JP2015115367A - Surface emission laser array - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-output surface emission laser array having in-phase phase synchronization.SOLUTION: A circulation laser 30 includes: a plurality of surface emission lasers 10; and optical waveguides 20, each optically connected to each of the surface emission lasers 10 for circulating an optical signal emitted from each of the surface emission lasers 10. Each of the surface emission lasers 10 is formed at positions of antinodes of an optical standing wave generated in a resonator composed of the surface emission lasers 10 and the optical waveguides 20.

Description

  The present invention relates to a surface emitting laser array having a structure in which light is emitted perpendicular to a semiconductor substrate.

  A vertical cavity surface emitting laser (VCSEL) is a device having excellent characteristics in terms of low power consumption and high-speed transmission. This device is applied to, for example, a mouse for a personal computer or a light source for Ethernet (registered trademark) short-range communication.

  In VCSEL, the laser resonator length is about two orders of magnitude shorter than that of a conventional waveguide type, so that the lifetime of photons is short, which is advantageous for high-speed modulation operation. However, since the VCSEL is a short resonator and the optical gain length is extremely shortened, it is necessary to make the reflectance of the exit surface extremely high for laser oscillation, and as a result, it is difficult to obtain a high output. There is a problem. In general, in order to obtain a high output, the emission area of the VCSEL is often increased.

  On the other hand, when a VCSEL is used as a light source for long-distance light transmission, it is necessary to set a single transverse mode in addition to obtaining high output. In this case, even if the element size of the VCSEL is increased, the near-field image of the VCSEL emission shape becomes a multimode, and the propagation constant changes corresponding to the mode. For this reason, the longitudinal mode becomes a multi-mode, and long-distance high-speed optical transmission cannot be realized. Therefore, if the VCSEL element size is reduced in order to achieve the single transverse mode, the light output is reduced due to the reduced emission diameter, and as a result, the VCSEL is not suitable for long-distance optical communication. .

  From the above viewpoint, a phase-locked laser in which VCSEL elements for realizing a single transverse mode are arrayed and the phases between the elements are synchronized is known (Non-Patent Document 1). In this laser, the phases of the elements are phase-locked by optical coupling between the VCSEL elements. When the phase between all the elements is locked in-phase, the outgoing beam of the far-field image has a single peak, and the light output increases with the number of elements. As a result, when viewed as a whole array element, single element laser oscillation is realized by one element, and high output can be obtained without losing coherence. Furthermore, since the emitted light in this case becomes interference light, the far-field image has a full width at half maximum of several degrees or less, and almost 100% of the emitted light can propagate to the optical fiber. However, even if the optical coupling is simply performed between the VCSEL elements, the neighboring elements are locked by being anti-phase, and high output can be obtained, but the shape of the output beam is multimodal. It is not suitable for optical transmission.

  In addition, in order to realize an in-phase far-field image, a conventional GaAs-based VCSEL is configured such that a pair of semiconductor DBRs (Distributed Bragg Reflectors) on the emission surface is removed or a photonic crystal is used. (Non-Patent Document 2).

D. Zhou and L. J. Mawst, Semiconductor laser Conf. 2000, pp61-62 D.F.Siriani et al., IEE Electronics lettersVo.46 No.10, 2010 pp.712-714

  However, the conventional VCSEL has a problem that a high output cannot be obtained by removing DBR, and that it is not easy to produce a photonic crystal that requires precise processing accuracy. Further, in the case of a VCSEL for long-distance transmission, an InP-based material that is a light emitting material having a long wavelength of, for example, 1.3 to 1.55 μm is often used so that transmission loss of the optical fiber is minimized. .

  The present invention has been made under the above circumstances, and an object thereof is to provide a high-power surface emitting laser array having in-phase phase synchronization.

  The present invention for solving the above-described problems includes a plurality of surface-emitting lasers and an optical device that is optically connected to each of the plurality of surface-emitting lasers and circulates an optical signal emitted from each surface-emitting laser. Each of the surface emitting lasers includes a waveguide, and is formed at an antinode of an optical regular wave generated in a resonator including each of the surface emitting lasers and the optical waveguide.

  Here, each of the surface emitting lasers may be arranged on a concentric circle so that the optical signal circulates.

  According to the present invention, it is possible to oscillate high-power light having in-phase phase synchronization.

It is a figure which shows an example of the cross-section of the surface emitting laser in 1st Embodiment. It is a figure which shows an example of the plane structure of the circumference | surroundings laser containing several surface emitting laser. It is a figure which shows the relationship between the electric current of a circumference laser, and optical output. It is a figure which shows an example of the far-field image which is a radiation pattern of the optical output of a circumference laser.

  Hereinafter, the configuration of the surface emitting laser array (circular laser) of the present invention will be described.

[Configuration of surface emitting laser]
First, the structure of the surface emitting laser 10 included in the circular laser of this embodiment will be described with reference to FIG. FIG. 1 is a diagram illustrating an example of a cross-sectional structure of a surface emitting laser 10 according to the present embodiment.

  The surface emitting laser 10 is configured to realize, for example, a long wavelength laser beam in the 1.3 μm band by excitation light incident from the side surface of the active layer. As shown in FIG. 1, the surface emitting laser 10 includes an InP substrate 1 on which a first reflective layer 2, spacer layers 4 a and 4 b including an active layer 3, and a second reflective layer. 5 are sequentially stacked. This stacked layer is formed, for example, by MOCVD (organic metal vapor phase method).

  In FIG. 1, the p-type electrode 7 is provided on the second reflective layer 5. The n-type electrode 8 is provided on the substrate 1, and a SiO layer 9 is further formed on the substrate 1.

  The first reflective layer 2 is composed of n-type InAlGaAs (λg = 1.2 μm) and InP, which are alternately stacked with a film thickness corresponding to λ / 4 with respect to an oscillation wavelength of λ = 1.3 μm. It is grown as a repeated multilayer layer paired with a layer (for example, 56 pair growth).

  The active layer 3 includes a quantum well structure made of InAlGaAs having compressive strain.

  The first spacer layer 4a is composed of an n-type InP layer. The second spacer layer 4b is composed of a p-type InP layer. In the present embodiment, the laser cavity length constituted by the active layer 3 and the spacer layers 4a and 4b is set to a thickness of 3 / (2λ).

  The second reflective layer 5 includes a p-type InAlGaAs layer and an n-type InGaAs layer on the tunnel junction. These p-type and n-type layers are grown highly doped.

[Configuration of circular laser]
Next, the configuration of the circumferential laser 30 including a plurality of the surface emitting lasers 10 described above will be described with reference to FIG.

  FIG. 2 is a diagram illustrating an example of a planar configuration of the circulating laser 30 including the plurality of surface emitting lasers 10.

  As shown in FIG. 2, the circular laser 30 includes ten surface emitting lasers 10 and an optical waveguide 20 optically connected to each surface emitting laser 10.

  The optical waveguide 20 has a donut-shaped (circular) circumferential portion. The optical waveguide 20 includes a first reflective layer 2 as an upper clad, an active layer 3 as a core, and a second reflective layer 5 as a lower clad. In addition, as the optical waveguide 20, configurations such as a slab structure and a ridge structure can be applied.

  Each of the surface emitting lasers 10 is arranged on a concentric circle so that an optical signal circulates. Each surface emitting laser 10 according to the present embodiment is disposed at a portion corresponding to the antinode position of the standing wave of light generated in the circulating laser 30 (resonator). Thereby, in the circulating laser 30, the signal light circulates in the resonator.

  Next, a method for manufacturing the circular laser 30 according to the present embodiment will be described with reference to FIGS. 1 and 2 again.

  In the circular laser 30, the second reflective layer 5 of the surface emitting laser 10, that is, the tunnel junction is patterned by a photolithography technique. In this case, the diameter of the element portion of the surface emitting laser 10 is 6 μm, the intermediate optical gain region of the element is a circle of 1 μm, and the element interval between adjacent surface emitting lasers 10 is 6 μm (distance between each circular edge of the surface emitting laser 10). And Parts other than the above are removed by etching, and 10 surface emitting lasers 10 are arranged on concentric circles.

  Next, crystal growth is performed again, and the entire device is covered with an InP layer. Finally, metamorphic GaAs / Al0.98Ga0.02As layers with different refractive indexes, which are alternately stacked with a thickness corresponding to 1 / 4λ for an optical wavelength of λ = 1.3 μm, are epitaxially grown sequentially. .

In the device forming process, a circular mask having a diameter of 100 μm is formed on the upper surface of the substrate 1. Thereafter, the metamorphic DBR layer is etched by RIE (Reactive Ion Etching) using SiCl ₄ gas. Then, a circular mesa of the surface emitting laser 10 itself and a concentric optical waveguide 20 are formed.

An AuGeNi electrode 8 is vapor-deposited on the upper surface of the element so as not to hit the oscillation beam vertically, and the electrode is removed in a circular shape in order to extract emitted light from the lower surface of the element. In order to prevent the laser-oscillated light from returning to the active layer 3, an SiO ₂ film 9 was formed as an antireflection film.

  In the circular laser 30 of this embodiment, a part or all of the current injected into the surface emitting laser 10 is injected into the optical waveguide 20. In addition, the active layer 3 that is a gain region is provided in the optical waveguide 20. As a result, the optical waveguide 20 becomes a gain waveguide type circular waveguide, and the nodes and antinodes of the standing wave generated in the resonator of the circulating laser 30 are fixed.

  Next, the optical characteristics of the circulating laser 30 will be described with reference to FIG. FIG. 3 is a diagram illustrating an example of the relationship between current and light output.

  In FIG. 3, the circular laser 30 was measured from the surface of the substrate 1 with the metamorphic layer having good thermal conductivity as the bottom surface.

  For example, in the case of 20 ° C., the threshold is 30 mA, and the maximum current of the entire device of the circulating laser 30 is 100 mA. At this time, the optical output was 40 mW. As shown in FIG. 3, the laser oscillation could be confirmed up to 60 ° C.

  Here, in the measurement of FIG. 3, when the oscillation spectrum of the circulating laser 10 was observed, it was observed that the oscillation wavelengths were integrated when the phase was locked. That is, it was confirmed that the phases of the surface emitting lasers 10 were synchronized.

  FIG. 4 is a diagram illustrating an example of a far-field image in the light emission direction of the circular laser 30. In FIG. 4, the horizontal axis represents current, and the vertical axis represents relative ratio.

  In the conventional case, four multimodality was observed in the far-field image when the adjacent elements are in reverse phase (relative ratio = about 1.0), but in this embodiment, the farfield image has unimodality. (Relative ratio = about 13). From this, it can be seen that the phases of the adjacent surface emitting lasers 10 are locked in opposite phases. That is, the effect of the optical gain layer provided between the surface emitting lasers 10 was confirmed.

  As described above, according to the circular laser 30 of the present embodiment, each surface emitting laser 10 is formed at the antinode of the optical regular wave generated in the resonator composed of each surface emitting laser 10 and the optical waveguide 20. The Thereby, a high output having in-phase phase synchronization can be realized.

  As mentioned above, although each embodiment was explained in full detail, you may make it change the material of a component, etc. FIG. For example, AlGaAs or the like may be applied as a constituent material.

  The number of the surface emitting lasers 10 may be changed to a number other than ten as long as the surface emitting lasers 10 are formed at the antinodes of the standing wave generated in the resonator. Further, the surface emitting laser 10 may be provided in the vicinity of the antinode of the standing wave generated in the resonator.

  The surface emitting laser 10 can also oscillate wavelengths other than the 1.3 μm band.

DESCRIPTION OF SYMBOLS 1 InP board | substrate 2 1st reflective mirror 3 Active layer 4a 1st spacer layer 4b 2nd spacer layer 5 2nd reflective mirror 10 Surface emitting laser 20 Optical waveguide 30 Circular laser

Claims (2)

A plurality of surface emitting lasers;
An optical waveguide optically connected to each of the plurality of surface emitting lasers for circulating an optical signal emitted from each surface emitting laser,
The surface-emitting laser array, wherein each surface-emitting laser is formed at an antinode of an optical regular wave generated in a resonator including each surface-emitting laser and the optical waveguide.   2. The surface emitting laser array according to claim 1, wherein each of the surface emitting lasers is arranged on a concentric circle so that the optical signal circulates.

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