JP4318038B2 - Optical element for optical communication module and optical communication module - Google Patents

Description

The present invention relates to an optical element for an optical communication module having a diffractive structure and an optical communication module disposed in a terminal for transmitting and receiving an optical signal using the optical element.

  Conventionally, in an optical communication system based on bidirectional transmission using light of different wavelengths, an optical communication module composed of a light receiving element, a light emitting element, etc. is arranged at an optical signal transmission / reception terminal, and each light transmitted and received is separated by a diffraction grating. Yes. An example of such a conventional optical communication module is shown in FIG. 16 (see Patent Document 1 below). In the conventional optical communication module of FIG. 16, the hologram optical element 111 is disposed between the support base 130 on which the semiconductor laser 110 and the photodiode 120 are mounted and the terminal 140 of the optical fiber 340. A diffraction grating 160 is formed on one surface, and a lens 170 is formed on the other surface of the substrate. According to the optical communication module as shown in FIG. 16, the size can be reduced and the cost can be reduced.

  However, as shown in FIG. 16, in the case of a grating, since it is necessary to ensure diffraction efficiency or to have no polarization dependence, an angle of 0 is used for the spectroscopy of different-order light, for example, zero-order light and first-order light. It can be separated only within .05 radians. This separation angle corresponds to 1.5 mm when the distance from the diffraction grating is 30 mm. As described above, in the optical module using the grating as shown in FIG. 16, it is difficult to ensure a large separation angle. For this reason, in order to avoid an increase in the size of the optical module package, light emission from a semiconductor laser or the like is required. It is necessary to dispose the element and a light receiving element such as a photodiode at a spatially close distance.

Then, the optical crosstalk between the emitted light from the light emitting element and the incident light to the light receiving element becomes a problem. In particular, since the incident light has a lower light intensity than the emitted light, the influence of the emitted light on the incident light is likely to be a problem. In this case, a decrease in diffraction efficiency of the incident light in the diffraction grating becomes a problem.
Japanese Patent Laid-Open No. 5-241049

In view of the above-described problems of the prior art, the present invention provides a relative diffraction efficiency with respect to incident light in order to reduce the influence of optical crosstalk between the light emitted from the light emitting element and the light incident on the light receiving element. It is an object of the present invention to provide an optical element for an optical communication module and an optical communication module that can be improved.

The optical element according to this reference example includes a plurality of diffraction regions having different diffraction structures on an optical surface.

  According to this optical element, the efficiency of the diffracted light incident on the light receiving element can be increased by a diffraction area having a relatively large diffraction efficiency among a plurality of diffraction areas having different diffraction structures. Even if the efficiency of the emitted light from the light emitting element is lowered in another diffraction region having a relatively small diffractive structure, it does not matter so much. Thereby, the diffraction efficiency regarding incident light can be relatively increased, and the influence of optical crosstalk between outgoing light and incident light can be reduced.

  In the optical element, the optical surface includes a non-diffractive region having no diffractive structure, so that the efficiency of light emitted from the light emitting element can be increased.

An optical element for an optical communication module according to the present invention is an optical element for an optical communication module used in an optical communication module in which light having different wavelengths is transmitted bidirectionally by arranging a light emitting element, a light receiving element, and an optical fiber. When the incident light from the fiber and the outgoing light from the light emitting element pass through the optical surfaces opposite to each other, there are an incident light region through which the incident light passes and an outgoing light region through which the outgoing light passes through the optical surface. A shared region that partially overlaps with each other and an incident light dedicated region through which only the incident light passes are formed. The shared region has an echelon diffraction structure, and the incident light dedicated region has a blaze diffraction structure. that is, with emitted as converging light to the light receiving element 1-order diffracted light of the incident light, and emits the 0 order light of the emitted light as focused on the optical fiber And features.

According to this optical element for an optical communication module, by forming a shared region having a diffractive structure in which each part of the incident light region and the outgoing light region overlaps, each dedicated region that does not overlap in the incident light region and the outgoing light region In addition, since the incident light exclusive area has a blazed diffraction structure with a relatively large diffraction efficiency, the diffraction efficiency related to the incident light can be relatively increased, and the optical cross between the emitted light and the incident light can be increased. It is possible to reduce the influence of talk.

In the optical element, the at least part of the incident light region may correspond to an incident light dedicated region other than the shared region.

The incident light region can be configured to have a diffractive structure having a relatively large diffraction efficiency. That is, the entire incident light region of the incident light dedicated region and the common region can have a diffraction structure with relatively high diffraction efficiency.

The common area may have a diffractive structure having a relatively small diffraction efficiency. That is, in the incident light region, only the incident light dedicated region has a diffraction structure having a relatively large diffraction efficiency.

The outgoing light dedicated region other than the shared region in the outgoing light region may have an echelon diffractive structure or a non-diffractive region having no diffractive structure. Further, the outgoing light dedicated region can be the non-diffractive region, and in this case, the region in the optical plane that does not belong to the incident light region or the outgoing light region has an echelon diffraction structure. Can be.

  In addition, the region in the optical plane that does not belong to the incident light region or the outgoing light region has the same diffractive structure as the adjacent incident light region or the outgoing light region, thereby facilitating processing and manufacturing. It becomes easy to do.

  Examples of the diffractive structure include a blazed diffractive structure, an echelon diffractive structure, and a binary diffractive structure. In general, the diffraction efficiency decreases in this order.

  Further, the emitted light can be laser light, and even if the laser light source is a Fabry-Perot semiconductor laser and the wavelength fluctuation is large, the influence of the wavelength fluctuation is suppressed by using the 0th-order light as the emitted light. Can do.

  The incident light can be incident on the optical element from an optical fiber whose exit end face is inclined with respect to the optical axis of the optical element.

  In the optical surface, the incident light region may have a substantially circular shape, and the emission light region may have a substantially elliptical shape. Thereby, a common area, an incident light dedicated area, and an outgoing light dedicated area can be provided in the incident light area and the outgoing light area.

  In addition, when the incident light includes light of a plurality of wavelengths, the incident light is diffracted by the diffraction structure of the incident light region, and the diffraction angle of the diffracted light can be different depending on the wavelength.

  The optical element may have a light collecting function. Moreover, each diffraction structure of the above-mentioned optical element can be formed on the optical surface by an electron beam drawing method.

  An optical communication module according to the present invention includes the above-described optical element, a light receiving element on which light from an optical fiber terminal enters through the optical element, and light through the optical element toward the optical fiber terminal. And a light emitting element that emits light.

  According to this optical communication module, the diffraction efficiency related to the incident light can be relatively increased by the above-described optical element, so that optical crosstalk between the emitted light from the light emitting element and the incident light to the light receiving element can be achieved. The influence can be reduced.

  In the optical communication module, it is preferable that an exit end face of the optical fiber terminal is inclined with respect to an optical axis of the optical element.

  Further, the light emitting element is constituted by a Fabry-Perot semiconductor laser, which can contribute to cost reduction of the optical communication module.

  Preferably, the light receiving element includes a plurality of light receiving portions, and diffracted lights having different diffraction angles due to the diffraction structure are incident on the light receiving portions according to the diffraction angles. Thereby, when incident light contains light of a plurality of wavelengths, light of each wavelength can be separated and multiplex reception is possible.

In the optical communication module, a first collimator lens is disposed between the optical element and the light emitting element, a second collimator lens is disposed on the optical fiber terminal side as the optical element, and the second The collimator lens has a focal length longer than the focal length f2 obtained by the following equation, and the outgoing light region or the common region of the second collimator lens has no diffraction structure or an echelon diffraction structure. It is preferable that a diffraction structure having a relatively small diffraction efficiency is formed, and the non-diffractive region or a region other than the diffraction structure is formed in a diffraction structure having a relatively large diffraction efficiency such as a blaze diffraction structure. As a result, when the light from the light emitting element is guided to the optical fiber terminal, the resulting light forms an image wider than the core diameter on the end face of the optical fiber terminal, and the coupling efficiency is reduced, but the light from the light emitting element is reduced. Alignment to the fiber end is facilitated, and the diffractive angle on the receiving side is increased by using a blazed structure or the like having a relatively large diffraction efficiency other than the outgoing light region or shared region of the second collimator lens. The diffraction efficiency can be prevented from decreasing.

f2 = α * f1 (A)
However, f1: Focal length α of the first collimator lens: sin ((divergence angle of emitted light from light emitting element) / (divergence angle of emitted light from optical fiber))

The outgoing light region or the common region is configured as a ring-shaped diffraction grating, and the focal length of the portion of the ring-shaped diffraction grating is increased, so that CWDM (Coarse Wavelength Division Multiplexing) is preferable.

According to the optical element for an optical communication module of the present invention, since the diffraction efficiency with respect to incident light can be relatively increased, the influence of optical crosstalk between the emitted light and the incident light can be reduced. Further, according to the optical communication module of the present invention, it is possible to reduce the influence of optical crosstalk between the light emitted from the light emitting element and the light incident on the light receiving element by the above-described optical element.

  The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view showing an optical path of the optical communication module according to the present embodiment.

  As shown in FIG. 1, the optical communication module according to the present embodiment is configured to be elongated in the direction of the optical axis p of the optical fiber 16 as a whole, and is a diffraction grating that is an optical element disposed in the vicinity of the end face 17 of the optical fiber 16. 10, a condenser lens 15 disposed between the end face 17 and the diffraction grating 10, a light emitting element 11 disposed on the optical axis p on the opposite side so as to face the end face 17 of the optical fiber 16, and light emission A lens 13 placed in front of the element 11.

  The optical communication module of FIG. 1 includes a light receiving element 12 disposed on an extension line slightly inclined from the diffraction grating 10 with respect to the optical axis p, and a lens 14 disposed in front of the light receiving element 12. The end face 17 of the optical fiber 16 is slightly inclined with respect to a plane perpendicular to the optical axis p.

  1 is housed in a case as a whole and used in a light-shielded state, and an optical fiber 16 extending to the outside can be connected to an optical cable network of the optical communication system.

  The light emitting element 11 is composed of, for example, a Fabry-Perot semiconductor laser. Light having a wavelength λ10 (for example, 1.31 μm) emitted from the light emitting element 11 passes through the diffraction grating 10 via the lens 13. Then, the light (0th-order light) that is not diffracted by the diffraction grating 10 is collected on the end face 17 through the condenser lens 15 as outgoing light, and transmitted to the outside through the optical fiber 16.

  The light receiving element 12 is composed of, for example, a photodiode, and the light transmitted from the optical fiber 16 and emitted from the end face 17 is diffracted by the diffraction grating 10 via the condenser lens 15, and has a wavelength λ1 (for example, 1.49 μm). The first-order diffracted light is bent from the optical axis p, enters the light receiving element 12 via the lens 14, and is converted into an electric signal.

  The optical communication module of FIG. 1 can be applied to an optical communication system that transmits optical signals having different wavelengths by the wavelength division multiplexing method. For example, the optical fiber 16 is connected to the optical cable network of the optical communication system. A module terminal (not shown) is inserted into an insertion port of a connection device such as a router and connected to a personal computer or the like. In this way, optical signals having different wavelengths are transmitted in both the upstream and downstream directions within the same optical fiber 16 by the optical communication module of FIG. 1, so that communication can be performed via the Internet or the like by a personal computer or the like. It becomes possible.

  Next, each region occupied by the light emitted from the light emitting element 11 and the light incident on the light receiving element 12 in FIG. 1 on the optical surface of the diffraction grating 10 will be described with reference to FIGS.

  FIG. 2 is a schematic view showing the arrangement and the coordinate system of the main part of FIG. FIG. 3 is a side view of an essential part for explaining an inclined end face of the optical fiber of FIG. FIG. 4 is a schematic view showing the positional relationship among the light emitting element of FIG. 2, each ideal lens, and the inclined end face of the optical fiber. FIG. 5 is a plan view schematically showing an outgoing light region and an incident light region on the optical surface of the diffraction grating 10 of FIG.

  In FIG. 2, it is assumed that the lenses 13 and 15 in FIG. 1 are ideal lenses having no blur or aberration, and the laser semiconductor (LD) as the light emitting element 11 is located at the focal position of the lens 13, and the optical fiber 16. Is installed at the position with the highest coupling efficiency.

  Next, as shown in FIG. 3, when the inclination angle of the end face 17 of the optical fiber 16 is 6 °, for example, and the equivalent refractive index n of the optical fiber 16 is 1.4682, the following expression ( As obtained from 1), light travels obliquely by 2.828 ° with respect to the optical axis p from the optical fiber 16.

sin ⁻¹ (1.4682 × sin (6 °)) − 6 ° = 2.828 ° (1)

  On the other hand, referring to FIG. 4, the laser light from the semiconductor laser (LD) of the light emitting element 11 is spread in the x direction (the vertical direction in FIG. 4) in FIG. 2 and the y direction (FIG. 4). If the lens 13 having a divergence angle θy (half width) in the vertical direction of the paper and having a focal length f0 becomes parallel light, the luminous flux becomes an ellipse having the size of the following expressions (2) and (3). .

  Rx = f0 · tan (θx) (2)

  Ry = f0 · tan (θy) (3)

  In order for this light beam to enter the end face 17 at an angle θ0 corresponding to the inclination angle of 2.828 ° of the optical fiber 16 of FIG. 3, y0 obtained from the center of the lens 15 from the center of the lens 15 by the following equation (4). The light emitting element 11 and the lens 13 are shifted in parallel to the optical axis p so that the optical axis of the parallel light passes through a position separated in the direction y only.

y0 = f1 · tan θ0 (4)
Here, f1 is the focal length of the lens 15 on the optical fiber side.

  Therefore, the shadow (emitted light region) formed on the lens 15 on the optical fiber side by the laser light (emitted light) from the semiconductor laser (LD) is an elliptical region that satisfies the following expression (5).

(x / Rx) ² + ((y−y0) / Ry) ² ≦ 1 (5)

  Further, the shadow (incident light region) formed on the optical fiber side lens 15 by the incident light that travels from the end face 17 of the optical fiber 16 toward the light receiving element 12 is a circular region having a radius r that satisfies the following equation (6). It becomes.

x ² + (y−y0) ² ≦ r ² (6)

  Note that, when the effective diameter (radius r1) of the lens 13 on the semiconductor laser (LD) side is smaller than the elliptical light beam formed by the semiconductor laser (LD), the emission light region is This is a region that satisfies both of the above-described equations (5) and (6) (r = r1).

  As can be seen from the above results, an elliptical outgoing light region according to the above equation (5) and an incident light region according to the above equation (6) are formed in the diffraction grating 10 disposed between the lens 13 and the lens 15. However, the outgoing light region and the incident light region may not be completely coincident with each other, and one of them may not be included in the other, and each region may have a dedicated region.

  That is, as shown in FIG. 5, a substantially elliptical outgoing light region 1 and a substantially circular incident light region 2 are formed on the optical surface 3 of the diffraction grating 10 on the light emitting element 11 side in FIG. A part of the outgoing light region 1 and a part of the incident light region 2 overlap to form a common region C.

  Accordingly, the outgoing light region 1 includes a shared region C and an outgoing light dedicated region B through which only outgoing light that is light from the light emitting element 11 passes. The incident light region 2 includes a shared region C and a substantially crescent-shaped incident light dedicated region D on both sides of the shared region C so that only incident light directed to the light receiving element 12 passes.

  Next, different diffractive structures formed on the optical surface 3 of the diffraction grating 10 in FIG. 5 corresponding to the regions A, B, C, and D will be described with reference to FIGS.

  FIG. 6 is a table showing combinations (eight types) of a plurality of diffractive structures and non-diffraction regions formed in the regions A to D of the optical surface 3 of the diffraction grating 10 of FIG. FIG. 7 is a side sectional view partially and schematically showing the blazed diffraction structure and the echelon diffraction structure formed on the optical surface 3 of the diffraction grating 10 of FIG. FIG. 8 is a cross-sectional perspective view schematically showing the blaze diffraction structure and the echelon diffraction structure of FIG.

  As shown in FIGS. 5 and 6, in the combination 1, the incident light dedicated region D is formed in a blazed diffraction structure, and the portions other than the incident light dedicated region D are formed in an echelon diffraction structure. That is, the incident light dedicated region D is a blazed diffractive structure with relatively high diffraction efficiency, and the shared region C, the outgoing light dedicated region B, and the region A in the optical surface 3 other than the regions B, C, D are blazed diffractive structures. It is an echelon diffraction structure with lower diffraction efficiency.

  As shown in FIGS. 7 and 8, the blazed diffraction structure 4 has an inclined surface 4a having a relatively steep inclination and a small area, and an inclined surface 4b having a relatively gentle inclination and a large area, having a predetermined pitch t and a predetermined height. The length h is repeatedly formed. Further, the echelon diffractive structure 5 is configured by repeatedly forming a plurality of steps each having a predetermined width s and a predetermined depth d.

  Further, as shown in FIGS. 7 and 8, at the boundary between the blazed diffractive structure 4 and the echelon diffractive structure 5, the blazed diffractive structure 4 is inclined relatively slowly and has a large area, and the echelon diffractive structure 5 It is formed so that the direction in which each level difference falls is the same direction.

  As described above, until now, the light emitted from the light emitting element 11 having a high light intensity has been easily adversely affected to the incident light to the light receiving element 12 having a low light intensity. According to the optical communication module 1, the efficiency of the diffracted light of the incident light to the light receiving element 12 can be increased by the incident light dedicated region D in which the blazed diffraction structure having a relatively large diffraction efficiency is formed. Can be relatively increased, and the influence of optical crosstalk between incident light and outgoing light can be reduced.

  On the other hand, even if the efficiency of the outgoing light from the light emitting element 11 is reduced by the outgoing light region 1 due to the echelon diffraction structure having a relatively small diffraction efficiency, the light intensity of the outgoing light can be controlled by the current control of the light emitting element 11 or the like. Because there is, it does not matter so much.

  In addition, since the light emitting element 11 is a Fabry-Perot semiconductor laser, zero-order light is used as the emitted light even when the wavelength variation is large, so that the influence due to the wavelength variation can be suppressed. Further, since the Fabry-Perot semiconductor laser is low in cost, it can contribute to the cost reduction of the optical communication module.

  In addition, as shown in FIGS. 5 and 6, the combination of the plurality of diffractive structures formed in the regions A to D of the optical surface 3 of the diffraction grating 10 and the non-diffracting regions is not limited to the combination 1, and other The combination 2-8 may be sufficient.

  That is, in the combination 2, the shared region C and the outgoing light dedicated region B (that is, the outgoing light region 1) have an echelon diffraction structure, and the other region A and the incident light dedicated region D have a blaze diffraction structure. Thereby, the processing of the optical surface 3 becomes easy, and the diffraction efficiency of incident light can be improved.

  In the combination 3 of FIG. 6, the shared region C is an echelon diffractive structure, the outgoing light dedicated region B is a non-diffractive region that does not form a diffractive structure, and the other region A and the incident light dedicated region D are blazed diffractive structures. ing. Thereby, the efficiency of emitted light can be improved.

  Further, in the combination 4 in FIG. 6, the outgoing light dedicated region B is a non-diffractive region where a diffraction structure is not formed, and the other regions A, C, and D are blazed diffraction structures. Thereby, the efficiency of emitted light can be improved as compared with the combination 1.

  Further, in the combinations 5, 6, 7 and 8, the diffractive structures and non-diffracted regions of the regions A to D are determined as in the combination of FIG.

  Next, a method for manufacturing a diffraction grating in which the blazed diffraction structure and the echelon diffraction structure shown in FIGS. 7 and 8 are arranged in the combination 1 of FIGS. 5 and 6 will be described with reference to FIGS. FIG. 9 is a view for explaining procedures (a) to (c) for producing the diffraction gratings of FIGS. 5 to 8 by an electron beam drawing method.

  The electron beam writing method is, for example, as proposed by the present inventors in Japanese Patent Application No. 2002-249614, and a desired drawing pattern is formed on the surface of an optical element such as a diffraction grating by an electron beam. It can be formed with high precision on the order of submicrons by three-dimensional drawing.

  First, as shown in FIG. 9A, an outer peripheral surface 80a of a base material 80 made of a cylindrical resin material serving as a matrix is cut based on the outer diameter 81 of the base material 80, and the error is 0.5 μm or less. Centering is performed with accuracy, and then the circular flat surface 82 on one end surface of the substrate 80 is processed by cutting.

  Next, as shown in FIG. 9B, the concentric circle 83 is processed by cutting with the outer peripheral surface 80a as a reference, the center of the plane 82 is aligned with the concentric circle 83 as a reference, and the diffraction grating pattern is drawn by electron beam drawing. Is formed on the resist. Marks for determining the XY axes are processed as necessary. In this case, the resist thickness is about 2 μm, for example.

  As shown in the plan view of FIG. 9C, the base material 80 manufactured as described above has a diffraction pattern corresponding to the diffraction grating structure of the combination 1 in FIGS. A pattern is formed in the resist.

  Next, the substrate 80 is processed by dry etching using a plasma shower or the like using the resist diffraction grating pattern formed by electron beam drawing as a mask. The diffraction grating pattern is transferred onto the substrate 80 by this dry etching.

  Next, an electroformed mold is manufactured using a base material formed by dry etching as a base material, and the diffraction grating is formed by using the mold, so that the diffraction grating 10 of the combination 1 in FIGS. Get. Note that the diffractive lens may be press-molded using the base material directly as a mother mold.

  Next, Examples (a) to (f) in the case where the combination 1 in FIG. 6 is adopted as the structure of the diffraction grating in FIG. 1 will be described with reference to FIGS. 10, 11, and 12. 10 to 12 show the optical arrangements of the lenses 13 to 15, the diffraction grating 10, and the end face 17 of the optical fiber 16 in the center of the drawing (Examples (a) to (f)), and the left side of the drawing. FIG. 6 shows a plan view of the light emitting element and the light receiving element, and further shows each region A to D on the optical surface of the diffraction grating of FIG. 5 on the right side of the figure.

  In the embodiments (a) to (d) shown in FIGS. 10 and 11, the relative positions of the light emitting element 11 and the lens 13 with respect to the central axis p of the optical fiber 16 are changed, and y0 in FIG. 4 in the direction y in FIG. (C) and (d) are examples in which the optical fiber 16 is further rotated 180 ° from the positions (a) and (b). As shown on the right side of FIGS. 10 and 11, the optical surface 3 of the diffraction grating 10 is formed with an outgoing light dedicated area B, a shared area C, an incident light dedicated area D, and an area A other than the areas B to D, respectively. A diffractive structure is formed in combination 1 in FIG. 6 corresponding to each of the regions A to D.

  In the embodiments (e) and (f) shown in FIG. 12, the optical fiber 16 is rotated by 90 ° from the arrangement position of the embodiments (a) and (b) about the central axis p, and the light emitting element 11 and This is an example in the case where the relative position of the lens 13 with respect to the optical fiber 16 is changed in the direction x in FIG. 2, and as shown on the right side in FIG. C, an incident light dedicated region D, and a region A other than regions B to D are formed, and a diffractive structure is formed in combination 1 of FIG. 6 corresponding to each region A to D.

  Table 1 shows the calculation results of the diffraction efficiency regarding the emitted light using the 0th-order light in the above-described Examples (a) to (f) and the final coupling efficiency of the optical arrangement shown in FIGS. 10 to 12.

  Table 2 shows the calculation results of the diffraction efficiency relating to the incident light in the above-described Examples (a) to (f) and the final coupling efficiency of the optical arrangement shown in FIGS.

  Further, in Tables 1 and 2, the diffraction efficiency of the comparative example and the optical arrangement shown in FIGS. 10 to 12 are the same as the arrangement shown in FIGS. The calculation results of the final coupling efficiency are also shown.

  In the above calculation, θx = 17 °, θy = 34 °, θ0 = 2.828 °, f0 = 0.7 mm, and f1 = 3 mm in the above formulas (1) to (6). Further, the utilization efficiency of the 0th-order light of the emitted light was set to 98%, and the diffraction efficiency of the blazed diffraction structure was set to 92%. Further, the pitch t of the blazed diffraction structure of FIG. 7 was 36 μm, the height h was 3 μm, the width s of each step of the echelon diffraction structure was 9 μm, and the depth d was 5 μm.

  As can be seen from Table 1, with respect to the emitted light, the diffraction efficiency and the final coupling efficiency are lower in each of the examples (a) to (f) than in the comparative example. In any of the examples (a) to (f), the diffraction efficiency and the final coupling efficiency are higher than those in the comparative example.

  As described above, according to the optical arrangements of FIGS. 10 to 12 and the structure of the diffraction grating 10 of the embodiments (a) to (f), the light receiving element 12 is provided by the incident light dedicated region D of the blazed diffraction structure having a large diffraction efficiency. While the efficiency of the diffracted light incident on the light can be increased, the output light region 1 of the echelon diffractive structure having a relatively low diffraction efficiency reduces the efficiency of the emitted light from the light emitting element 11, and the relative efficiency of the incident light is relatively low. I was able to increase it.

  As described above, the best modes and examples for carrying out the present invention have been described. However, the present invention is not limited to these, and various modifications are possible within the scope of the technical idea of the present invention. is there. For example, in FIG. 1, each diffraction structure is formed on the optical surface 3 on the light emitting element 11 side of the diffraction grating 10, but may be formed on the optical surface on the opposite optical fiber 16 side. May be formed on the optical surface 3, and a diffractive structure of another region may be formed on the optical surface on the opposite side.

  Further, the condensing lens 15 may be an optical element, and a diffraction structure similar to that shown in FIG. In this case, each diffractive structure may be formed on one of the optical surfaces, or a diffractive structure in one region may be formed on one optical surface, and a diffractive structure in another region may be formed on the other optical surface. Also good.

  The optical communication module of FIG. 1 divides the light receiving element 12 into a plurality of light receiving portions 12b, 12c, and 12d arranged in an array as shown in FIG. In addition, diffracted light having different diffraction angles by the diffraction grating 10 may be configured to enter each of the light receiving portions 12b, 12c, and 12d according to the diffraction angles.

  According to the configuration of FIG. 13, each wavelength of the optical multiplexed signal is, for example, 1.31 μm at the emission light wavelength λ10 from the light emitting element 11, and the wavelength of light incident from the end face 17 of the optical fiber 16 is λ0 = 1. .47 [mu] m, [lambda] 1 = 1.49 [mu] m, and [lambda] 2 = 1.51 [mu] m, a plurality of optical signals having different wavelengths can be separately received by the light receiving units 12b to 12d. By performing downstream wavelength division multiplexing (WDM) communication in this way, various data, such as digital television broadcasts, moving images, still images, audio, digital data communications, etc., carried on the optical signal of each wavelength can be converted into a single optical signal. Can be received through fiber.

  FIG. 14 shows a modification of the optical communication module. In the optical communication module of FIG. 14, the light from the light emitting unit 11 passes through the two collimator lenses 13 and 15 as in FIG. The light incident on the end surface 17 and further emitted from the end surface 17 of the optical fiber 16 is incident on the light receiving unit 12 configured in the array shape of FIG. 13 through the two collimator lenses 15 and 14. is there. In FIG. 14, the optical surface 15 a on the lens 13 side of the collimator lens 15 is configured in a diffractive structure in the same manner as the optical surface 3 in FIG. 5, and light from the end surface 17 of the optical fiber 16 is reflected on the optical surface 15 a of the lens 15. Diffracted by the diffractive structure, the optical path is bent with respect to the optical axis p and forms an image on the light receiving surface 12 a of the light receiving unit 12.

  The focal length of the collimator lens 15 on the optical fiber 16 side in FIG. 14 is made longer than the focal length f2 obtained by the following equation (A), and the outgoing light region or shared region in FIG. A non-diffractive region or an echelon diffractive structure is formed, and a region other than the non-diffractive region or the echelon diffractive structure is configured as a blaze diffractive structure. As a result, when the light from the light emitting element 11 is guided to the end face 17 of the optical fiber 16, the resulting light forms an image wider than the core diameter on the end face 17 of the optical fiber 16, and the coupling efficiency decreases. Alignment between the light emitting element 11 and the optical fiber 16 is facilitated, and by using a blazed structure other than the emitted light region or the common region portion of the collimator lens 15, the diffraction angle on the receiving side is increased and the diffraction efficiency is increased. It can be prevented from dropping.

f2 = α * f1 (A)
However, f1: Focal length α of the collimator lens 13: sin ((divergence angle of emitted light that is laser light from the light emitting element 11) / (divergence angle of emitted light from the optical fiber 16))

  For example, the area ratio on the optical surface 15a of the collimator lens 15 is 25% (−6 dB) of the outgoing light portion (no diffractive structure or echelon diffractive structure) to the optical fiber 16, and other peripheral portions (blazed diffraction). If the structure) is about 75% (-1.2 dB), the beam diameter on the end face 17 of the optical fiber 16 is almost twice that of the core. In this case, the focal length of the collimator lens 15 is the above formula (A). Is approximately twice the value of f2 given by.

  Further, in FIG. 14, the outgoing light region or the common region on the optical surface 15 a of the collimator lens 15 is configured as a ring-shaped diffraction grating 18 as shown in FIG. 15, and the focal length of the ring-shaped diffraction grating portion is increased. Thus, the optical communication module can cope with CWDM (Coarse Wavelength Division Multiplexing) in which the wavelength multiplexing interval is particularly coarse, for example, 20 nm. That is, since the light received by the optical communication module is emitted from the collimator lens 15 and then converges on the array-shaped light receiving unit 12, the transmitted light converges on the array-shaped light receiving unit 12 toward the collimator lens 15. Since the light beam diverges at the same angle and needs to be adjusted to obtain a desired divergence angle after passing through the collimator lens 13, the adjustment work is less than adjusting the optical system to obtain a parallel light beam. Increase. In order to solve such a problem, a ring-shaped diffraction grating 18 is provided in a portion through which the outgoing light of the optical surface 15a of the collimator lens 15 passes, so that the power of the lens in this portion is reduced, and the light incident on the collimator lens 15 Can be focused on the end face 17 of the optical fiber 16, and the adjustment of the optical system becomes easy.

It is the schematic which shows the optical path of the optical communication module by this Embodiment. It is the schematic which shows the principal part arrangement structure of FIG. 1, and its coordinate system. It is a principal part side view for demonstrating the inclined end surface of the optical fiber of FIG. It is the schematic which shows the arrangement | positioning relationship between the light emitting element of FIG. 2, each ideal lens, and the inclined end surface of an optical fiber. It is a top view which shows roughly the emitted light area and incident light area in the optical surface of the diffraction grating 10 of FIG. 6 is a table showing combinations (eight types) of a plurality of diffractive structures and non-diffracted regions formed in each region A to D of the optical surface 3 of the diffraction grating 10 of FIG. FIG. 6 is a side sectional view partially and schematically showing a blazed diffraction structure and an echelon diffraction structure formed on the optical surface 3 of the diffraction grating 10 of FIG. 5. FIG. 8 is a cross-sectional perspective view schematically showing the blazed diffraction structure and the echelon diffraction structure of FIG. 7. It is a figure for demonstrating the procedure (a) thru | or (c) which produces the diffraction grating of FIGS. 5-8 by the electron beam drawing method. For Examples (a) and (b), the optical arrangement of each lens 13 to 15 of FIG. 1, the diffraction grating 10 and the end face 17 of the optical fiber 16 is shown in the center of the figure, and the light emitting element and the light receiving element are shown on the left side of the figure. FIG. 6 shows a plan view, and further shows each region A to D on the optical surface of the diffraction grating of FIG. 5 on the right side of the drawing. In Examples (c) and (d), the optical arrangement of the end surfaces 17 of the lenses 13 to 15, the diffraction grating 10, and the optical fiber 16 in FIG. 1 is shown in the center of the figure, and the light emitting element and the light receiving element are shown on the left side in the figure. FIG. 6 shows a plan view, and further shows each region A to D on the optical surface of the diffraction grating of FIG. 5 on the right side of the drawing. For Examples (e) and (f), the optical arrangement of the lenses 13 to 15, the diffraction grating 10, and the end face 17 of the optical fiber 16 in FIG. FIG. 6 shows a plan view, and further shows each region A to D on the optical surface of the diffraction grating of FIG. 5 on the right side of the drawing. It is a perspective view which shows roughly the modification of the light-receiving part of the light receiving element of FIG. It is the schematic which shows the optical path in the modification of the optical communication module by this Embodiment. FIG. 15 is a side view schematically showing an annular diffraction grating partially formed on the optical surface 15a of the collimator lens 15 of FIG. It is sectional drawing which shows the conventional optical communication module which provides a diffraction grating on a lens, and isolate | separates each light of transmission and reception.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Outgoing light area 2 Incident light area 3 Optical surface 4 Blaze diffraction structure 4a Inclined surface 4b Inclined surface 5 Echelon diffraction structure 10 Diffraction grating (optical element)
DESCRIPTION OF SYMBOLS 11 Light emitting element 12 Light receiving element 12b-12d Multiple light-receiving part 13 Lens, collimator lens 14 Lens 15 Condensing lens, Collimator lens 16 Optical fiber 17 End surface 18 Ring-shaped diffraction grating A Area B other than area B, C, D Radiation exclusive area C Common area D Incident light exclusive area

Claims (15)

In an optical element for an optical communication module used for an optical communication module in which light having different wavelengths is transmitted bidirectionally by arranging a light emitting element, a light receiving element and an optical fiber,
When incident light from an optical fiber and outgoing light from a light emitting element pass through optical surfaces on opposite sides, an incident light region through which the incident light passes and an outgoing light region through which the outgoing light passes through the optical surface, Forming a shared region where each part overlaps and a dedicated region for incident light through which only the incident light passes,
Together with the Echelon diffractive structure in the common region, the have a blazed structure in the incident light only area, with emitted as converging light to the light receiving element 1-order diffracted light of the incident light, the outgoing light An optical element for an optical communication module , wherein the 0th-order light is emitted so as to be condensed on the optical fiber .   2. The optical communication module optical according to claim 1, wherein a region dedicated to outgoing light other than the shared region in the outgoing light region is a diffraction-free region having an echelon diffraction structure or not having a diffraction structure. element.   The optical element for an optical communication module according to claim 2, wherein the outgoing light dedicated region is the diffraction-free region.   4. The optical element for an optical communication module according to claim 3, wherein a region in the optical surface that does not belong to the incident light region or the outgoing light region has an echelon diffraction structure.   The region in the optical plane that does not belong to the incident light region or the outgoing light region has the same diffractive structure as the adjacent incident light region or the outgoing light region. Optical element for optical communication module.   6. The optical element for an optical communication module according to claim 1, wherein the emitted light is laser light.   The optical communication module optical according to any one of claims 1 to 6, wherein the incident light is incident on the optical element from an optical fiber whose exit end face is inclined with respect to the optical axis of the optical element. element.   The optical element for an optical communication module according to any one of claims 1 to 7, wherein the incident light region has a substantially circular shape on the optical surface, and the emission light region has a substantially elliptical shape.   9. The incident light according to claim 1, wherein when the incident light includes light having a plurality of wavelengths, the incident light is diffracted by a diffractive structure of the incident light region, and the diffraction angle of the diffracted light varies depending on the wavelength. An optical element for an optical communication module according to Item.   The optical element for an optical communication module according to claim 1, further comprising a light collecting function.   The optical element for an optical communication module according to claim 1, wherein the diffractive structure of the optical surface is formed by an electron beam drawing method. An optical element for an optical communication module according to any one of claims 1 to 11,
And the light receiving element which light from the optical fiber is incident through the optical element,
An optical communication module comprising: the light emitting element that emits light toward the optical fiber through the optical element.   The optical communication module according to claim 12, wherein an emission end face of the optical fiber is inclined with respect to an optical axis of the optical element.   14. The optical communication module according to claim 12, wherein the light emitting element is configured by a Fabry-Perot semiconductor laser.   15. The light receiving element according to claim 12, wherein the light receiving element includes a plurality of light receiving portions, and diffracted light having different diffraction angles by the diffraction structure is incident on each light receiving portion according to the diffraction angles. The optical communication module according to claim 1.

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