Optical functional devices

Abstract

The present invention provides an optical functional device in which both an input optical fiber and an output optical fiber are arranged on one surface of a housing, thereby maintaining low crosstalk between input and output light and achieving excellent optical characteristics. The optical functional device comprises a housing that houses an optical functional element, an input optical fiber, and an output optical fiber, wherein both the input optical fiber and the output optical fiber are fixed to one surface of the housing. The optical functional device comprises a first reflection surface that reflects input light emitted from the input optical fiber toward the direction of an output light path; a second reflection surface that reflects the input light reflected by the first reflection surface toward the optical functional element; and a third reflection surface that reflects output light from the optical functional element away from the optical axis of the input optical fiber. The optical axis of leakage light that is reflected by the first reflection surface and then passes through the second reflection surface, or an extension line obtained by extending the optical axis within an optical propagation medium through which the leakage light can propagate, does not include a portion that coincides with the optical axis of the output light reflected by the third reflection surface.

Description

Technical Field

[0001] The present invention relates to an optical functional device that performs an optical function such as light modulation, and more particularly to an optical functional device in which both an input optical fiber and an output optical fiber are arranged on one surface of a housing. Background Art

[0002] High-speed and high-capacity optical fiber communication systems often utilize optical transmission devices incorporating waveguide-type optical elements (hereinafter referred to as optical modulators) that perform optical modulation. Among these, optical modulators using LiNbO3 (hereinafter referred to as LN), which exhibits an electro-optical effect, as substrates offer low optical loss and broadband optical modulation characteristics compared to modulators using semiconductor materials such as indium phosphide (InP), silicon (Si), or gallium arsenide (GaAs). Consequently, these optical modulators are widely used in high-speed and high-capacity optical fiber communication systems.

[0003] The modulation method in the optical fiber communication system has been influenced by the trend of increasing transmission capacity in recent years, and multi-level modulation such as QPSK (Quadrature Phase Shift Keying) and DP-QPSK (Dual Polarization-Quadrature Phase Shift Keying) and the transmission form using polarization multiplexing in multi-level modulation have become the mainstream.

[0004] The recent rapid spread of internet services has led to a further increase in the volume of communication information, and research on the continued advancement of high-speed, high-capacity optical communication systems is also progressing. In optical communication systems exceeding 400Gbps, the symbol rate of the modulated signal reaches 64Gbaud, 96Gbaud, or even higher. This leads to significant degradation of the modulated signal due to connections through the DSP, modulator driver, and high-frequency interfaces between modulators. Meanwhile, the demand for device miniaturization remains constant. In addition to miniaturizing the optical modulator itself, there is also progress in integrating the electronic circuitry and optical modulator into a single housing, creating an optical modulator device.

[0005] For example, a solution has been proposed in which an optical modulator and a high-frequency driver amplifier for driving the optical modulator are integrated and housed in a housing, and the optical input and output parts are arranged in parallel on one surface of the housing, thereby reducing the degradation of the modulation signal caused by the high-frequency connection and realizing a small, integrated optical modulator.

[0006] As such an optical modulator, there has been known a structure in which an input optical fiber for guiding input light into a housing and an output optical fiber for guiding output light from an optical modulator element housed in the housing to the outside of the housing are arranged side by side at two positions on one surface of the housing via a group of independent mechanical components (holding components) (see patent document 1).

[0007] In the optical modulation module described in Patent Document 1, an input optical fiber and an output optical fiber, arranged on one surface of a housing housing an optical modulation element, are optically coupled to the optical modulation element via a spatial optical system interposed between lenses. Furthermore, in this optical modulation module, the arrangement of components within the housing is devised to effectively secure the path of light propagating within the space within the housing, thereby miniaturizing the housing housing the optical modulation element and electronic circuitry.

[0008] However, in this optical modulation module, the input and output optical fibers are arranged on one surface of the housing. Meanwhile, the optical modulation element used within the housing has a light input portion and a light output portion on two different end surfaces of the rectangular substrate forming the optical modulation element when viewed from above. Therefore, for example, the input light path from the input optical fiber to the light input portion is longer than the light path from the light output portion to the output optical fiber. Consequently, reducing the coupling loss of light from the input optical fiber to the light input portion becomes somewhat difficult. In this longer portion of the optical path, deformation of the housing due to temperature fluctuations and other factors can also lead to variations in light loss, such as tilting or deviation of the light propagation axis from its optimal position.

[0009] As a countermeasure to reducing this coupling loss, a possible approach is to arrange both the light input and light output sections of the light modulator on one end face of the substrate that forms the light modulator. However, in this case, the spatial propagation path of the input light from the input fiber and the spatial propagation path of the output light to the output fiber are mixed in the narrow space between the one end face of the substrate where the light input and light output sections are arranged and the input and output fibers installed on one surface of the housing. As a result, in this configuration, crosstalk between the input and output lights is exacerbated.

[0010] As a structure related to the above-mentioned prior art, Patent Document 2 describes a structure in which two output optical fibers arranged on one surface of a housing are optically coupled to the respective optical output ends of two optical modulators arranged opposite the two optical fibers. In the optical transmission device described in Patent Document 2, two beam-shifting prisms are used to shift the optical axes of the output lights emitted from the optical output ends of the two optical modulators in different directions, thereby increasing the distance between the optical axes. This improves the spatial separation of the two output lights, thereby suppressing the deterioration of crosstalk between the output lights. Furthermore, the distance between the two optical fibers arranged on one surface of the housing is increased, thereby improving the operability of adjusting and securing the optical fibers to the housing.

[0011] However, the structure described in Patent Document 2 is one in which two output optical fibers are arranged on a single surface of the housing, and the two output lights from the two optical modulators propagate in the same direction toward this single surface. In this structure, where the input and output optical fibers are arranged on a single surface of the housing, i.e., the input and output lights can propagate in opposite directions relative to this single surface, no measures are provided to improve crosstalk from the input light to the output optical fibers. Since the input light does not experience optical loss or modulation loss in the modulator, the intensity of the light is over 10 dB higher than that of the output light, and this effect cannot be ignored.

[0012] Patent Document 1: Japanese Patent Application Laid-Open No. 2014-167546

[0013] Patent Document 2: Japanese Patent Application Laid-Open No. 2015-172630 Summary of the Invention

[0014] Problems to be solved by the invention

[0015] In view of the above background, in an optical functional device in which both an input optical fiber and an output optical fiber are arranged on one surface of a housing that accommodates an optical waveguide element, it is required to ensure low crosstalk between input light from the input optical fiber and output light coupled to the output optical fiber to achieve good optical characteristics.

[0016] Solutions to Problems

[0017] One embodiment of the present invention comprises: an optical functional element; a housing for accommodating the optical functional element; an input optical fiber for guiding input light input to the optical functional element into the housing; and an output optical fiber for guiding output light consisting of output light from the optical functional element to the outside of the housing, wherein the input optical fiber and the output optical fiber are both fixed to one surface of the housing, and the optical functional device comprises: a first reflecting surface for reflecting the input light emitted from the input optical fiber in a direction where an optical path of the output light is located; a second reflecting surface for reflecting the input light reflected by the first reflecting surface toward the optical functional element; and a third reflecting surface for reflecting the output light from the optical functional element in a direction away from the optical axis of the input optical fiber, wherein the optical axis of leakage light that passes through the second reflecting surface after being reflected by the first reflecting surface or an extended line obtained by extending the optical axis in an optical propagation medium in which the leakage light can propagate does not include a portion that coincides with the optical axis of the output light reflected by the third reflecting surface.

[0018] According to another aspect of the present invention, a blocking body for blocking leakage light that is reflected by the first reflection surface and then passes through the second reflection surface is provided between the second reflection surface and the third reflection surface on the optical axis.

[0019] According to another embodiment of the present invention, the optical axis of the leakage light that is reflected by the first reflection surface and then passes through the second reflection surface, or the extension line of the optical axis, is separated from the optical axis of the outgoing light reflected by the third reflection surface by a distance greater than the value of the beam diameter of the leakage light.

[0020] According to another aspect of the present invention, an optical axis of the leakage light reflected by the first reflecting surface and then transmitted through the second reflecting surface and an optical axis of the outgoing light reflected by the third reflecting surface are not parallel to each other.

[0021] According to another aspect of the present invention, the third reflecting surface is not arranged on the extension line of the optical axis of the leakage light that is reflected by the first reflecting surface and then passes through the second reflecting surface.

[0022] According to another embodiment of the present invention, the optical functional element is formed of an optical waveguide formed on a substrate, and an end of the input waveguide receiving the input light and an end of the output waveguide emitting the output light are arranged on the same end surface of the substrate.

[0023] Effects of the Invention

[0024] According to the present invention, in an optical functional device in which both an input optical fiber and an output optical fiber are arranged on one surface of a housing that accommodates an optical waveguide element, crosstalk between input light from the input optical fiber and output light coupled to the output optical fiber can be kept low, thereby achieving excellent optical characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a diagram showing the structure of the optical modulation device according to the first embodiment of the present invention.

[0026] Figure 2 yes Figure 1 A detailed partial view of section A of the light modulation device shown.

[0027] Figure 3 This is a partial detailed view of the light modulation device according to the first modification of the first embodiment.

[0028] Figure 4 This is a partial detailed view of the light modulation device according to the second modified example of the first embodiment.

[0029] Figure 5 This is a partial detailed view of the light modulation device according to the third modified example of the first embodiment.

[0030] Figure 6 This is a partial detailed view of the light modulation device according to the fourth modified example of the first embodiment.

[0031] Figure 7 It is a diagram showing the structure of an optical modulation device according to a second embodiment of the present invention.

[0032] Figure 8 yes Figure 7 A detailed partial view of section B of the light modulation device shown.

[0033] Figure 9 yes Figure 8 The section B is shown along the line IX-IX.

[0034] Figure 10 This is a partial detailed view of the light modulation device according to the first modified example of the second embodiment.

[0035] Figure 11 This is a partial detailed view of the light modulation device according to the second modification of the second embodiment.

[0036] Label Description

[0037] 100, 100-1, 100-2, 100-3, 100-4, 500, 500-1, 500-2…Optical modulator, 102…Optical modulator element, 104…Casing, 105…Surface, 106…Input optical fiber, 107…Bottom, 108…Output optical fiber, 110…Drive circuit, 112…Circuit board, 114, 120, 122…Pins, 116, 118…Relay board, 124, 126…Terminator, 128…Light input and output surfaces, 130…Microlens array, 132…Polarization combiner, 134, 134-1, 134-2, 134-3, 134-4, 136, 534, 536, 536-1, 536-2…Beam deflection prism, 140, 148…Ferrules, 142, 150 ...sleeve, 144, 152, 200a, 200b, 200c...lens, 146, 154...lens holder, 202...input waveguide, 204a, 204b...output waveguide, 210, 210-1, 210-2, 210-3, 210-4, 212, 212-1, 212-2, 212-3, 212-4, 220, 222, 22 4. 610, 612, 620, 620-1, 620-2, 622, 622-1, 622-2, 920, 922, 924…reflecting surface, 214, 216, 218, 314, 414, 614, 616, 816, 914, 916, 918, 1016…optical axis, 400…blocking object, 932…half-wavelength plate, 936…prism. DETAILED DESCRIPTION

[0038] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0039] [First embodiment]

[0040] First, a first embodiment of the present invention will be described. Figure 1 1 is a diagram showing the structure of an optical functional device, that is, an optical modulation device, which is a first embodiment of the present invention. Figure 1 In FIG. 1 , the right and left figures are respectively a top view and a side view of the light modulator 100. Figure 2 yes Figure 1 A detailed view of section A in the top view on the right.

[0041] The optical modulator device 100 includes, for example, an optical functional element that performs optical modulation, namely, an optical modulator 102, a shell 104 that accommodates the optical modulator 102, an input optical fiber 106 that guides input light to the optical modulator 102, and an output optical fiber 108 that guides the modulated light (modulated light) emitted from the optical modulator 102 to the outside of the shell 104.

[0042] The housing 104 is, for example, a hexahedron having a substantially rectangular shape with a long side of approximately 30 mm and a short side of approximately 12 mm when viewed from above. An input optical fiber 106 and an output optical fiber 108 are arranged on one surface 105, whose short side, as shown on the left side of the figure, is a side thereof. The input optical fiber 106 and the output optical fiber 108 are optically coupled to the light modulator 102 via windows (not shown) provided on the surface 105 of the housing 104.

[0043] The input optical fiber 106 and the output optical fiber 108 are arranged side by side at two independent locations on one surface 105 of the housing 104, respectively, by two different sets of holding members. The input optical fiber 106 is fixed to the housing 104 by a ferrule 140, a flanged sleeve 142, and a lens holder 146 with a lens 144 fixed therein, which constitute one set of holding members. Similarly, the output optical fiber 108 is fixed to the housing 104 by a ferrule 148, a flanged sleeve 150, and a lens holder 154 with a lens 152 fixed therein, which constitute the other set of holding members.

[0044] The housing 104 also houses a circuit substrate 112, which is equipped with a drive circuit (driver circuit) 110 for operating the light modulator 102. The drive circuit 110 is composed of an amplifier for amplifying the modulation signal, but in addition, it may also include a signal processing IC (DSP, digital signal processing). The drive circuit does not necessarily have to be mounted on the substrate. The circuit substrate can be arranged and connected around the IC of the drive circuit. The IC can be mounted on the housing directly or through a heat dissipation component for heat dissipation. Moreover, it can be a ceramic package that integrates the circuit substrate and the housing. The housing 104 is also provided with a plurality of pins 114 for receiving modulation signals supplied from the outside. The power supply and control signal of the drive circuit are connected to pins 120 and 122 provided on the side wall of the housing 104. Housing 104 houses relay boards 116 and 118 for relaying electrical signals output from a monitor light-receiving element (not shown) included in light modulator 102. Sidewalls of housing 104 are provided with pins 120 and 122 for outputting these electrical signals to the outside of housing 104. These pins 120 and 122 may be located on only one side.

[0045] The optical modulator 102 is comprised of, for example, an optical waveguide (dashed lines in the figure) formed on an LN substrate and a plurality of electrodes (not shown) that control the light waves propagating through the waveguide. These electrodes form a high-frequency transmission line. A high-frequency signal output by the driver circuit 110 is input to one end of these electrodes, and terminators 124 and 126, each having approximately the same impedance as the transmission line, are connected to the other ends. As a result, the high-frequency signal propagates through these electrodes as a traveling wave, modulating the light input to the optical modulator 102.

[0046] The two relay boards 116 and 118 are positioned on the upper and lower sides of the housing 104, respectively, across the optical modulator 102, for connection to pins 120 and 122 provided on the opposing upper and lower sidewalls of the housing 104. Furthermore, the two terminators 124 and 126 are also positioned on the upper and lower sides of the housing 104, respectively, across the optical modulator 102, for reasons such as ease of placement of the electrodes on the LN substrate. Furthermore, to prevent degradation and attenuation of high-frequency signals and minimize inter-port characteristic variations, the multiple high-frequency wiring from the pins 114 to the modulator is preferably arranged with short, approximately center-symmetrical wiring. Consequently, to ensure sufficient space for each of the relay boards 116 and 118 and each of the terminators 124 and 126 on the upper and lower sides of the optical modulator 102, the optical modulator 102 is positioned, for example, at the center of the housing 104 in the width direction (vertical direction).

[0047] The optical modulator 102 is a modulator that performs DP-QPSK modulation, for example. A single linearly polarized light is inputted from the light incident / exit surface 128, which is the end surface on the left side of the figure. This input light is incident on the input waveguide 202 ( Figure 2 ), it is folded back and branched into two light waves in the optical modulator 102 and modulated respectively. The modulated linear polarized light, i.e., the two output lights, are emitted from the two output waveguides 204a and 204b whose ends are set at the light incident and output surfaces 128 respectively. That is, the optical modulator 102 is provided with the end of the input waveguide 202 for receiving the input light and the end of the output waveguides 204a and 204b for emitting the output light on the same end surface (specifically, the light incident and output surfaces 128) of the substrate on which the optical waveguide is formed. The light incident and output surfaces 128 of the optical modulator 102 are also provided with a lens 200a, 200b, 200c ( Figure 2 ) of the micro lens array 130.

[0048] In optical functional elements such as the optical modulator 102, which are constructed using optical waveguides formed on a substrate, the waveguide spacing between the input waveguide 202 and the output waveguides 204a and 204b at the light input / output surface 128 is typically between several hundred μm and several millimeters, making it difficult to arrange the input optical fiber 106 and the output optical fiber 108 with the same spacing on the surface 105 of the housing 104. Furthermore, as described above, the optical modulator 102 is typically arranged in the center of the housing 104 in its width direction. Meanwhile, the input optical fiber 106 and the output optical fiber 108 are secured to the lens holder and ferrule by welding at multiple points around their periphery using methods such as YAG welding. This facilitates welding if the spacing is wide. Furthermore, to mitigate the effects of deformation of the housing 104 caused by fluctuations in ambient temperature, the optical fibers are typically arranged symmetrically with respect to the centerline of the housing 104 in its width direction.

[0049] Therefore, in the optical modulator 100, the optical axes of the input optical fiber 106 and the output optical fiber 108 are shifted in the translation direction, and two beam shifting prisms 134 and 136 are used to make the distance between the optical axes close to the same level as the distance between the waveguides. The beam shifting prisms 134 and 136 are, for example, located at the bottom surface 107 ( Figure 1 (left figure) The input light from the input optical fiber 106 and the output light to the output optical fiber 108 are arranged in a parallel plane in a manner shifted along the translation direction.

[0050] Reference Figure 2 After the input light from the input optical fiber 106 is collimated by the lens 144, it is shifted in the translational direction toward the optical axis of the output optical fiber 108 by the beam deflection prism 134. The light is then focused by the lens 200a of the microlens array 130 and incident on the input waveguide 202. The beam deflection prism 134 is composed of two reflective surfaces 210 and 212. The reflective surface 210 corresponds to the first reflective surface, which reflects the input light emitted from the input optical fiber 106 toward the optical path of the output light. The reflective surface 212 corresponds to the second reflective surface, which reflects the input light reflected by the reflective surface 210 toward the optical modulation element 102, which serves as an optical functional element.

[0051] Furthermore, the two linearly polarized outgoing beams emitted from the output waveguides 204a and 204b of the optical modulator 102 are collimated by the two lenses 200b and 200c of the microlens array 130 and then combined into one output beam by the polarization combiner 132. The polarization combiner 132 is composed of, for example, a half-wavelength plate and a polarization combining prism.

[0052] The output light from the polarization combiner 132 is shifted in the translational direction toward the optical axis of the output optical fiber 108 by the beam deflection prism 136. The light is then focused by the lens 152 and coupled to the output optical fiber 108. The beam deflection prism 136 is comprised of two reflective surfaces 220 and 222. The reflective surface 220 corresponds to a third reflective surface that reflects the outgoing light from the optical modulation element 102, which serves as an optical functional element, away from the optical axis of the input optical fiber 106.

[0053] Furthermore, in particular, the optical modulator 100 of this embodiment is configured so that the optical axis 214 of the leakage light, which is reflected by the one reflective surface 210 of the beam deflecting prism 134 in the direction of the optical path of the outgoing light and passes through the other reflective surface 212 of the beam deflecting prism 134, or a line obtained by extending the optical axis 214 within the optical propagation medium through which the leakage light propagates (hereinafter simply referred to as "within the optical propagation medium"), does not include a portion that coincides with the optical axis of the outgoing light reflected by the reflective surface 220 of the beam deflecting prism 136. The optical propagation medium includes solid media such as glass, gaseous media, and vacuum space through which the leakage light propagates, and does not include objects such as metal that do not transmit the leakage light.

[0054] Typically, at the interface between two different media through which light propagates (e.g., a light-reflecting surface or a light-transmitting surface), a portion of incident light on the interface is split and propagates in a direction different from the rest due to slight contamination or irregularities in the smoothness of the interface. Consequently, light leaks through reflective surfaces such as reflective surfaces 210, 212, 220, and 222, generating stray light that degrades crosstalk between input and output light.

[0055] In contrast, in the optical modulator 100 having the above-described structure, leakage light that passes through the reflective surface 212 and travels in the direction of the output light path does not include a portion whose optical axis 214 coincides with the optical axis 216 of the output light generated by the reflective surface 220 and traveling in the direction away from the input optical fiber 106. Therefore, this leakage light does not mix with the output light reflected by the reflective surface 220. Consequently, in the optical modulator 100, deterioration of crosstalk (hereinafter referred to as simply crosstalk) between the input light and the output light caused by the introduction of the light beam deflection prisms 134 and / or 136 can be effectively suppressed.

[0056] To effectively suppress the increase in crosstalk, the distance d1 between the optical axis 214 of the leakage light in the input light that passes through the reflective surface 212, or a line extending the optical axis 214 within the light propagation medium, and the optical axis 216 of the output light reflected by the reflective surface 220 in the same direction as described above, is preferably greater than the beam diameter of the leakage light. Specifically, the optical axis 214 of the leakage light that passes through the reflective surface 212, which serves as the second reflective surface, after being reflected by the reflective surface 210 (the first reflective surface), is preferably separated from the optical axis 214 (the optical axis 214) or a line extending the optical axis 214 within the light propagation medium, by a distance d1 greater than the beam diameter of the leakage light. To avoid redundancy, references such as "the reflective surface 210 (the first reflective surface)" will be referred to simply as "the first reflective surface 210."

[0057] Next, a modification of the optical modulation device 100 according to the above-described embodiment will be described.

[0058] <First Modification of First Embodiment>

[0059] Next, a first modification of the optical modulation device 100 will be described. Figure 3 This is a diagram showing the structure of the optical modulator 100-1 according to the first modified example, and corresponds to the structure of the A portion of the optical modulator 100. Figure 2 It should be noted that the optical modulation device 100-1 Figure 3 The unrecorded part has the same Figure 1 The same structure of the optical modulation device 100 shown in FIG. Figure 1 Furthermore, in Figure 3 In, about Figure 2 The same structural elements as those of the optical modulation device 100 are used. Figure 2 The same reference numerals as in Figure 2 Description.

[0060] Figure 3 The optical modulation device 100-1 shown has Figure 1 and Figure 2 The optical modulator 100 shown has the same structure as the optical modulator 100, but differs in that beam deflecting prisms 134-1 and 136-1 are used instead of beam deflecting prisms 134 and 136. Beam deflecting prisms 134-1 and 136-1 have the same structure as beam deflecting prisms 134 and 136, but their left-right dimension (the distance between the light input and output surfaces facing left and right in the figure) is shorter than that of beam deflecting prisms 134 and 136.

[0061] The beam deflecting prism 134-1 includes reflecting surfaces 210-1 and 212-1, which correspond to the first and second reflecting surfaces, respectively, similar to the reflecting surfaces 210 and 212 of the beam deflecting prism 134. Similarly, the beam deflecting prism 136-1 includes reflecting surfaces 220-1 and 222-1, which correspond to the reflecting surfaces 220 and 222 of the beam deflecting prism 136. Here, the reflecting surface 220-1 corresponds to the third reflecting surface.

[0062] Figure 3 The paths of incident light and outgoing light in the optical modulation device 100-1 are shown in FIG. Figure 2 The optical modulator 100 shown is the same as that shown in FIG. However, as described above, the distance between the light incident and exit surfaces of the beam deflecting prisms 134-1 and 136-1 is smaller than that of the beam deflecting prisms 134 and 136, respectively. Therefore, the beam deflecting prisms 134-1 and 136-1 are arranged in the housing 104 so that the positions on the left and right sides are different from each other.

[0063] Thus, in the optical modulator 100 - 1 , similarly to the optical modulator 100 , leakage light of input light that passes through the reflective surface 212 - 1 is not mixed with output light reflected by the reflective surface 220 - 1 , thereby effectively suppressing deterioration of crosstalk.

[0064] Furthermore, in the optical modulator 100-1, the beam deflecting prisms 134-1 and 136-1 are arranged so as to be offset from one another in the horizontal direction shown in the figure. Therefore, the beam deflecting prism 136-1 is not present on the extension line of the optical axis 214 of the leaked light that passes through the reflective surface 212-1, and no other optical components are present. Consequently, the optical modulator 100-1 also avoids the generation of scattered light caused by the leaked light entering or reflecting off other optical components, thereby further suppressing crosstalk compared to the optical modulator 100.

[0065] <Second Modification of First Embodiment>

[0066] Next, a second modification of the optical modulation device 100 will be described. Figure 4 This is a diagram showing the structure of the optical modulator 100-2 according to the second modified example, and is equivalent to the diagram showing the structure of the A portion of the optical modulator 100. Figure 2 It should be noted that the optical modulation device 100-2 Figure 4 The unrecorded part has the same Figure 1 The same structure of the optical modulation device 100 shown in FIG. Figure 1 Furthermore, in Figure 4 In, about Figure 2 The same structural elements as those of the optical modulation device 100 are used. Figure 2The same reference numerals as in Figure 2 Description.

[0067] Figure 4 The optical modulation device 100-2 shown has Figure 1 and Figure 2 The optical modulator 100 shown has the same structure as the optical modulator 100, but differs in that a beam deflecting prism 134-2 is used instead of the beam deflecting prism 134. The beam deflecting prism 134-2 has the same structure as the beam deflecting prism 134, and includes reflecting surfaces 210-2 and 212-2, which correspond to the first and second reflecting surfaces, respectively, similar to the reflecting surfaces 210 and 212.

[0068] However, unlike beam deflecting prism 134, beam deflecting prism 134-2 is tilted clockwise relative to beam deflecting prism 136. That is, optical modulator 100-2 is configured such that the optical axis 314 of leakage light reflected by first reflective surface 210 and then transmitted through second reflective surface 212 is non-parallel to the optical axis of third reflective surface 220, but has a certain angle θ that is not zero. Thus, in optical modulator 100-2, similar to optical modulator 100, the optical axis 314 of leakage light transmitted through second reflective surface 212-2, of input light reflected by first reflective surface 210-2 in the direction of the optical path of outgoing light, or a line obtained by extending this optical axis 314 within the optical propagation medium, does not include a portion that coincides with the optical axis 216 of outgoing light reflected by third reflective surface 220.

[0069] Through the above structure, in the optical modulator 100-2, as in the optical modulator 100, the above leakage light will not be mixed with the output light reflected by the reflecting surface 220-1, thereby effectively suppressing the deterioration of crosstalk caused by the introduction of the beam deflection prism 134 and / or 136.

[0070] <Third Modification of First Embodiment>

[0071] Next, a third modified example of the optical modulation device 100 will be described. Figure 2 In the illustrated optical modulator 100, the reflective surfaces 210 and 212, serving as the first and second reflective surfaces, constitute one beam deflecting prism 134, while the reflective surface 220, serving as the third reflective surface, constitutes the other beam deflecting prism 136. However, the first, second, and third reflective surfaces do not necessarily need to constitute the beam deflecting prisms as in this embodiment. These reflective surfaces can constitute any optical component, and the arrangement of such optical components is also arbitrary. Furthermore, if there are multiple outgoing light beams emitted from an optical functional element (e.g., the optical modulator 102), multiple third reflective surfaces may be provided to correspond to each of the outgoing light beams.

[0072] The optical modulation device 100 - 3 of the third modified example shown below is an example thereof, and a plurality of third reflecting surfaces constitute a multi-functional prism having both a beam deflection function and a polarization combining function.

[0073] Figure 5 This is a diagram showing the structure of the optical modulator 100-3 according to the third modified example, and is equivalent to the diagram showing the structure of the A portion of the optical modulator 100. Figure 2 It should be noted that the optical modulation device 100-3 Figure 5 The unrecorded part has the same Figure 1 The same structure of the optical modulation device 100 shown in FIG. Figure 1 Furthermore, in Figure 5 In, about Figure 2 The same structural elements as those of the optical modulation device 100 are used. Figure 2 The same reference numerals as in Figure 2 Description.

[0074] Figure 5 The optical modulation device 100-3 shown has Figure 1 and Figure 2 The optical modulator 100 shown in FIG. 1 has the same structure as the optical modulator 100, but differs in that a beam deflecting prism 134-3 is used instead of the beam deflecting prism 134, and a prism 936 is used instead of the beam deflecting prism 136. Beam deflecting prism 134-3 has the same structure as beam deflecting prism 136, and includes reflective surfaces 210-3 and 212-3, which correspond to the first and second reflective surfaces, respectively, similar to the reflective surfaces 210 and 212 of beam deflecting prism 134. However, the position of beam deflecting prism 134-3 within the housing 104 is shifted upward, as shown, compared to beam deflecting prism 134.

[0075] Prism 936, unlike beam deflection prism 136, has both beam deflection and polarization combining functions. Specifically, prism 936 includes two reflective surfaces, 920 and 924, which correspond to third reflective surfaces. Reflective surface 920 is a total reflection surface, while reflective surface 924 is composed of a polarization combining film formed, for example, on the interface between two glass panels. Furthermore, these reflective surfaces 920 and 924 reflect the two linearly polarized light beams that constitute the outgoing light. Specifically, reflective surface 920 reflects one linearly polarized light beam emitted from output waveguide 204a, while reflective surface 924 transmits this linearly polarized light beam and reflects the other linearly polarized light beam emitted from output waveguide 204b, whose polarization direction has been rotated 90 degrees by half-wavelength plate 932. Thus, prism 936 functions as a polarization combiner. Furthermore, prism 936 includes reflective surface 922, which reflects the polarization-combined output light beam toward output optical fiber 108. Thus, the prism 936 also functions as a beam deflecting prism.

[0076] Furthermore, the optical modulator 100-3 is configured such that the optical axis 914 of the leakage light of the input light that passes through the reflective surface 212-3 as the second reflective surface is separated from the optical axes 916 and 918 of the outgoing light reflected by the two reflective surfaces 920 and 924 corresponding to the third reflective surface by a distance d3.

[0077] Thus, in the optical modulator 100 - 3 , similarly to the optical modulator 100 , leakage light transmitted through the second reflection surface 212 - 3 is not mixed with the outgoing light reflected by the third reflection surfaces 920 and 924 , thereby effectively suppressing deterioration of crosstalk.

[0078] <Fourth Modification of First Embodiment>

[0079] First, a fourth modification of the optical modulation device 100 will be described. Figure 6 This is a diagram showing the structure of the optical modulator 100-4 according to the fourth modified example, and is equivalent to the diagram showing the structure of the A portion of the optical modulator 100. Figure 2 It should be noted that the optical modulation device 100-4 Figure 6 The unrecorded part has the same Figure 1 The same structure of the optical modulation device 100 shown in FIG. Figure 1 Furthermore, in Figure 6 In, about Figure 2 The same structural elements as those of the optical modulation device 100 are used. Figure 2 The same reference numerals as in Figure 2 Description.

[0080] Figure 6The optical modulation device 100-4 shown has Figure 1 and Figure 2 The optical modulator 100 shown has the same structure as the optical modulator 100, but differs in that a beam deflecting prism 134-4 is used instead of the beam deflecting prism 134. The beam deflecting prism 134-4 has the same structure as the beam deflecting prism 134, and includes reflecting surfaces 210-4 and 212-4, which correspond to the first and second reflecting surfaces, respectively, similar to the reflecting surfaces 210 and 212.

[0081] However, the beam deflecting prism 134-4 is different from the beam deflecting prism 134. The optical axis 414 of the leakage light that passes through the second reflective surface 212-4, or a line obtained by extending the optical axis 414 within the light propagation medium, can be aligned with the optical axis 216 of the outgoing light reflected by the third reflective surface 220 of the beam deflecting prism 136. Furthermore, in the optical modulator 100-4, a blocking member 400 is provided between the second reflective surface 212-4 and the third reflective surface 220, on the optical axis 414 of the leakage light that passes through the second reflective surface 212-4 after being reflected by the first reflective surface 210-4. This blocking member 400 blocks the leakage light. Therefore, in the optical modulator 100-4, the optical axis 414 of the leakage light passing through the second reflection surface 212-4 in the input light reflected by the first reflection surface 210-4 in the direction of the optical path of the outgoing light, or the line obtained by extending the optical axis 414 in the light propagation medium, does not include a part that is consistent with the optical axis 216 of the outgoing light reflected by the third reflection surface 220.

[0082] Here, the shield 400 can be, for example, a black-plated aluminum plate. Furthermore, the shield 400 is fixed to a base (not shown) that fixes the beam deflecting prism 136 , and the base is fixed to the bottom surface of the housing 104 , thereby being disposed within the housing 104 together with the beam deflecting prism 136 .

[0083] Through the above structure, in the optical modulator 100-4, as in the optical modulator 100, the above leakage light will not be mixed with the output light reflected by the reflecting surface 220, thereby effectively suppressing the deterioration of crosstalk caused by the introduction of the beam deviation prism 134-4 and / or 136.

[0084] [Second embodiment]

[0085] Next, a second embodiment of the present invention will be described. Figure 7 1 is a diagram showing the structure of an optical modulator 500 which is an optical functional device according to the second embodiment. Figure 7 In FIG. 5 , the right and left figures are respectively a top view and a side view of the light modulator 500. Figure 8 yes Figure 7 The detailed view of part B in the top view on the right. Figure 9 yes Figure 8 It should be noted that in order to avoid lengthy description and facilitate understanding, Figure 9 In the figure, description of the polarization combiner 132 and description of a base for fixing optical components such as the light modulator 102 are omitted.

[0086] It should be noted that in Figure 7 、 Figure 8 In, about Figure 1 、 Figure 2 The same components as those of the optical modulation device 100 of the first embodiment shown in FIG. Figure 1 、 Figure 2 The same reference numerals as in Figure 1 、 Figure 2 Description.

[0087] The optical modulation device 500 has Figure 1 、 Figure 2 The optical modulation device 100 shown in FIG. 1 has the same structure as the optical modulation device 100, but differs in that the beam deflection prisms 534 and 536 are used instead of the beam deflection prisms 134 and 136. Figure 8 As shown, beam deflecting prism 534 has the same structure as beam deflecting prism 134, and includes reflecting surfaces 610 and 612, which correspond to the first and second reflecting surfaces, respectively, similar to reflecting surfaces 210 and 212. Furthermore, beam deflecting prism 536 has the same structure as beam deflecting prism 136, and includes reflecting surfaces 620 and 622, which correspond to reflecting surfaces 220 and 222. Here, reflecting surface 620, like reflecting surface 220, corresponds to the third reflecting surface.

[0088] In particular, in the optical modulation device 500, as Figure 9 As shown in FIG. 1 , the beam shifting prism 534 that shifts the input light from the input optical fiber 106 is arranged at an angle (i.e., at an angle relative to the bottom surface 107) relative to the beam shifting prism 536 that is arranged parallel to the bottom surface 107 of the housing 104. In this respect, the optical modulator 500 differs from the optical modulator 100 of the first embodiment in which both the beam shifting prisms 134 and 136 are arranged in a plane parallel to the bottom surface 107 of the housing 104 so that the input light from the input optical fiber 106 and the output light to the output optical fiber 108 are shifted in the translation direction. It should be noted that in Figure 9 700 and 702 respectively represent the position of the incident point of the input light from the input optical fiber 106 to the beam deflection prism 534 and the position of the exit point of the output light from the beam deflection prism 536 to the output optical fiber 108.

[0089] With the above-described structure, in the optical modulator 500, the optical axis 614 of the leakage light reflected by the first reflection surface 610 of the beam deflection prism 534 and then transmitted through the second reflection surface 612 is not parallel to the optical axis 616 of the outgoing light reflected by the third reflection surface 620 of the beam deflection prism 536, and has a predetermined angle ψ1 that is not equal to 0. Therefore, in the optical modulator 500, Figure 1 Similarly to the optical modulator 100 shown, the optical axis 614 of the leakage light that is reflected by the first reflecting surface 610 and then passes through the second reflecting surface 612, or a line obtained by extending the optical axis 614 within the optical propagation medium, does not include a portion that coincides with the optical axis 616 of the outgoing light reflected by the third reflecting surface 620. Consequently, in the optical modulator 500, similar to the optical modulator 100 of the first embodiment, mixing of the leakage light with the output light reflected by the reflecting surface 620 is prevented, effectively suppressing the deterioration of crosstalk caused by the introduction of the beam deflecting prisms 534 and / or 536.

[0090] Next, a modification of the optical modulation device 500 according to the second embodiment will be described.

[0091] <First Modification of Second Embodiment>

[0092] First, a first modification of the optical modulation device 500 will be described. Figure 10 1 is a diagram showing the structure of the optical modulator 500-1 according to the first modified example, and corresponds to a diagram showing the structure of the optical modulator 500 taken along the line IX-IX. Figure 9 It should be noted that the optical modulation device 500-1 Figure 10 The unrecorded part has the same Figure 7 and Figure 8 The same structure of the optical modulation device 500 is shown, and the above-mentioned Figure 7 and Figure 8 Furthermore, in Figure 10 In, about Figure 9 The same structural elements as those of the optical modulation device 500 are used. Figure 9 The same reference numerals as in Figure 9 Description.

[0093] The optical modulation device 500-1 has Figure 9 The optical modulator 500 shown has the same structure as the optical modulator 500, but differs in that a beam deflecting prism 536-1 is used instead of the beam deflecting prism 536. The beam deflecting prism 536-1 has the same structure as the beam deflecting prism 536, and includes reflecting surfaces 620-1 and 622-1, which are similar to the reflecting surfaces 620 and 622. Here, the reflecting surface 620-1 corresponds to the third reflecting surface, similar to the reflecting surface 620.

[0094] However, in the optical modulator 500-1, the beam deflecting prism 536-1 is arranged to be tilted in the opposite direction to the beam deflecting prism 534 with respect to the bottom surface 107 of the housing 104. Therefore, in the optical modulator 500-1, the optical axis 614 of the leakage light that has passed through the second reflection surface 612 of the beam deflecting prism 534 is closer to the optical axis 816 of the output light that has been reflected by the third reflection surface 620-1 of the beam deflecting prism 536-1. Figure 9 The angle ψ1 shown is larger than the angle ψ2. As a result, in the optical modulation device 500-1, Figure 9 Compared with the optical modulation device 500 shown in FIG. 1 , the deterioration of crosstalk can be suppressed more effectively.

[0095] In addition, in the optical modulation device 500-1, by adjusting the tilt angle of the beam deflection prism 536-1, the Figure 10 The position of the exit point of the output light from the beam shifting prism 536-1 is indicated by reference numeral 802 in FIG. Therefore, in the optical modulator 500-1, the height of the optical axis position of the input optical fiber 106 from the bottom surface 107 of the housing 104 (corresponding to the position of the point indicated by reference numeral 700) and the height of the optical axis position of the output optical fiber 108 from the bottom surface 107 (corresponding to the position of the point indicated by reference numeral 802) can be made the same. Thus, in the optical modulator 500-1, the fixed positions of the input optical fiber 106 and the output optical fiber 108 in the surface 105 of the housing 104 can be arranged at a position with respect to the widthwise center line of the housing 104 (i.e., at Figure 7 The symmetrical position of the surface 105 (the single-dotted line in the left figure that crosses the surface 105 in the left-right direction of the figure) can more stably maintain the light coupling efficiency between the input optical fiber 106 and the output optical fiber 108 and the optical modulator 102 relative to the deformation of the shell 104 caused by changes in ambient temperature, etc.

[0096] <Second Modification of Second Embodiment>

[0097] Next, a second modification of the optical modulation device 500 will be described. Figure 11 1 is a diagram showing the structure of the optical modulator 500-2 according to the second modified example, and is equivalent to a diagram showing the structure of the optical modulator 500 taken along the line IX-IX. Figure 9 It should be noted that the optical modulation device 500-2 Figure 11 The unrecorded part has the same Figure 7 and Figure 8 The same structure of the optical modulation device 500 is shown, and the above-mentioned Figure 7 and Figure 8 Furthermore, in Figure 11 In, about Figure 9The same structural elements as those of the optical modulation device 500 are used. Figure 9 The same reference numerals as in Figure 9 Description.

[0098] The optical modulation device 500-2 has Figure 9 The optical modulator 500 shown has the same structure as the optical modulator 500, but differs in that a beam deflecting prism 536-2 is used instead of the beam deflecting prism 536. The beam deflecting prism 536-2 has the same structure as the beam deflecting prism 536, and includes reflective surfaces 620-2 and 622-2, which are similar to the reflective surfaces 620 and 622. Here, the reflective surface 620-2 corresponds to the third reflective surface.

[0099] However, in the optical modulator 500-2, the beam deflecting prism 536-2 is tilted relative to the bottom surface 107 of the housing 104 in the same direction as the beam deflecting prism 534. Consequently, in the optical modulator 500-2, the optical axis 614 of the leakage light that has passed through the second reflecting surface 612 of the beam deflecting prism 534 is positioned parallel to and separated by a distance d4 from the optical axis 1016 of the output light reflected by the third reflecting surface 620-1 of the beam deflecting prism 536-2. It should be noted that in this case, the distance d4 is preferably equal to or greater than the beam diameter of the leakage light.

[0100] By adopting the above structure, in the optical modulator 500-2, as in the optical modulator 500, leakage light passing through the second reflective surface 612 is prevented from mixing with the output light reflected by the third reflective surface 620-2, thereby suppressing the increase in crosstalk caused by the introduction of the beam deflection prisms 534 and 536-2. It should be noted that in the above structure, the output position of the output light from the beam deflection prism 536-2 is as follows: Figure 11 The ratio shown in the bid number 902 Figure 9 The emission position indicated by reference numeral 702 is moved upward as shown in the figure, so the fixed position of the output optical fiber 108 in the surface 105 of the housing 104 also needs to be moved to a corresponding position.

[0101] It should be noted that the present invention is not limited to the configurations of the above-described embodiment and its modified examples, and can be implemented in various forms without departing from the spirit and scope of the invention.

[0102] For example, in the optical modulator devices 100, 500 and their modified examples, the third reflection surface that reflects the outgoing light from the optical modulator element 102 serving as an optical functional element in a direction away from the optical axis of the input optical fiber 106 is set to be a reflection surface 220, etc., or 620, etc. of the beam shifting prism 136, etc., or 536, etc. that shifts the optical axis of the output light in the translation direction, but is not limited to this.

[0103] For example, in Figure 2 In addition to the reflective surface 220 of the beam deflection prism 136 that deflects the output light in the translation direction, the reflective surface 224 constituting the polarization combiner 132 may also serve as a third reflective surface that reflects the outgoing light from the optical modulator 102 in a direction away from the optical axis of the input optical fiber 106. Therefore, the optical axis 214 of the leakage light of the input light that passes through the reflective surface 212 toward the direction of the output light path is configured so that the optical axis 214 or the line obtained by extending the optical axis 214 in the optical propagation medium does not include a portion that coincides with the optical axis 218 of the outgoing light reflected by the reflective surface 224. Moreover, in this case, the distance d2 (see FIG. 2 ) between the optical axis 214 of the leakage light of the input light that passes through the reflective surface 212 or the extended line thereof in the optical propagation medium and the optical axis 218 of the outgoing light reflected by the reflective surface 224 is 1 / 4 (0.175 mm / s). Figure 2 ) is also preferably greater than the beam diameter of the leakage light, similarly to the distance d1 described above.

[0104] In the optical modulation device 100 of the first embodiment, the optical axis 214 of the leakage light of the input light is Figure 2 Although the optical axis 214 is located to the left of the optical axis 216 of the outgoing light reflected by the reflective surface 220 and to the left of the optical axis 218 of the outgoing light reflected by the reflective surface 224, the position of the optical axis 214 is not limited to this. The optical axis 214 of the leakage light of the input light may be located to the right of the optical axes 216 and 218 of the outgoing light reflected by the reflective surfaces 220 and 224, or between the optical axes 216 and 218 of the outgoing light, as long as the optical axis 214 or a line obtained by extending the optical axis 214 within the light propagation medium does not include a portion that coincides with the optical axes 216 and 218 of the outgoing light reflected by the reflective surfaces 220 and 224, respectively.

[0105] In the first and second embodiments, as an example of an optical functional device, the optical modulators 100 and 500 are shown as including an optical modulator 102 for performing light modulation as an optical functional element, which is formed by an optical waveguide formed on a substrate made of LN. However, the optical functional device is not limited to this. The optical functional device of the present invention may include an optical functional element having any function in any manner to achieve the function.

[0106] Such functions are not limited to optical modulation; they can also be configured as optical switches, polarization rotation, optical routing, and the like. Furthermore, optical functional elements are not limited to LN and can be waveguide-type or integral elements using other semiconductor materials such as Si. Furthermore, alternatively, the optical modulator 102 in the above-described embodiment arranges the ends of the input waveguide 202 for receiving input light and the ends of the output waveguides 204a and 204b for emitting output light, which are formed on the substrate, on one surface of the substrate, namely, the light input and output surfaces 128, but the present invention is not limited thereto. The optical functional element included in the optical functional device of the present invention can be configured to receive and emit any number of light inputs and any number of light outputs on different surfaces of the optical functional element.

[0107] As described above, the optical functional device of this embodiment, namely, the optical modulator 100, includes: the optical modulator 102 serving as an optical functional element; a housing 104 housing the optical modulator 102; an input optical fiber 106 guiding input light to the optical modulator 102 into the housing 104; and an output optical fiber 108 guiding output light, consisting of light emitted from the optical modulator, out of the housing 104. The input optical fiber 106 and the output optical fiber 108 are each fixed to one surface 105 of the housing 104. Furthermore, the optical modulator 100 includes: a first reflective surface 210 reflecting the input light emitted from the input optical fiber 106 in the direction of the optical path of the output light; a second reflective surface 212 reflecting the input light reflected by the first reflective surface 210 toward the optical modulator 102; and a third reflective surface 220 reflecting the output light from the optical modulator 102 away from the optical axis of the input optical fiber 106. Furthermore, in the optical modulator 100, the optical axis 214 of the leakage light that is reflected by the first reflection surface 210 and then passes through the second reflection surface 212, or the extended line obtained by extending the optical axis 214 within the optical propagation medium in which the leakage light can propagate, does not include a portion that is consistent with the optical axis 216 of the outgoing light reflected by the third reflection surface 220.

[0108] With this configuration, in an optical functional device in which both the input fiber 106 and the output fiber 108 are arranged on one surface of the housing 104 , crosstalk between input light from the input fiber 106 and output light to the output fiber 108 can be kept low, thereby achieving good optical characteristics.

[0109] Furthermore, in the optical modulator 100-4, a blocking member 400 is provided on the optical axis 414 of the leaked light that has been reflected by the first reflective surface 210-4 and then passed through the second reflective surface 212-4, and between the second reflective surface 212-4 and the third reflective surface 220. This configuration eliminates restrictions on the relative positions of the first reflective surface 210-4, the second reflective surface 212-4, and the third reflective surface 220, and enables low crosstalk between the input light and the output light, thereby achieving excellent optical characteristics.

[0110] In addition, in the optical modulator 100 (or 500-2), the optical axis 214 (or 614) of the leakage light that is reflected by the first reflection surface 210 (or 610) and then passes through the second reflection surface 212 (or 612) is configured so that the optical axis 214 (614) or the above-mentioned extension line of the optical axis 214 (614) in the above-mentioned light propagation medium is separated from the optical axis 216 (or 1016) of the outgoing light reflected by the third reflection surface 220 (or 620-2) by a distance d1 (or d4) that is larger than the value of the beam diameter of the above-mentioned leakage light.

[0111] In addition, in the optical modulator 100-2 (or 500 or 500-1), the optical axis 314 (or 614) of the leakage light that is reflected by the first reflecting surface 210-2 (or 610) and passes through the second reflecting surface 212-2 (612) and the optical axis 216 (or 616 or 816) of the outgoing light reflected by the third reflecting surface 220 (or 620 or 620-1) are not parallel to each other.

[0112] According to the above configuration, the optical axis of the leaked light of the input light and the optical axis of the output light can be effectively separated, thereby achieving good optical characteristics with less crosstalk.

[0113] Furthermore, for example, in the optical modulator 100, the third reflective surface 220 may not be positioned on the extension line within the optical propagation medium of the optical axis 214 of the leakage light that is reflected by the first reflective surface 210 and then passes through the second reflective surface 212. This configuration further reduces crosstalk between the input light and the output light, achieving even better optical characteristics.

[0114] Furthermore, in the above-described embodiment, the optical functional element illustrated as an example of the light modulator 102 is composed of an optical waveguide formed on a substrate, and the ends of the input waveguide 202 for receiving input light and the ends of the output waveguides 204a and 204b for emitting output light are arranged on one end face of the substrate, namely, the light input and output surfaces 128. With this structure, in an optical functional device in which optical components are densely arranged between the light input and output surfaces 128 of the light modulator 102 and the surface 105 of the housing 104 on which the input optical fiber 106 and the output optical fiber 108 are disposed, crosstalk from the input light to the output light can be reduced, thereby achieving excellent optical characteristics.

Claims

1. An optical functional device having: Optical functional elements; a housing for accommodating the optical functional element; an input optical fiber for guiding the input light input to the optical functional element into the housing; and An output optical fiber guides the output light consisting of the outgoing light from the optical functional element to the outside of the housing, wherein The input optical fiber and the output optical fiber are both fixed on one surface of the housing, The optical functional device has: a first reflecting surface, reflecting the input light emitted from the input optical fiber toward the direction of the optical path of the output light; a second reflecting surface, reflecting the input light reflected by the first reflecting surface toward the optical functional element; and The third reflecting surface reflects the outgoing light from the optical functional element in a direction away from the optical axis of the input optical fiber. The optical axis of the leakage light reflected by the first reflection surface and then transmitted through the second reflection surface, or the extended line obtained by extending the optical axis in the light propagation medium through which the leakage light can propagate, does not include a portion that coincides with the optical axis of the outgoing light reflected by the third reflection surface.

2. The optical functional device according to claim 1, wherein: A blocking body for blocking leakage light that is reflected by the first reflection surface and then passes through the second reflection surface is provided at a position between the second reflection surface and the third reflection surface on the optical axis.

3. The optical functional device according to claim 1, wherein: The optical axis of the leakage light reflected by the first reflection surface and then transmitted through the second reflection surface or the extension of the optical axis is separated from the optical axis of the outgoing light reflected by the third reflection surface by a distance greater than a beam diameter of the leakage light.

4. The optical functional device according to claim 1, wherein: The optical axis of the leakage light reflected by the first reflecting surface and then transmitted through the second reflecting surface and the optical axis of the outgoing light reflected by the third reflecting surface are not parallel to each other.

5. The optical functional device according to claim 1, wherein: The third reflecting surface is not arranged on the extended line of the optical axis of the leakage light that is reflected by the first reflecting surface and then passes through the second reflecting surface.

6. The optical functional device according to any one of claims 1 to 5, wherein The optical functional element is composed of an optical waveguide formed on a substrate, and an end portion of the input waveguide for receiving the input light and an end portion of the output waveguide for emitting the output light are arranged on the same end surface of the substrate.

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