present invention.

[0037] Figure 10 This is a diagram illustrating the characteristics of the optical side input / output circuit of the present invention.

[0038] Figure 11 This is a diagram illustrating the characteristics of the optical side input / output circuit of the present invention.

[0039] Figure 12 This is a diagram illustrating the characteristics of the optical side input / output circuit of the present invention.

[0040] Figure 13 This is a diagram illustrating the characteristics of the optical side input / output circuit of the present invention.

[0041] Figure 14 This is a diagram illustrating the characteristics of the optical side input / output circuit of the present invention.

[0042] Figure 15 This is a diagram illustrating the method of grating formation.

[0043] Figure 16 This is a diagram illustrating the optical side input / output circuit of the present invention.

[0044] Figure 17 This is a diagram illustrating the optical side input / output circuit of the present invention.

[0045] Figure 18 This is a diagram illustrating the optical connector of the present invention.

[0046] Figure 19 This is a diagram illustrating the optical connector of the present invention. Detailed Implementation

[0047] Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to these embodiments. Furthermore, in this specification and the accompanying drawings, elements with the same reference numerals denote identical constituent elements.

[0048] (Implementation Method 1)

[0049] Figure 1 This is a diagram illustrating the optical side input / output circuit 301 of this embodiment. The optical side input / output circuit 301 includes:

[0050] A tapped head 10 is formed with a tapped waveguide 53, which outputs higher-order modes of light propagating in the core 51 of the optical fiber 50 from the side of the optical fiber 50; and

[0051] The grating section 20, located in the front stage of the tap head 10 in the direction of light propagation, has a grating 21 formed on the core 51 of the optical fiber 50 to convert light of the desired wavelength from the basic mode to the higher-order mode.

[0052] Optical fiber 50 consists of core 51 with a diameter d c The diameter d of optical fiber 50 f The refractive index n of core 51 core (Refractive index excluding the grating portion), refractive index n of cladding 52 clad A step-index fiber is defined. Fiber 50 has a grating section 20 and a tapped section 10 sequentially formed along its long side. The direction in which light can be incident on the tapped waveguide 53 is defined as the waveguide direction. Figure 1 In this configuration, the optical waveguide direction is from left to right. Furthermore, the tap direction of the tapped waveguide 53, from the core 51 towards the side of the optical fiber 50, is defined as the tap direction. Figure 1 In this context, the tap direction is the direction that is tilted in the same direction as the optical waveguide.

[0053] The grating section 20 uses a long-period grating to convert only the desired wavelength of light propagating in the core 51 of the fiber 50 into the LP11 mode. The grating structure can be realized, for example, by femtosecond laser processing, CO2 laser processing, or pressing of the grating.

[0054] The tap 10 has a tapped waveguide 53 extending from the center of the core 51 at an angle α toward the side of the fiber 50 (the interface of the cladding 52). The tap 10 is controlled by adjusting the angle α between the tapped waveguide 53 and the core 51, and the diameter d of the tapped waveguide 53. t The refractive index of the tapped waveguide 53 is used to selectively extract only the LP11 mode from the core 51.

[0055] Here, the light coupled from core 51 to tapped waveguide 53 is defined as tapped light, and the light propagating as is in core 51 is defined as transmitted light. For example, by connecting the light-receiving element to the output end (side of fiber 50) of tapped head 10, it is possible to extract and receive only tapped light from fiber 50.

[0056] In the tap 10, the coupling efficiency from core 51 to tapped waveguide 53 strongly depends on the propagation mode of the light propagating in core 51. This is because higher-order modes are less restricted and more easily coupled to tapped waveguide 53. Therefore, it is possible to transfer only higher-order modes to the tapped waveguide.

[0057] Here, in order to couple only higher-order modes to tapped waveguide 53, the refractive index and diameter d of tapped waveguide 53 are... t The values ​​of are important. If these values ​​are too large, the NA of the tapped waveguide 53 increases, and the LP01 mode is more easily coupled, thus increasing the loss of transmitted light. On the other hand, if these values ​​are too small, the NA of the tapped waveguide 53 decreases, making it difficult for higher-order modes to couple, thus reducing the coupling efficiency of tapped light to the tapped waveguide 53. That is, the refractive index and diameter d of the tapped waveguide 53 need to be appropriately determined. t The value of .

[0058] Furthermore, in order to efficiently couple the light of higher-order modes to the tapped waveguide 53 and allow the light of the fundamental mode to propagate in a state confined within the core 51, α needs to be sufficiently small to allow mode transfer in a thermally insulating manner (see, for example, Non-Patent Document 2). If α is large, the LP01 mode is also affected by the tapped waveguide 51 and coupled with the radiating mode, resulting in loss. Therefore, an upper limit value of α is determined from the viewpoint of the loss of the LP01 mode. On the other hand, α can take any value greater than 0, but the total length L of the tap 10 is determined according to α by the following formula. tap Therefore, the lower limit of α is determined from the perspective of the propagation loss of the tapped waveguide 53 and the requirements for the total length of the equipment.

[0059] [Mathematical Expression 1]

[0060]

[0061] In mathematical formula (1), the unit of α is radian.

[0062] In typical single-mode optical fibers, the diameter d of fiber 50 is... f For example, to make the suction head L 125 μm tap For values ​​below 5cm, α needs to be set to 0.07° or higher.

[0063] The grating section 20 has a grating 21 with a spacing Λ. For example, the grating 21 is a long-period fiber grating (LPG). In order to convert only an arbitrary wavelength λ from the LP01 mode to the LP11 mode in the grating section 20, the spacing Λ is set to satisfy the following formula.

[0064] [Mathematical Expression 2]

[0065] Λ=λ / (n eff1 -n eff2 )

[0066] Here, the effective refractive index of the fundamental mode (LP01) propagating in core 51 is set to n. eff1 The effective refractive index of the higher-order mode (LP11) is set to n. eff2Let λ be the wavelength in a vacuum. Furthermore, the effective refractive index refers to the effective refractive index without the grating.

[0067] Figure 2 This describes the effective refractive index n of the basic mode. eff1 The effective refractive index n of the higher-order mode (LP11) eff2 A graph showing the relationship between grating spacing Λ and wavelength λ. Figure 2 The horizontal axis represents wavelength λ, the first vertical axis represents effective refractive index, and the second vertical axis represents grating spacing Λ. The optical fiber is constructed in the same manner as typical single-mode optical fibers, with a core radius of 4.1 μm and a relative refractive index difference Δ between the core and the grating spacing. core The calculations are performed using a step-type refractive index distribution of 0.35%. Additionally, the relative refractive index difference Δ of the core... core Defined by the following formula.

[0068] [Mathematical Expression 3]

[0069]

[0070] The dashed line represents the effective refractive index n of the LP01 mode relative to wavelength λ. eff1 The dotted line represents the effective refractive index n of the LP11 mode relative to wavelength λ. eff2 The solid line represents the refractive index of the cladding (1.444 at all wavelengths), and the dashed line represents the grating spacing Λ for the transition from LP01 mode to LP11 mode relative to wavelength λ.

[0071] Furthermore, the grating section 10 needs to be a structure capable of propagating the LP11 mode. For example, in Figure 2 The structure described herein does not contain the LP11 mode in the region above 1.3 μm, therefore light above 1.3 μm cannot be extracted as tap light. The propagation condition for higher-order modes is defined as V > 2.4 using the normalized frequency V value of the following formula (see, for example, Non-Patent Document 3).

[0072] [Mathematical Expression 4]

[0073]

[0074] That is, the core diameter d needs to be set. c (in mathematical expression (4) by d) core (represented by) the refractive index n of the core core and the relative refractive index difference Δ of the core core So that the wavelength of the light that is to be output as the tap light is greater than 2.4.

[0075] Figure 3This is a graph illustrating the relationship between the grating length Lg at a wavelength of 1.1 μm and the coupling amount between modes. Here, the coupling amount refers to the power of each mode output from the grating section 20 after normalizing to the incident light power when the LP01 mode is incident on the grating section 20. The grating spacing Λ is based on... Figure 2 The dashed line is 435 μm at a wavelength of 1.1 μm.

[0076] By varying the grating length Lg, the various coupling quantities change. That is, by adjusting the grating length Lg of the grating section 20 in conjunction with the power desired to be extracted from the tapped waveguide 53, the conversion efficiency to the LP11 mode can be controlled.

[0077] Figure 4 This is a diagram illustrating the structure and characteristics of the extraction head 10. Figure 4 Figure (a) illustrates the structure of the tap 10. A tapped waveguide 53 is formed in the core 51 at an angle α. The refractive index of the core 51 is n. core The refractive index of cladding 52 is n clad The tapped waveguide 53 can be fabricated within the fiber 50 using femtosecond laser processing technology, as shown in Non-Patent Document 1. In this case, the modulation amount of the refractive index of the core 51 and cladding 52 based on the femtosecond laser (the refractive index difference varying due to the laser) is defined as δn. core and δn clad Therefore, the refractive index of the tapped waveguide 53 in the portion overlapping with the core 51 is n. core +δn core The portion overlapping with cladding 52 is n. clad +δn clad .

[0078] Figure 4 (b) and Figure 4 (c) is an explanation from Figure 4 The diagram in (a) shows the electric field distribution when the arrow points towards the head of the pump and 10 incident light. Figure 4 (b) is a diagram of the incident light in LP01 mode. Figure 4 (c) is a diagram of incident light in LP11 mode. Additionally, as for wavelength 1280nm, d... c =8.2um, Δ core =0.35%, α=0.1°, d t =5μm for calculation. Furthermore, the Ge addition in typical single-mode fibers is only a few mol%, a trace amount. Therefore, due to material dependence, the difference in refractive index modulation between the core 51 and cladding 52 caused by the femtosecond laser can be considered sufficiently small. Thus, δn can be considered... core With δn clad Roughly equal, δn core =δn clad=δn=0.005. Afterwards, δn core and δn clad It is recorded as δn.

[0079] like Figure 4 As shown in (b), the light in LP01 mode is not coupled to the tapped waveguide 53 and continues to propagate in the core 51. On the other hand, as Figure 4 As shown in (c), the LP11 mode light is coupled to the tapped waveguide 53 and does not propagate in the core 51. Thus, by properly designing the tapped waveguide 53, it is possible to selectively couple only the LP11 mode light to the tapped waveguide 53 and extract it.

[0080] As the optical side input / output circuit 301, it is preferable that the transmitted light experiences low loss at the tap head 10. If multiple stages of the optical side input / output circuit 301 are to be connected, it is preferable that the loss of each optical side input / output circuit 301 is suppressed to below 0.5 dB. Figure 5 This is a graph illustrating the α dependence of the transmitted light loss (insertion loss of tap 10) experienced at tap 10 when LP01 mode light is incident on tap 10. The solid line, dotted line, and dashed line represent the diameter d of the tapped waveguide, respectively. t With core diameter d c Data for ratios of 0.86, 0.73, and 0.37. In addition, other parameters include the refractive index modulation amount δn = 0.005, and the ratio of the refractive index modulation amount to the refractive index difference between the core and cladding δn / (n core -n clad ) = 0.98, wavelength 1280nm, d c =8.2μm, d t =5μm, Δ core =0.35%.

[0081] The insertion loss of the tap 10 increases monotonically with respect to α. For example, to suppress the insertion loss to below 0.5 dB, it is only necessary to adjust the α values ​​at d... t / d c Among 0.37, 0.74, and 0.86, α can be set to below 0.8°, 0.55°, and 0.35°.

[0082] On the other hand, as the optical side input / output circuit 301, it is preferable to couple the LP11 mode light as far as possible to the tapped waveguide 53. In order to extract and receive the LP11 mode light, a coupling efficiency of 50% or more is preferred. Figure 6 This is a graph illustrating the α-dependence of coupling efficiency to tapped waveguide 53 when LP11 mode light is incident on tapped head 10. The meanings of each line and the parameters are... Figure 5 The meaning and parameters are the same.

[0083] The coupling efficiency in the head 10 decreases monotonically in proportion to α. For example, to obtain a coupling efficiency of over 50%, it is only necessary to [address the coupling efficiency in d]. t / d c For values ​​of 0.37, 0.74, and 0.86, α can be set to below 0.25°, 0.6°, and 0.23°, respectively.

[0084] Figure 7 This is a graph illustrating the relationship between insertion loss and coupling efficiency for the core structure. With α = 0.1, let n... core d c And wavelength variation to keep the V value constant. In this example, α = 0.1°, δn = 0.005, δn / (n core -n clad ) = 0.98, d t =5μm.

[0085] Figure 7 (a) and Figure 7 (b) is an explanation of d c =8.2μm and make Δ core The graph shows the insertion loss for LP01 mode and the coupling efficiency of LP11 mode for tapped waveguide 53 under varying conditions. Figure 7 (c) and Figure 7 (d) is an explanation of Δ core =0.35% and make d c The graph shows the insertion loss for LP01 mode and the coupling efficiency towards tapped waveguide 53 for LP11 mode under varying conditions. The wavelength was adjusted to fix each V value at V = 2.44. (The last sentence appears to be incomplete and possibly refers to a graph with varying d values.) t / d c Δ loss of LP01 mode when = 0.98 core High dependence (refer to) Figure 7 (a) solid line), but in other structures, it can be confirmed that the dependence on the core structure is small.

[0086] Figure 8 This indicates that V = 2.44, α = 0.1°, δn = 0.005, and δn / (n core -n clad ) = 0.98, wavelength 1280nm, d c =8.2μm, Δ core The coupling efficiency of the LP11 mode at 0.35% is d t / d c Dependency diagram. From Figure 8 It can be seen that when 0.33≤d t / d c The coupling efficiency is over 50% in regions ≤0.87.

[0087] according to Figure 7 and Figure 8 , in 0.33≤d t / d c In the region ≤0.87, the coupling efficiency is above 50%. If the V value is fixed, the dependence on the core structure is considered to be small. Therefore, the following description uses the V value, where 0.33 ≤ d t / d c Calculations are performed within the region ≤0.87. Afterwards, the core structure is d. c =8.2μm, Δ core =0.35%, by changing the wavelength, the value of V is kept constant. However, if 0.33≤d t / d c Within the range of ≤0.87, even if the core structure changes, as long as the V value remains the same, the same characteristics can be obtained.

[0088] Figure 9 This is a graph illustrating the range of α for the LP01 mode where the insertion loss is below 0.5 dB. Figure 9 In, make δn / (n core -n clad ), V, d t / d c Changes, such as Figure 5 As shown, the maximum value of α that suppresses the insertion loss of LP01 mode to below 0.5dB is obtained. Figure 9 (a), (b), and (c) represent the maximum values ​​of α when V = 2.4, 3.1, and 3.9, respectively. Figure 9 In this context, the darker the black color, the smaller α needs to be. As mentioned above, the tap head 10 needs to be a structure for LP11 mode propagation; therefore, the minimum V value for LP11 mode propagation, V = 2.4 or higher, is considered the design region. Furthermore, in this invention, as mentioned above, it is preferable that the extracted tap light has high coupling efficiency.

[0089] Figure 10 This means that in Figure 9 This is a graph showing the range of the maximum value of the coupling efficiency (coupling efficiency of the LP11 mode to the tapped waveguide when the insertion loss of the LP01 mode is below 0.5 dB) obtained in the region of α (below the maximum value of α). Additionally, the minimum value of α is 0.1. Figure 10 (a), (b), and (c) are data for V = 2.4, V = 3.1, and V = 3.9, respectively. For example, it can be seen that in... Figure 10 In (b) with V = 3.1, in

[0090] δn / (n core -n clad <0.4

[0091] δn / (n core -n clad >1.4, and

[0092] d t / d c In the region <0.45, there is no region with a coupling efficiency greater than 0.5, and sufficient tap light cannot be obtained.

[0093] Similarly, it can be seen that in Figure 10 In (c) with V = 3.9, in

[0094] δn / (n core -n clad <0.8

[0095] δn / (n core -n clad >1.4, and

[0096] d t / d c In regions with a coupling efficiency of less than 0.68, there are no regions with a coupling efficiency of more than 0.5, so sufficient tap light cannot be obtained.

[0097] δn / (n) needs to be set core -n clad ),d t / d c This ensures that the coupling efficiency is at least in a region other than the region where it will not be greater than 0.5 (the region where the coupling efficiency is less than 0.5). Figure 11 This is a diagram illustrating the region where the coupling efficiency is above 0.5, determined by varying the V value. Figure 11 The mathematical expression (solid line) for (a) is d. t / d c The V-value dependence indicates that the region above the solid line is where the coupling efficiency may be greater than 0.5. Figure 11 The two mathematical expressions (dashed and solid lines) of (b) are δn / (n core -n clad The V-value dependence of ) indicates that the region between the two straight lines is where the coupling efficiency may be higher than 0.5. Additionally, as Figure 7 As illustrated in the core structure dependency description, in 0.33≤d t / d c Represented within the range of ≤0.87.

[0098] Based on the above, in order to suppress the insertion loss of the LP01 mode and obtain a coupling efficiency of over 50% for the LP11 mode, at least δn / (n) needs to be set. core -nclad ) and d t / d c So as to satisfy the following formula.

[0099] [Mathematical Expression 5]

[0100] d t / d c ≥0.24V-0.27

[0101] 0.33≤d t / d c ≤0.87、

[0102] 0.28V - 0.35 ≤ δn / (n core -n clad ≤0.03V+1.28

[0103] In addition, through the Figure 9 and Figure 10 By comparison, the maximum value of α within the aforementioned region can be determined. Figure 9 and Figure 10 In the region where the coupling efficiency is above 0.5, the maximum value of α is 1.5, and at least in the region where α is above 1.5, tap light above 0.5 cannot be extracted. Figure 12 This is a graph illustrating the dependence of the V value on the maximum allowable α value. According to... Figure 12 We need to set α to satisfy the following formula.

[0104] [Mathematical Expression 6]

[0105] α≤-0.57V 2 +2.65V -1.48

[0106] Figure 13 (a) is a graph illustrating the wavelength dependence of the insertion loss of the tap 10. Figure 13 (b) is a graph illustrating the wavelength dependence of the coupling efficiency of the P11 mode to the tapped waveguide 53. The parameter of the tap 10 is d. c =8.2μm, Δ core =0.35%, α=0.1, d t =4μm, δn / (n core -n clad ) = 0.98. In Figure 13 The description indicates that within a 100nm bandwidth, the wavelength dependence of the insertion loss is less than 0.5dB, and the wavelength dependence of the coupling efficiency is less than 5%, which is sufficiently small. Therefore, within a bandwidth of approximately 100nm, the same insertion loss and coupling efficiency can be obtained even by changing the wavelengths of the tapped and transmitted light.

[0107] (Implementation Method 2)

[0108] The grating section 20 described in Embodiment 1 envisions a structure and wavelength for propagation of two modes. On the other hand, in the wavelength region where the LP11 mode does not propagate, for example, the refractive index of the core of the grating section 20 as a whole is changed (increased) by femtosecond laser processing, thereby enabling the LP11 mode to propagate in the grating section 20.

[0109] Here, it is considered that the refractive index of the core of the grating section 20 as a whole is higher than that of the core 51 of other parts, and that the light containing the LP11 mode excited in the grating section 20 is incident on the tap head 10. Figure 14 This is a graph illustrating the α-dependence of coupling efficiency of LP11 mode light (wavelength 1550nm) coupled to tapped waveguide 53 under this condition. Figure 14 The dashed line, dotted line, dotted line, and solid line within the line are respectively d t / d c The data are 0.49, 0.61, 0.73, and 0.85. Additionally, the parameters are d. c =8.2μm, Δ core =0.35%, α=0.1, d t =4μm, δn / (n core -n clad =0.98.

[0110] according to Figure 14 If the refractive index of the core is increased in the fiber section of the pre-stage of the tap 10 and the LP11 mode is excited in that section, then even if the tap 10 is a structure that does not propagate light in the LP11 mode, it is possible to selectively couple light in the LP11 mode to the tap waveguide 53.

[0111] (Implementation Method 3)

[0112] Figure 15 This is a diagram illustrating the method of forming the grating section 20. Figure 15 Figure (A) is a diagram illustrating the pressing type (non-patent document 4) of the external pressing clamp 25 from the optical fiber 50. Figure 15 (B) is a diagram illustrating an ultrasonic method (non-patent document 5) in which ultrasonic waves 26 are irradiated from the outside of optical fiber 50 to utilize the acousto-optic effect.

[0113] If it is a press-type mechanism, the grating spacing of the grating section 20 can be adjusted by the pressing amount and spacing of the clamp 25; if it is an ultrasonic mechanism, the grating spacing of the grating section 20 can be adjusted by the intensity and frequency of the ultrasonic wave 31. Therefore, Figure 15 The method shown allows for external control of the coupling amount and the extracted wavelength. Furthermore, the press-fit method eliminates the need to remove the cladding of fiber 50, thus minimizing the impact on the core wire.

[0114] (Implementation Method 4)

[0115] Figure 16 This diagram illustrates the optical side input / output circuit 302 of this embodiment. The optical side input / output circuit 302 is characterized in that, compared to the optical side input / output circuit 301 described in Embodiment 1, multiple groups of taps 10 and grating sections 20 are continuously arranged on the optical fiber 50. By arranging multiple such groups in the light propagation direction, the optical side input / output circuit 302 can control the path at any location within the transmission channel and provide multi-level optical power supply.

[0116] (Implementation Method 5)

[0117] Figure 17 This diagram illustrates the optical side input / output circuit 303 of this embodiment. Compared to the optical side input / output circuit 302 described in Embodiment 4, the optical side input / output circuit 303 further includes a light receiver 30, which is disposed on the side of the optical fiber 50 and receives the light output from the tap 10. Figure 17 As shown, tapped light can be received by attaching a light receiver 30 to the side of the optical fiber 50. The optical side input / output circuit 303 can serve as an optical power supply system that converts the tapped light into electricity, for example, to power multiple sensor terminals separately.

[0118] (Implementation Method 6)

[0119] Figure 18 and Figure 19 This figure illustrates the optical connector 350 of this embodiment. The optical connector 350 includes an optical side input / output circuit 304. Compared to the optical side input / output circuit 301 described in Embodiment 1, the optical side input / output circuit 304 further includes a light receiver 30, which is disposed on the side of the optical fiber 50 and receives light output from the tap 10. In Embodiment 5, multiple light receivers 30 are provided, but this embodiment is an example of a single light receiver 30. Reference numeral 45 indicates the sheathing of the optical fiber 50.

[0120] The optical connector 350 includes a sleeve 43 housing an optical side input / output circuit 304 and a connector plug 44 for connecting to other optical connectors. The connector plug 44 is typically of the SC, FC, LC, or MPO type. By inserting the optical side input / output circuit 304 into the optical connector 350, connection to other optical fibers 50a can be easily achieved, and optical side input / output from the optical fiber 50 can be realized.

[0121] (Key Points)

[0122] The optical side input / output circuits and optical connectors described in embodiments 1 to 6 selectively couple only higher-order modes to the tap by utilizing the difference in the amount of coupling between modes in the tap head, thereby enabling the output of only arbitrary wavelengths from the side of the optical fiber.

[0123] (Effect)

[0124] The optical side input / output circuits and optical connectors described in embodiments 1 to 6 enable wavelength selectivity in the optical side input / output technology, allowing arbitrary power to be extracted from light of any wavelength in the transmission channel. For example, power supply light can be extracted in multiple stages for sensor control, or path control can be achieved based on wavelength by inputting the extracted light into other optical fibers.

[0125] Explanation of reference numerals in the attached figures

[0126] 10: Head extraction

[0127] 20: Grating section

[0128] 21: Long-period fiber grating (LPG)

[0129] 30: Light receiver

[0130] 43: Sleeve

[0131] 44: Connector plug

[0132] 45: Covering

[0133] 50, 50a: Optical fiber

[0134] 51: Core

[0135] 52: Cladding

[0136] 53: Tapped waveguide

[0137] 301~304: Optical side input / output circuit

[0138] 350: Optical Connector

Claims

1. A side-mounted optical input / output circuit, characterized in that... include: A tapped head is formed with a tapped waveguide, which is physically connected to the core of the optical fiber and extends from the core to the surface of the optical fiber. The tapped waveguide outputs higher-order modes of light propagating in the core of the optical fiber from the side of the optical fiber. as well as A grating section, located in the front stage of the tap head in the direction of light propagation, has a grating formed on the core of the optical fiber to convert light of the desired wavelength from the basic mode to the higher-order mode.

2. The optical side input / output circuit according to claim 1, characterized in that, The grating section has a normalized frequency V of 2.4 or higher at the desired wavelength. The tap head satisfies d t / d c ≥0.24V-0.27、 0.33≤d t / d c ≤0.87、 0.28V - 0.35 ≤ δn / (n core -n clad )≤0.03V+1.28, and α≤-0.57V 2 +2.65V-1.48, Where, d t d is the diameter of the tapped waveguide. c δn is the diameter of the core of the optical fiber, and n is the refractive index change of the tapped waveguide relative to the optical fiber. core and n clad These are the refractive indices of the core and cladding of the optical fiber, respectively, and α is the angle between the core and the tapped waveguide of the optical fiber, in degrees.

3. The optical side input / output circuit according to claim 1, characterized in that, The refractive index of the core of the grating section is higher than that of the core of the tap head.

4. The optical side input / output circuit according to any one of claims 1 to 3, characterized in that, Multiple groups of the tap head and the grating section are arranged consecutively on the optical fiber.

5. The optical side input / output circuit according to any one of claims 1 to 3, characterized in that, It also includes a light receiver disposed on the side of the optical fiber to receive the light output from the tap.

6. The optical side input / output circuit according to claim 4, characterized in that, It also includes a light receiver disposed on the side of the optical fiber to receive the light output from the tap.

7. An optical connector, characterized in that, Includes the optical side input / output circuit as described in any one of claims 1 to 6.

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