RU2423764C1 - Resonator on modes of whispering gallery with vertical radiation output - Google Patents

Abstract

FIELD: electricity. ^ SUBSTANCE: resonator has circular section and is made in the form of a revolution solid. The revolution solid comprises an active area, facing layers and a part of a substrate. A generatrix of the side surface of the revolution solid is inclined relative to the normal line of a heterostructures. ^ EFFECT: possibility to output radiation, which is wideband by wave length, in vertical direction. ^ 2 dwg

Description

The invention relates to resonators of semiconductor lasers with a beam emitting surface based on heterostructures.

The creation of vertically emitting lasers with good quality of the output beam, created on one semiconductor wafer (substrate) in one technological process, is one of the most urgent tasks of semiconductor optoelectronics. Currently, vertically emitting lasers based on Bragg mirrors (the so-called VCSEL lasers - vertical cavity surface emitting laser) are used for these purposes [1]. In such lasers, instead of waveguide layers on both sides of the active region (as in standard heterolasers), Bragg mirrors are grown that hold the vertically propagating mode within the active region [1]. This mode partially exits through the upper contact, creating laser radiation with a fairly wide (Gaussian) beam. Unfortunately, firstly, the manufacture of Bragg mirrors is a rather delicate (expensive) procedure. Secondly, the current in such lasers flows through these mirrors, which degrades the injection of carriers and reduces the efficiency. This is especially important for long-wavelength interband and intraband cascade lasers (and even more so for terahertz cascade lasers), for which an approach based on such Bragg mirrors is not applied at all. Thirdly, with increasing laser area in the plane of the semiconductor wafer, higher modes appear that degrade the quality of the output beam.

An approach based on the use of circular resonators on whispering gallery modes is possible to create a multiple laser system on a single semiconductor wafer. Such a circular resonator has the form of a cylinder, the base of which is a circle. The manufacture of these resonators is very simple and cheap compared to VCSEL lasers. However, in circular resonators on whispering gallery modes, the laser field is concentrated inside the resonator and does not go outside. There are known designs of a semiconductor laser with a resonator based on modes of a whispering gallery of a non-circular shape (in the form of a cylinder whose base is non-circular). The use of such a resonator makes it possible to control the type of radiation pattern in the plane of the laser structure. In this case, the radiation output turns out to be horizontal — in the plane of the heterostructure (see US patent 6333944, H01S 3/081, 3/083, publ. December 25, 2001). The horizontal output of laser radiation does not make it possible to combine radiation from a combination of such lasers made on one substrate into one output beam.

In the quantum cascade laser described in US 6836499, H01S 5/00, 5/10, 5/34, publ. 12/28/2004, the output of radiation also occurs in the horizontal plane, while this design allows you to control the radiation pattern using a special horn located in the horizontal plane. This analogue has the same drawback as the previous one.

The closest analogue to the present invention is the design of the resonator on whispering gallery modes, providing vertical output of laser radiation (US 5343490, H01S 5/00, 5/10, 5/18, publ. 09/30/1994, "Whispering Mode Micro-Resonator" ( "Whispering microcavity")). This patent describes a device that is a circular resonator in which, due to reflection from the outer surface of the semiconductor cylinder, electromagnetic modes such as a whispering gallery arise. This device can operate in modes below the threshold (that is, as an LED), and above the threshold (like a laser). In this case, the output of electromagnetic radiation is carried out mainly in the plane of a circular resonator made of a semiconductor structure. To carry out a vertical output of radiation perpendicular to the plane of the structure or at some angle, risks or recesses are applied to the upper surface of the resonator (by chemical etching or by mechanical means), arranged periodically so that the distance between them is approximately equal to the generation wavelength in this sample. Thus, this radiation output device is selective (narrow-band) at a wavelength, since it provides efficient emission of only those waves whose wavelength in the sample coincides with the distance between the applied risks. In this patent it is reported that in this resonator a vertical narrow-band radiation output can also be carried out using gratings deposited on the lower or upper surface.

The disadvantage of the prototype resonator is that it provides the output of a narrowband signal - electromagnetic waves - with a predetermined wavelength. There are many articles and patents describing such selective devices for outputting radiation from resonators in whispering gallery modes.

The problem solved by this invention is the development of a resonator laser whispering gallery modes, providing output broadband wavelength radiation in the vertical direction.

The specified technical result is ensured by the fact that the developed resonator, like the prototype resonator of a semiconductor heterolaser based on whispering gallery modes with vertical output, has a circle shape in any horizontal section, i.e. made with a circular cross section.

New in the developed resonator is that the resonator is made in the form of a body of revolution, which includes an active region, cover layers and a part of the substrate, while the generatrix of the side surface of the body of revolution has an inclination with respect to the normal of the heterostructure.

The main difference from the prototype of the device proposed by the authors — a resonator based on whispering gallery modes with a special shape of the resonator generatrix — consists in the fact that the proposed device does not have any patterns or structures applied to the resonator boundaries, and therefore there are no distinguished wavelength scales. As a result, the design of the resonator with a vertical output of radiation proposed by the authors is broadband in the radiation wavelength: any whispering gallery mode at any radiation frequency will effectively radiate upward (or downward to the substrate, depending on the inclination of the side generatrix of the resonator). An additional advantage in this case is the absence of the need to manufacture a periodic modulating structure, which can be a very difficult (expensive) business for short-wave lasers.

The invention is represented by the following drawings:

figure 1 shows a diagram of a laser with a resonator on the whispering gallery modes with a vertical output of radiation into the substrate due to the inclined shape of the cavity wall in the form of a body of revolution;

figure 2 shows photographs of a fabricated semiconductor laser based on a heterostructure with the output of radiation in the vertical plane, carried out due to the inclined side surface of the laser (on the left is a photograph of a section of the laser, on the right is its top view).

Figure 1 schematically shows an example of the shape of the generatrix of the proposed resonator from a semiconductor heterostructure. The resonator, made in the form of a body of revolution, is formed by the lateral surfaces of the core 1, cover layers 2 and part of the substrate 3 of the heterostructure. The inclination of the generatrix 4 of the body of revolution with respect to the normal 5 of the heterostructure provides the output of radiation from this resonator into the substrate 3 of the structure. In the general case, the cross section of such a resonator with a vertical plane has the shape of a section of a body of revolution, in particular, for example, a paraboloid, cone or sphere, and can also have a more complex shape. The presence on the side surface of the laser of sections inclined with respect to the normal 5 of the heterostructure will lead to the fact that the wave of laser radiation when reflected from the side surface will gradually flow in the vertical direction (see figure 1). The use of various shapes of the cross sections of the resonator leads to a different spatial intensity distribution in the output laser beam. Since the proposed design does not have any selective elements, it is broadband in the radiation wavelength and, thus, allows us to solve the problem.

The resonator of the proposed form with an inclined lateral surface can be made, for example, by chemical etching of semiconductor heterostructures.

Figure 2 shows microphotographs of semiconductor injection heterolasers made by the authors based on InAsSb / InAsSbP heterostructures with radiation output in the vertical direction due to the inclined side surface of the resonator in the form of a body of revolution: on the left is a laser chip (side view); on the right is a view of a laser diode (top view). The authors also fabricated similar resonators in whispering gallery modes with non-selective vertical radiation output due to the oblique generatrix for optical-pumped heterolasers based on CdHgTe heterostructures. These are the simplest examples of non-selective vertical output of radiation from resonators of semiconductor heterolasers based on whispering gallery modes. The generator of the resonator can be modulated along the slope, it (the generator) can be multi-element-step, for example, to obtain a narrower radiation pattern of the output laser beam, etc.

Thus, the authors have demonstrated whispering gallery mode lasers with a vertical radiation output system (Fig. 2). The obtained effect of the vertical output of laser radiation lies in the fact that in the vertical direction (perpendicular to the plane of the heterostructure) the intensity of the output radiation was several times greater than in other directions.

The developed resonator can be used to create on one semiconductor wafer in one technological cycle a multiple laser system with good quality of the beam emerging in the vertical direction.

1. Iga, Kenichi (2000), "Surface-emitting laser - Its birth and generation of new optoelectronics field", IEEE Journal of Selected Topics in Quantum Electronics 6 (6): 1201-1215; Soda et al., Haruhisa (1979), "GaInAsP / InP Surface Emitting Injection Lasers", Japanese Journal of Applied Physics 18 (12): 2329-2330; Koyama et al., Fumio (1988), "Room temperature cw operation of GaAs vertical cavity surface emitting laser", Trans. IEICE, E71 (11): 1089-1090.

Claims (1)

A semiconductor heterolaser resonator based on a whispering gallery mode with a circular cross section and a vertical radiation output, characterized in that the resonator is made in the form of a body of revolution, which includes an active region, cladding layers and a part of the substrate, while forming a side surface of the body of revolution has an inclination with respect to to the normal of the heterostructure.

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