KR20070074750A - Vertical external cavity surface emitting laser - Google Patents

Abstract

A vertical external cavity surface emitting laser is provided to obtain a pumping power for excitation emission of laser chip through a low output laser diode by combing the polarized light from at least two optical sources to progress at the same path through a polarized optical element. A vertical external cavity surface emitting laser includes a laser chip(23), an external cavity mirror, and a pumping unit(10) having a plurality of optical sources(11,13) and a polarized optical element(15). The laser chip(23) illuminates laser light having a predetermined wavelength. The external cavity mirror is arranged on an outer part of the laser chip(23), and forms a resonator with the laser chip(23). The pumping unit(10) is arranged on a plane or a rear plane on which the laser light of the laser chip illuminates. The pumping unit(10) provides pumping light to the laser chip(23). The plurality of optical sources(11,13) illuminate predetermined polarized light. The polarized optical element(15) is arranged between the optical source(11,13) and the plurality of laser chips(23). The polarized optical element(15) enables the light illuminated from the plurality of optical sources(11,13) to progress along an optical path by penetrating or reflecting the incident light according to the polarized direction.

Description

External external cavity surface emitting laser

1 is a schematic diagram showing an optical arrangement of a conventional external resonator type surface emitting laser (VECSEL).

2 is a schematic diagram showing an optical arrangement of a VECSEL according to an embodiment of the present invention.

3 is a perspective view illustrating the polarization optical device of FIG. 2;

4 is a graph showing a change in transmittance according to the wavelength of the polarizing optical device of FIG.

5 is a schematic diagram showing an optical arrangement of a VECSEL according to another embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

10 ... Pumping unit 11 ... First light source

13 second light source 15 polarization optical element

17 ... focusing lens 21, 41 ... heatsink

23, 43 ... laser chip 25 ... first mirror

27 second mirror 31, 51 birefringence filter

33, 53 ... SHG decision 45 ... External resonator mirror

The present invention relates to an external resonator type surface emitting laser, and more particularly, to an external resonator type surface emitting laser having an improved pumping structure in a laser chip.

The External External Cavity Surface Emitting Laser (hereinafter referred to as VECSEL) replaces the upper mirror of the Vertical Cavity Surface Emitting Laser (VCSEL) with an external mirror to increase the gain area. This is one of the surface-emitting lasers to obtain high power of several W to several tens of W or more.

The VECSEL includes a laser chip having a DBR (Distributed Bragg Reflector) layer and an active layer. The active layer is excited by a pump beam irradiated from a pumping light source to emit light having a predetermined wavelength. Here, since the power of the light emitted from the active layer increases as the power of the pump beam irradiated from the pumping light source increases, the pumping light source needs to increase its light power.

On the other hand, the general VECSEL adopts a single laser diode (hereinafter referred to as LD) as a pumping light source. LD having an output of 4 to 5 W is small in size with a width of several mm in the LD module. There is an advantage, but there is a problem that the pumping power is insufficient. 7W LD is expensive, LD characteristics are very unstable, and the width and length of the LD module are very large, several tens of millimeters. In addition, 17W and 32W LDs have a width and length of several tens of millimeters, respectively, and are very large, require a high threshold current, and have difficulty in focusing a pumping beam.

In view of this, the prior art has disclosed a VECSEL with two pumping light sources as shown in FIG.

Referring to FIG. 1, a conventional VECSEL is formed by bonding a laser chip 1 having a mirror 2 and an active layer 3 to one surface of the laser chip 1. A heat sink 4 for dissipating heat, an outer mirror 7 disposed to face the laser chip 1 so as to be spaced apart to constitute an external resonator, and a pumping beam for irradiating a pumping beam to the active layer 3 Include the unit. The active layer 3 has a multi-quantum well structure and provides a gain region. On the outer surface of the active layer 3, an output window layer 3a to which light excited by the active layer 3 is irradiated, and an anti-reflective coating layer 3b are formed in this order. Therefore, the light irradiated to the outer mirror 7 through the output window layer 3a is resonated between the concave reflective surface 7a of the outer mirror 7 and the mirror 2 constituting the laser chip 1. Only the laser beam of a specific wavelength is irradiated through the outer mirror 7.

The pumping unit is disposed obliquely on the upper surface of the laser chip 1 to irradiate pumping light to the active layer 3. To this end, the pumping unit is disposed in the first and second pumping light sources 5a and 5b and the paths of propagation of the light emitted from each of them, and the first and second focusing lenses 6a and 6b to focus incident light. It includes.

As such, in the case of using the light irradiated from the two pumping light sources, there is an advantage in that a problem of shortage of pumping power can be largely solved even if LD having a relatively low output is used as the pumping light source.

On the other hand, in the optical arrangement of the pumping unit, the first and second pumping light sources 5a and 5b are arranged obliquely on the upper and left sides of the upper surface of the laser chip 3, and in order to focus the light irradiated from each of the two sheets, Since the focusing lenses 6a and 6b are employed, the optical arrangement of the pumping unit is difficult and the size of the entire VECSEL is large.

Accordingly, the present invention has been made in view of the above-described problems, and provides a high output pumping beam by using a plurality of pumping light sources having a low output, and further reduces the size of the optical system to make the overall size smaller. It is an object of the present invention to provide an external resonator type surface emitting laser having a structure.

An external resonator type surface emitting laser according to the present invention for achieving the above object comprises: a laser chip for generating and irradiating laser light having a predetermined wavelength; An external resonator mirror disposed outside the laser chip and forming a resonator together with the laser chip; And a pumping unit disposed on or on a surface to which the laser light of the laser chip is irradiated, the pumping unit providing pumping light to the laser chip, wherein the pumping unit includes a plurality of light sources that respectively irradiate light having a predetermined polarization; ; A polarizing optical element disposed between the light source and the plurality of laser chips and configured to transmit or reflect incident light according to the polarization direction so that the light emitted from each of the plurality of light sources travels in one optical path. It features.

Hereinafter, an external resonator type surface emitting laser (VECSEL) according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

2 is a schematic diagram illustrating an optical arrangement of a VECSEL according to an embodiment of the present invention.

Referring to the drawings, the VECSEL according to the present invention comprises a laser chip 23 for generating and irradiating laser light of a predetermined wavelength, a pumping unit 10 for providing pumping light to the laser chip 23, External resonator mirrors 25 and 27 are formed together with the laser chip 23.

The laser chip 23 includes an active layer that is excited by pumping light and emits light of a predetermined wavelength, and a distributed Bragg reflector (DBR) layer. The DBR layer is a mirror layer that reflects the laser light generated from the active layer to the external resonance mirrors 25 and 27 so that the laser light resonates between the external resonance mirrors 25 and 27 and the DBR layer 21b. . Here, the heat sink 21 is preferably further included on one surface of the laser chip 23. The heat sink 21 emits heat generated by the laser chip 23 to the outside.

The pumping unit 10 is disposed on a surface to which the laser light of the laser chip 23 is irradiated or on a rear surface thereof to provide pumping light to the laser chip 23.

2 illustrates that the pumping unit 10 is formed on the surface to which the laser light of the laser chip 23 is irradiated. The pumping unit 10 includes a plurality of light sources 11 and 13 for irradiating light of a predetermined polarization, and the polarized optics disposed between the plurality of light sources 11 and 13 and the laser chip 23. Element 15. The pumping unit 10 has a size of approximately 20 mm in width and length, respectively, and can be miniaturized.

FIG. 2 shows a plurality of light sources that include a first light source 11 for irradiating light of first polarization, for example S-polarized light, and light of second polarization, for example, P-polarized light, having a different polarization direction from the first polarization. The second light source 13 to be irradiated is shown as an example. Here, each of the first and second light sources 11 and 13 may be composed of a laser diode LD. In this case, each of the laser diodes constituting the first and second light sources 11 and 13 may have a power of 4 to 5 W, and may be a small low-power LD having a width of several mm of the module. .

In addition, LDs constituting each of the first and second light sources 11 and 13 may have the same configuration. In this case, the LD may change the polarization direction of the light irradiated to the polarization optical element 15 by changing its optical arrangement. That is, by arranging the LD constituting the second light source 13 by 90 degrees with respect to the optical arrangement of the LD constituting the first light source 11, the polarization directions of the light of the first polarized light and the light of the second polarized light are mutually different. You can do it differently.

The polarization optical element 15 transmits or reflects incident light according to the polarization direction, so that the light irradiated from each of the first and second light sources 11 and 13 is directed toward one path, that is, the laser chip 23. Proceed to the path.

To this end, the polarizing optical element 15 is preferably composed of a cubic polarizing beam splitter having a structure as shown in FIG. In this case, the polarizing optical element is the first incident surface 15a, to which the light of the first polarized light, for example, the S-polarized light B _R , is incident, and the light B _T of the second polarized light, such as the P-polarized light, is incident. Enters through the second incident surface 15b, the polarization selective transmission surface 15c, and the first and second incident surfaces 15a and 15b and passes through the polarization selective transmission surface 15c in the same traveling path. An exiting surface 15d through which the exiting light B _O which proceeds is emitted is provided.

That is, the polarization selective transmission surface 15c reflects the light B _R of the first polarized light incident through the first incident surface 15a and the second incident through the second incident surface 15b. The polarized light B _T is transmitted. 4 is a graph showing the degree of transmittance according to the wavelength change of the polarizing optical device according to the present invention. Referring to FIG. 4, the polarization optical element reflects almost all light having a transmittance of approximately 0% for light of S polarization in the wavelength range shown in the graph, while having a transmittance of approximately 90% or more for light of P polarization. It can be seen that it transmits almost all light.

Therefore, as shown in FIG. 2, the light of predetermined polarization irradiated from each of the first and second light sources 11 and 13 disposed at different positions is selectively selected according to the polarization direction thereof. Can be transmitted through or reflected from the polarization selective transmission surface 15c so as to travel in the same path.

Here, the pumping unit 10 may further include a focusing lens 17 for focusing the light irradiated from the first and second light sources 11 and 13 so that the focused light is irradiated onto the laser chip 23. Can be. The focusing lens 17 is irradiated from the first and second light sources 11 and 13, and an optical path through which the light of the first and second polarized light synthesized through the polarizing optical element 15 proceeds in common. It is preferable that it is provided in the phase. In this case, by condensing all the light irradiated from the first and second light sources 11 and 13 through one focusing lens 17, the configuration is simplified more than the conventional configuration employing two lenses. The advantage is that you can.

Meanwhile, in the present embodiment, the first and second light sources 11 and 13 are illustrated as examples using a plurality of light sources, but these are merely exemplary and various modifications are possible. That is, the light source may be composed of three or more. In addition, in selecting the polarization direction of the light irradiated from the light source, in addition to the configuration of determining the polarization direction by changing the optical arrangement of the laser diode of the same structure, the configuration to change the polarization direction by providing a phase delay plate on the optical path It is also possible. In addition to the cubic polarization beam splitter described above as an example of the polarization optical element 15, a configuration in which a flat polarization beam splitter or an X-cube polarizer is employed may be employed.

The external resonator mirror includes first and second mirrors 25 and 27. The first mirror 25 is spaced apart from the laser chip 23 and is inclined with respect to the incident optical axis of the light irradiated from the laser chip 23. The surface of the first mirror 25 facing the laser chip 23 and the second mirror 27 is a concave reflection surface 25a.

The second mirror 27 forms an external resonator and is disposed to face the first mirror 25 to reflect back the light incident from the first mirror 25 toward the first mirror 25. .

Preferably, each of the first and second mirrors 25 and 27 is coated to have a different reflectance and transmittance depending on the wavelength of the incident light. For example, the first mirror 25 reflects the laser light of a predetermined wavelength irradiated from the laser chip 23 and determines a second harmonic generation (hereinafter referred to as SHG) crystal (described later). At least a portion of the laser light wavelength converted by 33) may be coated to transmit. In addition, the second mirror 27 may be coated to have a high reflectance for the wavelength-converted laser light, but to have a slight transmittance for the unconverted laser light.

Here, the SHG crystal 33 and the birefringence filter 31 may be further provided between the laser chip 23 and the second mirror 27. The SHG crystal 33 is disposed on an optical path between the first mirror 25 and the second mirror 27 to halve the wavelength of the laser light irradiated from the laser chip 23. Convert to light of wavelength. For example, when the wavelength of the laser light irradiated from the laser chip 23 is 1064 nm, the wavelength of the laser light converted through the SHG 33 is 532 nm.

The birefringent filter 31 is disposed on an optical path between the laser chip 23 and the first mirror 25 to allow only this laser light to resonate by passing only laser light of a predetermined wavelength.

5 is a schematic view showing an optical arrangement of the VECSEL according to another embodiment of the present invention.

Referring to the drawings, VECSEL according to another embodiment of the present invention is a laser chip 43 for generating and irradiating laser light of a predetermined wavelength, a pumping unit 10 for providing pumping light to the laser chip 43 and And an external resonator mirror 45 forming a resonator together with the laser chip 43.

The laser chip 43 includes an active layer that is excited by pumping light and emits light having a predetermined wavelength, and a DBR layer. Since the laser chip 43 is substantially the same as the laser chip 23 according to an embodiment, a detailed description thereof will be omitted. Shall be.

It is preferable that a heat sink 41 further emitting heat generated from the laser chip 43 to one surface, for example, a back surface from which the laser chip 43 is emitted, to the outside. The pumping unit 10 is disposed on a surface to which the laser light of the laser chip 43 is irradiated or on a rear surface thereof to provide pumping light to the laser chip 43. FIG. 5 illustrates that the pumping unit 10 is formed on the rear surface of the surface to which the laser light of the laser chip 43 is irradiated. In this case, the heat sink 41 is formed of a transparent material through which the pumping light irradiated from the pumping unit 10 is transmitted, or has an opening (not shown) formed to pass the pumping light.

Configuration and operation of the pumping unit 10 is substantially the same as the pumping unit according to an embodiment, the detailed description thereof will be omitted.

The external resonator mirror 45 forms an external resonator and is disposed to face the laser chip 43 to reflect back a part of the incident light toward the laser chip 43. The outer resonator mirror 45 has a surface facing the laser chip 43 as a concave reflecting surface 45a, so that most of the resonant laser light is out of the laser chip 43 and the outer resonator mirror 45. Suppress

Preferably, the outer resonator mirror 45 is coated to have a different reflectance and transmittance according to the wavelength of the incident light. For example, the laser light of the predetermined wavelength irradiated from the laser chip 43 may be reflected, and at least a portion of the wavelength-converted laser light by the SHG crystal 53 described later may be coated to transmit.

Here, the SHG crystal 53 and the birefringence filter 51 may be further provided between the laser chip 43 and the external resonator mirror 45.

The VECSEL according to the present invention configured as described above is a pumping unit having at least two light sources operating at a relatively low power, a small size, and a low driving current. Pumping power can be replenished by synthesizing to travel in the same path using the device. Therefore, it is possible to provide pumping power necessary for excitation light emission of the laser chip with low output LD.

In addition, since it has a structure that focuses the light irradiated from a plurality of light sources through one focusing lens, there is an advantage that the manufacturing cost can be lowered, and the overall configuration of the pumping unit can be made compact.

The above embodiments are merely exemplary, and various modifications and equivalent other embodiments are possible to those skilled in the art.

Therefore, the true technical protection scope of the present invention should be defined within the following claims.

Claims (8)

A laser chip for generating and irradiating laser light having a predetermined wavelength; An external resonator mirror disposed outside the laser chip and forming a resonator together with the laser chip; And a pumping unit disposed on a surface of the laser chip to which the laser light is irradiated or a rear surface thereof to provide pumping light to the laser chip. The pumping unit, A plurality of light sources each irradiating light of a predetermined polarization; A polarizing optical element disposed between the light source and the plurality of laser chips and configured to transmit or reflect incident light according to the polarization direction so that the light emitted from each of the plurality of light sources travels in one optical path. An external resonator type surface emitting laser. The method of claim 1, The polarizing optical element, First and second incident surfaces to which light is incident; An emission surface from which light is emitted; And a polarization selective transmission surface that reflects light of the first polarized light incident through the first incident surface and transmits light of the second polarized light incident through the second incident surface. laser. The method of claim 2, The plurality of light sources, A first light source disposed to face the first incident surface and radiating light of a first polarization in a direction of the polarizing beam splitter; And a second light source disposed to face the second incidence surface, the second light source irradiating light of a second polarization in the direction of the polarization beam splitter. The method according to any one of claims 1 to 3, The pumping unit, And a focusing lens disposed between the polarizing optical element and the laser chip to focus light irradiated onto the laser chip. The method according to any one of claims 1 to 3, The external resonator mirror, A first mirror spaced apart from the laser chip and inclined with respect to the incident optical axis of the light irradiated from the laser chip to convert a traveling path of the incident light; And a second mirror disposed to face the first mirror to reflect the light reflected from the first mirror and incident to the first mirror, the second mirror forming an external resonator. The method of claim 5, An SHG crystal disposed on an optical path between the first mirror and the second mirror and converting a wavelength of the laser light irradiated from the laser chip into a half wavelength; A birefringent filter disposed on an optical path between the laser chip and the first mirror and configured to pass only laser light having a predetermined wavelength; An external resonator type surface emitting laser further comprising: a heat sink formed on one surface of the laser chip, the heat sink releasing heat generated from the laser chip to the outside. The method according to any one of claims 1 to 3, The external resonator mirror, And a mirror disposed to face the laser chip and reflecting part of the incident light back toward the laser chip to form an external resonator. The method of claim 7, wherein An SHG crystal disposed on an optical path between the laser chip and the mirror and converting the wavelength of the laser light irradiated from the laser chip into 1/2 wavelength; A birefringent filter disposed on an optical path between the laser chip and the mirror and configured to pass only laser light having a predetermined wavelength; An external resonator type surface emitting laser further comprising: a heat sink formed on one surface of the laser chip, the heat sink releasing heat generated from the laser chip to the outside.

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