JP4803992B2 - Light emitting device, optical transmission system, and vertical cavity surface emitting semiconductor laser element - Google Patents

Description

  The present invention relates to a light-emitting device, an optical transmission system, and a vertical-cavity surface-emitting semiconductor laser element including a vertical-cavity surface-emitting semiconductor laser element suitable for large-capacity optical transmission.

  In recent years, optical transmission technology has been developed not only in trunk transmission networks but also in LANs, access systems, and home networks. For example, in Ethernet, a transmission capacity of 10 Gbps has been developed. In the future, further increase in transmission capacity is required, and an optical transmission system exceeding 10 Gbps is expected.

  In a light source for optical transmission having a transmission capacity of 10 Gbps or less, a direct modulation method in which output light intensity is modulated by modulating an injection current of a semiconductor laser is mainly used. However, it has been difficult to operate a semiconductor laser at a modulation frequency exceeding 10 GHz by direct modulation. Therefore, as a light source for optical transmission exceeding 10 Gbps, a method of modulating light output from a semiconductor laser with an external modulator has been developed. However, the external modulation method has a demerit that the module size is large and the number of parts is large so that the cost is high. For this reason, the optical transmission technology including an external modulator is not suitable for a system used by a general user such as a LAN or a home network even if it is used for an expensive system such as a trunk line system.

  On the other hand, in recent years, a vertical cavity surface emitting semiconductor laser element (VCSEL) has been used as a light source for LAN and optical interconnection. VCSELs have lower power consumption than conventional edge-emitting semiconductor lasers, and have superior features in cost reduction because they can be inspected in the wafer state without the need for cleavage in the manufacturing process. Yes. For this reason, a VCSEL by direct modulation is expected as a large capacity optical LAN exceeding 10 Gbps and a light source for optical interconnection.

  As a method for modulating the VCSEL at high speed, the following reports have been made so far.

  That is, Patent Document 1 discloses a modulation-doped stacked structure in which two-dimensional carriers can be generated in order to inject current into an active region without passing through an upper multilayer reflector and reduce lateral resistance at this time. , Thereby reducing the VCSEL resistance and increasing the electrical modulation band limited by the resistance (R) and capacitance (C).

  Further, in Patent Document 2, a quantum well layer that absorbs intersubbands is provided in the vicinity of a light emitting layer, and when modulated signal light is input, the carrier distribution is modulated by intersubband absorption of the quantum well layer, and the carriers in the light emitting layer A technique is also shown in which the density is also modulated, the light emission output is modulated, and thus the response speed is increased without being affected by the CR time constant or the carrier transport effect.

  Further, in Patent Document 3, a lateral cavity type semiconductor laser that performs light injection excitation on a VCSEL is formed on the same substrate, and the forbidden band width of the active layer of the VCSEL is the same as that of the lateral cavity type semiconductor laser. A technology that increases the VCSEL modulation frequency by inputting a modulated optical signal of a lateral cavity type semiconductor laser as external modulation is shown, which is set smaller than the forbidden bandwidth to increase the optical pumping efficiency. Yes.

  Non-Patent Document 1 discloses a technique for injecting light of a DFB laser into a VCSEL to synchronize the oscillation wavelength of the VCSEL (injection lock), thereby increasing the relaxation oscillation frequency of the VCSEL to 22.8 GHz. Has been.

JP 2002-185079 A JP 2002-204039 A JP-A-7-249824 IEICE technical report OPE2003-218, LQE3003-155

  In Patent Document 1 described above, the response speed when the electrical modulation signal output from the driver circuit modulates the carrier density of the light emitting layer of the VCSEL is improved. In Patent Document 2 and Patent Document 3, the influence of an electrical response speed delay when a current flows through the element is eliminated by inputting a modulated optical signal from the outside.

  However, none of the structures can increase the critical frequency at which the stimulated emission rate cannot follow the carrier density change in the light emitting layer, that is, the relaxation oscillation frequency. Therefore, the modulation speed is limited by the relaxation oscillation frequency.

  On the other hand, in Non-Patent Document 1, the photon density inside the VCSEL is increased by injecting light synchronized with the oscillation mode of the VCSEL from the outside. The internal photon density is related to the relaxation oscillation frequency, and the relaxation oscillation frequency of the VCSEL can be increased by increasing the internal photon density. However, in the above method, it is necessary to make the wavelength of the laser light injected from the outside exactly match the resonance mode wavelength of the VCSEL. When the wavelength shift is about several nanometers, the mode is not synchronized and the relaxation oscillation frequency cannot be increased. This necessitates wavelength tuning and temperature control, which complicates the apparatus configuration.

  The present invention relates to a light-emitting device, an optical transmission system, and a vertical-cavity surface-emitting semiconductor laser device that have a simple configuration and are capable of high-speed modulation, suitable for large-capacity transmission with a high relaxation oscillation frequency and a transmission capacity per channel exceeding 10 Gbps. The purpose is to provide.

In order to achieve the above object, a first aspect of the invention is a vertical cavity surface emitting semiconductor laser device having a plurality of resonators sandwiched by a multilayer reflector on a substrate, and a modulation pulse. A plurality of resonators of the vertical cavity surface emitting semiconductor laser element are optically coupled to form one resonance mode, and each resonator has a resonance mode. Each of the active layers has a gain with respect to the same resonance mode wavelength, and one of the active layers is electrically connected to the modulation pulse power source. And the other active layer of the active layers is electrically connected to the excitation DC power source and electrically connected to the modulation pulse power source for the same resonance mode. Electrically connected to the active layer and the excitation DC power source The A light emission device that looks like and the active layer for oscillating mode synchronously, multilayer reflector adjacent the substrate, and / or, the conductivity type of the multilayer reflector of the outermost surface , N-type .

  According to a second aspect of the present invention, there is provided the light emitting device according to the first aspect, wherein means for constricting a current injected into each active layer of the vertical cavity surface emitting semiconductor laser element is provided. The area of current confinement with respect to the active layer electrically connected to the modulation pulse power supply is larger than the area of current confinement with respect to the active layer electrically connected to the excitation DC power supply. It is characterized by.

  According to a third aspect of the present invention, in the light emitting device according to the second aspect, as a means for confining a current to an active layer electrically connected to the excitation DC power source, a refractive index difference in a horizontal lateral direction is provided. It is characterized in that a structure having is used.

  According to a fourth aspect of the present invention, in the light emitting device according to the second aspect, the high resistance region formed by ion implantation as means for confining current to the active layer electrically connected to the modulation pulse power source. Is used.

According to a fifth aspect of the present invention, in the light emitting device according to any one of the first to fourth aspects, the active layer electrically connected to the modulation pulse power source includes a quantum well layer and a barrier. It is composed of a multiple quantum well structure in which a plurality of layers are stacked, and the barrier layer is doped with p-type impurities in the range of 1 × 10 ¹⁸ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ .

Also. According to a sixth aspect of the present invention, in the light emitting device according to any one of the first to fifth aspects, the active layer includes a mixed crystal semiconductor of nitrogen and another group V element. It is characterized by that.

According to a seventh aspect of the present invention, there is provided an optical transmission system comprising the light emitting device according to any one of the first to sixth aspects.

The invention according to claim 8 is provided with a plurality of resonators sandwiched by a multilayer reflector on a substrate, and the plurality of resonators are optically coupled to form one resonance mode. An active layer is provided in each resonator, and the active layer has a gain with respect to the same resonance mode wavelength, and current injection means for injecting a current into each active layer And a current confinement means for constricting the current injected from the current injection means, and the conductivity type of the multilayer reflector adjacent to the substrate and / or the multilayer reflector on the outermost surface side is n-type. It is characterized by being.

According to a ninth aspect of the present invention, in the vertical cavity surface emitting semiconductor laser device according to the eighth aspect of the present invention , at least one of the active layers is a multiple layer in which a plurality of quantum well layers and barrier layers are stacked. The barrier layer is doped with p-type impurities in a range of 1 × 10 ¹⁸ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ .

The invention according to claim 10 is the vertical cavity surface emitting semiconductor laser device according to claim 8, wherein at least one of the active layers is a mixture containing nitrogen and another group V element. It is characterized by being a crystal semiconductor.

According to an eleventh aspect of the present invention, in the vertical cavity surface emitting semiconductor laser device according to the eighth aspect , a structure having a refractive index difference in a horizontal transverse direction is used as the current constricting means. The current confinement area by the constriction means is different for each active layer.

According to a twelfth aspect of the present invention, in the vertical cavity surface emitting semiconductor laser device according to the eighth aspect of the present invention, as the current constricting means, a structure having a refractive index difference in a horizontal lateral direction, and a high height formed by ion implantation The resistance region is provided for each different active layer, and the constriction area by the current confinement means having the refractive index difference in the horizontal and lateral directions is smaller than the confinement area by the high resistance region formed by ion implantation. It is a feature.

According to the first to sixth aspects of the present invention, a plurality of resonators are optically coupled to form one resonance mode, and the modulation pulse power supply is electrically connected to the same resonance mode. And the active layer electrically connected to the excitation DC power source oscillate in mode synchronization, thereby increasing the photon density inside the VCSEL element and increasing the relaxation oscillation frequency of the VCSEL. Can do. Further, since the conductivity type of the multilayer-film reflective mirror adjacent to the substrate and / or the multilayer-film reflective mirror on the outermost surface side is n-type, the resistance of the element can be reduced, and the power consumption of the light emitting device Can be reduced, and the electrical modulation band of the VCSEL increases. Thereby, a light emitting device capable of high-speed modulation exceeding 10 Gbps with a simple configuration can be provided.

  In particular, according to the invention described in claim 2, in the light-emitting device according to claim 1, means for constricting the current injected into each active layer is provided, and is electrically connected to the modulation pulse power supply. The current confinement area for the active layer is larger than the current confinement area for the active layer electrically connected to the excitation DC power supply, so that it is electrically connected to the modulation pulse power supply. In addition, the resistance of the current confinement portion in the active layer is reduced, and the electrical modulation band can be increased. In addition, the gain at the center corresponding to the fundamental transverse mode can be selectively increased, and the light output of the fundamental transverse mode can be increased.

  According to a third aspect of the present invention, in the light emitting device according to the second aspect, as a means for confining current to the active layer electrically connected to the excitation DC power source, the refractive index in the horizontal lateral direction is provided. By using a structure having a difference, it is possible to increase the light output while maintaining the fundamental transverse mode.

  The light-emitting device according to claim 4 is the light-emitting device according to claim 2, wherein the high-resistance region is formed by ion implantation as means for confining current to the active layer electrically connected to the modulation pulse power source. Is used, the capacitance component of the high resistance region corresponding to the active layer electrically connected to the modulation pulse power supply is reduced, and the electrical modulation band can be further increased.

According to a fifth aspect of the present invention, in the light emitting device according to any one of the first to fourth aspects, the active layer electrically connected to the modulation pulse power source includes a quantum well layer. It is composed of a multiple quantum well structure (MQW) in which a plurality of barrier layers are stacked, and the barrier layer is doped with p-type impurities in the range of 1 × 10 ¹⁸ cm ⁻³ to 1 × 10 ¹⁹ cm ^−3. The differential gain of the active layer of the multiple quantum well structure can be increased, and the relaxation oscillation frequency of the VCSEL can be increased.

According to a sixth aspect of the present invention, in the light emitting device according to any one of the first to fifth aspects, the active layer includes a mixed crystal semiconductor of nitrogen and another group V element. Accordingly, a VCSEL having a wavelength of 1.31 μm in which the dispersion of the quartz optical fiber is zero can be formed, and thus a light emitting device suitable for large capacity transmission of 10 Gbps or more can be formed.

Further, the optical transmission system according to claim 7, wherein, by which a light-emitting device according to any one of claims 1 to 6, direct high speed modulation more than 10Gbps (e.g. 40 Gbps) of the VCSEL modulation Is possible. Therefore, a large-capacity optical transmission system can be constructed at low cost without using an external modulator or an electronic cooling element.

According to an eighth aspect of the present invention, the substrate includes a plurality of resonators sandwiched between upper and lower layers by a multilayer reflector, and the plurality of resonators are optically coupled to form a single resonance mode. Active layers are provided in the respective resonators, the active layers have a gain with respect to the same resonance mode wavelength, and currents for injecting currents into the respective active layers are formed. An injecting means and a current constricting means for constricting the current injected from the current injecting means are provided, and the conductivity type of the multilayer film reflecting mirror adjacent to the substrate and / or the multilayer film reflecting mirror on the outermost surface side is n A vertical cavity surface emitting semiconductor laser device (VCSEL) characterized in that the VCSEL has a plurality of active layers provided in different resonators, and each resonator is optically coupled. A single resonance mode, and a plurality of active layers Since all have gains with respect to the same resonance mode wavelength, when current is injected into each active layer, oscillation occurs in mode synchronization, so that the photon density inside the device can be increased, and the relaxation oscillation frequency of the VCSEL Will increase. Further, since the high reflectivity is required, the multilayer film reflecting mirror adjacent to the substrate and / or the multilayered film reflecting mirror on the outermost surface side is formed in an n-type to reduce the element resistance. This increases the electrical modulation band of the VCSEL. Therefore, the VCSEL can be modulated at high speed.

According to a ninth aspect of the present invention, in the vertical cavity surface emitting semiconductor laser device according to the eighth aspect , at least one of the active layers includes a plurality of quantum well layers and barrier layers. Vertical cavity surface, wherein the barrier layer is doped with a p-type impurity in the range of 1 × 10 ¹⁸ cm ⁻³ to 1 × 10 ¹⁹ cm ^−3. A light-emitting semiconductor laser element (VCSEL), in which a plurality of resonators each including an active layer are optically coupled to form one resonance mode, and each active layer oscillates in mode synchronization. Therefore, the relaxation frequency is improved by increasing the photon density inside the device. Furthermore, at least one active layer is composed of a multiple quantum well structure (MQW) in which a plurality of quantum well layers and barrier layers are stacked, and p-type impurities are 1 × 10 ¹⁸ cm ⁻³ to 1 × 10 10 in the barrier layers. ^Since doping is performed in the range of ¹⁹ cm ⁻³ , the differential gain of the multiple quantum well active layer is increased, and the relaxation oscillation frequency of the VCSEL can be further increased. Therefore, the modulation speed of the VCSEL can be further improved.

According to a tenth aspect of the present invention, in the vertical cavity surface emitting semiconductor laser device according to the eighth aspect , at least one of the active layers contains nitrogen and another group V element. A vertical cavity surface emitting semiconductor laser device (VCSEL) characterized in that the VCSEL includes a plurality of resonators each including an active layer and optically coupled to one resonance mode. Since each active layer oscillates in mode synchronization, the photon density inside the device is increased to improve the relaxation oscillation frequency. Furthermore, since at least one active layer is a mixed crystal semiconductor of nitrogen and another group V element, the differential gain of the active layer can be increased and the relaxation oscillation frequency can be improved. Therefore, the modulation speed of the VCSEL can be further improved. In addition, since a VCSEL having a wavelength of 1.31 μm band in which the dispersion of the quartz optical fiber is zero can be formed, the high-speed modulation characteristics of the present invention can be utilized.

According to an eleventh aspect of the present invention, in the vertical cavity surface emitting semiconductor laser device according to the eighth aspect , a structure having a refractive index difference in the horizontal and lateral directions is used as the current confinement means. A vertical cavity surface emitting semiconductor laser device (VCSEL) characterized in that a current confinement area by the current confinement means is different for each active layer, and the VCSEL includes a plurality of resonators each including an active layer optically. Are coupled to each other to form one resonance mode, and each active layer oscillates in mode synchronization, so that the photon density inside the device can be increased. Further, as the current confinement means, a structure having a refractive index difference in the horizontal transverse direction is used, and the current confinement area by the current confinement means is different for each active layer. Conversely, the higher-order transverse mode is more lossy, and the central gain corresponding to the fundamental transverse mode can be selectively increased, so that the fundamental transverse mode is maintained. The light output can be increased. On the other hand, in a current confinement structure with a wide constriction area, the resistance of the current confinement portion is reduced, so that the CR time constant can be reduced and the electrical modulation band can be increased, thus further improving the modulation speed of the VCSEL. Can be made.

According to a twelfth aspect of the present invention, in the vertical cavity surface emitting semiconductor laser device according to the eighth aspect, the current constricting means is formed by a structure having a refractive index difference in a horizontal transverse direction and ion implantation. High resistance regions are provided for different active layers, and the constriction area by the current confinement means having a refractive index difference in the horizontal and lateral directions is smaller than the confinement area by the high resistance region formed by ion implantation. A vertical cavity surface emitting semiconductor laser device (VCSEL) characterized in that a plurality of resonators each including an active layer are optically coupled to form one resonance mode, Since each active layer oscillates in mode synchronization, the photon density inside the device can be increased. Furthermore, as a current confinement means, a structure having a refractive index difference in the horizontal horizontal direction and a high resistance region formed by ion implantation are provided for different active layers, respectively. Since the confinement area by the current confinement means has a smaller confinement area by the high resistance region formed by ion implantation, in the current confinement structure by the high resistance region formed by ion implantation, both capacitance and resistance can be reduced. The electrical modulation band can be increased. In the current confinement structure where the constriction area is narrow and the refractive index difference is in the horizontal direction, the light of the fundamental transverse mode is confined, and conversely the oscillation of the higher order transverse mode is suppressed, so the fundamental transverse mode is maintained. Can increase the light output. Due to the above effects, the VCSEL can be operated at high speed.

  Hereinafter, the best mode for carrying out the present invention will be described.

(First form)

  A first aspect of the present invention is a vertical cavity surface emitting semiconductor laser device having a plurality of resonators sandwiched between multilayer reflectors on a substrate, a modulation pulse power supply, and an excitation DC power supply The plurality of resonators of the vertical cavity surface emitting semiconductor laser device are optically coupled to form one resonance mode, and an active layer is provided in each resonator. Each active layer has a gain with respect to the same resonance mode wavelength, and one of the active layers is electrically connected to a modulation pulse power source, The other active layer is electrically connected to the excitation DC power supply, and for the same resonance mode, is electrically connected to the active layer electrically connected to the modulation pulse power supply and the excitation DC power supply. Oscillates in mode synchronization with the active layer It is characterized in Rukoto.

  When a semiconductor laser is directly modulated, causes for limiting the modulation band include CR time constant, carrier transport effect, relaxation oscillation frequency, and the like. In particular, the relaxation oscillation frequency is a limit frequency at which the stimulated emission speed cannot follow the carrier density change in the light emitting layer, and is an essential limitation in the case of direct modulation.

  The relaxation oscillation frequency fr is generally expressed by the following equation (Equation 1).

  In Equation 1, Γ is an optical confinement factor, g is a differential gain, S is a photon density, and τp is a photon lifetime. According to Equation 1, the relaxation oscillation frequency fr can be increased as the photon density S is increased. However, when carriers are highly injected into the light emitting layer, gain saturation occurs due to carrier overflow, element heat generation, or the like, and the photon density cannot be increased. Therefore, the relaxation vibration frequency is suppressed to about 10 GHz.

  A light emitting device according to a first aspect of the present invention includes a vertical cavity surface emitting semiconductor laser element having a plurality of resonators sandwiched between multilayer reflectors on a substrate, a modulation pulse power supply, and an excitation A plurality of resonators of the vertical cavity surface emitting semiconductor laser element are optically coupled to form one resonance mode, and each resonator has an active mode, respectively. Each active layer has a gain with respect to the same resonance mode wavelength, and one of the active layers is electrically connected to a modulation pulse power source, and The other active layers of the active layers are electrically connected to the excitation DC power source, and are electrically connected to the excitation layer and the excitation DC power source electrically connected to the modulation pulse power source for the same resonance mode. Oscillates in mode synchronization with the active layer (That is, a plurality of resonators are optically coupled to form one resonance mode, and the same resonance mode is electrically connected to the modulation pulse power source) And the active layer electrically connected to the excitation DC power source oscillates in mode synchronization), thereby increasing the photon density inside the vertical cavity surface emitting semiconductor laser (VCSEL) device to alleviate the VCSEL. The vibration frequency can be increased. Thereby, a light emitting device capable of high-speed modulation exceeding 10 Gbps can be formed with a simple configuration.

  Hereinafter, a case where there are two resonator structures will be described as an example. The first resonator structure is provided with a first active layer, and the second resonator structure is provided with a second active layer. The first active layer is electrically connected to the modulation pulse power supply, and by modulating the current injected into the first active layer, the carrier density in the first active layer changes, and the light The output intensity is modulated. The second active layer is electrically connected to the excitation DC power source, and stimulated emission occurs when a DC current is injected, and laser oscillation occurs when the current exceeds the threshold current.

  The first active layer and the second active layer are provided in different resonator structures. However, the first resonator structure and the second resonator structure are optically coupled to form one resonance mode. Forming. Further, both the first active layer and the second active layer have a gain with respect to the same resonance mode wavelength. Therefore, the oscillation light when current is injected into the first active layer and the oscillation light when current is injected into the second active layer oscillate at the same wavelength and are mode-locked. As a result, the photon density generated in the second active layer is added in the same mode to the photon density generated by current injection into one active layer, so that the photon density inside the device is increased as compared with the conventional case. be able to. Accordingly, the relaxation oscillation frequency of the VCSEL is increased, and a light emitting device capable of high-speed modulation exceeding 10 Gbps can be realized.

  In order to take advantage of the characteristics of the light-emitting device of the present invention, even when the modulation pulse power source injected into the first active layer is OFF, laser oscillation is caused by injecting current from the excitation DC power source into the second active layer. It is preferable to be maintained. As a result, the gain of the first active layer can be increased with a small injection pulse current, so that the gain of the first active layer can be kept high up to a higher light output.

  Note that the modulation pulse power supply electrically connected to the first active layer can also have a function of adding a DC bias current to the pulse current. When a DC bias current is applied to the first active layer up to the vicinity of the oscillation threshold current and a pulse current is further superimposed, the time required for accumulating the carrier density necessary for laser oscillation in the first active layer is shortened. As a result, the oscillation delay time is reduced. Therefore, the response of laser oscillation to the pulse current applied to the first active layer is improved, and the modulation speed can be further improved.

  In the VCSEL of the present invention, since the first active layer and the second active layer are provided in different resonator structures, the distance between the first active layer and the second active layer is increased. Can be released. Therefore, electrical crosstalk and thermal crosstalk between the first active layer and the second active layer can be reduced.

  Further, the VCSEL reported in Non-Patent Document 1 described above increases the photon density inside the VCSEL by injecting light synchronized with the oscillation mode from an external edge-emitting (DFB) semiconductor laser. For this reason, it is necessary to make the wavelength of the laser light injected from the outside exactly match the resonance mode wavelength of the VCSEL. On the other hand, in the present invention, the light emitted from the active layer connected to the excitation DC power supply is laser-oscillated in the same resonance mode as the light emitted from the active layer connected to the modulation pulse power supply. The internal photon density can always be increased at the same wavelength. Therefore, it is not necessary to strictly control the oscillation wavelength of the excitation light, and high-speed modulation can be realized with a simple device configuration.

  In the present invention, since the structure for generating the excitation light is also a VCSEL structure, the power consumption required for generating the excitation light can be reduced as compared with the edge emitting semiconductor laser.

  Note that a literature “Electronics Lett., Vol. 38, No. 12, pp 278-280 (2002)” reports a VCSEL structure having two active layers in a resonator. The VCSEL has a three-terminal structure, and has a structure in which current is independently injected into two active layers. However, the two active layers for current injection are provided in the same resonator structure, and the structure is different from the present invention.

  Further, in the document “Electronics Lett., Vol. 34, No. 14, pp1405-1407 (1998)”, a structure in which 0.85 μm band VCSEL for excitation and 1.3 μm band VCSEL are integrated is reported. However, in this report example, the resonance modes of the two resonator structures are not coupled and oscillate at independent oscillation wavelengths. For this reason, the internal light output cannot be increased in mode synchronization as in the present invention, and the relaxation oscillation frequency is not increased. Therefore, the structure and operating principle are different from the present invention.

  Further, a document “CLEO2001, CtuB1 (2001)” reports a VCSEL in which two resonators having an active layer are optically coupled. However, no high-speed modulation operation as in the present invention has been reported.

  In the present invention, it is desirable that the first active layer and the second active layer are provided at the antinodes in the optical standing wave distribution in the VCSEL element. Thereby, the coupling efficiency between the optical standing wave and the active region increases, and the threshold value can be reduced.

  Further, in order to improve the temperature characteristics of the VCSEL, the gain peak wavelength of the active region at room temperature can be shifted to the short wavelength side with respect to the resonance mode wavelength. At this time, the wavelength shift amount in the first active layer and the wavelength shift amount in the second active layer are not necessarily matched. It is only necessary that the resonance mode wavelength is within the gain spectrum band of each active layer.

  The case where there are two resonators has been described above as an example, but the number of resonators can be further increased. In this case, one active layer to which a modulation signal is input can be used, and another active layer can be used for excitation (direct current can be injected into the other active layer and used for excitation).

(Second form)
According to a second aspect of the present invention, in the light emitting device according to the first aspect, means for constricting a current injected into each active layer of the vertical cavity surface emitting semiconductor laser element is provided. The current confined area with respect to the active layer electrically connected to the pulse power supply is characterized by being wider than the current confined area with respect to the active layer electrically connected to the excitation DC power supply. .

  As described above, in the second embodiment, the light emitting device of the first embodiment is provided with means for constricting the current injected into each active layer, and is electrically connected to the modulation pulse power supply. The area electrically confined to the active layer is wider than the area confined to the active layer electrically connected to the excitation DC power supply, so that the activity electrically connected to the modulation pulse power supply is The resistance of the current confinement portion in the layer is reduced, and the electrical modulation band can be increased. In addition, the gain at the center corresponding to the fundamental transverse mode can be selectively increased, and the light output of the fundamental transverse mode can be increased.

  Hereinafter, a case where there are two resonator structures will be described as an example. That is, as an example, as described in the first embodiment, the first resonator structure is provided with the first active layer, and the second resonator structure is provided with the second active layer. In the first active layer and the second active layer, a structure for confining the injected current is provided, and the area where the current is confined with respect to the first active layer is the second active layer. In contrast, it is assumed that the area is larger than the current confined area.

  In this way, by increasing the area for confining the current with respect to the first active layer to which the modulation signal is input, the resistance of the current confinement portion in the first active layer is reduced, and thus the first active layer is reduced. The CR time constant when modulating the current injected into the layer can be reduced and the electrical modulation bandwidth can be increased.

  In the second active layer electrically connected to the excitation DC power source, current is injected into a region narrower than the current injection region of the first active layer. As a result, the gain at the center corresponding to the fundamental transverse mode can be selectively increased, and thus the optical output of the fundamental transverse mode can be increased.

(Third form)
According to a third aspect of the present invention, in the light emitting device of the second aspect, there is a difference in refractive index in the horizontal and lateral directions as means for confining current to the active layer electrically connected to the excitation DC power source. The structure is used.

  Thus, in the third mode, in the light emitting device of the second mode, as a means for confining current to the active layer electrically connected to the excitation DC power source, a refractive index difference is set in the horizontal and lateral directions. By using the structure having, the light output can be increased while maintaining the fundamental transverse mode.

  That is, in the third embodiment, a horizontal refractive index difference is formed in the current confinement portion with respect to the second active layer in an area narrower than the current injection region of the first active layer to which the modulation pulse power supply is connected. The light is confined in the center. Therefore, the fundamental transverse mode light is confined, and conversely, the higher order transverse mode has a large loss, and thus oscillation is suppressed. Thereby, it is possible to increase the light output while maintaining the basic transverse mode.

  As the current confinement means in which the refractive index difference is formed in the horizontal direction, for example, an Al oxide confinement structure that selectively oxidizes a semiconductor layer containing Al from the side surface, or an air that selectively etches the etching layer from the side surface by side etching. A gap structure can be used.

  In the Al oxide confinement structure, an AlOx insulating layer is formed by oxidizing a semiconductor layer containing Al, and no current flows in the oxidized region. As a result, the current is confined to a region that is not oxidized. In addition, since the non-oxidized region has a higher refractive index than the oxidized region, a difference in refractive index occurs in the horizontal direction, and light can be confined in the horizontal and horizontal direction.

  In the air gap structure, the current is confined by flowing only in the semiconductor layer that is not side-etched. Since the refractive index is higher than that of the region where the unetched semiconductor layer is etched, light can be confined in the horizontal and lateral directions as in the Al oxide confinement structure.

(4th form)
According to the fourth aspect of the present invention, in the light emitting device of the second aspect, a high resistance region formed by ion implantation is used as means for confining current to the active layer electrically connected to the modulation pulse power supply. It is characterized by being able to.

  In the fourth embodiment, a high resistance region formed by ion implantation is used as a means for current confinement with respect to the active layer electrically connected to the modulation pulse power supply, whereby the modulation pulse power supply is electrically connected. The capacitance component of the high resistance region corresponding to the connected active layer is reduced, and the electrical modulation band can be further increased.

  That is, when heavy metal such as proton, oxygen, Cr, or Fe is ion-implanted into the semiconductor layer, the implanted region has high resistance, and current can be confined to the region where ion is not implanted. The high resistance region formed by ion implantation is thicker in the stacking direction than the Al oxide constriction structure or the air gap structure. Therefore, the capacitance component formed by the high resistance region for the first active layer to which the modulation signal is input is reduced as compared with the case where the Al oxide confinement structure or the air gap structure is used. Therefore, the CR time constant when modulating the current injected into the first active layer is reduced, and the electrical modulation band can be increased.

(5th form)
According to a fifth aspect of the present invention, in the light emitting device according to any one of the first to fourth aspects, the conductivity type of the multilayer reflector adjacent to the substrate and / or the multilayer reflector on the outermost surface side is: It is characterized by being n-type.

  The multilayer mirror adjacent to the substrate and the multilayer mirror on the outermost surface side need to have a high reflectance in order to reduce the threshold current of the VCSEL. On the other hand, in the multilayer mirror provided between the resonators, the resonators need to be optically coupled, so that the reflectance needs to be lowered.

  When the multilayer mirror is formed of a semiconductor, high reflectance can be obtained by alternately stacking semiconductor layers having different refractive indexes so as to satisfy the Bragg reflection condition and increasing the number of stacked layers. In general, a VCSEL requires a stacking number of 20 cycles or more.

  When semiconductor layers having different refractive indexes are stacked, a hetero barrier is formed at the interface. In the semiconductor layer, the effective mass of holes is about an order of magnitude larger than the effective mass of electrons, so it is difficult for holes to tunnel through the heterobarrier. For this reason, the resistance of the multilayer reflector having the p-type semiconductor laminated is higher than that of the multilayer reflector having the n-type semiconductor layer laminated.

  Therefore, in the fifth embodiment, a multilayer film reflector adjacent to the substrate and / or the multilayer film reflector on the outermost surface side is formed in an n-type, which requires a high reflectivity and increases the number of stacked layers. By doing so, the resistance of the element is reduced. Thereby, the power consumption of the light emitting device can be reduced.

(Sixth form)
According to a sixth aspect of the present invention, in the light-emitting device according to any one of the first to fourth aspects, the multilayer reflector adjacent to the substrate and / or the multilayer reflector on the outermost surface side has a low carrier concentration. It is characterized by being a layer.

  As the carrier concentration of the semiconductor layer constituting the multilayer mirror increases, light absorption by free carriers increases. Furthermore, in the p-type semiconductor layer, light absorption due to absorption between valence bands increases as the hole concentration increases.

  The multilayer-film reflective mirror adjacent to the substrate and / or the multilayer-film reflective mirror on the outermost surface side needs to have a high reflectance in order to reduce the threshold current of the VCSEL. For this reason, the number of laminated multilayer mirrors is increased to several tens of layers. By reducing the carrier concentration of each semiconductor layer in the multilayer reflector that is adjacent to the substrate and / or the multilayer reflector on the outermost surface, the internal absorption loss of the VCSEL is effectively reduced. can do. Therefore, the threshold current of the VCSEL can be further reduced, and the external quantum efficiency can be increased.

  As described above, in the sixth embodiment, the multilayer film reflecting mirror adjacent to the substrate and / or the multilayer film reflecting mirror on the outermost surface side is a low carrier concentration layer, thereby suppressing light absorption and high reflection. Rate mirrors can be formed, reducing the VCSEL threshold current and increasing the external quantum efficiency.

The carrier concentration of the low carrier concentration layer is 5 × 10 ¹⁷ cm ⁻³ in order to reduce the free carrier absorption in the semiconductor layer to less than 10 cm ⁻¹ and suppress the influence of light absorption loss. The following is desirable.

(7th form)
According to a seventh aspect of the present invention, in the light emitting device according to any one of the first to sixth aspects, the active layer electrically connected to the modulation pulse power source is a multiple layer in which a plurality of quantum well layers and barrier layers are stacked. It is composed of a quantum well structure (MQW) and is characterized in that the barrier layer is doped with p-type impurities in the range of 1 × 10 ¹⁸ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ .

By doping the barrier layer of the MQW structure with p-type impurities in the range of 1 × 10 ¹⁸ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ , the injection electron density necessary for laser oscillation is reduced, and the differential gain g is increased. Can be increased. From Equation 1, the relaxation frequency of the VCSEL can be further increased by combining the effect of increasing the differential gain g with the effect of increasing the photon density S in the VCSEL element.

When the doping concentration of the p-type impurity with respect to the barrier layer is smaller than 1 × 10 ¹⁸ cm ⁻³ , the effect of increasing the differential gain is hardly seen. Further, when the doping concentration of the p-type impurity with respect to the barrier layer is higher than 1 × 10 ¹⁹ cm ⁻³ , the crystal quality of the barrier layer is deteriorated. Accordingly, it is desirable that the doping concentration of the p-type impurity with respect to the barrier layer is in the range of 1 × 10 ¹⁸ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ .

As described above, in the seventh embodiment, the active layer electrically connected to the modulation pulse power source is composed of a multiple quantum well structure (MQW) in which a plurality of quantum well layers and barrier layers are stacked. Is doped with p-type impurities in the range of 1 × 10 ¹⁸ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ , the differential gain of the active layer of the multiple quantum well structure can be increased, and further the relaxation of VCSEL The vibration frequency can be increased.

  Note that C, Zn, Be, Mg, or the like can be used as the p-type impurity. In particular, C is suitable because it is difficult to thermally diffuse even when doped at a high concentration, so that a steep doping profile can be formed.

(8th form)
According to an eighth aspect of the present invention, in the light emitting device according to any one of the first to seventh aspects, the active layer includes a mixed crystal semiconductor of nitrogen and another group V element. Yes.

  Examples of mixed crystal semiconductors of nitrogen and other Group V elements include GaNAs, GaInNAs, GaNAsP, GaInNAsP, GaNAsSb, GaInNAsSb, GaNAsPSb, and GaInNAsPSb. The mixed crystal semiconductor is a long wavelength band material system capable of crystal growth on a GaAs substrate. Hereinafter, GaInNAs will be described as an example.

  GaInNAs can increase the confinement barrier height of conduction band electrons with a barrier layer such as GaAs as high as 300 meV or more, so that the overflow of electrons is suppressed and it has good temperature characteristics. In addition, a distributed Bragg reflector having high reflectivity and high thermal conductivity using an AlGaAs material system can be used, and a vertical cavity surface emitting semiconductor laser having good performance in a long wavelength band can be formed.

  An object of the present invention is to provide a directly modulated light source that enables large-capacity transmission exceeding 10 Gbps by improving the modulation frequency. In a high transmission band of 10 Gbps or more, the transmission distance is limited by the dispersion of the quartz optical fiber. By using a mixed crystal semiconductor of nitrogen and other group V elements such as GaInNAs in the active region, a VCSEL having a wavelength of 1.31 μm in which the dispersion of the quartz optical fiber is zero can be formed. You can save it.

  Thus, in the eighth embodiment, the active layer contains a mixed crystal semiconductor of nitrogen and other group V elements, so that the VCSEL with a wavelength of 1.31 μm in which the dispersion of the quartz optical fiber is zero is obtained. Thus, a light-emitting device suitable for large-capacity transmission of 10 Gbps or more can be formed.

(9th form)
According to a ninth aspect of the present invention, there is provided an optical transmission system including the light emitting device according to any one of the first to eighth aspects.

  The light emitting device enables high-speed modulation (for example, 40 Gbps) exceeding 10 Gbps by direct modulation of VCSEL. Therefore, it is an inexpensive configuration that does not use an external modulator or an electronic cooling element. Therefore, a large-capacity optical transmission system can be constructed at a low cost.

(10th form)
According to a tenth aspect of the present invention, a plurality of resonators sandwiched between multilayer reflectors are provided on a substrate, and the plurality of resonators are optically coupled to form one resonance mode. An active layer is provided in each resonator, the active layer has a gain with respect to the same resonance mode wavelength, and current injection means for injecting current into each active layer; A current confining means for constricting the current injected from the current injecting means, and the conductivity type of the multilayer reflector adjacent to the substrate and / or the multilayer reflector on the outermost surface side is n-type This is a vertical cavity surface emitting semiconductor laser device (VCSEL).

  That is, in the vertical cavity surface emitting semiconductor laser device (VCSEL) according to the tenth aspect of the present invention, a plurality of active layers are provided in different resonators. Each resonator is optically coupled to form one resonance mode. The plurality of active layers all have a gain with respect to the same resonance mode wavelength. Therefore, even if current is injected into each active layer, it oscillates at the same wavelength and is mode-locked. As a result, the photon density generated in the other active layer is added in the same mode to the photon density generated by current injection into one active layer, so that the photon density inside the device can be increased as compared with the conventional case. it can. Accordingly, the relaxation oscillation frequency of the VCSEL is increased, and a high-speed modulation operation is possible.

  The active layer is preferably provided at the antinode position in the optical standing wave distribution in the VCSEL. Thereby, the coupling efficiency between the optical standing wave and the active layer increases, and the threshold current can be reduced.

  The tenth aspect of the present invention is characterized in that the conductivity type of the multilayer-film reflective mirror adjacent to the substrate and / or the multilayer-film reflective mirror on the outermost surface side is n-type. The multilayer mirror adjacent to the substrate and the multilayer mirror on the outermost surface side need to have a high reflectance in order to reduce the threshold current of the VCSEL. On the other hand, in the multilayer mirror provided between the resonators, the resonators need to be optically coupled, so that the reflectance needs to be lowered.

  That is, when the multilayer-film reflective mirror is formed of a semiconductor, high reflectance can be obtained by alternately stacking semiconductor layers having different refractive indexes so as to satisfy the Bragg reflection condition and increasing the number of stacked layers. In general, a VCSEL requires a stacking number of 20 cycles or more. When semiconductor layers having different refractive indexes are stacked, a hetero barrier is formed at the interface. In the semiconductor layer, the effective mass of holes is about an order of magnitude larger than the effective mass of electrons, so it is difficult for holes to tunnel through the heterobarrier. For this reason, the resistance of the multilayer reflector having the p-type semiconductor laminated is higher than that of the multilayer reflector having the n-type semiconductor layer laminated.

  Therefore, in the tenth embodiment of the present invention, since a high reflectivity is required, the multilayer film reflecting mirror adjacent to the substrate and / or the multilayer film reflecting mirror on the outermost surface side is formed in an n-type. This reduces the resistance of the element. As a result, the CR time constant is reduced, and the electrical modulation band can be increased. In addition, power consumption of the VCSEL can be reduced.

  Thus, in the VCSEL of the tenth embodiment, a plurality of active layers are provided in different resonators, and each resonator is optically coupled to form one resonance mode, and the plurality of active layers are all Since it has gain with respect to the same resonance mode wavelength, it oscillates in mode synchronization when current is injected into each active layer, so that the photon density inside the device can be increased, and the relaxation oscillation frequency of the VCSEL To increase. Further, since the high reflectivity is required, the multilayer film reflecting mirror adjacent to the substrate and / or the multilayered film reflecting mirror on the outermost surface side is formed in an n-type to reduce the element resistance. This increases the electrical modulation band of the VCSEL. Therefore, the VCSEL can be modulated at high speed.

(Eleventh form)
An eleventh aspect of the present invention includes a plurality of resonators sandwiched between multilayer reflectors on a substrate, and the plurality of resonators are optically coupled to form one resonance mode. An active layer is provided in each resonator, the active layer has a gain with respect to the same resonance mode wavelength, and current injection means for injecting current into each active layer; Current confining means for confining the current injected from the current injecting means, and the multilayer film reflecting mirror adjacent to the substrate and / or the multilayer film reflecting mirror on the outermost surface side is a low carrier concentration layer. This is a feature of a vertical cavity surface emitting semiconductor laser device (VCSEL).

  In the VCSEL of the eleventh aspect of the present invention, similarly to the tenth aspect, a plurality of resonators each including an active layer are optically coupled to form one resonance mode, and each active layer is a mode. Since it oscillates synchronously, the photon density inside the device is increased and high-speed modulation operation becomes possible.

  Furthermore, the VCSEL of the eleventh aspect is characterized in that the multilayer mirror adjacent to the substrate and / or the multilayer mirror on the outermost surface side is a low carrier concentration layer. As the carrier concentration of the semiconductor layer constituting the multilayer mirror increases, light absorption by free carriers increases. Furthermore, in the p-type semiconductor layer, light absorption due to absorption between valence bands increases as the hole concentration increases. On the other hand, the multilayer reflector adjacent to the substrate and / or the multilayer reflector on the outermost surface side needs to have a high reflectance in order to reduce the threshold current of the VCSEL. For this reason, the number of laminated multilayer mirrors is increased to several tens of layers. In the eleventh embodiment, the internal absorption loss of the VCSEL is effectively reduced by reducing the carrier concentration of each semiconductor layer in the multilayer mirror and / or the multilayer mirror on the outermost surface adjacent to the substrate having a large number of layers. The threshold current of the VCSEL can be further reduced. Also, the external quantum efficiency can be increased.

The carrier concentration of the low carrier concentration layer is 5 × 10 ¹⁷ cm ⁻³ or less in order to reduce the free carrier absorption in the semiconductor layer to less than 10 cm ⁻¹ and suppress the influence of light absorption loss. It is desirable to be.

  Thus, in the VCSEL of the eleventh embodiment, a plurality of resonators each including an active layer are optically coupled to form one resonance mode, and each active layer oscillates in mode synchronization. High-speed modulation operation is possible by increasing the photon density inside the device. Furthermore, since the multilayer reflector adjacent to the substrate and / or the multilayer reflector on the outermost surface is a low carrier concentration layer, the internal absorption loss of the VCSEL can be reduced, the threshold current of the VCSEL is reduced, the external The quantum efficiency can be improved.

(Twelfth embodiment)
In a twelfth aspect of the present invention, a plurality of resonators sandwiched between multilayer reflectors are provided on a substrate, and the plurality of resonators are optically coupled to form one resonance mode. An active layer is provided in each resonator, the active layer has a gain with respect to the same resonance mode wavelength, and current injection means for injecting current into each active layer; Current confining means for confining the current injected from the current injecting means, and at least one of the active layers has a multiple quantum well structure in which a plurality of quantum well layers and barrier layers are stacked. The vertical cavity surface emitting semiconductor laser device (VCSEL) is characterized in that the barrier layer is doped with p-type impurities in the range of 1 × 10 ¹⁸ cm ⁻³ to 1 × 10 ¹⁹ cm ^−3. ).

  In the VCSEL of the twelfth aspect of the present invention, similarly to the tenth aspect, a plurality of resonators each including an active layer are optically coupled to form one resonance mode, and each active layer is a mode. In order to oscillate synchronously, the photon density inside the element is increased to improve the relaxation oscillation frequency.

Furthermore, in the VCSEL of the twelfth embodiment, at least one active layer is configured by a multiple quantum well structure (MQW) in which a plurality of quantum well layers and barrier layers are stacked, and a p-type impurity is 1 × 10 in the barrier layer. It is characterized by being doped in the range of ¹⁸ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ .

By doping the barrier layer of the MQW structure with p-type impurities in the range of 1 × 10 ¹⁸ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ , the injection electron density necessary for laser oscillation is reduced, and the differential gain g is increased. Can be increased. The effect of increasing the differential gain g can be used in combination with the effect of increasing the photon density S in the VCSEL element to further increase the relaxation oscillation frequency of the VCSEL. Therefore, the modulation speed of the VCSEL can be further improved.

When the doping concentration of the p-type impurity with respect to the barrier layer is smaller than 1 × 10 ¹⁸ cm ⁻³ , the effect of increasing the differential gain is hardly seen. Further, if the doping concentration of the p-type impurity with respect to the barrier layer is higher than 1 × 10 ¹⁹ cm ⁻³ , the crystal quality of the barrier layer is deteriorated. Accordingly, it is desirable that the doping concentration of the p-type impurity with respect to the barrier layer is in the range of 1 × 10 ¹⁸ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ .

  As the p-type impurity, C, Zn, Be, Mg, or the like can be used. In particular, C is suitable because it is difficult to thermally diffuse even when doped at a high concentration, so that a steep doping profile can be formed.

Thus, in the VCSEL of the twelfth embodiment, a plurality of resonators each including an active layer are optically coupled to form one resonance mode, and each active layer oscillates in mode synchronization. The relaxation oscillation frequency is improved by increasing the photon density inside the device. Furthermore, at least one active layer is composed of a multiple quantum well structure (MQW) in which a plurality of quantum well layers and barrier layers are stacked, and p-type impurities are 1 × 10 ¹⁸ cm ⁻³ to 1 × 10 10 in the barrier layers. ^Since doping is performed in the range of ¹⁹ cm ⁻³ , the differential gain of the multiple quantum well active layer is increased, and the relaxation oscillation frequency of the VCSEL can be further increased. Therefore, the modulation speed of the VCSEL can be further improved.

(13th form)
A thirteenth aspect of the present invention includes a plurality of resonators sandwiched between multilayer reflectors on a substrate, and the plurality of resonators are optically coupled to form one resonance mode. An active layer is provided in each resonator, the active layer has a gain with respect to the same resonance mode wavelength, and current injection means for injecting current into each active layer; Current confinement means for confining the current injected from the current injection means, and at least one of the active layers is a mixed crystal semiconductor containing nitrogen and another group V element This is a vertical cavity surface emitting semiconductor laser device (VCSEL).

  In the VCSEL of the thirteenth aspect of the present invention, similarly to the tenth aspect, a plurality of resonators each including an active layer are optically coupled to form one resonance mode, and each active layer is a mode. Since it oscillates synchronously, the photon density inside the device is increased and high-speed modulation operation becomes possible.

  Furthermore, the VCSEL of the thirteenth aspect is characterized in that at least one active layer is a mixed crystal semiconductor of nitrogen and another group V element.

  Examples of mixed crystal semiconductors of nitrogen and other Group V elements include GaNAs, GaInNAs, GaNAsP, GaInNAsP, GaNAsSb, GaInNAsSb, GaNAsPSb, and GaInNAsPSb. The mixed crystal semiconductor is a long wavelength band material system capable of crystal growth on a GaAs substrate. Hereinafter, GaInNAs will be described as an example.

  When N is added to GaInAs, the position of the conduction band edge is greatly lowered. Therefore, GaInNAs can increase the height of the conduction band electron confinement barrier with the barrier layer such as GaAs to 300 meV or more. Therefore, the energy difference between the ground level and the excited level formed in the active layer is increased, and the differential gain of the active layer can be increased. Therefore, the relaxation vibration frequency is improved.

  It is another object of the present invention to provide a direct modulation light source that enables high-capacity transmission exceeding 10 Gbps by improving the modulation frequency. In a high transmission band of 10 Gbps or more, the transmission distance is limited by the dispersion of the quartz optical fiber. By using a mixed crystal semiconductor of nitrogen and other group V elements such as GaInNAs in the active region, a VCSEL having a wavelength of 1.31 μm band in which the dispersion of the quartz optical fiber is zero can be formed. Can be used.

  Thus, in the VCSEL of the thirteenth embodiment, a plurality of resonators each including an active layer are optically coupled to form one resonance mode, and each active layer oscillates in mode synchronization. The relaxation oscillation frequency is improved by increasing the photon density inside the device. Furthermore, since at least one active layer is a mixed crystal semiconductor of nitrogen and another group V element, the differential gain of the active layer can be increased and the relaxation oscillation frequency can be improved. Therefore, the modulation speed of the VCSEL can be further improved. In addition, since a VCSEL having a wavelength of 1.31 μm band in which the dispersion of the quartz optical fiber is zero can be formed, the high speed modulation characteristics of the present invention can be utilized.

(14th form)
In a fourteenth aspect of the present invention, a plurality of resonators sandwiched between multilayer reflectors are provided on a substrate, and the plurality of resonators are optically coupled to form one resonance mode. An active layer is provided in each resonator, the active layer has a gain with respect to the same resonance mode wavelength, and current injection means for injecting current into each active layer; A current constricting means for constricting the current injected from the current injecting means, and the current constricting means has a structure having a refractive index difference in the horizontal and lateral directions. A vertical cavity surface emitting semiconductor laser device (VCSEL) characterized in that the constriction area differs for each active layer.

  In the VCSEL according to the fourteenth aspect of the present invention, as in the tenth aspect, a plurality of resonators each including an active layer are optically coupled to form one resonance mode, and each active layer is a mode. Since it oscillates synchronously, the photon density inside the device can be increased.

  Further, the fourteenth embodiment is characterized in that a structure having a refractive index difference in the horizontal transverse direction is used as the current confinement means, and the current confinement area by the current confinement means is different for each active layer.

  Current confinement means for forming a refractive index difference in the horizontal direction includes, for example, an Al oxide confinement structure that selectively oxidizes a semiconductor layer containing Al from the side surface, and an air gap structure that selectively side-etches the etching layer from the side surface. There is.

Here, in the Al oxide confinement structure, since an AlO _x insulating layer is formed by oxidizing a semiconductor layer containing Al, no current flows in the oxidized region. As a result, the current is confined to a region that is not oxidized. In addition, since the non-oxidized region has a higher refractive index than the oxidized region, it has a function of confining light in the horizontal and horizontal directions due to a difference in refractive index in the horizontal direction.

  In the air gap structure, the current is confined by flowing only in the semiconductor layer that is not side-etched. Since the refractive index is higher than that of the region where the unetched semiconductor layer is etched, the light is similarly confined in the horizontal and horizontal directions.

  Among the current confinement structures provided with the plurality of active layers, the current confinement structure having a small current confinement area functions to confine light in the central portion. Therefore, the light in the fundamental transverse mode is confined, and conversely, the loss in the higher order transverse mode becomes large. As a result, the oscillation in the high-order transverse mode is suppressed. In the current confinement structure having the narrowest current confinement area, the gain at the center corresponding to the fundamental transverse mode can be selectively increased. Therefore, it is possible to increase the light output while maintaining the basic transverse mode.

  On the other hand, in the current confinement structure having a wide constriction area, the resistance of the current confinement portion is reduced. Therefore, the operating voltage can be reduced and an increase in power consumption can be suppressed.

  When the current injected into the active layer corresponding to the current confinement structure with a wide constriction area is modulated according to the modulation signal, the CR time constant is reduced because the resistance of the current confinement portion is low, and the electrical modulation band is increased. Can do. On the other hand, for the active layer corresponding to the current confinement structure with a narrow constriction area and high resistance, the photon density inside the device is increased without causing a decrease in the electrical modulation speed by flowing a direct current for excitation. Can be made. Therefore, high-speed modulation operation of the VCSEL can be realized by direct modulation.

  Thus, in the VCSEL of the fourteenth form, a plurality of resonators each including an active layer are optically coupled to form one resonance mode, and each active layer oscillates in mode synchronization. The photon density inside the device can be increased. Further, as the current confinement means, a structure having a refractive index difference in the horizontal transverse direction is used, and the current confinement area by the current confinement means is different for each active layer. Conversely, the higher-order transverse mode is more lossy, and the central gain corresponding to the fundamental transverse mode can be selectively increased, so that the fundamental transverse mode is maintained. The light output can be increased. On the other hand, in a current confinement structure with a wide constriction area, the resistance of the current confinement portion is reduced, so that the CR time constant can be reduced and the electrical modulation band can be increased, thus further improving the modulation speed of the VCSEL. Can be made.

(15th form)
In a fifteenth aspect of the present invention, a plurality of resonators sandwiched between multilayer reflectors are provided on a substrate, and the plurality of resonators are optically coupled to form one resonance mode. An active layer is provided in each resonator, the active layer has a gain with respect to the same resonance mode wavelength, and current injection means for injecting current into each active layer; A current confining means for confining the current injected from the current injecting means, and as the current constricting means, a structure having a refractive index difference in the horizontal and lateral directions, and a high resistance region formed by ion implantation, Vertical resonance characterized in that the constriction area by the current confinement means having a refractive index difference in the horizontal transverse direction is smaller than the confinement area by the high resistance region formed by ion implantation, provided for different active layers. Type surface emitting half A body laser element (VCSEL).

  In the VCSEL of the fifteenth aspect of the present invention, as in the tenth aspect, a plurality of resonators each including an active layer are optically coupled to form one resonance mode, and each active layer is a mode. Since it oscillates synchronously, the photon density inside the device can be increased.

  Further, in the fifteenth embodiment, as the current confinement means, a structure having a difference in refractive index in the horizontal direction and a high resistance region formed by ion implantation are provided for different active layers, respectively. It is characterized in that the constriction area by the current constriction means having the refractive index difference in the direction is smaller than the constriction area by the high resistance region formed by ion implantation.

  By ion-implanting heavy metals such as proton, oxygen, Cr, and Fe into the semiconductor layer, the implanted region has a high resistance, so that current can be confined to the region where no ion is implanted. The high resistance region formed by ion implantation is thicker in the stacking direction than the Al oxide constriction structure or the air gap structure. Therefore, the capacitance component formed by the high resistance region is reduced as compared with the case where the Al oxide constriction structure or the air gap structure is used. In addition, since the constriction area by the high resistance region formed by ion implantation is wider than the constriction area by the current constriction means having a refractive index difference in the horizontal and lateral directions, the resistance of the current confinement portion is reduced. Accordingly, both the capacitance and the resistance can be reduced, the CR time constant when modulating the current injected into the active layer is further reduced, and the electrical modulation band can be increased.

  In addition, the current confinement structure having a refractive index difference in the horizontal horizontal direction with a narrow constriction area functions to confine light in the center. Accordingly, the light in the fundamental transverse mode is confined, and conversely, oscillation in the higher order transverse mode is suppressed. Therefore, it is possible to increase the light output while maintaining the basic transverse mode. As a result, the photon density inside the device can be increased, and the VCSEL can be operated at high speed.

  As described above, the vertical cavity surface emitting semiconductor laser elements (VCSEL) according to the tenth to fifteenth aspects of the present invention are characterized in that active layers are provided in different resonators.

  In order to pass a current through the pn junction including the active layer, it is necessary to apply a junction voltage substantially corresponding to the band gap energy of the active layer. Therefore, Joule heat is generated in response to the voltage drop in the pn junction including the active layer. In the case of having a plurality of active layers capable of independently injecting current, heat is generated in each active layer. For this reason, if the active layers are close to each other, the heat generated by one active layer causes thermal crosstalk that lowers the light emission efficiency of the other active layer. In the VCSEL of the present invention, the active layers are provided in different resonators, and the distance between the active layers can be increased, so that the thermal crosstalk between the active layers can be reduced.

  Further, the semiconductor multilayer film provided between the active layer and the active layer includes a low refractive index layer and a high refractive index layer. Since the low refractive index layer lowers the refractive index as much as possible, the band gap energy is set high. Therefore, a low-refractive index layer having a high hetero barrier height is provided between the active layer and the active layer, so that carriers do not easily overflow from one active layer to the other active layer. Therefore, electrical crosstalk between active layers can also be reduced.

  Thus, in the VCSEL of the fifteenth embodiment, a plurality of resonators each including an active layer are optically coupled to form one resonance mode, and each active layer oscillates in mode synchronization. The photon density inside the device can be increased. Furthermore, as a current confinement means, a structure having a refractive index difference in the horizontal horizontal direction and a high resistance region formed by ion implantation are provided for different active layers, respectively. Since the confinement area by the current confinement means has a smaller confinement area by the high resistance region formed by ion implantation, in the current confinement structure by the high resistance region formed by ion implantation, both capacitance and resistance can be reduced. The electrical modulation band can be increased. In the current confinement structure where the constriction area is narrow and the refractive index difference is in the horizontal direction, the light of the fundamental transverse mode is confined, and conversely the oscillation of the higher order transverse mode is suppressed, so the fundamental transverse mode is maintained. Can increase the light output. Due to the above effects, the VCSEL can be operated at high speed.

  Example 1 is an example corresponding to the first aspect of the present invention. FIG. 1 is a diagram showing a light emitting device of Example 1 of the present invention. The light emitting device of FIG. 1 includes a vertical cavity surface emitting semiconductor laser element (VCSEL) as a light source.

This VCSEL has a p-type lower distributed Bragg reflector (DBR) 102, a p-type AlAs layer 103, an Al _0.3 Ga _0.7 As first spacer layer 104, a GaAs / Al _{0. 3} Ga _0.7 As multiple quantum well first active layer 105, n-type Al _0.3 Ga _0.7 As second spacer layer 106, n-type DBR 107, Al _0.3 Ga _0.7 As third spacer layer 108 GaAs / Al _0.3 Ga _0.7 As multiple quantum well second active layer 109, Al _0.3 Ga _0.7 As fourth spacer layer 110, p-type Al _0.99 Ga _0.01 As layer 111, The p-type upper DBR 112 is sequentially stacked (a stacked structure is configured).

Here, the p-type lower DBR 102 is formed by alternately stacking p-type Al _0.2 Ga _0.8 As layers and p-type Al _0.9 Ga _0.1 As layers with a quarter wavelength thickness. .

The n-type DBR 107 is formed by alternately stacking n-type Al _0.2 Ga _0.8 As layers and n-type Al _0.9 Ga _0.1 As layers with a quarter wavelength thickness.

The p-type upper DBR 112 is formed by alternately stacking p-type Al _0.2 Ga _0.8 As layers and p-type Al _0.9 Ga _0.1 As layers with a quarter wavelength thickness.

  Then, the first mesa structure is formed by etching in a cylindrical shape from the surface of the laminated structure to the middle of the n-type DBR 107. Further, the second mesa structure is formed by etching in a cylindrical shape with a size larger than that of the first mesa structure until the p-type lower DBR 102 is reached.

Then, from the side surfaces of the first mesa structure and the second mesa structure, the p-type AlAs layer 103 and the p-type Al _0.99 Ga _0.01 As layer 111 are selectively oxidized, and the AlO _x insulating region 116 is formed. Is formed. At this time, the oxide constriction opening area of the p-type AlAs layer 103 and the oxidation confinement opening area of the p-type Al _0.99 Ga _0.01 As layer 111 were made substantially equal.

  A ring-shaped p-side upper electrode 113 is formed on the surface of the p-type upper DBR 112 except for the light emitting portion. An n-side electrode 114 is formed on the bottom surface of the first mesa structure (the top of the second mesa structure). A p-side lower electrode 115 is formed on the back surface of the p-type GaAs substrate 101.

  The p-side upper electrode 113 and the n-side electrode 114 are electrically connected to the modulation pulse power source 117. The modulation pulse power source 117 has a function of modulating a current applied between the p-side upper electrode 113 and the n-side electrode 114 in accordance with an externally modulated signal. The n-side electrode 114 and the p-side lower electrode 115 are electrically connected to the excitation DC power source 118.

  The VCSEL in FIG. 1 includes a first resonator sandwiched between the p-type lower DBR 102 and the n-type DBR 107, and a second resonator sandwiched between the n-type DBR 107 and the p-type upper DBR 112. The Bragg reflection wavelengths of the p-type lower DBR 102, the n-type DBR 107, and the p-type upper DBR 112 are all 0.85 μm. The resonator lengths of the two resonators are both designed to have an optical distance of 0.85 μm. By reducing the number of lamination periods of the n-type DBR 107 to three, the two resonators are optically coupled to form one resonance mode. Further, the first active layer 105 and the second active layer 109 are located on the antinode of the optical standing wave distribution in the resonator.

In the light emitting device having such a configuration, when a forward current is passed between the n-side electrode 114 and the p-side lower electrode 115 from the excitation DC power source 118, GaAs / Al _0.3 Ga _0.7 As multiplexing is performed. Carriers are injected into the quantum well first active layer 105 to recombine light emission and emit light in the 0.85 μm band. At this time, the current is confined by the AlO _x insulating region 116 in which the p-type AlAs layer 103 is selectively oxidized. The light emitted from the first active layer 105 resonates in a composite resonator in which the p-type lower DBR 102, the n-type DBR 107, and the p-type upper DBR 112 are optically coupled. Light is emitted continuously.

  5A and 5B are diagrams for explaining the operation of the light-emitting device of Example 1. FIG. FIG. 5A is a diagram showing the relationship between the current (1) of the excitation DC power supply 118 and the optical output of the VCSEL. At this time, the current of the modulation pulse power supply is zero. In the light emitting device of Example 1, the light output P0 is output by setting the current (1) of the excitation DC power supply 118 at the position Ib shown in FIG.

Further, when a pulse current is applied between the p-side upper electrode 113 and the n-side electrode 114 from the modulation pulse power source 117, carriers are transferred to the second active layer 109 of GaAs / Al _0.3 Ga _0.7 As multiple quantum wells 109. Are injected to recombine the light and emit light in the 0.85 μm band. At this time, the current is confined by the AlO _x insulating region 116 in which the p-type Al _0.99 Ga _0.01 As layer 111 is selectively oxidized. The light emitted from the second active layer 109 resonates in a composite resonator in which the p-type lower DBR 102, the n-type DBR 107, and the p-type upper DBR 112 are optically coupled. Light is emitted according to the modulation signal.

  Since the first active layer 105 and the second active layer 109 have the same band gap and oscillate in the same resonance mode in which two resonators are coupled, oscillation when current is injected into the first active layer 105 The light and the oscillation light when current is injected into the second active layer 109 oscillate at the same wavelength. At this time, when the current injected into the second active layer 109 is modulated in the range of 0 to Im in the state where the current is continuously injected into the first active layer 105 and oscillated, it is shown in FIG. Thus, the light output intensity is modulated between P0 and P1. Since the light generated in the second active layer 109 is added in the same mode to the light generated by injecting current into the first active layer 105, the photon density inside the VCSEL element can be increased. Thereby, the relaxation oscillation frequency of VCSEL can be increased.

  Even if the current injected into only a single active layer is increased, the gain is saturated due to carrier overflow, and the optical output cannot be increased. Increasing the thickness of one active layer can increase the carrier density for gain saturation, but the active layer position deviates from the antinode position of the optical standing wave distribution inside the VCSEL device. The ratio of coupling with light decreases, and the gain does not increase substantially. Further, in the multiple quantum well active layer, when the number of quantum wells is increased, carrier injection becomes non-uniform and it becomes difficult to obtain a high gain.

  In the present invention, a plurality of active layers having means for independently injecting current are provided, and each active layer is provided at the antinode position of the optical standing wave distribution, and the current injected into each active layer is controlled. As a result, carrier overflow in each active layer is suppressed, and gain saturation is unlikely to occur up to a higher light output. Therefore, the relaxation oscillation frequency is increased and high-speed modulation is possible.

  Example 2 is an example corresponding to the second, third, and fifth modes. FIG. 2 is a diagram showing a light-emitting device according to Example 2 of the present invention. The light emitting device in FIG. 2 includes a VCSEL as a light source.

This VCSEL has an n-type lower DBR 202, an Al _0.2 Ga _0.8 As first spacer layer 203, a GaInAs / GaAs multiple quantum well first active layer 204, an Al _0.2 Ga ₀ on an n-type GaAs substrate 201. _.8 As second spacer layer 205, p-type AlAs layer 206, p-type DBR 207, p-type second AlAs layer 208, Al _0.2 Ga _0.8 As third spacer layer 209, GaInAs / GaAs multiple quantum well second active The layer 210, the Al _0.2 Ga _0.8 As fourth spacer layer 211, and the n-type upper DBR 212 are sequentially stacked (a stacked structure is configured).

Here, the n-type lower DBR 202 is formed by alternately stacking n-type GaAs layers and n-type Al _0.9 Ga _0.1 As layers at a quarter wavelength thickness.

The p-type DBR 207 is formed by alternately stacking p-type GaAs layers and p-type Al _0.9 Ga _0.1 As layers at a quarter wavelength thickness.

Further, the n-type upper DBR 212 is formed by alternately stacking n-type GaAs layers and p-type Al _0.9 Ga _0.1 As layers with a quarter wavelength thickness.

  Then, the first mesa structure is formed by etching from the surface of the laminated structure to the middle of the p-type DBR 207 in a cylindrical shape. Further, the second mesa structure is formed in a larger size than the first mesa structure and is etched into a cylindrical shape until reaching the n-type lower DBR 202.

Then, the p-type first AlAs layer 206 and the p-type second AlAs layer 208 are selectively oxidized from the side surfaces of the first mesa structure and the second mesa structure, and the AlO _x insulating region 116 is formed. At this time, the p-type first AlAs layer 206 was fabricated such that the oxidized constriction opening area of the p-type second AlAs layer 206 was larger than the oxidation constriction opening area of the p-type second AlAs layer 208.

  A ring-shaped n-side upper electrode 213 is formed on the surface of the n-type upper DBR 212 except for the light emitting portion. A p-side electrode 214 is formed on the bottom surface of the first mesa structure (the top of the second mesa structure). An n-side lower electrode 215 is formed on the back surface of the n-type GaAs substrate 201.

  The n-side upper electrode 213 and the p-side electrode 214 are electrically connected to the excitation DC power source 118. The p-side electrode 214 and the n-side lower electrode 215 are electrically connected to the modulation pulse power source 117.

  In the VCSEL of FIG. 2, by reducing the number of stacking periods of the p-type DBR 207, the two resonators are optically coupled to form one resonance mode. In addition, since the band gaps of the first active layer 204 and the second active layer 210 are equal and oscillate in the same resonance mode in which two resonators are coupled, when current is injected into the first active layer 204 And the oscillation light when current is injected into the second active layer 210 oscillate at the same wavelength (0.98 μm). The laser beam generated in response to the modulated electric signal input from the modulation pulse power source 117 to the second active layer 210 and the light generated by current injection from the excitation DC power source 118 to the first active layer 204 are in the same mode. In addition, the photon density inside the VCSEL element is increased, and the relaxation oscillation frequency of the VCSEL can be increased.

  In the second embodiment, in the DBR that passes when the direct current for excitation is injected into the second active layer 210, the upper DBR 212 on the outermost surface side where the number of stacked layers increases due to the necessity of high reflectivity is n-type. By forming, the resistance of the element is reduced. In addition, since the oxidized constriction opening area for confining current to the first active layer 204 to which the modulation signal is input is made larger than the oxidized constriction opening area for the second active layer 210, the current in the first active layer 204 is The resistance of the constriction is reduced. Therefore, the CR time constant when modulating the current injected into the first active layer 204 is reduced, and the electrical modulation band can be increased.

  In the second active layer 210 electrically connected to the excitation DC power source 118, a current is injected into a region narrower than the current injection region of the second active layer 204. As a result, the gain at the center corresponding to the fundamental transverse mode can be selectively increased, and the light output of the fundamental transverse mode can be increased.

  Further, in the oxidized constriction structure, since the non-oxidized region has a higher refractive index than the oxidized region 116, the refractive index difference is generated in the horizontal direction and the light is confined in the horizontal horizontal direction. In the current confinement portion of the p-type second AlAs layer 208, an area narrower than the current injection region of the first active layer 204 to which the modulation pulse power source 117 is connected, a horizontal lateral refractive index difference is formed, and light is transmitted to the central portion. It is structured to be confined in. Therefore, the fundamental transverse mode light is confined, and conversely, the higher order transverse mode has a large loss, and thus oscillation is suppressed. Thereby, it is possible to increase the light output while maintaining the basic transverse mode.

  Due to the above effects, in the second embodiment, it is possible to increase the output while maintaining the basic transverse mode, and the relaxation oscillation frequency of the VCSEL can be further increased as compared with the first embodiment, and 10 Gbps. High-speed direct modulation exceeding 1 is possible.

  In addition, the lower DBR 202 adjacent to the substrate where the number of stacked layers is increased because high reflectivity is necessary, and the resistance of the element is reduced by forming the conductivity type as n-type, and the power consumption of the light emitting device Can be reduced.

  Example 3 is an example corresponding to the fourth, sixth, seventh, and eighth modes. FIG. 3 is a diagram showing a light emitting device of Example 3 of the present invention. The light emitting device in FIG. 3 includes a VCSEL as a light source.

  This VCSEL has an undoped lower DBR 301, a p-type GaAs first spacer layer 302, a GaInNAs / GaAs multiple quantum well first active layer 304, an n-type GaAs second spacer layer 305, an n-type DBR 306, on an n-type GaAs substrate 201. An n-type GaAs third spacer layer 307, a GaInNAs / GaAs multiple quantum well second active layer 308, a p-type GaAs fourth spacer layer 309, and an undoped upper DBR 310 are sequentially stacked (a stacked structure is configured).

Here, the non-doped lower DBR 301 is formed by alternately stacking a non-doped GaAs layer and a non-doped Al _0.9 Ga _0.1 As layer with a quarter wavelength thickness.

  A p-type AlAs layer 303 having a layer thickness of 30 nm is provided in the p-type GaAs first spacer layer 302.

The n-type DBR 306 is formed by alternately stacking n-type GaAs layers and n-type Al _0.9 Ga _0.1 As layers at a quarter wavelength thickness.

The non-doped upper DBR 310 is formed by alternately stacking a non-doped GaAs layer and a non-doped Al _0.9 Ga _0.1 As layer with a quarter wavelength thickness.

  The first mesa structure is formed by etching in a cylindrical shape from the surface of the laminated structure to the surface of the p-type GaAs fourth spacer layer 309. Further, the second mesa structure is formed in a size larger than that of the first mesa structure and etched into a cylindrical shape until reaching the n-type DBR 306. Further, the third mesa structure is formed in a cylindrical size until reaching the p-type GaAs first spacer layer 302 having a size larger than that of the second mesa structure and below the p-type AlAs layer 303. Yes.

Then, from the side surface of the third mesa structure, the p-type AlAs layer 303 is selectively oxidized to form the AlO _x insulating region 116. In addition, in the vicinity of the second active layer 308, proton ions are implanted outside the first mesa structure to form a high resistance region 311. The high resistance region 311 forms a current confinement structure with respect to the second active layer 308. At this time, the narrow opening area of the high resistance region 311 was made larger than the oxidized narrow opening area of the p-type AlAs layer 303.

  A ring-shaped p-side upper electrode 113 is formed on the bottom surface of the first mesa structure (the top of the second mesa structure). A ring-shaped n-side electrode 114 is formed on the bottom surface of the second mesa structure (the top of the third mesa structure). A p-side lower electrode 115 is formed on the bottom surface of the third mesa structure.

  The p-side upper electrode 113 and the n-side electrode 114 are electrically connected to the modulation pulse power source 117. The n-side electrode 114 and the p-side lower electrode 115 are electrically connected to the excitation DC power source 118.

  The light emitting device of Example 3 has the same effect as the light emitting device of Example 2. Further, as a means for confining current to the second active layer 308 electrically connected to the modulation pulse power source 117, a high resistance region 311 formed by ion implantation is used. The thickness of the high resistance region 311 formed by ion implantation in the stacking direction is about 0.2 μm, which is thicker than that of the Al oxide confinement structure. Therefore, the capacitance component formed by the high resistance region for the second active layer 308 to which the modulation signal is input is reduced, and the electrical modulation band when modulating the current injected into the second active layer 308 can be further increased. it can.

In addition, the lower DBR 301 and the uppermost DBR 310 on the outermost surface side adjacent to the substrate where the number of stacked layers is increased because high reflectivity is required are formed of a non-doped layer. Since the carrier concentration is a low carrier concentration of 2 × 10 ¹⁷ cm ⁻³ , light absorption by free carriers is suppressed, and a reflector with high reflectance can be formed. Therefore, the threshold current of the VCSEL can be reduced and the external quantum efficiency can be increased.

  The current is injected into the active layer from the electrodes provided in the p-type GaAs spacer layers 302 and 309 without passing through the lower DBR 301 and the uppermost DBR 310 on the outermost surface side.

  In the light emitting device of Example 3, GaInNAs which is a mixed crystal semiconductor of nitrogen and other group V elements is used for the quantum well layers of the first active layer 304 and the second active layer 308. Therefore, a light source having a wavelength of 1.31 μm in which the dispersion of the quartz optical fiber is zero can be formed, so that the high-speed modulation characteristic of the present invention can be utilized.

Further, the p-type impurity C is doped 3 × 10 ¹⁸ cm ⁻³ to the GaAs barrier layer of the second active layer 308. Thereby, the injection electron density necessary for laser oscillation is reduced, and the differential gain g of the second active layer 308 can be increased. From Equation 1, the relaxation frequency of the VCSEL can be further increased by combining the effect of increasing the differential gain g with the effect of increasing the photon density S in the VCSEL element. Therefore, it is possible to provide a light source that can be directly modulated at 40 Gbps.

  Example 4 is an example corresponding to the ninth mode. FIG. 4 is a diagram illustrating an optical transmission system according to a fourth embodiment. Referring to FIG. 4, in this optical transmission system, an electrical signal is converted into an optical signal in an optical transmission unit 401 and introduced into an optical fiber cable 404, and light guided through the optical fiber cable 404 is transmitted by an optical reception unit 402. It is again converted into an electrical signal and output.

  The optical transmission unit 401 and the optical reception unit 402 are integrated in one package to constitute an optical transmission / reception module 403. The optical fiber cable 404 has two pairs for sending and receiving, and can communicate bidirectionally.

  In the optical transmission unit 401 of the optical transmission system of FIG. 4, the light emitting device of Example 3 is used as a light source. The light emitting device of Example 3 has an improved relaxation oscillation frequency, and can transmit an optical signal of 40 Gbps without using an external modulator. In addition, temperature control by an electronic cooling element is unnecessary, and it can be manufactured at low cost. Therefore, a 40 Gbps large capacity optical transmission system can be constructed at low cost.

  Example 5 is an example corresponding to the fourteenth aspect. FIG. 6 is a diagram illustrating a vertical cavity surface emitting semiconductor laser device (VCSEL) according to a fifth embodiment.

Referring to FIG. 6, an n-type lower DBR 202 is stacked on an n-type GaAs substrate 201. Here, the n-type lower DBR 202 is formed by alternately stacking n-type GaAs layers and n-type Al _0.9 Ga _0.1 As layers at a quarter wavelength thickness. On the n-type lower DBR 202, a GaAs first spacer layer 601, a GaInNAs / GaAs multiple quantum well first active layer 304, a GaAs second spacer layer 602, a p-type AlAs layer 206, and a p-type DBR 207 are stacked. . Here, the p-type DBR 207 is formed by alternately stacking p-type GaAs layers and p-type Al _0.9 Ga _0.1 As layers at a quarter wavelength thickness. On the p-type DBR 207, a p-type second AlAs layer 603, a GaAs third spacer layer 604, a GaInNAs / GaAs multiple quantum well second active layer 308, a GaAs fourth spacer layer 605, and an n-type upper DBR 212 are sequentially laminated. ing. Here, the n-type upper DBR 212 is formed by alternately stacking n-type GaAs layers and p-type Al _0.9 Ga _0.1 As layers with a quarter wavelength thickness.

  Then, the first mesa structure is formed by etching in a cylindrical shape from the surface of the stacked structure to the middle of the p-type DBR 207. Further, the second mesa structure is formed by etching in a cylindrical shape with a size larger than that of the first mesa structure until reaching the n-type lower DBR 202.

Further, the p-type first AlAs layer 206 is selectively oxidized from the side surface of the second mesa structure, and the AlO _x insulating region 116 is formed. In addition, the p-type second AlAs layer 603 is selectively side-etched from the side surface of the first mesa structure to form an air gap structure 606. At this time, the oxidized constriction opening area of the p-type first AlAs layer 206 is made smaller than the air gap constriction opening area of the p-type second AlAs layer 603.

  A ring-shaped n-side upper electrode 213 is formed on the surface of the n-type upper DBR 212 except for the light emitting portion. A p-side electrode 214 is formed on the bottom surface of the first mesa structure (the top of the second mesa structure). An n-side lower electrode 215 is formed on the back surface of the n-type GaAs substrate 201.

  In the VCSEL of FIG. 6, by reducing the number of lamination periods of the p-type DBR 207 (for example, 3 periods), the two resonators are optically coupled to form one resonance mode. In addition, since the band gaps of the first active layer 304 and the second active layer 308 are equal and have a gain with respect to a resonance mode in which two resonators are coupled, the first active layer 304 has The oscillation light when the current is injected and the oscillation light when the current is injected into the second active layer 308 oscillate at the same wavelength (1.3 μm) in mode synchronization. Therefore, the photon density inside the VCSEL element can be increased and the relaxation oscillation frequency of the VCSEL can be increased as compared with the case where there is one active layer.

  In addition, the element resistance is reduced by forming the conductivity type of the upper DBR 212, which has a large number of layers due to the necessity of high reflectivity, as an n-type. In addition, since the air gap constriction opening area for confining current to the second active layer 308 is larger than the oxidation confinement opening area for the first active layer 304, the resistance of the current confinement portion in the second active layer 308 is increased. Is reduced.

Furthermore, since the dielectric constant of the side etching region 606 is lower than the dielectric constant of the AlO _x insulating region 116, the parasitic capacitance component in the side etching region can be reduced. Therefore, the CR time constant when modulating the current injected into the second active layer 308 is reduced, and the electrical modulation band can be increased.

  In the first active layer 304, a current is injected into a region narrower than the current injection region of the second active layer 308. As a result, the gain of the central portion corresponding to the fundamental transverse mode can be selectively increased, so that the light output of the fundamental transverse mode can be increased.

  From the above effects, the relaxation oscillation frequency of the VCSEL can be increased, and a high-speed modulation operation exceeding 10 Gbps is possible.

  In the VCSEL of the fifth embodiment, the n-side upper electrode 213 and p-side electrode 214 for injecting current into the second active layer 308 having a high electrical modulation band are connected to the modulation pulse power source, and the first active layer By connecting the p-side electrode 214 and the n-side lower electrode 215 for injecting current into 304 to the excitation DC power supply, high-speed modulation performance can be effectively exhibited.

  Example 6 is an example corresponding to the fifteenth aspect. FIG. 7 is a diagram illustrating a vertical cavity surface emitting semiconductor laser device (VCSEL) according to a sixth embodiment.

Referring to FIG. 7, an n-type lower DBR 202 is stacked on an n-type GaAs substrate 201. Here, the n-type lower DBR 202 is formed by alternately stacking n-type GaAs layers and n-type Al _0.9 Ga _0.1 As layers at a quarter wavelength thickness. On the n-type lower DBR 202, a GaAs first spacer layer 601, a GaInNAs / GaAs multiple quantum well first active layer 304, a GaAs second spacer layer 602, and a p-type DBR 207 are stacked. Here, the p-type DBR 207 is formed by alternately stacking p-type GaAs layers and p-type Al _0.9 Ga _0.1 As layers at a quarter wavelength thickness. On the p-type DBR 207, a p-type AlAs layer 701, a GaAs third spacer layer 604, a GaInNAs / GaAs multiple quantum well second active layer 308, a GaAs fourth spacer layer 605, and an n-type upper DBR 212 are sequentially laminated. Yes. Here, the n-type upper DBR 212 is formed by alternately stacking n-type GaAs layers and p-type Al _0.9 Ga _0.1 As layers with a quarter wavelength thickness.

  Then, a mesa structure is formed by etching in a cylindrical shape from the surface of the laminated structure to the middle of the p-type DBR 207. From the side of the mesa structure, the p-type AlAs layer 701 is selectively side-etched to form an air gap region 606.

  In addition, proton ions are implanted from the bottom of the mesa structure in the vicinity of the first active layer 304 to form a high resistance region 311. The high resistance region 311 forms a current confinement structure with respect to the first active layer 304. At this time, the constriction opening area of the high resistance region 311 is fabricated to be larger than the air gap constriction opening area of the p-type AlAs layer 701.

  A ring-shaped n-side upper electrode 213 is formed on the surface of the n-type upper DBR 212 except for the light emitting portion. A p-side electrode 214 is formed on the bottom surface of the mesa structure. An n-side lower electrode 215 is formed on the back surface of the n-type GaAs substrate 201.

  In the VCSEL of FIG. 7, by reducing the number of stacking periods of the p-type DBR 207, two resonators are optically coupled to form one resonance mode. Since the band gaps of the first active layer 304 and the second active layer 308 are equal and have a gain with respect to the same resonance mode in which two resonators are coupled, the first active layer 304 has The oscillation light when the current is injected and the oscillation light when the current is injected into the second active layer 308 oscillate at the same wavelength (1.3 μm) in mode synchronization. Therefore, the photon density inside the VCSEL element can be increased and the relaxation oscillation frequency of the VCSEL can be increased as compared with the case where there is one active layer.

  In addition, the element resistance is reduced by forming the conductivity type of the lower DBR 202, which has a large number of layers due to the necessity of high reflectivity, to be n-type. Further, since the constriction opening area of the high resistance region 311 for confining current with respect to the first active layer 304 is made larger than the air gap constriction opening area for the second active layer 308, the current in the first active layer 304 is The resistance of the constriction is reduced.

  Furthermore, the high resistance region 311 formed by ion implantation is thicker in the stacking direction than the Al oxide constriction structure or the air gap structure. Therefore, the capacitance component formed by the high resistance region 311 is reduced as compared with the case where the Al oxide constriction structure or the air gap structure is used. Therefore, the CR time constant when modulating the current injected into the first active layer 304 is reduced, and the electrical modulation band can be improved.

  In the air gap constriction structure with a narrow constriction area, the refractive index is higher than that of the region where the unetched semiconductor layer is etched, so that the light is confined in the central portion. Accordingly, the light in the fundamental transverse mode is confined, and conversely, oscillation in the higher order transverse mode is suppressed.

  In the second active layer 308, a current is injected into a region narrower than the current injection region of the first active layer 304. Thereby, the gain of the center part corresponding to the fundamental transverse mode can be selectively increased. Therefore, it is possible to increase the light output while maintaining the basic transverse mode. Thereby, the photon density inside the device is further increased, and the VCSEL can be operated at high speed.

In the VCSEL of Example 6, the p-side electrode 214 and the n-side lower electrode 215 for injecting current into the first active layer 304 having a high electrical modulation band are connected to the modulation pulse power source, and the second active layer By connecting the n-side upper electrode 213 and the p-side electrode 214 for injecting current into 308 to the excitation DC power supply, high-speed modulation performance can be effectively exhibited.

1 is a diagram showing a light emitting device of Example 1. FIG. 6 is a diagram showing a light emitting device of Example 2. FIG. 6 is a diagram showing a light emitting device of Example 3. FIG. FIG. 10 illustrates an optical transmission system according to a fourth embodiment. FIG. 6 is a diagram for explaining the operation of the light-emitting device of Example 1. 6 is a view showing a vertical cavity surface emitting semiconductor laser according to Example 5. FIG. 6 is a view showing a vertical cavity surface emitting semiconductor laser according to Example 6. FIG.

Explanation of symbols

101 p-type GaAs substrate 102 p-type Al _0.2 Ga _0.8 As / Al _0.9 Ga _0.1 As Lower DBR
103 p-type AlAs layer 104 AlGaAs first spacer layer 105 GaAs / AlGaAs multiple quantum well first active layer 106 AlGaAs second spacer layer 107 n-type Al _0.2 Ga _0.8 As / Al _0.9 Ga _0.1 As DBR
108 AlGaAs third spacer layer 109 GaAs / AlGaAs multiple quantum well second active layer 110 AlGaAs fourth spacer layer 111 p-type AlGaAs layer 112 p-type Al _0.2 Ga _0.8 As / Al _0.9 Ga _0.1 As Upper DBR
113 Upper p-side electrode 114 n-side electrode 115 Lower p-side electrode 116 AlO _x insulating region 117 Pulse power source for modulation 118 DC power source for excitation 201 n-type GaAs substrate 202 n-type GaAs / Al _0.9 Ga _0.1 As Lower DBR
203 AlGaAs first spacer layer 204 GaInAs / GaAs multiple quantum well first active layer 205 AlGaAs second spacer layer 206 p-type first AlAs layer 207 p-type GaAs / Al _0.9 Ga _0.1 As DBR
208 p-type second AlAs layer 209 AlGaAs third spacer layer 210 GaInAs / GaAs multiple quantum well second active layer 211 AlGaAs fourth spacer layer 212 n-type GaAs / Al _0.9 Ga _0.1 As upper DBR
213 Upper n-side electrode 214 P-side electrode 215 Lower n-side electrode 301 Non-doped GaAs / Al _0.9 Ga _0.1 As Lower DBR
302 p-type GaAs first spacer layer 303 p-type AlAs layer 304 GaInNAs / GaAs multiple quantum well first active layer 305 n-type GaAs second spacer layer 306 n-type GaAs / AlGaAs DBR
307 n-type GaAs third spacer layer 308 GaInNAs / GaAs multiple quantum well second active layer 309 p-type GaAs fourth spacer layer 310 non-doped GaAs / Al _0.9 Ga _0.1 As upper DBR
311 High resistance region 401 Optical transmitter 402 Optical receiver 403 Optical transceiver module 404 Optical fiber cable 601 GaAs first spacer layer 602 GaAs second spacer layer 603 p-type second AlAs layer 604 GaAs third spacer layer 605 GaAs fourth spacer layer 606 Side etching region 701 p-type AlAs layer

Claims (12)

A vertical resonator type surface emitting semiconductor laser element having a plurality of resonators sandwiched between upper and lower layers by a multilayer reflector on a substrate, a modulation pulse power source, and an excitation DC power source, the vertical resonator type A plurality of resonators of the surface emitting semiconductor laser element are optically coupled to form one resonance mode, and an active layer is provided in each resonator, and each of the active layers is the same. And one active layer of the active layers is electrically connected to the modulation pulse power source, and another active layer of the active layers. Is electrically connected to the excitation DC power supply, and for the same resonance mode, an active layer electrically connected to the modulation pulse power supply and an activity electrically connected to the excitation DC power supply. Layer oscillates in mode synchronization A light emission device while creating, multilayer reflector adjacent the substrate, and / or, the light emitting device multilayer mirror conductivity type on the outermost surface side, characterized in that it is a n-type. 2. The light emitting device according to claim 1, further comprising means for constricting a current injected into each active layer of the vertical cavity surface emitting semiconductor laser element, and electrically connected to the modulation pulse power source. A light emitting device characterized in that an area where current is confined with respect to the active layer formed is wider than an area where current is confined with respect to the active layer electrically connected to the excitation DC power source. 3. The light emitting device according to claim 2, wherein a structure having a refractive index difference in a horizontal and lateral direction is used as means for confining current to an active layer electrically connected to the excitation DC power source. Light-emitting device. 3. The light emitting device according to claim 2, wherein a high resistance region formed by ion implantation is used as means for confining current to an active layer electrically connected to the modulation pulse power source. . 5. The light-emitting device according to claim 1 , wherein the active layer electrically connected to the modulation pulse power source has a multiple quantum well structure in which a plurality of quantum well layers and barrier layers are stacked. A light emitting device comprising: a barrier layer doped with a p-type impurity in a range of 1 × 10 ¹⁸ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ . 6. The light emitting device according to claim 1 , wherein the active layer includes a mixed crystal semiconductor of nitrogen and another group V element. An optical transmission system comprising the light emitting device according to any one of claims 1 to 6 . A plurality of resonators sandwiched between upper and lower layers by a multilayer mirror are provided on a substrate, and the plurality of resonators are optically coupled to form one resonance mode. An active layer is provided, the active layer has a gain with respect to the same resonance mode wavelength, and current injection means for injecting current into each active layer and current injected from the current injection means Current-restricting means for constricting the substrate, and the conductivity type of the multilayer-film reflective mirror adjacent to the substrate and / or the multilayer-film reflective mirror on the outermost surface side is n-type, Surface emitting semiconductor laser element. 9. The vertical cavity surface emitting semiconductor laser device according to claim 8, wherein at least one of the active layers has a multiple quantum well structure in which a plurality of quantum well layers and barrier layers are stacked. A vertical cavity surface emitting semiconductor laser device, wherein the layer is doped with p-type impurities in the range of 1 × 10 ¹⁸ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ . 9. The vertical cavity surface emitting semiconductor laser device according to claim 8, wherein at least one of the active layers is a mixed crystal semiconductor containing nitrogen and another group V element. Cavity type surface emitting semiconductor laser device. 9. The vertical cavity surface emitting semiconductor laser device according to claim 8, wherein the current confinement means uses a structure having a refractive index difference in a horizontal transverse direction, and the current confinement area by the current confinement means is different for each active layer. A vertical cavity surface emitting semiconductor laser device characterized in that: 9. The vertical cavity surface emitting semiconductor laser device according to claim 8, wherein the current confinement means includes a structure having a refractive index difference in a horizontal lateral direction and a high resistance region formed by ion implantation in different active layers. Vertical cavity surface emitting semiconductor characterized in that a constriction area by a current confinement means having a refractive index difference in the horizontal transverse direction is smaller than a constriction area by a high resistance region formed by ion implantation Laser element.

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