Optical characteristic adjustment method for optical fiber coupler

Abstract

Provided is an optical characteristic adjustment method for an optical fiber coupler (3) that comprises an optical fiber (1) that has a polished side surface and has been placed so as to be capable of communication and an optical waveguide (2) that has a polished side surface and is optically coupled to the optical fiber (1). The method involves connecting one end of the optical waveguide (2) to a power meter (8) and connecting the other end of the optical waveguide (2) to a transmission device (5) via an optical multiplexer / demultiplexer (6), outputting communication light (22) from the transmission device (5), measuring the optical power of the communication light (22) as a first optical power by means of the power meter (8), calculating the insertion loss of the optical fiber coupler (3) on the basis of the first optical power, estimating a branching ratio from the calculated insertion loss, and aligning the optical fiber (1) and the optical waveguide (2) on the basis of the estimated branching ratio.

Description

Method for Adjusting Optical Characteristics of Optical Fiber Coupler

[0001] The present disclosure relates to a method for adjusting optical characteristics of an optical fiber coupler including a side polished optical fiber.

[0002] As a wiring method for an optical communication network that provides optical services at high speed and low cost, the PON (Passive Optical Network) method is known (see Non-Patent Document 1). In the PON method, an optical splitter is used to branch an optical signal into a plurality of signals, and a single optical fiber is shared by a plurality of users, realizing an economical optical communication network wiring method. The optical splitter in the PON method is laid in advance according to demand.

[0003] However, when demand arises in an unexpected location, there is no optical splitter installed there in advance. That is, it is impossible to respond to this demand without cutting the optical fiber during communication. Therefore, as an optical multiplexing / demultiplexing technology capable of demultiplexing light from an optical fiber during communication or multiplexing light onto an optical fiber, a manufacturing method of an optical fiber coupler using the optical fiber side polishing method has been studied (see Non-Patent Document 2).

[0004] “Technical Foundation Course GE-PON Technology”, NTT Technical Journal, 2005.8Takui Uematsu et al, “Optical Coupling Technique Based on Fiber Side-Polishing Without Service Interruption,” IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 34, NO. 19, 1 OCTOBER 2022

[0005] In the above optical multiplexing / demultiplexing technology, it is important to evaluate optical characteristics such as the splitting ratio and insertion loss of the optical fiber coupler. To adjust these optical characteristics, it is necessary to introduce a light source and an optical power meter. However, in order to install these devices on an optical fiber during communication, it is necessary to cut the optical fiber during communication once, causing the communication to be interrupted.

[0006] The purpose of this disclosure is to provide a method for fabricating an optical fiber coupler using an optical fiber side polishing method on an optical fiber in communication, which allows for adjustment of optical characteristics such as branching ratio and insertion loss without interrupting communication.

[0007] A method for adjusting the optical characteristics of an optical fiber coupler according to one aspect of the present disclosure, comprising an optical fiber that is in a communicable state and side-polished, and an optical waveguide that is side-polished and optically coupled to the optical fiber, includes: connecting a first power meter to one end of the optical waveguide and a transmission device to the other end of the optical waveguide via an optical multiplexer / demultiplexer; outputting a first communication light from the transmission device; measuring the optical power of the first communication light as a first optical power using the first power meter; calculating the insertion loss of the optical fiber coupler based on the first optical power; estimating a branching ratio from the calculated insertion loss; and performing a first alignment between the optical fiber and the optical waveguide based on the estimated branching ratio.

[0008] According to this disclosure, when fabricating an optical fiber coupler using an optical fiber side polishing method on an optical fiber in communication, it is possible to adjust the optical characteristics such as the branching ratio and insertion loss without interrupting communication.

[0009] Figure 1A shows the first manufacturing procedure for a side-polished optical fiber coupler. Figure 1B shows the second manufacturing procedure for a side-polished optical fiber coupler. Figure 1C shows the third manufacturing procedure for a side-polished optical fiber coupler. Figure 2 shows a first configuration example for adjusting the optical characteristics of the optical fiber coupler 3. Figure 3 shows a second configuration example for adjusting the optical characteristics of the optical fiber coupler 3. Figure 4 shows a third configuration example for adjusting the optical characteristics of the optical fiber coupler 3. Figure 5 shows a fourth configuration example for adjusting the optical characteristics of the optical fiber coupler 3. Figure 6 shows a fifth configuration example for adjusting the optical characteristics of the optical fiber coupler 3. Figure 7 shows a sixth configuration example for adjusting the optical characteristics of the optical fiber coupler 3.

[0010] Embodiments of this disclosure will be described below with reference to the drawings. In the drawings, the same parts are denoted by the same reference numerals and their descriptions are omitted.

[0011] This disclosure relates to a method for adjusting the optical properties of optical multiplexing and demultiplexing technology using side polishing of optical fibers during communication, specifically a technique for adjusting the positions of side polished optical fibers without interrupting communication. This disclosure is applicable to optical waveguides such as glass optical fibers and plastic fibers, which are common in long-distance communication.

[0012] The optical fiber coupler 3 according to this embodiment comprises an optical fiber 1 that is in a communication-ready state and has been side-polished, and an optical waveguide 2 that is side-polished and optically coupled to the optical fiber 1. The optical fiber coupler 3 is manufactured by side-polishing the optical fiber 1 that is in a communication-ready state.

[0013] First, let's explain how to manufacture this optical fiber coupler 3. Figures 1A to 1C show steps 1 to 3 of the manufacturing process for the optical fiber coupler 3, respectively.

[0014] (Procedure 1) As shown in Figure 1A, transmission devices 4A and 4B are connected to both ends of the optical fiber 1, and the two devices communicate using communication light 20 and communication light 21 propagating through the optical fiber 1. In this state, a part of the optical fiber 1 in the longitudinal direction is bent, forming a bent portion M1. Communication light 20 leaks out from the bent portion M1 as leaked light 20a. Leaked light from communication light 21 (not shown) also leaks out from the bent portion M1. However, in the configuration shown in Figure 1A, the monitoring device 24 is assumed to observe the leaked light 20a of the communication light 20.

[0015] (Procedure 2) As shown in Figure 1B, a bent portion M2 is formed by bending another portion of the optical fiber 1 in the longitudinal direction in order to polish the optical fiber 1. The bent portion M2 is located upstream of the bent portion M1 with respect to the propagation direction of the communication light 20. Next, the sides of the bent portion M2 (i.e., the covering portion 1c and the cladding portion 1b) are polished up to the vicinity of the core 1a (see Figure 1C). As the side polishing progresses near the core 1a, some of the communication light 20 begins to leak from the polished surface of the bent portion M2, and its intensity gradually increases. On the other hand, the communication light 20 leaks from the polished surface of the bent portion M2 before it leaks from the polished surface of the bent portion M1. Therefore, the intensity of the leaked light 20a from the bent portion M1 observed by the monitoring device 24 gradually decreases as the polishing progresses.

[0016] The measurement values ​​on the monitoring device 24 change with the polishing time of the bent portion M2. In other words, by observing the intensity of the leaked light 20a at the bent portion M1, the polishing process at the bent portion M2 can be indirectly understood. When the measurement values ​​on the monitoring device 24 reach a predetermined value, the polishing of the bent portion M2 is terminated. At the same time, the bend of the bent portion M1 is returned to its original state.

[0017] (Procedure 3) As shown in Figure 1C, an optical waveguide 2 is prepared in which the coating portion 2c and cladding portion 2b have been polished to a thickness of a few micrometers or less from the core 2a. Then, the polished surface D1 of the bent portion M2 of the optical fiber 1 and the polished surface D2 of the bent portion M3 of the optical waveguide 2 are joined to each other. Next, the positions of the cores 1a and 2a are moved relative to each other by sliding one or both polished surfaces so that the distance d between the cores 1a and 2a changes, and they are held in a position where the desired branching ratio is obtained. That is, the cores 1a and 2a are aligned with each other. This forms an optical fiber coupler 3 with a side polishing type optical fiber.

[0018] As described above, during communication, a portion of the longitudinal side surface of the optical fiber 1 is polished down to the vicinity of the core 1a. Even with polishing down to the vicinity of the core 1a, the propagation of communication light 20 within the core 1a is maintained, and communication is maintained. On the other hand, the optical waveguide 2, to which the optical fiber 1 is joined, is also polished down to the vicinity of the core 1a beforehand. Then, the polished surfaces of the optical fiber 1 and the optical waveguide 2 are joined surface-to-surface, and a so-called centering is performed to adjust their positions so that the cores 1a and 2a are closer to each other. Through this centering, the cores 1a and 2a are optically coupled, and a portion of the communication light can be moved to the adjacent core. In other words, the light input to the optical fiber 1 or the optical waveguide 2 can be combined and decomposed.

[0019] By forming an optical fiber coupler 3 using such side-polished optical fibers 1, it is possible to continue providing the specified service to the user without interrupting communication before construction, even when constructing a new route by connecting to an existing route. Furthermore, unlike communication networks with existing optical splitters, there are no restrictions on the insertion location of the new optical fiber.

[0020] Next, a method for adjusting the optical characteristics of the optical fiber coupler 3 according to this embodiment will be described. Figure 2 is a diagram showing a first configuration example for adjusting the optical characteristics of the optical fiber coupler 3. The optical fiber 1 is connected to a communication network installed between an OLT (Optical Line Terminal) 4, which is a PON (Passive Optical Network) transmission device, and an ONU (Optical Network Unit) 5, which is also a transmission device. In the PON system, time-division multiplexed communication and time-division multiple access communication are performed.

[0021] As described above, the optical fiber coupler 3 is composed of an optical fiber 1 and an optical waveguide 2, each of which has been side-polished. As shown in Figure 2, the optical fiber coupler 3 has four ports f1, f2, g1, and g2. Of these ports, ports f1 and f2 are composed of the optical fiber 1, and ports g1 and g2 are composed of the optical waveguide 2. That is, port g1 is provided as one end of the optical waveguide 2, and port g2 is provided as the other end of the optical waveguide 2. Furthermore, with respect to the junction surface (optical coupling portion) of the optical fiber 1 and the optical waveguide 2 in the direction of light propagation, ports f1 and g1 are located on one side of the optical fiber coupler 3, and ports f2 and g2 are located on the other side of the optical fiber coupler 3.

[0022] An OLT 4 is connected to the optical fiber 1. A blocking filter 7 is inserted between the OLT 4 and the optical fiber coupler 3. The blocking filter 7 is made of, for example, FBG (Fiber Bragg Grating) or a dielectric multilayer film, and blocks unwanted light propagating toward the OLT 4 (for example, light from the test light source 12 in the third configuration example). A PON power meter (first power meter) 8 is connected to port g1 of the optical fiber coupler 3. The PON power meter 8 is a power meter that can measure the optical power of communication light output in bursts from a transmission device such as an ONU (for more information on PON power meters, see, for example, the following URL: https: / / www.optoscience.com / our-vendors / exfo / handheld / PPM-350D.html). Note that the power meter (first power meter) connected to port g1 is not limited to a PON power meter, as long as it can measure the optical power of the communication light mentioned above.

[0023] An optical splitter 6, a type of optical multiplexer / demultiplexer, is connected to port g2 of the optical fiber coupler 3. An ONU 5 and an optical power meter (second power meter) 9 are connected to the optical splitter 6. The communication light (second communication light) 20 output from the OLT 4 propagates through the optical fiber 1, passes through the optical fiber coupler 3 and the optical splitter 6, and is received by the ONU 5. The communication light 20 output from the OLT 4 propagates through the optical fiber 1, passes through the optical fiber coupler 3 and the optical splitter 6, and the optical power of the communication light 20 (second optical power) is measured by the optical power meter 9.

[0024] A PON power meter 8 is connected to one end of the optical waveguide 2 (i.e., port g1), and an ONU 5 is connected to the other end of the optical waveguide 2 (i.e., port g2) via an optical splitter 6. A communication light (first communication light) 22 is output from the ONU 5. The communication light 22 passes through the optical splitter 6 and the optical fiber coupler 3, and its optical power is measured by the PON power meter 8 as the first optical power. The insertion loss of the optical fiber coupler 3 is measured by measuring the optical power of the communication light 22 output from the ONU 5 using the PON power meter 8 before alignment. In the PON system, the communication light 22 output from the ONU 5 is output in bursts, so the PON power meter 8 is used to measure the optical power.

[0025] Next, the alignment method for the optical fiber 1 and the optical waveguide 2 for optical multiplexing and demultiplexing will be explained. The alignment device 16 shown in Figure 1C is used to adjust the positions of the two. The alignment device 16 is connected to a control unit (not shown) configured by a computer or the like, and the control unit performs calculations and controls such as estimation based on the measured values ​​obtained from each measuring device. First, while measuring the optical power of the communication light 20 output from the OLT 4 with the optical power meter 9, alignment (second alignment) is performed before performing the first alignment described later. The optical power to be received by the ONU 5 is estimated from the optical power measured by the optical power meter 9 (i.e., the second optical power). By measuring the insertion loss of each port of the optical splitter 6 in advance, it is possible to estimate the optical power to be received by the ONU 5 from the measured value of the optical power meter 9.

[0026] While estimating the received light power of the ONU 5 using the optical power meter 9, the system continues to adjust until the measured optical power (second optical power) exceeds a predetermined value (threshold). This predetermined value is the value at which the minimum received light power of the ONU 5 is estimated. When the ONU 5 receives communication light 20 that is equal to or greater than the minimum received light power, it outputs communication light 22.

[0027] Next, the first alignment (first alignment) is performed while measuring the communication optical fiber 22 output from the ONU 5 using the PON power meter 8. The insertion loss of the optical fiber coupler 3 is measured from the optical power measured by the PON power meter 8. The insertion loss can be measured by pre-measuring the optical power of the communication optical fiber 22 output from the ONU 5, the insertion loss of each port of the optical splitter 6, and the loss of the optical fiber between the ONU 5 and the PON power meter 8.

[0028] The measurable insertion loss is the insertion loss from port g2 to port g1 of the optical fiber coupler 3. By measuring the insertion loss, it is possible to estimate the branching ratio from port g2 to port f1 of the optical fiber coupler 3. For example, if the insertion loss is AdB, the branching ratio is given by equation (1): Branching ratio = 1 - 10 Ａ／１０ ... (1)

[0029] In this way, by connecting the PON power meter 8 to the optical fiber coupler 3 and analyzing the measurement results, the branching ratio and insertion loss, which are optical characteristics of the optical fiber coupler 3, can be estimated or measured. Then, alignment is performed so that the estimated branching ratio becomes the desired branching ratio. That is, alignment is performed between the optical fiber 1 and the optical waveguide 2 based on the estimated branching ratio. This is how the optical fiber coupler 3 is manufactured. During this manufacturing process, communication via the optical fiber 1 is not interrupted. In other words, according to this embodiment, when manufacturing an optical fiber coupler 3 on an optical fiber 1 that is in the process of communicating, the branching ratio and insertion loss, which are optical characteristics, can be adjusted without interrupting communication.

[0030] Figure 3 shows a second configuration example for adjusting the optical characteristics of the optical fiber coupler 3. As shown in Figure 3, a 2x2 optical coupler 10, a type of optical multiplexer / demultiplexer, may be used instead of the optical splitter 6. By connecting a PON power meter (third power meter) 8' to the 2x2 optical coupler 10, the PON power meter 8' measures the optical power of the communication light 22 from the ONU 5 via the 2x2 optical coupler 10 as the third optical power. This makes it possible to estimate the optical power of the input light of the communication light 22 from the ONU 5 to the optical fiber coupler 3. That is, the insertion loss can be calculated based on the optical power measured by the PON power meter 8' and the optical power measured by the PON power meter 8. By pre-measuring the insertion loss of each port of the 2x2 optical coupler 10, the optical power of the input light of the communication light 22 from the ONU 5 to the optical fiber coupler 3 can be estimated. This eliminates the need to pre-measure the optical power of the communication light 22 from the ONU 5.

[0031] Figure 4 shows a third configuration example for adjusting the optical characteristics of the optical fiber coupler 3. As shown in Figure 4, a 1x3 optical splitter 11, which is a type of optical multiplexer / demultiplexer, may be used instead of the optical splitter 6. By connecting the test light source 12 to the 1x3 optical splitter 11, connecting the WDM coupler 13 to the optical fiber coupler 3, and connecting the optical power meter 9' to the WDM coupler 13, the insertion loss of the optical fiber coupler 3 at the wavelength of the test light can be measured.

[0032] By pre-measuring the insertion loss of each port of the 1x3 optical splitter 11, the optical power of the test light 23 from the test light source 12 to the optical fiber coupler 3 is estimated. By pre-measuring the insertion loss of each port of the WDM coupler 13, the optical power of the test light 23 output from the optical fiber coupler 3 is estimated. This allows the insertion loss of the test light 23 in the optical fiber coupler 3 to be estimated. Furthermore, the branching ratio can be estimated from the estimated insertion loss using Equation 1.

[0033] The WDM coupler 13 combines and decomposes the wavelengths of the test light 23 output from the test light source 12 and the communication light 22 output from the ONU 5. The branching ratio and insertion loss of the communication light 20 from the OLT 4 can be estimated from the branching ratio and insertion loss of the wavelengths of the test light 23 and the communication light 22. The branching ratio is generally given by equation (2): Branching ratio = sin ２ (κL) ... (2) κ is the coupling coefficient and L is the working length. Generally, the coupling coefficient κ increases at longer wavelengths, so when the working length L is short, the branching ratio increases with longer wavelengths.

[0034] Generally, the test wavelength is 1650 nm, which is longer wavelength than the communication light wavelengths 20 and 22 of the transmission devices OLT 4 and ONU 5. Therefore, for example, if the wavelength of communication light 20 of OLT 4 is 1490 nm and the wavelength of communication light 22 of ONU 5 is 1310 nm, the branching ratio of the wavelength of test light 23 and the wavelength of communication light 22 of ONU 5 can be estimated from equation (1), and thus the branching ratio of the wavelength of communication light 20 of OLT 4 can be estimated to be between the estimated branching ratio of the wavelength of test light 23 and the wavelength of communication light 22 of ONU 5.

[0035] Figure 5 shows a fourth configuration example for adjusting the optical characteristics of the optical fiber coupler 3. As shown in Figure 5, a bandpass filter 14 may be installed between the optical fiber coupler 3 and the PON power meter 8. The communication light 22 passes through the bandpass filter 14 between the optical fiber coupler 3 and the PON power meter 8. When multiple optical fiber couplers 3 are installed on the optical fiber 1 and multiple ONUs 5 are installed, the optical power of the communication light 22 output from the multiple ONUs 5 is received by the PON power meter 8. Therefore, the bandpass filter 14 may be used to allow only the communication light 22 output from the ONU 5 connected to the optical fiber coupler 3 to which the bandpass filter 14 is connected to to pass through.

[0036] Figure 6 shows a fifth configuration example for adjusting the optical characteristics of the optical fiber coupler 3. Figure 7 shows a sixth configuration example for adjusting the optical characteristics of the optical fiber coupler 3. As shown in Figure 6, the bandpass filter 14 and the 2x2 optical coupler 10 may be combined. That is, the 1x2 optical splitter 6 in the fourth configuration example may be replaced with the 2x2 optical coupler 10 and PON power meter 8' in the second configuration example. Also, as shown in Figure 7, by connecting a spectrum analyzer 15 to the optical fiber coupler 3 instead of the PON power meter 8, the wavelength of the communication light 22 output from the ONU 5 can be measured. The wavelength transmitted through the bandpass filter 14 can be confirmed.

[0037] So far, we have described how to measure and estimate the optical properties of the optical fiber coupler 3. Next, we will describe how to adjust the optical properties of the optical fiber coupler 3 using the aligner 16. For example, by installing the aligner 16 in the optical waveguide 2 for optical multiplexing and demultiplexing of the optical fiber coupler 3 as shown in Figure 1, the optical properties of the optical fiber coupler 3 can be adjusted on-site. This is because it is possible to change the distance between the cores of the optical fiber 1 and the optical waveguide 2 for optical multiplexing and demultiplexing, as well as the length of the coupling.

[0038] When adjusting the optical properties of the optical fiber coupler 3 on-site, the adjustment method of this embodiment can be used to align the side-polished optical fibers of the optical fiber coupler 3 while measuring the optical properties, thereby aligning the optical fiber coupler 3 to the desired optical properties. The aligner 16 may be a manually operated moving stage or an electrically operated moving stage. Furthermore, the aligner 16 may be composed of a combination of multiple moving stages so that it can align multiple axes (the x, y, and z axes in Euclidean space and the rotation axes with respect to the xy, yz, and zx planes).

[0039] Furthermore, it is desirable to combine the aligner 16 with a rotating stage. Alternatively, the optical characteristics of the optical fiber coupler 3 may be displayed on a display or other indicator, and the optical characteristics may be adjusted using the aligner 16 while observing the displayed value. Alternatively, the motorized stage or rotating stage may be controlled by a program to measure and estimate the optical characteristics of each coordinate, obtain the coordinate that is closest to the desired optical characteristics from among the optical characteristics of each coordinate, and automatically adjust the optical characteristics by controlling the motorized stage or rotating stage to that coordinate.

[0040] 1 Optical fiber 2 Optical waveguide 3 Optical fiber coupler 4 OLT (Transmission device) 4A, 4B Transmission device 5, 5' ONU (Transmission device) 6 1x2 optical splitter 7 Blocking filter 8, 8' PON power meter 9, 9' Optical power meter 10 2x2 coupler 11 1x3 optical splitter 12 Test light source 13 WDM coupler 14 Bandpass filter 16 Aligner 20 Communication light 20a Leakage light 21 Communication light 22 Communication light f1, f2 Ports g1, g2 Ports M1-M3 Bending section

Claims

1. A method for adjusting the optical characteristics of an optical fiber coupler comprising an optical fiber that is in a communication-ready state and has been side-polished, and an optical waveguide that has been side-polished and is optically coupled to the optical fiber, wherein a first power meter is connected to one end of the optical waveguide, and a transmission device is connected to the other end of the optical waveguide via an optical multiplexer / demultiplexer, and a first communication light is output from the transmission device; the optical power of the first communication light is measured by the first power meter as the first optical power; the insertion loss of the optical fiber coupler is calculated based on the first optical power; the branching ratio is estimated from the calculated insertion loss; and a first alignment is performed between the optical fiber and the optical waveguide based on the estimated branching ratio.

2. A method for adjusting the optical characteristics of an optical fiber coupler according to claim 1, wherein the second communication light propagated from the optical fiber through the optical multiplexer is measured as a second optical power by a second power meter, and a second alignment is performed between the optical fiber and the optical waveguide until the second optical power reaches a predetermined value, before performing the first alignment.

3. A method for adjusting the optical characteristics of an optical fiber coupler according to claim 1 or 2, comprising measuring the optical power of the first communication optical fiber from the transmission device via the optical multiplexer / demultiplexer as the third optical power using a third power meter, and calculating the insertion loss based on the measured third optical power and the first optical power.

4. The optical characteristic adjustment method for an optical fiber coupler according to claim 3, wherein the first communication light output from the transmission device passes through a bandpass filter between the optical fiber coupler and the first power meter.

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