JP2014086642A - Optical module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical module suitable for high speed modulation, in which increase in the electrical resistance and decrease in the reliability are suppressed, at a low cost.SOLUTION: An optical module includes a surface-emitting laser element having a lower reflector and an upper reflector constituting an optical resonator, an active layer located between the lower reflector and the upper reflector, and outputting laser signal light of horizontal multi-mode by application of a modulation signal. When operating the surface-emitting laser element with a modulation signal, first suppression ratio of the intensity of higher-order mode light of secondary mode to the intensity of main mode light in the horizontal mode of the laser signal light is adjusted to a value for suppressing the mode competition noise contained in the laser signal light.

Description

  The present invention relates to an optical module using a surface emitting laser element.

  In relatively short-distance optical transmission such as optical interconnection, an optical module using a surface emitting laser element (Vertical Cavity Surface Emitting Laser: VCSEL) as a signal light source may be used. For example, Patent Document 1 discloses a multimode VCSEL that performs laser oscillation in a plurality of transverse modes.

JP-A-7-170231

  However, the multi-mode VCSEL has a problem that mode competition noise due to a plurality of transverse modes is likely to occur. Mode competition noise degrades the transmission characteristics of the multi-mode VCSEL, and can be a factor that hinders the increase in communication speed by high-speed modulation.

  On the other hand, in a single mode VCSEL that oscillates substantially in a single transverse mode, laser oscillation in a high-order transverse mode is suppressed, so that mode competition noise is suppressed. However, for example, in a surface emitting laser element using a selective oxide layer as a current confinement structure, the aperture diameter of the selective oxide layer is reduced to limit the area of the light emitting region of the active layer, thereby realizing single mode oscillation. An increase in electrical resistance or a decrease in reliability may occur. Also, single mode VCSELs can be expensive because they have a lower manufacturing yield than multimode VCSELs.

  The present invention has been made in view of the above, and it is an object of the present invention to provide an optical module that is suitable for high-speed modulation and low cost, in which an increase in electrical resistance and a decrease in reliability are suppressed.

  In order to solve the above-described problems and achieve the object, an optical module according to the present invention includes a lower reflecting mirror and an upper reflecting mirror constituting an optical resonator, and between the lower reflecting mirror and the upper reflecting mirror. And a surface emitting laser element that outputs a transverse multi-mode laser signal light by applying a modulation signal, and the laser signal when the surface emitting laser element is operated by the modulation signal. The first suppression ratio of the intensity of the second-order higher-order mode light with respect to the intensity of the main mode light in the transverse mode of light is adjusted to a value that suppresses mode-competitive noise included in the laser light signal. And

  In the optical module according to the present invention as set forth in the invention described above, the first suppression ratio is a range in which the relative intensity noise of the laser signal light is lower than a reference value by 10 dB / Hz or more.

  In the optical module according to the present invention as set forth in the invention described above, the first suppression ratio is 35 dB or more.

  The optical module according to the present invention is characterized in that, in the above invention, the intensity of the third or higher order mode light in the transverse mode of the laser signal light is lower than the intensity of the second order mode light.

  In the optical module according to the present invention, the first suppression ratio is 40 dB or more in the above invention, and the intensity of the first-order higher-order mode light with respect to the intensity of the main mode light in the transverse mode of the laser signal light. The second suppression ratio is 10 dB or more.

  The optical module according to the present invention is the optical module according to the above invention, wherein the surface emitting laser element is disposed between the upper reflecting mirror and the active layer, and the outer periphery of the current injection unit is formed by a current injection unit and a selective oxidation heat treatment. And a thickness of the current confinement layer or a diameter of the current injection portion is adjusted so that the first suppression ratio becomes the value. And

  In the optical module according to the present invention as set forth in the invention described above, the upper reflecting mirror is formed of a multilayer film, and each layer constituting the multilayer film is formed around a flat portion located in a light output region and the flat portion. And each of the flat portions is formed so that the area decreases in the light output direction.

  According to the present invention, an increase in electrical resistance, a decrease in reliability, and the like are suppressed, and there is an effect that an optical module that is suitable for high-speed modulation and low in cost can be realized.

1 is a schematic diagram of an optical module according to Embodiment 1. FIG. FIG. 2 is a schematic cross-sectional view of the surface emitting laser element shown in FIG. FIG. 3 is a diagram illustrating an output light spectrum of the example. FIG. 4 is a diagram illustrating the relationship between the suppression ratio and RIN. FIG. 5 is a diagram showing an output light spectrum of a comparative example. FIG. 6 is a diagram illustrating an eye diagram of the example. FIG. 7 is a diagram showing an eye diagram of a comparative example. FIG. 8 is a schematic cross-sectional view of another embodiment of a surface emitting laser element that can be used in the optical module according to the first embodiment. FIG. 9 is a diagram showing a main part of Modification 1 of the surface emitting laser element shown in FIG. FIG. 10 is a diagram showing a main part of a second modification of the surface emitting laser element shown in FIG.

  Embodiments of an optical module according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. Moreover, in each drawing, the same code | symbol is attached | subjected suitably to the same or corresponding element. Furthermore, it should be noted that the drawings are schematic, and dimensional relationships between elements may differ from actual ones. Even between the drawings, there are cases in which portions having different dimensional relationships and ratios are included. In the following, a mode in terms such as single mode and multi-mode means a transverse mode.

(Embodiment 1)
FIG. 1 is a schematic diagram of an optical module according to Embodiment 1 of the present invention. The optical module 1000 includes a surface emitting laser element 100 disposed on a substrate B, a mirror 20, and an optical fiber 30.

  A controller C for driving the surface emitting laser element 100 is connected to the surface emitting laser element 100. On the side of the end face of the optical fiber 30, a mirror 20 as an optical coupling means is disposed. The mirror 20 and the optical fiber 30 are supported by a support member (not shown) so as to have a suitable arrangement. The surface emitting laser element 100 is disposed below the mirror 20. The controller C drives the surface emitting laser element 100 to output the laser signal light L1. The laser signal light L1 output from the surface emitting laser element 100 is reflected by the mirror 20, optically coupled to the optical fiber 30, propagates through the optical fiber 30, and is output to the outside.

  FIG. 2 is a schematic cross-sectional view of the surface emitting laser element shown in FIG. As shown in FIG. 1, a surface emitting laser element 100 includes an undoped lower DBR (Distributed Bragg Reflector) laminated on a substrate 1 made of n-type GaAs having a surface orientation (001) and functioning as a lower multilayer reflector. Mirror 2, n-type contact layer 3, n-side electrode 4, n-type cladding layer 5, active layer 6, p-type cladding layer 7, current confinement layer 8, p-type spacer layer 9, p-type contact layer 10, p-side electrode 11 and an upper dielectric DBR mirror 12 that functions as an upper reflecting mirror.

  The p-type contact layer 10 and the n-type contact layer 3 are disposed between the lower DBR mirror 2 and the upper dielectric DBR mirror 12. The active layer 6 is disposed between the lower DBR mirror 2 and the upper dielectric DBR mirror 12. The current confinement layer 8 is disposed between the p-type contact layer 10 and the active layer 6. The p-type spacer layer 9 is interposed between the current confinement layer 8 and the p-type contact layer 10. The p-side electrode 11 is formed on the p-type contact layer 10, and the n-side electrode 4 is formed on the n-type contact layer 3.

  The stacked structure from the n-type cladding layer 5 to the p-type contact layer 10 is formed as a mesa post M formed into a columnar shape by an etching process or the like. The mesa post diameter is, for example, 30 μm. The n-type contact layer 3 extends on the outer peripheral side of the mesa post M. The lower DBR mirror 2 and the upper dielectric DBR mirror 12 constitute an optical resonator.

The lower DBR mirror 2 is formed on an undoped GaAs buffer layer (not shown) stacked on the substrate 1 made of n-type GaAs. The lower DBR mirror 2 includes, for example, 40.5 pairs of compound semiconductor layers in which an Al _0.9 Ga _0.1 As layer functioning as a low refractive index layer and a GaAs layer functioning as a high refractive index layer are paired. It is formed as a semiconductor multilayer film mirror having a periodic structure. The layer thickness of each layer constituting the composite semiconductor layer of the lower DBR mirror 2 is λ / 4n (λ: laser oscillation wavelength, n: refractive index). For example, when λ is 1.06 μm, the Al _0.9 Ga _0.1 As layer has a thickness of about 88 nm, and the GaAs layer has a thickness of about 76 nm.

  The n-type contact layer 3 and the n-type cladding layer 5 are formed using n-type GaAs as a material.

The p-type cladding layer 7 is formed using p-type AlGaAs (for example, Al _0.3 Ga _0.7 As is desirable). The p-type spacer layer 9 is formed using p-type AlGaAs as a material. The p-type contact layer 10 is formed using p-type GaAs as a material.

A p-type or n-type dopant is added to the n-type cladding layer 5, the p-type cladding layer 7, and the p-type spacer layer 9 so that the carrier concentration is, for example, about 1 × 10 ¹⁸ cm ⁻³ , The conductivity type is p-type or n-type. The carrier concentrations of the n-type contact layer 3 and the p-type contact layer 10 are, for example, about 2 × 10 ¹⁸ cm ⁻³ and 3 × 10 ¹⁹ cm ⁻³ , respectively.

The current confinement layer 8 includes an opening 8a as a current injection portion and a selective oxidation layer 8b as a current confinement portion. The opening 8a is made of Al _1-x Ga _x As (0 ≦ x <0.2), and the selective oxidation layer 8b is made of (Al _1-x Ga _x ) ₂ O ₃ . X is 0.02, for example.

The current confinement layer 8 is formed by subjecting an Al-containing semiconductor layer made of Al _1-x Ga _x As to selective oxidation heat treatment. That is, the selective oxidation layer 8b is formed in a ring shape on the outer periphery of the opening 8a by oxidizing the Al-containing semiconductor layer by a predetermined range from the outer periphery of the mesa post M along the laminated surface. The selective oxidation layer 8b has an insulating property, and the current injected from the p-side electrode 11 is narrowed and concentrated in the opening 8a, whereby the current density injected into the active layer 6 immediately below the opening 8a. It has a function to enhance. The opening diameter of the opening 8a is, for example, 6 μm to 7 μm. The thickness of the current confinement layer 8 is 20 nm to 30 nm, for example. As a result, the surface emitting laser element 100 oscillates in multimode.

  The active layer 6 has an MQW-SCH structure in which both sides of a multiple quantum well (MQW) layer in which well layers and barrier layers are alternately stacked are sandwiched between separate confinement heterostructure (Separate Confinement Heterostructure) layers. The well layer is made of a material selected so as to emit light having a desired wavelength, for example, a GaInAs-based semiconductor material. The barrier layer is made of, for example, GaAs. The active layer 6 is a spontaneous emission light including light having a wavelength of, for example, 1.0 μm to 1.1 μm (referred to as 1.0 μm band) due to a current injected from the p-side electrode 11 and confined by the current confinement layer 8. The composition and layer thickness of the semiconductor material are set so as to emit light.

The upper dielectric DBR mirror 12 has a periodic structure in which, for example, 9 pairs of composite dielectric layers each having a pair of SiO ₂ layer functioning as a low refractive index layer and SiNx layer functioning as a high refractive index layer are laminated. As in the lower DBR mirror 2, the thickness of each layer is λ / 4n.

  The p-side electrode 11 is formed in a ring shape along the outer extension of the p-type contact layer 10. On the other hand, the n-side electrode 4 is formed on the surface of the extended portion of the n-type contact layer 3 extending on the outer peripheral side of the mesa post M, and is formed in a C shape so as to surround the periphery of the mesa post M.

  Next, the operation of the surface emitting laser element 100 will be described. First, the controller C applies a bias voltage and a modulation voltage signal between the p-side electrode 11 and the n-side electrode 4 to inject current. In the p-type contact layer 10, p-side carriers (holes) flow in the horizontal direction in the drawing, and then pass through the p-type spacer layer 9 and concentrate in the opening 8 a of the current confinement layer 8 to increase the density. In this state, it is injected into the active layer 6. On the other hand, n-side carriers (electrons) are injected from the n-side electrode 4 into the active layer 6 through the n-type contact layer 3 and the n-type cladding layer 5.

  As described above, the surface emitting laser element 100 has a so-called double intracavity structure in which both the p-side carrier and the n-side carrier are injected into the active layer without passing through the DBR mirror.

  The active layer 6 into which carriers are injected generates spontaneous emission light. The generated spontaneous emission light is laser-oscillated at any wavelength in the 1.0 μm wavelength band by the optical amplification action of the active layer 6 and the action of the optical resonator. As a result, the surface emitting laser element 100 outputs the laser signal light L1 including the modulation signal from the upper dielectric DBR mirror 12.

  Here, by adjusting the thickness of the current confinement layer 8 and the opening diameter of the opening 8a, the laser signal light L1 is output in a multimode. FIG. 3 is a diagram showing an output light spectrum of the surface emitting laser element of the example in which the thickness of the current confinement layer 8 is 20 nm and the opening diameter of the opening 8a is 6.5 μm. The modulation speed of the modulation voltage signal is 10 Gbps, and the bias current is 5 mA. As shown in FIG. 3, the spectrum of the laser signal light L1 includes components of the main mode light M1, the first-order higher-order mode light M2, the second-order higher-order mode light M3, and the higher-order higher-order mode light. included.

  In FIG. 3, the light intensity is in decibels. Therefore, the suppression ratio of the intensity of the second-order higher-order mode light M3 with respect to the intensity of the main mode light M1 is a value represented by the difference between the two intensities, and is −5 dBm − (− 45 dBm) = 40 dB. At this time, mode competition noise included in the laser signal light L1 is suppressed.

  This will be specifically described below. FIG. 4 shows the suppression ratio of the intensity of the second-order higher-order mode light to the intensity of the main mode light and the relative intensity of the laser signal light in the surface-emitting laser element having the same configuration as the surface-emitting laser element 100 shown in FIG. It is a figure which shows the relationship with noise (Relative Intensity Noise: RIN). The black square points indicate the measurement data points, and the solid line indicates the fitting curve obtained by the least square method of the measurement data points. RIN on the vertical axis is a value normalized to a value per frequency of 1 Hz. In the surface emitting laser element used for the measurement, the thickness of the current confinement layer and the opening diameter of the opening are adjusted in order to set the suppression ratio to various values.

  As shown in FIG. 4, when the suppression ratio is low, the value of RIN is large. However, as the suppression ratio increases, the value of RIN decreases, and at 35 dB or more, the change of RIN is small with respect to the change of the suppression ratio. , RIN is a stable region.

  According to the knowledge obtained by the inventors of the present invention through intensive studies to suppress mode competition noise, the suppression ratio (first suppression ratio) of the intensity of the second-order higher-order mode light with respect to the intensity of the main-mode light is By adjusting the value, mode competition noise included in the laser signal light can be suppressed. For example, in the case of FIG. 4, the suppression ratio is preferably adjusted to 35 dB or more, and more preferably adjusted to 40 dB or more.

  Further, the first suppression ratio is preferably adjusted to a range in which RIN is lower than the reference value by 10 dB / Hz or more. Examples of the reference value include general standards, but may be -128 dB / Hz, for example. In that case, it is preferable that RIN be −138 dB / Hz or less.

  The reason why the mode competition noise can be effectively suppressed by adjusting the suppression ratio between the main mode light and the second-order higher-order mode light is considered as follows. That is, the main mode light is the LP01 mode, and the second order higher order mode light is the LP02 mode. However, in both the LP01 mode and the LP02 mode, the near-field image (NFP) has an intensity at the center of the light emitting region. Since it has a peak and the symmetry of the light pattern is similar, the light easily transitions between both modes, and it is considered that the contribution to the mode competition noise is large. Therefore, the mode competition noise can be effectively suppressed by adjusting the suppression ratio between the two mode lights having a large contribution.

  As for the relationship between the main mode light and the other higher order modes, it is preferable that the intensity of the third or higher order mode light is lower than the intensity of the second order mode light and that mode competition noise is suppressed. Further, the mode competition is that the first suppression ratio is 40 dB or more, and the suppression ratio (second suppression ratio) of the first-order higher-order mode light intensity to the main mode light intensity is 5 dB or more and 40 dB or less. This is preferable in terms of noise suppression. For example, in the case of FIG. 3, the second suppression ratio is −5 dBm − (− 15 dBm) = 10 dB.

  Next, in the surface-emitting laser element having the same configuration as the surface-emitting laser element 100 shown in FIG. 2, the surface of the comparative example in which the thickness of the current confinement layer 8 is 40 nm and the opening diameter of the opening 8a is 6.5 μm. A light emitting laser element was fabricated and its operating characteristics were measured.

  FIG. 5 is a diagram showing an output light spectrum of the surface emitting laser element of the comparative example. Note that the modulation speed of the modulation voltage signal during operation is 10 Gbps, and the bias current is 5 mA. In the output light spectrum shown in FIG. 5, the spectrum of the laser signal light includes the main mode light M11, the first-order higher-order mode light M12, the second-order higher-order mode light M13, and the higher-order higher-order mode light. Ingredients included. However, the first suppression ratio and the second suppression ratio were both less than 10 dB.

  Next, the eye diagrams of the laser signal light output from the surface emitting laser elements of the example and the comparative example were measured under the same conditions as the conditions for measuring the output light spectrum of FIGS. The extinction ratio of the modulation signal was set to 6 dB.

  FIG. 6 is a diagram illustrating an eye diagram of the example. FIG. 7 is a diagram showing an eye diagram of a comparative example. As shown in FIGS. 6 and 7, in the eye diagram of the comparative example, the trace was thick. This phenomenon indicates that the jitter of the laser signal light is large and the error rate of the transmission data is high in the comparative example. On the other hand, in the eye diagram of the example, the trace remained thin. This phenomenon indicates that the jitter of the laser signal light is small and the error rate of the transmission data is low in the embodiment.

  As described above, in the optical module 1000 according to the first embodiment, since the surface emitting laser element 100 is multimode oscillation, an increase in electrical resistance and a decrease in reliability are suppressed, and the cost is low. Furthermore, since mode competition noise is suppressed, it is suitable for high-speed modulation.

  Next, another embodiment of the surface emitting laser element that can be used in the optical module according to Embodiment 1 will be described. FIG. 8 is a schematic cross-sectional view of another embodiment of a surface emitting laser element that can be used in the optical module according to the first embodiment. The surface emitting laser element 200 includes a lower DBR mirror 2, an n-type contact layer 3, an n-side electrode 4, an n-type cladding layer 5, an active layer 6, a current confinement layer 8, and a p-type spacer layer stacked on a substrate 1. 9, a p-type contact layer 10, a p-side electrode 21, an intermediate layer 23, and an upper dielectric DBR mirror 22.

  The lower DBR mirror 2, n-type contact layer 3, n-side electrode 4, n-type cladding layer 5, active layer 6, current confinement layer 8, p-type spacer layer 9 and p-type contact layer 10 are shown in FIG. Since it is the same as the corresponding element of the light emitting laser element 100, description is abbreviate | omitted.

  The intermediate layer 23 is formed between the p-type contact layer 10 and the upper dielectric DBR mirror 22 and includes a first layer 23a and a second layer 23b.

  The first layer 23a is, for example, a phase adjustment layer, a protective layer, a nonlinear layer, or an absorption layer. The phase adjustment layer is formed of a dielectric having a refractive index different from that of the mesa post M, for example, and has a function of adjusting the phase of the laser signal light output from the surface emitting laser element 200. The protective layer is formed of a dielectric, for example, and has a function of protecting the upper surface of the mesa post M. The nonlinear layer is formed of, for example, silicon nitride, and has a function of causing a nonlinear optical effect to the laser signal light output from the surface emitting laser element 100 and generating higher-order harmonics. The absorption layer has a function of absorbing high-order harmonics, for example. Similarly to the first layer 23 a, the second layer 23 b is a layer that functions as a phase adjustment layer, a protective layer, a nonlinear layer, an absorption layer, or the like, or the lowermost layer of the upper dielectric DBR mirror 22.

  The p-side electrode 21 is formed in a ring shape along the outer extension of the p-type contact layer 10. On the inner peripheral side of the p-side electrode 21, an extending portion 21 a that extends to the top of the intermediate layer 23 is formed.

The upper dielectric DBR mirror 22 is formed as a dielectric multilayer mirror having a periodic structure in which, for example, nine pairs of composite dielectric layers each composed of a SiO ₂ layer and a SiNx layer are laminated.

  Here, the upper dielectric DBR mirror 22 is formed so as to cover the intermediate layer 23 and the p-side electrode 21. Since the extending portion 21a of the p-side electrode 21 extends above the intermediate layer 23, each layer constituting the upper dielectric DBR mirror 22 has a ring-shaped convex portion 22a on the extending portion 21a. It is formed. A flat portion 22b located in the output region of the laser signal light is formed on the inner peripheral side of the convex portion 22a.

  The convex portions 22a around the flat portion 22b of each layer are formed so that the inner diameter decreases in the light output direction. The line L is a line connecting the tops of the convex portions 22a, but the line L is inclined inward (on the flat portion 22b side). Thereby, each flat part 22b is also formed so that an area becomes small toward the output direction of light.

  In the surface emitting laser element 200, the flat portions 22b of the respective layers constituting the upper dielectric DBR mirror 22 are formed in such a manner that the area decreases in the light output direction. The laser oscillation is suppressed. For example, by adjusting the area of each flat portion 22b and the extent to which the area is reduced (that is, the inclination angle of the line L), the intensity of the second-order higher-order mode light with respect to the intensity of the main-mode light included in the laser signal light is adjusted. The suppression ratio (first suppression ratio) and the suppression ratio of other higher-order mode light can be adjusted. Thereby, mode competition noise included in the laser signal light output from the surface emitting laser element 200 can be suppressed. Further, by controlling the shape and area of the opening of the p-side electrode 21, the intensity of the secondary mode can be controlled. If the opening is enlarged, the uniformity of carrier injection becomes poor, and a secondary mode having an intensity distribution in a portion away from the central axis of the mesa tends to oscillate. Therefore, mode competition noise can be reduced by narrowing the area of the opening of the electrode and making current injection uniform.

  FIG. 9 is a diagram showing a main part of Modification 1 of the surface emitting laser element shown in FIG. The configuration of the surface emitting laser element 300 from the mesa post M to the substrate side is the same as that of the surface emitting laser element 200 shown in FIG.

  The p-side electrode 31 is formed in a ring shape along the extension of the mesa post M. The intermediate layer 33 is formed so that the outer peripheral surface thereof substantially coincides with the inner peripheral surface of the p-side electrode 31. The intermediate layer 33 is, for example, a phase adjustment layer, a protective layer, a nonlinear layer, or an absorption layer. Further, the intermediate layer 33 may be composed of a first layer and a second layer, like the intermediate layer 23 shown in FIG.

The upper dielectric DBR mirror 32 is formed as a dielectric multilayer mirror having a periodic structure in which, for example, 9 pairs of composite dielectric layers each having a SiO ₂ layer and a SiNx layer are stacked. Note that the number of layers is omitted.

  Here, since the thickness of the intermediate layer 33 is thinner than the thickness of the p-side electrode 31, the step S is formed in a circular shape by the surface 33 a of the intermediate layer 33 and the p-side electrode 31. Thereby, on the step S, a ring-shaped convex portion 32a is formed in each layer constituting the upper dielectric DBR mirror 32. A flat portion 32b located in the output region of the laser signal light is formed on the inner peripheral side of the convex portion 32a.

  The convex portions 32a of each layer are formed so that the inner diameter becomes smaller toward the light output direction. A line L connecting the tops of the respective convex portions 32a is inclined inward (on the flat portion 32b side). As a result, each flat portion 32b is also formed so that its area decreases in the light output direction.

  In the surface emitting laser element 300, the flat portions 32b of the respective layers constituting the upper dielectric DBR mirror 32 are formed in such a manner that the area decreases in the light output direction. The laser oscillation is suppressed. Therefore, similarly to the surface-emitting laser element 200, the suppression ratio (first suppression ratio) of the intensity of the second-order higher-order mode light with respect to the intensity of the main mode light included in the laser signal light output from the surface-emitting laser element 300. In addition, the suppression ratio of other higher-order mode light can be adjusted. Thereby, mode competition noise included in the laser signal light output from the surface emitting laser element 300 can be suppressed.

  FIG. 10 is a diagram showing a main part of a second modification of the surface emitting laser element shown in FIG. The configuration of the surface emitting laser element 400 from the mesa post M to the substrate side is the same as that of the surface emitting laser element 200 shown in FIG.

  The p-side electrode 41 is the same as the p-side electrode 41 shown in FIG. The intermediate layer 43 is, for example, a phase adjustment layer, a protective layer, a nonlinear layer, or an absorption layer, and has an outer diameter such that a gap G is formed between the outer peripheral surface and the inner peripheral surface of the p-side electrode 41. Have.

The upper dielectric DBR mirror 42 is formed as a dielectric multilayer mirror having a periodic structure in which, for example, 9 pairs of composite dielectric layers each having a SiO ₂ layer and a SiNx layer are stacked. Note that the number of layers is omitted.

  As in the case of the surface emitting laser element 300, the thickness of the intermediate layer 43 is thinner than the thickness of the p-side electrode 41, so that the step S is circular due to the surface 43 a of the intermediate layer 43 and the p-side electrode 41. Is formed. Thus, on the step S, a ring-shaped convex portion 42a is formed in each layer constituting the upper dielectric DBR mirror 42. A flat portion 42b located in the laser signal light output region is formed on the inner peripheral side of the convex portion 42a. Further, the gap G forms a groove 42c between the flat portion 42b and the convex portion 42a.

  In the surface emitting laser element 400, as in the surface emitting laser element 300, each flat portion 42b of each layer constituting the upper dielectric DBR mirror 42 is formed so that the area decreases in the light output direction. Therefore, laser oscillation of higher order mode light is suppressed. Therefore, similarly to the surface emitting laser element 300, the suppression ratio (first suppression ratio) of the intensity of the second-order higher-order mode light with respect to the intensity of the main mode light included in the laser signal light output from the surface emitting laser element 400. In addition, the suppression ratio of other higher-order mode light can be adjusted. Thus, mode competition noise included in the laser signal light output from the surface emitting laser element 400 can be suppressed.

  The present invention can also be applied to a surface emitting laser element that does not have an intracavity structure. That is, the present invention can also be applied to a surface emitting laser element having a structure in which carriers injected into the active layer are injected into the active layer via the lower DBR mirror and / or the upper and lower DBR mirrors.

  In the above embodiment, the n-type semiconductor layer is disposed below the active layer and the p-type semiconductor layer is disposed above the active layer. The n-type semiconductor layer is disposed above the active layer, A p-type semiconductor layer may be disposed below the active layer.

  In the above embodiment, the material, size, etc. of the compound semiconductor are set for the 1.0 μm wavelength band. However, each material, size, and the like are appropriately set according to the desired oscillation wavelength of the laser beam, and are not particularly limited. For example, an InP-based material may be used as a semiconductor material constituting each semiconductor layer. In this case, the Al-containing layer can be composed of an InAlAs layer.

  Further, the present invention is not limited by the above embodiment. What was comprised combining each component mentioned above suitably is also contained in this invention. Further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspect of the present invention is not limited to the above-described embodiment, and various modifications can be made.

DESCRIPTION OF SYMBOLS 1, B board | substrate 2 Lower DBR mirror 3 n-type contact layer 4 n-side electrode 5 n-type cladding layer 6 active layer 7 p-type cladding layer 8 current confinement layer 8a opening 8b selective oxidation layer 9 p-type spacer layer 10 p-type contact Layer 11, 21, 31, 41 P-side electrode 12, 22, 32, 42 Upper dielectric DBR mirror 22a, 32a, 42a Projection 22b, 32b, 42b Flat part 20 Mirror 21a Extension part 23, 33 Intermediate layer 23a First 1st layer 23b 2nd layer 30 Optical fiber 33a, 43a Surface 42c Groove 100, 200, 300, 400 Surface emitting laser element 1000 Optical module G Gap M Mesa post S Step

Claims (7)

  A transverse multimode laser signal by applying a modulation signal, comprising: a lower reflecting mirror and an upper reflecting mirror constituting an optical resonator; and an active layer disposed between the lower reflecting mirror and the upper reflecting mirror. A surface-emitting laser element that outputs light, and the second-order higher-order mode light intensity relative to the intensity of the main-mode light in the transverse mode of the laser signal light when the surface-emitting laser element is operated by a modulation signal. The optical module according to claim 1, wherein the suppression ratio is adjusted to a value that suppresses mode competition noise included in the laser light signal.   2. The optical module according to claim 1, wherein the first suppression ratio is a range in which a relative intensity noise of the laser signal light is lower than a reference value by 10 dB / Hz or more.   The optical module according to claim 1, wherein the first suppression ratio is 35 dB or more.   4. The optical module according to claim 1, wherein the intensity of the third-order or higher-order mode light in the transverse mode of the laser signal light is lower than the intensity of the second-order mode light. .   The first suppression ratio is 40 dB or more, and the second suppression ratio of the intensity of the first-order higher-order mode light with respect to the intensity of the main mode light in the transverse mode of the laser signal light is 10 dB or more. The optical module as described in any one of Claims 1-4.   The surface-emitting laser element includes a current confinement layer that is disposed between the upper reflecting mirror and the active layer, and includes a current injection portion and a selective oxidation layer formed on the outer periphery of the current injection portion by a selective oxidation heat treatment. The thickness of the current confinement layer or the diameter of the current injection portion is adjusted so that the first suppression ratio becomes the value. Light module.   The upper reflecting mirror is composed of a multilayer film, and each layer constituting the multilayer film has a flat part located in the light output region and a convex part formed around the flat part, and the flat parts are The optical module according to claim 1, wherein the optical module is formed so that an area decreases toward an output direction of light.