JP2005331879A - Optical module, optical communications system and electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical communication module capable of reducing signal distortion in using a multimode laser beam, as well as reducing signal quality deterioration due to positional deviation between an optical fiber and a light-emitting element, and to provide an optical communications system and electronic equipment which use the module. <P>SOLUTION: The optical module is equipped with a light-emitting element 13 that oscillates a multimode laser beam and a repeater waveguide 21, that is arranged on the optical axis between the light-emitting element 13 and a waveguide 19 through which the laser beam from the light-emitting element 13 propagates and that is designed to relay optical coupling there between. In this optical module, the repeater waveguide 21 is structured such that the core part 24 is surrounded with a clad part 26, and that a stepwise refractive index distribution is formed between the core part 24 and the clad part 26. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical module, an optical communication apparatus, and an electronic apparatus that are preferably used in an optical communication system.

In recent years, development of optical communication systems has been progressing due to demands for higher speed and larger capacity of information communication.
Such an optical communication system basically has a configuration in which a light emitting element that converts an electrical signal into an optical signal and a light receiving element that converts an optical signal into an electrical signal are connected by an optical fiber. An optical module for optically connecting an optical element and an optical fiber is used in order to allow the optical element such as a light emitting element and a light receiving element and an optical fiber to be attached or detached. For example, Patent Document 1 (Japanese Patent Laid-Open No. 2000-349307) discloses an optical module that can position an optical element and an optical fiber by using a through hole formed in a substrate. In this optical module, the optical fiber and the optical element are directly coupled by abutting the optical fiber with the optical element through the through hole.
JP 2000-349307 A

  By the way, in general, a combination of a surface-emitting type semiconductor laser (VCSEL) and a multimode optical fiber is advantageous for optical transmission over a short distance in terms of communication speed and cost. For a multimode optical fiber, a graded index (GI) fiber with improved dispersion characteristics is usually used to suppress modal dispersion. In the GI fiber, a refractive index distribution is formed so that the refractive index difference becomes smaller in the core as it approaches the cladding. Therefore, when the surface emitting semiconductor laser and the GI fiber are directly coupled as in the optical communication module of Patent Document 1, the emission angle of the surface emitting semiconductor laser is large and the distance between the surface emitting semiconductor laser and the optical fiber is long. As a result, the outside light having a large radiation angle can enter only a portion with a small NA away from the center of the GI fiber, and the phenomenon that the coupling with the GI fiber cannot be performed occurs. Here, the surface-emitting type semiconductor laser emits multi-mode light, and light having a larger emission angle emits light in a higher-order mode, and this higher-order mode light cannot be coupled to the GI fiber, so the signal is distorted. Will occur. On the other hand, when the surface emitting semiconductor laser and the GI fiber are directly coupled, the adjustment margin between the surface emitting semiconductor laser and the GI fiber is small, so that the signal quality is significantly deteriorated due to the positional deviation.

  Accordingly, the present invention provides an optical communication module, an optical communication apparatus, and an electronic apparatus that can reduce signal distortion when using multimode laser light and can reduce signal quality degradation due to positional deviation between an optical fiber and a light emitting element. The purpose is to provide.

  In order to solve the above problems, the present invention provides an optical axis of a light emitting element (laser light source) that oscillates multimode laser light, and a waveguide that propagates the laser light oscillated from the light emitting element. A relay waveguide that relays optical coupling between the light emitting element and the waveguide, and the relay waveguide has a structure in which a core portion is surrounded by a cladding portion, The present invention provides an optical module in which a stepped refractive index distribution is formed between the clad portion and the clad portion.

  According to such a configuration, the angle and the incident position of light incident on the waveguide can be variously changed by passing the waveguide in which the stepwise refractive index distribution is formed between the core portion and the cladding portion. Is possible. As a result, the incident position to the waveguide is determined by the emission angle of the laser beam from the light emitting element, and even when only a certain amount of light can be optically coupled to the waveguide, the correlation between the incident position and the emission angle is obtained. Therefore, it is possible to transmit a signal having a substantially uniform distribution. Therefore, for example, in a laser beam having a correlation between the emission angle and the mode, only light of a specific emission angle mode cannot be incident, and problems such as distortion in the transmitted signal can be solved. In addition, since the incident positions of various mode lights on the end face of the waveguide are randomized, it is possible to increase the margin for position adjustment, and it is possible to reduce deterioration of signal quality due to misalignment of the adjustment position. It becomes. Here, the stepwise refractive index distribution means that the refractive index n1 in the core part is substantially uniform and the refractive index n1 of the core part is higher than the refractive index n2 of the cladding part (n1> n2). Say.

  As such a relay waveguide, for example, a step index type optical waveguide is used, and for example, an optical fiber piece composed of a step index type multimode optical fiber can be used.

  According to another aspect of the present invention, the light emitting element is disposed on an optical axis of a light emitting element that oscillates multimode laser light, and the light emitting element and a waveguide that propagates laser light oscillated from the light emitting element. And an optical fiber piece that relays optical coupling between the optical waveguide and the waveguide; and a base material that mounts the light emitting element and holds the optical fiber piece and the waveguide. An optical module composed of a mode optical fiber is provided.

  According to such a configuration, it is possible to variously change the angle and the incident position of the light incident on the waveguide by passing the optical fiber piece composed of the step index type multimode optical fiber. As a result, the incident position to the waveguide is determined by the emission angle of the laser light from the light emitting element, and even when only a certain amount of light can be optically coupled to the waveguide, such an incident position and an emission angle. Therefore, it is possible to transmit a signal with a substantially uniform distribution. Therefore, for example, in a laser beam having a correlation between the emission angle and the mode, only light of a specific emission angle mode cannot be incident, and problems such as distortion in the transmitted signal can be solved. In addition, since the incident positions of various mode lights on the end face of the waveguide are randomized, it is possible to increase the margin for position adjustment, and it is possible to reduce deterioration of signal quality due to misalignment of the adjustment position. It becomes. Further, the light emitting element, the optical fiber piece, and the waveguide can be accurately positioned with a simple structure. Examples of the holding means for holding the optical fiber piece and the furnace include holes such as through holes provided in the base material.

  The waveguide is, for example, a graded index optical waveguide, and is preferably a graded index multimode optical fiber (hereinafter also referred to as GI fiber). In the GI fiber, a refractive index distribution is formed such that the refractive index difference decreases as the distance from the cladding increases in the core. Therefore, particularly when the light emitting element and the GI fiber are directly coupled, light having a large radiation angle cannot be coupled and the signal tends to be distorted. However, the step index type multimode optical fiber ( Such an inconvenience can be solved by using an optical fiber piece composed of an SI optical fiber for relaying.

  It is preferable that the core diameter of the optical fiber piece is the same as or smaller than the core diameter of the optical fiber. According to this, the coupling efficiency with the optical fiber can be further improved.

  The core diameter of the optical fiber piece is preferably larger than the core diameter of the optical fiber. According to this, since it becomes possible to increase the position adjustment margin of the optical fiber and to attenuate the amount of light transmitted to the optical fiber, an attenuator (attenuator) used for light amount adjustment is omitted. It becomes possible.

  The NA of the optical fiber piece is preferably larger than the NA of the optical fiber. According to this, the angle margin of the optical fiber can be expanded.

  It is preferable that the optical fiber piece has at least a tapered portion where the core diameter increases from the incident side toward the emission side. According to this, it is possible to change the NA on the incident side and the emission side of the optical fiber piece. Therefore, the NA can be changed in various ways according to the application and the like, and the degree of freedom in design is expanded.

  It is preferable that the axial length of the optical fiber piece is a length that allows incident light incident at the maximum light receiving angle of the optical fiber piece to be reflected four times or more. If the incident light incident at the maximum light receiving angle of the optical fiber piece can be reflected four or more times, a substantially stable coupling efficiency between the optical fiber piece and the optical fiber can be obtained.

  When the vertical axis represents the coupling efficiency of the optical fiber piece and the horizontal axis represents the length of the optical fiber piece, when the relationship between the coupling efficiency and the length is approximated by an attenuation curve, The length of the optical fiber piece in the longitudinal direction is preferably such that the attenuation curve takes a substantially maximum value. According to this, good coupling efficiency can be obtained.

  Another aspect of the present invention is an optical communication device including the above optical module. According to this, since the optical module is provided, it is possible to provide a highly reliable optical communication device.

  Here, “optical communication device (optical transceiver)” means not only a device including both a configuration related to transmission of an optical signal (such as a light emitting element) and a configuration related to reception of an optical signal (such as a light receiving element), as well as transmission. The apparatus (so-called optical transmission module) provided only with the structure which concerns on this, and the apparatus (so-called optical reception module) provided only with the structure which concerns on reception are also included.

  Still another aspect of the present invention includes the optical module as an optical transmission module, and further includes a light receiving element such as a PD (Photo Diode) that receives an optical signal transmitted from the optical fiber (waveguide), and the light. An optical communication device including an optical receiving module having an optical fiber piece configured by a GI fiber that relays optical coupling between a fiber and the light receiving element.

  According to such a configuration, since the GI fiber is used as the optical fiber piece on the receiving side, the spread of the laser light is small and the light receiving area can be reduced, so that the communication speed can be further increased. It becomes possible.

  Another aspect of the present invention is an electronic device including the optical module. According to this, it becomes possible to provide a highly reliable electronic device.

  Here, “electronic device” means a device in general that realizes a certain function using an electronic circuit or the like, and its configuration is not particularly limited. For example, a personal computer, a PDA (portable information terminal device) In addition, various devices that perform information communication with an external device or the like using light such as an electronic notebook as a transmission medium.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a diagram for explaining an example of an optical module according to the first embodiment of the present invention, and FIG. 2 is a partially enlarged view of FIG. As shown in FIG. 1, the optical communication module of this embodiment includes a base material 11, a light emitting element 13, an optical fiber piece 21, a ferrule 15, a translucent resin film 16, a wiring film 17, and a sealing material 18. Composed. An optical communication device is configured including the optical communication module and an external substrate 30 on which electronic circuits and the like are further arranged.

  The base material 11 supports each element constituting the optical communication module, and has a through hole 12 into which the optical fiber 19 can be inserted. The base material 11 can be configured using various materials such as conductive materials such as stainless steel, aluminum, and copper, and non-conductive materials such as glass, resin, and ceramics. For example, in this embodiment, the base material 11 is comprised using ceramics.

  The through hole 12 is formed in a shape that does not cause a substantial gap between the inner wall of the through hole 12 and the optical fiber piece 21 and the ferrule 15 when the ferrule 15 provided around the optical fiber 19 is inserted. The As a result, the optical fiber 19 can be fixed to the through-hole 12 and the alignment with the light emitting element 13 can be performed at the same time. Note that when the ferrule 15 is not provided in the optical fiber 19, the through hole 12 corresponding to the shape of the optical fiber 19 is formed.

  The light emitting element 13 is disposed on the through hole 12 via the translucent resin film 16 and emits signal light including a plurality of modes of laser light toward the optical fiber 19 inserted into the through hole 12. To do. As such a light emitting element 13, a surface emitting semiconductor laser (VCSEL) etc. are used, for example. In this embodiment, a VCSEL (for example, wavelength 850 nm) is flip-chip bonded to the translucent resin film 16 face down. The light emitting element 13 is positioned with reference to the through hole 12, the optical fiber 14, or the ferrule 15.

  The multimode optical fiber (waveguide) 19 is an optical fiber capable of propagating a plurality of modes, and plays a role of propagating the multimode laser light oscillated from the light emitting element 13 to the other. In the present embodiment, a graded index (GI) type multimode optical fiber (GI fiber) is used as the optical fiber 19. The core 20 of the GI fiber is formed such that the refractive index decreases substantially continuously as it goes away from the center, and has the same refractive index as the cladding at the boundary with the cladding. Therefore, the GI fiber has a curved (square type) refractive index distribution between the core portion 20 and the cladding portion 25.

  The translucent resin film 16 is disposed on one surface of the base material 11 so as to cover the entire through hole 12. The light emitting element 13 and the optical fiber 19 are optically coupled through the translucent resin film 16. The translucent resin film 16 can be formed using, for example, a resin that transmits light, such as polyimide or epoxy resin. A polyimide film is preferably used from the viewpoints of good light transmission, flexibility and easy handling. Further, a gap between the two is eliminated at the joint surface between the translucent resin film 16 and the optical fiber 19, the refractive index is matched between the optical fiber 19 and the translucent resin film 16, and the optical signal is scattered. A refractive index matching material (so-called matching oil) for preventing light loss due to the above may be permeated. Thereby, the optical coupling efficiency can be increased. In addition, as a refractive index matching material, the epoxy resin etc. which have the translucency similar to the underfill material mentioned later, etc. can be used, for example. When FPC is used for the translucent resin film 16, an adhesive or an adhesive sheet that bonds the FPC and the substrate may be used as the refractive index matching material.

  The wiring film 17 is responsible for signal transmission between the light emitting element 13 and an external electronic circuit (external circuit) (not shown) disposed on the external substrate 30, and is transparent using a conductor such as copper. A predetermined shape (wiring pattern) is formed on the optical resin film 16. In order to cope with the high-speed operation of the light-emitting element 13, it is preferable that a microstrip line suitable for transmitting a high-frequency signal is configured including the translucent resin film 16 and the wiring film 17.

The sealing material 18 is formed on the translucent resin film 16 so as to cover the entire light emitting element 13 in order to protect the light emitting element 13 as necessary. As such a sealing material 18, an epoxy resin etc. are used, for example.
The optical fiber piece 21 plays a role of relaying transmission / reception of optical signals between the light emitting element 13 and the optical fiber 19. That is, the optical fiber piece 21 guides laser light including a plurality of modes from the light emitting element 13 to the optical fiber 19 and optically couples them. The optical fiber piece 21 used in the present invention is composed of a step index type multimode fiber (SI fiber), and the laser light oscillated from the light emitting element 13 is reflected in the optical fiber piece 21 in a complicated manner. Is repeated and emitted from various angles and emission positions different from the incident light. Thereby, since the incident position and incident angle on the end face of the optical fiber 19 also change variously, it is possible to eliminate the correlation between the radiation angle of the light emitting element 13 and the incident position on the end face of the optical fiber 19. Therefore, the correlation between the incident position and the mode of the laser beam can be eliminated, and various laser beams can be uniformly incident on the optical fiber 19.

  The SI fiber has a structure in which the periphery of the core part is covered with a clad part, and has a step-like refractive index distribution between the core part and the clad part.

  The operation of the optical fiber piece (relay waveguide) 21 will be described in more detail from the viewpoint of optical coupling between the VCSEL (light emitting element 13) and the GI fiber (optical fiber 19).

  The numerical aperture (NA) of the core 20 of the GI fiber is the largest at the center, gradually decreases with distance from the center, and becomes zero at the boundary with the cladding. For example, the NA distribution of a GI fiber having a core diameter of 50 μm and NA of 0.21 (in air, 12.1 degrees on one side) is expressed by the following formula (1).

  When direct coupling (direct coupling) between the VCSEL and the GI fiber is performed, depending on the distance between the VCSEL and the GI fiber, the outside beam with a large radiation angle exceeds the NA limit of the GI fiber, and optical coupling cannot be performed. A light component may be generated (see FIG. 16). Usually, in a VCSEL that oscillates in a multimode, there is a dependency between an oscillation mode and a radiation angle, and a specific mode is emitted at a specific angle. In general, the higher the mode, the larger the radiation angle tends to be. Here, if all the light emitted at a radiation angle greater than a specific angle cannot be incident, a specific mode (especially a higher mode) cannot be incident. It will be. Since the light emission characteristic (IL characteristic) of the laser beam is determined by the sum of the light amounts of all modes, if the specific mode cannot be incident in this way, the IL characteristic is distorted and transmitted as a result. There is a problem that the optical signal is distorted.

  The radiation angle that can be coupled to the GI fiber is obtained from the above equation (1) and the following NA definition equation (2).

  Here, for example, the emission angle (numerical aperture NA) of the VCSEL is NA = 0.25 (in air, 14.5 degrees on one side), and the optical distance L from the emission point of the VCSEL to the entrance (end face) of the GI fiber is When L = 70 μm (in air), only light within R = 12.8 μm and NA = 0.18 (in air, 10.4 degrees on one side) is coupled. Further, since the emission part of the VCSEL has a circular shape with a diameter of about 10 μm, for example, the effective NA is further reduced.

  Here, if a positional shift occurs between the VCSEL and the GI fiber, the light beam that can be optically coupled is further limited. Therefore, considerable accuracy is required for position adjustment between the VCSEL and the GI fiber.

  However, according to the optical fiber piece 21 as described above, before the laser light emitted from the VCSEL reaches the GI fiber, the optical path of the light in each mode is changed to eliminate the dependency on the radiation angle and the oscillation mode. Is possible. Therefore, almost all modes of light can be coupled with the GI fiber little by little, mode deviation is reduced, and distortion of the transmitted signal is improved.

  Next, a preferable length and arrangement in relation to the substrate 11 will be briefly described. The optical fiber piece 21 is a fragment having an axial length shorter than the distance between the one surface (first surface) 23 and the other surface (second surface) 24 of the base material 11, and the upper surface side of the base material 11. 23. The optical fiber piece 21 and the optical fiber to be inserted have substantially the same diameter. The optical fiber piece 21 is positioned by the through hole 12 and fixed by press-fitting or bonding into the through hole 12. Further, the optical fiber piece 21 also plays a role of preventing an impact upon insertion / removal of the optical fiber 19 from being directly transmitted to the light emitting element 13. Thereby, the lifetime of the optical communication module can be extended. A ferrule 22 may be formed around the optical fiber piece 21 as necessary.

  The preferable length of the optical fiber piece 21 will be described from the viewpoint of the coupling efficiency with the optical fiber 19. The relationship between the coupling efficiency between the optical fiber piece 21 and the optical fiber 19 and the length of the optical fiber piece 21 was calculated by computer simulation. In order to simplify the calculation, the calculation was performed only for light that passes through the plane parallel to the axis of the optical fiber piece 21 including the midpoint of the core portion of the optical fiber piece 21 schematically. The refractive index in the core of the optical fiber piece 21 was 1.5, and the refractive index between the VCSEL (light emitting element 13) and the optical fiber piece 21 was 1.5. The GI fiber (optical fiber 19) has a core diameter of 50 μm and NA of 0.21. The results are shown in FIGS.

  FIG. 3 is a diagram showing the relationship between the radiation angle of the VCSEL (light emitting element 13) used for the calculation and the output. Here, the output (power) is shown as a relative value when the maximum value of the light amount is used as a reference. As shown in FIG. 3, it can be seen that the VCSEL has a ring-like radiation characteristic.

  FIG. 4 is a graph showing the relationship between the length of the optical fiber piece 21 when the core diameter of the optical fiber piece 21 is 50 μm and the coupling efficiency between the optical fiber piece 21 and the GI fiber. As shown in FIG. 4, the coupling efficiency (coupling efficiency) varies depending on the length (axial length) of the optical fiber piece 21, draws an attenuation curve, and the axial length of the optical fiber piece 21 is the maximum light reception of the optical fiber piece 21. When the incident light incident at an angle has a length that can be reflected four times or more, the light is focused (stabilized) to a predetermined coupling efficiency. Therefore, it is preferable that the length of the optical fiber piece 21 is such that incident light can be reflected four times or more because good coupling efficiency can be obtained. Since the length required for one reflection is core diameter × core refractive index / NA = 0.05 × 1.5 / 0.21 = 0.357, it is considered to be about 1.43 mm in four reflections. It is done. Calculation results of the radiation angle and relative light quantity at each length L (length at points a to f in FIG. 4) when the optical fiber piece 21 having such a length that the attenuation curve shows the maximum value and the minimum value is used. It shows in FIGS.

  FIG. 5 (corresponding to the point a) shows the measurement result of the radiation angle and the relative light quantity when the core diameter φ of the optical fiber piece 21 is 50 μm and the length L is 105 μm. Here, L = 105 μm corresponds to direct coupling with an optical distance of 70 μm. The coupling efficiency at this time is as good as 73.6%.

  FIG. 6 (corresponding to the point b) shows the measurement result of the radiation angle and the relative light quantity when the core diameter φ of the optical fiber piece 21 is 50 μm and the length L is 305 μm. In this case, the coupling efficiency is as low as 23.3%, and light having a radiation angle larger than about 6 degrees is not coupled, resulting in a large signal distortion.

  FIG. 7 (corresponding to the point c) shows the measurement results of the radiation angle and the relative light quantity when the core diameter φ of the optical fiber piece 21 is 50 μm and the length L is 425 μm. In this case, the coupling efficiency is a good value of 76.5%, and the coupling is performed up to a light having a relatively large radiation angle.

  FIG. 8 (corresponding to the point d) shows the measurement result of the radiation angle and the relative light quantity when the core diameter φ of the optical fiber piece 21 is 50 μm and the length L is 675 μm. The coupling efficiency at this time is as low as 49.7%, and light larger than the radiation angle of about 8 degrees is not coupled, and the signal distortion is large.

  FIG. 9 (corresponding to the point e) shows the measurement result of the radiation angle and the relative light quantity when the core diameter φ of the optical fiber piece 21 is 50 μm and the length L is 825 μm. The coupling efficiency at this time is as good as 66%, and the coupling is performed up to a light having a relatively large radiation angle.

  FIG. 10 (corresponding to the point f) shows the measurement result of the radiation angle and the relative light quantity when the core diameter φ of the optical fiber piece 21 is 50 μm and the length L = 1500 μm. The coupling efficiency at this time is as good as 63.5%, and the light is coupled up to a relatively large radiation angle.

  FIG. 11 shows the measurement results of the radiation angle and relative light quantity when the optical fiber piece 21 has a core diameter φ = 50 μm and a length L = 10000 μm (10 mm). The coupling efficiency at this time is as good as 63.2%, and vignetting (the state in which light cannot be optically coupled) is also subdivided, and almost all radiation angles including relatively large radiation angles are included. The light is uniformly coupled and good results are obtained.

  According to the present embodiment, it is possible to variously change the angle and the incident position of the light incident on the GI fiber as the waveguide 19 by passing the optical fiber piece 21 composed of the SI fiber. As a result, the incident position on the GI fiber is determined by the emission angle of the laser light from the light emitting element 13, and even when only a certain amount of light can be optically coupled to the waveguide 19, such an incident position and an emission angle. Therefore, it is possible to transmit a signal with a substantially uniform distribution. Therefore, for example, in a laser beam having a correlation between the emission angle and the mode, only light of a specific emission angle mode cannot be incident, and problems such as distortion in the transmitted signal can be solved. In addition, since the incident positions of various mode lights on the end face of the waveguide 19 are randomized, it is possible to increase the margin for position adjustment, and to reduce signal quality deterioration due to adjustment position deviation. It becomes possible. In addition, the light emitting element 13, the optical fiber piece 21, and the waveguide 19 can be accurately positioned with a simple structure. Accordingly, it is possible to provide an optical module capable of high-quality and high-speed transmission at a low cost and with a high yield.

  In the above example, the core diameter of the optical fiber piece 21 is the same as the core diameter of the optical fiber as the waveguide 19, but is not limited to this. For example, the core diameter of the optical fiber piece 21 is The core diameter of the optical fiber 19 may be smaller. In the above example, light with NA of 0.21 or more and luminous flux that does not satisfy the condition of the above formula (1) are not coupled with the optical fiber 19 and disappear through the cladding portion 25. However, if the core diameter of the optical fiber piece 21 is smaller than the core diameter of the optical fiber 19, the coupling efficiency can be improved.

  FIG. 12 shows the measurement results of the radiation angle and relative light quantity when the core diameter φ of the optical fiber piece 21 is 35 μm and the length L is 10000 μm. In this case, the coupling efficiency is very good at 80.6%, and the light having a relatively large radiation angle is coupled.

(Second Embodiment)
In the first embodiment, the case where the core diameter of the optical fiber piece 21 is the same as or smaller than the core diameter of the optical fiber as the waveguide 19 has been described. In the second embodiment, a case where the core diameter of the optical fiber piece 21 is larger than the core diameter of the optical fiber 19 will be described.

FIG. 13 is a partially enlarged view for explaining the optical module according to the second embodiment.
Under stable driving conditions of the light emitting element 13 such as a VCSEL, the optical power is usually large, and when the laser beam is viewed directly, there is a possibility of causing harm to the eyes. Therefore, for example, when an optical communication system is constructed, an attenuator (attenuator) is often arranged on the communication path depending on how it is used.

  In such a case, as shown in FIG. 13, if the core diameter of the optical fiber piece 21 is made larger than the core diameter of the optical fiber 19, the coupling efficiency between the optical fiber piece 21 and the optical fiber 19 decreases. It is possible to attenuate the amount of laser light transmitted by the amount of light that is not coupled to the optical fiber 19. The outgoing light emitted from the optical fiber piece 21 has no correlation between the outgoing position, outgoing direction and mode, and various mode lights are emitted at different positions and outgoing angles. Distortion can also be kept to a minimum, and signal quality can be stably attenuated.

  FIG. 14 shows the measurement results of the radiation angle and relative light amount when the core diameter φ of the optical fiber piece 21 is 65 μm and the length L is 10000 μm. The coupling efficiency at this time is attenuated to 48.5%. However, as shown in FIG. 14, vignetting (state in which light cannot be optically coupled) is also subdivided, so a relatively large radiation angle. The light of almost all the radiation angles including the light of is uniformly coupled, and is excellent in the preservation of the signal shape, that is, the data quality.

  The attenuation can be easily controlled by the core diameter of the relay fiber. Furthermore, by increasing the core diameter of the optical fiber piece 21, it is possible to widen the position adjustment margin between the VCSEL 13 and the optical fiber piece 21 or between the optical fiber piece 21 and the optical fiber 19. Therefore, since it becomes easy to manufacture, it is possible to provide an optical module at a lower cost and with a higher yield.

(Third embodiment)
FIG. 15 is a partially enlarged view for explaining the optical module according to the third embodiment.
In this embodiment, as shown in FIG. 15, the optical fiber piece 21 is gently tapered from the incident surface of the laser light incident from the light emitting element 13 toward the emitting surface. An example of such an optical fiber piece 21 is one having a core diameter of 50 μm on the entrance side, a core diameter of 80 μm on the exit side, and a length (axial length) of 2 mm. When the optical fiber piece 21 having such a shape is used, the NA of the high NA light gradually decreases as the multiple reflection is repeated in the optical fiber piece 21, so that the NA that can be coupled with the optical fiber 19 is reduced. It tends to be a luminous flux. In this example, the NA 0.25 luminous flux is reduced to about NA 0.19 by four reflections, and can be coupled.

  For this reason, a higher signal distortion improvement effect can be obtained, and higher quality and higher speed signal transmission can be achieved. Further, the amount of light can be attenuated in the same manner as in the second embodiment by setting the core diameter on the emission side. In addition, the change of the core diameter from the incident side of the optical fiber piece 21 to the output side may not necessarily be linear. Therefore, the boundary line in the cross-sectional view of the core part 24 and the clad part 26 from the incident side to the emission side may be a curve. Moreover, the change of the core diameter from the incident side to the output side of the optical fiber piece 21 may be continuous or intermittent. Therefore, you may have a taper part in part.

(Optical communication device and electronic equipment)
The optical module according to the present invention is suitable for use in an optical communication device (optical transceiver). The optical communication device may include a receiving module in addition to the optical module as described above as a light emitting module. As a receiving module used on such a receiving side, a light receiving element such as a PD (Photo Diode) is used instead of the light emitting element 13 in FIG. 1, and a GI fiber is used as the optical fiber piece 21 instead of the SI fiber. Are preferred. This is because the GI fiber is more advantageous in increasing the speed because the spread of the laser beam is smaller and the light receiving area can be reduced than the SI fiber. Therefore, by using such a receiving module, an optical communication apparatus capable of further increasing the speed can be provided.

  Such an optical communication device can be used for various electronic devices that perform information communication with an external device or the like using light as a transmission medium, such as a personal computer or a so-called PDA (portable information terminal device). is there.

FIG. 1 is a diagram for explaining an example of an optical module according to the first embodiment of the present invention. FIG. 2 is a partially enlarged view of FIG. FIG. 3 is a diagram showing the relationship between the emission angle and output of the VCSEL used for the calculation. FIG. 4 is a graph showing the relationship between the length of the optical fiber piece when the core diameter of the optical fiber piece is 50 μm and the coupling efficiency between the optical fiber piece and the GI fiber. FIG. 5 (corresponding to the point a) shows the measurement results of the radiation angle and the relative light quantity when the core diameter φ = 50 μm and the length L = 105 μm of the optical fiber piece. FIG. 6 (corresponding to the point b) shows the measurement result of the radiation angle and the relative light quantity when the core diameter φ = 50 μm and the length L = 305 μm of the optical fiber piece. FIG. 7 (corresponding to the point c) shows the measurement results of the radiation angle and the relative light quantity when the core diameter φ of the optical fiber piece is 50 μm and the length L is 425 μm. FIG. 8 (corresponding to the point d) shows the measurement result of the radiation angle and the relative light quantity when the core diameter φ = 50 μm and the length L = 675 μm of the optical fiber piece. FIG. 9 (corresponding to the point e) shows the measurement result of the radiation angle and the relative light quantity when the core diameter φ of the optical fiber piece is 50 μm and the length L is 825 μm. FIG. 10 (corresponding to the point f) shows the measurement result of the radiation angle and the relative light quantity when the core diameter φ = 50 μm and the length L = 1500 μm of the optical fiber piece. This FIG. 11 shows the measurement results of the radiation angle and relative light quantity when the core diameter φ of the optical fiber piece is 50 μm and the length L is 10000 μm (10 mm). FIG. 12 shows the measurement results of the radiation angle and relative light quantity when the core diameter φ of the optical fiber piece is 35 μm and the length L is 10000 μm. FIG. 13 is a partially enlarged view for explaining the optical module according to the second embodiment. FIG. 14 shows the measurement results of the radiation angle and relative light amount when the core diameter φ of the optical fiber piece is 65 μm and the length L is 10000 μm. FIG. 15 is a partially enlarged view for explaining the optical module according to the third embodiment. FIG. 16 is a diagram for explaining a conventional optical module as a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Base material, 12 ... Through-hole, 13 ... Light emitting element, 14 ... Optical fiber piece, 15 ... Ferrule, 16 ... Translucent resin film, 17 ... Wiring Membrane, 18 ... Sealing material, 19 ... Waveguide (optical fiber), 20 ... Core (part), 21 ... Optical fiber piece, 22 ... Ferrule, 23 ... Upper surface side , 24 ... Core part, 25 ... Cladding part, 26 ... Cladding part, 30 ... External substrate

Claims (12)

A light-emitting element that oscillates multimode laser light;
A relay waveguide that is disposed on an optical axis of the light emitting element and a waveguide that propagates laser light emitted from the light emitting element, and relays optical coupling between the light emitting element and the waveguide;
An optical module, wherein the relay waveguide has a structure in which a core part is surrounded by a clad part, and a stepped refractive index distribution is formed between the core part and the clad part . A light-emitting element that oscillates multimode laser light;
An optical fiber piece disposed on the optical axis of the light emitting element and a waveguide propagating a laser beam oscillated from the light emitting element, and relaying optical coupling between the light emitting element and the waveguide;
A substrate on which the optical element is mounted and holding the optical fiber piece and the waveguide;
And the optical fiber piece is composed of a step index multimode fiber.   The optical module according to claim 1, wherein the waveguide is a graded index optical waveguide.   The optical module according to claim 3, wherein the optical fiber is a graded index multimode optical fiber.   The optical module according to claim 3 or 4, wherein a core diameter of the optical fiber piece is the same as or smaller than a core diameter of the optical fiber.   The optical module according to claim 3 or 4, wherein a core diameter of the optical fiber piece is larger than a core diameter of the optical fiber.   The optical module according to claim 3, wherein an NA of the optical fiber piece is larger than an NA of the optical fiber.   The optical module according to any one of claims 3 to 7, wherein the optical fiber piece has at least a tapered portion in which a core diameter increases from an incident side toward an emission side.   9. The optical module according to claim 3, wherein an axial length of the optical fiber piece is a length that allows incident light incident at a maximum light receiving angle of the optical fiber piece to be reflected four times or more.   When the vertical axis represents the coupling efficiency of the optical fiber piece and the horizontal axis represents the length of the optical fiber piece, when the relationship between the coupling efficiency and the length is approximated by an attenuation curve, The optical module according to claim 3, wherein a length of the optical fiber piece in a longitudinal direction is a length at which the attenuation curve takes a substantially maximum value.   An optical communication apparatus comprising the optical module according to claim 1. An electronic apparatus comprising the optical module according to claim 1.

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