CN101567520A - Hollow beam pumping emission semiconductor laser of vertical external chamber surface - Google Patents

Abstract

The invention provides a hollow beam pumped vertical external cavity surface-emitting semiconductor laser, which includes a semiconductor laser (1), a transmission fiber (2), a collimator lens (3), a Cassegrain telescopic system (4), a coupling lens ( 5), a beam splitting prism (6), an external cavity surface emitting epitaxial wafer (7), a copper heat sink (8) and an output mirror (9). The hollow beam is used as the pumping light, and the pumping area is separated from the center of the lasing area to reduce the laser area of the external cavity surface emitting epitaxial wafer by taking advantage of its characteristics of adjustable dark spot size, no heating effect and propagation invariance. Thermal effect and micro-strain, improve light-to-light conversion efficiency and output power, improve output beam quality and output spectrum stability. When the pumping power is 2W, the conversion efficiency is 11% higher than that of the common Gaussian beam as the pump source, and the output is a circularly symmetric near-diffraction-limited beam with a beam quality M ² ≈1. It can be used in criminal investigation, optical information storage, image display, medical instrument and underwater detection.

Description

Hollow beam pumped vertical external cavity surface emitting semiconductor laser

technical field

The patent of the present invention relates to a hollow beam pumped vertical external cavity surface emitting semiconductor laser.

Background technique

Optically pumped vertical cavity surface emitting semiconductor lasers have outstanding advantages such as good spatial light intensity distribution, large output power range, small size, and good beam quality, which make optically pumped vertical external cavity surface emitting semiconductor lasers have a wide range of applications. Optically pumped vertical external cavity surface emitting semiconductor lasers combine the construction methods of semiconductor pumped solid-state lasers and vertical external cavity surface emitting semiconductor lasers, absorbing the advantages of both, can output high-quality fundamental mode Gaussian beams of surface emitting lasers, and High power comparable to edge-emitting lasers can be obtained. The chip has a simple structure, no PN junction, no electrical contact, which greatly simplifies the growth process and improves reliability; there is no current injection, which eliminates the corresponding thermal effect on the additional resistance; the chip is grown with non-doped semiconductor materials, reducing The optical loss caused by free carrier absorption is eliminated, the outstanding advantages such as low damage to the pumping element, high reliability and large output power range make the output power stability higher; from the optical pump laser From the perspective of resonator design, it is similar to semiconductor-pumped solid-state thin-film lasers, which reduces the thermal effect, but the wavelength can be flexibly designed; at the same time, the pumping efficiency can also be greatly improved, which can effectively improve the conversion efficiency and The threshold power is more flexible than the design of semiconductor-pumped solid-state thin-film lasers.

Heat dissipation is the bottleneck for the expansion of optically pumped vertical external-cavity surface-emitting lasers to high power, and it is also a key issue that affects the light-to-light conversion efficiency. There are two main factors that cause the gain reduction of the surface-emitting semiconductor chip: one is that the peak gain of a single quantum well is reduced due to temperature rise; the other is that the thermal effect makes the antinode of the laser field and the position of the quantum well stagger, thereby reducing the absorption efficiency. The coupling strength is weakened. The thermal effect of the surface-emitting semiconductor chip affects the normal operation of the device. Effective thermal management of the optically pumped vertical external cavity surface-emitting laser is one of the key issues to improve its output laser power, efficiency and beam quality.

With the increase of the pump light power, the problem of thermal effect becomes more and more serious. Overcoming the thermal effect and obtaining good output laser characteristics have become a research hotspot. Researchers have successively reported the following methods to improve laser output characteristics by improving its thermal characteristics, such as by thinning the surface-emitting semiconductor chip substrate [Peter Brick, Stephan Lutgen, Tony Albrecht, et al. High-efficiency high-power semiconductor disclaser .Proc of SPIE.4993(2003):50-56], Improving the bonding process between the heat sink and the chip and the light-emitting surface of the chip and the transparent material with high thermal conductivity [William J Alford, Thomas D Raymond, and Andrew AAllerman.Highpower and good beam quality at 980nm from a vertical external-cavity surface-emitting laser.J.Opt.Soc.Am.B.2002,19(4):663-666] and other methods to achieve good heat dissipation; Type reflector [Ki-Sung Kim, Jaeryung Yoo, Gibum Kim, et al. Enhancement of Pumping Efficiency in a Vertical-External-Cavity Surface-Emitting Laser IEEE PHOTONIC S TECHNOLOGYLETTERS.2007, 19(23): 1925-1927] and strain Compensation quantum well structure [Li Fan, Jorg Hader, Marc Schillgalies, et al. High-Power Optically Pumped VECSEL Using a Double-Well Resonant Periodic Gain Structure. IEEE Photonics Technology Letters. 2005, 17(9): 1764-1766] and other methods to reduce thermal effects To improve the output characteristics of the laser. The above method of improving the thermal characteristics of surface-emitting semiconductor chips alleviates the influence of thermal effects on output laser characteristics to a certain extent, but there is still a certain gap between the pursuit of high power, high efficiency and high beam quality in practical applications.

Conventional optically pumped vertical external-cavity surface-emitting lasers are based on ordinary Gaussian beams as the pumping source. The pumping region and the lasing region overlap, resulting in a large thermal effect. When the pumping power is large, the surface-emitting semiconductor chip An increase in temperature will reduce the effective gain of the laser, and the output power will reach saturation, and in severe cases, fluorescence quenching will occur.

Contents of the invention

In order to overcome the overlapping of the pumping area and the lasing area of the optically pumped vertical external cavity surface emitting laser and the serious problem of thermal effect, and improve the output characteristics of the laser, the invention provides a hollow beam pumped vertical external cavity surface emitting laser.

As shown in accompanying drawings 1 and 2, the hollow beam pumped vertical external cavity surface emitting semiconductor laser of the present invention includes a semiconductor laser 1, a transmission fiber 2, a collimating lens 3, a Cassegrain telescopic system 4, and a coupling lens 5 , beam splitting prism 6, external cavity surface emitting epitaxial wafer 7, copper heat sink 8 and output mirror 9; wherein, the pump laser beam emitted by the semiconductor laser 1 is output through the transmission fiber 2, and the collimator lens 3 outputs the laser beam output by the fiber For collimation, the Cassegrain telescopic system 4 converts the collimated beam into a hollow beam and then focuses it through the coupling lens 5, and the focused light is incident on the external cavity surface-emitting epitaxial wafer 7 through the beam splitter 6 for pumping excitation. The fluorescence generated after the external cavity surface emitting epitaxial wafer 7 is excited oscillates between the Bragg reflector of the epitaxial wafer 7, the inclined surface of the dichroic prism 6 and the output mirror 9 to form a laser output;

The Cassegrain telescopic system 4 is composed of a convex reflector and a hollow concave reflector, and the light beam incident on the convex reflector diverges and is reflected by the concave reflector to form a hollow light beam;

The beam-splitting prism 6 is a cube composed of two isosceles right-angle prisms, the transmittance of the pump laser beam is higher than 99%, and the interface of the two isosceles right-angle prisms is highly reflective to the 45-degree incident laser fluorescence;

As shown in Figure 2, described external cavity surface emitting epitaxial wafer 7 is made of substrate 11, buffer protective layer 12, window layer 13, barrier region 14, quantum well active region 15 and Bragg reflector 16; On the substrate 11, the buffer protection layer 12, the window layer 13, the barrier region 14, the quantum well active region 15, the barrier region 14 and the Bragg reflector 16 are sequentially grown by molecular beam epitaxy; the buffer protection layer 12 is to avoid Oxidation and lattice mismatch of window layer 13 in direct contact with air; window layer 13 diffuses to the material surface with carriers generated by barrier region 14; quantum well active region 15 selects a strain compensation quantum well structure, and each period A layer of barrier region is grown for the absorption of pumping light, the quantum well is at an integer multiple of 1/2 wavelength, and the number of quantum wells is 3-15 for multiple growth periods; the Bragg reflector 16 adopts more than 25 pairs of 1/2 4. Alternate structure of high and low refractive index materials with wavelength thickness to ensure a reflectivity higher than 99% for laser light;

The light-emitting surface of the external cavity surface-emitting epitaxial wafer 7 is bonded to a transparent diamond film 10 , and the back is bonded to a copper heat sink 8 to discharge the waste heat generated by itself.

Beneficial effects: the present invention adopts the hollow beam as the pumping light, utilizes its features such as adjustable dark spot size, no heating effect, and propagation invariance, so that the center of the pumping area is separated from the center of the lasing area to reduce the surface emission epitaxy of the external cavity. It is an effective method to improve the light-to-light conversion efficiency and output power, improve the output beam quality and output spectrum stability by controlling the thermal effect and micro-strain in the lasing region of the chip. When the pumping power is 2W, the conversion efficiency ^is increased by 11% when the hollow beam is used as the pumping source than the ordinary Gaussian beam as the pumping source. It can provide a good light source for optoelectronic information industries such as criminal investigation, optical information storage, image display, biomedical instruments, and underwater detection.

Description of drawings

Fig. 1 is a schematic block diagram of a hollow beam pumped vertical external cavity surface emitting semiconductor laser.

FIG. 2 is a schematic diagram of the structure of an external-cavity surface-emitting epitaxial wafer 7 .

Detailed ways

Embodiment 1 As shown in the accompanying drawings 1 and 2, the hollow beam pumped vertical external cavity surface emitting semiconductor laser of the present invention consists of a semiconductor laser 1, a transmission fiber 2, a collimating lens 3, a Cassegrain telescopic system 4, The coupling lens 5, the beam splitting prism 6, the external cavity surface emitting epitaxial wafer 7, the copper heat sink 8 and the output mirror 9 are composed; wherein, the pump laser beam emitted by the semiconductor laser 1 is output through the transmission optical fiber 2, and the collimating lens 3 outputs the optical fiber The laser beam is collimated, and the Cassegrain telescopic system 4 transforms the collimated beam into a hollow beam, which is then focused by a coupling lens 5. The focused light is incident on an external-cavity surface-emitting epitaxial wafer 7 through a beam splitter 6 for pumping. Pu incentives. The fluorescence generated after the external cavity surface emitting epitaxial wafer 7 is excited oscillates between the Bragg reflector of the epitaxial wafer 7 , the inclined surface of the dichroic prism 6 and the output mirror 9 to form laser output.

The semiconductor laser 1 is an 808 nm edge-emitting laser.

The transmission fiber 2 is a silica fiber with a core diameter of 400um and a numerical aperture of 0.22.

The Cassegrain Telescope System 4 is composed of a convex mirror and a hollow concave mirror. The beam incident on the convex mirror diverges and is reflected by the concave mirror to form a hollow beam. The reflectivity of the reflecting surface is higher than 99%. %.

Dichroic prism 6 is a cube composed of two isosceles right-angle prisms, the transmittance of the pump laser beam is higher than 99%, and the interface of the two isosceles right-angle prisms is highly reflective to the 45-degree incident laser fluorescence, and the reflectivity is higher than 99.8%.

As shown in Figure 2, the external-cavity surface-emitting epitaxial wafer 7 is composed of a substrate 11, a buffer protection layer 12, a window layer 13, a barrier region 14, a quantum well active region 15, and a Bragg mirror 16; wherein, on the substrate 11 The buffer protection layer 12, the window layer 13, the barrier region 14, the quantum well active region 15, the barrier region 14 and the Bragg mirror 16 are grown sequentially by molecular beam epitaxy; the substrate 11 is GaAs or InP, and the external cavity surface emission After the epitaxial wafer 7 is prepared, the substrate 11 is thinned to 500um by chemical etching. The buffer protection layer 12 is to avoid oxidation and lattice mismatch of the window layer 13 in direct contact with air. The carrier in the window layer 13 diffuses to the surface of the material by means of the anti-barrier region 14 . The quantum well active region 15 selects a strain-compensated quantum well structure, and a layer of barrier regions is grown in each cycle for the absorption of pump light. The quantity is 3-15 pcs. The Bragg reflector 16 adopts an alternate growth structure of 25 pairs of high and low refractive index materials with a thickness of more than 1/4 wavelength, so as to ensure a reflectivity higher than 99% for laser light.

The light emitting surface of the external cavity surface-emitting epitaxial wafer 7 is bonded to a transparent diamond film 10 , and the back is bonded to a copper heat sink 8 so as to realize the dissipation of waste heat generated by itself.

When the pumping power is 2W, the conversion efficiency ^is increased by 11% when the hollow beam is used as the pumping source than the ordinary Gaussian beam as the pumping source.

Claims (1)

1. A hollow beam pumped vertical external cavity surface-emitting semiconductor laser, characterized in that it includes a semiconductor laser (1), a transmission fiber (2), a collimating lens (3), a Cassegrain telescopic system (4), a coupling Lens (5), beam splitting prism (6), external cavity surface emitting epitaxial wafer (7), copper heat sink (8) and output mirror (9); the pumping laser beam that described semiconductor laser (1) sends passes through The output of the transmission fiber (2), the collimating lens (3) collimates the laser beam output from the fiber, the Cassegrain telescopic system (4) converts the collimated beam into a hollow beam and then passes through the coupling lens (5) Focusing, the focused light is incident on the external cavity surface emitting epitaxial wafer (7) through the dichroic prism (6) for pumping excitation; the fluorescence generated by the external cavity surface emitting epitaxial wafer (7) is excited on the external cavity surface emitting epitaxial wafer (7 ) between the Bragg reflector, the inclined surface of the dichroic prism (6) and the output mirror (9) to oscillate to form a laser output; The Cassegrain telescopic system (4) is made up of a convex reflector and a hollow concave reflector, the light beam incident on the convex reflector diverges and is reflected by the concave reflector to form a hollow light beam; The beam-splitting prism (6) is a cube composed of two isosceles right-angle prisms, the transmittance of the pump laser beam is higher than 99%, and the interface between the two isosceles right-angle prisms is highly reflective to incident laser fluorescence at 45 degrees ; Described external cavity surface emission epitaxial wafer (7) is made of substrate (11), buffer protection layer (12), window layer (13), barrier region (14), quantum well active region (15) and Bragg reflector (16) constitutes; On the described substrate (11), growth buffer protection layer (12), window layer (13), barrier region (14), quantum well active region (15), barrier region are grown sequentially by molecular beam epitaxy (14) and Bragg reflector (16); described quantum well active region (15) selects the strain compensation quantum well structure, and each cycle all grows a barrier region for the absorption of pumping light, and the quantum well is in Integer multiples of 1/2 wavelength, multiple cycles of growth, the number of quantum wells is 3-15; the Bragg reflector (16) adopts an alternating structure of 25 pairs of high and low refractive index materials with a thickness of more than 1/4 wavelength; A transparent diamond film (10) is bonded on the light-emitting surface of the external-cavity surface-emitting epitaxial wafer (7), and a copper heat sink (8) is bonded on the back.

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