JP2005322761A - Surface light-emitting laser characteristics evaluation system and surface light emitting type laser characteristics evaluation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a surface light emitting type laser characteristics evaluation system and a surface light emitting type laser characteristics evaluation method evaluating characteristics of a lower laser elementary substance. <P>SOLUTION: Improvements are added to the surface light emitting type laser characteristics evaluation system for evaluating the surface light emitting type laser characteristics. An upper reflective element formed of an upper distribution reflective layer is adhered onto the lower laser element formed of a lower distribution reflective layer and an active layer on a first substrate. The evaluation system comprises a reflective part, an optical resonator formed of the lower distribution reflective layer of the lower laser element before sticking the reflective part and the upper reflective element, and an optical fiber for transmitting the laser beam oscillated by the optical resonator to the main part of the system. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention evaluates the characteristics of a surface-emitting laser in which an upper reflective element with an upper distributed reflective layer is bonded to a lower laser element with a lower distributed reflective layer and an active layer formed on a first substrate. More particularly, the present invention relates to a surface-emission laser characteristic evaluation apparatus and a surface-emission laser characteristic evaluation method capable of evaluating the characteristics of a single lower laser element.

  First, a surface emitting laser that is a target for characteristic evaluation will be described. A surface emitting laser (VCSEL (Vertical Cavity Surface Emitting Laser)) has a structure in which a semiconductor layer is sandwiched between an upper distributed reflection layer and a lower distributed reflection layer formed of a multilayer film or the like. It is. The semiconductor layer is formed of a multilayer including an active layer and a spacer layer (also referred to as a cladding layer) sandwiching the active layer. The upper distributed reflection layer and the lower distributed reflection layer form an optical resonator, and laser light is emitted in the direction perpendicular to the semiconductor substrate from the back surface or top surface of the semiconductor substrate. Such a surface emitting laser is used as a light source for optical communication or a light source for optical measurement.

  As the surface emitting laser, for example, there is one in which a lower distributed reflection layer, an active layer, and an upper distributed reflection layer are integrally formed on a semiconductor substrate which is a first substrate (see, for example, Patent Document 1).

  As another example, a lower distributed reflection layer (for example, DBR (Distributed Bragg Reflector) layer) and an active layer are formed on a semiconductor substrate to form a lower laser element (also called a half VCSEL). Separately from this lower laser element, an upper distributed reflection layer (for example, a dielectric multilayer film mirror made of SiO 2 / TiO 2) is formed on a second substrate (for example, Si substrate) to form an upper reflection element. . In some cases, the upper reflective element is bonded to the upper side of the active layer of the lower laser element with a bonding layer, and the lower DBR layer of the lower laser element and the dielectric multilayer mirror of the upper reflective element form an optical resonator. (For example, refer to Patent Documents 2 and 3). The upper reflective element is a micro electro-mechanical system (MEMS: a micro electro-mechanical system in which movable parts and electronic circuits are integrated using semiconductor micro-machining technology), and the electrostatic force generated by applying voltage is used as the driving force. The oscillation wavelength can be made variable by moving the dielectric multilayer mirror up and down.

  FIG. 3 is a configuration diagram showing an example of a conventional surface emitting laser characteristic evaluation apparatus for evaluating the characteristics of such a surface emitting laser (integrally formed) (see, for example, Patent Document 4). In FIG. 3, the surface emitting laser 10 includes a lower DBR layer 12, an active layer 13, an upper DBR layer 14, and an upper electrode 15 provided on a semiconductor substrate 11, and a lower electrode 16 provided on the back surface of the substrate 11. When a voltage is applied between the upper electrode 15 and the lower electrode 16, an upper DBR layer 14, an upper spacer layer (not shown), an active layer 13, a lower spacer layer (not shown), A current flows through the DBR layer 12 and the substrate 11 to the lower electrode 16. At this time, holes and electrons are coupled in the active layer 13 having the narrowest band gap, and light is emitted. The light is amplified by the optical resonator and emitted as laser light.

  The fine-tuning base 20 fixes the surface emitting laser 10 and can finely adjust the tilt angles θx and θy along the x axis, the y axis, the z axis in the vertical direction, and xy on the horizontal plane. Move to position or adjust emission angle.

  The optical fiber 30 has a fiber end face disposed close to the light emitting surface of the surface emitting laser 10 and transmits the laser light from the surface emitting laser 10 to the characteristic evaluation apparatus main body 50. The optical fiber fine-tuning table 40 fixes the optical fiber 30 and can be moved finely in each of the x-axis, y-axis, and z-axis directions. Approach to the distance and position.

  The apparatus main body 50 includes a current source 51 and a measuring instrument 52, and the current source 51 outputs a current to the surface emitting laser 10. The measuring device 52 measures the laser light transmitted through the optical fiber 30 (optical power, optical spectrum, etc.) and evaluates the characteristics of the surface emitting laser 10. For example, the light emission characteristics (so-called IL characteristics) are evaluated from the characteristics of the oscillation wavelength, the current output from the current source 51 and the optical power of the surface emitting laser 10.

  Next, FIG. 4 is a configuration diagram illustrating another example of a conventional surface emitting laser characteristic evaluation apparatus that performs characteristic evaluation of a bonded type surface emitting laser. Here, the same components as those in FIG. In FIG. 4, a surface emitting laser 60 is fixed to the fine movement base 20 instead of the surface emitting laser 10 as an object to be evaluated. In the surface emitting laser 60, a lower laser element 60a and an upper reflecting element 60b are bonded together. In the lower laser element 60a, a lower DBR layer 62, an active layer 63, and an upper electrode 64 are provided on a semiconductor substrate (first substrate) 61, and a lower electrode 65 is provided on the back surface of the substrate 61.

  The upper reflective element 60b has a dielectric multilayer mirror 67 on the lower side of the Si substrate (second substrate) 66 (which will be the surface when the substrate 66 is processed, but will be described in the direction in FIG. 4 after bonding). An electrode 68 for driving the MEMS is provided on the upper surface, a voltage is applied from the current source 51, and a current flows. The bonding layer 69 is, for example, solder, and bonds the upper electrode 64 of the lower laser element 60a and the substrate 66 of the upper reflecting element 60b.

  When a voltage is applied between the upper electrode 64 and the lower electrode 65, an upper spacer layer (not shown), an active layer 63, a lower spacer layer (not shown), and a lower DBR layer 62 are formed from the upper electrode 64. A current flows through the substrate 61 to the lower electrode 65. At this time, holes and electrons are coupled in the active layer 63 having the narrowest band gap, and light is emitted. The light is amplified by an optical resonator formed by the lower DBR layer 62 and the dielectric multilayer mirror 67, and laser is emitted. It is emitted as light (in FIG. 4, the upper surface side of the substrate 61).

  Further, a voltage is applied by the current source 51 to the upper electrode 64 and the electrode 68 that are shared with the MEMS drive, and the dielectric multilayer mirror 67 is moved up and down. As a result, the resonator length is changed to a desired oscillation wavelength.

Japanese Patent No. 2546133 JP 2004-87903 A (paragraph numbers 0018-0040, FIG. 1-5) Japanese Patent Laid-Open No. 2002-289969 (paragraph numbers 0062-0065, FIG. 4) JP 2003-23212 A

  As described above, the surface emitting laser characteristic evaluation apparatus transmits the laser light from the surface emitting lasers 10 and 60 to the apparatus main body 50 through the optical fiber 30 to perform the characteristic evaluation. That is, it is assumed that laser light is input to the apparatus main body 50.

  However, in the case of the bonded type surface emitting laser 60, the lower laser element 60a alone emits only LEDs, whereas the monolithically integrated surface emitting laser 10 is integrated. Therefore, even if the lower laser element 60a has remarkably bad characteristics, there is a problem that the characteristic evaluation cannot be performed unless the upper reflective element 60b is bonded.

  Accordingly, an object of the present invention is to realize a surface emitting laser characteristic evaluating apparatus and a surface emitting laser characteristic evaluating method capable of performing characteristic evaluation of a lower laser element alone.

The invention described in claim 1
A surface emitting laser for evaluating the characteristics of a surface emitting laser in which an upper reflective element having an upper distributed reflective layer is bonded onto a lower laser element having a lower distributed reflective layer and an active layer formed on a first substrate In the characteristic evaluation device,
An optical resonator is formed by the reflection portion and the lower distributed reflection layer of the lower laser element before bonding the upper reflection element, and the laser light oscillated by the optical resonator is applied to the apparatus body. It has an optical fiber for transmission.

The invention according to claim 2 is the invention according to claim 1,
The reflection part of the optical fiber is a highly reflective film formed on the fiber end face on the side where the light from the lower laser element is incident.
The invention according to claim 3 is the invention according to claim 2,
The optical fiber is characterized in that the end face of the fiber is formed as a concave surface.
The invention according to claim 4 is the invention according to claim 1,
The reflection part of the optical fiber is a diffraction grating formed in a direction perpendicular to the direction of the core.
The invention according to claim 5 is the invention according to any one of claims 1 to 4,
The core diameter of the optical fiber is larger than the beam diameter of the light emitted from the lower laser element.

The invention described in claim 6
A surface emitting laser for evaluating the characteristics of a surface emitting laser in which an upper reflective element having an upper distributed reflective layer is bonded onto a lower laser element having a lower distributed reflective layer and an active layer formed on a first substrate In the characterization method,
Forming an optical resonator with a reflection portion provided in an optical fiber and a lower distributed reflection layer of a lower laser element before bonding the upper reflection element;
Transmitting the laser beam oscillated by the optical resonator to the main body of the apparatus through the optical fiber, and evaluating the characteristics of the lower laser element;
Screening the lower laser element by this characteristic evaluation;
And a step of bonding the selected lower laser element and the upper reflecting element together.

The present invention has the following effects.
According to the first to fifth aspects of the present invention, the optical fiber is provided with a reflection portion, and an optical resonator is formed by the reflection portion and the lower distributed reflection layer of the lower laser element before the upper reflection element is attached. Laser oscillation can be performed without attaching the upper reflecting element to the lower laser element. Thereby, the characteristic evaluation of the lower laser element alone can be performed. Accordingly, the lower laser element having poor characteristics can be selected before bonding, and the yield of the surface emitting laser can be improved and the cost can be reduced.

  Further, when the characteristics are evaluated for the first time after bonding, the characteristics are poor, and it is difficult to identify the cause of whether the characteristics of the lower laser element or the upper reflecting element are poor. However, since the characteristics of the lower laser element can be evaluated, it is easy to identify the cause even if the characteristics of the surface emitting laser are poor after bonding.

  According to the third aspect, since the fiber end surface is formed as a concave surface, even if the beam diameter of the light emitted from the lower laser element increases as the distance from the lower laser element increases, it is reflected by the highly reflective film. The collected light can be efficiently focused on the lower laser element. Therefore, it is possible to reduce the diffraction loss.

  According to the fifth aspect, since the core diameter of the optical fiber is larger than the beam diameter of the light emitted from the lower laser element, the laser-oscillated light is efficiently transmitted to the optical fiber without the need for strict position adjustment and alignment. Combine well.

  According to the sixth aspect of the present invention, an optical resonator is formed by the reflecting portion provided in the optical fiber and the lower distributed reflecting layer of the lower laser element before the upper reflecting element is bonded, and the laser beam oscillated by the optical resonator. Is transmitted to the apparatus main body through an optical fiber, and the characteristics of the lower laser element are evaluated. Then, after selecting the lower laser element by the characteristic evaluation, the upper reflecting element is bonded. Thereby, the characteristic evaluation of the lower laser element alone can be performed. Accordingly, the lower laser element having poor characteristics can be selected before bonding, and the yield of the surface emitting laser can be improved and the cost can be reduced.

  Further, when the characteristics are evaluated for the first time after bonding, the characteristics are poor, and it is difficult to identify the cause of whether the characteristics of the lower laser element or the upper reflecting element are poor. However, since the characteristics of the lower laser element can be evaluated, it is easy to identify the cause even if the characteristics of the surface emitting laser are poor after bonding.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a structural sectional view showing an embodiment of the present invention. Here, the same components as those in FIG. In FIG. 1, only the lower laser element 60 a of the surface emitting laser 60 is fixed to the fine movement base 20. That is, the lower laser element 60 a alone before the upper reflecting element 60 b is bonded by the bonding layer 69 is fixed to the fine movement base 20. Therefore, the current source 51 outputs a current only to the upper electrode 64 and the lower electrode 65.

  An optical fiber 70 is provided instead of the optical fiber 30. The optical fiber 70 is fixed to the optical fiber fine adjustment base 40. Further, in the optical fiber 70, a high reflection film 71 is coated on the fiber end surface on the side on which light from the lower laser element 60 a is incident, and the other fiber ends are connected to the measuring instruments 52. The high reflection film 71 is a reflection part and is designed to have a high reflectance near the oscillation wavelength of the surface emitting laser 60. The core diameter of the optical fiber 70 may be any size, but is preferably larger than the beam diameter of the light emitted from the lower laser element 60a.

The operation of such an apparatus will be described.
By adjusting the fine movement table 20 and the fine movement table 40, the high reflection film 71 formed on the fiber end surface of the optical fiber 70 is brought close to a desired distance on the light emitting surface of the surface emitting laser 60. As a result, the lower DBR layer 62 and the highly reflective film 71 form an optical resonator.

  Subsequently, when a voltage is applied from the current source 51 between the upper electrode 64 and the lower electrode 65, the upper spacer layer (not shown), the active layer 63, and the lower spacer layer (not shown) are drawn from the upper electrode 64. A current flows through the lower DBR layer 62 and the substrate 61 to the lower electrode 65. At this time, in the active layer 63 having the narrowest band gap, a hole and an electron are coupled to emit light, which is amplified by an optical resonator formed by the lower DBR layer 62 and the highly reflective film 71, and laser oscillation To do. Then, the laser light oscillated is transmitted through the high reflection film 71 of the optical fiber 70 and transmitted to each measuring instrument 52 of the apparatus main body 50 through the optical fiber 70.

  The measuring device 52 evaluates the characteristics of the lower laser element 60a of the surface emitting laser 60 from the laser light from the optical fiber 70 and the output value of the current source 51.

  Further, by this characteristic evaluation, the lower laser element 60a having poor characteristics is removed and selected. Then, the selected lower laser element 60 a and upper reflection element 60 b having good characteristics are bonded together by the bonding layer 69. Furthermore, the optical fiber 70 is replaced with the optical fiber 30 shown in FIG. 4, and the characteristics of the surface emitting laser 60 after bonding are evaluated in the same manner as in FIG.

  As described above, the high reflection film 71 is provided on the fiber end surface of the optical fiber 70, and an optical resonator is formed by the high reflection film 71 and the lower DBR layer 62 of the lower laser element 60a before the upper reflection element 60b is attached. Therefore, laser oscillation can be performed without bonding the upper reflecting element 60b to the lower laser element 60a. Thereby, the characteristic evaluation of the lower laser element 60a alone can be performed. Accordingly, the lower laser element 60a having poor characteristics can be selected before bonding, so that the yield of the surface emitting laser 60 can be improved and the cost can be reduced.

  Further, when the characteristics are evaluated for the first time after bonding, the characteristics are poor, and it is difficult to identify the cause of whether the characteristics of the lower laser element 60a are poor or the characteristics of the upper reflective element 60b are bad. However, since the characteristics of the lower laser element 60a can be evaluated, it is easy to identify the cause even if the characteristics of the surface emitting laser 60 are poor after bonding.

  Further, since the resonator length can be arbitrarily set by adjusting the position of the optical fiber 70 by the fine moving base 40, the oscillation wavelength can be arbitrarily set.

  Further, since the core diameter of the optical fiber 70 is larger than the beam diameter of the light emitted from the lower laser element 60a, the laser-oscillated light is efficiently coupled to the optical fiber 70 without the need for precise position adjustment and alignment. To do.

In addition, this invention is not limited to this, The following may be sufficient.
In the apparatus shown in FIG. 1, the configuration in which the high-reflection film 71 is coated on the flat fiber end surface is shown. However, the fiber end surface of the optical fiber 70 may be processed into a spherical concave surface and the high-reflection film 71 may be coated. . For example, you may comprise as shown in FIG. Here, the same components as those in FIG. In FIG. 2, the fiber end surface of the optical fiber 70 is processed into a concave surface, and the highly reflective film 71 is coated along the concave surface.

  The operation of such an apparatus is substantially the same as that of the apparatus shown in FIG. In general, light emitted from the lower laser element 60a is approximated by a Gaussian beam, and the beam diameter increases as the distance increases. Here, if the fiber end face is parallel to the substrate 61, the light escapes sideways at a constant rate each time it is reflected, and does not efficiently return to the lower laser element 60a. On the other hand, since the fiber end surface is formed as a concave surface, even if the beam diameter of the light emitted from the lower laser element 60a increases as the distance from the lower laser element 60a increases, the light reflected by the high reflection film 71 Is efficiently focused on the lower laser element 60a. Therefore, it is possible to reduce the diffraction loss.

  Further, the fiber end surface may be formed as a convex surface instead of a concave surface. When the concave or convex surface is formed as described above, the transverse mode of the laser beam can be selected.

  Further, in the apparatus shown in FIG. 1, a configuration is shown in which the reflection portion is formed by coating the fiber end face of the optical fiber 70 with the high reflection film 71, but an optical fiber grating may be used instead of the optical fiber 70. That is, the diffraction grating of the optical fiber grating serves as a reflection portion, and the diffraction resonator and the lower DBR layer 62 constitute an optical resonator. The optical fiber grating is obtained by providing a refractive index distribution on an optical fiber by a method such as ultraviolet irradiation and forming a diffraction grating in a direction perpendicular to the direction of the core.

It is the block diagram which showed the 1st Example of this invention. It is the block diagram which showed the 2nd Example of this invention. It is the block diagram which showed an example of the conventional surface emitting laser characteristic evaluation apparatus. It is the block diagram which showed the other example of the conventional surface emitting laser characteristic evaluation apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 Fine moving table 40 Optical fiber fine moving table 50 Apparatus main body 51 Measuring instrument 52 Current source 60 Surface emitting laser 60a Lower laser element 61 Semiconductor substrate (1st board | substrate)
62 Lower DBR layer (lower distributed reflective layer)
63 Active layer 70 Optical fiber 71 High reflection film (reflection part)

Claims (6)

A surface emitting laser for evaluating the characteristics of a surface emitting laser in which an upper reflective element having an upper distributed reflective layer is bonded onto a lower laser element having a lower distributed reflective layer and an active layer formed on a first substrate In the characteristic evaluation device,
An optical resonator is formed by the reflection portion and the lower distributed reflection layer of the lower laser element before bonding the upper reflection element, and the laser light oscillated by the optical resonator is applied to the apparatus body. A surface emitting laser characteristic evaluation apparatus comprising an optical fiber for transmission.   2. The surface emitting laser characteristic evaluation apparatus according to claim 1, wherein the reflection part of the optical fiber is a highly reflective film formed on the fiber end face on the side on which light from the lower laser element is incident.   3. The surface emitting laser characteristic evaluation apparatus according to claim 2, wherein the optical fiber has a concave end surface.   2. The surface emitting laser characteristic evaluation apparatus according to claim 1, wherein the reflection portion of the optical fiber is a diffraction grating formed in a direction perpendicular to the direction of the core.   5. The surface emitting laser characteristic evaluation apparatus according to claim 1, wherein a core diameter of the optical fiber is larger than a beam diameter of light emitted from the lower laser element. A surface emitting laser for evaluating the characteristics of a surface emitting laser in which an upper reflective element having an upper distributed reflective layer is bonded onto a lower laser element having a lower distributed reflective layer and an active layer formed on a first substrate In the characterization method,
Forming an optical resonator with a reflection portion provided in an optical fiber and a lower distributed reflection layer of a lower laser element before bonding the upper reflection element;
Transmitting the laser beam oscillated by the optical resonator to the main body of the apparatus through the optical fiber, and evaluating the characteristics of the lower laser element;
Screening the lower laser element by this characteristic evaluation;
A method for evaluating a surface emitting laser characteristic, comprising the step of bonding the selected lower laser element and the upper reflecting element.

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