JP3317891B2 - Optical function element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical functional device, and more particularly to an optical functional device having a surface emitting laser structure.

[0002]

2. Description of the Related Art Heretofore, there has been known an element in which a planar element and an end face element are combined. For example, Japanese Unexamined Patent Publication
Japanese Patent No. 29625 discloses a bistable semiconductor laser provided with an optical waveguide structure for coupling externally injected light to a surface emitting laser having a saturable absorption layer. In this laser, the bistable state can be switched between ON and OFF by external light injected from the optical waveguide.

Japanese Patent Application Laid-Open No. 7-249824 discloses that a surface emitting laser and a lateral cavity semiconductor laser are combined and light is injected from the lateral cavity semiconductor laser to the surface emitting laser. A method for laser oscillation or light modulation of a surface emitting laser is described.

[0004]

However, in these conventional laser devices, since the volume of the intersection of the optical axis between the planar device and the lateral device is small, the interference of light between the planar device and the lateral device is small. was there. Therefore, the desired light-light injection effect was not sufficiently obtained.

Further, in the conventional structure, there is a problem that the electrical modulation of one element affects the other element due to insufficient electrical separation between the planar element and the lateral element.

Further, although proposals have been made on bistable elements and light injection oscillation, no application to optical functional elements having other functions has been known at all.

The present invention has been made in view of such a problem, and provides an optical functional device capable of obtaining efficient interaction between laser light of a surface emitting laser and light in a lateral optical waveguide. The purpose is to:

Another object of the present invention is to provide an optical functional device capable of obtaining an efficient interaction between the laser light of a surface emitting laser and the laser light of a lateral cavity semiconductor laser.

Further, according to the present invention, the electrical separation between the surface emitting device and the lateral device can be achieved by perfecting the electrical separation between the surface emitting laser and the lateral optical waveguide or the lateral cavity semiconductor laser. It is an object of the present invention to provide an optical function element free from the influence of modulation.

It is a further object of the present invention to provide a novel optical functional device in which a surface emitting laser is combined with a lateral optical waveguide or a lateral cavity semiconductor laser.

[0011]

According to the present invention, there is provided a surface emitting laser which emits a single transverse mode linearly polarized light in a direction perpendicular to a substrate and a waveguide which guides light horizontally to the substrate on the same semiconductor substrate. And an optical functional element having the surface emitting laser and the optical axis of the waveguide intersecting with each other. In this case, the optical function element has a plurality of surface emitting lasers according to the intended function, and the optical axes of the plurality of surface emitting lasers intersect with the optical axis of one waveguide. be able to.

Similarly, a plurality of waveguides may be provided, and the optical axes of the plurality of waveguides may intersect the optical axis of one surface emitting laser.

In order to construct these optical function elements, a pair of upper and lower distributed reflection type (DBR: Distributed Bragg) composed of a semiconductor periodic multilayer film is formed on a semiconductor substrate.
Reflector) and an intermediate layer including an active layer sandwiched between the pair of resonators, wherein a part of the upper reflector has a side wall perpendicular or nearly perpendicular to the substrate. By having a post structure whose plane shape is rectangular,
The surface emitting laser is formed in the post structure, and the waveguide is formed by oxidizing the side surface of one of the layers of the multilayer film forming the distributed reflection type mirror to lower the refractive index. be able to.

In these cases, by providing a resonator structure in the waveguide, an edge-emitting laser can be simultaneously provided on the same substrate.

To form such a structure, for example,
An AlGaAs layer or an AlAs layer having a large Al composition ratio and an AlG layer having a smaller Al composition ratio are formed on a semiconductor substrate.
aAs layers or GaAs layers are alternately formed and laminated, and the lower D
A step of forming a BR mirror, a step of forming an intermediate layer including a quantum well active layer thereon, and a step of
an AlGaAs layer or an AlAs layer having a large composition ratio;
An AlGaAs layer having a smaller Al composition ratio or Ga
Forming an upper DBR mirror by alternately forming and laminating an As layer; forming a resist mask by optical exposure; etching the upper DBR mirror halfway to form a post structure; Using a resist mask to form the above-described laminated structure into a mesa shape, and forming a DB from the side of the mesa in a heated steam atmosphere.
AlGaAs layer or AlAs having a large Al composition ratio of R
And a step of oxidizing the layer.

In the present invention, since efficient interaction between the light of the surface emitting laser and the light of the lateral waveguide can be achieved, it can be used as various optical functional elements.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure and manufacturing method of an optical functional device according to the present invention will be described below.

[Embodiment 1] This embodiment will be described with reference to FIGS. As shown in the perspective view of FIG. 1, the optical functional device 1 of this embodiment has a surface emitting laser and a lateral waveguide 3 whose optical axis is orthogonal to the surface emitting laser below a post structure 5. FIG. 2 is a sectional view of FIG.
1 is a cross-sectional view of FIG. 1B, and FIG. 4 is a cross-sectional view of FIG. 1C. A method for manufacturing the optical function device structure will be described below. As a film forming method, molecular beam epitaxy (MBE) or metal organic chemical vapor deposition (MOCVD) can be used.

First, an Al (Ga) As layer 11 and a GaAs layer 12 having a large Al composition ratio are alternately formed and laminated on a GaAs substrate 10, and a lower DBR mirror 6 (distributed Bragg reflector) is sufficiently reflected. Is formed to a thickness sufficient to obtain.
An intermediate layer 8 including an In _0.2 Ga _0.8 As quantum well active layer is formed thereon. Further, an Al (Ga) As layer 11 and a GaAs layer 12 having a large Al composition ratio are alternately formed and laminated thereon, and the upper DBR mirror 9 is formed to a thickness sufficient to obtain sufficient reflection.

A resist mask is formed on the substrate by optical exposure, and is etched halfway through the upper DBR mirror 9 by reactive ion beam etching (RIBE) using chlorine gas to form a post structure 5. This post structure has a rectangular shape of 6 μm × 4 μm in a plan view seen from above.

Further, a resist mask is formed again by using optical exposure, and a mesa 4 is formed by RIBE. After that, DB is placed on the side of the mesa 4 in a steam atmosphere at 460 ° C.
When the Al (Ga) As layer 11 of R is oxidized, as shown in FIG.
An oxide layer 14 in which (Ga) As is oxidized is formed, and an Al (Ga) As layer 15 which is not oxidized in the center of the mesa remains in the center of the mesa structure 4.

Looking at the structure thus formed, FIG.
In the section including the post structure as shown in (section in FIG. 1A), a surface emitting laser having a resonator structure including an upper DBR 9 and a lower DBR 6 is formed at the upper and lower ends.

Further, as shown in FIG. 3 (cross section in FIG. 1B), in the cross section not including the post structure, since the number of layers of the upper DBR is small and a resonator having sufficient reflectance is not formed, No light emitting laser is formed.

2 and 3, in the mesa structure 4, the ends of the upper DBR 9 and the lower DBR 6 are oxidized, and the oxide layer 14 in which Al (Ga) As is oxidized has a refractive index. Is 1.7 and unoxidized Al (G
a) The refractive index of the As layer 15 is 3.0 and that of GaAs is 3.0.
6, the refractive index is relatively high at the center of the mesa structure. That is, it has a waveguide structure, and light in the mesa stripe direction is confined at the center.

FIG. 4 is a sectional view taken along the line C in FIG. As shown in the figure, under the post structure 5, a surface emitting laser is formed, and at the same time, a waveguide structure is formed on the left and right sides of the paper. As shown in FIG. 4, on both sides of the post structure 5, ion-implanted regions 21 in which protons are ion-implanted are formed.
Is particularly preferable because the surface emitting laser section and the waveguide section are electrically insulated.

In the structure described above, since the planar shape of the post structure is a small rectangular shape, a single transverse mode oscillation and linearly polarized light can be obtained in the surface emitting laser. That is, as described in Japanese Patent Application Laid-Open No. 8-181391, the planar shape (cross-section in a plane parallel to the substrate) of the post structure of the DBR is reduced to, for example, a size of 6.5 × 6.5 μm or less. When the rectangular shape is used, the horizontal mode also becomes the single mode. Furthermore, as described in the present embodiment, when one side is a rectangle shorter than the other side, the polarization direction is a direction along the longer side of the rectangle. In actually applying the optical functional device of the present embodiment, it is desirable to appropriately adjust the polarization direction according to the desired function so as to obtain the best result.

The interaction between the light of the surface emitting laser and the light propagating in the lateral waveguide takes place in the very small volume active layer directly below the post structure. Therefore, in the conventional method, the interaction is small, and it is difficult to obtain a sufficient light-light injection effect from the waveguide. However, in the present invention, since the oscillation of the surface emitting laser is linearly polarized light of a single transverse mode as in this embodiment, the light injected from the waveguide is not dispersed into many modes, and the efficiency is improved. Good interaction is obtained.

When the optical functional device of the present embodiment is used, light can be injected into the surface emitting laser from a waveguide portion horizontal to the substrate, so that it can be performed by a simple system such as coupling with an ordinary fiber.

In the above description, the upper and lower DBRs are represented by A
Although an alternately laminated structure of an Al (Ga) As layer and a GaAs layer having a large l composition ratio was used, an alternately laminated structure of an AlAs layer and a GaAs layer, or Al (Ga) A having a large Al composition ratio was used.
An alternate layered structure of an s layer and an AlGaAs layer having a smaller Al composition ratio than the s layer may be used. In any case, the layer having a large Al composition ratio is easily oxidized.

In the surface emitting laser portion obtained by the post structure, the electrode portion has been omitted from the above description, but an electrode structure capable of injecting current from outside the upper DBR and the lower DBR is provided. A mode in which laser oscillation or modulation by current injection is combined with oscillation or modulation by light injection from a waveguide, or oscillation or modulation of a surface emitting laser only by light injection from a waveguide without forming an electrode structure. Any of the configurations in which the above is performed is possible.

[Second Embodiment] In the structure of the first embodiment, when an electrode is provided outside the upper DBR and the lower DBR of the waveguide portion and both ends are cleaved, an optical functional device to which an edge emitting type semiconductor laser is further added. Can be formed. In this structure, the optical axes of the surface emitting laser and the edge emitting laser intersect. Surface emitting laser structure,
Since the waveguide structure of the edge emitting laser is the same as that of the first embodiment, the light of the edge emitting laser and the light of the edge emitting laser efficiently interact, and the edge emitting laser efficiently oscillates or modulates the surface emitting laser. Can be.

In this case, as described in the first embodiment, since the surface emitting laser and the edge emitting laser are electrically separated from each other, an electric modulation signal applied to one element affects the other. Nothing.

[Embodiment 3] The structure of this embodiment is shown in FIG.
Shown in That is, the groove 16 is provided to separate the surface emitting laser from the lateral waveguide. By cleaving the end, an edge emitting laser oscillating by a resonator formed by the cleavage plane 17 and the side surface of the groove is formed. The groove can be formed, for example, by etching using a normal photoresist. By providing the groove, the electrical separation between the surface emitting laser and the edge emitting laser can be performed more completely. Portions other than the groove can be configured in the same manner as in the first or second embodiment.

Also, a resonator structure can be formed by forming a Bragg dispersive mirror (DBR) using a grating instead of a groove.

[Embodiment 4] In this embodiment, a structure similar to that of the optical functional element shown in Embodiment 1 is manufactured. However, the long side of the 6 × 4 μm post structure is parallel to C in FIG. 1 so that the linearly polarized light emitted from the surface emitting laser is in the direction parallel to C in FIG. 1 (waveguide direction). Form.
Electrodes are provided above and below the surface emitting laser to oscillate by current injection.

When the surface emitting laser is emitting light, light that is stronger than the light emitted from the surface emitting laser is injected in the direction C from the waveguide. The polarization direction of the injected light propagating through the waveguide is A
, And perpendicular to the polarization of the surface emitting laser unit.
Since the carrier that has contributed to the oscillation of the surface emitting laser is consumed by the stimulated emission due to the injected light, the polarized light parallel to the direction A becomes dominant. The diffraction loss increases, and the oscillation of the surface emitting laser stops.

When the injection of light from the waveguide portion is stopped, the surface emitting laser emits polarized light parallel to C as before.

As described above, in this embodiment, it is possible to realize a light-light switch or a light modulation element that controls the emitted light of the surface emitting laser with the light from the waveguide structure. As described in the first embodiment, in the optical device of the present invention, the interaction between the light of the surface emitting laser and the light in the lateral direction from the waveguide structure is large, and switching or modulation can be performed efficiently. .

In this embodiment, the second embodiment
As shown in the above, the lateral waveguide may be an edge-emitting semiconductor laser, and similarly, may have a resonator structure as shown in the third embodiment.

Embodiment 5 As shown in FIG. 6, an optical functional device is manufactured in the same manner as in Embodiment 4, except that two post structures 5 are provided. That is, two surface emitting lasers are coupled to the waveguide. As described in the fourth embodiment, when light is injected from the lateral waveguide while the surface emitting laser is oscillated in advance, the oscillation of the two surface emitting lasers is stopped, and the light injection from the lateral waveguide is stopped. Then, the oscillation of the two surface emitting lasers resumes.

Here, for example, H,
When an optical signal digitally modulated as H, H, L is given,
Optical signals L, L, L, and H can be obtained from the surface emitting laser. When the pitch L between the two surface emitting lasers is sufficiently short with respect to the modulation speed, specifically, 1
When modulating at Gbps (one cycle 1 ns), one cycle 1
If the adjacent surface emitting laser emits the same signal within 10 ps of / 100, it can be used as a fan-out. When the pitch is roughly estimated from this (the traveling speed of light at a refractive index of 1 is about 0.2 m / ns, so if the refractive index in the waveguide is 3, 0.07 m / ns), if it is 700 μm or less, it is used as a fan-out. it can.

In this embodiment, the form in which two surface emitting lasers are provided on the same lateral waveguide is shown. However, by setting the number to N, the function of 1: N fan-out (multiple output) can be achieved. Realize. That is, according to the present embodiment, it is possible to easily obtain an optical functional element as an optical signal distributor.

[Embodiment 6] In Embodiment 5, an optical functional element as a delay element which can add an arbitrary delay if the pitches of a plurality of surface emitting lasers provided on the same lateral waveguide are separated and properly adjusted. Obtainable.

[Seventh Embodiment] In the fifth embodiment, if N outputs are N parallel outputs, an optical functional element as an optical serial-parallel converter can be realized.
In this case, the pitch of the surface emitting lasers is set so that the delay time between the surface emitting lasers matches the modulation speed of the input signal. When 1 Gbps modulation is performed on an element having a surface emitting laser pitch of 700 μm, serial light from the waveguide can be converted into N parallel outputs. However, since the reading timing on the parallel side is only once for the serial N clock, it is necessary to pay close attention to the timing.

Embodiment 8 An optical functional device is manufactured in the same manner as in Example 1, except that the post structure is changed to 6 × 6 μm. When the post structure is such that the two sides are equal, polarization bistability appears. That is, it can be driven with a current such that the polarization in the C direction is stable when increasing the current, and the polarization in the A direction is stable when decreasing the current. As shown in FIG. 7, when the injection current is increased, 3-6
Polarization bistability is observed at mA (the current at which polarization bistability appears varies slightly depending on the element).

Using this property, an optical functional device as an optical gate can be formed. On the surface emitting laser output side,
A polarizer that allows only polarized light in the C direction is installed. That is, when the drive current is 6 mA or more, the gate is open so that the signal from the waveguide is directly transmitted to the light emitted from the surface emitting laser. On the other hand, if the driving current is set to 3-6 mA, for example, 5 mA, the polarization does not change once in the A direction due to light injection from the waveguide direction.
e.

Ninth Embodiment In the eighth embodiment, an optical functional device as a 1 × N gate switch can be realized by coupling N surface emitting lasers to the same lateral waveguide.

[Embodiment 10] In the interaction due to light injection, there is a difference between the oscillation wavelength on the injection side and the wavelength on the input side, and an optimum value for detuning. Therefore, a plurality of surface emitting lasers are coupled to the same lateral waveguide, and the respective oscillation wavelengths are shifted by, for example, 5 nm. The oscillation wavelength can be adjusted by changing the thickness of the intermediate layer. As shown in FIG. 8, when a multi-wavelength light 20 is input from a lateral waveguide to an element having many such surface emitting lasers having different oscillation wavelengths, the light-light Since the interaction occurs, wavelength demultiplexing can be performed.

As described above, in the present embodiment, an optical functional device as a wavelength demultiplexer can be realized.

[Embodiment 11] In one surface emitting laser,
Multiple transverse waveguides can be combined. FIG.
(Plan view) is an example in which two waveguides are coupled to one surface emitting laser. The waveguide 18 in the vertical direction on the paper and the waveguide 19 in the horizontal direction on the paper are formed on the same plane of the substrate, and the surface emitting laser is formed by two lights, the light injected from the waveguide 18 and the light injected from the waveguide 19. Can be modulated, so that an optical function element that performs a higher function can be realized.

The structure of this embodiment may be formed such that the mesa shape in the first embodiment becomes a cross shape.

In this embodiment, the lateral waveguide may be an edge-emitting semiconductor laser as shown in the second embodiment, and a resonator structure as shown in the third embodiment may be used.

[0053]

According to the present invention, it is possible to provide an optical functional device capable of obtaining efficient interaction between laser light of a surface emitting laser and light in a lateral optical waveguide.

Further, according to the present invention, the electrical separation between the surface emitting laser and the lateral optical waveguide is ensured, so that the electrical modulation of one element does not affect the other element and the noise is reduced. It is possible to provide an optical functional element having a small number.

Further, according to the present invention, it is possible to provide an optical function element having various functions which have not been known hitherto.

[Brief description of the drawings]

FIG. 1 is a perspective view showing one example of an optical functional device of the present invention.

FIG. 2 is a view showing a cross section A of FIG. 1;

FIG. 3 is a view showing a cross section B of FIG. 1;

FIG. 4 is a view showing a cross section C of FIG. 1;

FIG. 5 is a cross-sectional view of one example of the optical functional device of the present invention.

FIG. 6 is a perspective view of an example of the optical functional device of the present invention.

FIG. 7 is a view for explaining polarization bistability in one example of the optical functional device of the present invention.

FIG. 8 is a diagram for explaining how input light of multiple wavelengths is demultiplexed in one example of the optical functional device of the present invention.

FIG. 9 is a plan view showing an example of the optical functional device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical functional element 3 Lateral waveguide 5 Post structure 6 Lower DBR mirror 8 Intermediate layer 9 Upper DBR mirror 10 GaAs substrate 11 Al (Ga) As layer with a large Al composition ratio 12 GaAs layer 14 Al (Ga) As is oxidized Oxidized layer 15 Al (Ga) As layer not oxidized 16 Groove 17 Cleaved surface 18 Waveguide in vertical direction on paper 19 Waveguide in horizontal direction on paper 20 Multiwave light 21 Ion implantation region

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-7-64139 (JP, A) JP-A-6-29625 (JP, A) JP-A-7-249824 (JP, A) JP-A-60-1985 256124 (JP, A) JP-A-8-116130 (JP, A) Applied Physics Vol. 66, No. 2 (1997) 117-122

Claims (12)

(57) [Claims] 1. A planar shape is rectangular on the same semiconductor substrate.
With a single transverse mode linear polarization ,
A surface emitting laser that emits light in the direction perpendicular to the substrate , the polarization direction of which is parallel to the long side of the rectangle;
Parallel to, and perpendicular to the polarization direction of the surface emitting laser
Light is guided horizontally to the substrate, and the optical axis crosses the surface emitting laser.
And a waveguide for the difference, the surface emitting laser that oscillates is the from the waveguide
An optical functional device controlled by light injected into a surface emitting laser . 2. The optical function element has a plurality of surface emitting lasers, and the optical axes of the plurality of surface emitting lasers intersect with the optical axis of one waveguide. 2. The optical functional device according to 1. 3. The semiconductor device according to claim 1, wherein the optical function element is provided on a semiconductor substrate.
One set of upper and lower layers consisting of a body periodic filmDistributed reflection mirror
And an intermediate layer including an active layer sandwiched between the pair of resonators.
The side wall is perpendicular or perpendicular to the substrate
Post structure with a rectangular shape when viewed at an angle close to right
The surface emitting laser is configured in the post structure.
The side surface of one layer of the multilayer film constituting the distributed reflection type mirror is
Oxidation reduces the refractive index
The road is constituted, The claim 1 characterized by the above-mentioned.2No
An optical functional device according to any of the preceding claims. 4. The optical function element further includes an edge-emitting laser on the same substrate, and the waveguide is a part of a resonator of the edge-emitting laser. 4. The optical functional element according to any one of 1 to 3 . 5. The optical functional device according to any one of claims 1 to 4, characterized in that the waveguide and the surface emitting laser is electrically isolated. 6. The optical functional device according to claim 5, wherein the surface emitting laser and the waveguide are electrically separated by an ion implantation region or a groove. 7. The plurality of surface emitting lasers are provided at a predetermined distance from each other along the waveguide, and the plurality of surface emitting lasers are identical to each other by an incident light signal from the waveguide. The optical functional device according to claim 1, which functions as a distributor that emits the signal of (1). 8. The plurality of surface emitting lasers are provided at a predetermined distance along the waveguide, and the plurality of surface emitting lasers are guided by an incident optical signal from the waveguide. 2. The optical functional device according to claim 1 , wherein the optical functional device functions as a delay device that emits a signal that is delayed as the light travels in the wave path in a traveling direction. 9. The plurality of surface emitting lasers are provided along the waveguide at a distance corresponding to a serial signal based on incident light from the waveguide, and the serial signal is transmitted to the plurality of surface emitting lasers. serial to the emission from the surface emitting laser as a parallel signal - parallel signal optical functional device according to claim 1, wherein the function as converting element. 10. A post structure having a post structure on the same semiconductor substrate.
Light that has two sides equal and becomes single transverse mode linearly polarized light is perpendicular to the substrate.
Surface emitting laser that emits in the vertical direction and post structure with polarization direction
The light of one side parallel to the polarization direction horizontally guided to the substrate, prior to
The surface emitting laser has a waveguide whose optical axis intersects , and the surface emitting laser shows polarization bistability by an injected current, and changes a polarization direction of the linearly polarized light by changing an injection current to the surface emitting laser. optical functional device functions as a gate switch for the input signal from the waveguide by changing. Wherein said plurality of oscillation wavelength of the surface emitting laser is set to be different from each other, an optical functional device according to claim 1, wherein the function as a demultiplexer for demultiplexing the wavelength of incident light from the waveguide. 12. One of the multilayer films constituting the distributed reflection type mirror is made of AlGaAs or A having a high Al composition ratio.
The optical functional device according to claim 3 , wherein the optical functional device is 1As.