JP5645546B2 - Surface emitting semiconductor laser and optical transmission device - Google Patents

Description

  The present invention relates to a surface emitting semiconductor laser and an optical transmission device.

  In recent years, the optical link transmission capacity has been increasing at an accelerating rate, and a light source capable of high-speed transmission of about 100 Gbs and low power consumption is required. In order to use a surface emitting semiconductor laser for such a light source, the modulation speed of the surface emitting semiconductor laser must be further increased. One method for high-speed modulation of a surface emitting semiconductor laser is to form a surface emitting semiconductor laser and a lateral waveguide monolithically on a substrate and inject light into the surface emitting semiconductor laser from the lateral waveguide. There is one that switches or modulates light emitted from a surface emitting semiconductor laser (Patent Document 1). Furthermore, the increase in optical transmission capacity requires higher output of the surface emitting semiconductor laser. For example, by forming a light confinement region surrounded by a recess on the light emitting surface of a surface emitting semiconductor laser, the number of modes is reduced and high output is achieved (Patent Document 2).

  Patent Document 3 relates to a mode-locked edge-emitting semiconductor laser, and relates to a light absorber section that absorbs light by applying a reverse bias voltage and changing the refractive index of a modulation element, and a forward bias voltage. Is applied to form an active section that generates optical gain, enabling high-speed modulation and high output.

JP-A-11-274640 JP 2007-189033 A JP 2010-3930 A

  An object of the present invention is to provide a surface-emitting type semiconductor laser capable of high-speed modulation and an optical transmission device using the same.

According to a first aspect of the present invention, there is provided a light emitting portion that is formed on the substrate and emits laser light in a direction perpendicular to the substrate; A light propagation portion to be reflected and a reflection portion for reflecting the light propagated by the light propagation portion toward the light emitting portion, and a first layer comprising a laminated structure of a high refractive index layer and a low refractive index layer on the substrate. A first multilayer reflector, an active region capable of emitting light, and a second multilayer reflector having a laminated structure of a high refractive index layer and a low refractive index layer, and the light emitting unit 1 multilayer reflector, the active region and the second multilayer reflector, wherein the light emitting part emits laser light from the surface of the second multilayer reflector, and the light propagation part is Including the first multilayer reflector, the active region, and the second multilayer reflector, the light播部includes a light emitting region low equivalent refractive index area is smaller equivalent refractive index than the effective refractive index of, than the low equivalent refractive index region disposed between the low equivalent refractive index area and the reflective portion Including a high equivalent refractive index region having a high equivalent refractive index, and light leaked from the low equivalent refractive index region to the light propagating portion is transmitted between the first multilayer film reflector and the second multilayer film reflector. A surface emitting semiconductor laser that travels while being reflected, is reflected by the reflecting portion , and is reinjected into the light emitting portion through the low equivalent refractive index region.
2. The surface emitting semiconductor laser according to claim 1 , wherein the low equivalent refractive index region includes a groove formed in the second multilayer film reflector in a direction perpendicular to the substrate.
According to a third aspect of the present invention, the light emitting unit includes a current confinement layer in the vicinity of the active region, and the current confinement layer includes an oxidized region that is selectively oxidized and a non-oxidized region that is surrounded by the oxidized region. wherein the said non-oxidized region, said has a high equivalent refractive index than the oxidation region, a part of the light confined to the non-oxidized region is propagated to the light propagation unit, according to claim 1 or 2 A surface-emitting type semiconductor laser described in 1.
Claim 4, wherein the low equivalent refractive index region is formed in the non-oxidized region, the surface emitting semiconductor laser according to claim 3.
According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the reflecting portion is formed on a side wall of the first multilayer film reflecting mirror, the active region, and the second multilayer film reflecting mirror of the light propagation portion. The surface emitting semiconductor laser described.
According to a sixth aspect of the present invention, the first multilayer-film reflective mirror has a first conductivity type, the second multilayer-film reflective mirror has a second conductivity type different from the first conductivity type, and the light emitting unit A first electrode electrically connected to the first multilayer film reflector, and a second electrode electrically connected to the second multilayer film reflector, the first and second driving signals to the electrodes of the forward bias is applied, the surface-emitting type semiconductor laser according to 5 any one claims 1.
According to a seventh aspect of the present invention, a light emitting portion that is formed on the substrate and emits laser light in a direction perpendicular to the substrate, and at least part of the light emitted from the light emitting portion is formed in the horizontal direction with respect to the substrate. A first multilayer mirror having a laminated structure of a high refractive index layer and a low refractive index layer, an active region capable of emitting light, and a high refractive index. A second multilayer film reflecting mirror having a laminated structure of a refractive index layer and a low refractive index layer is formed, and the light emitting section includes the first multilayer film reflecting mirror, the active region, and the second multilayer film reflecting mirror. The light propagation part includes the first multilayer film reflector, the active region, and the second multilayer film reflector, and the light propagation part has a lower equivalent equivalent refractive index than the light emitting part region. A refractive index region, adjacent to the low equivalent refractive index region and from the low equivalent refractive index region And a high equivalent refractive index region having a high equivalent refractive index, and the low equivalent refractive index region is formed by a groove extending in a direction perpendicular to the substrate in the second multilayer-film reflective mirror, and emitted from the light emitting unit. Part of the light is propagated to the high equivalent refractive index region through the low equivalent refractive index region, and proceeds while being reflected between the first multilayer film reflecting mirror and the second multilayer film reflecting mirror. An optical transmission apparatus comprising: a type semiconductor laser; and drive signal applying means for applying a drive signal so as to adjust the amount of light propagated by the light propagation unit.
Claim 8, wherein the drive signal is a drive signal of the reverse bias light propagation is absorbed, the optical transmission apparatus according to claim 7.
The ninth multilayer reflector has a first conductivity type, the second multilayer reflector has a second conductivity type different from the first conductivity type, and the light emitting unit includes: A first electrode electrically connected to the first multilayer-film reflective mirror; and a second electrode electrically connected to the second multilayer-film reflective mirror, wherein the second electrode is The light propagation part includes a third electrode electrically connected to the second multilayer-film reflective mirror, and is formed so as to cover a surface of the second multilayer-film reflective mirror. The optical transmission device according to claim 8 , wherein the reverse bias drive signal is applied, and laser light is emitted from the surface of the second multilayer-film reflective mirror of the light propagation unit.
The light-emitting section includes a current confinement layer in the vicinity of the active region, and the current confinement layer includes a selectively oxidized oxidized region and a non-oxidized region surrounded by the oxidized region. wherein the said non-oxidized region has a high equivalent refractive index than the oxidized region, the portion of light confined in a non-oxidizing region is propagated to the light propagation unit, according to claim 8 or 9 An optical transmission device according to 1.
Claim 11, wherein the low equivalent refractive index area, wherein is formed in a non-oxidizing region, the optical transmission apparatus according to claim 10.
According to a twelfth aspect of the present invention, the light propagation unit further includes a fourth electrode electrically connected to the high equivalent refractive index region, and propagates according to a forward bias drive signal applied to the fourth electrode. The optical transmission device according to claim 8 , wherein the laser beam amplified is amplified.
According to a thirteenth aspect of the present invention, there is provided an optical transmission apparatus comprising: the surface emitting semiconductor laser according to any one of the first to sixth aspects; and a driving signal applying unit that applies a driving signal to the surface emitting semiconductor laser. .

According to the first aspect of the present invention, the surface-emitting type semiconductor laser can be modulated at a higher speed as compared with a case where the light propagation part for propagating a part of light in the horizontal direction with respect to the substrate is not provided. In addition, the amount of light propagating in the light propagation unit can be easily adjusted as compared with a device that does not include a reflection unit that reflects light propagated in the light propagation unit.
According to the invention of claim 2 , the groove of the low refractive index region can be easily formed as compared with the case where the light emitting part and the light propagation part are not formed on the same substrate.
According to the invention of claim 3 , optical confinement and current confinement can be performed simultaneously by the current confinement layer.
According to the invention of claim 4 , a part of the light confined in the non-oxidized region can be guided to the high equivalent refractive index region.
According to the fifth aspect of the present invention, it is possible to reflect the light effectively so that no loss of the amount of light propagated by the light propagation portion occurs.
According to the invention of claim 6 , the laser beam can be modulated in accordance with the drive signal.
According to the seventh aspect of the present invention, it is possible to provide an optical transmission device in which laser light is modulated at a high speed as compared with a device that does not include a light propagation portion that propagates a part of light in the horizontal direction with respect to the substrate.
According to the eighth aspect of the present invention, it is possible to modulate the laser beam at a higher speed than in the case where a reverse bias drive signal is not applied.
According to the ninth aspect of the present invention, it is possible to effectively absorb light as compared with a case where there is no light propagation portion to which a reverse bias drive signal is applied.
According to the invention of claim 10 , optical confinement and current confinement can be performed simultaneously by the current confinement layer.
According to the invention of claim 11 , light confined in the non-oxidized region can be guided to the high equivalent refractive index region.
According to the twelfth aspect of the present invention, it is possible to increase the output power of the laser light as compared with the case where the forward-bias drive signal is not applied and does not have the light propagation portion.
According to the invention of claim 13 , it is possible to transmit a high-speed modulated optical signal.

1A is a schematic plan view of a surface-emitting type semiconductor laser according to a first embodiment of the present invention, and FIG. It is a figure which shows the equivalent refractive index and optical confinement distribution of the surface emitting semiconductor laser which concerns on a 1st Example. It is a graph which shows the calculation result of the light distribution of the surface emitting semiconductor laser which concerns on a 1st Example. It is a graph which shows the calculation result of the frequency response characteristic of the surface emitting semiconductor laser which concerns on a 1st Example. It is a graph which shows the calculation result of the signal characteristic of the surface emitting semiconductor laser which concerns on a 1st Example. It is the typical top view of the surface emitting semiconductor laser which concerns on 2nd Example of this invention, and its BB sectional drawing. It is a graph which shows the optical amplification amount of the surface emitting semiconductor laser which concerns on a 2nd Example. It is a block diagram which shows the electrical constitution of the optical transmission apparatus using the surface emitting semiconductor laser which concerns on the Example of this invention. It is sectional drawing which shows one structural example of the optical transmission apparatus using the surface emitting semiconductor laser which concerns on the Example of this invention.

  Next, a surface-emitting type semiconductor laser (VCSEL: Vertical-Cavity Surface-Emitting Laser diode, hereinafter referred to as VCSEL) according to an embodiment of the present invention will be described with reference to the drawings. It should also be noted that the scale of the drawings is emphasized to make the features of the invention easier to understand and is not necessarily the same as the actual device scale.

  FIG. 1A is a schematic plan view of a VCSEL according to the first embodiment of the present invention, and FIG. 1B is a sectional view taken along line AA. As shown in the figure, the VCSEL 10 of the present embodiment is an n-type distributed Bragg reflector (hereinafter referred to as a distributed Bragg reflector) in which AlGaAs layers having different Al compositions are alternately stacked on an n-type GaAs substrate 100. DBR) 102, an active region 104 including a quantum well layer sandwiched between upper and lower spacer layers formed on the lower DBR 102, and AlGaAs layers having different Al compositions formed on the active region 104, which are alternately stacked. The upper DBR 108 of the mold is laminated. The VCSEL 10 shown in FIG. 1 (a) has a post structure in which one end is semicircular and the other end is rectangular.

In the n-type lower DBR 102, for example, a plurality of pairs of an Al _0.92 Ga _0.08 As layer and an Al _0.16 Ga _0.84 As layer are stacked as a stack of a high refractive index layer and a low refractive index layer. The thickness of each layer is λ / 4n _r (where λ is the oscillation wavelength and n _r is the refractive index of the medium), and these are alternately stacked in 40 cycles. The carrier concentration after doping silicon which is an n-type impurity is, for example, 3 × 10 ¹⁸ cm ⁻³ .

The lower spacer layer of the active region 104 is an undoped Al _0.6 Ga _0.4 As layer, the quantum well active layer is an undoped GaAs quantum well layer and an undoped Al _0.3 Ga _0.7 As barrier layer, and the upper spacer The layer is an undoped Al _0.6 Ga _0.4 As layer.

The p-type upper DBR 108 is formed by stacking a plurality of pairs of, for example, an Al _0.92 Ga _0.08 As layer and an Al _0.16 Ga _0.84 As layer as a stack of a high refractive index layer and a low refractive index layer. The thickness of each layer is lambda / 4n _r, to 24 cycles are alternately stacked. The carrier concentration after doping with carbon which is a p-type impurity is, for example, 3 × 10 ¹⁸ cm ⁻³ . A current confinement layer 106 made of a p-type Al _0.98 Ga _0.02 As layer (or AlAs layer) is formed in the lowermost layer of the upper DBR 108 or in the inside thereof. Further, a contact layer having a high impurity concentration (for example, 1 × 10 ¹⁹ cm ⁻³ ) made of p-type GaAs may be formed on the uppermost layer of the upper DBR 108.

The current confinement layer 106 has an Al composition higher than that of the lower DBR 102 and the upper DBR 108, and oxidation proceeds faster in the oxidation process. When the post structure as shown in FIG. 1A is oxidized, an oxidized region 106A (hatched portion in FIG. 1B) selectively oxidized from the side wall of the post structure to the inside, and an oxidized region 106A. A non-oxidized region 106B surrounded by is formed. The planar shape of the non-oxidized region 106B substantially reflects the planar shape of the post structure. 106C illustrated in FIG. 1A indicates a boundary between the oxidized region 106A and the non-oxidized region 106B. Preferably, the diameter D1 of the semicircular portion of the non-oxidized region 106A is 3 microns or less, which is a size that allows the fundamental transverse mode oscillation. The refractive index of the oxidized region 106A is about 1.7, the refractive index of the non-oxidized region (Al _0.98 Ga _0.02 As) 106B is about 3.0, and light enters the non-oxidized region 106B having a high refractive index. It becomes possible to confine. The non-oxidized region 106 </ b> A is a conductive region and has a function of increasing the density of carriers injected from the electrodes and supplying them to the active region 104.

  A metal semicircular p-side electrode 110 is formed on the upper DBR 108. The p-side electrode 110 is made of, for example, a metal in which Au or Ti / Au is laminated, and the p-side electrode 110 is electrically connected to the upper DBR 108. An n-side electrode 112 is formed on the back surface of the substrate 100.

  Thus, the light emitting unit 130 having a vertical resonator structure is formed on the substrate 100, and a forward drive signal is applied between the p-side electrode 110 and the n-side electrode 112, so that the surface of the upper DBR 108 is removed. Laser light is emitted in a direction perpendicular to the substrate. Here, the forward bias applies a positive voltage to the p-type semiconductor layer in the semiconductor laser and a negative voltage to the n-type semiconductor layer, and the reverse bias refers to the p-type semiconductor layer in the semiconductor laser. A negative voltage is applied to the n-type semiconductor layer, and a positive voltage is applied to the n-type semiconductor layer. However, the negative voltage includes a ground potential (GND).

  Furthermore, in this embodiment, the light propagation part 140 is formed monolithically on the side part of the light emitting part 130. The light propagation unit 140 includes a low equivalent refractive index region 120 having a relatively small equivalent refractive index and a slow light unit 122 of a high equivalent refractive index region that propagates light guided from the low equivalent refractive index region 120. The low equivalent refractive index region 120 and the slow light part 122 are configured using a semiconductor layer substantially the same as the light emitting part 130. Preferably, the low equivalent refractive index region 120 includes a trench formed in the upper DBR 108 in a direction perpendicular to the substrate. The trench 120 is formed so as to be adjacent to the inside of the boundary 106C shown in FIG. 1A, that is, adjacent to the non-oxidized region 106B in which the light generated in the light emitting unit 130 is confined. The equivalent refractive index used in this specification is an effective refractive index of a semiconductor multilayer film having a different refractive index stacked in a direction perpendicular to the substrate (the refractive index of the multilayer film is the refractive index of a single layer). Is determined by an equivalent refractive index method.

  The reason why the trench 120 is formed in the boundary 106 </ b> C is to easily guide part of the light generated by the light emitting unit 130 to the slow light unit 122. Therefore, the trench 120 does not completely confine the light of the light emitting unit 130 but needs to be formed at a position, depth, and width (D2) such that a part of the trench 120 leaks to the slow light unit 122. The shape of the trench 120 does not matter, but here it is formed in a rectangular shape. In this embodiment, the substantial diameter D1 of the non-oxidized region 106B of the light emitting portion 130 is 2 μm, the width D2 of the trench 120 is 1 μm, and the distance D3 of the slow light portion 122 is 6 μm.

  FIG. 2 shows the relationship between the equivalent refractive index of the VCSEL 10 and the optical confinement distribution. In the figure, a step-like line indicates an equivalent refractive index, and a curve indicates a light confinement distribution. A region D0 having a low equivalent refractive index NL (see FIG. 1A) corresponds to the oxidized region 106A of the light emitting unit 130, and a region D1 having a high equivalent refractive index NH corresponds to the non-oxidized region 106B and has a low equivalent. A region D2 having a refractive index NL corresponds to the trench 120 of the light propagation unit 140, and a region D3 having a high equivalent refractive index NH corresponds to the slow light unit 122 of the light propagation unit 140.

  By continuously forming the regions D0, D1, D2, and D3 having high and low equivalent refractive indexes, most of the light generated in the light emitting unit 130 is confined in the region D1. The fundamental lateral mode light Lin confined in the region D1 has a Gaussian distribution. However, the trench 120 (region D2) does not completely confine the light Lin, but the slow light portion 122 does not completely confine the light. Lead to. Even laser light that is vertically resonated in the light emitting unit 130 includes laser light having a slight inclination angle from the vertical direction. Therefore, part of the light at the base is guided to the region D3 having a high equivalent refractive index via the region D2 having a low equivalent refractive index. Since the light guided to the slow light unit 122 is confined in the slow light unit 122 and propagates in the horizontal direction while being resonated in the direction of the inclination angle in the vertical resonator, the slow light unit apparently appears. The speed of light propagating horizontally through 122 appears to be slow.

  At the end of the light propagation unit 140 facing the light emitting unit 130, a light reflection unit 150 is provided as a light amount adjusting unit that adjusts the amount of light propagated by the light propagation unit 140. The light reflecting portion 150 is made of a low refractive index insulating member such as SiO 2 or a metal such as gold. It is desirable that the light reflection portions 150 are formed on the side walls of the lower DBR 102, the active region 104, and the upper DBR 108 to reflect the light so as not to cause a large loss of light. The light propagated in the light propagation unit 140 is reflected toward the direction opposite to the direction propagated by the light reflection unit 150, that is, toward the light emitting unit 130, and the light is injected into the light emitting unit 130 again. The

  FIG. 3 is a graph showing the calculation result of the light distribution of the VCSEL of this example. The horizontal axis is distance (μm), and the vertical axis is relative intensity. In the figure, the range of 0-2 μm corresponds to the diameter D1 of the non-oxidized region 106B, and laser oscillation with a Gaussian distribution having a large relative intensity occurs. The range of 2-3 μm corresponds to the width D2 of the trench 120, and here, light having a small relative intensity is generated. The range of 3-9 μm corresponds to the distance D3 of the slow light part 122, and indicates the laser light that is confined in the slow light part 122 and propagates.

  As described above, the light propagating through the slow light part 122 travels while being reflected between the lower DBR 102 and the upper DBR 108, so that the light actually travels even if the horizontal distance D3 of the slow light part 122 is small. The distance to be performed (optical path length) corresponds to several hundred times the distance D3. Therefore, the propagation time T of the light reflected by the light reflecting part 150 and reciprocating in the slow light part 122 has the same effect as if the speed of light was delayed.

  When a forward bias drive signal is applied to the p-side electrode 110 and the n-side electrode 112, oscillation occurs in the light emitting unit 130, and laser light having an oscillation wavelength of 850 nm is emitted from the surface of the upper DBR 108. This oscillation has a certain internal loss. Further, part of the light generated in the light emitting unit 130 is propagated in the horizontal direction through the light propagation unit 140, reflected by the light reflecting unit 150, and then injected into the light emitting unit 130 again. By re-injecting the laser light after this propagation time T, the amount of laser light increases, and modulation at a frequency corresponding to the propagation time T becomes easy. Since the propagation time T is a function of the geometric configuration of the slow light unit 122, that is, the distance D3 of the slow light unit 122 and the number of pairs of upper and lower DBR semiconductor layers, the slow light unit 122 is appropriately adjusted. Thus, the VCSEL 10 can be modulated at high speed.

  FIG. 4 is a graph comparing the calculation results of the frequency response characteristics of the VCSEL of the present embodiment and the VCSEL of the conventional structure. The vertical axis represents response (dB), and the horizontal axis represents modulation frequency (GHz). When the decrease in signal strength is allowed up to −3 dB, the modulation frequency is about 25 GHz in the conventional VCSEL having a structure not including the light propagation unit, whereas the modulation frequency is about the VCSEL 10 of the present embodiment. It can be improved up to about 35 GHz.

FIG. 5 shows an eye pattern for comparing the calculation results of the signal characteristics of the VCSEL of the present embodiment and the VCSEL of the conventional structure. This is an example when a pseudo-random signal PRBS having a word length of 2 ⁸ −1 is transmitted at 40 Gbps as a transmission condition. It can be seen that the quality of the eye pattern of the VCSEL of this embodiment shown in FIG. 5B is superior to that of the VCSEL having the conventional structure shown in FIG.

  Next, a second embodiment of the present invention will be described. FIG. 6 shows a schematic plan view of a VCSEL 10A according to the second embodiment and a cross-sectional view taken along line BB. It should be noted that the same reference numerals are assigned to components equivalent to those in the first embodiment.

  The VCSEL 10 according to the first embodiment is directly modulated, whereas the VCSEL 10A according to the second embodiment is externally modulated. As shown in FIG. 6, in the VCSEL 10A, the lower DBR 102 and the upper DBR 108, which are formed on the substrate 100 and sandwich the active region 104, constitute the light emitting unit 130A, as in the first embodiment. The example light emitting unit 130A is different in that the p-side electrode 110A covers the light emitting surface of the upper DBR 108. A forward bias drive voltage is always applied between the p-side electrode 110A and the n-side electrode 112 of the light emitting unit 130A, and the light generated thereby is reflected by the p-side electrode 110A. A lot of light is guided to the light absorption unit 200.

  The light absorbing unit 200 is formed monolithically on the side of the light emitting unit 130A. As in the first embodiment, the light absorbing unit 200 propagates the guided laser beam and the trench 120 for guiding a part of the light generated by the light emitting unit 130A to the slow light unit 122A. And a slow light portion 122A that selectively absorbs laser light. The depth of the trench 120 is formed shallower than in the first embodiment.

  The slow light part 122A of the second embodiment has a pair of p-side drive electrodes 210 formed on the upper DBR 108, as shown in FIG. The drive electrode 210 is electrically connected to the upper DBR 108 of the slow light unit 212A, and a reverse bias drive pulse signal is applied between the p-type drive electrode 210 and the n-side electrode 112. When a reverse bias voltage is applied to the slow light portion 122A, the refractive index of the active region 104 changes and light passing therethrough is absorbed. Such a light absorption principle is known as an electro absorption modulator. When an electric field is applied to a quantum well formed of a semiconductor heterojunction, the EA modulator has a long wavelength at the absorption edge. Modulation is performed using the property of shifting to the side.

  The laser light Lm guided in the lateral direction from the light emitting unit 130A is propagated in the horizontal direction while being reflected from the lower DBR 102 of the slow light unit 122A in the vertical resonator of the upper DBR 108. For this reason, even if the horizontal distance D3 of the slow light portion 122A is small, the laser light Lm passes through the active region 104 at a number corresponding to several hundred times the distance, and the laser light Lm is more effective. Absorbed. As a result, laser light Ln that is switched or modulated in accordance with the frequency f of the drive pulse signal is emitted from the surface of the upper DBR 108 of the light absorbing unit 200 (an area corresponding to the boundary 106C).

  Next, a third embodiment of the present invention will be described. In the second embodiment, an example in which light is absorbed by applying a reverse bias drive pulse signal to the slow light unit 122A is shown. However, in the third example, a forward drive voltage is applied to the slow light unit 122A. Is applied to amplify the laser light Lm guided from the light emitting unit 130A. The light absorption unit 200 shown in FIG. 6 is referred to as an optical amplification unit 220 in the third embodiment. The optical amplifier 220 is known as a semiconductor optical amplifier (SOA).

  When a forward bias drive voltage is applied between the p-side drive electrode 210 and the n-side electrode 112, carriers are injected from the electrode, and the gain of the laser light in the optical amplifier 220 is amplified. Since the laser light Lm injected from the light emitting unit 130 is propagated in the horizontal direction while being reflected in the vertical resonator of the slow light unit 122A, it passes through the active region 104 many times. As a result, the laser light Lm The gain is amplified, and high-power laser light Ln is emitted from the surface of the upper DBR 108 of the slow light portion 112A.

  FIG. 7 is a graph showing the amount of optical amplification of the optical amplifier of the third embodiment. The vertical axis represents gain, and the horizontal axis represents current density. As can be seen from the figure, the gain increases as the current density increases. That is, when the injection amount from the carrier from the optical amplifying unit 220 increases, the gain increases.

  In the second and third embodiments described above, the light absorbing part 200 and the light amplifying part 220 are individually formed on the side part of the light emitting part 130A, but the light absorbing part 200 is provided on the side part of the light emitting part 130A. It is also possible to form both the optical amplifying unit 220 and the optical amplifying unit 220. For example, the laser light Lm injected from the light emitting unit 130A may be amplified by the optical amplification unit 220 with a constant gain, and the amplified laser light may be selectively absorbed (modulated) by the light absorption unit 200. On the contrary, the light injected from the light emitting unit 130A may be selectively absorbed (modulated) by the light absorbing unit 200, and the modulated laser light may be amplified by the light amplifying unit 220. When both the light absorption unit 200 and the light amplification unit 220 are provided, it is necessary to separately form the p-side drive electrode.

  FIG. 8 is a block diagram illustrating a configuration of an optical transmission apparatus using the VCSEL of the present embodiment. The optical transmission apparatus 300 of this embodiment drives a forward bias drive signal S1 for driving the light emitting unit 130 / 130A, a reverse bias drive signal S2 for driving the light absorbing unit 200, and the optical amplifier 220. A drive unit 310 that generates a forward bias drive signal S3. Of course, when driving the VCSEL 10 of the first embodiment, the drive signals S2 and S3 are unnecessary, and when driving the VCSEL 10A of the second embodiment, the drive signal S3 is unnecessary.

  FIG. 9 is a cross-sectional view illustrating a configuration example of the optical transmission apparatus according to the present embodiment. The optical transmission device 400 includes a metal stem 420 on which an electronic component 410 on which a VCSEL 10 / 10A and a drive unit 310 are formed is mounted. The stem 420 is covered with a hollow cap 430, and a ball lens 440 is fixed to the center of the cap 430. ing. A cylindrical housing 450 is further attached to the stem 420, and an optical fiber 470 is fixed to an end of the housing 450 via a ferrule 460. The laser light modulated from the electronic component 410 is collected by the ball lens 440, and the light is incident on the optical fiber 470 and transmitted. In addition to the ball lens, other lenses such as a biconvex lens and a plano-convex lens can be used.

  The preferred embodiment of the present invention has been described in detail above, but the present invention is not limited to the specific embodiment, and various modifications can be made within the scope of the present invention described in the claims. Deformation / change is possible. In the above embodiment, a VCSEL using an AlGaAs compound semiconductor has been illustrated, but a VCSEL using a group III-V compound semiconductor layer other than this may be used. Furthermore, the shape of the post structure of the VCSEL in the above embodiment is merely an example, and other shapes may be used.

10: surface emitting semiconductor laser 100: GaAs substrate 102: lower DBR 104: active region 106: current confinement layer 106A: oxidized region 106B: non-oxidized region 106C: boundary 108: upper DBR 110: p-side electrode 112: n-side electrode 120: Trench
122, 122A: Slow light part 130, 130A: Light emitting part 140: Light propagation part 150: Light reflection part 200: Light absorption part 210: P side drive electrode 220: Light amplification part

Claims (13)

A light emitting unit that is formed on the substrate and emits laser light in a direction perpendicular to the substrate;
A light propagation part that is formed on the substrate and propagates a part of the light emitted from the light emitting part in a horizontal direction with the substrate;
A reflection unit that reflects the light propagated by the light propagation unit toward the light emitting unit ;
On the substrate, a first multilayer reflector having a laminated structure of a high refractive index layer and a low refractive index layer, an active region capable of emitting light, and a laminated structure of a high refractive index layer and a low refractive index layer A second multilayer reflector comprising:
The light emitting unit includes the first multilayer film reflecting mirror, the active region, and the second multilayer film reflecting mirror, and the light emitting unit emits laser light from a surface of the second multilayer film reflecting mirror. ,
The light propagation part includes the first multilayer film reflector, the active region, and the second multilayer film mirror,
The light propagation part includes a low equivalent refractive index area having an equivalent refractive index smaller than that of a light emitting part area, and the low equivalent refractive index area disposed between the low equivalent refractive index area and the reflecting part. And a high equivalent refractive index region having a higher equivalent refractive index than
The light leaked from the low equivalent refractive index region to the light propagation part travels while being reflected between the first multilayer film reflecting mirror and the second multilayer film reflecting mirror, and is reflected by the reflecting part . A surface emitting semiconductor laser re-injected into the light emitting portion through the low equivalent refractive index region. 2. The surface emitting semiconductor laser according to claim 1, wherein the low equivalent refractive index region includes a groove formed in the second multilayer mirror in a direction perpendicular to the substrate. The light emitting unit includes a current confinement layer in the vicinity of the active region, and the current confinement layer includes an oxidized region selectively oxidized and a non-oxidized region surrounded by the oxidized region. The oxidized region has a higher equivalent refractive index than the oxidized region;
The portion of the light confined to the non-oxidized region is propagated to the light propagation portion, the surface emitting semiconductor laser according to claim 1 or 2. The surface emitting semiconductor laser according to claim 3 , wherein the low equivalent refractive index region is formed in the non-oxidized region. The reflective portion, the first multilayer-film reflective mirror of the light propagating unit is formed on the sidewalls of the active region and the second multilayer-film reflective mirror, the surface-emitting type according to 4 any one claims 1 Semiconductor laser. The first multilayer-film reflective mirror has a first conductivity type, the second multilayer-film reflective mirror has a second conductivity type different from the first conductivity type, and the light emitting unit includes the first conductivity type A first electrode electrically connected to the multilayer mirror, and a second electrode electrically connected to the second multilayer reflector, and forward to the first and second electrodes drive signal bias is applied, the surface-emitting type semiconductor laser according to 5 any one claims 1. A light emitting unit that is formed on the substrate and emits laser light in a direction perpendicular to the substrate;
A light propagation part that is formed on the substrate and propagates at least a part of the light emitted from the light emitting part in the horizontal direction with the substrate;
On the substrate, a first multilayer reflector having a laminated structure of a high refractive index layer and a low refractive index layer, an active region capable of emitting light, and a laminated structure of a high refractive index layer and a low refractive index layer A second multilayer reflector comprising:
The light emitting unit includes the first multilayer reflector, the active region, and the second multilayer reflector,
The light propagation part includes the first multilayer film reflector, the active region, and the second multilayer film mirror,
The light propagation part includes a low equivalent refractive index region having an equivalent refractive index smaller than that of the light emitting part region, and a high equivalent refractive index adjacent to the low equivalent refractive index region and having a higher equivalent refractive index than the low equivalent refractive index region. The low equivalent refractive index region is formed by a groove extending in a direction perpendicular to the substrate in the second multilayer-film reflective mirror, and a part of the light emitted from the light emitting part is the low equivalent A surface-emitting type semiconductor laser that propagates through the refractive index region to the high equivalent refractive index region and travels while being reflected between the first multilayer film reflecting mirror and the second multilayer film reflecting mirror;
Drive signal applying means for applying a drive signal so as to adjust the amount of light propagating in the light propagation section;
An optical transmission device comprising: The optical transmission device according to claim 7 , wherein the drive signal is a reverse-biased drive signal in which propagated light is absorbed. The first multilayer reflector has a first conductivity type, and the second multilayer reflector has a second conductivity type different from the first conductivity type;
The light emitting unit includes a first electrode electrically connected to the first multilayer-film reflective mirror and a second electrode electrically connected to the second multilayer-film reflective mirror, The two electrodes are formed so as to cover the surface of the second multilayer-film reflective mirror,
The light propagation unit includes a third electrode electrically connected to the second multilayer-film reflective mirror, and the reverse bias drive signal is applied to the third electrode, and the light propagation unit includes the third electrode. The optical transmission device according to claim 8 , wherein laser light is emitted from the surface of the second multilayer-film reflective mirror. The light emitting unit includes a current confinement layer in the vicinity of the active region, and the current confinement layer includes an oxidized region selectively oxidized and a non-oxidized region surrounded by the oxidized region. The oxidized region has a higher equivalent refractive index than the oxidized region;
The optical transmission device according to claim 8 or 9 , wherein a part of the light confined in the non-oxidized region is propagated to the light propagation unit. The optical transmission device according to claim 10 , wherein the low equivalent refractive index region is formed in the non-oxidized region. The light propagation unit further includes a fourth electrode electrically connected to the high equivalent refractive index region, and transmits a laser beam propagated according to a forward bias drive signal applied to the fourth electrode. The optical transmission device according to claim 8 , wherein the optical transmission device amplifies. A surface-emitting type semiconductor laser according to any one of claims 1 to 6 ,
Drive signal applying means for applying a drive signal to the surface emitting semiconductor laser;
An optical transmission device comprising:

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